1) They've cried wolf enough times at this point that I'm always skeptical about every new announcement.
2) This is yet more indirect evidence - they've found visual evidence of changing patterns that could look like streams, and in the same areas spectra give the chemical "fingerprints" of assorted salts (not table salt, NaCl, but chemically similar) which as far as we know can only form in water.
To me, if the evidence is indirect, we will need a lot more of it than if we actually saw liquid H2
O flowing and used spectra to confirm it was water. Right now we have circumstantial evidence of things that look like stream beds (but could be caused by other liquid solvents, or a remote chance they're caused by wind), and we a number of chemicals which as far as we know can only form in water (not only these salts, but also the hematite blueberries from a few years back). However the hypothesis "this can only form in water" is one of those things we can never actually prove true, just eliminate more and more untrue possibilities.
So to me as a watcher of all this, it's just a waiting game. If there really is liquid water, then little pieces of evidence like this (and the hematite blueberries) will continue to build up until at some point the molehill has become a mountain and it'll be generally accepted by all planetary astronomers (and then all astronomers, and then the world) that yes, there's liquid water on Mars.
3) Water is a key building block for life, so the next question is "is there life on Mars?" Assuming this liquid water exists, it is transient - it's seasonal, appearing only in local summer. If it's transient liquid water, I will need to see some pretty solid evidence to believe that there is current single-cellular life. If it's persistent liquid water I will switch over entirely and I will assume that there's single-cellular life until proven otherwise. Even if it didn't evolve on Mars, we've sent missions there and it's impossible to sterilize everything completely, plus bits of Earth have been knocked off from impacts and landed on Mars so it might've been seeded with Earth life millennia ago. If it's possible to sustain some form of life on Mars, I guarantee you that it's there.Originally posted on Dreamwidth. comments there. Comment here or there.