Posted on 01/28/2003 11:50:07 AM PST by 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.
Its prehelion precesses also.
Ding! Ding! Ding! We have a winner. They use wobbles to detect planets, they see only the wobbliest systems, and they conclude that planetary systems are too wobbly to support Earth-like worlds. Nicely done.
I disagree. The Earth will continue to slow down as the moon recedes and eventually the Earth and the Moon will be locked together into a mutual orbit around a common center of mass. There will be perturbations by the Sun and Jupiter; however, they should not cause the Earth/Moon system to decouple.
What you are really saying is that the difference in angular momentum of the Earth's current rotation and it's rotation when it will be phase-locked with the moon is insufficient to raise the moon's velocity above the Earth's escape velocity, right?
OTOH, if the change in the Earth's angular momentum were in excess of what is required to make the moon exceed the Earth's escape velocity, then we would eventually wave "bye-bye" to the moon....
Whoa... better watch out... some school district interpret that little bronze ball to be a BULLET! You could get your entire class expelled!
Wouldn't that be a 'circular argument?'
Sorry... couldn't resist.
Exactly. At present we lack the kind of technological capabilities required to assess planetary genesis, evolution, orbit and life-support conditions.
I agree. As far as intelligent life? I truly do not know. I hear arguments from both sides on this issue. SETI is a VERY long shot at finding out. But IMHO, it is worth the effort.
The total angular momentum of the earth moon system, which is spin angular momentum plus the orbital angular momentum, is constant. (The Sun plays apart also) Friction of the oceans caused by the tides is causing the Earth to slow down a tiny bit each year. This is approximately two milliseconds per century causing the moon to recede by about 4 centimeters per year. As the Earth slows down, the Moon must recede to keep the total angular momentum a constant. In other words as the spin angular momentum of the earth decreases, the lunar orbital angular momentum must increase. Here is an interesting side note. The velocity of the moon will slow down as the orbit increases.
The escape velocity of the Earth is about 11Km/sec and the current orbital velocity of the moon is about 1.026km/sec.
Thanks :-)
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