Washington - A Nasa robot has snapped pictures showing glints of light on the Martian horizon, which some UFO enthusiasts have seized on as a sign of alien life on the planet.Not so, said the US space agency.More likely, the images of bright spots taken on 2 and 3 April are a product of the sun's glare or cosmic rays, Nasa said in a statement.In fact, similar glints of light are seen all the time in images taken by the Curiosity rover, a multibillion dollar unmanned vehicle equipped with cameras and drilling instruments that is exploring Mars."In the thousands of images we've received from Curiosity, we see ones with bright spots nearly every week," said Justin Maki of Nasa's Jet Propulsion Laboratory in Pasadena, California."These can be caused by cosmic-ray hits or sunlight glinting from rock surfaces, as the most likely explanations."Furthermore, the "bright spots appear in images from the right-eye camera of the stereo Navcam, but not in images taken within one second of those by the left-eye camera," the space agency said in a statement.Nasa's explanation may not dampen enthusiasm among believers in alien life on Mars, such as the website operated by UFO Sightings Daily which said the lights could offer proof of extraterrestrial beings."This could indicate there is intelligent life below the ground and uses light as we do," the site proclaimed.Nasa's Curiosity rover landed on the dry, dusty planet in 2012 on a mission to search for signs that life may have once been able to thrive there.