Odds against Earth-like planets

http://news.bbc.co.uk/2/hi/science/nature/2701977.stm ^ | January 28, 2003 | Dr David Whitehouse

[conservativecorner]

Earth-like worlds circling stars in orbital zones suitable for life may be few and far between in the cosmos, according to new research. In the first comprehensive study of extrasolar planetary systems, astronomers have shown that in most of them it would not be possible to keep an Earth-like world in orbit around a star so that it was neither too hot nor too cold for life.

In general, other planetary systems fall into two types: those with Jupiter-like worlds circling close to their parent star, and those with more distant Jupiters in elliptical orbits.

In both systems, maintaining an Earth-like world in a temperate orbit is difficult, although not in all cases impossible.

"This work shows us just how unusual our own Solar System is when compared with the other planetary systems," Dr Kristen Menou of Princeton University, US, told BBC News Online.

Habitable zone

Eighty-five planetary systems were studied, all that were known when the research was carried out.

Dr Menou said: "They fall into two categories: large planets circling very close to their sun - the so-called 'hot Jupiters', and systems with Jupiter-like planets in distant non-circular orbits."

Dr Menou, along with Dr Serge Tabachnik, created computer dynamical models of the known exoplanetary systems to see if it was possible for Earth-like worlds to exist for long periods in the so-called habitable zone.

This work shows us just how unusual our own Solar System is when compared to the other planetary systems

Dr Kristen Menou, Princeton University

This zone is the region around a star in which a planet would be able to sustain liquid water, being neither too close to the star for it all to be vaporised, nor too distant that it all freezes.

In our Solar System, the Earth is in the middle of the habitable zone. Astronomers believe such a position is essential for life to develop and thrive.

But it seems difficult for worlds to stay in the habitable zone in the majority of the extrasolar planetary systems found so far.

"We found that in the systems with the distant Jupiters, these worlds can disrupt the orbit of any Earth-like world in the habitable zone," says Dr Menou.

"Any Earth-like world in the temperate zone would either crash on to its parent star or be slung out into interstellar space," he added.

Over half of the planetary systems studied had distant Jupiters making them unlikely to contain habitable Earth-like worlds.

"We have identified some systems where distant Jupiters would pull Earth-like worlds into elliptical orbits that keep them inside the habitable zone. Such worlds would have dramatic and extreme seasons. We don't know how that would affect the development of life."

Cast asunder

The new analysis of the systems containing hot Jupiters shows that Earth-like worlds could remain orbiting in the temperate zone, seemingly an encouraging finding.

"The good news is that in about a quarter of the systems we studied, there could be habitable planets present."

But even in these systems, Earth-like worlds may have been cast asunder.

Current models of the evolution of planetary systems have hot-Jupiters reaching their tight orbits by migrating inwards from more distant ones.

This means that as they slowly travelled sunwards, they would have scattered any smaller worlds that got in their way, suggesting that there could be no Earth-like worlds in hot Jupiter systems at all.

"The way we are trying to get out of this pessimistic position," says Dr Menou, "is by seeing if Earth-like worlds could form in a planetary system after the inward migration of Jupiter worlds."

The research is to be published in a forthcoming edition of the Astrophysical Journal.

[Burkeman1]

Oh. I agree with you. My .01 figure was pulled out of thin air. But I believe there are plenty of Earth sized planets out there (with gravity equal to 1 Earth G more or less) that could one day be settled by Humans.

But as to the question if they have even a suitable atmosphere, much less liquid water, much less even primitive life, much less intelligent life- it is statiscally almost impossible. If there is intelligent life out there it is almost certainly in another galaxy and there are billions of galaxies. Humanity will never encounter another intelligent species even if we develop the technology to travel to neighhboring galaxies. I agree- SETI is a waste of time.

[<1/1,000,000th%]

I looked at a bunch of stars. I didn't see any planets either.

[pjd]

Either there's a super-heavy companion in some orbit,...

OK. I agree with you completely now that I understand your point.

[longshadow]

****"If our rather ordinary star and solar system has two,....."*****

See, I'm just a dumb truck driver, but how do you get to "our rather ordinary"?

"Rather ordinary" refers to the word "star," not "solar system."

We've catalogue boat loads of stars, and our sun is very ordinary in comparison to the range of stellar types and sizes out there.... in fact, it's a bit on the puny end of the range.

[PatrickHenry]

We're type M, in the main sequence (yellow color on the chart):

[longshadow]

Hey; nice H-R diagram!

[donh]

The Sun is expected to swallow up this planet in about 5 billion years as it enters the Red Giant phase of life. It will subsequently convulse, and spew the major portion of its mass into space.

Sell short.

[donh]

What the article doesn't state though is that planetary systems without Jupiter like outer planets cannot support advanced life either, because the large Jupiter like gas giants are required to keep catastrophic meteors from impacting any life bearing planets in the habital zone.

Huh? What space science book did you get this from? I disagree with your statement, though as shoemaker-levy showed us, an outer planet can capture an occasional comet/asteroid.

I don't think you're getting the point. A large jupiter-like planet serves as a vacuum sweeper to mop up all the loose chunks of rock in accentric orbits that might eventually slam into a life-bearing inner planet. Leaving only chunks of rock whose orbits are similarly close to circular, such as ours. (And therefore, a great deal less likely to hit us.) This has the effect of greatly reducing the impact hazards on the road. Considering that we came very close to losing all of life on this planet 5 times from known impacts, this is not an inconsiderable service, which must be counted as a major element in assessing the probability of life on a given planet.

[Aracelis]

That's why I think SETI is just a waste of money and perfectly good imagination.

Why does this myth continue to be believed???

SETI uses NO tax-dollars!!!

Now, if you'd like to remove our personal liberties and make it impossible to voluntarily fund SETI or contribute our scientific knowledge to the endeavor, that's a different matter entirely...I think it would be called fascism.

[Magnum44]

I'll see your arguement over the long haul (millions/billions of years). I am not a space/life science guy, just an orbit mechanics and satellite design guy. I only expect to be around for about 8 or 9 jupitor orbits myself. :^)

[PatrickHenry]

Dead thread bump.

[Eaker]

It is alive again as it is quite interesting.

http://www.freerepublic.com/focus/f-bloggers/1646385/posts

[Recovering_Democrat]

May be as rare as an intelligent idea from a Democrat party leader?

BWA HA HA HA HA HA HA HA HA HA HA HA!

[MikefromOhio]

I love how these blanket statements come out when we haven't even discovered 1% of 1% of 1% of the universe yet.

[ChessExpert]

I liked the article and most of the comments. Here is a criticism, perhaps minor, perhaps not:

"The way we are trying to get out of this pessimistic position," says Dr Menou, "is by seeing if Earth-like worlds could form in a planetary system after the inward migration of Jupiter worlds."

Why is this a pessimistic position? Why are we trying to get out of this pessimistic position? This sounds like biased science. How about if he reported that this was an optimistic finding and explained how he was trying to protect this optimistic finding from challenges? Sure, the direction of bias would be different. But would the extent of bias be any different?

How many people have we sent to Africa and elsewhere to prove (biological) evolution? How many have we sent to disprove evolution? Unless those numbers are about the same, we may have had biased science.

I think the ideal is to avoid favorites that you try to prove or disprove. A good scientific environment would have investigators report without concern for fear or favor, and let the chips fall where they may.