Nearby Exoplanets Options

[JRehling]

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

[Steve G]

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.

[JRehling]

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.

[JRehling]

Various updates:

Two planets, potentially habitable, have been discovered orbiting Teegarden's Star:
https://www.nationalgeographic.com/science/...eegardens-star/

A visual (IR) search for planets orbiting Alpha Centauri A and B is now underway, with observations already far along. It is not likely that a close Earth analogue could be observed now, but other planets whose existence could either boost or deflate the possibility of an Earth analogue could be detected.
https://www.space.com/alien-planets-alpha-c...ough-watch.html

Aggregating reports from different researchers, we now have reports of 7 ~Earth-sized and ~Earth-temperature planets orbiting 6 of the 17 closest red dwarfs, all within 14 light years. This is in line with Kepler estimates of planetary frequency suggesting that "eta Earth" for red dwarfs is on the order of 0.4 to 0.5 such planets per star. (FWIW, Barnard's Star is probably excluded from the possibility because of the detection of other planets orbiting it, with observations that could have detected an earthlike planet if it existed.)

Currently, no planet discovery methods except the transiting method (which requires exceptional luck regarding orbital inclination) is capable of having discovered Earth-sized and Earth-temperature planets orbiting K or G stars, and any such discoveries will likely require visual detection via JWST or 30-meter class ground observatories. This is sensitive to the proximity of such systems, so there are probably four that stand above the rest in future searches: Alpha Centauri A and B, with their unique closeness; Epsilon Eridani, known to possess larger outer planets; and, Tau Ceti, known to possess super-Earths bracketing the habitable zone on both sides with an intriguing gap in between that does not contain any larger planet and which, given known systems, is highly suggestive that some smaller planet could be present right in the habitable zone.

These approximately 11 planets + opportunities largely define the set of any possibly habitable planets which will be characterized with spectroscopy as that capability comes online in the next few years. Of the four M and G stars where we only hope for such a planet to exist, the expected number of such planets is roughly 1, but we will simply have to wait and see if that number is higher or lower. It is not impossible that more candidates will emerge among the remaining nearby red dwarfs, though in many cases, the current status of non-detection equals evidence against the existence of an Earth analogue. Overall, the number of nearby Earth analogue candidates is plausibly between 7 and 15, with the most likely number to be approximately 9.

These nearby non-transiting exoplanets define one major direction for future study. Transiting exoplanets (Earth analogue or otherwise) allow a completely separate technique for followup study, and allow for systems at greater distance to be characterized, but, again, depend on the exceptional luck of a transit, which will only apply to very roughly 2% of cases.

Exciting times!