|David A. Aguilar (CfA)|
In considering the likelihood of there being intelligent and technically proficient extraterrestrial life that we might be able to detect using the technical means available to us, it is important to understand the Drake Equation, discussed by Carl Sagan in the video clip below:
The fact that there are billions, perhaps trillions, more stars in elliptical galaxies that might have solar systems including earth-like planets, while it does greatly increase the likelihood of there being extraterrestrial life, even extraterrestrial intelligent life, doesn't affect our chances of discovering such life. However, the discovery of Gliese 581g nearby in our galaxy does point toward a higher probability of our discovering extraterrestrial life.
The third story does affect the Drake Equation. This is the discovery, by NASA scientist Felisa Wolfe-Simon and her astrobiology team, of bacteria living in California's Mono Lake (photo at top of post) that have substituted arsenic for phosphorus in their chemical makeup. Until now all known living things have included compounds of the following elements: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. Other elements, such as calcium and iron, are essential to some life forms, such as ourselves, but the preceding six have been common to all.
What this tells us is that "life" is a bit more flexible than we previously believed, and may arise or survive in environments we thought couldn't support it. Whether substitutions other than arsenic for phosphorus--for example, the often speculated-about silicon for carbon--are possible isn't known, but the fact that one works at least suggests that others might. This means we can assign a higher value to the "N" sub "e" (number of planets with environments suitable for life) term in the Drake Equation, and perhaps as well to the "f" sub "l" (fraction of such planets on which life evolves) term.
So, are we any closer to finding extraterrestrial life? No, but it seems our chances are better than we thought before.