VIRTIS view of the Earth (IR-1)
VIRTIS was one of the instruments aboard Rosetta that were active during the spacecraft's third Earth swingby on 13 November 2009. This image was taken by VIRTIS several hours after closest approach, when the spacecraft was at about 230 000 km from the Earth's surface and receding again from the planet.
One of the two channels of the VIRTIS instrument is the Mapper (VIRTIS-M), a hyperspectral imager that collects image data simultaneously in 864 narrow, adjacent spectral bands (colours). The observations in different sets of narrow bands can be combined to generate different views of the Earth.
This image (called "IR-1" in the related composite image "VIRTIS spectral images of the Earth", linked from the right-hand menu) shows the Earth in the infrared spectral range. It was made using a combination of colours with the R, G and B channels of the image selected at 4.92 µm, 2.25 µm and 1.20 µm respectively.
In this spectral range the Earth has a completely different appearance than in the visible as VIRTIS-M is sensitive both to the reflected solar radiation and to the emitted thermal radiation. This is the reason why the night side shows up in this image.
The cyan areas are related to high altitude clouds, which are particularly bright in the near infrared range on the dayside. Landforms appear pink.