In what has become a regular yearly occurrence, the Spirit rover is looking for a comfortable warm spot to spend the Martian winter. Spirit is heading toward a north-facing slope, where it is hoped the rover can eke out enough sunlight to keep its systems ticking over until Summer. A number of such slopes were considered and rejected, and Spirit is now heading toward a particular promising one at the northern end of Home Plate, an intriguing geologic feature that had taken up several months research time for the rover. The 60-meter drive is worth the risk, as the slope provides a 25-degree incline that will maximise the available sunlight. Spirit can't afford to be cavalier about where it hunkers down for winter. After a long dust storm, the solar panels are covered in dust, so every extra bit of power will be crucial to survival this year. Unlike the rover’s sister Opportunity, they cannot count on a lucky gust of wind to clean the cells. Opportunity is in a windy locale; the area that Spirit is traversing now is almost windless. It is hoped that Spirit can be bedded down by the 1st January 2008, but it may then have to stay under cover for eight months.
The European Mars Express orbiter has been looking beneath the surface of Mars, at a particularly odd area known as the Medusae Fossae. The Medusae Fossae roughly forms the divide between lowland and highland regions along the Martian equator and has long intrigued geologists because the material it is composed of has been seen to absorb radar waves, leading to them been referred to as called "stealth" regions. Until now, no one has been sure how thick these deposits are, or what they might be composed of. The only reasonable certainty is that the material is relatively new, at least in a geologic sense, as there is little sign of disturbance by impact craters. Now the Mars Express Orbiter, which uses longer wavelengths than Earth-based radar experiments, has been able to make some intriguing observations.
The material it turns out is in places up to 2.5 kilometres (1.4 miles) thick in places, but there is still some uncertainty as to their composition. They could be volcanic ash deposits from now-buried vents or nearby volcanoes, or perhaps deposits of wind-blown materials eroded from Martian rocks. Most excitingly, they could be ice-rich deposits, somewhat similar to the layered ice deposits at the poles of the planet, but formed when the spin axis of Mars tilts over, making the equatorial region colder. Unfortunately, this later scenario seems the most unlikely, as the water vapour pressure on Mars is so low that any ice near the surface would quickly evaporate. The electrical properties of the layers suggest that they could be poorly packed, fluffy, dusty material, but this also has its detractors, since if it hard to understand how 2.5 kilometres of dust could retain such a lose composition. So the mystery of the Medusae Fossae endures, but we are step closer to understanding it.