TRAPPIST-1 : Transiting Earth-Sized Planets Around a Nearby Ultracool Dwarf

Taking account of spots and faculae on TRAPPIST-1 leads to increased density estimates for the planets:

Rackham, Apai & Giampapa "The Transit Light Source Problem: False Spectral Features and Incorrect Densities for M Dwarf Transiting Planets"
https://arxiv.org/abs/1711.05691

Papaloizou et al. "The TRAPPIST-1 system: Orbital evolution, tidal dissipation, formation and habitability"
https://arxiv.org/abs/1711.07932

Suggestions that there are two subsystems of planets when considering tidal behaviour. The habitable planet candidates would be d, e and f.

ESO press release :

http://www.eso.org/public/unitedkingdom/news/eso1805/?lang

TRAPPIST-1 Planets Probably Rich in Water

First glimpse of what Earth-sized exoplanets are made of

A new study has found that the seven planets orbiting the nearby ultra-cool dwarf star TRAPPIST-1 are all made mostly of rock, and some could potentially hold more water than Earth. The planets' densities, now known much more precisely than before, suggest that some of them could have up to 5 percent of their mass in the form of water — about 250 times more than Earth's oceans. The hotter planets closest to their parent star are likely to have dense steamy atmospheres and the more distant ones probably have icy surfaces. In terms of size, density and the amount of radiation it receives from its star, the fourth planet out is the most similar to Earth. It seems to be the rockiest planet of the seven, and has the potential to host liquid water

The paper :
http://www.eso.org/public/archives/releases/sciencepapers/eso1805/eso1805a.pdf

The nature of the TRAPPIST-1 exoplanets

Well that seems more realistic than the sub-Neptune compositions suggested before. Definitely looks like the rockier composition of c vs b is holding up. TRAPPIST-1e looking very interesting now.

Another update, this time from HST. None of the inner five planets have hydrogen exospheres.

http://hubblesite.org/news_release/news/2018-07

Interesting... TRAPPIST-1d as a low-density water world then?

The ESO article is now on arXiv.

The nature of the TRAPPIST-1 exoplanets
https://arxiv.org/abs/1802.01377

These spectra show the chemical makeup of the atmospheres of four Earth-size planets orbiting within or near the habitable zone of the nearby star TRAPPIST-1. The habitable zone is a region at a distance from the star where liquid water, the key to life as we know it, could exist on the planets’ surfaces. Credit: NASA/ESA/Z. Levy (STScI

The paper is now on arXiv.

The Near-Infrared Transmission Spectra of TRAPPIST-1 Planets b, c, d, e, f, and g and Stellar Contamination in Multi-Epoch Transit Spectra
https://arxiv.org/abs/1802.02086

Edit: Another paper

Atmospheric reconnaissance of the habitable-zone Earth-sized planets orbiting TRAPPIST-1
https://arxiv.org/abs/1802.02250

Possible Bright Starspots on TRAPPIST-1
https://arxiv.org/abs/1803.04543

Quote :

The M8V star TRAPPIST-1 hosts seven roughly Earth-sized planets and is a promising target for exoplanet characterization. Kepler/K2 Campaign 12 observations of TRAPPIST-1 in the optical show an apparent rotational modulation with a 3.3 day period, though that rotational signal is not readily detected in the Spitzer light curve at 4.5 μm. If the rotational modulation is due to starspots, persistent dark spots can be excluded from the lack of photometric variability in the Spitzer light curve. We construct a photometric model for rotational modulation due to photospheric bright spots on TRAPPIST-1 which is consistent with both the Kepler and Spitzer light curves. The maximum-likelihood model with three spots has typical spot sizes of Rspot/R⋆≈0.004 at temperature Tspot≳5300±200 K. We also find that large flares are observed more often when the brightest spot is facing the observer, suggesting a correlation between the position of the bright spots and flare events. In addition, these flares may occur preferentially when the spots are increasing in brightness, which suggests that the 3.3 d periodicity may not be a rotational signal, but rather a characteristic timescale of active regions.

There was a paper that appeared on Nature on 19 Mar 2018 that suggested that the planets at TRAPPIST-1 were far less dense than originally measured, with densities (and consequently compositions) that implied they were volatile-rich and migrated inward from beyond the ice line.

Inward migration of the TRAPPIST-1 planets as inferred from their water-rich compositions
https://www.nature.com/articles/s41550-018-0411-6

Note that this is in significant conflict with the reuslts upthread that showed that the planets have just a few percent at most water by mass. There's a thread on twitter about this:
https://twitter.com/exohugh/status/979075844709797889

Apparently due to the time it took for Nature's peer review process, despite the low-density result being submitted much earlier than the Grimm, et al. result, it got presented later with its own press release in Astronomy, which came out today:
http://www.astronomy.com/news/2018/03/trappist-1-system-may-have-too-much-water-to-support-life

I'm not really qualified to have an opinion on which is better analysis, but it's worth noting that the order of these studies is backwards. The higher-density result of Grimm et al is the more recent work.

https://www.drewexmachina.com/2018/04/18/alien-skies-the-view-from-trappist-1e/

Alien Skies : The View from TRAPPIST-1e

http://cosmicdiary.org/fmarchis/2018/04/20/an-update-on-the-potential-habitability-of-trappist-1-no-aliens-yet-but-weve-learned-a-lot/

An Update on the Potential Habitability of TRAPPIST-1. (Franck Marchis)

« …After 2020, if everything goes well with JWST and if the space telescope provides the superb data that we expect, we might have a crude map of the TRAPPIST-1 planets, similar to the rough image of Pluto made with Hubble Space Telescope and later validated by the New Horizons Spacecraft… »
??

There was a paper from late last year that suggested planet-planet occultations could be used to construct maps but this would require a much more powerful telescope than JWST

Planet-Planet Occultations in TRAPPIST-1 and Other Exoplanet Systems
https://arxiv.org/abs/1711.05739

TRAPPIST-1e Has a Large Iron Core
https://arxiv.org/abs/1804.10618

Quote :

The TRAPPIST-1 system provides an exquisite laboratory for understanding exoplanetary atmospheres and interiors. Their mutual gravitational interactions leads to transit timing variations, from which Grimm et al. (2018) recently measured the planetary masses with precisions ranging from 5% to 12%. Using these masses and the <5% radius measurements on each planet, we apply the method described in Suissa et al. (2018) to infer the minimum and maximum CRF (core radius fraction) of each planet. Further, we modify the maximum limit to account for the fact that a light volatile envelope is excluded for planets b through f. Only planet e is found to have a significant probability of having a non-zero minimum CRF, with a 0.7% false-alarm probability it has no core. Our method further allows us to measure the CRF of planet e to be greater than (49 +/- 7)% but less than (72 +/- 2)%, which is compatible with that of the Earth. TRAPPIST-1e therefore possess a large iron core similar to the Earth, in addition to being Earth-sized and located in the temperature zone.

Updated Compositional Models of the TRAPPIST-1 Planets
https://arxiv.org/abs/1806.10084

Quote :

After publication of our initial mass-radius-composition models for the TRAPPIST-1 system in Unterborn et al. (2018), the planet masses were updated in Grimm et al. (2018). We had originally adopted the data set of Wang et al., 2017 who reported different densities than the updated values. The differences in observed density change the inferred volatile content of the planets. Grimm et al. (2018) report TRAPPIST-1 b, d, f, g, and h as being consistent with <5 wt% water and TRAPPIST-1 c and e has having largely rocky interiors. Here, we present updated results recalculating water fractions and potential alternative compositions using the Grimm et al., 2018 masses. Overall, we can only reproduce the results of Grimm et al., 2018 of planets b, d and g having small water contents if the cores of these planets are small (<23 wt%). We show that, if the cores for these planets are roughly Earth-sized (33 wt%), significant water fractions up to 40 wt% are possible. We show planets c, e, f, and h can have volatile envelopes between 0-35 wt% that are also consistent with being totally oxidized and lacking an Fe-core entirely. We note here that a pure MgSiO3 planet (Fe/Mg = 0) is not the true lowest density end-member mass-radius curve for determining the probability of a planet containing volatiles. All planets that are rocky likely contain some Fe, either within the core or oxidized in the mantle. We argue the true low density end-member for oxidizing systems is instead a planet with the lowest reasonable Fe/Mg and completely core-less. Using this logic, we assert that planets b, d and g likely must have significant volatile layers because the end-member planet models produce masses too high even when uncertainties in both mass and radius are taken into account.

Since the upcoming SPECULOOS automated late-M dwarf survey is the successor to TRAPPIST, it looks like they're going to give TRAPPIST-1 an additional designation of SPECULOOS-1.
https://www.exoplanetscience2.org/programme/speculoos-transit-survey-hunting-red-worlds

SPECULOOS or TRAPPIST ??

https://twitter.com/LucaPlanets/status/1014430046394740736

Quote :

Demory: an eight Mars-sized planet at the outskirts of the TRAPPIST-1 system? Answer’s maybe... there’s something in the data but must be checked by followup observations #Exoplanets2

The 0.6-4.55μm broadband transmission spectra of TRAPPIST-1 planets
https://arxiv.org/abs/1807.01402

Quote :

The TRAPPIST-1 planetary system represents an exceptional opportunity for the atmospheric characterization of temperate terrestrial exoplanets with the upcoming James Webb Space Telescope (JWST). Assessing the potential impact of stellar contamination on the planets' transit transmission spectra is an essential precursor step to this characterization. Planetary transits themselves can be used to scan the stellar photosphere and to constrain its heterogeneity through transit depth variations in time and wavelength. In this context, we present our analysis of 169 transits observed in the optical from space with K2 and from the ground with the SPECULOOS and Liverpool telescopes. Combining our measured transit depths with literature results gathered in the mid/near-IR with Spitzer/IRAC and HST/WFC3, we construct the broadband transmission spectra of the TRAPPIST-1 planets over the 0.6-4.5 μm spectral range. While planets b, d, and f spectra show some structures at the 200-300ppm level, the four others are globally flat. Even if we cannot discard their instrumental origins, two scenarios seem to be favored by the data: a stellar photosphere dominated by a few high-latitude giant (cold) spots, or, alternatively, by a few small and hot (3500-4000K) faculae. In both cases, the stellar contamination of the transit transmission spectra is expected to be less dramatic than predicted in recent papers. Nevertheless, based on our results, stellar contamination can still be of comparable or greater order than planetary atmospheric signals at certain wavelengths. Understanding and correcting the effects of stellar heterogeneity therefore appears essential to prepare the exploration of TRAPPIST-1's with JWST.

[url=C:\Users\Inspiron\Downloads\nowe masy.jpg_large]C:\Users\Inspiron\Downloads\nowe masy.jpg_large[/url]
New masses seems even more interesting

tommi59 wrote:

[url=C:\Users\Inspiron\Downloads\nowe masy.jpg_large]C:\Users\Inspiron\Downloads\nowe masy.jpg_large[/url]
New masses seems even more interesting