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The Question

(Submitted April 14, 1997)

I would like to know what would happen if a comet was hit by the full force of a solar flare from the Sun?

The Answer

Thanks for your question on comets and solar flares. A large solar flare hitting a comet like Hale-Bopp would certainly cause a noticeable brightening of the comet for a period of time. A solar flare contains high energy photons and particles, and is released from the Sun in a relatively short amount of time (a few minutes). The ion tail of comet Hale-Bopp, which is comprised largely of charged particles as opposed to the heavier dust particles making up the dust tail, could possibly show complex structure or discontinuities, depending on the structure of the magnetic field in and around the flare. There are some helpful figures of the solar wind interacting with a comet in the review of the magnetosphere which can be found at http://www-ssc.igpp.ucla.edu/ssc/tutorial/magnetosphere.html

If a comet got close enough to the Sun to pass "through" a solar flare, it would most likely be vaporized and wouldn't have fared much better even without a flare. Flares don't really reach out very far (in an astronomical sense) from the surface of the Sun. On the other hand, the particles that flares release stream outward to well beyond the orbit of the Earth. It's these particles that can cause the effects mentioned in the previous paragraph.

Another type of solar event, a coronal mass ejection, reaches far out into space and could also cause all of the effects mentioned above. They are generally associated with filament liftoffs. You may have seen videos of long tendrils of matter lifting off from the "edge" or limb of the Sun - these are filaments.

There are also some excellent animations from LASCO, one of the instruments on the ESA/NASA SOHO Sun observing satellite that show the dynamic behavior of the solar wind and, in one case, a sungrazing comet. These are located at http://sohowww.nascom.nasa.gov/data/realtime/realtime-c3.html

Regards,
Padi Boyd and Karen Smale,
for the Ask an Astrophysicist Team

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