Nasa announced last week that its rover had found methane gas on Mars, and around the time a Chinese-led team of scientists has reported finding an organic, coal-like substance in a meteorite knocked off the Red Planet. Both discoveries are prompting debate about life on earth's neighbour. The researchers found traces of organic carbon bound to elements such as nitrogen, sulphur and phosphorus, in a structure similar to that of coal found on earth. Their findings were detailed in this month's cover article of academic journal Meteoritics and Planetary Science . Zhang Jianchao , a co-author of the paper and planetary physicist with the Chinese Academy of Sciences' Institute of Geology and Geophysics, said the team was confident the coal-like substance came from Mars. "We've spent more than half a year conducting the most stringent … tests," Zhang said. Tissint, the name of the meteorite in which the substance was found, was knocked off Mars by an asteroid collision more than 700,000 years ago and contained evidence of water on the Red Planet. The coal-like substance contained high levels of deuterium, an isotope of hydrogen that is rare on earth but abundant on Mars. Some particles were also wrapped in ancient molten rocks formed long before the meteoroid fell to earth, probably at the time of the asteroid collision. The substance - like coal on earth - was also notable for its lack of the heavy carbon isotope C-13, which suggested that biological activities had produced the high concentration of the lighter carbon isotopes. The finding pointed to the possibility of life on Mars, the scientists said. Professor Philippe Gillet - a co-author of the paper and director of the Earth and Planetary Sciences Laboratory at École polytechnique fédérale de Lausanne in Switzerland - said the findings reignited the debate on whether there was life on Mars. "Our conclusions are such that they will rekindle the debate as to the possible existence of biological activity on Mars - at least in the past," he said.