The third largest piece of Mars on Earth is available to buy at Christie’s Deep Impact: Martian, Lunar and other Meteorites online sale which runs to February 23. It is estimated at $500,000-800,000. Specimens of Mars are by far among the rarest substances on our planet with less than 600 lbs (275 kg) known to exist. These samples arrived here after having been blasted off Mars following an asteroid impact and are identified by their mineralogical, chemical and isotopic signatures. NWA 12690, the third largest piece of Mars on Earth, weighs 20 pounds (9.1 kilograms). Following an analysis by a panel of scientists, this meteorite joined the official registry of scientific record, the Meteoritical Bulletin. Highlights at this auction of 66 lots include meteorites containing the oldest matter humankind can touch and others with gemstones from outer space. Estimates range from $400 to $800,000 and 62 lots are offered with no reserve.