Rosetta Spots Water Cycle On Comet; Weather Pattern Linked To Sunlight

According to a European Space Agency statement, the Rosetta probe has made observations of Comet 67P/Churyumov-Gerasimenko that have illuminated the nature of a daily cycle of sublimation and freezing that provides new ice to the comet’s surface. This gas flows away from the comet, carrying dust particles along and building up the characteristic bright tail and halo.Rosetta reached Comet 67P/Churyumov-Gerasimenko in August 2014 and has been studying it up close for over a year.

The researchers examined the information gathered from Rosetta’s Visible and Infrared Thermal Imaging Spectrometer (VIRTIS), which is installed in the “neck” region of the comet.

“We found a mechanism that replenishes the surface of the comet with fresh ice at every rotation: this keeps the comet “alive”, De Sanctis said.

The water-ice cycle of a comet follows a daily routine, indicates data collected by Rosetta the space probe from Europe. The water ice on the surface of the comet sublimates into gas and flows away from the comet when sunlight falls on it. The surface of the comet rapidly cools again as the comet rotate and the same region falls into darkness. But the deeper ice stays warm for a while, so it can keep turning to gas and finding its way outward through the porous material. The team behind the discovery suspects that the ice is replenished from below, through fissures that grow during the day as the sun’s intense rays scorch the surface.

The scientists also calculated how much water vapor was being emitted by the patch that they analyzed with VIRTIS and showed that this accounted for about 3 percent of the total amount of water vapor coming out from the whole comet at the same time, as measured by Rosetta’s MIRO microwave sensor.

Measurements have revealed the underlying cycle whereby the volume of ice varies on the comet’s surface, a cycle that coincides with changes in solar illumination.

Here’s the most recent look at Comet 67P.

When the sun comes back again, the molecules in the most recent ice layer then start to sublimate and the entire cycle of outgassing begins again. As the comet rotates, parts of it pass into and out of the sunlight, leading to different processes.

The finding helps resolve a puzzle about why a comet’s surface can be relatively free of ice, such as what has been observed on 67P and other comets, even though the bodies are outgassing water.

“It’s not a surprise that the comet contains ice, but direct evidence of water on the surface is a real novelty”, says Holger Sierks of the Max Planck Institute for Solar System Research in Göttingen, Germany. The Rosetta spacecraft has been monitoring the comet since August 2014.