Planetary scientist Samuel Kounaves at Tufts University in Boston also said there likely was no connection.
So, though working full-time as a planetary scientist, Mr Shoemaker taught himself astronomy, and in 1973 began a regular scan of the skies.
According to Ian Crawford, a planetary scientist at Birkbeck, University of London, the moon is the best place to look to find more evidence.
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Planetary scientist James Westphal used his money for a vacation to Fiji, and Wes Jackson, an environmentally correct farmer, used his to build an addition to his house.
Besides the contributions from rovers and landers, "our view of the red planet has largely been restricted to looking at the surface" from orbiting spacecraft, said lead researcher Gareth Morgan, a planetary scientist at the Smithsonian Institution.
"We have found a habitable environment which is so benign and supportive of life that if you had been on the planet, the water would have been pure enough to drink, " said planetary scientist John Grotzinger, at the California Institute of Technology, who is the mission's project scientist.
"We can go back in time and understand the conditions under which planets began to form, " said Thomas Prettyman, a senior scientist at the Planetary Science Institute in Tucson, Ariz.
"We have had very detailed mapping of that basin from images, from orbital spectral data, but we have not had high-resolution of its interior structure, " Grail's chief scientist, Prof Maria Zuber, who has been speaking at the Lunar and Planetary Science Conference (LPSC) in The Woodlands, Texas, told BBC News.
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Rover mission managers named the outcrop as a tribute to Mars scientist Ronald Greeley (1939-2011), who served as a mission team member and taught planetary science at Arizona State University.
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