Atmosphere Detected around Super-Earth GJ 1132b

by Paul Gilster on April 7, 2017

There’s interesting news this morning about planets around M-dwarfs. A team of astronomers led by John Southworth (Keele University, UK) has detected an atmosphere around the transiting super-Earth GJ 1132b. While we’ve examined the atmospheres of gas giants and have detected atmospheres on the super-Earths 55 Cancri e and GJ 3470 b, GJ 1132b is the smallest world yet where we’ve detected one. 39 light years from Earth in the constellation Vela, the transiting planet is 1.4 Earth radii in size, with a mass 1.6 times that of our world.

We’re continuing to move, in other words, into the realm of lower-mass planets when we study planetary atmospheres, an investigation that will be crucial as we look for biosignatures in distant solar systems. With GJ 1132b, we’re dealing with a planet too close to its star to be habitable (it receives 19 times more stellar radiation than the Earth does, and has an equilibrium temperature of 650 K, or 377° C). But finding a thick atmosphere here is encouraging given the level of flare and stellar wind activity on M-dwarfs.

Such activity could strip a planet of its atmosphere in some scenarios, so the survival of atmospheres on planets in the habitable zone of similar stars remains in play. In GJ 1132b, we have a planet whose atmosphere has evidently persisted for billions of years.

The GJ 1132b work was done with the GROND imager attached to the 2.2 m ESO/MPG telescope at La Silla. GROND (Gamma-ray Burst Optical/Near-infrared Detector) is normally used to study Gamma Ray Burst afterglows at seven different wavelengths from the optical to near-infrared, allowing rapid follow-up spectroscopic observations at other telescopes, but it can also be used to study exoplanets as well as optical, X-ray and radio transients.

Using GROND, the researchers could measure the decrease in brightness as the planet’s atmosphere absorbed some of the starlight while passing in front of the star in transit. The team’s intention was to determine the radius of the planet in each of the seven passbands (filters) for which it could obtain transit lightcurves, analyzing the significance of variations between the passbands in terms of atmospheric composition.

The result: The planet appeared larger at some wavelengths than others, an indication of an atmosphere opaque to specific wavelengths while transparent otherwise. The average radius of the planet could be separated out into a surface radius of 1.375 Earth radius overlaid by this atmosphere, which increases the observed radius at the wavelengths mentioned.

Simulating different atmospheres through follow-up work from team members at the University of Cambridge and the Max Planck Institute for Astronomy, Southworth and company found that an atmosphere rich in water and methane fit their observations. As to what the planet’s surface composition might be, two possibilities emerge. From the paper:

We find that the mass and radius are consistent with two broad compositional regimes. Firstly, an exactly Earth-like composition, with 33% iron, 67% silicates and no volatile layer, is inconsistent with the data within the 1σ uncertainties. But, a composition with higher silicate-to-iron fraction, including a pure silicate planet, is ostensibly consistent with the data, albeit marginally.

So perhaps a rocky world, or perhaps not:

On the other hand, the data are also consistent with a large range of H2O mass fractions between 0% and 100% in our models. In principle, consideration of temperature-dependent internal structure models would lead to larger model radii for the same composition… and therefore could lower the upper limit on the water mass fraction. Nevertheless, the mass and radius of GJ 1132 b allow for a degenerate set of solutions ranging between a purely silicate bare-rock planet and an ocean planet with a substantial H2O envelope.

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Image: Artist’s impression of the exoplanet GJ 1132 b, which orbits the red dwarf star GJ 1132. Credit: MPIA.

The authors advocate extensive follow-up work on this planet with instruments like the Hubble Space Telescope, ESO’s Very Large Telescope, and the James Webb Space Telescope. In particular, we can begin to delve into the atmosphere here to look for its constituents:

Intermediate-band photometry at 900 nm or bluer than 500 nm would enable finer distinctions to be made between competing model spectra and a clearer understanding of the chemical composition of the planetary atmosphere. The planet’s mean density measurement is also hindered by the weak detection of the velocity motion of the host star, an issue which could be ameliorated with further radial velocity measurements using large telescopes. Finally, infrared transit photometry and spectroscopy should allow the detection of a range of molecules via the absorption features they imprint on the spectrum of the planet’s atmosphere as backlit by its host star.

We’re getting close to the day when improved space- and ground-based installations will allow us to use transmission spectroscopy to look for biosignatures in the atmospheres of planets in the habitable zone of nearby red dwarfs, markers like oxygen, ozone, methane and carbon dioxide in a simultaneous presence that would indicate replenishment by living systems. We’re not there yet, but what we have here is a demonstration that a planet with 1.6 Earth’s mass in a tight orbit of its red dwarf host is capable of holding on to an extensive atmosphere.

The paper is Southwork et al., “Detection of the atmosphere of the 1.6 Earth mass exoplanet GJ 1132B,” Astronomical Journal Vol. 153, No. 4 (31 March 2017). Abstract / preprint.

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{ 22 comments… read them below or add one }

Jim Franklin April 7, 2017 at 12:11

Interesting that they rule out the planet as being habitable, yet one possible scenario has it as a “water world”, although the surface may be scolding hot, lower down, depending on the depth of the ocean, temperatures may be more conducive to life, afterall we know that water bodies become stratified, just like atmosphere’s, and so it is conceivable that at lower levels life based on chemo-synthetics is possible.

I also wonder if the planet has a magnetic field, as that may be a reason for it retaining an atmosphere when it orbits such an active star.

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Brett Bellmore April 9, 2017 at 9:05

It’s rather unlikely that the water surface is cooler than the atmosphere. Maybe at the poles?

A likely scenario here is a ball of water that’s hot enough through to be above the critical point; “Gaseous” all the way down, with no real surface.

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Andrew LePage April 10, 2017 at 8:26

> Interesting that they rule out the planet as being habitable,

It is ruled out because the stellar flux of GJ 1132b is ten times greater than that of Venus – this is FAR greater than even the most wildly optimistic (and unrealistic) definition of the habitable zone. Even if this is a “water world”, it would be more akin to a mini-Neptune with super-hot water being kept liquid at a temperatures of many hundreds (or even thousands) of degrees because of atmospheric pressure in the kilobar to hundreds of kilobar range or more – far outside any conditions which could be considered “habitable” for any sort of life based on organic compounds.

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Tulse April 10, 2017 at 10:18

What kind of chemistry happens at those temperatures and pressures? Are any sorts of long-chain molecules possible?

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Alexander Tolley April 10, 2017 at 13:26

Diamond, graphene. We can make plastics like polyethylene under high pressures and temperatures.

Life is ruled out primarily because we have no examples that can live under such extreme conditions. High in the atmosphere is no escape as radiation will tear molecules apart.

We can always speculate about some exotic chemistry that will work under such conditions, but as with exotic conditions in our own solar system, there is no evidence [yet] that life can exist there.

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Alexander Tolley April 7, 2017 at 12:25

But finding a thick atmosphere here is encouraging given the level of flare and stellar wind activity on M-dwarfs.

If the planet is a terrestrial type, then this would be very good news indeed. It would bode well for similar planets in the habitable zone around such stars.

I look forward to a number of such reports around other stars so that we get some statistics about atmospheres that would help crystallize our thinking about planetary atmospheres and the possibility of life.

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Tulse April 7, 2017 at 12:31

If the planet potentially has a water ocean at this level of insolation, is that because the atmospheric pressure is sufficient to prevent the water from completely vaporizing, or would some other mechanism(s) be involved?

And, more interestingly to me, if the planet has a liquid ocean under these conditions, can habitability be ruled out completely?

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Michael Fidler April 8, 2017 at 20:31

It seems that many of these planets around M dwarfs would be water worlds that could protect life from the harmful effects of the UV and X-rays.

So maybe this is the most common intelligent creature:
https://www.sciencealert.com/octopus-and-squid-evolution-is-officially-weirder-than-we-could-have-ever-imagined
https://www.scientificamerican.com/article/curiouser-and-curiouser-octopuss-evolution-is-even-stranger-than-thought/
https://www.newscientist.com/article/2127103-squid-and-octopus-can-edit-and-direct-their-own-brain-genes/

ALIENS! Hiding in plain sight!
Yes, they are just hiding in the earths oceans waiting! It will not be long before they change there genes and and take over!!!

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DJ Kaplan April 7, 2017 at 12:52
Michael Fidler April 8, 2017 at 20:19

The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets.
https://arxiv.org/abs/1703.10375
“The size of a planet is an observable property directly connected to the physics of its formation and evolution. We used precise radius measurements from the California-Kepler Survey (CKS) to study the size distribution of 2025 Kepler planets in fine detail. We detect a deficit in that distribution at 1.5-2.0 R⊕. This gap splits the population of close-in (P < 100 d) small planets into two size regimes: RP < 1.5 R⊕ and RP = 2.0-3.0 R⊕, with few planets in between. Planets in these two regimes have nearly the same intrinsic frequency based on occurrence measurements that account for planet detection efficiencies. The paucity of planets between 1.5 and 2.0 R⊕ supports the emerging picture that close-in planets smaller than Neptune are composed of rocky cores measuring 1.5 R⊕ or smaller with varying amounts of low-density gas that determine their total sizes."

Super-Earth GJ 1132b is at the upper end so it seems to be a good chance that 1.5 R⊕ or smaller can hold onto there atmosphere!

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Ronald April 9, 2017 at 13:48

This is very relevant information, in accordance with, and a confirmation of other publications on this topic.
Worthy of a separate post.

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tommi59 April 7, 2017 at 14:26

Assessed planet radius 1.4 earth is such large because stellar radius was increased significantly in last paper what is not the case so the true radius is maximum 1.2 earth consistent with previous papers and planet has earth like composition

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DJ Kaplan April 7, 2017 at 16:01

1.2 is a horse of a different color!

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FrankH April 7, 2017 at 14:55

There’s a recent paper on arXiv:
“The cosmic shoreline: the evidence that escape determines which planets have atmospheres, and what this may mean for Proxima Centauri b”

by Kevin J. Zahnle, David C. Catling

https://arxiv.org/abs/1702.03386

Figure 1 in the paper shows isolation vs escape velocity; it’s clear that this the determinant for a planet holding on to an atmosphere; magnetic fields are nice to have, but not having a magnetic filed != losing the atmosphere, in most cases.

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Robert Feyerharm April 8, 2017 at 10:31

This paper has encouraging news but it doesn’t completely rule out scenarios where GJ 1132 b originally possessed a much thicker atmosphere, most of which has been cooked off over billions of years, or else GJ 1132 b is still in the process of losing its atmosphere to flares and UV radiation from GJ 1132 (the age of GJ 1132 is in the 0 to 10 billion years range according to Exoplanet.eu (http://exoplanet.eu/catalog/gj_1132_b/), therefore it’s quite possible it’s a young & active star).

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Ashley Baldwin April 16, 2017 at 19:38

I think the mass/radius relationship here is consistent ( considering Dressing et al’s graph of plotted known mass/ radius planets ) with an Ice or ( less likely ) gas giant progressively having its volatile rich atmospheric envelope stripped away by the aggressive stellar flux over billions of years. Ultimately culminating in an erstwhile ” evaporated core ” though not in this instance in any way habitable .

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ole burde April 9, 2017 at 8:15

If GJ 1132 b is a hot waterplanet ,where the atmosphere gradually i being ‘cooked off ‘ , then there could be a high Oxygen concentration in that atmosphere . The hydrogen would escape to space , creating at a high-pressure O2 atmosphere , which would then increase the boiling-point of a planet-covering ocean . Such a system would of course loose oxygen to space as well , but this relatively small quantity would be resupplied from the dissociation of water … Also the O2 would have very little concentration in almost-boiling water , preventing perhaps large scale oxygenation of planetary seabed ….it is possible to imagine an EQUILIBRIUM STATE of such a system , which could maintain a high pressure O2 atmosphere for a very long time, as long as the water would last …and if the ocean was a big fraction of the planets mass from the start , the process of loosing water could possibly take billions of years …..and we know that deep ocean -bacteria can survive in temperature of 400 Celsius as long as water doesn’t boil ..

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Alexander Tolley April 9, 2017 at 14:20

…..and we know that deep ocean -bacteria can survive in temperature of 400 Celsius as long as water doesn’t boil ..

This is not the case. I wonder if you just misinterpreted something like this:

Conditions are so challenging that no complex organisms can survive them. Animals generally struggle when they are exposed to temperatures much above 50C – true even of the Pink Pompeii worms that live next to deep-sea hydrothermal vents spewing out water at 400C onto the ocean floor.

source

Extreme thermophiles have been found to tolerate 120C, and perhaps a little more. 400C is out of the question.

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Robert G April 10, 2017 at 4:38

“What we have here is a demonstration that a planet with 1.6 Earth’s mass in a tight orbit of its red dwarf host is capable of holding on to an extensive atmosphere.”

More than 2/3 of the stars in the milky way are red dwarfs. My understanding is that these have essentially been written off from the search for life, because their flaring behaviour was assumed to (a) expose their inner planets to too high a radiation load and (b) likely strip the atmosphere from any close planet. This result seems to indicate that not only can a close-in planet retain an atmosphere, but that the atmosphere can be a hefty, thick one. A thick atmosphere can act as a good radiation shield. Consider that the ‘habitable altitudes’ of Venus’ atmosphere are well screened from radiation by the atmosphere, even without a strong magnetic field.

This result looks to me to put a very heavy hand on the probability scales: it substantially alters our best state of knowledge ‘prior’ about how many stars in the galaxy have potentially habitable worlds. It shifts the Drake equation by quite a lot.

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RobFlores April 10, 2017 at 11:53

A steam pressure cooker, mercilessly irradiated world.
Rules out life form:

But in the back of our minds; this is the type of world were the fevered imagination can make the nightmares out of possible alien morphology

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Bounty April 10, 2017 at 16:44

What would the cloud albedo be like on a steam planet?

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Michael Fidler April 14, 2017 at 10:18

The methane (CH4) got my curiosity up and found this interesting and perplexing information: “Venus – the atmosphere contains a large amount of methane from 60 km (37 mi) to the surface according to data collected by the Pioneer Venus Large Probe Neutral Mass Spectrometer[76]”
https://en.wikipedia.org/wiki/Methane
This is from the sighted material:
http://onlinelibrary.wiley.com/doi/10.1029/93GL00513/epdf?r3_referer=wol&tracking_action=preview_click&show_checkout=1&purchase_referrer=en.wikipedia.org&purchase_site_license=LICENSE_DENIED

So is this a error caused by corrosive acids in Venus’s atmosphere? What is the effect of high temperatures and UV on methane on these planets like GJ 1132b? Methane in either gas or solid form is seen thru out the solar system but how much of it is being created by life?

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