Exoplanets - Planets Beyond Our Solar System

[Waspie_Dwarf]

NASA's Spitzer Finds Hints of Planet Birth Around Dead Star

The NASA press release is reproduced below:

NASA's Spitzer Space Telescope has uncovered new evidence that planets might rise up out of a dead star's ashes.

The infrared telescope surveyed the scene around a pulsar, the remnant of an exploded star, and found a surrounding disk made up of debris shot out during the star's death throes. The dusty rubble in this disk might ultimately stick together to form planets.

Image above: This artist's concept depicts a type of dead star called a pulsar and the surrounding disk of rubble discovered by NASA's Spitzer Space Telescope. Image credit: NASA/JPL-Caltech

+ Related animation (6.5Mb): This artist's animation depicts the explosive death of a massive star, followed by the creation of a disk made up of the star's ashes.

+ Full caption/high resolution for animation and image

+ Related podcast

+ Related images from media telecon site

This is the first time scientists have detected planet-building materials around a star that died in a fiery blast.

"We're amazed that the planet-formation process seems to be so universal," said Dr. Deepto Chakrabarty of the Massachusetts Institute of Technology in Cambridge, principal investigator of the new research. "Pulsars emit a tremendous amount of high energy radiation, yet within this harsh environment we have a disk that looks a lot like those around young stars where planets are formed."

A paper on the Spitzer finding appears in the April 6 issue of Nature. Other authors of the paper are lead author Zhongxiang Wang and co-author David Kaplan, both of the Massachusetts Institute of Technology.

The finding also represents the missing piece in a puzzle that arose in 1992, when Dr. Aleksander Wolszczan of Pennsylvania State University found three planets circling a pulsar called PSR B1257+12. Those pulsar planets, two the size of Earth, were the first planets of any type ever discovered outside our solar system. Astronomers have since found indirect evidence the pulsar planets were born out of a dusty debris disk, but nobody had directly detected this kind of disk until now.

The pulsar observed by Spitzer, named 4U 0142+61, is 13,000 light-years away in the Cassiopeia constellation. It was once a large, bright star with a mass between 10 and 20 times that of our sun. The star probably survived for about 10 million years, until it collapsed under its own weight about 100,000 years ago and blasted apart in a supernova explosion.

Some of the debris, or "fallback," from that explosion eventually settled into a disk orbiting the shrunken remains of the star, or pulsar. Spitzer was able to spot the warm glow of the dusty disk with its heat-seeking infrared eyes. The disk orbits at a distance of about 1 million miles and probably contains about 10 Earth-masses of material.

Pulsars are a class of supernova remnants, called neutron stars, which are incredibly dense. They have masses about 1.4 times that of the sun squeezed into bodies only 10 miles wide. One teaspoon of a neutron star would weigh about 2 billion tons. Pulsar 4U 0142+61 is an X-ray pulsar, meaning that it spins and pulses with X-ray radiation.

Any planets around the stars that gave rise to pulsars would have been incinerated when the stars blew up. The pulsar disk discovered by Spitzer might represent the first step in the formation of a new, more exotic type of planetary system, similar to the one found by Wolszczan in 1992.

"I find it very exciting to see direct evidence that the debris around a pulsar is capable of forming itself into a disk. This might be the beginning of a second generation of planets," Wolszczan said.

Pulsar planets would be bathed in intense radiation and would be quite different from those in our solar system. "These planets must be among the least hospitable places in the galaxy for the formation of life," said Dr. Charles Beichman, an astronomer at NASA's Jet Propulsion Laboratory and the California Institute of Technology, both in Pasadena, Calif.

The Jet Propulsion Laboratory manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech. JPL is a division of Caltech. Spitzer's infrared array camera, which made the pulsar observations, was built by NASA's Goddard Space Flight Center, Greenbelt, Md. The instrument's principal investigator is Dr. Giovanni Fazio of the Harvard-Smithsonian Center for Astrophysics.

For more information about Spitzer, visit:

http://www.spitzer.caltech.edu/spitzer

Media contact:

Whitney Clavin

Jet Propulsion Laboratory, Pasadena, Calif.

(818) 354-4673

Erica Hupp/Grey Hautaluoma

Headquarters, Washington

(202) 358-1237/0668

2006-049

Source: NASA - Explore the Universe - Stars and Galaxies

Edited April 5, 2006 by Waspie_Dwarf

[Waspie_Dwarf]

Trio of Neptunes and their Belt

The European Southern Observatory (ESO) press release pr-18-06 is reproduced below:

18 May 2006
Under embargo till 17 May 19:00 CET

Trio of Neptunes and their Belt

HARPS Instrument Finds Unusual Planetary System


Using the ultra-precise HARPS spectrograph on ESO's 3.6-m telescope at La Silla (Chile), a team of European astronomers have discovered that a nearby star is host to three Neptune-mass planets. The innermost planet is most probably rocky, while the outermost is the first known Neptune-mass planet to reside in the habitable zone. This unique system is likely further enriched by an asteroid belt.


The HARPS measurement reveal the presence of three planets with masses between 10 and 18 Earth masses around HD 69830, a rather normal star slightly less massive than the Sun. The planets' mean distance are 0.08, 0.19, and 0.63 the mean distance between the Earth and the Sun. From previous observations, it seems that there exists also an asteroid belt, whose location is unknown. It could either lie between the two outermost planets, or farther from its parent star than 0.8 the mean Earth-Sun distance.


This image is taken from a point of view inside the asteroid belt, which is assumed here to lie between the two outermost planets.

"For the first time, we have discovered a planetary system composed of several Neptune-mass planets", said Christophe Lovis, from the Geneva Observatory and lead-author of the paper presenting the results [1].

During more than two years, the astronomers carefully studied HD 69830, a rather inconspicuous nearby star slightly less massive than the Sun. Located 41 light-years away towards the constellation of Puppis (the Stern), it is, with a visual magnitude of 5.95, just visible with the unaided eye. The astronomers' precise radial-velocity measurements [2] allowed them to discover the presence of three tiny companions orbiting their parent star in 8.67, 31.6 and 197 days.

"Only ESO's HARPS instrument installed at the La Silla Observatory, Chile, made it possible to uncover these planets", said Michel Mayor, also from Geneva Observatory, and HARPS Principal Investigator. "Without any doubt, it is presently the world's most precise planet-hunting machine" [3].


Measurements of the radial velocity of the star HD 69830 obtained by HARPS on the ESO 3.6m telescope at La Silla as a function of time, from November 2004 till February 2005 (a) and from mid-October 2005 till February 2006 (. The two innermost planets are clearly revealed, while the presence of the third one becomes clear when removing the signal of the inner planets and binning the data points (one per observing run), as shown in ©. The lower parts of (a) and ( show the residuals from the best fit indicated by the solid line.


The HARPS radial velocity measurements of HD 69830 are folded with the orbital periods of the three discovered planets: 8.67, 31.6 and 197 days, respectively. In each case, the contribution of the two other planets has been subtracted. The solid line shows the best fit to the measurements, corresponding to minimum masses of 10.2, 11.8 and 18.1 Earth masses. Note that the full span of the vertical axis is only 13 m/s! Error bars indicate the accuracy of the measurements. The integration time was 4 minutes on average for the first 18 measurements (shown as open dots), and was increased to 15 minutes for the remaining points (full dots). The latter measurements are therefore of much higher quality.

The detected velocity variations are between 2 and 3 metres per second, corresponding to about 9 km/h! That's the speed of a person walking briskly. Such tiny signals could not have been distinguished from 'simple noise' by most of today's available spectrographs.

The newly found planets have minimum masses between 10 and 18 times the mass of the Earth. Extensive theoretical simulations favour an essentially rocky composition for the inner planet, and a rocky/gas structure for the middle one. The outer planet has probably accreted some ice during its formation, and is likely to be made of a rocky/icy core surrounded by a quite massive envelope. Further calculations have also shown that the system is in a dynamically stable configuration.


Illustration of the possible formation process and present day structure of the planetary system around HD 68930. The three planets form from embryos originally located at larger distances (dashed ellipses) than the present ones (indicated by solid ellipses at 0.07, 0.18 and 0.63 the mean Earth-Sun distance). The embryos of the inner and middle planets start interior to the ice line, so that these two planets build up from rocky planetesimals and gas. The two planets consist of a central rocky core (in brown) and an envelope of gas (in gray). The embryo of the outermost planet starts beyond the ice line, and the planet accumulates a large amount of ice at the beginning of its formation. The planet finally consists of a central rocky core (brown), surrounded by a shell of water (ice or liquid - in blue), and a quite massive gas envelope (gray).

The outer planet also appears to be located near the inner edge of the habitable zone, where liquid water can exist at the surface of rocky/icy bodies. Although this planet is probably not Earth-like due to its heavy mass, its discovery opens the way to exciting perspectives.

"This alone makes this system already exceptional", said Willy Benz, from Bern University, and co-author. "But the recent discovery by the Spitzer Space Telescope that the star most likely hosts an asteroid belt is adding the cherry to the cake."

With three roughly equal-mass planets, one being in the habitable zone, and an asteroid belt, this planetary system shares many properties with our own solar system.

"The planetary system around HD 69830 clearly represents a Rosetta stone in our understanding of how planets form", said Michel Mayor. "No doubt it will help us better understand the huge diversity we have observed since the first extra-solar planet was found 11 years ago."

Video footage and animations are available on this page.

Notes

[1]: These results appear in the 18 May issue of the research journal Nature ("Discovery of an extrasolar planetary system with three Neptune-Mass Planets", by C. Lovis et al.). The team is composed of Christophe Lovis, Michel Mayor, Francesco Pepe, Didier Queloz, and Stéphane Udry (Observatoire de l'Université de Genève, Switzerland), Nuno C. Santos (Observatoire de l'Université de Genève, Switzerland, Centro de Astronomia e Astrofisica da Universidade de Lisboa and Centro de Geofisica de Evora, Portugal), Yann Alibert, Willy Benz, Christoph Mordasini (Physikalisches Institut der Universität Bern, Switzerland), François Bouchy (Observatoire de Haute-Provence and IAP, France), Alexandre C. M. Correia (Universidade de Aveiro, Portugal), Jacques Laskar (IMCCE-CNRS, Paris, France), Jean-Loup Bertaux (Service d'Aéronomie du CNRS, France), and Jean-Pierre Sivan (Laboratoire d'Astrophysique de Marseille, France).

[2]: A planet in orbit around a star will manifest its presence by pulling the star in different directions, thereby changing by rather small amounts its measured velocity. Astronomers therefore measure with very high precision the velocity of a star to detect the signature of one or more planets.

[3]: The High Accuracy Radial velocity Planet Searcher (HARPS) at the ESO La Silla 3.6-m telescope is dedicated to the discovery of extrasolar planets. It is a fibre-fed high-resolution echelle spectrograph that has demonstrated a long-term precision of about 1 m/s.

Source: ESO Press Release pr-18-06 Edited June 1, 2007 by Waspie_Dwarf

[TooFarGone]

Wow, thats pretty incredible....great artist depictions too.

[Waspie_Dwarf]

Astronomers Use Innovative Technique to Find Extrasolar Planet

Artist's Concept of Transiting Planet XO-1b
This artist's impression shows a dramatic close-up of the extrasolar planet XO-1b passing in front of a Sun-like star 600 light-years from Earth. The Jupiter-sized planet is in a tight four-day orbit around the star.

Credit: NASA, ESA and G. Bacon (STScI)

Image Type: Artwork
STScI-PRC2006-22a

An international team of professional and amateur astronomers, using simple off-the-shelf equipment to trawl the skies for planets outside our solar system, has hauled in its first "catch."

The astronomers discovered a Jupiter-sized planet orbiting a Sun-like star 600 light-years from Earth in the constellation Corona Borealis. The team, led by Peter McCullough of the Space Telescope Science Institute in Baltimore, Md., includes four amateur astronomers from North America and Europe.

Using modest telescopes to search for extrasolar planets allows for a productive collaboration between professional and amateur astronomers that could accelerate the planet quest.

"This discovery suggests that a fleet of modest telescopes and the help of amateur astronomers can search for transiting extrasolar planets many times faster than we are now," McCullough said. The finding has been accepted for publication in the Astrophysical Journal.

McCullough deployed a relatively inexpensive telescope made from commercial equipment to scan the skies for extrasolar planets. Called the XO telescope, it consists of two 200-millimeter telephoto camera lenses and looks like a pair of binoculars. The telescope is on the summit of the Haleakala volcano, in Hawaii.

"To replicate the XO prototype telescope would cost $60,000," McCullough explained. "We have spent far more than that on software, in particular on designing and operating the system and extracting this planet from the data."

McCullough's team found the planet, dubbed X0-1b, by noticing slight dips in the star's light output when the planet passed in front of the star, called a transit. The light from the star, called XO-1, dips by approximately 2 percent when the planet XO-1b passes in front of it. The observation also revealed that X0-1b is in a tight four-day orbit around its parent star.

Although astronomers have detected more than 180 extrasolar planets, X0-1b is only the tenth planet discovered using the transit method. It is the second planet found using telephoto lenses. The first, dubbed TrES-1, was reported in 2004. The transit method allows astronomers to determine a planet's mass and size. Astronomers use this information to deduce the planet's characteristics, such as its density.

The team confirmed the planet's existence by using the Harlan J. Smith Telescope and the Hobby-Eberly Telescope at the University of Texas's McDonald Observatory to measure the slight wobble induced by the planet on its parent star. This so-called radial-velocity method allowed the team to calculate a precise mass for the planet, which is slightly less than that of Jupiter (about 0.9 Jupiter masses). The planet also is much larger than its mass would suggest. "Of the planets that pass in front of their stars, XO-1b is the most similar to Jupiter yet known, and the star XO-1 is the most similar to the Sun," McCullough said, although he was quick to add, "but XO-1b is much, much closer to its star than Jupiter is to the Sun."

The astronomer's innovative technique of using relatively inexpensive telescopes to look for eclipsing planets favors finding planets orbiting close to their parent stars. The planet also must be large enough to produce a measurable dip in starlight.

The planet is the first discovered in McCullough's three-year search for transiting extrasolar planets. The planet quest is underwritten by a grant from NASA's Origins program.

McCullough's planet-finding technique involves nightly sweeps of the sky using the XO telescope in Hawaii to note the brightness of the stars it encounters. A computer software program sifts through many thousands of stars every two months looking for tiny dips in the stars' light, the signature of a possible planetary transit. The computer comes up with a few hundred possibilities. From those candidates, McCullough and his team select a few dozen promising leads. He passes these stars on to the four amateur astronomers to study the possible transits more carefully.

From September 2003 to September 2005, the XO telescope observed tens of thousands of bright stars. In that time, his team of amateur astronomers studied a few dozen promising candidate stars identified by McCullough and his team. The star X0-1 was pegged as a promising candidate in June 2005. The amateur astronomers observed it in June and July 2005, confirming that a planet-sized object was eclipsing the star. McCullough's team then turned to the McDonald Observatory in Texas to obtain the object's mass and verify it as a planet. He received the news of the telescope's observation at 12:06 a.m. Feb. 16, 2006, from Chris Johns-Krull, a friend and colleague at Rice University.

"It was a wonderful feeling because the team had worked for three years to find this one planet," McCullough explained. "The discovery represents a few bytes out of nearly a terabyte of data: It's like trying to distill gold out of seawater."

The discovery also has special familial significance for the astronomer. "My father's mentor was Harlan J. Smith, the man whose ambition and hard work produced the telescope that we used to acquire the verifying data."

McCullough believes the newly found planet is a perfect candidate for study by the Hubble and Spitzer space telescopes. Hubble can measure precisely the star's distance and the planet's size. Spitzer can actually see the infrared radiation from the planet. By timing the disappearance of the planet behind the star, Spitzer also can measure the "ellipticity," or "out-of-roundness," of the planet's orbit. If the orbit is elliptical, then the varying gravitational force would result in extra heating of the planet, expanding its atmosphere and perhaps explaining why the object's diameter seems especially large for a body of its calculated mass.

"By timing the planet's passages across the star, both amateur and professional astronomers might be lucky enough to detect the presence of another planet in the XO-1 system by its gravitational tugs on XO-1b," McCullough said. "It's even possible that such a planet could be similar to Earth."

Release Date: 1:00PM (EDT) May 18, 2006
Release Number: STScI-2006-22

Source: Hubblesite - Newsdesk Edited June 1, 2007 by Waspie_Dwarf

[Waspie_Dwarf]

Understanding "Hot Jupiters"

The Astronomy & Astrophysics press release is reproduced below:

Interiors of extrasolar planets: A first step

Released on May 30th, 2006

“A correlation between the heavy element content of transiting extrasolar planets and the metallicity of their parent stars”, by Guillot et al.

To be published in Astronomy & Astrophysics.

This press release is issued as a collaboration with the CNRS and Astronomy & Astrophysics.
--------------------------------------------------------------------------------

A team of European astronomers, led by T. Guillot (CNRS, Observatoire de la Côte d’Azur, France), will publish a new study of the physics of Pegasids (also known as hot Jupiters) in Astronomy & Astrophysics. They found that the amount of heavy elements in Pegasids is correlated to the metallicity of their parent stars. This is a first step in understanding the physical nature of the extrasolar planets.

Up to now, astronomers have discovered 188 extrasolar planets, among which 10 are known as “transiting planets”. These planets pass between their star and us at each orbit (Figure 1). Given the current technical limitations, the only transiting planets that can be detected are giant planets orbiting close to their parent star known as “hot Jupiters” or Pegasids. The ten transiting planets known thus far have masses between 110 and 430 Earth masses (for comparison, Jupiter, with 318 Earth masses, is the most massive planet in our Solar System).


Fig. 1 - Animation of a typical Pegasid system, with both the star and planet drawn to scale. Here, the planet orbits the star in just 3.5 days. For comparison, the Earth orbits the Sun every single year, and Mercury, which has the shortest orbital period in the solar system, orbits the Sun every 88 days.

Although rare, transiting planets are the key to understanding planetary formation because they are the only ones for which both the mass and radius can be determined. In principle, the obtained mean density can constrain their global composition. However, translating a mean density into a global composition needs accurate models of the internal structure and evolution of planets. The situation is made difficult by our relatively poor knowledge of the behaviour of matter at high pressures (the pressure in the interiors of giant planets is more than a million times the atmospheric pressure on Earth). Of the nine transiting planets known up to April 2006, only the least massive one could have its global composition determined satisfactorily. It was shown to possess a massive core of heavy elements, about 70 times the mass of the Earth, with a 40 Earth-mass envelope of hydrogen and helium. Of the remaining eight planets, six were found to be mostly made up of hydrogen and helium, like Jupiter and Saturn, but their core mass could not be determined. The last two were found to be too large to be explained by simple models.

Considering them as an ensemble for the first time, and accounting for the anomalously large planets, Tristan Guillot and his team [1] found that the nine transiting planets have homogeneous properties, with a core mass ranging from 0 (no core, or a small one) up to 100 times the mass of the Earth, and a surrounding envelope of hydrogen and helium. Some of the Pegasids should therefore contain larger amounts of heavy elements than expected. When comparing the mass of heavy elements in the Pegasids to the metallicity of the parent stars, they also found a correlation to exist, with planets born around stars that are as metal-rich as our Sun and that have small cores, while planets orbiting stars that contain two to three times more metals have much larger cores, as shown in Figure 2. Their results will be published in Astronomy & Astrophysics.

Planet formation models have failed to predict the large amounts of heavy elements found this way in many planets, so these results imply that they need revising. The correlation between stellar and planetary composition has to be confirmed by further discoveries of transiting planets, but this work is a first step in studying the physical nature of extrasolar planets and their formation. It would explain why transiting planets are so hard to find, to start with. Because most Pegasids have relatively large cores, they are smaller than expected and more difficult to detect in transit in front of their stars. In any case, this is very promising for the CNES space mission COROT to be launched in October, which should discover and lead to characterization of tens of transiting planets, including smaller planets and planets orbiting too far from their star to be detected from the ground.

What of the tenth transiting planet? XO-1b was announced very recently (see NASA press release) and is also found to be an anomalously large planet orbiting a star of solar metallicity. Models imply that it has a very small core, so that this new discovery strengthens the proposed stellar-planetary metallicity correlation.



Fig. 2 - Correlation between the amount of heavy elements in the transiting planets and the metallicity of their parent stars.

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[1] The team includes T. Guillot (France), N.C. Santos (Portugal), F. Pont (Switzerland), N. Iro (USA), C. Melo (Germany), I. Ribas (Spain).

--------------------------------------------------------------------------------

A correlation between the heavy element content of transiting extrasolar planets and the metallicity of their parent stars by T. Guillot, N.C. Santos, F. Pont, N. Iro, C. Melo, I. Ribas.
To be published in Astronomy & Astrophysics (DOI number: 10.1051/0004-6361:20065476)
Full article available in PDF format

Source: Astronomy & Astrophysics press release

[Waspie_Dwarf]

Do 'Planemos' Have Progeny?

The European Southern Observatory (ESO) press release pr-19-06 is reproduced below:

6 June 2006
Under Embargo Until 17:30 CEST (11:30 A.M. EDT) Monday 5 June 2006

Do 'Planemos' Have Progeny?

Planetary-Mass Objects Found to be Surrounded by Discs

Two new studies, based on observations made with ESO's telescopes, show that objects only a few times more massive than Jupiter are born with discs of dust and gas, the raw material for planet making. This suggests that miniature versions of the solar system may circle objects that are some 100 times less massive than our Sun.

These findings are to be presented Monday, 5 June at the American Astronomical Society meeting in Calgary, Canada.

Since a few years, it is known that many young brown dwarfs, 'failed stars' that weigh less than 8 percent the mass of the Sun, are surrounded by a disc of material. This may indicate these objects form the same way as did our Sun.

The new findings reveal that the same appears to be true for their even punier cousins, sometimes called planetary mass objects or 'planemos'. These objects have masses similar to those of extra-solar planets, but they are not in orbit around stars - instead, they float freely through space.

"Our findings, combined with previous work, suggest similar infancies for our Sun and objects that are some hundred times less massive", says Valentin D. Ivanov (ESO), co-author of the first study.


Optical spectra of the six planetary mass object candidates, along with those of comparison objects. The dotted lines mark the location of Hα while the dashed line corresponds to a telluric absorption feature.

"Now that we know of these planetary mass objects with their own little infant planetary systems, the definition of the word 'planet' has blurred even more," adds Ray Jayawardhana, from the University of Toronto (Canada) and lead author of the study. "In a way, the new discoveries are not too surprising - after all, Jupiter must have been born with its own disc, out of which its bigger moons formed."

Unlike Jupiter, however, these planemos are not circling stars. In their study, Jayawardhana and Ivanov used two of ESO's telescopes - Antu, the 8.2-metre Unit Telescope no. 1 of the Very Large Telescope, and the 3.5-metre New Technology Telescope - to obtain optical spectra of six candidates identified recently by researchers at the University of Texas at Austin. Two of the six turned out to have masses between five to 10 times that of Jupiter while two others are a tad heftier, at 10 to 15 times Jupiter's mass. All four of these objects are 'newborns', just a few million years old, and are located in star-forming regions about 450 light-years from Earth. The planemos show infrared emission from dusty discs that may evolve into miniature planetary systems over time.

In another study, Subhanjoy Mohanty (Harvard-Smithsonian Center for Astrophysics, CfA), Ray Jayawardhana (Univ. of Toronto), Nuria Huelamo (ESO) and Eric Mamajek (also at CfA) used the Very Large Telescope, this time with its adaptive optics system and infrared camera NACO, to obtain images and spectra of a planetary mass companion discovered at ESO two years ago around a young brown dwarf that is itself about 25 times the mass of Jupiter. This planetary mass companion is the first-ever exoplanet to have been imaged (see ESO 12/05).


VLT NACO J-band image, showing the 2M1207Ab system: the planetary companion is visible near the lower left rim of the brown dwarf, at a separation of 769 mas. North is up, East is left.

The brown dwarf, dubbed 2M1207 for short and located 170 light-years from Earth, was known to be surrounded by a disc. Now, this team has found evidence for a disc around the eight-Jupiter-mass companion as well.

"The pair probably formed together, like a petite stellar binary", explains lead author Mohanty, "instead of the companion forming in the disc around the brown dwarf, like a star-planet system."

"Moreover", Jayawardhana adds, "it is quite likely that smaller planets or asteroids could now form in the disc around each one."

Source: ESO Press Release pr-19-06

[Waspie_Dwarf]

Jupiter's "Big Brother" Has Moon-Forming Dust Disk

The Harvard-Smithsonian Center for Astrophysics press release is reproduced below:

Release No.: 06-16
For Release: For Release: 9:30 a.m. MDT (11:30 a.m. EDT) Monday, June 5, 2006

Jupiter's "Big Brother" Has Moon-Forming Dust Disk

Calgary, AB - Earth's Moon was created by an early collision with another large planetary body. It was a "chip off the old block." Mars captured its asteroidal moons as they passed by. But Jupiter made its own moons out of dust and gas remaining from its formation. Now, observations by astronomer Subhanjoy Mohanty of the Harvard-Smithsonian Center for Astrophysics (CfA) and his colleagues provide the first direct evidence for a dusty disk around a distant planet that in mass would be Jupiter's "big brother."

Astronomers have discovered a dusty disk around the 8-Jupiter-mass object called 2M1207B, shown here in an artist's conception. That disk eventually may form one or more moons like those orbiting the giant planets of our solar system. As seen from Earth, 2M1207B lies in the constellation Centaurus, which is also home to the peculiar galaxy NGC 5128 shown in the upper left of this image. Credit: David A. Aguilar (CfA)

"It is quite possible that moons or moonlets could form out of this disk, just as they have around the giant planets in our own solar system," said Mohanty.

Mohanty presented the discovery today in a press conference at the 208th meeting of the American Astronomical Society. Other members of the team are Ray Jayawardhana (University of Toronto), Nuria Huélamo (ESO) and Eric Mamajek (CfA).

The team studied a planetary mass object known as 2MASS1207-3932B, which is located about 170 light-years from Earth in the direction of the constellation Centaurus. 2M1207B, as it is abbreviated, orbits a tiny brown dwarf star at a separation of about 40 astronomical units, or 3.7 billion miles - comparable to the size of Pluto's orbit. That separation is much larger than typical for binary brown dwarf systems. The wide separation may indicate that the duo formed in relative isolation, far from passing stars that could have pulled them apart.

"This system probably won't survive for long. It won't last 5 billion years like our solar system has," said Mamajek. "All it would take is for a more massive interloper star to come along and yank the planet away from the brown dwarf."

Observations by Mohanty's team showed that the brown dwarf has a mass of about 25 Jupiters and a temperature of 4100 degrees Fahrenheit (2600 K). Its companion 2M1207B weighs about 8 times Jupiter and has a temperature of 2400 degrees F (1600 K). Both objects are warm due to their young age of 5-10 million years, having retained the heat of formation.

Given those temperatures, the team then calculated the expected brightness of both objects. The brown dwarf matched predictions but its companion was about 8 times fainter than expected. After examining several potential causes, the team concluded that the only plausible explanation was the presence of an edge-on dusty disk that blocked most of the planet's light. The planet is seen only in light scattered from the disk.

Spectral analysis shows that 2M1207B is a gas giant like Jupiter with no solid surface. As a result, it would be a poor abode for life. Any moons that might form around it, however, could prove more hospitable.

The large mass of 2M1207B relative to the brown dwarf star poses a puzzle for planetary formation theories. Typical planets like those in our solar system are less than one-hundredth the size of the central star. In contrast, 2M1207B holds one-third as much mass as the brown dwarf.

"Mass ratios of that size are more typical for binary stars than for planetary systems," said Mohanty. "2M1207B probably formed like a star, together with the brown dwarf, rather than from core accretion like giant planets around other stars."

Mohanty and his colleagues plan to study the polarization of light from 2M1207B in order to investigate the inclination of its disk as well as the size of dust grains within the disk. Further studies await the next generation of large telescopes, such as the Giant Magellan Telescope and the Atacama Large Millimeter Array, which may be able to directly detect the disk around the planetary mass companion.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.


Source: CfA Press Release

[Waspie_Dwarf]

Planet-Forming Disks Might Put the Brakes on Stars

Astronomers using NASA's Spitzer Space Telescope have found evidence that dusty disks of planet-forming material tug on and slow down the young, whirling stars they surround.

Young stars are full of energy, spinning around like tops in half a day or less. They would spin even faster, but something puts on the brakes. While scientists had theorized that planet-forming disks might be at least part of the answer, demonstrating this had been hard to do until now.


Image above: This artist's concept shows a
dusty planet-forming disk in orbit around a
whirling young star.
Image credit: NASA/JPL-Caltech.
+ Larger view
+ Video: Spitzer's Spin on Stars (14Mb)

"We knew that something must be keeping the stars' speed in check," said Dr. Luisa Rebull of NASA's Spitzer Science Center, Pasadena, Calif. "Disks were the most logical answer, but we had to wait for Spitzer to see the disks."

Rebull, who has been working on the problem for nearly a decade, is lead author of a new paper in the July 20 issue of the Astrophysical Journal. The findings are part of a quest to understand the complex relationship between young stars and their burgeoning planetary systems.

Stars begin life as collapsing balls of gas that spin faster and faster as they shrink, like twirling ice skaters pulling in their arms. As the stars whip around, excess gas and dust flatten into surrounding pancake-like disks. The dust and gas in the disks are believed to eventually clump together to form planets.

Developing stars spin so fast that, left unchecked, they would never fully contract and become stars. Prior to the new study, astronomers had theorized that disks might be slowing the super speedy stars by yanking on their magnetic fields. When a star's fields pass through a disk, they are thought to get bogged down like a spoon in molasses. This locks a star's rotation to the slower-turning disk, so the shrinking star can't spin faster.

To prove this principle, Rebull and her team turned to Spitzer for help. Launched in August of 2003, the infrared observatory is an expert at finding the swirling disks around stars, because dust in the disks is heated by starlight and glows at infrared wavelengths.

The team used Spitzer to observe nearly 500 young stars in the Orion nebula. They divided the stars into slow spinners and fast spinners, and determined that the slow spinners are five times more likely to have disks than the fast ones.

"We can now say that disks play some kind of role in slowing down stars in at least one region, but there could be a host of other factors operating in tandem. And stars might behave differently in different environments," Rebull said.

Other factors that contribute to a star's winding down over longer periods of time include stellar winds and possibly full-grown planets.

If planet-forming disks slow down stars, does that mean stars with planets spin more slowly than stars without planets? Not necessarily, according to Rebull, who said slowly spinning stars might simply take more time than other stars to clear their disks and develop planets. Such late-blooming stars would, in effect, give their disks more time to put on the brakes and slow them down.

Ultimately, the question of how a star's rotation rate is related to its ability to support planets will fall to planet hunters. So far, all known planets in the universe circle stars that turn around lazily. Our sun is considered a slowpoke, currently plodding along at a rate of one revolution every 28 days. And, due to limits in technology, planet hunters have not been able to find any extrasolar planets around zippy stars.

"We'll have to use different tools for detecting planets around rapidly spinning stars, such as next-generation ground and space telescopes," said Dr. Steve Strom, an astronomer at the National Optical Astronomy Observatory, Tucson, Ariz.

Other members of Rebull's team include Drs. John Stauffer of the Spitzer Science Center; S. Thomas Megeath at the University of Toledo, Ohio; and Joseph Hora and Lee Hartmann of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass. Hartmann is also affiliated with the University of Michigan, Ann Arbor.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology. Caltech manages JPL for NASA.

For an animation depicting how disks slow stars and more information about Spitzer, visit www.spitzer.caltech.edu/spitzer.

Media contact: Whitney Clavin (818) 354-4673
Jet Propulsion Laboratory, Pasadena, Calif.

2006-094

Source: NASA - Exploring the Universe - Stars and Galaxies

[Roj47]

I really do enjoy reading these links..... Many thanks.

My questions is however -

Is there any theory as to the effect that the speed of rotation of a star would have on surrounding planets?

i.e. What would the potential difference if any be to Earth between the Sun rotating every 28 days and twice daily.

I guess the other assumption would be that at twice dailt the Sun would be compact enough to actually be a star, but I go beyond my knowledge and understanding here.

regards

[leadbelly]

Take this for what it is- a guess.

The Sun is a mid-life dwarf yellow star, with an onion-like interior. There are layers that move at different rates. Add to this, the electromagnetic field lines running north to south,

and things wind and unwind every eleven years. The field lines gradually wrap around the Sun latitudinaly, which leads to tension, which leads to flairs amd coronal mass discharges.

Those can have more of a detrimental effect on planets if they lack sufficient magnetospheres.

For example, Mars would in its past have been a more deadly place to be during solar storm cycles, compared to Earth. Because Mars is smaller, retains less atmosphere, and has less magnetosphere due to it's less molten iron core, any theoretical primitive life would have been more irradiated, especially during solar storms.

Thus, as you speed up the Sun's rotation, you might shorten the time between storm cycles, making them a frequently occurring fact of life. For us, that could cause damage to satellites, and fry the electric transformers on Earth, if the storms were severe enough.

I also imagine that if the sun were to rotate at a very high rate of speed, for instance, once every two hours, it would probably start to break up.

[Roj47]

Thank you, and a very interesting idea.

Sun spots is something I can look up as are solar flares.

Kind regards

[Bella-Angelique]

Perhaps 26 to 30 day stars are the ones most likely then to have earth sized planets worth exploring.

[Waspie_Dwarf]

Stars can rotate at very rapid rates without breaking up. This is because they are not solid bodies. However it would become highly oblate, being very obviously flattened at the poles and bulging at the equator.

[Roj47]

Perhaps 26 to 30 day stars are the ones most likely then to have earth sized planets worth exploring.

Now that would be a very very interesting theory to establish.

However is it not the planets forming that reduce the speed. If so...... would the question be -

Perhaps 26 to 30 day stars are the ones most likely to have planets witgh the ability to sustain life.

Edited July 25, 2006 by Roj47

[leadbelly]

"If planet-forming disks slow down stars, does that mean stars with planets spin more slowly than stars without planets? Not necessarily, according to Rebull, who said slowly spinning stars might simply take more time than other stars to clear their disks and develop planets...

So far, all known planets in the universe circle stars that turn around lazily. Our sun is considered a slowpoke, currently plodding along at a rate of one revolution every 28 days. And, due to limits in technology, planet hunters have not been able to find any extrasolar planets around zippy stars..."

Evidently, it has been the case that when we employ the two common methods currently used to detect planets, the planets have been around "slowpoke" stars.

And, sustaining life is a relative term. You could have a "zippy" star with harsh light, and a planet at sufficient orbital distance, to allow extremophiles, or at best bacteria in liquid conditions, to survive against heat, light, maybe meteors in a younger star system...

But, all things considered, conditions identicle to Earth, or our sun at least, could be the ideal scenario.

[leadbelly]

When I said the sun might begin to break up at one rotation every two hours, I did not mean in large measure. I meant some of it may move away, and what I had in mind was that it would orbit the sun, perhaps in a circumstellar disk.

I agree that a star could become increasingly oblate, and not involve any shells (like a puffing variable, or a red giant), or orbiting disks. But, what I had in mind was an extreme rotation of the Sun. I probably should not guess like this, but it seemed plausible that our sun could shed material from "extreme" rotation.

My idea was that surface material might acieve not so much escape velocity, but a ballistic orbit. And, that is my idea of break up, in this instance.

Take for example, the solar wind. It ranges from 200 kms to 700 kms; avgs. 450 kms. On the slow end, it somehow "circumvents" solar escape velocity of 617 kms. I am not going for escape velocity, but ballistic orbit speeds.

If the Sun were to spin-

50 times faster would be one rotation every 13.5 minutes, or every 13.5 hours to remove

surface material at a ballistic speed.

Rotating 300 times faster than it currently spins, it would rotate every 2.25 hours.

The current speed at the equator is 7174 km/h. (7174*300 =2152200 km/hr = 1 rotation/ 2.25hr). This would be 597 km/sec. 597 kms is adequate for surface protons and electrons to be at a constant ballistic speed.

But, given the fact there are forces I do not understand, allowing protons and electrons to move out into the solar wind at less than escape velocity, that must mean that the current conditions are special, and I may not simply be able to extrapolate current solar wind conditions out to the future.

Because if the sun's rotational speed is increased, and if that increases internal mixing and friction and heat; and if the additional heat, in turn, reduces the magnetic field strength of the Sun, then perhaps that alters the escape mechanism for matter currently ejected through today's special process, which means less than escape velocity.

At some point, the magnetic mechanisms are reduced, and instead of regular emissions,

flares, and CMEs, centrifugal force starts to slough of considerable quantites of matter.

It may not all happen at once, but would possibly take millions of years.

The aim of this is to point out that at some point, the velocity of centrifugal force will balance Newtonian gravity at the equator. Effectively, some gravity vanishes near the surface, and if material is hot enough, and below a critical density, it may move away from the surface, and go into orbit around the bulk of the star.

[poleshift]

The Sun is a mid-life dwarf yellow star, with an onion-like interior. There are layers that move at different rates.

Interesting description. Wondering why they can not do the fusion of hydrogen to helium yet. Pressure, gravity, temperature, or other factors?

[Startraveler]

But, given the fact there are forces I do not understand, allowing protons and electrons to move out into the solar wind at less than escape velocity, that must mean that the current conditions are special, and I may not simply be able to extrapolate current solar wind conditions out to the future.

The velocity at which the solar wind leaves the Sun is not necessarily the velocity it'll have when detected. More importantly, the solar wind doesn't leave from the surface of the sun but rather far above it in the corona.

The aim of this is to point out that at some point, the velocity of centrifugal force will balance Newtonian gravity at the equator. Effectively, some gravity vanishes near the surface, and if material is hot enough, and below a critical density, it may move away from the surface, and go into orbit around the bulk of the star.

That's true. In fact there are not-quite-explained Keplerian equatorial disks that sometimes form around Be stars, a subset of class B stars. Now Be stars are known to rotate fast, faster than any other stars except stellar remnants like pulsars so the original suspicion was that perhaps they were rotating near enough to their critical velocity of rotation (at which, as you pointed out, the effective gravity vanishes) that their outer layers might be leaking off. Current thought, as far as I know, is that Be stars aren't rotating quite that close to the critical velocity but there are some who've suggested recently that current thought needs rethinking. So there's a chance (slim maybe) that this isn't just idle speculation but something that really happens out there.

Edited July 30, 2006 by Startraveler

[leadbelly]

Excellent points, Startraveler. The subject of stellar mechanics is obviously very interesting, from their inception all the way to more advanced stages.

Two things come to mind- Population III star formation, and those stars which I believe are said to orbit the Milky Way's galactic nuclei.

In the former case, they did not have dusty disks. And, the article says the dusty disk scenario relates primarily to certain cases. A qualification.

And in the latter, normal stars are supposedly encountering a region near a massive black hole and possibly getting spun up. It must not be too "injurious", because they are neither ejected, or stripped of material (I will certainly be corrected on these, and so it goes!)

Thanks again.

[Roj47]

Not really into the cut and paste scenario, but thought this may interest

Quote

The idea, based on the leading planet-formation theory, is that small objects collect more material and, if they don't collide with another big object, become planets.

Star of the show

Only 55 Cancri consistently yielded a world similar in size and orbital distance to Earth. Our planet sits in what's called a habitable zone, just the right distance from the Sun to allow liquid water.

"Our simulations typically produced one terrestrial planet in the habitable zone of 55 Cancri, with a typical mass of about half an Earth mass," said Sean Raymond, a postdoctoral researcher at the University of Colorado who worked on the project while a doctoral student at the University of Washington. "In many of the simulations, these planets accreted a decent amount of water-rich material from farther out in the disk."

The research, funded by NASA and the National Science Foundation, is described in a recent issue of the Astrophysical Journal.

A computer simulation is of course far from reality. But research like this can guide astronomers to solar systems worthy of further investigation as search technology improves.

"Our assumptions are quite optimistic, but not crazy by any means, and we start our simulations with a decent amount of material for terrestrial planets to form," Raymond told SPACE.com. "If we are wrong about this, then only smaller, perhaps Mars-sized planets could form in the habitable zone."

http://www.space.com/scienceastronomy/0608...ce_tuesday.html

[Waspie_Dwarf]

Planet Or Failed Star?
NASA's Hubble Telescope Photographs One of Smallest Stellar Companions Ever Seen

Astronomers using NASA's Hubble Space Telescope have photographed one of the smallest objects ever seen around a normal star beyond our Sun. Weighing in at 12 times the mass of Jupiter, the object is small enough to be a planet. The conundrum is that it's also large enough to be a brown dwarf, a failed star. The Hubble observation of the diminutive companion to the low-mass red dwarf star CHXR 73 is a dramatic reminder that astronomers do not have a consensus in deciding which objects orbiting other stars are truly planets -- even though they have at last agreed on how they will apply the definition of "planet" to objects inside our solar system.

Credit: NASA, ESA and K. Luhman (Penn State University)

Source: HubbleSite - Newsdesk

[Waspie_Dwarf]

CHXR 73 A and B - Red Dwarf and Substellar Companion (Annotated)

This NASA Hubble Space Telescope image shows one of the smallest objects ever seen around a normal star. Astronomers believe the object is a brown dwarf because it is 12 times more massive than Jupiter. The brown dwarf candidate, called CHXR 73 B, is the bright spot at lower right. It orbits a red dwarf star, dubbed CHXR 73, which is a third less massive than the Sun. At 2 million years old, the star is very young when compared with our middle-aged 4.6-billion-year-old Sun.

CHXR 73 B orbits 19.5 billion miles from its star, or roughly 200 times farther than Earth is from the Sun.

The star looks significantly larger than CHXR 73 B because it is much brighter than its companion. CHXR 73 B is 1/100 as bright as its star. The cross-shaped diffraction spikes around the star are artifacts produced within the telescope's optics. The star is 500 light-years away from Earth.

Hubble's Advanced Camera for Surveys snapped the image in near-infrared light on Feb. 10 and 15, 2005. The color used in the image does not reflect the object's true color.

Members of the research team are K. L. Luhman, Penn State University; J. C. Wilson, M. F. Skrutskie, M. J. Nelson, and D. E. Peterson, University of Virginia; W. Brandner, Max-Planck Institute for Astronomy; and J. D. Smith, M. C. Cushing, and E. Young, University of Arizona.


Credit:NASA, ESA and K. Luhman (Penn State University)

Image Type:Astronomical/Illustration

Source: HubbleSite - Newsdesk Edited June 1, 2007 by Waspie_Dwarf

[Waspie_Dwarf]

Artist's View of Red Dwarf and Substellar Companion

This is an artist's concept of the red dwarf star CHXR 73 (upper left) and its companion CHXR 73 B in the foreground (lower right) weighing in at 12 Jupiter masses. CHXR 73 B is one of the smallest companion objects ever seen around a normal star beyond our Sun.

Estimated to be 12 times the mass of Jupiter, the object is small enough to be a planet, but also large enough to be a brown dwarf, a failed star. The NASA Hubble Space Telescope discovery of this diminutive companion to a low-mass star is a dramatic reminder that astronomers do not have a consensus in deciding which objects orbiting other stars are truly planets.

CHXR 73 B is 19.5 billion miles from its red dwarf sun (roughly 200 times farther than Earth is from our Sun). The youthful, 2-million-year-old star is one-third the mass of our Sun and lies approximately 500 light-years away in the Chamaeleon I star-forming region in our Galaxy.

Credit: NASA, ESA and G. Bacon (STScI)

Image Type: Artwork
STScI-PRC2006-31b

Source: HubbleSite - Newsdesk Edited June 1, 2007 by Waspie_Dwarf

[Waspie_Dwarf]

Strange New Planet Baffles Astronomers

The Harvard-Smithsonian Center for Astrophysics press release is reproduced below:

Release No.: 06-24
For Release: EMBARGOED until 10:00 a.m. EDT, September 14, 2006

Strange New Planet Baffles Astronomers


The newly discovered world HAT-P-1 has baffled astronomers, since
it is puffed up much larger than theory predicts. HAT-P-1 has a radius
about 1.38 times Jupiter's but contains only half Jupiter's mass.
Credit: David A. Aguilar (CfA)

Washington, DC - Using a network of small automated telescopes known as HAT, Smithsonian astronomers have discovered a planet unlike any other known world. This new planet, designated HAT-P-1, orbits one member of a pair of distant stars 450 light-years away in the constellation Lacerta.

"We could be looking at an entirely new class of planets," said Gaspar Bakos, a Hubble fellow at the Harvard-Smithsonian Center for Astrophysics (CfA). Bakos designed and built the HAT network and is lead author of a paper submitted to the Astrophysical Journal describing the discovery.

With a radius about 1.38 times Jupiter's, HAT-P-1 is the largest known planet. In spite of its huge size, its mass is only half that of Jupiter.

"This planet is about one-quarter the density of water," Bakos said. "In other words, it's lighter than a giant ball of cork! Just like Saturn, it would float in a bathtub if you could find a tub big enough to hold it, but it would float almost three times higher."

HAT-P-1 revolves around its host star every 4.5 days in an orbit one-twentieth of the distance from Earth to the Sun. Once each orbit, it passes in front of its parent star, causing the star to appear fainter by about 1.5 percent for more than two hours, after which the star returns to its previous brightness.

HAT-P-1's parent star is one member of a double-star system called ADS 16402 and is visible in binoculars. The two stars are separated by about 1500 times the Earth-Sun distance. The stars are similar to the Sun but slightly younger - about 3.6 billion years old compared to the Sun's age of 4.5 billion years.

Although stranger than any other extrasolar planet found so far, HAT-P-1 is not alone in its low-density status. The first planet ever found to transit its star, HD 209458b, also is puffed up about 20 percent larger than predicted by theory. HAT-P-1 is 24 percent larger than expected.

"Out of eleven known transiting planets, now not one but two are substantially bigger and lower in density than theory predicts," said co-author Robert Noyes (CfA). "We can't dismiss HD209458b as a fluke. This new discovery suggests something could be missing in our theories of how planets form."

Theorists had already considered a number of possibilities to explain the large size of HD 209458b, but so far without success. The only way to puff up these giant planets beyond the size calculated from planetary structure equations would be to supply additional heat to their interiors. Simple heating of the surface due to the host star's proximity would not work. (If it could, all close-in transiting giant planets should be expanded, not just two of them.)

One way to inject energy into the planet's center is by tipping it on its side, similar to Uranus in the solar system. A planet in that state orbiting close to its star would be subjected to tidal heating of the interior. But according to Smithsonian astronomer Matthew Holman (who was not a member of the discovery team), "the circumstances required to tip over a planet are so unusual that this would seem unlikely to explain both known examples of inflated worlds."

According to co-author Dimitar Sasselov (CfA), "Another explanation for HD 209458b's large size was tidal heating due to an eccentric orbit, but recent observations have pretty much ruled that out."

The scientists will continue observing HAT-P-1 to see if such an explanation could hold in this case, but "until we can find an explanation for both of these swollen planets, they remain a great mystery," Sasselov said.

The HAT network consists of six telescopes, four at the Smithsonian Astrophysical Observatory's Whipple Observatory in Arizona and two at its Submillimeter Array facility in Hawaii. These telescopes conduct robotic observations every clear night, each covering an area of the sky 300 times the size of the full moon with every exposure.

HAT searches for planets by watching for stars that dim slightly when an orbiting planet crosses directly in front of the star as viewed from Earth - a sort of mini-eclipse. Transits offer astronomers a unique opportunity to measure a planet's physical size from the amount of the dimming. Combined with the mass, which is determined by measuring the amount of the star's wobble as the planet orbits it, researchers then calculated a planet's density. Measurements of the wobble of HAT-P-1's parent star were led by co-author Debra Fischer of San Francisco State University.

Major funding for HATnet was provided by NASA. More information about HAT is available online at http://www.cfa.harvard.edu/~gbakos/HAT/.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.


Source: CfA Press Release

[Waspie_Dwarf]

Astronomers Reveal First Alien I.D. Chart

The Harvard-Smithsonian Center for Astrophysics press release is reproduced below:

Release No.: 06-25
For Release: EMBARGOED until 10:00 a.m. EDT, September 14, 2006

Astronomers Reveal First Alien I.D. Chart


Earth's early atmosphere of nitrogen, methane and carbon dioxide was
hostile to life as we know it, but friendly to the first methane-loving
bacteria. Astronomers modeled the history of Earth's atmosphere
to learn what fingerprints to seek on alien worlds.
Credit: David A. Aguilar (CfA)

Washington, DC - It is only a matter of time before astronomers find an Earth-sized planet orbiting a distant star. When they do, the first questions people will ask are: Is it habitable? And even more importantly, is there life present on it already? For clues to the answers, scientists are looking to their home planet, Earth.

Astronomers Lisa Kaltenegger of the Harvard-Smithsonian Center for Astrophysics (CfA) and Wesley Traub of NASA's Jet Propulsion Laboratory and CfA, propose using Earth's atmospheric history to understand other planets.

"Good planets are hard to find," said Kaltenegger. "Our work provides the signposts astronomers will look for when examining truly Earth-like worlds."

Geologic records show that Earth's atmosphere has changed dramatically during the past 4.5 billion years, in part because of life forms developing on our planet. Mapping what gases comprised Earth's atmosphere during its history, Kaltenegger and Traub propose that by looking for similar atmospheric compositions on other worlds, scientists will be able to determine if that planet has life on it, and if so, that life's evolutionary stage.

To date, all extrasolar planets have been studied indirectly, for example by monitoring the way a host star wobbles as the planet's gravity tugs it. Only four extrasolar planets have been detected directly, and they are massive Jupiter-sized worlds. The atmosphere of one of these worlds was detected by another CfA scientist, David Charbonneau, using NASA's Spitzer Space Telescope. The next generation of space-based missions such as NASA's Terrestrial Planet Finder (TPF) and ESA's Darwin will be able to directly study nearby Earth-sized worlds.

Astronomers particularly want to observe the visible and infrared spectra of distant terrestrial planets to learn about their atmospheres. Particular gases leave signatures in a planet's spectrum, like fingerprints or DNA markers. By spotting those fingerprints, researchers can learn about an atmosphere's composition and even deduce the presence of clouds.

Today, Earth's atmosphere consists of about three-fourths nitrogen and one-fourth oxygen, with a small percentage of other gases like carbon dioxide and methane. But four billion years ago, no oxygen was present. Earth's atmosphere has evolved through six distinct epochs, each characterized by a particular mix of gases. Using a computer code developed by Traub and CfA colleague Ken Jucks, Kaltenegger and Traub modeled each of Earth's six epochs to determine what spectral fingerprints would be seen by a distant observer.

"By studying Earth's past, we can learn about the present state of other worlds," Traub explained. "If an extrasolar planet is found with a spectrum similar to one of our models, we potentially could characterize that planet's geological state, its habitability, and the degree to which life has evolved on it."

To better understand these time periods, or "epochs," and to put them into perspective, one can scale the Earth's 4.5-billion-year history down to one year, attaching dates beginning with January 1 - the date the Earth formed.


EPOCH 0 - February 12
At Epoch 0 (3.9 billion years ago), the young Earth possessed a turbulent, steamy atmosphere composed mostly of nitrogen, carbon dioxide and hydrogen sulfide. The days were shorter and the Sun was dimmer, shining as a red orb through our orange brick-colored sky. The one ocean that covered our entire planet was a muddy brown that absorbed bombardment from incoming meteors and comets. Carbon dioxide helped warm our world since the infant Sun was a third less luminous than today. Although no fossils survived from this time period, isotopic signatures of life may have been left behind in Greenland rocks.


EPOCH 1 - March 17
About 3.5 billion years ago (Epoch 1), the planet landscape featured volcanic island chains poking out of the vast global ocean. The first life on Earth was anaerobic bacteria - bacteria that could live without oxygen. These bacteria pumped large amounts of methane into the planet's atmosphere, changing it in detectable ways. If similar bacteria exist on another planet, future missions like TPF and Darwin could detect their fingerprint in the atmosphere.


EPOCH 2 - June 5
About 2.4 billion years ago (Epoch 2), the atmosphere reached its maximum methane concentration. The dominant gases were nitrogen, carbon dioxide, and methane. Continental landmasses were beginning to form. Blue green algae began pumping large amounts of oxygen into the atmosphere. Big changes were about to happen.

"I'm sorry to say the first signs of E.T. probably won't be a radio or TV broadcasts; instead, it could be oxygen from algae," lamented Kaltenegger.


EPOCH 3 - July 16
Two billion years ago (Epoch 3), these first photosynthetic organisms shifted the atmosphere's balance permanently-they produced oxygen, a highly reactive gas that cleared out much of the methane and carbon dioxide, while also suffocating the anaerobic, methane-producing bacteria. In doing so, the planet's atmosphere gained its first free oxygen. The landscape now was flat and damp. With volcanoes smoking in the distance, brilliantly colored pools of greenish-brown scum created a sheen on the stench-filled water. The oxygen revolution was fully underway.

"The introduction of oxygen was catastrophic to the dominant life on Earth at that time; it poisoned it," Traub said. "But at the same time, it made multicellular life, including human life, possible."


EPOCH 4 - October 13
At 800 million years ago, the Earth entered Epoch 4, with continuing increases in oxygen levels. This time period coincides with what is now known as the "Cambrian Explosion." Beginning 550 to 500 million years ago, the Cambrian Period is a significant marker post in the history of life on Earth: It is the time most major animal groups first appear in the fossil records. The Earth was now covered with swamps, seas and a few active volcanoes. The oceans were teaming with life.


EPOCH 5 - November 8
Finally, 300 million years ago in Epoch 5, life had moved from the oceans onto land. The Earth's atmosphere had reached its current composition of primarily nitrogen and oxygen. This was the beginning of the Mesozoic period that included the dinosaurs. The scenery looked like Jurassic Park on a Sunday afternoon.


EPOCH 6 - December 31 (11:59:59)
The intriguing question that remains is: What would Epoch 6, the time period humans occupy today, look like? Could we detect the telltale signs of alien technologies on distant worlds?

As the general consensus builds among scientist that human activity has altered Earth's atmosphere by inputting carbon dioxide as well as gases like Freon, could we identify the spectral fingerprints of those byproducts on other worlds? Although Earth-orbiting satellites and balloon experiments can measure these changes here at home, detecting similar effects on a distant world are beyond even the capabilities of upcoming programs like Terrestrial Planet Finder and Darwin. It will take gigantic flotillas of future space-based infrared telescopes to be able to accomplish those measurements.

"As daunting as this challenge sounds," said Kaltenegger, "I do believe in the next few decades we will know whether or not our little blue world is all alone in the Universe or if there are neighbors out there waiting to meet us."

This research was funded by NASA.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Source: CfA Press Release