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.

[conservativecorner]

In the beginning God created the heavens and the earth...Genesis 1

[Libertarianize the GOP]

http://www.freerepublic.com/perl/bump-list

[anobjectivist]

Hmm. The problem with any hypothesis about habitable planets is the technology we use to "discover" the existence of planets orbiting stars is based on the effects those planets have on their stars (wobbly stars, planet transits creating decrease in luminosity, doppler effect of orbiting star).

The methods we use to determine planets have a tendency only to report large (jupiter scale), close-orbiting planets. To my knowledge, even if we were able to go as far away from our own planet as we are from the stars being observed with jupiter like planets, and we looked back at our star, we would probably not detect any planet but jupiter/saturn if that. Our current technology makes it seem like we are alone in the universe but once we get an orbiting inteferometer working we'll be able to identify planets by more than just their effects on their host stars. (we could detect planets by infrared radiation, reflected light, etc., things that we cannot do realistically with 99.999999999999% of the stars out there with current technology) A whole new universe will be ours to see.

[Mr. K]

I think it is a miracle in itself that planets sustain (nearly) circular orbits- do you have any cluse how little it would take to knock them out of the precise balance of mass/speed that puts it into orbit? (circular OR otherwise)

[anobjectivist]

Additionally:

The fact that there are billions of stars in the universe and we have only detected around 100 of these stars with close, jupiter like planets suggests the opposite of what this article reports. In all likelyhood, the planets we are detecting are the rare ones (big enough to show up after observation with simple telescopes), the more common planets are too small or too far away from their host star to be observable by our current method. Thus, any real studies on the limited data that our technology affords at the moment should be taken as premature, incorrect guesses.

[Pres Raygun]

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.

[Psycho_Bunny]

This article really reads like the work of someone desperate to make the news.

[Bloody Sam Roberts]

...and we looked back at our star, we would probably not detect any planet but jupiter/saturn if that.

I think the best analogy I've heard is that it is like trying to detect a speck of dust orbiting a 100 watt light buld from 100 meters away.

[anobjectivist]

To our limited knowledge of planetary formation, yes that would make sense, however life-bearing planets could have a possibility of surviving without jovian planets. The thing is they would have to age more (endure a longer period of bombardment) before life really takes off.

Also, I doubt that we can detect jovian planets at the same distance from our sun as jupiter except in the nearest stars.

[Dog Gone]

85 solar systems is not exactly a representative sampling of the galaxy, much less the entire universe.

If only 1 in 85 has an earthlike planet, how many would that make?

60 bazillion?

[Poohbah]

85 solar systems is not exactly a representative sampling of the galaxy, much less the entire universe.

If only 1 in 85 has an earthlike planet, how many would that make?

60 bazillion?

Give or take a kajillion :o)

[Burkeman1]

There are about 100 billion stars in the milky way alone. If only 0.01 percent had Earth like planets that still means ten million Earth like worlds just in our galaxy alone.

[MattinNJ]

bttt for later read.

[steve-b]

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.

These two cases (particularly the former) are considerably easier to detect than the case of a Jovian in a distant circular orbit. Thus, the available data shows a strong selection bias.

[anobjectivist]

Yup, and all we need is more sophisticated equipment orbiting somewhere (prefereably a lagrange point) with big enough detectors and an interferometer setup and we might be able to actually see a few blue pixels coming from an earth-like planet. And once we get the light from these planets, we could do a simple spectrum analysis and find out what we have.

[chilepepper]

I've heard this argument before and believe it is the exact inverse of playing the lottery: don't fight against billions and billions of stars

you cannot win such a bet. there is no doubt in my mind that there are MANY planets out there that will support life, and a fair sized subset of those will be very earthlike...

[Mr. K]

but getting them into an orbit - out of the infinite number of places they could go is astounding

[RightWhale]

This is the central hypothesis of the book "Rare Earth," copyright 2000, Peter D. Ward and Donald Brownlee. Since this contradicts Sagan's hypothesis, the idea was not popular at the time. However, it is gaining acceptance.