Artist's conception of the Gliese 581 system by Lynette Cook, via NASA

Digital Journal ran a slightly hyperbolic headline this morning, “Habitable planets like Earth ‘now in the billions'”:

An international team of astronomers have discovered “billions of planets” not much bigger than Earth and have the potential to sustain life, BBC News reports.
Planets like Earth are circling the faint stars in the Milky Way according to the new research. The estimate for the number of so called “Super-Earths” are based on detections of the number of red-dwarf stars in the Galaxy.

Harps employs an indirect method of detection that infers the existence of orbiting planets from the way their gravity makes a parent star appear to twitch in its motion across the sky.

The team’s leader Xavier Bonfils from the Observatoire des Sciences de l’Univers de Grenoble, France said:

“Our new observations with Harps mean that about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet.

“Because red dwarfs are so common – there are about 160 billion of them in the Milky Way – this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone.”

The only reason this isn’t quite as exciting as it sounded to my un-scientifically-trained ear at first is because “discovered” doesn’t necessarily mean “directly identified.” I think most people know that, but the way it’s phrased makes it sound much more earth-shattering (pun sort of intended) than it is. Based on the findings made so far, it seems safe to extrapolate, but it’s not like the researchers will be publishing a billion-entry guidebook to the planets of the Milky Way. It almost seems like the headline and lead-in to this story were specifically designed to disappoint laypeople.

The team investigated a total of 102 of carefully chosen red dwarfs, which are stars that are dimmer and cooler than our sun.

The team found nine super-earths, which are planets with mass one to ten times the size of Earth, with two of these planets being inside the habitable zone of their stars.

So we’ve gone from “billions” to nine, with two in the “Goldilocks zone.” And about that whole “habitable” thing…

Liquid water is deemed a necessity for life to develop on potentially habitable planets.

“The habitable zone around a red dwarf, where the temperature is suitable for liquid water to exist on the surface, is much closer to the star than the Earth is to the Sun,” commented co-researcher Stephane Udry from the Geneva Observatory.

“But red dwarfs are known to be subject to stellar eruptions or flares, which may bathe the planet in X-rays or ultraviolet radiation, and which may make life there less likely.”

We know there is life on earth that can exist without liquid water, or even oxygen. It’s kind of a leap to assume that all life needs liquid water, although every mechanism of evolution that we know of required liquid water at some point. It also doesn’t help that no one has ever come up with a clear, concise definition of “life” in a biological sense (cf. viruses). Alien life is highly unlikely to be anywhere near our level of technological advancement, and is most likely to be microbial. Aliens certainly won’t look anything like Rachel Nichols. Won’t that be a disappointment?

Getting back to the number of planets, keep in mind that this is only about the Milky Way galaxy, which is one of at least a hundred billion galaxies in the known universe. That’s potentially (I think this is the scientific term) a shitload of planets. Unless we come up with some kind of wormhole or super-warp technology, though, we’ll never know very much about planets in other galaxies.

So this is exciting news. Just don’t get too carried away with it.

On the other hand, we could just send James Cameron to look for other planets. That guy goes everywhere.

Photo credits: Artist’s conception of the Gliese 581 system by Lynette Cook, via NASA; Rachel Nichols as Gaila in “Star Trek,” from Historyguy.com [Fair use]