Editing Comet Hyakutake (section)

=== X-ray emission ===
[[File:X-rays from Hyakutake.jpg|thumb|right|150px|[[X-ray]] emission from Hyakutake, as seen by the [[ROSAT]] satellite]]

One of the great surprises of Hyakutake's passage through the inner Solar System was the discovery that it was emitting [[X-rays]], with observations made using the ''[[ROSAT]]'' satellite revealing very strong X-ray emission.{{r|Glanz_1996}} This was the first time a comet had been seen to do so, but astronomers soon found that almost every comet they looked at was emitting X-rays. The emission from Hyakutake was brightest in a crescent shape surrounding the nucleus with the ends of the crescent pointing away from the Sun.{{r|Cravens_2002}}

The cause of the X-ray emission is thought to be a combination of two mechanisms. Interactions between energetic solar wind particles and cometary material evaporating from the nucleus is likely to contribute significantly to this effect.{{r|Lisse_1996}} [[Thomas E. Cravens]] was the first to propose an explanation in early 1997.<ref>{{cite journal
| last = Cravens
| first = T. E.
| date = 1997
| title = Comet Hyakutake x-ray source: Charge transfer of solar wind heavy ions
| journal = Geophysical Research Letters
| volume = 24
| issue = 1
}}</ref> Reflection of solar X-rays is seen in other Solar System objects such as the [[Moon]], but a simple calculation assuming even the highest X-ray reflectivity possible per molecule or dust grain is not able to explain the majority of the observed flux from Hyakutake, as the comet's atmosphere is very tenuous and diffuse. Observations of comet [[C/1999 S4 (LINEAR)]] with the [[Chandra X-ray Observatory|''Chandra'' satellite]] in 2000 determined that X-rays observed from that comet were produced predominantly by charge exchange collisions between highly charged [[carbon]], [[oxygen]] and [[nitrogen]] minor ions in the solar wind, and neutral water, oxygen and hydrogen in the comet's coma.{{r|Lisse_2001}}