STEREO sees coronal mass ejection tear comet tail off

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.
This is an animation of Comet Encke flying through the solar storm as witnessed by the STEREO satellite. Credit: NASA

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.

Image Credit: NASA
High resolution image

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.

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.

Source: Goddard Space Flight Center
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