Did the Phoenix lander spot liquid water on Mars?

A team of researchers analyzing images and data gathered by the now-defunct Phoenix spacecraft believes that the lander spotted liquid water on Mars—and that such liquid may be common on the Red Planet. But even within the Phoenix science team, not everyone is convinced.

In a study (pdf) set to be presented next week at the Lunar and Planetary Science Conference in the Woodlands, Tex., Nilton Renno, a professor of atmospheric, oceanic and space sciences at the University of Michigan at Ann Arbor, and his co-authors say that drops of saline appeared where the lander disturbed the Red Planet's surface. Renno is a co-investigator on the Phoenix mission's science team.

The researchers present photographs (right; click to enlarge) showing mysterious shifting blobs on the surface of the lander (highlighted in green), which they believe are drops of brine that splashed up during landing and remained in liquid form. Perchlorate salts, which Phoenix discovered in the Martian soil, could lower the freezing point of the liquid and allow it to persist at the frigid temperatures found on the Red Planet.

But another Phoenix co-investigator, physicist Michael Hecht of the NASA Jet Propulsion Laboratory in Pasadena, Calif., is dubious. "I am not skeptical about the possibility of liquid water existing on Mars in general," he says. "The only area in which Nilton Renno and I disagree is whether there is liquid water in these droplets on the lander struts." Hecht is the lead scientist for Phoenix's MECA experiment, which turned up the Martian perchlorates this past summer.

The physical evidence for liquid consists of "grainy photographs blown up from the corner of another photograph, and that's part of the issue," Hecht says. "The quality of the evidence is somewhat weak." And the behavior of the blobs, he says, is not consistent with that of perchlorate brines.

Hecht believes that frost is a more likely explanation for the blobs than liquid water. "To me, that's the obvious conclusion, and to say that they're liquid is the extraordinary conclusion," he says. "Generally we pick the ordinary unless there's a compelling reason to accept the extraordinary. And I don't see that compelling reason."