GJ 1132b Predicted to Have a Water Rich Atmosphere & Magma Ocean

PREDICTIONS OF THE ATMOSPHERIC COMPOSITION OF GJ 1132b

Authors:

Schaefer et al

Abstract:

GJ 1132b is a nearby Earth-sized exoplanet transiting an M dwarf, and is among the most highly characterizable small exoplanets currently known. In this paper, we study the interaction of a magma ocean with a water-rich atmosphere on GJ 1132b and determine that it must have begun with more than 5 wt% initial water in order to still retain a water-based atmosphere. We also determine the amount of O2 that can build up in the atmosphere as a result of hydrogen dissociation and loss. We find that the magma ocean absorbs at most ~10% of the O2 produced, whereas more than 90% is lost to space through hydrodynamic drag. The most common outcome for GJ 1132b from our simulations is a tenuous atmosphere dominated by O2, though, for very large initial water abundances, atmospheres with several thousands of bars of O2 are possible. A substantial steam envelope would indicate either the existence of an earlier H2 envelope or low XUV flux over the system's lifetime. A steam atmosphere would also imply the continued existence of a magma ocean on GJ 1132b. Further modeling is needed to study the evolution of CO2 or N2-rich atmospheres on GJ 1132b.

A Better way to Tell if a Terrestrial Exoplanet is a Venus or Earth

A new method for analyzing the chemical composition of stars may help scientists winnow the search for Earth 2.0.

Yale University researchers Debra Fischer and John Michael Brewer, in a new study that will appear in the Astrophysical Journal, describe a computational modeling technique that gives a clearer sense of the chemistry of stars, revealing the conditions present when their planets formed. The system creates a new way to assess the habitability and biological evolution possibilities of planets outside our solar system.

"This is a very useful, easy diagnostic to tell whether that pale blue dot you see is more similar to Venus or the Earth," said Fischer, a Yale professor of astronomy. "Our field is very focused on finding Earth 2.0, and anything we can do to narrow the search is helpful."

Lead author Brewer, a postdoctoral researcher at Yale, has used the technique previously to determine temperature, surface gravity, rotational speed, and chemical composition information for 1,600 stars, based on 15 elements found within those stars. The new study looks at roughly 800 stars, focusing on their ratio of carbon to oxygen, and magnesium to silicon.

Brewer explained that understanding the makeup of stars helps researchers understand the planets in orbit around them. "We're getting a look at the primordial materials that made these planets," he said. "Knowing what materials they started with leads to so much else."

For instance, the new study shows that in many cases, carbon isn't the driving force in planetary composition. Brewer found that if a star has a carbon/oxygen ratio similar to or lower than that of our own Sun, its planets have mineralogy dominated by the magnesium/silicon ratio. About 60% of the stars in the study have magnesium/silicon ratios that would produce Earth-like compositions; 40% of the stars have silicate-heavy interiors.

"This will have a profound impact on determining habitability," Brewer said. "It will help us make better inferences about which planets will be ones where life like ours can form."

In addition to helping identify planets more like Earth, the study sheds light on the occurrence of "diamond" planets -- planets with a high carbon-to-oxygen abundance. Brewer and Fischer found that it is "exceedingly rare" to find a star with a carbon/oxygen ratio high enough to produce a diamond planet. In fact, the new data reveals that the star of the much discussed diamond planet, 55 Cancri e, does not have a high enough carbon/oxygen ratio to support its nickname.

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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.

Gliese 1132b is a Venus Analog With An Oxygen Rich Atmosphere but no Life (probably)

The distant planet GJ 1132b intrigued astronomers when it was discovered last year. Located just 39 light-years from Earth, it might have an atmosphere despite being baked to a temperature of around 450 degrees Fahrenheit. But would that atmosphere be thick and soupy or thin and wispy? New research suggests the latter is much more likely.

Harvard astronomer Laura Schaefer (Harvard-Smithsonian Center for Astrophysics, or CfA) and her colleagues examined the question of what would happen to GJ 1132b over time if it began with a steamy, water-rich atmosphere.

Orbiting so close to its star, at a distance of just 1.4 million miles, the planet is flooded with ultraviolet or UV light. UV light breaks apart water molecules into hydrogen and oxygen, both of which then can be lost into space. However, since hydrogen is lighter it escapes more readily, while oxygen lingers behind.

"On cooler planets, oxygen could be a sign of alien life and habitability. But on a hot planet like GJ 1132b, it's a sign of the exact opposite - a planet that's being baked and sterilized," said Schaefer.

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Gliese 832d: a Venus Analog Terrestrial World

An Earth-Like Planet in GJ 832 System

Authors:

Satyal et al

Abstract:

Stability of planetary orbits around GJ 832 star system, which contains inner (GJ 832c) and outer (GJ 832b) planets, is investigated numerically and the detailed phase-space analysis are performed. The stability of the system is de?ned in terms of its lifetime, which is its survival time during the orbital integration period, and the maximum eccentricity, emax attained by the orbits during the evolution processes. A special emphasis is given to the existence of stable orbits for an Earth-like planet that is injected between the inner and outer planets. Thus, numerical simulations are performed for three and four bodies in elliptical orbits (or circular for special cases), and a large number of initial conditions that covers the whole phase-space of the existing bodies are used. The results presented in the phase-space maps for GJ 832c indicates the least deviation of the eccentricity from its nominal value, which is then used to determine its inclination regime. Also, the Earth-like planet displays stable orbital con?gurations for at least one billion years. Then, the radial velocity curves based on the signature from the Keplerian motion are generated for the Earth-like planet to estimate its distance from the star and its mass-limit. The synthetic RV signal suggests that an additional planet (1M? ? mass ? 15M?) with dynamically stable con?guration may be residing between 0.25 - 2.0 AU from the star. We have provided an estimated number of RV observations for the additional planet for further observational veri?cation.

OGLE-2013-BLG-0723: The Circum Brown Dwarf Orbiting Venus Might be a False Positive

A New Non-Planetary Interpretation of the Microlensing Event OGLE-2013-BLG-0723

Authors:

Han et al

Abstract:

Recently, the discovery of a Venus-mass planet orbiting a brown-dwarf host in a binary system was reported from the analysis of the microlensing event OGLE-2013-BLG-0723. We reanalyze the event considering the possibility of other interpretations. From this, we find a new solution where the lens is composed of 2 bodies in contrast to the 3-body solution of the previous analysis. The new solution better explains the observed light curve than the previous solution with Δχ2∼202, suggesting that the new solution is a correct model for the event. From the estimation of the physical parameters based on the new interpretation, we find that the lens system is composed of two low-mass stars with ∼0.2 M⊙ and ∼0.1 M⊙ and located at a distance ∼3 kpc. The fact that the physical parameters correspond to those of the most common lens population located at a distance with a large lensing probability further supports the likelihood of the new interpretation. Considering that two dramatically different solutions can approximately explain the observed light curve, the event suggests the need of carefully testing all possible lens-system geometries.

Telling Apart ExoEarths and ExoVenuses With JWST

Telling twins apart: Exo-Earths and Venuses with transit spectroscopy

Authors:

Barstow et al

Abstract:

The planned launch of the James Webb Space Telescope in 2018 will herald a new era of exoplanet spectroscopy. JWST will be the first telescope sensitive enough to potentially characterize terrestrial planets from their transmission spectra. In this work, we explore the possibility that terrestrial planets with Venus-type and Earth-type atmospheres could be distinguished from each other using spectra obtained by JWST. If we find a terrestrial planet close to the liquid water habitable zone of an M5 star within a distance of 10 parsecs, it would be possible to detect atmospheric ozone if present in large enough quantities, which would enable an oxygen-rich atmosphere to be identified. However, the cloudiness of a Venus-type atmosphere would inhibit our ability to draw firm conclusions about the atmospheric composition, making any result ambiguous. Observing small, temperate planets with JWST requires significant investment of resources, with single targets requiring of order 100 transits to achieve sufficient signal to noise. The possibility of detecting a crucial feature such as the ozone signature would need to be carefully weighed against the likelihood of clouds obscuring gas absorption in the spectrum.

Gliese 832d: A new Venus Analog Found?

Earth may have a new neighbour, in the form of an Earth-like planet in a solar system only 16 light years away. The planet orbits a star named Gliese 832, and that solar system already hosts two other known exoplanets: Gliese 832b and Gliese 832c. The findings were reported in a new paper by Suman Satyal at the University of Texas, and colleagues J. Gri?th, and Z. E. Musielak.

Gliese 832B is a gas giant similar to Jupiter, at 0.64 the mass of Jupiter, and it orbits its star at 3.5 AU. G832b probably plays a role similar to Jupiter in our Solar System, by setting gravitational equilibrium. Gliese 832c is a Super-Earth about 5 times as massive as Earth, and it orbits the star at a very close 0.16 AU. G832c is a rocky planet on the inner edge of the habitable zone, but is likely too close to its star for habitability. Gliese 832, the star at the center of it all, is a red dwarf about half the size of our Sun, in both mass and radius.

The newly discovered planet is still hypothetical at this point, and the researchers put its mass at between 1 and 15 Earth masses, and its orbit at between 0.25 to 2.0 AU from Gliese 832, its host star.

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Only Impacts of Greater Than 300 km dia Would Have Long Term Effects on Venus (or Analogues)

Effect of a single large impact on the coupled atmosphere-interior evolution of Venus

Authors:

Gillmann et al

Abstract:

We investigate the effect of a single large impact either during the Late Veneer or Late Heavy Bombardment on the evolution of the mantle and atmosphere of Venus. We use a coupled interior/exterior numerical code based on StagYY developed in Gillmann and Tackley (Gillmann, C., Tackley, P.J. [2014]. J. Geophys. Res. 119, 1189–1217). Single vertical impacts are simulated as instantaneous events affecting both the atmosphere and mantle of the planet by (i) eroding the atmosphere, causing atmospheric escape and (ii) depositing energy in the crust and mantle of the planet. The main impactor parameters include timing, size/mass, velocity and efficiency of energy deposition. We observe that impact erosion of the atmosphere is a minor effect compared to melting and degassing triggered by energy deposition in the mantle and crust. We are able to produce viable pathways that are consistent with present-day Venus, especially considering large Late Veneer Impacts. Small collisions (less than 100 km radius) have only local and transient effects. Medium-sized impactors (100–400 km) do not have much more consequence unless the energy deposition is enhanced, for example by a fast collision. In that case, they have comparable effects to the largest category of impacts (400–800 km): a strong thermal anomaly affecting both crust and mantle and triggering melting and a change in mantle dynamics patterns. Such an impact is a global event and can be responsible for volcanic events focused at the impact location and near the antipode. Depending on the timing of the impact, it can also have major consequences for the long-term evolution of the planet and its surface conditions by either (i) efficiently depleting the upper mantle of the planet, leading to the early loss of its water or (ii) imposing a volatile-rich and hot atmosphere for billions of years.

GJ 1132b: a Terrestrial World, Potentially ExoVenus, 39.19 Light Years Away

A rocky planet transiting a nearby low-mass star

Authors:

Berta-Thompson et al

Abstract:

M-dwarf stars—hydrogen-burning stars that are smaller than 60 per cent of the size of the Sun—are the most common class of star in our Galaxy and outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M dwarfs host Earth-sized planets in great numbers: the average number of M-dwarf planets that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per star. The nearest such planets known to transit their star are 39 parsecs away, too distant for detailed follow-up observations to measure the planetary masses or to study their atmospheres. Here we report observations of GJ 1132b, a planet with a size of 1.2 Earth radii that is transiting a small star 12 parsecs away. Our Doppler mass measurement of GJ 1132b yields a density consistent with an Earth-like bulk composition, similar to the compositions of the six known exoplanets with masses less than six times that of the Earth and precisely measured densities. Receiving 19 times more stellar radiation than the Earth, the planet is too hot to be habitable but is cool enough to support a substantial atmosphere, one that has probably been considerably depleted of hydrogen. Because the host star is nearby and only 21 per cent the radius of the Sun, existing and upcoming telescopes will be able to observe the composition and dynamics of the planetary atmosphere.

pop sci link.

2nd pop sci link.

How Much Atmospheric Erosion Would a Venus Analog Orbiting an M Dwarf Host Star?

The Interaction of Venus-like, M-dwarf Planets with the Stellar Wind of Their Host Star

Authors:

Cohen et al

Abstract:

We study the interaction between the atmospheres of Venus-like, non-magnetized exoplanets orbiting an M-dwarf star, and the stellar wind using a multi-species Magnetohydrodynaic (MHD) model. We focus our investigation on the effect of enhanced stellar wind and enhanced EUV flux as the planetary distance from the star decreases. Our simulations reveal different topologies of the planetary space environment for sub- and super-Alfvenic stellar wind conditions, which could lead to dynamic energy deposition in to the atmosphere during the transition along the planetary orbit. We find that the stellar wind penetration for non-magnetized planets is very deep, up to a few hundreds of kilometers. We estimate a lower limit for the atmospheric mass-loss rate and find that it is insignificant over the lifetime of the planet. However, we predict that when accounting for atmospheric ion acceleration, a significant amount of the planetary atmosphere could be eroded over the course of a billion years.

How Common are Venus Analogs?

On the Frequency of Potential Venus Analogs from Kepler Data

Authors:

Kane et al

Abstract:

The field of exoplanetary science has seen a dramatic improvement in sensitivity to terrestrial planets over recent years. Such discoveries have been a key feature of results from the {\it Kepler} mission which utilizes the transit method to determine the size of the planet. These discoveries have resulted in a corresponding interest in the topic of the Habitable Zone (HZ) and the search for potential Earth analogs. Within the Solar System, there is a clear dichotomy between Venus and Earth in terms of atmospheric evolution, likely the result of the large difference (∼ factor of two) in incident flux from the Sun. Since Venus is 95\% of the Earth's radius in size, it is impossible to distinguish between these two planets based only on size. In this paper we discuss planetary insolation in the context of atmospheric erosion and runaway greenhouse limits for planets similar to Venus. We define a ``Venus Zone'' (VZ) in which the planet is more likely to be a Venus analog rather than an Earth analog. We identify 43 potential Venus analogs with an occurrence rate ($\eta_{\venus}$) of 0.32+0.05−0.07 and 0.45+0.06−0.09 for M dwarfs and GK dwarfs respectively.