* Astronomy

Some underground martian caves may have been spotted, thanks to 'skylight' holes into the caverns that have been photographed from above.
Glen Cushing, from the US Geological Survey (USGS) in Flagstaff, Arizona, got his first hint of the underground cave system from THEMIS (Mars Odyssey's Thermal Emission Imaging System) images of the Arsia Mons region near the equator of Mars. He spotted a system of pit craters, indicative of collapsed areas, and nestled among them half a dozen dark spots ranging in diameter from 100 to 252 metres.
Two of the seven possible openings found by Cushing have been probed using thermal infrared imaging, which shows that their temperature is pretty constant at any time of day: in daylight, the spots are cooler than the rest of the surface, but not as cool as shadowed areas, and at night the spots are warmer than their surroundings.

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This image of Mars was taken by Rosetta's Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS). It shows planet Mars in the pre-close-approach phase (updated with additional spectral information).


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Credit ESA

An orange (red), green and near-UV colour filter composite image of Mars; the UV channel (the blue colour) has been enhanced. The enhanced UV signal clearly shows the presence of the cloud system covering most of the Martian disk.
The image was acquired on 24 February at 19:28 CET from a distance of about 240 000 km; image resolution is about 5 km/pixel. Higher resolution images of Mars will be made available later.

Scientists using data from the HRSC experiment onboard ESA's Mars Express spacecraft have produced the first 'hiker's maps' of Mars. Giving detailed height contours and names of geological features in the Iani Chaos region, the maps could become a standard reference for future Martian research.

The maps are known as topographic maps because they use contour lines to show the heights of the landscape. The contour lines are superimposed upon high-resolution images of Mars, taken by the High-Resolution Stereo Camera (HRSC) onboard Mars Express. On Earth, such maps are used by hikers and planning authorities.
They are known in the UK as ordinance survey maps. Every country has its own equivalent. The contour lines themselves were determined using data from the HRSC.
This data has been transformed into three-dimensional computer models of Mars, known as the HRSC Digital Terrain Models (DTMs).
The new maps have been produced under the leadership of the Principal Investigator (PI) G. Neukum (Freie Universität Berlin), as part of the effort of the science and experiment team of the HRSC experiment, by J. Albertz and S. Gehrke of the Institute for Geodesy and Geoinformation Science, Technische Universität Berlin, in cooperation with the German Aerospace Centre (DLR), Institute of Planetary Research, Berlin.
They used the HRSC DTMs of the Iani Chaos region to produce a series of topographic maps at different scales, from 1:200 000 down to 1:50 000.
The researchers chose the Iani Chaos region because of its major topographical interest. It is covered in individual blocks and hills that form a chaotic pattern across the landscape.
These 'islands' of rocks are likely all that remains of a previous surface of Mars. The areas in between the islands collapsed when cavities formed below the surface. Initially these cavities may have been supported by the presence of ice, which melted due to volcanic heat. As the water flowed out into Ares Vallis, towards the northern lowlands of Mars, the landscape collapsed and formed the Iani Chaos region we see today.
The contour lines help the eye to understand the morphology of the surface shown in the images. On most of the maps, each line represents a difference of 250 metres in height. The maps also display the names of geographical features and the lines of Martian longitude and latitude.
The maps are a demonstration of the kind of products that can be derived from the HRSC experiment. The HRSC is on the way to providing enough data to create such maps for the whole of Mars. This would generate 10 372 particular map sheets, each covering an equal area of the Martian surface. The maps would be to a scale of 1:200 000.

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The seasons here on Earth roll by at a regular clip -- about three months for each one. Right now, we're just more than half way through winter in the northern hemisphere. In fact, we marked the halfway point last week with Groundhog Day.
But the seasons on other planets aren't always as regular. Consider Mars, where autumn begins in the northern hemisphere this week. The season will last about 146 Earth days. That's about two weeks longer than northern winter, and five weeks longer than summer.

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