GJ 1132 b earth-sized rocky planet at 39 l.y

http://news.mit.edu/2015/new-earth-sized-exoplanet-1111

The new planet, named GJ 1132b, is Earth-sized and rocky, orbiting a small star located a mere 39 light-years from Earth, making it the closest Earth-sized exoplanet yet discovered. Astrophysicists from MIT and elsewhere have published these findings today in the journal Nature.
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Berta-Thompson and his colleagues discovered the planet using the MEarth-South Observatory, a Harvard University-led array of eight 40-centimeter-wide robotic telescopes located in the mountains of Chile.
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Based on the amount of starlight the planet blocks, and the radius of the star, scientists calculated that planet GJ 1132b is about 1.2 times the size of Earth. From measuring the wobble of its host star, they estimate the planet’s mass to be about 1.6 times that of Earth. Given its size and mass, they could determine its density — and they believe it to be rocky, like Earth

Link Nature :
http://www.nature.com/nature/journal/v527/n7577/full/nature15762.html

The paper :
https://www.cfa.harvard.edu/MEarth/gj1132b.pdf

Now on arXiv
http://arxiv.org/abs/1511.03550

Twin of kepler 138 c both not very hot still retaining atmosphere without H2 ,He

At least this one is listed at EPE

http://exoplanet.eu/catalog/gj_1132_b/

I wonder how EPE's working lately. A lot of confirmed (transiting and non transiting, Kepler and "non-Kepler") planets haven't been listed.

This planet is already being called a Venus twin. Would this planet even have an substantial atmosphere? A 1.6 day orbit is close enough that I worry the atmosphere was long ago blown away by flares. Perhaps is it not too early to call it a super Mercury instead?

The paper addresses that very clearly. In short, if the atmosphere survived the star's youth, then it's fine. The planet's equilibrium temperature is no more than ~500K.

It's still outside of the "venus zone".

Looks like the MEarth team were right to say that their precision was limiting their ability to detect planets around mid-M-dwarfs. This is a very impressive detection for a ground-based telescope system, and it highlights the value of MEarth's dynamic observation strategy. Hopefully we'll be seeing a few more discoveries to join the once-lonely GJ 1214 b.

I must say that the mass detection is also pretty impressive for HARPS, as the star is pretty darn faint for the spectrograph (V = 13.5 is fainter than most other transiting planets detected from the ground!). It'll need improving to get a better idea of the planetary composition, but it's a strong start.

Though much less is known about the statistics of low-mass planetary systems for spectral types later than ~M2 (due to the lack of stars observable by Kepler in that region), this seems to be a fairly regular planet. The deep transits do definitely make it a notable target for near-future atmosphere characterisation, and it may become important in that regard, not entirely unlike GJ 1214 b.

Atmospheric detection!!!

Detection of the atmosphere of the 1.6 Earth mass exoplanet GJ 1132b
https://arxiv.org/abs/1612.02425

Detecting the atmospheres of low-mass low-temperature exoplanets is a high-priority goal on the path to ultimately detect biosignatures in the atmospheres of habitable exoplanets. High-precision HST observations of several super-Earths with equilibrium temperatures below 1000 K have to date all resulted in featureless transmission spectra, which have been suggested to be due to high-altitude clouds. We report the detection of an atmospheric feature in the atmosphere of a 1.6 Mearth transiting exoplanet, GJ 1132b, with an equilibrium temperature of ~600 K and orbiting a nearby M dwarf. We present observations of nine transits of the planet obtained simultaneously in the griz and JHK passbands. We find an average radius of 1.44 +/- 0.21 Rearth for the planet, averaged over all the passbands, which can be decomposed into a "surface radius" at ~1.35 Rearth, and higher contributions in the z and K bands. The z-band radius is 4 sigma higher than the continuum, suggesting a strong detection of an atmosphere. We deploy a suite of tests to verify the reliability of the transmission spectrum, which are greatly helped by the existence of repeat observations. The large z-band transit depth indicates strong opacity from H2O and/or CH4 or an hitherto unconsidered opacity. A surface radius of 1.35 +/- 0.21 Rearth allows for a wide range of interior compositions ranging from a nearly Earth-like rocky interior, with ~70% silicate and ~30% Fe, to a substantially H2O-rich water world. New observations with HST and existing ground-based facilities would be able to confirm the present detection and further constrain the atmospheric composition of the planet.

Interesting, so it looks like the atmospheric prediction that Schaefer et al. (2016) regarded as "most likely" (tenuous O₂-dominated atmosphere with little water content) isn't actually the case.

Host star density seems somewhat smaller due to 20% increasing stellar radius.Now it looks like planet has substantial atmosphere, can not figure out how being so close to host star planet has density of only 3.0g/cm3 and did not lose volatiles

This appears to have been missed:

A Search for Additional Bodies in the GJ 1132 Planetary System from 21 Ground-based Transits and a 100 Hour Spitzer Campaign

Quote :

We present the results of a search for additional bodies in the GJ 1132 system through two methods: photometric transits and transit timing variations of the known planet. We collected 21 transit observations of GJ 1132b with the MEarth-South array since 2015. We obtained 100 near-continuous hours of observations with the Spitzer Space Telescope, including two transits of GJ 1132b and spanning 60% of the orbital phase of the maximum period at which bodies coplanar with GJ 1132b would pass in front of the star. We exclude transits of additional Mars-sized bodies, such as a second planet or a moon, with a confidence of 99.7%. When we combine the mass estimate of the star (obtained from its parallax and apparent Ks band magnitude) with the stellar density inferred from our high-cadence Spitzer light curve (assuming zero eccentricity), we measure the stellar radius of GJ 1132 to be 0.2105^+0.0102_−0.0085 R_⊙, and we refine the radius measurement of GJ 1132b to 1.130±0.056R_⊕. Combined with HARPS RV measurements, we determine the density of GJ 1132b to be 6.2±2.0 g cm⁻³, with the mass determination dominating this uncertainty. We refine the ephemeris of the system and find no evidence for transit timing variations, which would be expected if there was a second planet near an orbital resonance with GJ 1132b.

The radii calculated by Southworth et al. are larger than those found in this paper and in the discovery paper, and it is worth considering why.

In the discovery paper, the stellar mass is estimated using the Delfosse et al. (2000) K-band luminosity - mass relationship, with its ~10% error. Then, to calculate the radius:

Quote :

From this mass, we use an empirical M_* - ρ_* relation¹⁹ calibrated to eclipsing binary systems to estimate a density of ρ_* = 29.6 ± 6.0 g cm^-3, corresponding to R_* = 0.207 ± 0.016 R_⊙ for GJ 1132. We adopt those values, noting that they agree with two other mass-radius relations: the radius predicted by long-baseline optical interferometry of single stars⁴⁰ is R_* = 0.211 ± 0.014 R_⊙, and that by the Dartmouth evolutionary models⁴¹ is R_* = 0.200 ± 0.016 R_⊙ (for [Fe/H] = -0.1, assuming a uniform prior on age between 1 Gyr and 10 Gyr).

Southworth et al. adopt the same mass, but to calculate the radius they use the stellar density implied by the transit parameters (implicitly assuming zero eccentricity). This results in ρ_* = 11.5^+5.2_-3.2 ρ_* = 16.2^+7.3_-4.5 g cm^-3 (2.2σ lower than the discovery paper) and R_* = 0.250 ± 0.030 R_⊙ (2.7σ higher than the discovery paper), and increases the planetary radius accordingly.

This paper (Dittmann et al.) uses the same methodology as Southworth et al. on their Spitzer lightcurve and find ρ_* = 19.4^+2.6_-2.5 ρ_* = 27.4^+3.7_-3.5 g cm^-3 and (as stated in the abstract) R_* = 0.2105^+0.0102_−0.0085 R_⊙, both being consistent with (and more precise than) the discovery paper values.

With three independent methods supporting a higher density (lower radius) in the discovery paper, and the same method finding a higher density in Dittmann et al., it seems probable that Southworth et al. are in error. The most probable root cause is that Southworth et al. overestimate the planetary impact parameter b (= underestimate the orbital inclination), which would directly result in an underestimated stellar density. This, in turn, is probably because Southworth et al. use ground-based lightcurves that do not adequately resolve transit ingress/egress (which is necessary for calculating b). This would explain why Dittmann et al, with the same methodology but a higher cadence, more precise lightcurve find values consistent with the discovery paper. This bears out when comparing the values, as Southworth et al. give i = 86.6 ± 0.8° while Dittmann et al. give i = 88.68^+0.40_-0.33°. This suggests that determination of stellar density via lightcurve modelling should perhaps be treated with caution when applied to poorly resolved transits.

Thus the Dittmann et al. stellar and planetary parameters are probably the most accurate currently published. With R_p = 1.130 ± 0.056 R_⊕ and ρ_p = 6.2 ± 2.0 g cm^-3, the planet does not appear to have a large atmosphere, contra Southworth et al.

It should be noted that this does not challenge the main results of Southworth et al. (differing transit depth per wavelength = atmospheric detection), and indeed their defense of their results from confounding issues suggests it is correct. However, the change in planetary radius means that the implications of the detection for GJ 1132 b's atmosphere may need to be revised w.r.t Southworth et al.'s interpretation.

Sirius_Alpha wrote:

Atmospheric detection!!!

Detection of the atmosphere of the 1.6 Earth mass exoplanet GJ 1132b
https://arxiv.org/abs/1612.02425

https://www.scientificamerican.com/article/signs-of-alien-air-herald-a-new-era-of-exoplanet-discoveries/

Signs of Alien Air Herald a New Era of Exoplanet Discoveries
New efforts hint that nearby world GJ 1132 b may have an Earth-like atmosphere with water and methane

A second planet has been detected. A third signal exists but it's not clear what the origin is.

Radial velocity follow-up of GJ1132 with HARPS. A precise mass for planet 'b' and the discovery of a second planet
https://arxiv.org/abs/1806.03870

Detection of an Atmosphere on a Rocky Exoplanet
https://arxiv.org/abs/2103.05657

Quote :

We report the detection of an atmosphere on a rocky exoplanet, GJ 1132 b, which is similar to Earth in terms of size and density. The atmospheric transmission spectrum was detected using Hubble WFC3 measurements and shows spectral signatures of aerosol scattering, HCN, and CH4 in a low mean molecular weight atmosphere. We model the atmospheric loss process and conclude that GJ 1132 b likely lost the original H/He envelope, suggesting that the atmosphere that we detect has been reestablished. We explore the possibility of H2 mantle degassing, previously identified as a possibility for this planet by theoretical studies, and find that outgassing from ultrareduced magma could produce the observed atmosphere. In this way we use the observed exoplanet transmission spectrum to gain insights into magma composition for a terrestrial planet. The detection of an atmosphere on this rocky planet raises the possibility that the numerous powerfully irradiated Super-Earth planets, believed to be the evaporated cores of Sub-Neptunes, may, under favorable circumstances, host detectable atmospheres.

Or not?

ARES V: No Evidence For Molecular Absorption in the HST WFC3 Spectrum of GJ 1132 b
https://arxiv.org/abs/2104.01873