I might have mentioned the issues involving the James Webb Space Telescope’s MIRI instrument in my earlier post on in-flight maintenance and repair. MIRI is the Mid-Infrared Instrument that last summer had issues with friction in one of the wheels that selects between short, medium and longer wavelengths. Now there seems to be a problem, however slight, that affects the amount of light registered by MIRI’s sensors.
The problems seem minor and are under investigation, which is a good thing because we need MIRI’s capabilities to study systems like GJ 486, where a transiting rocky exoplanet may or may not be showing traces of water in an atmosphere that may or may not be there. MIRI should help sort out the issue, which was raised through observations with another JWST instrument, the Near-Infrared Spectrograph (NIRSpec). The latter shows tantalizing evidence of water vapor, but the problem is untangling whether that signal is coming from the rocky planet or the star.
This points to an important question. GJ 486b is about 30 percent larger than Earth and three times as massive, a rocky super-Earth orbiting its red dwarf host in about 1.5 Earth days. The proximity to the star almost demands tidal lock, with one side forever dark, the other facing the star. If the water vapor NIRSpec is pointing to actually comes from a planetary atmosphere, then that atmosphere copes with surface temperatures in the range of 430 Celsius and the continual bombardment of ultraviolet and X-ray radiation associated with such stars. That would be encouraging news for other systems in which rocky worlds orbit further out, in an M-dwarf’s habitable zone.
Sarah Moran (University of Arizona, Tucson) is lead author of the study, which has been accepted for publication at The Astrophysical Journal Letters:
“We see a signal, and it’s almost certainly due to water. But we can’t tell yet if that water is part of the planet’s atmosphere, meaning the planet has an atmosphere, or if we’re just seeing a water signature coming from the star.”
Image: This graphic shows the transmission spectrum obtained by Webb observations of rocky exoplanet GJ 486b. The science team’s analysis shows hints of water vapor; however, computer models show that the signal could be from a water-rich planetary atmosphere (indicated by the blue line) or from starspots from the red dwarf host star (indicated by the yellow line). The two models diverge noticeably at shorter infrared wavelengths, indicating that additional observations with other Webb instruments will be needed to constrain the source of the water signal. Credit: NASA, ESA, CSA, Joseph Olmsted (STScI).
The trick here is that we see GJ 486b transiting its star, allowing astronomers to deploy transmission spectroscopy, in which the light of the star passes through a planet’s atmosphere and affords information about which molecules are found there. This is done only after the star’s spectrum without the transiting planet has been observed. Dips in that spectrum during the transits tell the tale, but in this case we can’t be sure of their source. The flat spectrum during transits rises at short infrared wavelengths and water vapor seems to be the culprit, but stars can have water vapor of their own.
Thus starspots can’t be ruled out, even though there is as yet no evidence that the planet crossed any of these during the two transits for which these data were taken. Even a much hotter G-class star like our Sun can show traces of water vapor in sunspots, which are much cooler than the surrounding surface. An M-dwarf like GJ 486 is far cooler than the Sun, making water vapor detections in its starspots possible.
So imagine the scenario. If we do have an atmosphere here, we have to explain how it can exist despite the continual erosion forced by the star’s heat and irradiation. That would lead one to suspect volcanic replenishment as materials are ejected from the planet’s interior. An already scheduled JWST observational program using MIRI will study the planet’s dayside for signs of an atmosphere that can circulate heat. Hence the significance of fine-tuning MIRI’s small glitches to resolve a big question.
In the case that the upcoming MIRI observations cannot definitely detect an atmosphere, high precision shorter wavelength observations could provide evidence for or against an atmosphere on GJ 486b. Ultimately, our JWST NIRSpec/G395H stellar and transmission spectra, combined with retrievals and stellar models, suggest either an airless planet with a spotted host star or a significant planetary atmosphere containing water vapor. Given the agreement between our stellar modeling and atmospheric retrievals for the spot scenario, this interpretation may have a slight edge over a water-rich atmosphere. However, a true determination of the nature of GJ 486b remains on the horizon, with wider wavelength observations holding the key to this world’s location along the cosmic shoreline.
The paper is Moran et al., “High Tide or Riptide on the Cosmic Shoreline? A Water-Rich Atmosphere or Stellar Contamination for the Warm Super-Earth GJ~486b from JWST Observations,” accepted at The Astrophysical Journal Letters and available as a preprint.
The surface temperature of teh star is over 3000K. Why would water be detectable in the star spots rather than the molecule be broken up into ions of H and O? Could another source of a water signal be comets infalling towards the star?
If it does prove to be true that H2O is detected on the planet, this implies an atmosphere that has either survived the early flare stripping or has been replenished. All good prospects for finding life, if it has appeared.
If we can detect H2O in the atmosphere, doesn’t that imply that we could detect other atmospheric gases, notably CO2 and CH4 if the planet is lifeless or at the early stage of hosting life?
Interesting thoughts! Water has an overall enthalpy of -286 kJ/mol. Splitting that into two bonds and dividing one by the gas constant (8.314 J/mol K) gives me 17200 K for a comparable standard thermal energy. This calculation is too simplistic because not all reagents are at 1 atm and the electrons can be stripped one by one to weaken the bonds, but Wikipedia’s article “Molecules in stars” points at some references to water molecules at up to 6000K, including on the Sun.
Despite a century of global refugee crises, humans have done quite little to colonize polar, desert, alpine or oceanic regions. Nowadays the entire global community working together can’t even create a decent homeland for people on a tropical island like Bhasan Char. I would not have high expectations for the inhabitants of the sort of planet you describe, where the challenges may be more extreme. I’m also not convinced of the premise. The planet might have a day-orbit resonance other than 1:1 (which with a 1.5 day orbit could mean days shorter than Earth), or strong winds might prevent it from tidally locking (as proposed for Venus). The temperatures might be moderated by the atmosphere or reflective cloud layers. Maybe Gaia flowers cover the sun-facing side with mirror petals. :) Until AIs can punish people for doubting their predictions, we’ll need these folks to keep using their telescopes…
We should be able to detect other gases but not biosignature gases since the planets surface is too hot. I like the idea of volcanism due to tidal forces replenishing the atmosphere.
The expected temperature of &00K does make the planet seem more Venus-like and inhospitable to life. Yet Venus shows an almost complete absence of H2O in the atmosphere. Is the slightly lower temperature of GJ 486b sufficient to retain some water, or is much more active volcanism the answer? If volcanism, wouldn’t we expect CO2 and CH4 to be present too?
I can find no reference to tidal locking, but if there is, and the atmosphere is unable to transfer heat from the sunward side to the dark side, then there may be “temperate” zones, at least sufficient for extremophiles to live. This paper makes the case for an atmosphere, whether or not it has water.
Having said that, as you say, it does seem that this world is probably sterile.
That’s 800 degrees fahrenheit but would that only be at the subsolar point? The other question is after 8 billion years of evolution could there be a geologic barrier between the light and dark side? How high the permanent tide is on the ice/water ocean dark side may have long term effects that we have not seen anyplace else? Could there be other tidal effects such as heavy metals concentrating on the bright side? Could there be unusual electrical and magnetic activity between such close in planets like GJ 486b and their M Dwarf star.
1. Super earth.
2. Close to star.
3. High volcanic activity
4. Water mixing in interior of planet
5. Tidal heights on the dark oceans anti subsolar point.
Five questions we have no real understanding about in such worlds.
At 2.82 earth mass it may be volcanic even without tidal forces. The question is was when it formed, was it a water world? Before the M3.5 red dwarf had powered on, could this world have subducted a deep ocean layer into its internal structure?
The other possibility is cometary impacts resupply water and organics. The 1.5 day orbit would have a high chance of impacts from the many long orbit, deep space Oort cloud comets, some of which may have been resupplied by the star passage near other stars and swings through the galaxies arms.
The interesting possibility that such a high mass super earth could of developed a very deep volcanic ladened ice covered ocean like our still unexplored oceans with a permanent high tide on its tidally locked dark side. The very bright twilight between the dark and bright side on this and other such world’s may be where most intelligent life lives…
One of my favorite songs by Pink Floyd album “Dark Side of the Moon” called Eclipse sums it up well.
There is a hint that this is not unlike the argument of the superiority of the European populations – living between the frozen Arctic and the tropical equator on Earth. The human analogy breaks down because we evolved from tropical, old-World monkeys and apes. The changing climate may have driven our evolution. Our ancestors did migrate out of Africa, and settled in a range of climatic regimes. IDK if the temperate climate of Europe was important or not. Clearly, western civilization started in the warmer parts of Europe, but it also emerged in India too. Colder parts of Europe stayed relatively uncivilized. Is there so optimum climate, because the climate is not a factor in Diamond’s “Guns, Germs, and Steel”?
Unlike Earth, the extreme temperature range between sunward and anti-sunward poles of a tidally-locked planet may offer limited scope for an expansion of lands and therefore resources. Would an intelligent species build ever higher walls towards the sunward side as a solar shield, and pipe heat and light to the colder edge of the twilight zone, to expand the width of the inhabited zone? How much engineering could be achieved to expand the width of the temperate zone?
Has any SciFi/Fantasy author written about such a civilization? It seems on par with the Martians building canals to help irrigate their drying world.
Here is a very good analysis of Gl 486;
A detailed analysis of the Gl 486 planetary system.
https://www.aanda.org/articles/aa/full_html/2022/09/aa43548-22/aa43548-22.html
Download the Pdf version of because the tables are in the correct order in the article. The Table #1 is all the current nearest transiting exoplanets within 10 parsecs, something I have been looking for!
I have been giving some thought to the possibility that such planets may be oblong because of how close they are to their star. Considering that they may have a high internal water content and they should be volcanic, they may have been frozen in at birth to a oblong shape. That would also make the density lower since the transits are assumed to just show it as a round object.
One case of a oblong planet has been found: WASP-103b:
Cheops reveals a rugby ball-shaped exoplanet.
https://www.esa.int/Science_Exploration/Space_Science/Cheops/Cheops_reveals_a_rugby_ball-shaped_exoplanet
A large hot Jupiter with 1.5 Jupiter mass around a bright F8 star. The Gl 486b is too small and has a too faint a star to determine if it is oblong. It would be interesting to see what the atmospheric dynamics would be on a oblong world. Makes for a good Sci-Fi story…
While not prolate spheroid, Clement’s novel Mission of Gravity has the planet Mesklin as highly oblate, with gravity 2 orders of magnitude higher at the poles than at the equator. A classic SciFi novel.
A new Chinese space observatory mission in planning:
TianLin: a UV-optical large aperture space telescope for habitable worlds
“It is expected that the ongoing and future space-borne planet survey missions including TESS, PLATO will detect thousands of small to medium-sized planets via the transit technique, including over a hundred habitable terrestrial rocky planets. To conduct detailed study of these terrestrial planets, particularly those cool ones with wide orbits, the exoplanet community has proposed various followup missions. The currently proposed ESA mission ARIEL is a first step for this purpose, and it is capable of the characterizations of planets down to warm super-Earths. The NASA HabEx and LUVOIR missions are mega projects to further tackle down to habitable rocky planets, which are now merged and to be launched in 2040-2045 if approved. In the meanwhile, China is funding a concept study of a 6-m class UV to optical space telescope named Tianling (a Chinese word meaning neighbours in the sky) that aims to start its operation around 2035 and last for 5+ years.”