SPECULOOS exoplanet search and its prototype on TRAPPIST

SPECULOOS exoplanet search and its prototype on TRAPPIST

Authors:

Burdanov et al

Abstract:

One of the most significant goals of modern science is establishing whether life exists around other suns. The most direct path towards its achievement is the detection and atmospheric characterization of terrestrial exoplanets with potentially habitable surface conditions. The nearest ultracool dwarfs (UCDs), i.e. very-low-mass stars and brown dwarfs with effective temperatures lower than 2700 K, represent a unique opportunity to reach this goal within the next decade. The potential of the transit method for detecting potentially habitable Earth-sized planets around these objects is drastically increased compared to Earth-Sun analogs. Furthermore, only a terrestrial planet transiting a nearby UCD would be amenable for a thorough atmospheric characterization, including the search for possible biosignatures, with near-future facilities such as the James Webb Space Telescope. In this chapter, we first describe the physical properties of UCDs as well as the unique potential they offer for the detection of potentially habitable Earth-sized planets suitable for atmospheric characterization. Then, we present the SPECULOOS ground-based transit survey, that will search for Earth-sized planets transiting the nearest UCDs, as well as its prototype survey on the TRAPPIST telescopes. We conclude by discussing the prospects offered by the recent detection by this prototype survey of a system of seven temperate Earth-sized planets transiting a nearby UCD, TRAPPIST-1.

Do the Trappist-1 Worlds Have Water?

An international team of astronomers used the NASA/ESA Hubble Space Telescope to estimate whether there might be water on the seven earth-sized planets orbiting the nearby dwarf star TRAPPIST-1. The results suggest that the outer planets of the system might still harbour substantial amounts of water. This includes the three planets within the habitable zone of the star, lending further weight to the possibility that they may indeed be habitable.

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Enhanced interplanetary panspermia in the TRAPPIST-1 system

Enhanced interplanetary panspermia in the TRAPPIST-1 system

Authors:

Lingam et al

Abstract:
We present a simple model for estimating the probability of interplanetary panspermia in the recently discovered system of seven planets orbiting the ultracool dwarf star TRAPPIST-1 and find that panspermia is potentially orders of magnitude more likely to occur in the TRAPPIST-1 system compared with the Earth-to-Mars case. As a consequence, we argue that the probability of abiogenesis is enhanced on the TRAPPIST-1 planets compared with the solar system. By adopting models from theoretical ecology, we show that the number of species transferred and the number of life-bearing planets are also likely to be higher because of the increased rates of immigration. We propose observational metrics for evaluating whether life was initiated by panspermia on multiple planets in the TRAPPIST-1 system. These results are also applicable to habitable exoplanets and exomoons in other planetary systems.

The Potential Climates of the Trappist-1 System

Comparative Climates of TRAPPIST-1 planetary system: results from a simple climate-vegetation model

Authors:

Alberti et al

Abstract: 

The recent discovery of the planetary system hosted by the ultracool dwarf star TRAPPIST-1 could open new perspectives into the investigation of planetary climates of Earth-sized exoplanets, their atmospheres and their possible habitability. In this paper, we use a simple climate-vegetation energy-balance model to study the climate of the seven TRAPPIST-1 planets and the climate dependence on the global albedo, on the fraction of vegetation that could cover their surfaces and on the different greenhouse conditions. The model allows us to investigate whether liquid water could be maintained on the planetary surfaces (i.e., by defining a "surface water zone") in different planetary conditions, with or without the presence of greenhouse effect.

It is shown that planet TRAPPIST-1d seems to be the most stable from an Earth-like perspective, since it resides in the surface water zone for a wide range of reasonable values of the model parameters. Moreover, according to the model outer planets (f, g and h) cannot host liquid water on their surfaces, even for Earth-like conditions, entering a snowball state. Although very simple, the model allows to extract the main features of the TRAPPIST-1 planetary climates.

The Trappist-1 System may NOT be Habitable

The Threatening Environment of the TRAPPIST-1 Planets

Authors:

Garraffo

Abstract:
Recently, four additional Earth-mass planets were discovered orbiting the nearby ultracool M8 dwarf TRAPPIST-1, making a remarkable total of seven planets with equilibrium temperatures compatible with the presence of liquid water on their surface. Temperate terrestrial planets around an M-dwarf orbit close to their parent star, rendering their atmospheres vulnerable to erosion by the stellar wind and energetic electromagnetic and particle radiation. Here, we use state-of-the-art 3D magnetohydrodynamic models to simulate the wind around TRAPPIST-1 and study the conditions at each planetary orbit. All planets experience a stellar wind pressure between 103 and 105 times the solar wind pressure on Earth. All orbits pass through wind pressure changes of an order of magnitude and most planets spend a large fraction of their orbital period in the sub-Alfv\'enic regime. For plausible planetary magnetic field strengths, all magnetospheres are greatly compressed and undergo much more dynamic change than that of the Earth. The planetary magnetic fields connect with the stellar radial field over much of the planetary surface, allowing direct flow of stellar wind particles onto the planetary atmosphere. These conditions could result in strong atmospheric stripping and evaporation and should be taken into account for any realistic assessment of the evolution and habitability of the TRAPPIST-1 planets.

Constraining the Compositions of the TRAPPIST-1 Planets to Trace Snow Lines and Migration in M Dwarf Disks

Constraining the Compositions of the TRAPPIST-1 Planets to Trace Snow Lines and Migration in M Dwarf Disks

Authors:

Unterborn et al

Abstract:

The TRAPPIST-1 system, containing 7 transiting planets with constrained masses and radii, offers a singular opportunity to understand planet formation in another system. Not only can individual planets' bulk compositions be inferred, variations in composition (with respect to distance from the star) probe the composition of the TRAPPIST-1 disk and test models of planet formation. Other studies have shown that many of the TRAPPIST-1 planets are lower in density than rock and must either possess thick atmospheres or substantial liquid water/ice. The small masses of the planets argue against atmospheres. We use our ExoPlex mass-radius software package to constrain the fraction of each planet mass that is water. While we concur that planets f and g contain substantial (>50wt%) water/ice, we find b must be ≥6−8wt% water, but c must be ≤6−8wt% water. Since volatile fraction should increase with distance, the simplest interpretation is that both b and c each contain ≈7wt% water. Planets formed outside the snow line of TRAPPIST-1's disk are expected to contain ∼50wt% water ice like f and g, but the much lower ice abundances of b and c imply they formed inside the snow line. The TRAPPIST-1 system is marked by multiple mean motion resonances; for this and other reasons, substantial inward migration of the planets to their present orbits is inferred. We calculate the location of the snow line in the TRAPPIST-1 disk as a function of time. Depending on how rapidly the planets formed, the TRAPPIST-1 planets are at 1/2 to 1/8 of their starting distances from the star. While we infer that b and c formed inside the snow line, they contain much more water than planets formed inside the snow line in the Solar System (Earth is less than 0.1 wt% water), implying that the volatile gradient in TRAPPIST-1 was more gradual than in the Solar System.

Frequent Flaring in the TRAPPIST-1 System: Unsuited for Life?

Frequent Flaring in the TRAPPIST-1 System—Unsuited for Life?

Authors:

Vida et al

Abstract:
We analyze the K2 light curve of the TRAPPIST-1 system. The Fourier analysis of the data suggests P rot = 3.295 ± 0.003 days. The light curve shows several flares, of which we analyzed 42 events with integrated flare energies of 1.26 × 1030–1.24 × 1033 erg. Approximately 12% of the flares were complex, multi-peaked eruptions. The flaring and the possible rotational modulation shows no obvious correlation. The flaring activity of TRAPPIST-1 probably continuously alters the atmospheres of the orbiting exoplanets, which makes these less favorable for hosting life.

The Inner Most TRAPPIST-1 Exoplanets may Have Lost Their Atmospheres

Atmospheric escape from the TRAPPIST-1 planets and implications for habitability 

Authors: 

Dong et al 

Abstract: 

The presence of an atmosphere over sufficiently long timescales is widely regarded as one of the most prominent criteria associated with planetary surface habitability. We address the crucial question as to whether the seven Earth-sized planets transiting the recently discovered ultracool dwarf star TRAPPIST-1 are capable of retaining their atmospheres. To this effect, we carry out numerical simulations to characterize the stellar wind of TRAPPIST-1 and the atmospheric ion escape rates for all the seven planets. We also estimate the escape rates analytically and demonstrate that they are in good agreement with the numerical results. We conclude that the outermost planets of the TRAPPIST-1 system are capable of retaining their atmospheres over billion-year timescales, and are thus likely to be habitable. The consequences arising from our results are also explored in the context of abiogenesis, biodiversity, and searches for future exoplanets. In light of the many unknowns involved, these conclusions must be interpreted with due caution.

Trappist-1h MIGHT Have Once Been Habitable

A University of Washington-led international team of astronomers has used data gathered by the Kepler Space Telescope to observe and confirm details of the outermost of seven exoplanets or-biting the star TRAPPIST-1.

They confirmed that the planet, TRAPPIST-1h, orbits its star every 18.77 days, is linked in its orbital path to its siblings and is frigidly cold. Far from its host star, the planet is likely uninhabit-able -- but it may not always have been so.

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Trappist-1e Among Initial Observational Targets for the James Webb Space Telescope

Mission officials for NASA's James Webb Space Telescope announced some of the science targets the telescope will observe following its launch and commissioning. These specific observations are part of a program of Guaranteed Time Observations (GTO), which provides dedicated time to the scientists that helped design and build the telescope's four instruments.

"From the very first galaxies after the Big Bang, to searching for chemical fingerprints of life on Enceladus, Europa, and exoplanets like TRAPPIST-1e, Webb will be looking at some incredible things in our universe," said Eric Smith, James Webb Space Telescope Director at NASA Headquarters in Washington. "With over 2100 initial observations planned, there is no limit to what we might discover with this incredible telescope."

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U Oklahoma IDs Potential Make up of Trappist-1 Exoplanets

A University of Oklahoma post-doctoral astrophysics researcher, Billy Quarles, has identified the possible compositions of the seven planets in the TRAPPIST-1 system. Using thousands of numerical simulations to identify the planets stable for millions of years, Quarles concluded that six of the seven planets are consistent with an Earth-like composition. The exception is TRAPPIST-1f, which has a mass of 25 percent water, suggesting that TRAPPIST-1e may be the best candidate for future habitability studies.

"The goal of exoplanetary astronomy is to find planets that are similar to Earth in composition and potentially habitable," said Quarles. "For thousands of years, astronomers have sought other worlds capable of sustaining life."

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Prospects for detecting the Rossiter-McLaughlin effect of Earth-like planets: the test case of TRAPPIST-1b and c

Prospects for detecting the Rossiter-McLaughlin effect of Earth-like planets: the test case of TRAPPIST-1b and c

Authors:

Cloutier et al

Abstract:

The Rossiter-McLaughlin effect is the principal method of determining the sky-projected spin--orbit angle (β) of transiting planets. Taking the example of the recently discovered TRAPPIST-1 system, we explore how ultracool dwarfs facilitate the measurement of the spin--orbit angle for Earth-sized planets by creating an effect that can be an order of magnitude more ample than the Doppler reflex motion caused by the planet if the star is undergoing rapid rotation. In TRAPPIST-1's case we expect the semi-amplitudes of the Rossiter-McLaughlin effect to be 40−50 m/s for the known transiting planets. Accounting for stellar jitter expected for ultracool dwarfs, instrumental noise, and assuming radial velocity precisions both demonstrated and anticipated for upcoming near-infrared spectrographs, we quantify the observational effort required to measure the planets' masses and spin--orbit angles. We conclude that if the planetary system is well-aligned then β can be measured to a precision of ≲10∘ if the spectrograph is stable at the level of 2 m/s. We also investigate the measure of Δβ, the mutual inclination, when multiple transiting planets are present in the system. Lastly, we note that the rapid rotation rate of many late M-dwarfs will amplify the Rossiter-McLaughlin signal to the point where variations in the chromatic Rossiter-McLaughlin effect from atmospheric absorbers should be detectable.

Hunting for TRAPPIST-1-like Systems With the K2 Mission

Probing TRAPPIST-1-like systems with K2

Authors:

Demory et al

Abstract:

The search for small planets orbiting late M dwarfs holds the promise of detecting Earth-size planets for which their atmospheres could be characterised within the next decade. The recent discovery of TRAPPIST-1 entertains hope that these systems are common around hosts located at the bottom of the main sequence. In this Letter, we investigate the ability of the repurposed Kepler mission (K2) to probe planetary systems similar to TRAPPIST-1. We perform a consistent data analysis of 189 spectroscopically confirmed M5.5 to M9 late M dwarfs from campaigns 1-6 to search for planet candidates and inject transit signals with properties matching TRAPPIST-1b and c. We find no transiting planet candidates across our K2 sample. Our injection tests show that K2 is able to recover both TRAPPIST-1 planets for 10% of the sample only, mainly because of the inefficient throughput at red wavelengths resulting in Poisson-limited performance for these targets. Increasing injected planetary radii to match GJ1214b's size yields a recovery rate of 70%. The strength of K2 is its ability to probe a large number of cool hosts across the different campaigns, out of which the recovery rate of 10% may turn into bona-fide detections of TRAPPIST-1 like systems within the next two years.

TRAPPIST-1b & TRAPPIST-1c may Have Venus-like Atmospheres

A combined transmission spectrum of the Earth-sized exoplanets TRAPPIST-1 b and c

Authors:

de Wit et al

Abstract:

Three Earth-sized exoplanets were recently discovered close to the habitable zone of the nearby ultracool dwarf star TRAPPIST-1. The nature of these planets has yet to be determined, since their masses remain unmeasured and no observational constraint is available for the planetary population surrounding ultracool dwarfs, of which the TRAPPIST-1 planets are the first transiting example. Theoretical predictions span the entire atmospheric range from depleted to extended hydrogen-dominated atmospheres. Here, we report a space-based measurement of the combined transmission spectrum of the two inner planets made possible by a favorable alignment resulting in their simultaneous transits on 04 May 2016. The lack of features in the combined spectrum rules out cloud-free hydrogen-dominated atmospheres for each planet at 10-σ levels; TRAPPIST-1 b and c are hence unlikely to harbor an extended gas envelope as they lie in a region of parameter space where high-altitude cloud/haze formation is not expected to be significant for hydrogen-dominated atmospheres. Many denser atmospheres remain consistent with the featureless transmission spectrum---from a cloud-free water vapour atmosphere to a Venus-like atmosphere.

TRAPPIST-1 System Worlds Confirmed to be Rocky, Terrestrial

On May 2, scientists from MIT, the University of Liège, and elsewhere announced they had discovered a planetary system, a mere 40 light years from Earth, that hosts three potentially habitable, Earth-sized worlds. Judging from the size and temperature of the planets, the researchers determined that regions of each planet may be suitable for life.

Now, in a paper published today in Nature, that same group reports that the two innermost planets in the system are primarily rocky, unlike gas giants such as Jupiter. The findings further strengthen the case that these planets may indeed be habitable. The researchers also determined that the atmospheres of both planets are likely not large and diffuse, like that of the Jupiter, but instead compact, similar to the atmospheres of Earth, Venus, and Mars.

The scientists, led by first author Julien de Wit, a postdoc in MIT's Department of Earth, Atmospheric and Planetary Sciences, came to their conclusion after making a preliminary screening of the planets' atmospheres, just days after announcing the discovery of the planetary system.

On May 4, the team commandeered NASA's Hubble Space Telescope and pointed it at the system's star, TRAPPIST-1, to catch a rare event: a double transit, the moment when two planets almost simultaneously pass in front of their star. The researchers realized the planets would transit just two weeks before the event, thanks to refined estimates of the planets' orbital configuration, made by NASA's Spitzer Space Telescope, which had already started to observe the TRAPPIST-1 system.

"We thought, maybe we could see if people at Hubble would give us time to do this observation, so we wrote the proposal in less than 24 hours, sent it out, and it was reviewed immediately," de Wit recalls. "Now for the first time we have spectroscopic observations of a double transit, which allows us to get insight on the atmosphere of both planets at the same time."

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Can the JWST Determine if the Trappist-1 System Exoplanets are Habitable?

Habitable worlds with JWST: transit spectroscopy of the TRAPPIST-1 system?

Authors:

Barstow et al

Abstract:

The recent discovery of three Earth-sized, potentially habitable planets around a nearby cool star, TRAPPIST-1, has provided three key targets for the upcoming James Webb Space Telescope (JWST). Depending on their atmospheric characteristics and precise orbit configurations, it is possible that any of the three planets may be in the liquid water habitable zone, meaning that they may be capable of supporting life. We find that present-day Earth levels of ozone, if present, would be detectable if JWST observes 60 transits for innermost planet 1b and 30 transits for 1c and 1d.

Can The Trappist-1 Worlds Retain Water?

Water loss from Earth-sized planets in the habitable zones of ultracool dwarfs: Implications for the planets of TRAPPIST-1

Authors:

Bolmont et al

Abstract:

Ultracool dwarfs (UCD) encompass the population of extremely low mass stars (later than M6-type) and brown dwarfs. Because UCDs cool monotonically, their habitable zone (HZ) sweeps inward in time. Assuming they possess water, planets found in the HZ of UCDs have experienced a runaway greenhouse phase too hot for liquid water prior to entering the HZ. It has been proposed that such planets are desiccated by this hot early phase and enter the HZ as dry, inhospitable worlds. Here we model the water loss during this pre-HZ hot phase taking into account recent upper limits on the XUV emission of UCDs and using 1D radiation-hydrodynamic simulations. We address the whole range of UCDs but also focus on the planets b, c and d recently found around the 0.08 M⊙ dwarf TRAPPIST-1.

Despite assumptions maximizing the FUV-photolysis of water and the XUV-driven escape of hydrogen, we find that planets can retain significant amounts of water in the HZ of UCDs, with a sweet spot in the 0.04-0.06 M⊙ range. With our assumptions, TRAPPIST-1b and c can lose as much as 4 Earth Ocean but planet d - which may be inside the HZ depending on its actual period - may have kept enough water to remain habitable depending on its initial content. TRAPPIST-1 planets are key targets for atmospheric characterization and could provide strong constraints on the water erosion around UCDs.

TRAPPIST-1 System has Three Terrestrial Planets Near the Habitable Zone 40 Light Years Away

Temperate Earth-sized planets transiting a nearby ultracool dwarf star

Authors:

Gillon et al

Abstract:

Star-like objects with effective temperatures of less than 2,700 kelvin are referred to as ‘ultracool dwarfs’. This heterogeneous group includes stars of extremely low mass as well as brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion), and represents about 15 per cent of the population of astronomical objects near the Sun. Core-accretion theory predicts that, given the small masses of these ultracool dwarfs, and the small sizes of their protoplanetary disks there should be a large but hitherto undetected population of terrestrial planets orbiting them—ranging from metal-rich Mercury-sized planets to more hospitable volatile-rich Earth-sized planets. Here we report observations of three short-period Earth-sized planets transiting an ultracool dwarf star only 12 parsecs away. The inner two planets receive four times and two times the irradiation of Earth, respectively, placing them close to the inner edge of the habitable zone of the star. Our data suggest that 11 orbits remain possible for the third planet, the most likely resulting in irradiation significantly less than that received by Earth. The infrared brightness of the host star, combined with its Jupiter-like size, offers the possibility of thoroughly characterizing the components of this nearby planetary system.