STONE circles on Mars are prompting a rethink about the planet鈥檚 ancient climate.
Using cameras on NASA鈥檚 Mars Reconnaissance Orbiter, of the Open University in Milton Keynes, UK, and his colleagues mapped the Elysium Planitia, a region near the equator. They saw rings up to 23 metres across made up of stones sorted by size into concentric bands.
Advertisement
On Earth, similar structures form via repeated freezing and thawing of ice, but with the stones sorted into layers. Water in soil under stones freezes faster than in surrounding soil, and the expanding ice pushes the stones upwards. Larger stones rise faster, and so layers sorted by size form.
What sorts the material concentrically is a mystery, but if a freeze-thaw mechanism was responsible, there must have been liquid water near the surface recently. This would mean that the climate was once 40 to 60 掳C warmer than conventional estimates suggest.
from University College London thinks that the circles 鈥渨ould be an interesting target to look for evidence of past water on Mars鈥�.
