Scientists have studied samples recovered from Comet Wild-2 and say they've found complex carbon-rich molecules. These are of the type that could have been important precursor components of the initial reactions that give rise to life on Earth.
"Whatever it took to get life started, the more variety of molecules you had in the mix and the more they looked like the kinds of molecules that life uses now then the easier it should have been," Dr Scott Sandford from Nasa's Ames Research Center told BBC News.
The Stardust spacecraft flew past the 5km-wide icy "mud-ball" known as Comet 81P/Wild-2 in January 2004.
The probe swept up particles fizzing off the object's surface as it passed some 240km (149 miles) from the comet's core, or nucleus. These tiny grains, just a few thousandths or a millimetre in size, were then returned to Earth in a sealed capsule.