In case you haven’t heard, NASA has come out and stated that the Phoenix Lander has <gasp of wonder> found ice on Mars. The little lander dug a cute little trench with its shovel and uncovered some white stuff that over the course of several days disappeared in a manner consistent with water ice sublimating (changing from ice to gas) and that was inconsistent with dry ice sublimating.
Let me state for the record that watching ice on Mars sublimate from up close is just cool. Being able to say, ice behaves on Mars the way we thought it would, is important.
Having said that, I also have to say that I really wish folks would quite saying that Phoenix discovered ice on Mars. Folks, if you’ve got a 10 inch or larger telescope, take it outside next time Mars is in the sky. If you see a big white blob toward the end of one of the poles, you have observed ice on Mars.
For the past several decades – since before I was born – we have known that Mars’ poles have ice caps that grow and shrink with the seasons in a manner consistent with a mixture of water ice and dry ice. As early as 1976, scientists were reporting on measurements of atmospheric water vapor on Mars using Viking data (see here). With the more recent rounds of rovers, we’ve seen clear evidence of sub-surface ice from neutrons the ice fails to jettison when hit with cosmic rays (see here), and the mars rovers have found all sorts of minerals that could only have formed in water. Thus, we have evidence of past liquid water, current water vapor, and current water ice.
This means, we knew that there was water ice on Mars. Really. We had all the evidence we needed.
What is so valuable about this latest discovery is it takes that knowledge to the next step. Science is a building process and we grow our understanding one data point at a time. From Earth we knew Mars had polar caps, but we also thought it had seas. Once we started getting there with space probes, we learned it is a desert world whose only moisture is frozen, or perhaps under high pressure beneath the surface (where maybe it occasionally spurts out of gully walls). We could identify what acted in every way like ice when viewed from space, so we sent probes first to bright sunny areas near the equator to dig around for minerals that required water to form (fairly low risk as far as going to Mars with a rover was concerned). Having found those minerals, we then sent a lander to go sit on the ice (higher risk since sunlight is at a premium and the seasons are more extreme.) Now, we have seen the ice really seriously up close. We still haven’t been able to do a chemical analysis of the water however. We’ve still only looked at it.
The next big break through will come in technologically tasting the ice to see what flavors – what minerals, isotope combos, and inclusions of gas – permeate the ice (never taste the yellow snow). We’re going to get there in the coming days and it is the result of that test that I’m waiting for.
We are building knowledge. This is good. We aren’t discovering Mars has ice. That’s old news. Instead, we’re discovering the characteristics of that ice, which is its own kind of cool.