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Unmanned _ Telescopic Observations _ Nearby Exoplanets

Posted by: JRehling Nov 15 2017, 04:17 PM

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.

Posted by: Ron Hobbs Nov 15 2017, 09:26 PM

Excellent! Thank you for the link to the article.

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

I look forward to hearing more about this system.

Posted by: JRehling Nov 17 2017, 04:17 PM

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.

Posted by: JRehling Dec 6 2017, 04:40 PM

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 +.

Posted by: JRehling Feb 12 2018, 02:56 PM

New clues to the density (and composition) of the Trappist-1 exoplanets:

Posted by: JRehling Nov 15 2018, 04:38 AM

An article in Nature announces the discovery of a cold super-earth orbiting Barnard's Star.

I wonder if some super-earths might have warm surfaces due to greenhouse effect from a thick atmosphere, but I will leave that up to the experts.

This would mean that both of the closest red dwarfs and at least three of the closest four have planets orbiting them. The evidence is shaping up that nearly all red dwarfs have planetary systems, although the 5th and 6th closest, Luyten 726-8, are a binary pair that come within 2.1 AU of one another, which might make that system in particular an unusual case. This also makes five planetary systems within 11.1 light years. There could also be more with smaller planets, more distant planets, and/or an orbital inclination that hides planets from the radial velocity method.

Intrigue grows for the eventual observations from JWST (2021) and ELT (2024).

Posted by: Steve G Nov 15 2018, 01:46 PM

Bernard's star was the first star ever to have a suspected planet. In the sixties Peter van de Kamp claimed that he had detected a perturbation in the proper motion caused by a Jovian-class planet. It was eventually refuted but I'm glad to see the star finally has been confirmed as having a planet. Exciting news to have something so close to home.

Posted by: JRehling Nov 15 2018, 06:24 PM

Yeah, Steve, my public library had a book that flat-out stated that Barnard's Star had planets, so it's a sweet resolution to that long-running narrative – and, as is clear, this discovery cannot be the planet(s) that were claimed long ago.

I took a picture of Barnard's Star this summer so I can make a "video" of its proper motion over a span of year(s) – it's a pretty little dot, more orange than red. One distinction held by this system is that it's the closest planetary system (and closest star, period) that can be seen from north of the tropics.

With a nominal orbital distance of 0.4 AU, Barnard's Star b will have about 5 times the angular distance from its star that Proxima b will from Proxima Centauri. That is much less angular separation, however, than cases like Fomalhaut b, which is much farther from its primary than Neptune is from the Sun. Barnard's Star b will likely be one of the easiest exoplanets to resolve and one day reveal non-pointlike images of its surface.

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