Rosetta's comet has been seen changing color and brightness as it orbits closer to the Sun.
Comets are small icy bodies that heat up and begin to release gases when they pass close to the Sun. These icy bodies are typically dark-colored and are not known for glowing.
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But ESA researchers have observed something unusual about the comet called 67P/Churyumov- Gerasimenko. They have found that Rosetta’s comet has been changing its color and brightness as it orbits to the Sun.
Rosetta’s Visible and InfraRed Thermal Imaging Spectrometer, VIRTIS, have detected those changes in the northern hemisphere and equatorial regions which are directly lit by sunlight. The observations were made just few months after Rosetta spacecraft reached comet’s orbit (August 2014). At the same time, comet was moving along closer to the Sun, from about 542 million km to 438 million km.
When Rosetta arrived, it noticed that comet 67P is an extremely dark body and was reflecting just 6% of the visible light falling on it. This is because the majority of the surface was covered with a layer of dark and dry dust made out of minerals and organics. Since these minerals and organics are not evenly distributed, some of the surface appears slightly reddened while other shows up somewhat bluer.
Now, the old layer of dust is slowly disappearing as the comet is getting closer to the Sun and exposing a relatively fresher material, making its surface more reflective, brighter and richer in ice. VIRTIS is also indicating subtle changes in the composition of the comet as it has observed changes in light reflected from the surface over a wide range of visible and infrared wavelengths. Now surface is looking more bluish and overall, the brightness has increased by 34%. The change indicates that there is a lot of water ice lying beneath the surface of the comet.
“The overall trend seems to be that there is an increasing water-ice abundance in the comet’s surface layers that results in a change in the observed spectral signatures. In that respect, it’s like the comet is changing color in front of our eyes,” said lead author Gianrico Filacchione.
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“This evolution is a direct consequence of the activity occurring on and immediately beneath the comet's surface. The partial removal of the dust layer caused by the start of the by the start of gaseous activity is the probable cause of the increasing abundance of water ice at the surface.”