Posted on 07/30/2004 11:12:50 AM PDT by PatrickHenry
We could be alone in the Universe after all. The discovery during the past decade of over a hundred planets around other stars has encouraged many scientists to think that habitable planets like ours might be common. But a recent study tells them to think again.
Martin Beer of the University of Leicester, UK, and co-workers argue that our Solar System may be highly unusual, compared with the planetary systems of other stars. In a preprint published on Arxiv1 [footnote's link in original article], they point out that the alien planets we have seen so far could have been formed by a completely different process from the one that formed ours. If that is so, says Beer, "there won't necessarily be lots of other Earths up there".
Most of the planets around other stars, known as extrasolar planets, are detected from the wobble that they induce in their own sun's motion. This wobble is caused by the gravitational tug of the planet on the star. Because stars are much bigger than planets, the effect is tiny, and it is only in the past decade that telescopes have been sensitive enough to detect it.
Even then, the wobble is detectable only for giant planets, which are those about as big as Jupiter, the bloated ball of gas in our Solar System. It is not possible at present to detect planets as small as the Earth.
Jupiter is not habitable: it is too cold, and is mostly composed of dense gas. And it is unlikely that extrasolar giant planets would support life either. But astronomers generally assume that if they detect such a planet in a distant solar system, it is likely to be accompanied by other, smaller planets. And maybe some of the smaller planets in these systems are just like Earth.
This is what Beer and colleagues now dispute. They say that the properties of almost all the known extrasolar planets are quite different from those of Jupiter.
Hot Jupiters
There are 110 of these extrasolar planets, at the latest count, and they are all between about a tenth and ten times as massive as Jupiter. Most of them are, however, much closer to their sun than Jupiter is to ours: they are known as 'hot Jupiters'. They also tend to have more elongated orbits than those of Jupiter and the Earth, both of which orbit the Sun on almost circular paths.
Ever since Copernicus displaced the Earth from the centre of the Universe, astronomers have tended to assume that there is nothing special about our place in the cosmos. But apparently our planetary system might not be so normal after all. Is it just chance that makes Jupiter different from other extrasolar planets? Beer and his colleagues suspect not.
They suggest that other planets were not formed by the same kind of process that produced our Solar System, so they might not have smaller, habitable companions.
Different recipes
The planets in our Solar System were put together from small pieces. The cloud of gas and dust that surrounded our newly formed Sun agglomerated into little pebbles, which then collided and stuck together to form rocky boulders and eventually mini-planets, called planetesimals. The coalescence of planetesimals created rocky planets such as Earth and Mars, and the solid cores of giant planets such as Jupiter, which then attracted thick atmospheres of gas.
But that is not the only way to make a solar system. Giant planets can condense directly out of the gaseous material around stars, collapsing under their own gravity. This process, which generates giant planets with a wide range of orbital radii and eccentricities, does not seem capable of producing the rocky planets seen in our own Solar System, which is why it has generally been ignored.
Yet it might account very nicely for the known extrasolar planets. "It wouldn't surprise me if there are two different ways that planetary systems are formed," Beer says. But how can we know if that is the case? "Probably the best way is just to gather more observations," says Beer. Only then can we know how unusual we really are.
You've obviously never driven a Chevy Nova.
Beatcha!
Yes, that could be said.
OK, replace Chevy Nova with Ferrari. An Ferrari is more random than a Bike?
Why do you believe that?
Doh I must have skimmed right by that!
Depends on the driver... and your perspective!
It's not a belief. It had to do with organization and order. Something with more moving parts would have more degrees of freedom. More degrees of freedom implies more possible configurations at any given time which would lend itself to a stochastic approach.
Maybe you and Ken Miller can discuss TTSS…
Just watched a program on the Science Channel about that this week. One astronomer made the point that without the moon the Earth would wobble/roll over on its "side" by perhaps as much as 30 or 40 degrees or more, and considering that a measly wobble of 1 degree was responsible for the creation of the Sahara Desert and mass migration of ancient humans, there is no way humans could have survived such climatological instability and evolved the way we have. It seems humans owe their existence to the moon and the extremely, EXTREMELY improbable type of collision that created it.
You mean like that part in Joshua where the the folks who wrote the Bible had the sun rotating around the earth?
I believe it was "privelidged planet", sorry if somebody already told you, i don't feel like looking,.
Rare placemarker.
There was a fairly good discussion here about 2 months ago:
http://www.freerepublic.com/focus/f-news/1138670/posts
Science threads normally devolve into the two camps.
My initial assumption you were referring to "Rare Earth" was based on your choice of the words "a few years back."
I merely observed after checking your profile, and past posts that you had never posted anything indicating that you were an adherent of either camp.
You are correct. A GOOGLE search on "Kolmogorov complexity" gives lots of information. Kolmogorov's version is the easiest to use.
I know for a fact there is at least one earth-like planet.
(in fact, it happens to be in this very solar system)
Yes, it does.
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