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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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ngunn
post Jun 21 2019, 08:17 AM
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The Science Daily article contains these sentences:

But the system is located at a special place in the sky: from Teegarden's star you can see the planets of the solar system passing in front of the Sun.

"An inhabitant of the new planets would therefore have the opportunity to view the Earth using the transit method," says Reiners.


I plotted the RA and Dec in my little star atlas and can see that it certainly lies close to our ecliptic plane. However the planets in our system are very widely spaced compared with Teegarden's, TRAPPIST 1 and the like, also their orbital planes differ significantly, so I'm wondering which ones actually do transit as seen from Teegarden's star? They cannnot all do so for sure. (I've found a crude animation that appears to show them doing so but it uses coplanar orbits and is all out of scale.) Can anyone point me to some good information on this?
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JRehling
post Jun 24 2019, 01:55 AM
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QUOTE (ngunn @ Jun 21 2019, 01:17 AM) *
the planets in our system are very widely spaced compared with Teegarden's, TRAPPIST 1 and the like


A perhaps-transparent explanation: Tidal dynamics vary with the third power of distance, so close-in (portions of) systems are much more likely to be controlled by tides, with planetary orbital inclinations clustering near that of the star, and therefore near one another. This is therefore true of "habitable zones" of red dwarfs and, preferentially, most multi planet systems whose planets were discovered by the transit method.

The future work in characterizing exoplanets with spectroscopy (particularly ones that aren't extremely hot) will to a fair extent break down into a 2x2 matrix: {red dwarf, sunlike [KG dwarfs]} x {nearby enough to allow separation and direct imaging, transiting planets}. By and large, nearby and transiting end up [almost?] totally exclusive because of the low probability of an inclination that allows a transit.

Of those four possibilities, red dwarf + direct imaging will have a very small set of possibilities that could even begin and end with Proxima b for the time being, but hopefully the technology and circumstances will allow a few more. Transiting Earth analogues orbiting sunlike stars will be hard to study, too, for the simple reason that the long orbital period means a long wait between observations, and a few hours once a year means very limited signal-to-noise ratio and a serious constraint for earthbound observatories, which spend half the time in daylight.
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JRehling
post Aug 8 2019, 02:27 PM
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Here's a fresh update on the specific and unique case of Alpha Centauri:

https://www.scientificamerican.com/article/...tauris-planets/

It's interesting to know that relatively massive planets have been ruled out for Alpha Centauri A and B, which leaves us with a large probability, especially for B, that there are either terrestrial planets or none at all. It's also interesting to note that the increasing distance between A and B makes the search easier all the time. Finally, the best and latest visual search will post its results in October.

I'd add that the orbital period of any putative earthlike planet will compare to one year, which means that a visual search, to be thorough, has to include observations spread over at least a year because in any given month, a putative planet might be poorly positioned, either in terms of separation between the planet and its primary star or being positioned for the time being on the side that is unfortunately closer to the other star in the binary pair, and thus experience more stray light interference.

It seems likely that the ELT will resolve the issue definitively, either giving us the ability to perform spectroscopy on terrestrial planets orbiting Alpha Centauri or to establish that any planets there are too small to be very earthlike.
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dtolman
post Aug 14 2019, 03:11 PM
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Not sure the best place to put this... but researchers have used DSCOVR/EPIC data to create a simulated single image of the Earth - then used the light curve to create a two dimensional map of the Earth that manages to capture the rough shape of North America, Eurasia, Africa, and Australia/Antarctica.

A similar technique could be used for any exoplanet with static albedo features (such as oceans or continents).
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HSchirmer
post Aug 15 2019, 04:31 PM
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QUOTE (dtolman @ Aug 14 2019, 04:11 PM) *
Not sure the best place to put this... but researchers have used DSCOVR/EPIC data to create a simulated single image of the Earth - then used the light curve to create a two dimensional map of the Earth that manages to capture the rough shape of North America, Eurasia, Africa, and Australia/Antarctica.

A similar technique could be used for any exoplanet with static albedo features (such as oceans or continents).



Interesting article about locating a telescope near the Lagrange point, which would use diffraction through the outer atmosphere to create an image with up to 45,000 amplification.

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