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Nearby Exoplanets
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.

QUOTE

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JRehling
post Jan 16 2020, 08:03 PM
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Proxima c, a candidate planet orbiting Proxima Centauri at 1.5 AU.

https://www.scientificamerican.com/article/...e-of-proxima-c/
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JRehling
post Apr 16 2020, 07:02 PM
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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.
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JRehling
post Apr 22 2020, 08:34 PM
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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/
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JRehling
post Jun 7 2020, 04:25 AM
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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.
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ngunn
post Jun 10 2020, 07:09 AM
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Thanks for the interesting update and, in general, for keeping this thread refreshed with new information and ideas. I am always reminded as the curtain slowly lifts of the limitations imposed by observational selection and wonder about the remaining unseen planets in this and other systems.
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JRehling
post Jul 6 2020, 08:02 PM
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Another nearby system with interesting potential: Last month, the discovery of two warm/hot Super Earths around Lacaille 9352 (Gliese 887) was announced. This is actually the brightest red dwarf in the sky (or nearly so) at 10.7 light years away, and is near the boundary of classification as a K star rather than M. This alone is a notable discovery. What might be more interesting is the additional indication of a third planet with an orbital period of 51 days, because such a planet, if real, could be an earth-sized planet in the habitable zone. Moreover, such a planet might turn out to be outside the grip of tidal locking. I'm putting the cart before the horse with all those "if"s but the significance is that tidal locking might turn out to be a factor restricting habitability, and we know of very few earth-sized planets in habitable zones that aren't likely to be tidally locked, and we don't know of any that are this nearby. (Of course, we have yet to establish the rotation of any earth-sized exoplanets, but dynamical factors strongly imply this for many cases.)

I think we should be on the lookout for confirmation and followup in case Gliese 887 d exists. This, along with Alpha Centauri A and B, Tau Ceti, and Epsilon Eridani, offer five nearby possibilities for non-tidally locked earthlike planets that we will be able to observe directly. As yet, we have zero discoveries, so this mere hint of one is already something to pique the intrigue.
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HSchirmer
post Jul 9 2020, 12:38 PM
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QUOTE (HSchirmer @ Aug 15 2019, 04:31 PM) *
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.


I like the naming convention - Terrascope for Earth as lens, that would make the FOCAL / solar Einstein ring scope a Solscope?

Can't wait for the figures for the Jovascope...
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JRehling
post Dec 23 2020, 10:19 PM
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We obviously have not yet begun to learn about the climates or geology of terrestrial exoplanets or super-earths. Here's a paper suggesting that Proxima Centauri c might just be more earthlike than some of the "earthlike" terrestrial exoplanets orbiting red dwarfs.

http://www.sci-news.com/astronomy/super-ea...ment-09106.html

It seems to me that when one factor might make a planet relatively less earthlike, there is the possibility that another factor could make up for that, meaning that we might find some earthlike climates out there where the planet's physical parameters different from Earth's in two offsetting ways. For example, a harsh stellar wind that would strip away an atmosphere might be compensated for on a planet with higher escape velocity. Or, a planet with a strong greenhouse effect might end up with earthlike temperatures if it gets much less heat from its star. It will be a while before we find out, but Proxima c might well be the first place for which we get the answers – it's the closest super-earth we'll ever find.
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JRehling
post Feb 23 2021, 08:52 AM
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We've been waiting well over a year to hear about observations of Alpha Centauri made in 2019. Here we have the still provisional first report: the VLT may have discovered, in 10µm IR, a Neptune-sized exoplanet in the habitable zone of Alpha Centauri A.

As the article notes, any such detection would be slightly bad news for anyone hoping that an Earth-sized planet might exist in that niche. For now, the detection is uncertain. If it does turn out to be real, it leaves room for a more earthlike discovery on the edges of Alpha Centauri A's habitable zone, and Alpha Centauri B is still a possibility. In a subtle way, the lack of any detection at Alpha Centauri B may even be the best news, because it may mean that any such planet there is smaller, and more Earth-sized. Then again, it could be that other planets just happened to be in unfavorable locations in their orbits at the time of the observations.

Future observations await!

https://www.scientificamerican.com/article/...alpha-centauri/
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Decepticon
post Feb 23 2021, 09:53 PM
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A Earth-sized Moon sitting in orbit would be wishful thinking.

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JRehling
post Feb 24 2021, 12:36 AM
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If I had to guess, the large natural moon of a "Neptune" inside the ice line would be about the mass of Titania minus its ice mass, so more like Vesta than Earth, but I'm extrapolating from very low n!

For the hope of a close Earth analogue orbiting Alpha Centauri A, I think we have a better chance that this will be a false detection and a yet-undetected terrestrial planet will coincidentally be in its place. Or, that this planet is real and an earth-sized terrestrial planet will be outside of it, still in the habitable zone.

If this is a Neptune where we think it is, it would stand a good chance of holding this distinction: The exoplanet with the largest apparent diameter, and thus, likely the first we will ever image with detail… whenever appropriately powerful instruments come about.
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HSchirmer
post Feb 24 2021, 01:26 AM
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QUOTE (Decepticon)
A Earth-sized Moon sitting in orbit would be wishful thinking.


Eh, not entirely out of the realm of possibilities, but I guess they'd be more likely to be water-worlds?


QUOTE (JRehling @ Feb 24 2021, 01:36 AM) *
If I had to guess, the large natural moon of a "Neptune" inside the ice line would be about the mass of Titania minus its ice mass, so more like Vesta than Earth, but I'm extrapolating from very low n!


I will be interesting either way, especially because this may be our first glimpse of an ice giant with the primordial moon system intact. Given that in our solar system "we can't have nice things" and both our ice giants are a bit damaged.....
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JRehling
post Mar 14 2021, 06:20 AM
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This pushes the boundary of "nearby" a bit, but TESS has found a five-planet transiting system orbiting a sunlike star.

https://en.wikipedia.org/wiki/HD_108236

By the nature of TESS, it is a given that any of its discoveries are in short-period orbits, so while the solar system's fifth planet has an orbital period of 12 years, this system's fifth planet has an orbital period of under 30 days.

The estimated densities of the two inner planets are rather similar to Earth while the three outer planets have more Neptune-like densities.

High temperatures should make these planets rather unlike Earth but these are still of great interest because, as transiting planets only 211 LY away, these are still good candidates for follow-on study, because the apparent magnitude of the star (9.24) allows for good signal to noise ratio. For comparison, TRAPPIST-1, though much closer, is a red dwarf, and appears much dimmer. HD 108236's system may permit some breakthroughs in our understanding of the evolution of super Earths. Studies to characterize these planets will certainly book some time on JWST and terrestrial telescopes.
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