Memorable moment: I recall seeing Viking images of the Martian surface as a teenager, and realizing that planetary exploration was real and something I could participate in. I will never forget the first time I viewed Mars in 3-D using HiRISE [camera] images [from the Mars Reconnaissance Orbiter], and for the first time had the impression of what it might be like to actually stand on Mars.
Biggest surprise: The realization that there were once lakes on the surface. Although we’ve known about valleys and their relation to running water for some time, the identification of features requiring relatively large standing bodies of water is something that resonates with me. I grew up along the shores of Lake Champlain in New York, and that familiarity with lakes speaks to me about the possibility of habitable and more Earth-like conditions on Mars in the past.
Human landing: While I hope that humans will land on Mars in the next 20 years, I fear that it may take quite a bit longer.
Elon Musk, founder and CEO, Space Exploration Technologies. Advocate of human colonization of Mars.
Memorable moment: I find the thought of people one day looking up from the surface of Mars and seeing the blue dot of Earth really inspiring.
Biggest surprise: The discovery in recent years that Martian soil can be used to grow Earth plants with very little effort, apart from warming it up and adding fertilizer.
Human landing: Approximately 2025.
Matt Golombek, senior research scientist, Jet Propulsion Laboratory, Pasadena, California. Chief scientist on Mars Pathfinder mission and landing site scientist for the Mars Exploration Program.
Memorable moment: The landing of Mars Pathfinder on July 4, 1997, will always be my most memorable encounter with Mars, when after years of work on the mission we received back stunning new images from the surface. We were surprised at the public reaction to the landing, with front-page headlines for a week and the largest Internet following in history at that time.