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View Full Version : Alien life may require rare 'just-right' asteroid belts



iquestor
2012-Nov-02, 08:26 PM
Asteroid belts similar to the one between Mars and Jupiter appear to be rare beyond our solar system, implying that complex alien life may be rare as well, a new study reports.

More ... (http://www.foxnews.com/science/2012/11/02/alien-life-may-require-rare-just-right-asteroid-belts/?intcmp=features)

Buttercup
2012-Nov-02, 08:34 PM
I should think they're rare! Probably ours is a fluke. And how many planets might a system have to have, in order to chance an asteroid belt?

iquestor
2012-Nov-02, 08:54 PM
their reasoning sounds like Ward and Brownlee in Rare Earth where they speculate A Jupiter analog is requiremd for complex life.

Noclevername
2012-Nov-03, 12:21 AM
I don't think we have enough data to come to that conclusion yet. We would have to measure which planets have signs of life, which is beyond our current tech.

John Jaksich
2012-Nov-03, 02:45 AM
I don't think we have enough data to come to that conclusion yet. We would have to measure which planets have signs of life, which is beyond our current tech.

I tend to second that notion---well said!

MarianoRF
2012-Nov-04, 02:51 PM
I don't think we have enough data to come to that conclusion yet. We would have to measure which planets have signs of life, which is beyond our current tech.

I agree. We are still very very far from the tech required in order to explore the deep space.

IsaacKuo
2012-Nov-05, 04:08 PM
Bear in mind that this study suggests a 1 in 25 chance of a "just right" asteroid belt. This is not rare at all! It barely puts a dent into the Drake equation. With hundreds of billions of stars in our galaxy, this implies "only" billions and billions of just-right asteroid belts in our galaxy.

iquestor
2012-Nov-05, 04:30 PM
The article is also extrapolating based on known giant planets in Jupiter distance orbits whether they are there or not. This is probably not the last word on whther they are there, or not, and whether Life largely requires an asteroid belt, or doesn't. way too soon to tell, but not too soon to ask the question.

KABOOM
2012-Nov-06, 09:57 PM
The article is also extrapolating based on known giant planets in Jupiter distance orbits whether they are there or not. This is probably not the last word on whther they are there, or not, and whether Life largely requires an asteroid belt, or doesn't. way too soon to tell, but not too soon to ask the question.

Isn't there possibly a selection bias at play here as well. It is easier to detect Jupiter-sized planets that orbit their host suns at closer than Jupiter-distanced orbits. The closer the planets the easier it is to detect them. That is starting to change with new methods but when one goes calculating percentages out of the sample of known exo-planets the data set will be skewed towards "close in, easier to detect" planets.

glappkaeft
2012-Nov-07, 11:18 PM
Isn't there possibly a selection bias at play here as well. It is easier to detect Jupiter-sized planets that orbit their host suns at closer than Jupiter-distanced orbits. The closer the planets the easier it is to detect them. That is starting to change with new methods but when one goes calculating percentages out of the sample of known exo-planets the data set will be skewed towards "close in, easier to detect" planets.

This is bordering on nitpicking but if by "new methods" you mean the occultation method it still rather more likely to detect close large planets. The difference is that it is a bit less sensitive to size and that it currently can detect smaller planets than the radial velocity method.

Noclevername
2012-Nov-08, 01:57 AM
Bear in mind that this study suggests a 1 in 25 chance of a "just right" asteroid belt. This is not rare at all! It barely puts a dent into the Drake equation. With hundreds of billions of stars in our galaxy, this implies "only" billions and billions of just-right asteroid belts in our galaxy.

If that's rare, I'd hate to see medium.

whimsyfree
2012-Nov-14, 11:27 PM
This is bordering on nitpicking but if by "new methods" you mean the occultation method it still rather more likely to detect close large planets. The difference is that it is a bit less sensitive to size and that it currently can detect smaller planets than the radial velocity method.

I think you mean the transit method. Planets are generally too small to occult their primaries. Possibly the previous poster is referring to the micro-lensing method, which is not biased towards close-in planets. It seems to be biased towards planets with 1 < a < 4AU.

TooMany
2012-Dec-02, 08:14 PM
Isn't there possibly a selection bias at play here as well. It is easier to detect Jupiter-sized planets that orbit their host suns at closer than Jupiter-distanced orbits. The closer the planets the easier it is to detect them. That is starting to change with new methods but when one goes calculating percentages out of the sample of known exo-planets the data set will be skewed towards "close in, easier to detect" planets.

Detection of a Jupiter (same size and distance from same size star) via transit seems to be fairly difficult. If I've done my calculations correctly, the chance of a transiting alignment is about 1/2,000. The frequency of transit for a given system is 1 per 12 years. (The longest possible transit lasts for 1 day.) If we watched 2000 systems all having a Jupiter continuously for 12 years we would probably see one transit.

Does anybody know how close a Jupiter size planet has to be to detect by Doppler effect?

Could we detect a nearby Jupiter by imaging?

whimsyfree
2012-Dec-08, 12:22 AM
Detection of a Jupiter (same size and distance from same size star) via transit seems to be fairly difficult. If I've done my calculations correctly, the chance of a transiting alignment is about 1/2,000. The frequency of transit for a given system is 1 per 12 years. (The longest possible transit lasts for 1 day.) If we watched 2000 systems all having a Jupiter continuously for 12 years we would probably see one transit.

Does anybody know how close a Jupiter size planet has to be to detect by Doppler effect?


Since that's what they're using to search for Jupiter analogs (http://arxiv.org/abs/1211.7263), I conclude that Jupiter is detectable by the radial velocity method. I don't think any confirmed Jupiter analogs have been found yet. OGLE-2012-BLG-0026L b and c (http://arxiv.org/abs/1210.4265) are candidates but planets detected by micro-lensing are not regarded as confirmed.


Could we detect a nearby Jupiter by imaging?

No, not unless they are very young and hot.

TooMany
2012-Dec-08, 06:20 PM
Since that's what they're using to search for Jupiter analogs (http://arxiv.org/abs/1211.7263), I conclude that Jupiter is detectable by the radial velocity method. I don't think any confirmed Jupiter analogs have been found yet. OGLE-2012-BLG-0026L b and c (http://arxiv.org/abs/1210.4265) are candidates but planets detected by micro-lensing are not regarded as confirmed.

So RV is a far more practical way of finding them. They admit that the sample they have so far is very small. It takes a long time due to the orbital periods. We'll see. There may be many ways that systems can work that haven't been given much thought yet. I.e. it's a bit premature to conclude that a system has to be just like ours for life to emerge.

Our system is generously equipped with terrestrial planets (Venus, Earth, Mars). Earth happens to be right in the habitual zone, but with at least decent three shots at it, it's not too surprising that one is. The one in the middle is the winner in our case.

The asteroid belt article isn't very clear about why it matters. As I understand it, the asteroid belt does not contain the volatiles needed for life. If disruption occurs and asteroids reach the inner solar-system, it's not particularly good for life. Life could not get a start until after the late heavy bombardment. Isn't the question more about how the volatiles got here and do we need a Jupiter to bring them?

The amount of water on the Earth is in a rather amazing balance (yet another argument for rare civilization). Since 3/4 of the Earth is covered, it might seem that other likely scenarios are ocean-only planets. On the other hand we have the example of Mars which once had oceans but is now nearly dry on the surface, perhaps because it was too small to retain an atmosphere.