Rosetta finds water ice on Comet 67p

14 Jan 2016

Rosetta's muse: comet 67P/Churyumov-Gerasimenko, via ESA

Water, water everywhere. That seems to be our solar system’s mantra after Rosetta’s photographs of Comet 67P, which it has been tracking for years now, confirms ice under its crust.

Last year, Saturn’s moon Enceladus became NASA’s primary focus when water, an ocean in fact, was discovered under its surface.

A few months later and Mars stepped into the fray, with the Red Planet producing water of its own. Two similar discoveries, a freak occurrence?

Nope, because now Comet 67p, which Rosetta chased for years, stalked with a camera and even probed, has been found to be home to swathes of ice.

Oh baby, it’s cold outside

Patches of water ice are dotted all across 67p, with the ESA confident it comes from beneath its surface (rather than being acquired by crashing into other bodies in the solar system, for example).

And this ice is really, really cold. Scientists reckon it was -120oC on the comet at the time of the photographs, which were taken in late 2014.

“The various populations of icy grains on the surface of the comet imply different formation mechanisms, and different time scales for their formation,” said Gianrico Filacchione, lead author of the new study, which is published in the journal Nature.

Basically, smaller patches of ice might naturally occur from the comet’s rotation and orbit, spinning into sunlight and darkness every 12 hours.

Operation evaporation

Tiny specks of ice, as seen on Comet 67p, could also come from the growth of secondary ice crystals, which are packed together into visible clumps. An alternative way, though, is the sun heating up the comet, making the icy core evaporate and rise.

This idea is supported by laboratory experiments that simulate the sublimation behaviour of ice buried under dust, heated from above by sunlight.

These tests show that more than 80pc of the released water vapour does not make it up through the dust mantle, but rather is redeposited below the surface.

That makes for an icy grave for Philae, Rosetta’s probe that crash landed on Comet 67p in late 2014.

January marks the last chance for it to wake back up after six months of silence, but hopes are not high for any new developments.

Gordon Hunt was a journalist with Silicon Republic