Only thanks to a camera on board ESA’s Mars Express orbiter, which was not designed for this purpose at all, a group of researchers has found out what an unusual and huge cloud on Mars is all about. It appears regularly in the early morning beyond the field of view of most instruments at a huge shield volcano, is pulled in a few hours with rough speed into the long and then dissolves. Only with the help of the on-board surveillance camera of Mars Express it was first discovered and now investigated.
Always in the morning
As the scientists now explain in the Journal of Geophysical Research, they have determined that the giant cloud forms every morning shortly before sunrise in the spring and summer on Mars. It is therefore an "orographically excited" cloud, which is formed when wind is printed upwards on the slopes of the Arsia Mons volcano. For two and a half hours, the cloud is then pulled westward at over 600 kilometers per hour and reaches a height of 45 kilometers. In the process, it will be nearly 2000 kilometers long and 150 kilometers wide, according to the report. In the late morning, it breaks away from the volcano and disappears in the face of rising temperatures.
A cycle of the giant cloud (Source: ESA.0 IGO )
Despite its regular formation and striking appearance, the cloud was not visible to the orbiters on Mars because the research cameras only focus on comparatively narrow areas and the orbits are not favorably located for the morning events. It was only discovered with the so-called Visual Monitoring Camera (VMC) of Mars Express, which was only supposed to confirm the separation of the ESA lander Beagle 2. It has only a small resolution, but unlike other cameras in Mars orbit, it has a coarse field of view, the researchers explain. Its potential as a scientific tool was only recognized a few years ago; previously, it was considered an "Webcam of Mars", as it regularly photographs the Red Planet in its entirety.
With the VMC, the cloud was not only discovered, but also explored. Finally, it also provided data thanks to which other instruments and other orbiters could be directed to what is happening at dawn, which is not normally targeted. Knowing the regularity of the giant cloud, scientists were even able to detect it in archival images taken of Mars by NASA’s Viking 2 spacecraft in the 1970s. "These discoveries truly underline the strengths of Mars Express – its special orbit, its longevity, its sustained quality, and its ability to adapt to the needs of research", says Dmitry Titov of the European Space Agency. Mars Express has been orbiting the Red Planet since 2003.
Details of the giant cloud