Truth and the Devil

The news is in! An exciting discovery in the field of astronomy: a candidate for an Earth-like planet has been found! It’s exciting news for certain, though news that must be tempered. I’ll let Phil Plait explain:

The European Southern Observatory is reporting that they have found the most Earthlike planet yet orbiting another star. It has about 1.5 times the Earth’s diameter, and five times its mass. This makes it the smallest extrasolar planet yet found (two other planets have already been found orbiting that star, with 15 and 8 times Earth’s mass).

This is amazing enough! But it gets far, far better. The parent star, Gliese 581, is a red dwarf, meaning it’s smaller and cooler than the Sun. The as-yet unnamed planet orbits this star much closer than the Earth does the Sun; it stays about 11 million kilometers (6.7 million miles) from its star, while the Earth is 150 million km (93 million miles) from the Sun.

But remember, Gliese 581 is cooler than the Sun, so at this distance the planet would actually be very temperate: models show it would be between 0 and 40 Celsius! If that doesn’t grab you, then consider this:

That is warm enough for water to be a liquid.

So what we may have here is a terrestrial planet with liquid water on its surface.

I’ll sum up. Scientists have been using telescopes to find other planets for a few years now. This is a difficult job because, in addition to being rather small (compared to stars), planets don’t give off their own light. Therefore other methods are used to detect the presence of a planet: either a regular change in the luminosity of a star (when the planet passes in front of it), or a slight gravitation ebb from the pull of a smaller body on the star. Several hundred planets have been found using this method, but so far they’ve been rather massive, Jupiter-like gas giants which have a much lower probability of containing life (though their moons might).

This new planet Gliese 581c has a mass only 5 times that of Earth with a diameter of only 1.5 times Earth’s. And even though it’s sun is far older and weaker than ours, its orbit is closer, giving it the potential for having a similar surface temperature of Earth’s, and therefore the possibility of water.

You may notice all the qualifications here: maybe, possibly, may, potential; that’s because well there’s no picture of it yet. These are preliminary findings, but ones which I’m sure plenty of other scientists are anxious to verify.

However, I think the real excitement lies not in the finding of this one planet in particular, but what it means for astronomy and astrobiology in particular.

The real importance is not so much the discovery of this planet itself, but the fact that it shows that Earth-like planets are probably extremely common in the Universe.

There are 200 billion stars in our galaxy alone and many astronomers believe most of these stars have planets.

The fact that almost as soon as we have built a telescope capable of detecting small, earth-like worlds, one turns up right on our cosmic doorstep, shows that statistically, there are probably billions of earths out there.

As Seth Shostak says: “We’ve never found one close to being like the Earth until now. We are finding that Earth is not such an unusual puppy in the litter of planets.”

Of course, what this means for the potential for finding life, no one knows for sure. The only real ‘experiment’ we know of where life has occurred is our own planet. It’s possible (a possibility I find credible) that if the right conditions exist (such as liquid water), then life may be almost inevitable. And even if it’s not, this planet implies a frequency of Earth-like worlds that is quite astonishing, bringing the potential for life existing in our galaxy way up.

Say we’ve located approximately 230 planets so far, and one of them is Earth-like. Assume that’s a standard ratio (one that will likely improve as our detection methods improve), that could mean that 0.43% of all planets are Earth-like. Now, that might not seem like much, but with approximately 200 billion stars in the galaxy, that gives us at least tens or hundreds of millions of potentially Earth-like planets in the galaxy (some people might be critical of my fuzzy math, and for that apologize). The potential for life on other worlds is starting to look good.

Of course, we’re all interested in the possibility of advanced civilizations that we might be able to detect, but that’s most-assuredly of low probability. After life forms for the first time, it still has many obstacles to overcome. It has to not go extinct for several billion years, it has to develop sufficient complexity, it has to become intelligent, it then has to develop sufficient technologies (like radio transmission), and then it has to exist at roughly the same time our civilization does. An unlikely, though existent possibility.

Talking about alien civilizations at this point I believe is quite premature, as well as fairly anthropocentric. Humans are just one small example of life on this planet, and the discovery of any form of life on another planet, as primitive as it may be, is exciting enough to me, as is the discovery of the planet itself. What might it look like?

There is much more to learn about this planet. Getting an image of it is currently not possible: at a distance of 20 or so light years, Gliese 581 one of the closest stars in the sky, but still far too distant to separate the planet from the star. So I’m left wondering about this planet. Does it rotate once every orbit due to the gravitational interaction with its star? This is what has happened to every moon in the solar system; they spin at the same rate they go around their parent bodies, so they always show one face to their parent (which is why the Moon always has the same face toward us here on Earth). If so, how does this affect the atmosphere? Models indicate that the air should carry the warmth of the star around the planet, so the temperatures should actually be fairly moderate on both the day and night sides of such a world. But if it’s covered by an ocean, how does having one side of the planet eternally locked into daylight affect it?

Criminy, what would life be like on a tidally-locked ocean world?

Wow. One of my favorite aspects of science is taking an idea and running with it. I don’t encourage too much speculation beyond what’s known — and in this case we don’t know all that much — but it sure can be fun. Especially when what we’re starting with is so exciting.

A digression into religion is probably not necessary at this point, but the power of science to discover totally dwarfs that of religion. I am reminded of a quote by Carl Sagan:

How is it that hardly any major religion has looked at science and concluded, ‘This is better than we thought! The Universe is much bigger than our prophets said, grander, more subtle, more elegant’? Instead they say, ‘No, no, no! My god is a little god, and I want him to stay that way.’ A religion, old or new, that stressed the magnificence of the Universe as revealed by modern science might be able to draw forth reserves of reverence and awe hardly tapped by the conventional faiths.
—Carl Sagan