More than a month after its landing in the Martian arctic, Nasa's Phoenix probe has discovered that asparagus, green beans and turnips should grow nicely in the Martian soil under the right conditions, but that strawberries might not. The findings come via a so-called wet-chemistry laboratory, part of Phoenix's Meca (Microscopy, Electrochemistry and Conductivity Analyzer) instrument. This added water carried from Earth to some soil scooped from just beneath the surface.

Tests show the resulting mud to have a slightly alkaline pH level of between 8 and 9, comparable to sea water and favouring asparagus and the like (but, sadly for Martian tennis fans, not strawberries). The soil also contains several life-supporting nutrients including sodium, potassium, magnesium and chloride. Nitrogen, carbon and oxygen are absent, as are a few other trace minerals that any aspiring Martian horticulturist would need to supply. It is reassuring that nothing toxic has been found, and nothing that rules out the possibility of alien microbes surviving, if not thriving, deeper down where they would be shielded from harmful ultraviolet radiation.

Of still greater importance for future travellers is Phoenix's confirmation that water exists all around in the form of sub-surface ice. White chunks exposed by the craft's robotic arm, sublimate and vanish over a few days - too slowly to be frozen carbon dioxide, dry ice, which was probably the leading alternative.