Nasa rover discovers largest organic compounds yet found on Mars

Presence of long-chain alkanes in rock raises new questions about possible existence of life billions of years ago

Nasa's Curiosity rover has found the largest organic compounds ever seen on Mars, raising tantalising questions about whether life emerged on the red planet billions of years ago.

The compounds were detected in a 3.7bn-year-old rock sample collected in Yellowknife Bay, an ancient Martian lakebed that harboured all the necessary ingredients for life in the planet's warmer, wetter past.