Astronomy Picture of the Day

Explanation: How strange could alien life be? An indication that the fundamental elements that compose most terrestrial life forms might differ out in the universe was found in unusual Mono Lake in California, USA. Bacteria in Mono's lakebed gives indications that it not only can tolerate a large abundance of normally toxic arsenic, but possibly use arsenic as a replacement for phosphorous, an element needed by every other known Earth-based life form. The result is surprising -- and perhaps controversial -- partly because arsenic-incorporating organic molecules were thought to be much more fragile than phosphorous-incorporating organic molecules. Pictured above is 7.5-km wide Mono Lake as seen from nearby Mount Dana. The inset picture shows GFAJ-1, the unusual bacteria that might be able to survive on another world.