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I am a chemist, not an astronomer, and at last year's Astrobiology conference in Rotorua I gave a presentation on the reasons why life formation (more difficult than habitability) is likely to be restricted mainly to a low percentage of planets in the habitable zone around G type or heavy K type stars. To put estimates on this I need answers to two questions. The first is, I used a reference that the rate of primary stellar accretion is approximately proportional to the final mass squared. Can anyone put a range on this, or even better, a probability distribution? The second one is the planet LkCa 15b clearly shows the model of oligarchic formation is wrong because it shouldn't be there. The planet is roughly five times bigger than Jupiter and about three times further away from a star the same size as the sun, (approximately) and there is simply no time to form it, leaving aside models of oligarchic formation, while the Grand Tack model says no cores form that far out. My answer is monarchic growth, but now the issue is that growth must continue as long as the disk is there, and for Jupiter to be as small as it is, our star had to eject its accretion disk quickly, probably within 1 My after the primary stellar accretion. So the question is, do we have a probability distribution for how long accretion disks last after major stellar accretion? Sorry to have such a long question, but I felt it was necessary to get some idea of why so that the details of the answers would be helpful. Thanks in advance.
Thanks for your question! The questions during the live broadcast are fed either through Twitter at #AskAstrobio on @saganorg or via the main chat room at the bottom of the screen. This thread is for questions when the show is not live, for any scientist to answer. Apologies for the confusion!
But since your question is long, I will share a link to it with the moderators. =)
Excellent. I know it was too specific for the actual interview.
I can begin to answer your second question. Protoplanetary disks are typically thought to last 5-10 Myr. This is thought to have been the case for our solar system, and observations of nearby forming systems suggest the same time scales. I have attached a good paper to start.
I don't think lifetimes can be represented by a probability distribution, because (1) there isn't enough data and (2) lifetimes depend on start type, composition, multiplicity, and the stellar environment (e.g. presence of nearby high-mass stars whose radiation can lead to photoevaporation of the disk).
The point about LkCa 15 is the star is estimated as 2 - 3 My old and slightly smaller than the sun, and the planet LkCa 15b is about three times as far from the star as Jupiter and about 5 times bigger. Astronomers have noted gas pouring into the planet, so the question then is, why is Jupiter so small? The simplest answer I could come up with was the sun ejected the accretion disk much earlier (my guess was 1 My). The reason this is important is that if our star did eject its disk gases so early, that might explain why there are so many "super-Earths".
Thanks for the ApJ paper. I shall have to give it a close look.
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Hi i have some spiritual question..
No one is able to answer in india...
You may simply be seeing a reflection of the red light from your retina in your field of vision. This can happen if you stare at a light for too long. You would see that with your eyes closed or open. This seems like the most logical explanation - it is a physical phenomenon, rather than any kind of spiritual event. Please be careful when staring at bright lights because you may damage your eyesight.