The press release is reproduced below:

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

Laura Spector/Nancy Neal Jones
Goddard Space Flight Center, Greenbelt Md.
301-286-0918/0039
laura.a.spector@nasa.gov, nancy.n.jones@nasa.gov

RELEASE: 07-214

NASA Satellite Sees Solar Hurricane Detach Comet Tail

GREENBELT, Md. - A NASA satellite has captured the first images of a collision between a comet and a solar hurricane. It is the first time scientists have witnessed such an event on another cosmic body. One of NASA's pair of Solar Terrestrial Relations Observatory satellites, known as STEREO, recorded the event April 20.

The phenomenon was caused by a coronal mass ejection, a large cloud of magnetized gas cast into space by the sun. The collision resulted in the complete detachment of the plasma tail of Encke’s comet. Observations of the comet reveal the brightening of its tail as the coronal mass ejection swept by and the tail's subsequent separation as it was carried away by the front of the ejection. The researchers combined the images into a movie.

"We were awestruck when we saw these images," says Angelos Vourlidas, lead author and researcher at the Naval Research Laboratory, Washington. "This is the first time we've witnessed a collision between a coronal mass ejection and a comet and the surprise of seeing the disconnection of the tail was the icing on the cake."

Encke’s comet was traveling within the orbit of Mercury when a coronal mass ejection first crunched the tail then ripped it completely away. The comet is only the second repeating, or periodic, comet ever identified. Halley's comet was the first.

Scientists at the Naval Research Laboratory made the observations using the Heliospheric Imager in its Sun Earth Connection Coronal and Heliospheric Investigation telescope suite aboard the STEREO-A spacecraft. The results will be published in the Oct. 10 issue of the Astrophysical Journal Letters.

Coronal mass ejections are violent eruptions with masses greater than a few billion tons. They travel from 60 to more than 2,000 miles per second. They have been compared to hurricanes because of the widespread disruption they can cause when directed at Earth. These solar hurricanes cause geomagnetic storms that can present hazards for satellites, radio communications and power systems. However, coronal mass ejections are spread over a large volume of space, mitigating their mass and power to create an impact softer than a baby's breath.

Scientists have been aware of the disconnection of the entire plasma tail of a comet for some time, but the conditions that lead to these events remained a mystery. It was suspected that coronal mass ejections could be responsible for some of the disconnected events, but the interaction between a coronal mass ejection and a comet never had been observed.

Preliminary analysis suggests the disconnection likely is triggered by what is known as magnetic reconnection, in which the oppositely directed magnetic fields around the comet are crunched together by the magnetic fields in the coronal mass ejection. The comet fields suddenly link together, reconnecting, to release a burst of energy that detaches the comet's tail. A similar process takes place in Earth's magnetosphere during geomagnetic storms, powering the aurora borealis and other phenomena.

Comets are icy leftovers from the solar system's formation billions of years ago. They usually reside in the cold, distant regions of the solar system. Occasionally, the gravitational tug from a planet, another comet or a nearby star sends a comet into the inner solar system, where the sun's heat and radiation vaporizes gas and dust from the comet to form its tail. Comets typically have two tails: one of dust and a fainter one of electrically conducting gas called plasma.

"Even though STEREO is primarily designed to study coronal mass ejections, particularly their impact on Earth, we hope this impact will provide many insights to scientists studying comets," said Michael Kaiser, STEREO project scientist at NASA's Goddard Space Flight Center, Greenbelt, Md.

STEREO is the third mission in NASA's Solar Terrestrial Probes program, sponsored by NASA's Science Mission Directorate, Washington. Goddard manages the mission, instruments, and science center. The Heliospheric Imager was built in the United Kingdom by Rutheford Appleton Laboratory and the University of Birmingham with major contributions from the Naval Research Laboratory and the Centre Spatial de Liege, Belgium. Other international partners in the STEREO mission include the European Space Agency and France, Germany, Hungary and Switzerland.

For more information and the related images, visit:


Source: NASA Press Release 07-214

NASA Satellite Sees Solar Hurricane Tear Comet Tail Off
NASA's STEREO satellite captured the first images ever of a collision between a solar "hurricane", called a coronal mass ejection (CME), and a comet. The collision caused the complete detachment of the comet’s plasma tail.

Series of four still images taken from an animation showing Comet Encke flying through a solar storm as observed by the STEREO satellite.


Images above: This series of four still images were taken from an animation of Comet Encke flying through
the solar storm as witnessed by the STEREO satellite. Note Encke's tail being torn off by the coronal mass ejection
in the third still above.
Credit: NASA
+ View larger image
+ View animation (7Mb .mpg)

Comets are icy leftovers from the solar system's formation billions of years ago. They usually hang out in the cold, distant regions of the solar system, but occasionally a gravitational tug from a planet, another comet, or even a nearby star sends them into the inner solar system. Once there, the sun's heat and radiation vaporizes gas and dust from the comet, forming its tail. Comets typically have two tails, one made of dust and a fainter one made of electrically conducting gas, called plasma.

CMEs are large clouds of magnetized gas ejected into space by the sun. They are violent eruptions with masses upwards of a few billion tons traveling anywhere from 100 to 3,000 kilometers per second (62 to 1,864 miles/second). They have been compared to hurricanes because of the widespread disruption they can bring when directed at Earth; CMEs are known to cause geomagnetic storms that can present hazards for satellites, radio communications, and power systems.

Comet Encke was traveling within the orbit of Mercury when a CME scrunched the tail and eventually tore it off the comet. Scientists at the Naval Research Laboratory (NRL) made the observations using the Heliospheric Imager (HI) in NRL's Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) telescope suite aboard NASA's Solar Terrestrial Relations Observatory (STEREO)-A spacecraft.


Image above:: This is a still taken from a visualization
showing Comet Encke and the coronal mass ejection
erupting from the surface of the Sun.
Credit: NASA
+ View visualization (7Mb .mpg)

Scientists have been aware of this spectacular phenomenon, the disconnection of the entire plasma tail of a comet, for some time. However, the conditions that lead to these events remained a mystery.

Scientists suspected that CMEs could be responsible for some of the disconnection events, but the interaction between a CME and a comet had never been directly observed. Because the HI instrument can take many images rapidly, and the images are very detailed, scientists were able to obtain a series of images of the comet and tail disconnection as the event occurred.

The researchers combined the images into a movie. This never-before-seen movie was recorded on April 20, 2007, when a CME encountered comet Encke. The observations reveal the brightening of the comet tail as the CME swept by and its subsequent disconnection and transport by the CME front.

A preliminary analysis suggests that the tail was ripped away when magnetic fields bumped together in an explosive process called "magnetic reconnection." Oppositely directed magnetic fields around the comet "bumped into each" by the magnetic fields in the CME. Suddenly, these fields linked together--they "reconnected"--releasing a burst of energy that rent the comet's tail. A similar process takes place in Earth's magnetosphere during geomagnetic storms fueling, among other things, the Northern Lights.

"The comet had its own space weather event," said Angelos Vourlidas, Lead author and Researcher with the Naval Research Laboratory, Washington, DC. "We think it experienced a magnetic reconnection event very similar to what Earth experiences when CMEs impact our own protective magnetosphere."

The results are published online today in the Astrophysical Journal Letters Rapid Release website and in the October 10 print issue of the journal.


Andy Freeberg
Goddard Space Flight Center

Source: NASA - Missions - Stereo - News and Media Resources