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Nearby Exoplanets
JRehling
post Nov 15 2017, 04:17 PM
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There have been a few topics in recent years pertaining to exoplanets found circling nearby red dwarfs, particularly Proxima Centauri and Trappist-1. There's a new one to report, and I thought I'd give the topic a more general scope rather than specific to this one.

The star in question is Ross 128, and the planet's solar flux is between that of Earth and Venus. There's a good chance that this is potentially the most "habitable" exoplanet yet found, and is happily quite close (13th closest system), so that telescopes will be able to separate the light of the planet from that of the star. This is a circumstance that only a few nearby stars will permit in the foreseeable future, so Ross 128 is likely to figure large in our exoplanet studies over the next century.

https://www.eso.org/public/archives/release...36/eso1736a.pdf
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Ron Hobbs
post Nov 15 2017, 09:26 PM
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Excellent! Thank you for the link to the article.

Here is a link to the ESO release, which has cool artistic impressions videos.

https://www.eso.org/public/news/eso1736/

I look forward to hearing more about this system.

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JRehling
post Nov 17 2017, 04:17 PM
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A quick look outward:

Ross 128 is the 8th closest single red dwarf star. So far, we know of two ~earthsized planets in their ~HZs. Not a significant sample, and we don't know how many are yet to be found, but this is certainly suggestive that about a third of such stars have such planets. (The Doppler method can easily miss planets in orbits more or less perpendicular to our line of sight.) The true number may be much higher, because we don't have clear negatives yet on the other 6 of those 8.

Now, between Ross 128 and 20 light years out, there are 36 more single red dwarfs. Between 20 and 30 light years out, there are 75 more. And of course, there are 6 farther than Proxima Centauri and closer than Ross 128, making 117 more red dwarfs within 30 LY. If a third of those have such planets, we have dozens yet to find.

This says seriously good things about the sample we are going to be able to examine with followup studies.

The closest such transiting planet, however, may be quite a bit farther, but distance won't be a serious impediment for detection and characterization of those.

And, of course, there are also many multiple systems and bigger, hotter stars. We already know that the closest single non-red dwarf, Epsilon Eridani, probably has planets.

It's going to be an interesting few decades ahead for studying nearby terrestrial planets.
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JRehling
post Dec 6 2017, 04:40 PM
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A best-of-its-kind discovery: K2-18b (announced in 2015) is a transiting Super Earth 111 light years away. It orbits a red dwarf with a period of 32 days and has an equilibrium temperature very nearly equal to Earth's.

What's good: It transits! Studying the planet's atmosphere, therefore, can be done as the star's light passes through it, or by subtracting the planet's light from the system's as a whole when the star eclipses the planet. There is no need to resolve the planet, so the distance is not highly relevant to follow-up science.

This has also allowed an accurate measurement of mass and therefore density, and this reveals that the planet has a very earthlike density with 2.24x the radius and 8x the mass. This is itself a striking result as part of a new and growing survey of Super Earths, and the mystery of whether they are more like big Earths or little Neptunes. In most cases, we know the radius or the mass but not both.

What's bad: If we're looking for Earth analogues, the larger size may still mean that the atmosphere and climate are radically different from anything we've seen before. On the other hand, with red dwarf systems, there's a fear that flares could strip away an atmosphere and in this case, those two concerns potentially offset one another. Maybe a big planet with this high escape velocity could end up with an intact atmosphere that could even be more earthlike if a bit of it has been blasted away.

Add this to the short list of ones that we'll be watching closely over the next decade +.
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