April 5, 2001

10:45 AM

Life Elsewhere?In an attempt to get away from the Chinese-American situation, scientists have recently discovered 11 new planets, with one possibly inhabiting a "Life-Zone."
posted by da5id (9 comments total)

Actually, I was hoping we could steer away from that heated discussion.
posted by da5id at 10:45 AM on April 5, 2001

That is pretty amazing...it is strange, to grow up with only the local planets, and to read about the possibilities of finding more Someday.

and now, i dont' even remember when that first 'someday' was, and the planets keep piling up.
posted by th3ph17 at 12:55 PM on April 5, 2001

We'll have rocket-boots any day now, man.
posted by Doug at 1:12 PM on April 5, 2001

I wonder if the U.S. or China will colonize that planet first. . . . (ducks)
posted by CRS at 2:12 PM on April 5, 2001

Perhaps their rocketships will collide en route.
posted by youhas at 2:31 PM on April 5, 2001

So far, the extra-solar planets have been discovered by use of spectroscopes. What's going on is that a planet doesn't really go around a star. Actually, both revolve around a common center of gravity. So as the planet moves, the star also does. As it moves radially closer and further from us, this causes a Doppler shift in its emissions (which can be measured by looking for Hydrogen emission lines).

Some of the most exciting work in this is being done by the European Southern Observatory (in La Silla, Chile). First, they recently started using a fantastically sensitive spectroscope called ELODIE capable of measuring radial movement of 1 meter per second in a star.

There are limits on the ability of these instruments. First, the longer the orbital period of the planet, the longer it takes for enough data to be collected to determine both mass and orbital period of the planet, let alone get some idea of its shape. There are probably stars which they've been watching for which evidence of planets won't become apparent for fifty years or more.

Second, the more sensitive the spectroscope, the smaller the mass of a planet which can be detected or larger its orbit. A smaller planet or one in a larger orbit shifts the star less and causes less Doppler shift. That's why ELODIE is so exciting. It should be able to detect a planet whose orbit is similar to Earth with a mass of only ten times that of Earth. (Until now, they've been detecting planets with a mass ten times or more than that of Jupiter, in orbits much closer than that of Earth.)

So far, all the discoveries have thrown existing theories of planetary system formation into a cocked hat. Bode's Law appears to be in mortal peril; and no-one knows why the Solar system is so regular or why none of the other systems seems to be. (At least one of the new planets has a wildly eliptical orbit, the distance to the star varying by a factor of 26-fold over the orbit. (The earth's orbit is very regular, varying only a few percent. It's damned near circular. We are the furthest from the Sun during Winter in the Northern Hemisphere, at least until the axis of the earth's rotation changes.)

But the coolest thing of all is that sometime in the next year or so they're going to start using the VLT (at Paranal, Chile) in interferometer mode and then they'll be able to directly measure lateral shift of stars against the background. One reason this is important is that if the orbit of the suspected planet is more or less flat to us (i.e. we're well off the ecliptic of the system, which is likely the case for many planetary systems) then spectroscopes won't pick anything up because there won't be any radial movement. But lateral movement will always be present for any star system with planets.

It won't, however, be as sensitive as spectroscopic measurements of Doppler shift. But it may find planets around stars not yet known to have them.
posted by Steven Den Beste at 3:20 PM on April 5, 2001

Man... I think my brain is about to explode after reading that last post...

Truly a man who knows what he is talking about.

I bow in your direction. (truly... I am impressed)
posted by da5id at 5:02 PM on April 5, 2001

It's all pretty cool. NASA is also working on a next-generation space telescope dubbed the Terrestrial Planet Finder: think two half-sized Hubbles, orbiting the Sun beyond Earth, keeping station with each other using precise laser measurements. They're far enough apart to perform sophisticated interferometry on tiny objects as small as our own planet orbiting nearby stars.

It's neat to know a lot of the history of science fiction; as you read various stories you can watch the then-knowledge of the universe reflected and sometimes it was torn to bits later on. One thing that always cropped up was how uncommon something like Saturn's rings was. All these stories had aliens talking about how Earth was the one in the system with that neato ringed planet, or perhaps look for the ringed planet and head inward, if you're hungry. Then Voyagers 1 and 2 showed us that Jupiter, Uranus, and Neptune all have rings of their own. Now we have to assume it's a typical feature.

The same has happened with cosmology of planets. Once it was assumed they were common, but then we began to identify the life cycle of stars, and we began to wonder whether stars with planets were in fact rare. Not only the age, but also the mass and overall construction of a star probably figure into this equation, and we found that there were very many more of the type of star we assumed was planetless than the other way around.

But the moment we began throwing technology at the question successfully, they started turning up everywhere. The more planets means the more chance for life to develop. I suspect the habitable zone may be larger than thought, as well: life has been found on Earth everywhere we've looked, no matter how dry, how high, how deep, how hot, or how cold. Maybe life has an easier time of it than we've thought.

Hey, gotta keep up with Steven somehow.
posted by dhartung at 5:15 PM on April 5, 2001

Larry Niven wrote a story called "The Coldest Place", which turned out to be the dark side of Mercury. He assumed that it was tide-locked so that one face always pointed toward the Sun, the way that one side of Luna always faces towards the Earth. Were that true, the dark side of Mercury would indeed have been a very cold place (because Mercury has no atmosphere, and is too small to have sustained vulcanism this long, and there would be no other way to heat the dark side).

Then planetary scientists were able to measure it, and discovered, much to their astonishment, that Mercury is tide-locked in a 3:2 pattern with its orbit. A "day" on Mercury is 1.5 "years" long (Mercury years), and all parts of the surface are exposed to the Sun at various times. I believe no-one yet understands how this could happen nor why it is stable.

(In a later collection which included "The Coldest Place", after this discovery, Niven complained, half facetiously, "How am I supposed to write about the Solar System when they keep changing it?")

As to life and how common it is, there's no way to know yet -- and it depends on what you mean by "life". At this point, there is evidence of life in the oldest rocks found which were formed at a time when the temperature of the planet was such that life was possible. It's now thought that primitive life (prokaryotes) developed extremely soon after conditions permitted it (perhaps within a couple of hundred million years). But it took more than 3 billion years after that for the first eukaryotes to appear, and a long time after that for the first multicellular organisms. The history of macro-life on earth is relatively short (less than 700 million years out of 4.5 billion).

With the discovery of life at the bottom of the ocean which is not dependant on sunlight (relying on chemosynthesis and hot springs) the question of what a "habitable zone" is has changed rather radically. It used to be thought that life in this solar system could only happen in the range of the orbit of Earth, with an outside chance of life on Mars. It's now thought that there's a non-trivial chance that there's life on Europa under the icecap, though probably nothing beyond prokaryotes.

It's not possible yet to make any kind of intelligent estimate about how common life is in the universe. If we can discover a separate, independent creation of life in the Solar System (e.g. on Europa) then we at that point can conclude that life is tenacious and superabundant, and will appear nearly everywhere that it can possibly develop. (If there is indeed life on Europa, and if we can get some of it back here, then there are ways to conclusively determine if it is a separate event or an infection from Earth.)
posted by Steven Den Beste at 3:36 PM on April 6, 2001