Ulysses is a joint ESA/NASA mission studying the interplanetary medium and solar wind
in the inner heliosphere, beyond the Sun's equator, for the first time. The spacecraft's
high-inclination orbit around the Sun took it over the solar south pole in 1994 and then
the north pole in 1995. Ulysses then made a second southern solar pass above 70 deg
latitude during September 2000 to January 2001, and a similar northern pass during
September to December 2001. On 17 November 2006, the spacecraft started its third
passage over the Sun's south pole.

Ulysses' high-gain antenna points continuously towards Earth, returning data for 8 h
every day as it investigates the Sun's domain.

Credits: JPL-ESA, 1994

17 November 2006
On 17 November, the joint ESA-NASA Ulysses mission will reach another important milestone on its epic out-of-ecliptic journey: the start of the third passage over the Sun's south pole.

Launched in 1990, the European-built spacecraft is engaged in the exploration of the heliosphere, the bubble in space blown out by the solar wind. Given the capricious nature of the Sun, this third visit will undoubtedly reveal new and unexpected features of our star's environment.

The first polar passes in 1994 (south) and 1995 (north) took place near solar minimum, whereas the second set occurred at the height of solar activity in 2000 and 2001. "During the first polar passes, Ulysses found a well-ordered heliosphere, with clear differences between the solar wind at the poles and equator", says Richard Marsden, ESA's Ulysses Project Scientist and Mission Manager. "At solar maximum things were more complex, making it hard to distinguish any particular region from another."


Sketch of Ulysses' third solar orbit. The spacecraft, launched in 1990, made its first
polar passes in 1994 (south) and 1995 (north), near solar minimum. It made the second
set of polar passes in 2000 and 2001, at the height of solar activity. On 17 November
2006, the spacecraft started its third passage over the Sun's south pole.

Credits: ESA

As Ulysses approaches the polar regions for the third time, the Sun has settled down once again and will be close to its minimum. "Ulysses orbits the Sun once every 6.2 years, making it perfect for studying the 11-year solar activity cycle", says Marsden. "In fact, we can really say that Ulysses is exploring the heliosphere in four dimensions -covering all three spatial dimensions as well as time."

Even though the Sun will be close to its activity minimum just as it was in 1994-95, there is one fundamental difference: the Sun's magnetic field has reversed its polarity. In addition to the 11-year activity cycle, the Sun has a magnetic cycle of 22 years, known as the Hale Cycle. Ulysses, now in its 17th year in orbit, is giving scientists the chance to observe the heliosphere from a unique, out-of-ecliptic vantage point and with the same set of instruments over almost a complete Hale Cycle.

What is the Ulysses science team expecting to find this time around? "If our ideas are correct, the change in polarity of the Sun's magnetic field will have a clear effect on the way cosmic ray particles reach our location in the inner heliosphere", says Marsden. "During the last solar minimum, positively charged particles had a slightly easier time reaching the polar regions; this time, the negatively charged electrons should have the advantage."


But there could be surprises. In 1994, the pole-to-equator difference in the number of particles observed, although present, was much smaller than expected. This lead to several new models for the way charged particles move in the complex environment of interplanetary space. The new observations will test if these new theories are correct.

Another surprise from the first polar passes was the fact that the heliosphere is not as symmetric as scientists believed. The Sun's magnetic field was found to be slightly stronger in the south than in the north. "We'll be watching out for this effect as Ulysses swings from the south pole to the north in 2007", says Marsden.

Although important in its own right, Ulysses is also a key member of the fleet of spacecraft known as the Heliospheric Network that includes SOHO and NASA's ACE, Wind and Voyager spacecraft. The Network recently welcomed two new members, the twin STEREO spacecraft that were launched by NASA at the end of October. "We are really excited about the possibilities for joint observations using STEREO, ACE and SOHO during Ulysses' pole-to-pole transit in 2007", says Marsden.

Source: ESA - News

This artist's impression shows the ESA-NASA Ulysses spacecraft. Launched in 1990,
the European-built spacecraft visits both polar regions once every 6.2 years as it circles
the Sun in an orbit that is almost perpendicular to the ecliptic, the plane in which the
Earth and the planets move.

Credits: ESA - image by C.Carreau

7 February 2007
Today the joint ESA-NASA Ulysses mission has marked another high point in its mission. For the third time in a long and highly successful career, Ulysses has reached its maximum south solar latitude of 80 degrees as it flies over the Sun's southern polar cap.

Launched in 1990, the European-built spacecraft visits both polar regions once every 6.2 years as it circles the Sun in an orbit that is almost perpendicular to the ecliptic, the plane in which the Earth and the planets move.

Although originally designed for a mission lasting 5 years, the Ulysses space probe and its suite of 9 scientific experiments are still going strong after more than 16 years in orbit.

Operating the spacecraft has become more demanding over the years, however, as one consequence of the mission's longevity is a decrease in the electrical power available on board. "Ulysses uses a Radioisotope Thermoelectric Generator, or RTG for short, to generate the electricity needed for the spacecraft subsystems and science instruments", said Nigel Angold, ESA's Mission Operations Manager for Ulysses.

The RTG converts the heat produced by radioactive decay of its fuel into electrical power. "As a result of the decay process, the RTG output decreases with time", said Angold. In recent years, this has necessitated sharing the available power among the science instruments in such a way that key instruments are kept on permanently, while others are operated only part of the time.

Starting in May, as Ulysses comes closer to the Sun, one of the power-hungry heaters on board the spacecraft will be switched off. "This will free up sufficient power to have the full suite of instruments switched on during a key phase of the mission, the rapid transit from the south to the Sun’s north polar cap", said Richard Marsden, ESA's Ulysses Project Scientist and Mission Manager.

Source: ESA - News

"We must always remember with gratitude and admiration the first sailors who steered their vessels through storms and mists, and increased our knowledge of the lands … in the South."
--Roald Amundsen


February 7, 2007: Less than one hundred years ago, the south pole of Earth was a land of utter mystery. Explorers labored mightily to get there, fighting scurvy, wind, disorientation and a fantastic almost-martian cold. Until Roald Amundsen and Robert F. Scott reached the Pole in 1911 and 1912, it was terra incognita.

The situation is much the same today—on the sun.

"The sun's south pole is uncharted territory," says solar physicist Arik Posner of NASA headquarters. "We can barely see it from Earth, and most of our sun-studying spacecraft are stationed over the sun's equator with a poor view of higher latitudes."

There is, however, one spacecraft that can travel over the sun's poles: Ulysses, a joint mission of NASA and the European Space Agency. And today Ulysses is making a rare South Pole flyby.

"On February 7th, the spacecraft reaches a maximum heliographic latitude of 80oS—almost directly above the South Pole," says Posner who is the Ulysses Program Scientist for NASA.


Above: Ulysses, an artist's impression.
Credit: David Hardy/ESA.

Solar physicists are thrilled. Ulysses has flown over the sun's poles only twice before--in 1994-95 and 2000-01. The flybys were brief, but enough to prove that the poles are strange and interesting places.

Consider the following:

1. The sun's north magnetic north pole sticks out the south end of the sun. Magnetically, the sun is upside down!

"Most people don't know it, but we have the same situation here on Earth," notes Posner. "Our magnetic north pole sticks out of the geographic south pole."

Magnetically, Earth and sun have a lot in common. "Both the sun's and Earth's magnetic poles are constantly on the move, and they occasionally do a complete flip, with N and S changing places." This flipping happens every 11 years on the sun in synch with the sunspot cycle. It happens every 300,000 years or so on Earth in synch with--what? No one knows. "Studying the polar magnetic field of the sun might give us some clues about the magnetic field of our own planet."

2. There are holes over the sun's poles--"coronal holes." These are places where the sun's magnetic field opens up and allows solar wind to escape. "Flying over the sun's poles, you get slapped in the face by a hot, million mph stream of protons and electrons," he says. Ulysses is experiencing and studying this polar wind right now.

(Note: Earth has a polar hole, too--the ozone hole. The chemistry of the ozone hole is totally unrelated to the magneto-physics of coronal holes, but says Posner, "it is interesting that so many poles seem to have holes.")

3. Just as the sun's polar magnetic field allows solar wind out, it also allows galactic cosmic rays in. Could the space above the sun's poles be a place where we can sample interstellar matter without actually leaving the solar system? "That's what we thought before our first polar flyby in 1994," recalls Posner. "But we were wrong. Something is keeping cosmic rays out of the sun's polar regions. The current flyby gives us a chance to investigate this phenomenon."

4. Another mystery: There is evidence from earlier flybys that the north pole and the south pole of the sun have different temperatures. "We're not sure why this should be," says Posner, "and we're anxious to learn if it is still the case." Today's south polar flyby will be followed by a north polar flyby in early 2008, allowing a direct north vs. south comparison.


Above: The sun's south polar coronal hole. Solar wind flows out of the dark region in this false-color UV image.
Credit: SOHO.

In a sense, Ulysses is more like Richard E. Byrd than Amundsen or Scott. In November 1929, Byrd flew over Earth's south pole in a Ford Trimotor airplane named the Floyd Bennett. The plane barely gained enough altitude to overfly the high polar plateau, clearing some mountain peaks and glaciers by little more than a few hundred feet. Compasses were useless for direction-finding so close to the magnetic pole, and there were few landmarks in the white expanse below. Nevertheless, he managed to guide the plane straight to latitude 90 S.

Like Byrd, Ulysses is a flier. "Today the spacecraft is gliding 300 million km (2 AU) above the sun's 'Antarctic.' That's a safe distance and a good place to sample the sun's polar winds and magnetic fields."

In the long run, however, Ulysses will follow Scott: "Had we lived I should have had a tale to tell of hardihood, endurance and courage…," Scott wrote shortly before his entire party perished from cold. They reached the pole, famously chasing Amundsen, but never made it home again. Ulysses will never come home either, eventually perishing in the cold of space when its internal power sources fail. (For more on this, see Science@NASA's "Cold Peril").

To honor the common heritage of exploration, NASA's Science Mission Directorate dedicates its efforts during the Ulysses' South Pole flyby to Roald Amundsen, Robert F. Scott and Richard E. Byrd.

Amundsen, Scott, Byrd, and now Ulysses. Says Posner, "their stories will inspire generations to come."

Author: Dr. Tony Phillips | Production Editor: Dr. Tony Phillips | Credit: Science@NASA

____________________________________________

More to the story...

Ulysses -- mission home page

The International Heliophysical Year -- On the 50th anniversary of the International Geophysical Year (IGY), scientists worldwide have declared 2007 to be the International Heliophysical Year (IHY), dedicated to the study of the sun and its interactions with Earth.

"Ulysses' flyby of the sun's South Pole is a good beginning for the 2007 International Heliophysical Year," notes Posner. "Our dedication of the flyby to Amundsen, Scott and Byrd is intended to honor the IHY."

South Pole Explorers: Roald Amundsen, Robert F. Scott and Richard E. Byrd. See also the Antarctic Timeline of Discovery

Above: Ulysses' third orbit around the sun carries it over the South Pole in February 2007 and the North Pole in early 2008.

Cold Peril -- (Science@NASA) The NASA/ESA Ulysses spacecraft is perilously cold as it begins a newly extended mission to study the sun.

A Star with two North Poles -- (Science@NASA) Sometimes the Sun's magnetic field goes haywire.

Solar Flares on Steroids -- (Science@NASA) Solar flares that scorch Earth's atmosphere are commonplace. But scientists have discovered a few each year that are not like the others: they come from stars thousands of light years away. The Ulysses spacecraft is crucial for pinpointing these "solar flares on steroids."

Solar Spitwads -- (Science@NASA) Using data from the Ulysses spacecraft, researchers have discovered that high-energy particles from the Sun sometimes go in unexpected directions.

NASA's Future: The Vision for Space Exploration

Source: Science@NASA

The 16-year-old Ulysses spacecraft reaches what could be considered a low point in its mission observing the sun today - and solar scientists could not be happier. The European-manufactured, joint NASA- and ESA-managed spacecraft, has reached maximum latitude in its exploration of the heliosphere, the bubble in space blown out by the solar wind.

"At max latitude we are actually passing below the sun looking almost directly up at its south pole from 329 million kilometers (204 million miles) away," said Nigel Angold, Ulysses mission operations manager from the European Space Agency. "The trajectory provides a perspective of the sun no other spacecraft can equal."


Image above: OArtist's concept of Ulysses at sun's south pole.
Image Credit: NASA/JPL

This unusual perspective is courtesy of the spacecraft's one-of-its-kind 6.3-year-long orbit around the sun. An orbit that swings Ulysses both over and under the sun's polar regions and as far out as the orbit of Jupiter.

"Max latitude is the start of an important mission phase," said Dr. Ed Smith, Ulysses project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "The spacecraft will soon begin accelerating as it transits from below the sun's south pole to its equator and then up and over its north pole. This trajectory provides us a ringside seat to all the solar processes we want to observe."

This phase of the mission is expected to return high priority scientific observations revealing the changing sun and its effect on space during the ongoing minimum in the 11-year sunspot cycle. During this portion of the mission, Ulysses will rapidly scan the sun’s magnetic field, solar plasmas, solar radio noise, energetic particles, galactic cosmic rays and cosmic dust between the poles and the equator - imparting a more complete perspective of the sun's atmosphere.

Understanding the Earth's nearest star and its processes is paramount, as the space weather created by the sun has a huge effect on the third rock from it and its inhabitants. The sun's gaseous outer atmosphere can create huge space storms. This violent space weather, in turn, can affect Earth's electrical grid, cell phone communications, the functioning of satellites and the operation of astronauts in orbit.

This passage between the sun's poles is the third in the 17 years of Ulysses operations. The first transit occurred during the previous sunspot minimum in 1994 to 1995, and the second during sunspot maximum in 2000 to 2001. The opportunity to repeat the scientific investigations during the ongoing solar minimum is important because the sun's magnetic field has changed significantly since the previous minimum.

The Ulysses spacecraft was carried into Earth orbit in the cargo bay of the Space Shuttle Discovery on Oct. 6, 1990. From Earth orbit it was propelled toward Jupiter by solid-fuel motors. Ulysses passed Jupiter on Feb. 8, 1992; the giant planet's gravity bent the spacecraft's flight path downward and away from the ecliptic plane. This put it into a final orbit around the sun that would take it past the sun's north and south poles.

The spacecraft was built by Dornier Systems of Germany for the European Space Agency. NASA provided the launch via space shuttle and the upper stage boosters. The U.S. Department of Energy supplied a radioisotope thermoelectric generator which powers the spacecraft; science instruments were provided by both U.S. and European investigators. The spacecraft is operated from JPL by a joint team from the European Space Agency and NASA.

More information about NASA's Ulysses mission is available on the Web at http://ulysses.jpl.nasa.gov.

Media contacts: DC Agle 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.

Dwayne Brown 202-358-1726
NASA Headquarters, Washington

2007-012

Source: NASA - Exploring The Universe - Our Solar System

A joint ESA/NASA mission, Ulysses (named after the hero of Greek
legend) is charting the unknown reaches of space above and below the
poles of the Sun.

Credits: ESA

19 February 2007
Although very close to the minimum of its 11-year sunspot cycle, the Sun showed that it is still capable of producing a series of remarkably energetic outbursts - ESA-NASA Ulysses mission revealed.

In keeping with the first and second south polar passes (in 1994 and 2000), the latest high-latitude excursion of the joint ESA-NASA Ulysses mission has already produced some surprises. In mid-December 2006, although very close to the minimum of its 11-year sunspot cycle, the Sun showed that it is still capable of producing a series of remarkably energetic outbursts.

The solar storms, which were confined to the equatorial regions, produced quite intense bursts of particle radiation that were clearly observed by near-Earth satellites. Surprisingly, similar increases in radiation were detected by the instruments on board Ulysses, even though it was three times as far away and almost over the south solar pole. "Particle events of this kind were seen during the second polar passes in 2000 and 2001, at solar maximum," said Richard Marsden, ESA's Ulysses Project Scientist and Mission Manager. "We certainly didn't expect to see them at high latitudes at solar minimum!"

Scientists are busy trying to understand how the charged particles made it all the way to the poles. "Charged particles have to follow magnetic field lines, and the magnetic field pattern of the Sun near solar minimum ought to make it much more difficult for the particles to move in latitude," said Marsden.

One of the puzzles remaining from the first high-latitude passes in 1994 and 1995 has to do with the temperature of the Sun's poles. When Ulysses first passed over the south and then the north solar pole near solar minimum, it measured the temperatures of the large polar coronal holes.


Variations of the coronal temperature measured with the SWICS instrument on board
ESA-NASA’s Ulysses from December 1990 to January 2007. Solar wind flow from
coronal holes is characterized by high solar wind speed (700-800 kilometres per
second) and low coronal temperature (1 – 1.3 million Kelvin).

Credits: R. von Steiger and G. Gloeckler

"Surprisingly, the temperature in the north polar coronal hole was about 7 to 8 percent lower compared with the south polar coronal hole," said Professor George Gloeckler, Principal Investigator for the Solar Wind Ion Composition Spectrometer (SWICS) on board Ulysses.

"We couldn't tell then whether this was simply due to progressive cooling of both polar coronal holes as the Sun was approaching its minimum level of activity in 1996, or whether this was an indication of a permanently cooler north pole."

Now, as Ulysses again passes over the large polar coronal holes of the Sun at solar minimum we will finally have the answer. Recent SWICS observations show that the average temperature of the southern polar coronal hole at the current solar minimum is as low as it was 10 years ago in the northern polar coronal hole. "This implies that the asymmetry between north and south has switched with the change of the magnetic polarity of the Sun," said Gloeckler. The definitive proof will come when Ulysses measures the temperature of the north polar coronal during the next 15 months.

Source: ESA - News

February 20, 2007: One pole of the sun is cooler than the other. That's the surprising conclusion announced today by scientists who have been analyzing data from the ESA-NASA Ulysses spacecraft.

Ulysses is the only ship in the NASA or European fleet capable of flying over the sun's poles, a result of the spacecraft's uniquely-tilted orbit. Its ability to study the sun's unexplored polar regions is prized by solar physicists.

see captionUlysses' first polar flybys in 1994 and 1995 revealed the asymmetry—"a 7 to 8 percent difference in temperature," says Ulysses science team member George Gloeckler of the University of Maryland. The measurement was both mysterious and a little hard to believe. What would make the sun lopsided in this way?


Above: Ulysses over the sun's South Pole, an artist's concept.
Credit: ESA.

There's still no definitive answer to that question, but now at least researchers know the effect is real. Ulysses has returned to the sun's South Pole in 2007 and "recent observations show that the average temperature ... is virtually identical to what we saw 12 years ago," says Gloeckler.

Taking the sun's temperature is tricky business. The spacecraft can't descend to the surface and insert a thermometer. Instead, Ulysses samples the solar wind at a safe remove of 300 million km. "We measure the abundance of two oxygen ions found in the solar wind. The ratio O6+/O7+ tells us the temperature of the gas," explains Gloeckler. He is the principal investigator of the instrument onboard Ulysses that does this, the Solar Wind Ion Composition Spectrometer or "SWICS."

According to SWICS, the average temperature of the sun's polar wind is about one million degrees C. But over one pole the wind is about 80,000 degrees cooler than over the other pole.

Researchers believe the solar wind at Ulysses is telling them something about polar conditions close to the surface of the sun. "The solar wind comes from the poles," explains Arik Posner, Ulysses Program Scientist at NASA headquarters. "The sun's magnetic field opens up over the poles and allows some of the sun's atmosphere to escape." These openings are called "coronal holes," and the hot atmosphere that rushes out is the solar wind.

Back to the original question: What does the temperature difference mean? "Perhaps the structure of the sun's atmosphere over the two poles is different," he speculates.

We have an analogy here on Earth. The stratosphere over the South Pole is colder, on average, than the stratosphere over the North Pole. The reason has to do with the uneven distribution of land on Earth (most land is in the north) plus complex atmospheric circulation patterns.

In the case of the sun, the difference is not land but magnetism. Apparently, something about the sun's north magnetic pole keeps the solar atmosphere above it a trifle cooler. Proof: The "cool spot" follows the north magnetic pole when the sun's poles flip.


Above: Solar wind temperatures in millions of degrees Kelvin measured by Ulysses.
Credit: R. von Steiger and G. Gloeckler.
[Larger image]

"The sun's magnetic poles have reversed polarity since the 1994 flyby—an effect of the 11-year sunspot cycle," notes Posner. Lo and behold, "the temperature asymmetry has also reversed. So it appears to be a magnetic phenomenon."

When Ulysses finishes its current South Pole flyby, it will proceed to the other end of the sun for a North Pole flyby in early 2008. This will provide more clues to what's shaping up to be a very cool solar mystery.

Author: Dr. Tony Phillips | Production Editor: Dr. Tony Phillips | Credit: Science@NASA

____________________________________________

Web Links

Ulysses -- mission home page

South Pole Flyby (Science@NASA) -- the ESA-NASA Ulysses spacecraft is flying over uncharted territory, the mysterious South Pole of the sun.

Above: Ulysses' third orbit around the sun carries it over the South Pole in February 2007 and the North Pole in early 2008.

Cold Peril -- (Science@NASA) The NASA/ESA Ulysses spacecraft is perilously cold as it begins a newly extended mission to study the sun.

A Star with two North Poles -- (Science@NASA) Sometimes the Sun's magnetic field goes haywire.

Solar Flares on Steroids -- (Science@NASA) Solar flares that scorch Earth's atmosphere are commonplace. But scientists have discovered a few each year that are not like the others: they come from stars thousands of light years away. The Ulysses spacecraft is crucial for pinpointing these "solar flares on steroids."

NASA's Future: The Vision for Space Exploration

Source: Science@NASA

February 22, 2007: Imagine hiking across Antarctica, through ice, cold and bitter wind, enduring months of hardship, and finally arriving at the doorstep of the South Pole itself.

At that moment you get hit by a Sahara sandstorm.

That's the analogy scientists are using to describe what happened to the ESA-NASA Ulysses spacecraft last December. "Ulysses was approaching the South Pole of the sun when it was 'sandblasted' by a cloud of high-energy particles—protons, electrons and heavy ions," says Arik Posner, Ulysses Program Scientist at NASA headquarters. The cloud was as foreign to the sun's South Pole as a Sahara sandstorm would be to Antarctica.

The strange tale begins on Dec. 5, 2006.

Astronomers were in a state of excitement due to the sudden appearance of a giant and angry-looking sunspot on the sun's eastern limb—"sunspot 930," says Posner. On Dec. 5th it exploded, producing one of the strongest solar flares of the past 25 years. On the "Richter scale" of solar flares, X1 is considered intense; the Dec. 5th flare was an X9. A flash of X-rays announced the blast to sensors in Earth orbit, and moments later a cloud of protons, electrons and heavy ions came rushing out of the blast site. This is the cloud that pelted Ulysses.


Above: An X9-class solar flare on Dec. 5, 2006, recorded
by the GOES-13 Solar X-ray Imager.
Credit: NOAA.

The process repeated on Dec. 6th (X6) and Dec. 13th (X3). Each explosion created its own cloud of high-energy particles. "We call these clouds 'radiation storms,'" says Posner. "They are common after big flares."

What's strange about these storms is where they went—to the South Pole. "All three storms were detected by the Ulysses spacecraft," says University of New Hampshire physicist Bruce McKibben. He is principal investigator for COSPIN (Cosmic and Solar Particle INvestigation), an array of sensors onboard Ulysses that counts high energy particles. "The Dec. 6th event was particularly strong and rich in heavy ions."

The Dec. 6th storm was so strong, in fact, "that if Earth had been where Ulysses was, we would have experienced a full-fledged Ground-Level Event," says Prof. Bernd Heber of the Institute for Experimental and Applied Physics in Keil, Germany. In other words, the particles were capable of tunneling all the way through Earth’s atmosphere to reach the ground. Heber is principle investigator for the Kiel Electron Telescope (KET), a sensor onboard Ulysses able to detect such super-energetic electrons, protons and ions.


Above: Heavy ions (Z>2) counted by Ulysses over the sun's south pole vs. ACE over the sun's equator in Dec. 2006.
[More]

These observations add up to "a big puzzle," says McKibben. Sunspot 930 was near the sun's equator, while Ulysses was over the sun's South Pole. The sun's magnetic field should have kept the storms bottled up at low latitudes. How did they reach Ulysses?

It's a puzzle NASA is keen to solve. Solar radiation storms can cause communication blackouts on Earth; they can disable satellites in Earth-orbit; and in extreme cases they could be deadly to astronauts. "We need to be able to predict the trajectory of these storms," says Posner.

The key is the sun's magnetic field. Just as Earth's magnetic field guides compass needles, the sun’s magnetic field guides radiation storms. "Radiation storms consist of charged particles which naturally follow lines of magnetic force."

To forecast the path of a radiation storm, researchers have in the past relied on the "Parker spiral," a pioneering magnetic model developed by University of Chicago physicist Eugene Parker. According to his work, the sun's magnetic field emerges radially from the sun's surface and spirals outward into the solar system. "The spiral shape is caused by the spinning motion of the sun," explains Posner. "It's like a spiral stream of water from a spinning lawn sprinkler."


Above: The Parker Spiral.
Image credit: Steve Suess, NASA/MSFC..
[More]

The Parker spiral makes a straightforward prediction: Radiation storms that begin near the equator should remain near the equator. A storm might expand into the solar system and hit Earth, which is not far off the sun’s equatorial plane, but it should not hit Ulysses over the sun's South Pole.

Clearly, there's more to the story than a graceful spiral. The real solar magnetic field may contain kinks and twists that provide a polar passage, a route storms can travel from equator to poles. There is evidence for the idea: In 2000 and 2001, the last Solar Max, the sun's magnetic field was full of convoluted, non-Parkerian structures. "During that time, Ulysses experienced six high-latitude radiation storms," notes McKibben: data.

Mapping and understanding these passages, if they exist, is work for the future. Meanwhile, one thing is clear: "There is no place in the inner solar system completely safe from radiation storms," says Posner.

Author: Dr. Tony Phillips | Production Editor: Dr. Tony Phillips | Credit: Science@NASA

____________________________________________

More information

Ulysses -- mission home page

High latitude radiation storms -- this graph prepared by Bruce McKibben shows all the high-latitude radiation storms observed by Ulysses. Red events happened in 2000 and 2001; black denotes Dec. 2006.

A Cool Solar Mystery -- (Science@NASA) One pole of the sun is cooler than the other. That's the surprising conclusion of scientists who have been analyzing data from the ESA-NASA Ulysses spacecraft.

South Pole Flyby (Science@NASA) -- the ESA-NASA Ulysses spacecraft is flying over uncharted territory, the mysterious South Pole of the sun.

Cold Peril -- (Science@NASA) The NASA/ESA Ulysses spacecraft is perilously cold as it begins a newly extended mission to study the sun.

A Star with two North Poles -- (Science@NASA) Sometimes the Sun's magnetic field goes haywire.

Solar Flares on Steroids -- (Science@NASA) Solar flares that scorch Earth's atmosphere are commonplace. But scientists have discovered a few each year that are not like the others: they come from stars thousands of light years away. The Ulysses spacecraft is crucial for pinpointing these "solar flares on steroids."

NASA's Future: The Vision for Space Exploration

Source: Science@NASA

17 August 2007

This artist's impression shows the ESA/NASA Ulysses spacecraft. Launched in 1990, the European-built spacecraft visits both polar regions once every 6.2 years as it circles the Sun in an orbit that is almost perpendicular to the ecliptic, the plane in which Earth and the planets move.

Credits: ESA

Scientists from the Ulysses mission have proven that sounds generated deep inside the Sun cause the Earth to shake and vibrate in sympathy. They have found that Earth’s magnetic field, atmosphere and terrestrial systems, all take part in this cosmic sing-along.

David Thomson and Louis Lanzerotti, team members of the HISCALE experiment, on board Ulysses, together with colleagues Frank Vernon, Marc Lessard and Lindsay Smith, present evidence that proves that Earth moves to the rhythm of the Sun. They show that distinct, isolated tones, predicted to be generated by pressure and gravity waves in the Sun, are present in a wide variety of terrestrial systems.

Using highly sophisticated statistical techniques, Thomson and colleagues have discovered these same, distinct tones emitted by the Sun, in seismic data here on Earth. They have also found that Earth’s magnetic field and atmosphere, and even voltages induced on ocean cables, are all taking part in this cosmic sing-along.

Although these tones are all around us, it would not be possible for us to hear them, even if we listened very closely. Their pitch is too low for the human ear, typically 100-5000 microHertz (1 microHertz corresponds to 1 vibration every 278 hours). This is more than 12 octaves below the lowest note audible to humans. For comparison, the note to which orchestras tune their instruments (A above Middle C on a piano) corresponds to 440 Hertz.

Ulysses is a joint ESA/NASA mission studying the interplanetary medium and solar wind in the inner heliosphere, beyond the Sun's equator, for the first time.

The spacecraft's high-inclination orbit around the Sun took it over the solar south pole in 1994 and then the north pole in 1995. Ulysses then made a second southern solar pass above 70º South during September 2000 to January 2001, and a similar northern pass during September to December 2001. On 17 November 2006, the spacecraft started its third passage over the Sun's south pole.

Ulysses' high-gain antenna points continuously towards Earth, returning data for eight hours every day as it investigates the Sun's domain.

Credits: JPL/ESA

According to Thomson, data from Ulysses provided an important clue as to how these sounds generated deep inside the Sun reach the Earth.

The same techniques applied to the terrestrial data sets were first used on measurements of energetic particle fluxes and interplanetary magnetic fields recorded on board Ulysses.

Surprisingly, rather than being random in nature, the fluctuations in the data were made up of many discrete frequencies or tones, similar to the terrestrial data. These tones also corresponded well to those that theorists predict, should be generated by pressure and gravity waves in the Sun.

Some of these so-called solar oscillations had been observed optically using instruments on SOHO, and by dedicated networks of telescopes on the Earth. They are caused by pressure waves in the Sun, and are referred to as p-modes. The deeper sounds associated with the Sun’s gravity waves (g-modes) are far more elusive.

Just as seismologists on Earth use sound waves to probe the interior of our world, solar scientists would like to use g-modes to probe the core of the Sun, if only they could detect them. G-modes have been undetectable optically, so Thomson and colleagues’ evidence for them in interplanetary data was both unexpected and hard to explain at first.

This composite image shows a SOHO image of the Sun and an artist's impression of Earth's magnetosphere.

Credits: Magnetosphere: NASA, the Sun: ESA/NASA SOHO

They examined a wide range of data sets covering natural phenomena and technological systems in fields as diverse as telecommunications and seismology and continued to find new evidence of discrete tones with characteristics of solar oscillations in what was previously considered background “noise”. This added to the puzzle posed by the Ulysses findings.

Thomson believes that the key to the problem is magnetism. He suggests that the g-mode vibrations are picked up by the magnetic field at the Sun’s surface. Part of this magnetic field is then carried away from Sun into interplanetary space by solar wind, where it can be detected by space probes like Ulysses.

The magnetic field of the solar wind in turn interacts with the Earth’s magnetic field and causes it to vibrate in sympathy, retaining the characteristic g-mode signals. The motions of the geomagnetic field then couple into the solid Earth to produce small, but easily detectable, responses as Earth, with many of its technological systems, moves to the rhythm of the Sun.


Notes:

Ulysses is a joint mission between ESA and NASA.

ESA manages the mission operations and provided the spacecraft, built by Dornier Systems, Germany (now Astrium). NASA provided the Space Shuttle Discovery for launch and the inertial upper stage and payload-assist module to put Ulysses in its correct orbit. NASA also provided the radioisotope thermoelectric generator which powers the spacecraft and payload.

ESA’s ESTEC and ESOC are now managing the mission with NASA’s Jet Propulsion Laboratory (JPL). Ulysses is tracked by NASA’s Deep Space Network. A joint ESA/NASA team at JPL is overseeing spacecraft operations and data management. Teams from universities and research institutes in Europe and the United States provided the nine science instruments.


For more information:

Richard Marsden, ESA Ulysses Project Scientist
Email: richard.marsden @ esa.int

Source: ESA - Space Science - News

The University of Michigan press release is reproduced below:

Oct. 1, 2007

ANN ARBOR, Mich.—Comets are made of the most primitive stuff in the solar system. As hunks of rock and ice that never coalesced into more planets, they give researchers clues to the evolution of solar systems.

So a chance encounter between spacecraft Ulysses and Comet McNaught's ion tail has scientists in the University of Michigan's College of Engineering marveling at a stroke of luck and some surprising data.

The NASA/European Space Agency spacecraft is on a mission to study the sun's polar regions, and it carries an instrument run by U-M professors. In February, it flew through McNaught's ion tail 160 million miles from the comet's core.

Instrument readings showed there was "complex chemistry" at play, said U-M space science professor George Gloeckler, second author of a paper on the findings published Oct. 1 in Astrophysical Journal.

Gloeckler is the principal investigator on the Solar Wind Ion Composition Spectrometer (SWICS) aboard Ulysses, which measured the composition and speed of the comet tail and solar wind. The solar wind consists of high-speed streams of plasma that emanate from the sun's outer atmosphere. Not only did SWICS detect unexpected ions in the comet tail, it found that the tail had a major impact on the surrounding solar wind.

For the first time at a comet, researchers detected O3+ oxygen ions (atoms of oxygen with a positive charge because they have five electrons instead of eight). This suggests that the solar wind ions, originally missing most of their electrons, picked up some of their missing electrons when they passed through McNaught's atmosphere. The comet served as a source of electrons, said Michael Combi, a U-M space science professor who is an author of the paper.

SWICS also found that even at 160 million miles from the comet's nucleus, the tail had slowed the solar wind to half its normal speed. The solar wind would usually be about 435 miles per second at that distance from the sun, but inside the comet's ion tail, it was less than 249 miles per second.

"This was very surprising to me," Combi said. "Way past the orbit of Mars, the solar wind felt the disturbance of this little comet. It will be a serious challenge for us theoreticians and computer modelers to figure out the physics."

In 1996, Ulysses passed through the tail of comet Hyakutake and measurements indicated its tail didn't slow the solar wind at all.

The interaction between comets' tails and the solar wind has been studied for decades. A comet's ion tail always points away from the sun, whether the body is traveling toward or away from the sun along the comet's elliptical orbit. It was this finding that eventually led in 1958 to the discovery of solar wind. The magnetism and velocity of the solar wind are so strong it pushes the comet's tail forward.

Solar wind is blamed for the lack of an atmosphere on Mars and for geomagnetic storms that can cut out power on Earth. It is a major component of space weather, which scientists study because if affects satellites and humans in space.

As for what these observations say about the origins of the solar system, scientists don't know just yet.

"The composition of comets tells us about conditions approximately 4.5 billion years ago when the solar system was formed," Gloeckler said. "Here we got a direct sample of this ancient material which gives us the best information on cometary composition.

"We're still in the process of figuring out what it tells us," he said. "We're contributing part of the whole puzzle."

Space science professor Thomas Zurbuchen, a U-M author of the paper, likened Ulysses' pass to putting your hand in the waters of Lake Michigan and pulling out a fish.

"That's a pretty unlikely thing," Zurbuchen said. "And that is a lot like what happened when we caught the tail of a comet that happened to pass very near the sun.

"The benefits of such an observation are important," he said. "They constrain the interactions of such comets with the sun, including how the comets lose mass. They also examine the question of how a sudden injection of neutral and cold material interacts with hot solar-like plasmas. That occurs in other places of the universe and we were able to study it right here."

The paper is called "Encounter of the Ulysses Spacecraft with the Ion Tail of Comet McNaught." Astrophysical Journal is the same journal that published Eugene Parker's paper on the discovery of solar wind in 1958.

The Department of Atmospheric, Oceanic and Space Sciences is part of the University of Michigan College of Engineering, which is ranked among the top engineering schools in the country. Michigan Engineering boasts one of the largest engineering research budgets of any public university, at more than $130 million. Michigan Engineering has 11 departments and an NSF Engineering Research Centers. Within those departments and the center, there is a special emphasis on research in three emerging areas: nanotechnology and integrated microsystems; cellular and molecular biotechnology; and information technology. Michigan Engineering is seeking to raise $110 million for capital building projects and program support in these areas to further research discovery. Michigan Engineering's goal is to advance academic scholarship and market cutting-edge research to improve public health and well-being.

Source: U-M press release

When it was launched 17 years ago, scientists and mission engineers for the Ulysses project knew they should expect, well, the unexpected. After all, the joint NASA/European Space Agency-managed spacecraft was going where no spacecraft had gone before - above and below the sun's poles. But the surprises the team expected were wholly in the area of solar research - which would make sense, as the primary mission of the Ulysses spacecraft is to characterize the sun and its influence on the space environment. That was before the spacecraft met up with some of the solar system's most mysterious and beautiful deep-space nomads.

"Ulysses has flown through and acquired data from the tails of comets on three separate occasions," said Edward J. Smith of NASA's Jet Propulsion Laboratory in Pasadena, Calif. Smith serves as the U.S. project scientist for the Ulysses mission. "No other spacecraft in history has done that."


Image above: Artist concept of Ulysses spacecraft, with the sun in the
background.
Image credit: NASA/JPL-Caltech
+ Larger view

Ulysses' first cometary tail encounter occurred in 1996. Back then, comet Hyakutake was dazzling scientists and the public alike with its noteworthy appearances in the nighttime spring sky. On May 1, 1996, while Ulysses was cruising through space studying the solar wind, its data suddenly went wild for a few hours.

"As we were not looking for comets, we did not realize the significance of the data right away," said Smith. "The solar wind seemed to almost disappear and was replaced by gases not normally found in the solar wind, and the magnetic field in the solar wind was distorted."

At the time of the unexpected encounter, Ulysses was hundreds of millions of miles from comet Hyakutake and far beyond the visible tail. As their analysis began ruling out other possibilities, the science team came to a startling conclusion - Hyakutake's tail extended more than 480 million kilometers (300 million miles, or three times the distance from Earth to the sun), making it the longest comet tail ever recorded.

The once-in-a-lifetime chance encounter with a comet tail happened again in 2004 when Ulysses flew through the ion tailings of comet McNaught-Hartley. Unlike Hyakutake, comet McNaught-Hartley seemed to be at the wrong location for Ulysses to intercept its tail. By chance, an eruption of particles from the surface of the sun, called a coronal mass ejection, carried cometary material to Ulysses. Such a collision has recently been observed for the first time by NASA's Stereo spacecraft (_http://www.nasa.gov/mission_pages/stereo/news/encke.html). A movie (_http://www.nasa.gov/mpg/191284main_encke_scienceatnasa.mpg) shows the disruption and reformation of periodic comet Encke's tail.

Ulysses racked up its third, and perhaps most scientifically revealing, comet tail encounter this past February when it again flew through the ion tailings of a comet named McNaught (a different comet than the one encountered in 2004, but discovered by and named after the same astronomer). The nucleus of this comet McNaught was some 257 million kilometers (160 million miles) from the spacecraft during encounter. Ulysses' solar wind ion composition spectrometer instrument, developed by University of Michigan heliophysicist George Gloeckler, found that even at such a great distance, the tail had filled the solar outflow with unusual gases and molecules. In response, the solar wind that usually measures about 700 kilometers per second (435 miles per second) at that distance from the sun, was less than 400 kilometers per second (249 miles per second) inside the comet's tail, as measured by one of Ulysses' instruments called "Solar Wind Observations Over the Poles of the Sun."

The interaction between comets' tails and the solar wind has been studied for decades. A comet's ion tail always points away from the sun, whether the body is traveling toward or away from the sun along the comet's elliptical orbit. It was this finding that eventually led in 1958 to the discovery of solar wind. The magnetism and velocity of the solar wind are so strong, the effect pushes the comet's tail forward. A paper on Ulysses' latest crossing of a comet tail was published in the Oct. 1 issue of Astrophysical Journal.

"I recall saying a few years back that the odds that Ulysses' flight path would intersect that of a comet tail were probably less likely than finding a needle in a haystack," said Smith. "Now that we have encountered three, I cannot help wondering when nature will have another one in store for us."

Smith is part of an international science team that has been working Ulysses data since its 1990 launch from the payload bay of Space Shuttle Discovery. Ulysses scans the sun's magnetic field, solar plasmas, solar radio noise, energetic particles, galactic cosmic rays and cosmic dust between the poles and the equator - imparting a more complete perspective of the sun's atmosphere. Understanding Earth's nearest star and its processes is of paramount importance, as the space weather created by the sun has a huge effect on the third rock from it and its inhabitants. The sun's gaseous outer atmosphere can create huge space storms. This violent space weather, in turn, can affect Earth's electrical grid, cell phone communications, satellite functioning, and the operation of astronauts in orbit.

"Such unique science is a tribute to the durability of the mission and the intellectual curiosity of our science team," said Ed Massey of JPL, who serves as Ulysses' NASA project manager.

The Ulysses spacecraft was built by Dornier Systems of Germany for the European Space Agency. NASA provided the launch via space shuttle and the upper stage boosters. The U.S. Department of Energy supplied a generator that powers the spacecraft; science instruments were provided by both U.S. and European investigators. The spacecraft is operated from JPL by a joint team from the European Space Agency and NASA.

More information about NASA's Ulysses mission is available at _http://ulysses.jpl.nasa.gov.


Media contact: DC Agle/JPL
818-393-9011

Source: NASA - Exploring the Universe - Our Solar System

17 November 2007

This artist's impression shows the ESA/NASA Ulysses spacecraft. Launched in 1990, the European-built spacecraft visits both polar regions once every 6.2 years as it circles the Sun in an orbit that is almost perpendicular to the ecliptic, the plane in which Earth and the planets move.

Credits: ESA

ESA’s Science Programme Committee has unanimously approved to continue the operations of the highly successful Ulysses spacecraft until March 2009. This latest extension, for a period of 12 months, is the fourth in the history of the joint NASA/ESA mission.

In addition to pursuing its long-term goal of exploring the heliosphere in four dimensions – 3 spatial dimensions and time - Ulysses is a key member of the Heliospheric Network, the international fleet of spacecraft presently operating at many different locations in the heliosphere and beyond.

Ulysses’ joint measurements with the twin STEREO satellites that were launched in October 2006 are high on the list of priorities for the coming months.

“This new lease of life is great news for the international heliophysics community”, said Richard Marsden, ESA’s Mission Manager and Project Scientist for Ulysses. “No other spacecraft can provide the out-of-ecliptic measurements made by Ulysses. The Sun’s activity will soon pick up again, and there are plenty of unsolved questions to tackle.”

Among these unsolved questions is an apparent asymmetry in the temperature of the Sun’s polar coronal holes, which appears to be related to the magnetic polarity. This was discovered during the first high-latitude passes in 1994 and 1995, when the magnetically positive northern polar coronal hole was found to be cooler than the southern pole. Data acquired during the coming months will hopefully shed new light on this puzzle.



For a satellite in its eighteenth year in space, Ulysses is in remarkably good health. Nevertheless, in order to compensate for the steadily diminishing power output of the onboard radioisotope thermoelectric generator (RTG), the spacecraft operations team has had to devise a new operational strategy that will allow the majority of the scientific instruments to operate throughout the period covered by the extension without much power-sharing.

So what will the future have in store for Ulysses? “We’re all very pleased that we will stil get great scientific data for another year,” said Marsden. “Beyond that, we’ll have to wait and see.”

Ulysses has a finite lifetime, determined by technical limitations. There are no limitations to the science that we can still do. We are on an exploratory mission, probing the most fundamental processes of our solar system. Every bit of new data holds the promise of a new discovery of profound importance.

Source: ESA - Space Science - News

The Ulysses spacecraft continues to go where no other spacecraft has gone before, namely, over the Sun’s poles to study the Sun and its influence on the space environment. About a year after Ulysses once again crossed into the Sun's south polar cap, it has begun its journey over the north polar cap. Previous spacecraft have remained near the Sun’s equator where the Earth and other planets are located, however, Ulysses’ orbit is perpendicular or highly inclined to all other spacecraft orbits providing a unique perspective from which to study the Sun and its effect on surrounding space. Entry into the North Polar Cap is defined by the heliographic (solar) latitude of + 70 degrees. Ulysses will now proceed to its maximum latitude of 80 degrees and then return to 70 degrees in 15 March 2008 and exit the polar cap. Observations of the solar wind, magnetic field, solar energetic particles and cosmic rays obtained during this interval will be compared with those obtained in the South Polar Cap earlier this year in order to investigate differences, i.e., a North-South asymmentry or temporal differences - associated with changes on the Sun made evident by the network of in-ecliptic (solar equatorial) heliospheric spacecraft.



Understanding solar activity is important not only because the Sun is an average star that is available for close scrutiny but because it has important consequences for Earth and its inhabitants as we continue to move into a new era of space-based technology and are able to send people into space and its hazards. Solar activity and the sunspots are driven by the solar magnetic field that changes dramatically over a 22-year cycle. During the first Ulysses orbit, the Sun’s magnetic poles were positive with outward fields in the north and negative or inward fields in the south. During Ulysses second orbit at sunspot maximum, the Sun’s polar fields disappeared and then reappeared with the opposite sense, negative or inward in the north and positive or outward in the south. In addition, the strength of the polar fields is now about one-half of what they were during the first orbit. Consequently, Ulysses is currently poised to investigate this changed magnetic field and its effect on the solar wind, galactic cosmic rays and the other constituents in space.

Source: NASA - Ulysses

January 14, 2008

The Ulysses spacecraft today is making a rare flyby of the sun's north pole. Unlike any other spacecraft, Ulysses is able to sample winds at the sun's poles, which are difficult to study from Earth.

Ulysses has flown over the sun's poles three times before, in 1994-95, 2000-01 and 2007. Last week, solar physicists announced the first indications of a new solar cycle. Visiting the pole at this time may lead to new insights about solar activity.


+ Larger image
Artist concept of Ulysses making a north polar pass.
Image credit: NASA/JPL

"This is a wonderful opportunity to examine the sun's north pole within a transition of cycles," said Arik Posner, Ulysses program scientist at NASA Headquarters in Washington. "We've never done this before."

Many researchers believe the sun's poles are central to the 11-year ebb and flow of solar activity. When sunspots break up, their decaying magnetic fields are carried poleward by vast currents of plasma. This makes the poles a sort of graveyard for sunspots. Old magnetic fields sink beneath the polar surface 200,000 kilometers deep (about 124,000 miles), all the way down to the sun's inner magnetic dynamo, which generates the solar magnetic field. There, dynamo action amplifies the fields for use in future solar cycles.

"Just as Earth's poles are crucial to studies of terrestrial climate change, the sun's poles may be crucial to studies of the solar cycle," said Ed Smith, Ulysses project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

Each previous flyby revealed something interesting and mysterious. One puzzle has been the temperature of the sun's poles. In the previous solar cycle, the magnetic north pole was about 80,000 degrees Fahrenheit (more than 44,000 degrees Celsius), or 8 percent cooler than the south. The current flyby may help solve this puzzle because it comes less than a year after a similar south pole flyby in Feb. 2007. Mission scientists will be able to compare temperature measurements, north versus south, with hardly any gap between them.

Ulysses also discovered the sun's high-speed polar wind. At the sun's poles, the magnetic field opens up and allows solar atmosphere to stream out at a million miles per hour. By flying around the sun, covering all latitudes in a way that no other spacecraft can, Ulysses has been able to monitor this polar wind throughout the solar cycle and has found that it is acting a bit odd.

"Twelve years ago, just before the previous 'sea change' between solar cycles, the polar wind spilled down almost all the way to the sun's equator. But this time it is not. The polar wind is bottled up, confined to latitudes above 45 degrees, " said Posner.

Launched in Oct. 1990 from the space shuttle Discovery, Ulysses is a joint mission of NASA and the European Space Agency.

More information about NASA's Ulysses mission is available at _http://ulysses.jpl.nasa.gov.


Media contact: DC Agle/JPL
818-393-9011

Source: NASA/JPL - News Release

Jan. 14, 2008: Consider it a case of exquisite timing. Just last week, solar physicists announced the beginning of a new solar cycle and now, Jan. 14th, the Ulysses spacecraft is flying over a key region of solar activity--the sun's North Pole.

"This is a wonderful opportunity to examine the sun's North Pole at the onset of a new solar cycle," says Arik Posner, NASA Ulysses program scientist. "We've never done this before."

Launched in Oct. 1990 from the space shuttle Discovery, Ulysses is a joint mission of the European Space Agency and NASA. Unlike other spacecraft, Ulysses is able to fly over the sun's poles, looking down on regions that are difficult to see from Earth: diagram.


Above: An artist's concept of the Ulysses spacecraft.
Credit: ESA. [more]

Ulysses has flown over the sun's poles three times before in 1994-95, 2000-01 and 2007. Each flyby revealed something interesting and mysterious, but this one may be most interesting of all.

"Just as Earth's poles are crucial to studies of terrestrial climate change, the sun's poles may be crucial to studies of the solar cycle," explains Ed Smith, Ulysses project scientist at NASA's Jet Propulsion Laboratory.

Many researchers believe the sun's poles are central to the ebb and flow of the solar cycle. Consider the following: When sunspots break up, their decaying magnetic fields are carried toward the poles by vast currents of plasma. This makes the poles a sort of "graveyard for sunspots." Old magnetic fields sink beneath the polar surface two hundred thousand kilometers deep, all the way down to the sun's inner magnetic dynamo. There, dynamo action amplifies the fields for use in future solar cycles.

One big puzzle revealed by previous flybys is the temperature of the sun's poles. In the previous solar cycle, the magnetic north pole was about 80,000 degrees or 8% cooler than the south. Why should there be a difference? No one knows.

The current flyby may help solve the puzzle because it comes less than a year after a similar South Pole flyby in Feb. 2007. Mission scientists will be able to compare temperature measurements, north vs. south, with hardly any gap between them.

Ulysses also discovered the sun's high-speed polar wind. "At the sun's poles, the magnetic field opens up and allows solar atmosphere to stream out at a million miles per hour," says Smith.



By flying around the sun, covering all latitudes in a way that no other spacecraft can, Ulysses has been able to monitor this polar wind throughout the solar cycle--and it is acting a bit odd.

Posner explains: "Eleven years ago, during a similar 'sea change' between solar cycles, the polar wind spilled down almost all the way to the sun's equator. But this time it is not. The polar wind is bottled up, confined to latitudes above 45 degrees: data."

Is this a detail of little importance or a major anomaly, signaling new things to come? Again, no one knows, and that's why now is a good time to visit the sun's North Pole. "We'll be monitoring the magnetic field above the north pole to see what it's like during the change of solar cycles."

The flyby is underway. Stay tuned to Science@NASA for results
.



Ulysses home pages: NASA, ESA.

Cool Solar Mystery -- (Science@NASA) One pole of the sun is cooler than the other. That's the surprising conclusion of scientists who have been analyzing data from the ESA-NASA Ulysses spacecraft.

Cold Peril -- (Science@NASA) The NASA/ESA Ulysses spacecraft is perilously cold as it begins a newly extended mission to study the sun.

A Star with two North Poles -- (Science@NASA) Ulysses records an extraordinary upheaval in the sun's magnetic field.

Solar Spitwads -- (Science@NASA) Using data from the Ulysses spacecraft, researchers have discovered that high-energy particles from the Sun sometimes go in unexpected directions.

NASA's Future: The Vision for Space Exploration

Source: Science@NASA

[A joint ESA/NASA mission, Ulysses (named after the hero of Greek
legend) is charting the unknown reaches of space above and below the
poles of the Sun.

Credits: ESA

15 January 2008
On 14 January, almost a year after visiting the south solar pole, the Ulysses spacecraft reached the highest point of its orbit over the Sun’s northern polar cap. With this, Ulysses completed its third rapid south-to-north transit to date.

“This important milestone for the joint ESA-NASA mission also coincides with the start of a new cycle of solar activity”, explains Richard Marsden, ESA’s Ulysses Mission Manager. “It’s been calm on the space weather front recently and so we are looking forward to some solar fireworks over the coming months as the number of sunspots increases.”
As part of an impressive fleet of interplanetary spacecraft that includes the twin STEREO probes launched by NASA in 2006 and ESA’s SOHO observatory, Ulysses is ideally placed to provide a unique perspective as our star gears up for the next peak in its activity cycle. This is expected to occur around 2012.

Although the Sun has been relatively quiet during the past year, this has not meant that the spacecraft operations team has been able to sit back and relax. On the contrary, the rapid transit from south to north through perihelion is one of the most nerve-racking periods in the 6.2-year orbit of Ulysses, now in its 18th year of operations. This is because the spacecraft experiences a dynamic disturbance as it comes closer to the Sun, causing the spinning probe to wobble, a motion called ‘nutation’.

“We have to keep the nutation under control”, says Marsden, “otherwise we could lose contact with the spacecraft. Fortunately, the operations team has developed a robust strategy to tackle this problem, and there haven’t been too many scary moments this time around!” In fact, this strategy is so effective that the scientific measurements have hardly been affected. Nutation is expected to die away over the next few weeks as Ulysses once again heads away from the Sun.

A long-standing scientific puzzle that has been under investigation during the recent south-to-north transit is the clear north-south asymmetry in the structure of the heliosphere that was found when Ulysses visited the polar caps for the first time in 1994-95, also near solar minimum. At that time, the magnetic equator separating positive and negative magnetic fields was pushed 10 degrees southward with respect to the Sun’s rotational equator.

The reason for the offset is still not fully understood, and preliminary indications are that the recent data show much less of an effect than previously. However, further study is needed before firm conclusions can be drawn, as the Ulysses measurements are not conducted in each hemisphere simultaneously and temporal changes cannot be ruled out. Nevertheless, investigations of this kind demonstrate the value of long-term out-of-ecliptic observations that only Ulysses can supply.


For more information:

Richard Marsden, ESA Ulysses Mission Manager
Email: Richard.Marsden @ esa.int

Source: ESA - Space Science - News

22 February 2008

This artist's impression shows the ESA/NASA Ulysses spacecraft. Launched in 1990, the European-built spacecraft visits both polar regions once every 6.2 years as it circles the Sun in an orbit that is almost perpendicular to the ecliptic, the plane in which Earth and the planets move.

Credits: ESA

Ulysses, the mission to study the Sun’s poles and the influence of our star on surrounding space is coming to an end. After more than 17 years in space – almost four times its expected lifetime – the mission is finally succumbing to its harsh environment and is likely to finish sometime in the next month or two.

Ulysses is a joint mission between ESA and NASA. It was launched in 1990 from a space shuttle and was the first mission to study the environment of space above and below the poles of the Sun. The reams of data Ulysses has returned have forever changed the way scientists view the Sun and its effect on the space surrounding it.

Ulysses is in a six-year orbit around the Sun. Its long path through space carries it out to Jupiter’s orbit and back again. The further it ventures from the Sun, the colder the spacecraft becomes. If it drops to 2ºC, the spacecraft’s hydrazine fuel will freeze.

This has not been a problem in the past because Ulysses carries heaters to maintain a workable on-board temperature. The spacecraft is powered by the decay of a radioactive isotope and over the 17-plus years, the power it has been supplying has been steadily dropping. Now, the spacecraft no longer has enough power to run all of its communications, heating and scientific equipment simultaneously.

‘We expect certain parts of the spacecraft to reach 2ºC pretty soon,” says Richard Marsden, ESA’s Ulysses Project Scientist and Mission Manager. This will block the fuel pipes, making the spacecraft impossible to manoeuvre.

A joint ESA and NASA mission, Ulysses (named after the hero of Greek legend) is charting the unknown reaches of space above and below the poles of the sun.
Exploring our star's environment is vital if scientists are to build a complete picture of the sun, how it works and its effect on the solar system. In particular, the satellite is studying the solar wind that blows non-stop from the sun and carves a huge bubble in space called the heliosphere.

Ulysses is providing the first-ever map of the heliosphere from the equator to the poles.

Ulysses is equipped with a comprehensive range of scientific instruments. These are able to detect and measure solar wind ions and electrons, magnetic fields, energetic particles, cosmic rays, natural radio and plasma waves, cosmic dust, interstellar neutral gas, solar X-rays and cosmic gamma-ray bursts. This combination of experiments will help scientists understand the sun and its heliosphere, and perhaps the sun's influence on Earth's climate.

Ulysses was launched by the Space Shuttle Discovery in October 1990. It headed out to Jupiter, arriving in February 1992 for the gravity-assisted manoeuvre that swung the craft into its unique solar orbit. It passed over the sun's south pole in 1994, and the north pole in 1995.

Credits: ESA

In an attempt to solve this problem, the ESA-NASA project team approved a plan to temporarily shut off the main spacecraft transmitter. This would release 60 watts of power that could be channelled to the science instruments and the heater. When data was to be transmitted back to Earth, the team planned to turn the transmitter back on. Unfortunately, during the first test of this method in January, the power supply to the radio transmitter failed to turn back on.

“The decision to switch the transmitter off was not taken lightly. It was the only way to continue the science mission,” says Marsden, who is a 30-year veteran of the project, having worked on it for 12 years before the spacecraft was launched.

After many attempts, the Ulysses project team now consider it highly unlikely that the X-band transmitter will be recovered. They believe the fault can be traced to the power supply, meaning that the extra energy they hoped to gain cannot be routed to the heater and science instruments after all.

So, the spacecraft has lost its ability to send large quantities of scientific data back to Earth and is facing the gradual freezing of its fuel lines. This spells the end of this highly successful mission. “Ulysses is a terrific old workhorse. It has produced great science and lasted much longer than we ever thought it would,” says Marsden. “This was going to happen in the next year or two, it has just taken place a little sooner than we hoped.”

The team plan to continue operating the spacecraft in its reduced capacity for as long as they can over the next few weeks. “We will squeeze the very last drops of science out of it,” says Marsden.


For more information:

Richard Marsden, ESA Ulysses Project Scientist and Mission Manager
Email: Richard.Marsden @ esa.int

Source: ESA - Space Science - News

WASHINGTON - The joint NASA and European Space Agency Ulysses mission to study the sun and its influence on surrounding space is likely to cease operations in the next few months. The venerable spacecraft, which has lasted more than 17 years or almost four times its expected mission lifetime, is succumbing to the harsh environment of space.

Ulysses was the first mission to survey the space environment above and below the poles of the sun. The reams of data Ulysses returned have forever changed the way scientists view our star and its effects.


Artist concept of Ulysses and the sun.
› Larger view

"I remember when we got those first pictures of Ulysses floating out of the space shuttle Discovery's payload bay back in October of 1990 and thinking we had a great five years ahead of us," said Ed Massey, Ulysses project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "I never dared think that we would be receiving invaluable science data on a near continuous basis for more than 17 years. Ulysses has set the bar on solar science data collection quite high."

Science findings and discoveries from the mission were numerous and unprecedented. Examples include taking the first direct measurements of interstellar dust particles and interstellar helium atoms in the solar system and the discovery that the magnetic field leaving the sun is balanced across latitudes.

"The data and science output of this mission truly deserves to be named after the legendary explorer in Greek mythology," said Arik Posner, Ulysses program scientist, NASA Headquarters, Washington. "My compliments go out to the international team of scientists and engineers who built a spaceship and instrument payload that is highly sensitive, yet durable enough that it withstood the most extreme conditions in the solar system, including a polar passage of the giant planet Jupiter."

Since its Jupiter flyby in 1992, Ulysses has been in a six-year orbit around the sun. Its long path through space carries it out to Jupiter's orbit and back. The farther it ventures from the sun, the colder the spacecraft becomes. If it drops to 2 degrees Celsius (36 degrees Fahrenheit), the spacecraft's hydrazine fuel will freeze. This has not been a problem in the past because Ulysses carries heaters to maintain a workable onboard temperature.

The spacecraft is powered by the decay of a radioactive isotope. Over its 17-plus years, the power has been steadily dropping. The spacecraft no longer can run all of its communications, heating and scientific equipment simultaneously. "We expect certain parts of the spacecraft to reach 2 degrees Celsius pretty soon," said Richard Marsden, ESA project scientist and mission manager. This temperature drop will block the fuel pipes, making the spacecraft impossible to maneuver.

The NASA/ESA project team approved a plan to temporarily shut off the main spacecraft's X- band transmitter. This would release 60 watts of power, which could be channeled to the science instruments and the heater. The team planned to turn the transmitter back on when data was to be transmitted back to Earth. This would have made it possible to run Ulysses for up to another two years.

Unfortunately, during the first test of this approach in January, the power supply to the radio transmitter failed to turn back on. Engineers believe the fault can be traced to the transmitter's power supply, meaning that the extra energy they hoped to gain cannot be routed to the heater and science instruments. "The decision to switch the transmitter off was not taken lightly. It was the only way to continue the science mission," Marsden said.

After many attempts, the Ulysses project team now considers it highly unlikely that the X-band transmitter will be recovered. As a result, the spacecraft has lost its ability to send large quantities of scientific data back to Earth and is facing the gradual freezing of its fuel lines. The team plans to continue operating the spacecraft in its reduced capacity, using the alternate S-band transmitter, for as long as they can over the next few weeks.

"We will squeeze the very last drops of science out of it that we can," Marsden said. "Ulysses is a terrific old workhorse. It has produced great science and lasted much longer than we ever thought it would."

The Ulysses spacecraft was built by Dornier Systems of Germany for ESA. NASA provided the launch and the upper stage boosters. The U.S. Department of Energy, Washington, supplied the generator that powers the spacecraft; science instruments were provided by both U.S. and European investigators. The spacecraft is operated from JPL by a joint NASA/ESA team and has employed NASA's Deep Space Network for communications.

More information about NASA's Ulysses mission is available on the Web at:

_http://ulysses.jpl.nasa.gov

Media contact: DC Agle 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.
agle@jpl.nasa.gov

Dwayne Brown 202-358-1726
NASA Headquarters, Washington
dwayne.c.brown@nasa.gov

2008-031

Source: NASA - Solar System - Features