European Space Agency’s Rosetta spacecraft has discovered water ice on the outer surface of comet 67P. The water ice was detected on the bottom part of the main lobe of the dumbbell–shaped comet in a region called Imhotep.
Rosetta’s Visual and Infrared Thermal Imaging Spectrometer (VIRTIS) detected water ice in two areas on the comet’s Imhotep region. The water ice appeared as noticeably bright patches in visible light that was located on cliff walls and debris falls. Researchers believe that the water ices in two separate locations were created when sun’s heat vaporised the water ice found under the comet’s dust. The remnant water ice may have recondensed and did not leave the surface of the comet.
Scientists believe this phenomenon is because comets fly towards the sun and are hence, exposed to warm temperatures that cause the ice to sublimate or transform directly from solid to gas. What remains are materials similar to rocks, sand and ash on earth. This causes the surface of 67P to appear darker like most of the comets. Similarly, when the comet moves away from the sun, the temperature drops and the water ice condenses, paving the way for a thin layer of frost.