The European Space Authority (ESA)'s Rosetta space probe discovered water ice on the outer surface of a comet, a new discovery which sheds light on the evolution of comets. Thanks to the equipment aboard the Rosetta orbiter, scientists may have an insight on the evolution of this icy compound.

The ESA spacecraft first detected patches of exposed water ice on Comet 67P/Churyumov-Gerasimenko in June 2015. The probe has been revolving around the comet since August 2014.

According to the scientists' analysis of the images from Rosetta's Visual and Infrared Thermal Imaging Spectrometer (VIRTIS), two areas on the comet's Imhotep region contain the surface water ice. They appear as bright patches in visible light.

The researchers explained that the large grains of water ice in two separate locations on the surface of the comet were created when the sun's heat vaporized the water ice found under the comet's dust. The water ice may have recondensed and did not leave the surface of the comet.

"If the thin ice-rich layers that we see exposed close to the surface are the result of the comet's activity, then they represent its evolution, and it does not necessarily require global layering to have occurred early in the comet's formation history," Gianrico Filacchion, lead author of the study said in a statement.

Of the two large grains observed, the larger ones were the most interesting because they have created secondary crystals through the process called sintering. This process entails the compaction and compilation of smaller grains. Another process called, sublimation, wherein layers of water ice were buried and deposited under the comet's surface throughout its lifetime.

In the study published in the online journal, Nature, the results of laboratory works and experiments showed that 80 percent of the sublimating water ice is not exposed or released. Instead, these are recondensed or redeposited. As a result, ice layers are formed. The sublimation behavior as shown in simulations made by the researchers added to the knowledge on comets and their evolution.

This discovery will shed light on the evolution of not only Comet 67P,but of other comets from deep space. Additional knowledge and understanding on comets may help scientists study other bodies in space including asteroids, stars, and planets.