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

[JRehling]

Reanalysis of Kepler data finds one of the most promising earthlike candidate exoplanets yet:

https://www.nasa.gov/press-release/earth-si...asa-kepler-data

Key takeaways, in my opinion:

Kepler 1649-c is the second planet found in its system and the first has previously been called a candidate Venus-like planet.

The mass and density of the planet have not yet been measured.

The host star is a red dwarf. It has not been established yet how prone this star is to flares.

This is unusually close for a Kepler discovery

For a reasonably stringent definition of "earthlike" in terms of size and thermal radiation, this is only the fourth star found to host a transiting earthlike candidate. The other three are Kepler 186, TOI 700, and TRAPPIST-1, which hosts about two such candidates.

So, we have about five such candidates that transit their star, and these will all be outstanding candidates for examination with JWST, to see if we can assess their color, albedo, spectrum, temperature, and atmospheric composition. Of these, only one, Kepler 186f, does not orbit a red dwarf, and is therefore not tidally locked. That may be important for habitability, and also would allow us to determine a light curve and produce a low resolution map.

[JRehling]

Astronomers using the VLT may have detected Proxima c optically.

This result still lurks on the boundary between a suspected detection and an actual detection, and I think if you read the literature fairly, it remains possible that Proxima c doesn't even exist. Multiple lines of evidence (each individually not compelling) pointing to the same entity start to add up to some real evidence, but there's no formal way to assess the significance of an unknown signal.

Meanwhile a VLT campaign aimed at Alpha Centauri A and B last year has still not released its results.

The key takeaway is that optical studies of nearby exoplanets have not yet begun, but we're knocking on the door.

https://www.scientificamerican.com/article/...net-proxima-c1/

[JRehling]

The story of Proxima c has twisted and turned with a fourth result pointing to its existence and apparent confirmation. This is a unique case in all of exoplanet science as the evidence for its existence combines radial velocity, direct imaging, and astrometry (side-to-side motion).

http://astrobiology.com/2020/06/25-year-ol...centauri-c.html

Furthermore, careful studies of Proxima b have refined (and lowered) its estimated mass, and furthermore provided evidence of Proxima d: a planet with a mass of about 0.3 ME and an orbital period of 5.15 days.

All told, Proxima Centauri now has a possible "Mercury" to go along with its "Earth" and "Neptune." Proxima c (the Neptune) remains the best, possibly unsurpassable, case scenario for imaging a nearby exoplanet as the technologies become available.

There has still been no publication regarding VLT searches for possible planets orbiting Alpha Centauri A and B that took place at this time last year. Originally, the team was hopeful that they would have something to say, one way or the other, by October.