Moons of Mars attention when Houston's claim was repeated in earnest by a Soviet scientist, Iosif Shklovsky, who, based on a later-disproven density estimate, suggested Phobos was a hollow metal shell. Searches have been conducted for additional satellites. In 2003, Scott S. Sheppard and David C. Jewitt surveyed nearly the entire Hill sphere of Mars for irregular satellites. However scattered light from Mars prevented them from searching the inner few arcminutes where the satellites Phobos and Deimos reside. No new satellites were found to an apparent limiting red magnitude of 23.5, which corresponds to radii of about 0.09 km using an albedo of
Mars One 2013. Canadian former astronaut Julie Payette said during the opening speech for an International Civil Aviation Organization conference that she does not think Mars One "is sending anybody anywhere". In January 2014, German former astronaut Ulrich Walter strongly criticized the project for ethical reasons. Speaking with Tagesspiegel, he estimated the probability of reaching Mars alive at only 30%, and that of surviving there more than three months at less than 20%. He said, "They don't care what happens to those people in space... If my tax money were used for such a mission, I would organize a protest." Space tourist