Here, in fairly plain language, is what it means:
They've probably found an extremophile. Bacteria are remarkably resistant, they appear in sub-zero temperatures, high acidity, high temperatures, high salinity, all sorts of places.
Now we've found one that not only survives a high-arsenic environment, it can actually survive without phosphorus at all.
Yup, that's chemistry mumbo-jumbo to some. In essence, phosphorus makes the backbone to DNA, it's the chemical foundation of every single living organism on the planet. Technically, in the known universe. Every living cell has a strand of DNA made with a strand of phosphorus.
Arsenic could do the job though. The chemistry works. You can, in theory, have arsenic based life, and until today it was in exactly the same category as the "silicon based life" so beloved of science fiction. It was fiction, unsupported theory, hypothesis. Until today.
Today a very clever scientist (with a great website) announced that she'd diluted these bacteria down until there was no phosphorus left in the system. The bacteria were operating on an arsenic based genome.
Now, herein lies the rub: where does it come from? No, of course it's not extraterrestrial, but is it the same as phosphorus based life? In this case, it seems it is. It looks like a case of normal, everyday life adapting rather spectacularly rather than a new form of life (the "shadow biosphere" that has been suggested).
Either way, NASA were absolutely right to announce this as a discovery of significance to astrobiology. One of the following things have just been demonstrated in some style:
- Life based on a fundamentally different chemistry is not only possible, it actually exists!
- It might be the second spontaneous emergence of life ever observed by humans, with implications for the odds of life elsewhere.
- It might just be normal, boring, tedious Earth life surviving in ridiculous circumstances. Ones which are based on fundamental chemistry, suggesting that life can survive a far greater range than we previously gave it credit for, and echoing some (so far speculative) ideas about potential biochemistry for Titan, Enceladus and Europa to name a few we've already visited.
There was a lot of hype and expectation, but the fact remains, this is a highly significant breakthrough in both biochemistry and astrobiology, and has been led by the astrobiologists. This is a big discovery for a young field which carries some important answers about the nature of life.