A rock commonly found on Mars could, against expectations, preserve fossils, raising hopes that evidence of life on Mars may one day be found.
Sulphates such as gypsum occur all over Mars - including the area which NASA's Opportunity Rover is currently exploring. Meridiani Planum is a vast plain consisting almost entirely of such rocks.
The perceived wisdom was that these sulphates couldn't harbour fossils, as the processes that created them would inevitably crush tiny fossils to pieces.
But a team from the University of California has now found six fossilised algae in gypsum at a site in northern Italy. They include phytoplankton, diatoms, and cyanobacteria - pond scum, in other words.
NASA is currently considering several missions to explore the possibility of extraterrestrial life. Possibilities include robotic missions to Saturn's moons Titan and Enceladus.
But an attempt to bring Martian rocks back for study on Earth is also under consideration, and this latest discovery could make it appear a lot more worthwhile.