Solar Storm rips off Comet tail

A massive fireball of plasma and magnetism ejected from the Sun - a Coronal Mass Ejection (CME) – has ripped off Comet Encke’s tail when it smashed into it. Scientists from the US and UK using NASA’s STEREO spacecraft to study the Sun, witnessed this never before seen event. Their findings are reported in the Astrophysical Journal Letters on 10th October.

Over the years, ground-based observers have seen comets lose their tails, due to the solar wind, but we have never seen a Coronal Mass Ejection smash into a comet in this way and literally chop its tail off.

Professor Richard Harrison from STFC’s Rutherford Appleton Lab is lead investigator for the HI (Heliospheric Imager) Camera that caught the moment “This was a spectacular result - snapping the exact moment the violent Sun broke the tail from Comet Encke. People think of space as empty or quiet, I think we have clearly demonstrated what a dynamic and dangerous place it can be!”

Professor Keith Mason, Chief Executive of the STFC which operates the Rutherford Appleton Laboratory and funds UK participation in STEREO said “This event shows in graphic detail the sheer power of a solar storm. It’s not hard to imagine the effect it would have on a spacecraft! The twin STEREO spacecraft are providing valuable insight on such solar phenomena.”

A CME is a large cloud of magnetized gas ejected into space by the Sun. They are violent eruptions with masses upwards of a few billion tons travelling anywhere from 100 to 3,000 kilometres per second. CMEs are known to cause geomagnetic storms that can present hazards for satellites, radio communications and power systems.

Comet Encke was the second periodic comet identified after Comet Halley and was as far from the Sun as the planet Mercury when it was struck by the CME on 20th April 2007. Further study of the data will reveal more about both comets and the solar wind.

The Heliospheric Imager camera, built in the UK, which captured the moment is part of the SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation) instrument package, led by the US Naval Research Lab. "We were awestruck when we saw these images," says Dr 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."

Because of SECCHI’s high spatial and temporal resolution, scientists were able to make the never before seen observations on April 20, 2007. The HI camera recorded a series of images of the comet as the event occurred. The scientists were able to observe the brightening of the comet tail as the CME swept by and its subsequent disconnection and transport by the CME front.

The analysis suggests that the disconnection is triggered by a process known as magnetic reconnection where two magnetic fields are spliced together – in this case the magnetic fields around the comet itself and the field of the CME. This same process takes place in the Earth’s magnetosphere during geomagnetic storms.

"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.

Notes for editors

Contacts

• Julia Maddock - Science and Technology Facilities Council Press Office
  Tel: + 44 (0)1793 442094
  
  
• Professor Richard Harrison – HI Principal Investigator
  STFC Rutherford Appleton Laboratory
  Tel: + 44 (0)1235 446884
  
  
• Dr Chris Davis – (Chris is out of the office on October 2^nd, contactable via Julia Maddock)
  HI Scientist
  STFC Rutherford Appleton Laboratory
  Tel: + 44 (0)1235 446710

Images

Images and animation are available from the NASA website (link opens in a new window).

• An animation shows the processes at work.
• A visualisation (191190main_EnckeCU.mpg) shows a close up view of the Comet tail being snapped off, background stars removed.
• Another version of this is available from Julia Maddock in which the star background has not been removed and the disconnection event is clearly visible.

Video

• Video - A mpg clip of the Comet tail being ripped off by the Coronal Mass Ejection (1,491 KB)

SECCHI

SECCHI (Sun-Earth Connection Coronal and Heliospheric Investigation) which is formed of an extreme ultraviolet imager, two white-light coronographs and the heliospheric imager (HI - the UK component). These will study the 3D evolution of CMEs from birth near the Sun’s surface, through the corona, into the interplanetary medium to their eventual impact on Earth. If the STEREO mission is extended beyond its current 2-year term, the HI cameras will eventually (due to the geometry of the orbit) look back together towards the Earth and beyond, providing a unique stereo view of the solar system. Twin wide-field cameras in space also provide unexpected science opportunities. Possible investigations now being considered involve looking for extra-solar planets and studies of comets and the interplanetary medium.

STEREO

STEREO (Solar TErrestrial RElations Observatory) 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.

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