Jupiter may have a new ring that was created by a smash between moons.
The possible ring appears as a faint streak near Jupiter鈥檚 moon Himalia in an image taken by NASA鈥檚 New Horizons spacecraft. The telescopic camera aboard the Pluto-bound probe snapped the ring in September 2006 as the craft was closing in on Jupiter in the lead-up to a close encounter with the planet the following February.
鈥淲e were taking an image of Himalia to test the instrument. It was completely unexpected that something else was there,鈥� says Andy Cheng of the in Laurel, Maryland, chief scientist for the , which took the pictures.
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It is unclear if the new ring reaches all the way around the planet. No one knows when it formed, but crucially the Galileo spacecraft didn鈥檛 spot it before the end of its mission to Jupiter in 2003, says Cheng. 鈥淚f we鈥檙e right that it was very recent, it might not have existed before then,鈥� he says.
Moons at risk
Because the structure appears so close to Himalia, it may be the result of an impact that blasted material off the 170-kilometre-wide moon, suggest Cheng and colleagues in a study presented at the in Houston, Texas, earlier this month.
If so, it must be relatively new, because impact debris would quickly spread out and become invisible.
One of Jupiter鈥檚 moons, the diminutive 4-kilometre-wide S/2000聽J聽11, went missing after its discovery in 2000 and could have crashed into Himalia, destroying itself in the process, suggests the team.
The possible collision would be the third in a series of recent impacts seen in space. A comet or asteroid slammed into Jupiter last year and a comet-like object discovered in the asteroid belt in January is probably a cloud of debris from a recent collision between two asteroids.
All change
The New Horizons fly-by found that Jupiter has fewer moons with a diameter less than 16聽kilometres than expected. Researchers have previously suggested that small moons have been eroded away by micrometeorite impacts. But perhaps larger collisions also play a role, Cheng says.
鈥淥ur view of the solar system has changed. It鈥檚 not a static place where things stay the same for ever and ever,鈥� Cheng says.
He and his colleagues hope to learn more about the possible new Jupiter ring by taking more pictures of it with a ground-based telescope.
