I assume they measured the temperature and atmospheric pressure at the rover and have done the calculations to make sure it's actually possible that this was frozen H20 that sublimed? NASA is pretty smart, right?
At least here on Earth I would expect that a solid white material that sublimed was C02. Of course Mars is very different temperature and atmosphere-wise.
To answer my own question, according to Wikipedia, Mars' surface temperature is between −87 °C and −5 °C, and the atmospheric pressure is around 0.007 atm to 0.009 atm.
So while the pressure on Mars might be a little too high, it's pretty darn close. Wikipedia or that phase diagram could be wrong.
Also, I just came across this:
The atmospheric pressure on Mars is just a bit below the triple-point pressure. That's why the textbooks all say liquid water is unstable on the surface of Mars. Any liquid water will rapidly evaporate and the rest, cooled by evaporation, will freeze. Low spots on Mars may have pressures above the triple-point pressure, but are usually far too cold. Even if you did somehow get above 0 C on Mars and into the liquid field, you're so close to the vapor curve that water would rapidly evaporate. Even solid ice would quickly sublimate on Mars except in the very coldest areas.
"... I assume they measured the temperature and atmospheric pressure at the rover and have done the calculations to make sure it's actually possible that this was frozen H20 that sublimed? NASA is pretty smart, right? ..."
In the releases I've read there was no real direct evidence only observation that ...
""It must be ice," said Phoenix Principal Investigator Peter Smith of the University of Arizona, Tucson. "These little clumps completely disappearing over the course of a few days, that is perfect evidence that it's ice. There had been some question whether the bright material was salt. Salt can't do that."" ~ http://phoenix.lpl.arizona.edu/06_19_pr.php
So the headlines are a bit premature until they release an explanation of the measurements they are taking.
Why the second half of the title? I could give it a less if it was "broken" by Digg or Twitter or Slashdot or email - the only thing that matters is whether there is ice or not on Mars. You don't see CNN headlines suffixed with "as AP told us" or "and Reuters had it first!" etc.
It's interesting because it's unusual... People use Twitter to announce minutia like what movie they're currently watching, not significant scientific discoveries.
Likewise, if a politician used their SNL guest spot to announce their intention to withdraw from the presidential race, you can bet most headlines on the topic would include the words "on SNL".
Yeah I was being sarcastic and I 100% agree with the celebrity comment, even if it is a sad reality. Mars reporting via twitter isn't going to entice Joe Public to sign up for twitter. Real time reporting on celebrity nip slips and Brad and Angelina's children will.
At least here on Earth I would expect that a solid white material that sublimed was C02. Of course Mars is very different temperature and atmosphere-wise.