Super-earths around red dwarfs are common

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Super-earths around red dwarfs are common

Post by jyril on 28th March 2012, 4:56 pm

In the case you somehow missed this:

Many Billions of Rocky Planets in the Habitable Zones around Red Dwarfs in the Milky Way

A new result from ESO’s HARPS planet finder shows that rocky planets not much bigger than Earth are very common in the habitable zones around faint red stars. The international team estimates that there are tens of billions of such planets in the Milky Way galaxy alone, and probably about one hundred in the Sun’s immediate neighbourhood. This is the first direct measurement of the frequency of super-Earths around red dwarfs, which account for 80% of the stars in the Milky Way.

More accurately, the results suggest 41%-13%+54% of red dwarfs have super-Earths in the habitable zone.

On the other hand, less than 12% red dwarfs are expected to have gas giants.

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Re: Super-earths around red dwarfs are common

Post by Lazarus on 29th March 2012, 6:51 pm

Question is what is the nature of these super-Earth planets? Rocky or water-rich?
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Re: Super-earths around red dwarfs are common

Post by Sunchaser on 29th March 2012, 7:24 pm

Interesting...in the book Universe and Beyond (by Terrence Dickerson) it was theorized that red dwarf-gas giant pairings would be more common.

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Re: Super-earths around red dwarfs are common

Post by Sirius_Alpha on 29th March 2012, 8:12 pm

Sunchaser wrote:Interesting...in the book Universe and Beyond (by Terrence Dickerson) it was theorized that red dwarf-gas giant pairings would be more common.

Did he give a reason?
Giant planets being less common around red dwarfs is an easily expected consequence if you assume the disk mass scales with the star mass.

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Re: Super-earths around red dwarfs are common

Post by Sunchaser on 29th March 2012, 9:01 pm

According to the reasoning (it was a caption to an illustration...p 129 in my edition. Circa 1992...I guess its the 3rd edition) :

"A planet several times the mass of Jupiter orbiting a red dwarf star could be the most common type of planetary system in the universe. Red dwarfs are the most prevalent class of star, and becasue gas will be prsent in the primal nebula of any newborn star, giant planets should be able to form even if rocky planets like Earth cannot."

Again, that's from the Third Edition of Universe and Beyond, by Terrence Dickerson.

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Re: Super-earths around red dwarfs are common

Post by Neuron on 30th March 2012, 2:24 am

1992 ... that is before the discovery of the first planet around a main sequence star.

Heck, I've once read a 1970s or 1960s (not sure really when) Czechoslovak (I'm in Slovakia) book about space in a library that speculated that double stars are the normal outcome of disk formation and that the Solar system was a special case when the additional material condensed into planets instead.

It is not really stupid, just it is that people before 1995 did not know of any extrasolar planets, so there were many speculations that later were discovered to be absurd.

And I don't think red dwarfs have an abundance of gas planets and a deficiency in terrestrial planets. As far as I know, most red dwarfs are relativelyyoung stars, younger than the Sun. They are long lived, but many of them young in this era of the universe - Proxima Centauri for example will live for almost 2 trillion years, but it is only 4.85 billion year old, it is also more metal-rich than the Sun. That means they are usually metal rich stars, so superterrestrials are understandable. Before the universe reached a certain metallicity, red dwarfs were very rare. Those are the long term stars of the universe.

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Re: Super-earths around red dwarfs are common

Post by tommi59 on 30th March 2012, 3:08 am

I would easily bet that most super earth are water rich planets
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Re: Super-earths around red dwarfs are common

Post by Neuron on 30th March 2012, 3:50 am

tommi59 wrote:I would easily bet that most super earth are water rich planets

This can be a good thing in the long term survival of life. Very watery planets can replenish their atmospheres more than Earth twins, which is a very good thing considering the lifetime of red dwarfs.

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Re: Super-earths around red dwarfs are common

Post by Sunchaser on 30th March 2012, 7:28 am

I know '92 was before the confirmed detection of extrasolar planets around main sequence stars. (PSR 1257+12 is mentioned, having been discovered in '91.) Just discovering a dust disk was exciting enough.

I just brought out the old quote for nostalgia...Mr. Dickerson (at the time) seemed to indicate that planets orbiting two stars (a la Kepler-34) would be highly unlikely, or at least not worth looking into.

I think this latest finding opens many, many possiblities for nearby discoveries.

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Re: Super-earths around red dwarfs are common

Post by Neuron on 30th March 2012, 12:04 pm

When it comes to composition, I would not say they are all "ocean planets". My bet is 1/3 rocky/iron planets like Earth or Mecury, 1/3 ocean planets and 1/3 gas dwarfs. Some "super Earths" were actually discovered to be gas dwarfs/mini Neptunes after analysis of their transits, while others were discovered to be very dense, for example Kepler-10b is about as dense as iron http://en.wikipedia.org/wiki/Kepler_10b . I feel that most smaller superterrestrials will be rocky or even composed of iron or other metals with an Earthlike water content when they are in the habitable zone, and many larger superterrestrials will be "ocean planets" or even not actually superterrestrials but gas dwarfs/mini-Neptunes.

Too many big planets are assumed to be due to planetary migration. Most systems in which superterrestrials are found are more metal rich than the Solar system, meaning getting a planet of rock or iron with an Earthlike water content or even less is easy.

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Re: Super-earths around red dwarfs are common

Post by Sirius_Alpha on 30th March 2012, 1:11 pm

Keep in mind that those transiting super-Earths that were found to have high densities are also the ones that are close enough to the star to have lost a volatile-rich envelope if they had one in the past. Kepler-10 b may be a remnant of a mini-Neptune or µJovian.

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Re: Super-earths around red dwarfs are common

Post by tommi59 on 30th March 2012, 4:03 pm

I completely agree with you sirius as I mentioned about it previously we have to seperate planets with significant mass loss.If earth would be 10 % larger would be wholly covered by water.Besides seems to me that planets around red dwarf are denser than around G,F stars
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Re: Super-earths around red dwarfs are common

Post by Sirius_Alpha on 30th March 2012, 6:26 pm

We don't have very many known transiting planets around red dwarfs. So any comparison between the densities of those planets and planets around FGK stars would be premature.

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Re: Super-earths around red dwarfs are common

Post by tommi59 on 31st March 2012, 2:51 am

Only seems to me but for comparison we need to wait couple years
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