LHS 1140b Transiting rocky super-Earth found in habitable zone of quiet red dwarf star

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LHS 1140b Transiting rocky super-Earth found in habitable zone of quiet red dwarf star

Post by Led_Zep on 19th April 2017, 1:29 pm

ESO press release :

http://www.eso.org/public/unitedkingdom/news/eso1712/?lang

Newly Discovered Exoplanet May be Best Candidate in Search for Signs of Life
Transiting rocky super-Earth found in habitable zone of quiet red dwarf star

The newly discovered super-Earth LHS 1140b orbits in the habitable zone around a faint red dwarf star, named LHS 1140, in the constellation of Cetus (The Sea Monster) [1]. Red dwarfs are much smaller and cooler than the Sun and, although LHS 1140b is ten times closer to its star than the Earth is to the Sun, it only receives about half as much sunlight from its star as the Earth and lies in the middle of the habitable zone. The orbit is seen almost edge-on from Earth and as the exoplanet passes in front of the star once per orbit it blocks a little of its light every 25 days.
“This is the most exciting exoplanet I’ve seen in the past decade,” said lead author Jason Dittmann of the Harvard-Smithsonian Center for Astrophysics (Cambridge, USA). “We could hardly hope for a better target to perform one of the biggest quests in science — searching for evidence of life beyond Earth.”

The paper (free) : https://www.eso.org/public/archives/releases/sciencepapers/eso1712/eso1712a.pdf
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Re: LHS 1140b Transiting rocky super-Earth found in habitable zone of quiet red dwarf star

Post by Lazarus on 19th April 2017, 3:41 pm

Another habitable exoplanet? *yawn*

Actually no, good to have a nearby transiting HZ planet around a more luminous star than TRAPPIST-1, will be interesting to see how the conditions on the planets compare.

Though it's still something of an anomaly, given the apparent high rate of "habitable" terrestrial planets around M dwarf stars, that the habitable planet we are on (so far, the only confirmed planet with life) is located around what would appear to be an unusually massive host star.
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Re: LHS 1140b Transiting rocky super-Earth found in habitable zone of quiet red dwarf star

Post by Sirius_Alpha on 19th April 2017, 4:19 pm

Is the measured M dwarf "eta-Earth" actually higher than the G dwarf "eta-Earth"?
I suspect that final statement is probably prone to a number of observational biases.

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Re: LHS 1140b Transiting rocky super-Earth found in habitable zone of quiet red dwarf star

Post by Sirius_Alpha on 19th April 2017, 8:22 pm


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Re: LHS 1140b Transiting rocky super-Earth found in habitable zone of quiet red dwarf star

Post by Lazarus on 20th April 2017, 2:53 am

Even if the rate of HZ terrestrials around red dwarfs is comparable to that around G dwarfs, the Earth would still be atypical because there are more low mass stars than high mass ones. You'd need a ridiculously high G-dwarf eta-Earth to counteract that, or alternatively the eta-Earth for M dwarfs is substantially lower than the apparent occurrence rate for HZ terrestrials around M dwarfs, i.e. the vast majority of these "habitable" planets are not actually habitable.
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Re: LHS 1140b Transiting rocky super-Earth found in habitable zone of quiet red dwarf star

Post by Sirius_Alpha on 20th April 2017, 8:29 pm

Oh! I get what you were saying now. Yeah I agree that does seem odd.

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Re: LHS 1140b Transiting rocky super-Earth found in habitable zone of quiet red dwarf star

Post by Sirius_Alpha on 2nd July 2018, 8:50 pm

That is definitely interesting!

Also, LHS 1140b is pushed closer to the inner HZ edge by the Gaia data's distance determination for the star (as is Kepler-186f).

The Impact of Stellar Distances on Habitable Zone Planets
https://arxiv.org/abs/1807.00378

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Re: LHS 1140b Transiting rocky super-Earth found in habitable zone of quiet red dwarf star

Post by Sirius_Alpha on 8th July 2018, 8:44 pm

Minimizing the bias in exoplanet detection - application to radial velocities of LHS 1140
https://arxiv.org/abs/1807.02483

A rocky planet orbiting LHS 1140 with a period of 24.7d has been found based on the discovery of transits in its light and high precision radial velocity data (Dittmann et al. 2017). This discovery by two independent methods is an observational tour-de-force, however, we find that a conservative analysis of the data gives a different solution. A three planet system is apparent in the radial velocity data based on our diagnosis of stellar activity. We encourage further targeted photometric and radial velocity observations in order to constrain the mini-Neptune and super-Earth mass objects apparently causing the 3.8 and 90 day radial velocity signals. We use our package Agatha (this https URL) to provide a comprehensive strategy to disentangle planetary signals from stellar activity in radial velocity data.

This appears to be independent from the Charbonneau study presented upthread. This study finds evidence of 3 planets -- the already detected planet, a second planet at 92 days, and a third at 3.8 days, but they're less confident about the third planet. So since we have independent detection (and transits, most notably) of the 3.8 day planet from Charbonneau et al, this would seem to secure LHS 1140 as a 3-planet system.

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Re: LHS 1140b Transiting rocky super-Earth found in habitable zone of quiet red dwarf star

Post by tommi59 on 9th July 2018, 2:02 pm

If inner 3.8 days planet is transiting and second 24 days also so maybe third will transit too?
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Re: LHS 1140b Transiting rocky super-Earth found in habitable zone of quiet red dwarf star

Post by Sirius_Alpha on 2nd August 2018, 8:38 pm

A second planet with an Earth-like composition orbiting the nearby M dwarf LHS 1140
https://arxiv.org/abs/1808.00485

LHS 1140 is a nearby mid-M dwarf known to host a temperate rocky super-Earth (LHS 1140 b) on a 24.737-day orbit. Based on photometric observations by MEarth and Spitzer as well as Doppler spectroscopy from HARPS, we report the discovery of an additional transiting rocky companion (LHS 1140 c) with a mass of 1.81±0.39 MEarth and a radius of 1.282±0.024 REarth on a tighter, 3.77795-day orbit. We also obtain more precise estimates of the mass and radius of LHS 1140 b to be 6.98±0.98 MEarth and 1.727±0.032 REarth. The mean densities of planets b and c are 7.5±1.0 g/cm3 and 4.7±1.1 g/cm3, respectively, both consistent with the Earth's ratio of iron to magnesium silicate. The orbital eccentricities of LHS 1140 b and c are consistent with circular orbits and constrained to be below 0.06 and 0.31, respectively, with 90% confidence. Because the orbits of the two planets are co-planar and because we know from previous analyses of Kepler data that compact systems of small planets orbiting M dwarfs are commonplace, a search for more transiting planets in the LHS 1140 system could be fruitful. LHS 1140 c is one of the few known nearby terrestrial planets whose atmosphere could be studied with the upcoming James Webb Space Telescope.

At first glance it's not clear how this compares with the earlier study that showed a planet at 92 days, but they do see peaks in their periodogram in this period regime but note that they are likely due to stellar activity.

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Re: LHS 1140b Transiting rocky super-Earth found in habitable zone of quiet red dwarf star

Post by tommi59 on 3rd August 2018, 4:16 am

Well,at least we have another transiting planet around this star. Inclinations of planets b,c give big hope we can find another planets transiting in this system.Stellar activity is always problem if 92 days signal is due to planet we have big chance to find its transit.Larger radius for planet b places it in the radius gap valley despite 1.73 earth radius planet has rocky composition.Planet c composition can contain up to 6% of water, but proximity to the host star rules out large amount of water if not all water at all so ratio Fe/Mg is surely lower than earth 32/68,even lower than Trappist 1 planets
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Re: LHS 1140b Transiting rocky super-Earth found in habitable zone of quiet red dwarf star

Post by siyul on 9th August 2018, 3:08 am

Planet b with mass 6.98 ± 0.89 and radius 1.73 ± 0.03, assuming it has only <<1 wt% water, likely suggests the planet is composed of ~20~25 wt% core and ~75~80 wt% mantle. Zeng et al (2016) two-layered mass-radius relation, which accurately reproduces Earth and Venus core mass fraction, predicts the core mass fraction of planet b to be 0.23.
Since planet b and c formed in the same protoplanetary disk, it is reasonable to assume the refractory materials ratio, Fe/Mg and Mg/Si, should be widely similar. If the core to mantle ratio of planet c is also 0.25~0.33 like its neighbor, it likely contains ~10 wt% of water, equivalent to ~800 of Earth oceans. With this amount of water in mind, the planet c is unlikely to be desiccated within at least several billion years even it receives intense stellar radiation.
It will be interesting to show how the inner planet accreted more water than the outer planet, since snowline should be far from the star during accretion period, possibly by inward migration?
Rocky planets with radius greater 1.6-1.7 always exist extremely close to the host stars, because their super-Earth masse usually accrete massive hydrogen atmosphere and they were originally mini-Neptune, but later intense radiation blew the atmosphere away leaving only the rocky core. Planet b with such high mass and temperate radiation is still rocky, implying a currently less studied or unknown planet formation mechanism.

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Re: LHS 1140b Transiting rocky super-Earth found in habitable zone of quiet red dwarf star

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