'Pale blue dot' planets like Earth may make up only 1% of potentially habitable worlds

[rod]

FYI, I read this report and seems interesting in view of astrobiology and searching for life outside of Earth or if other planets exist that support biological life.

Discovery could dramatically narrow search for space creatures, https://phys.org/news/2022-10-discovery-narrow-space-creatures.html

"An Earth-like planet orbiting an M dwarf—the most common type of star in the universe—appears to have no atmosphere at all. This discovery could cause a major shift in the search for life on other planets. The work that led to the revelations about the no-atmosphere planet, named GJ 1252b, are detailed in the Astrophysical Journal Letters. This planet orbits its star twice during the course of a single day on Earth. It is slightly larger than Earth, and it is much closer to its star than Earth is to the sun, making GJ 1252b intensely hot as well as inhospitable."

I looked at this site and found a featureless spectra listed for GJ 1252 b. http://research.iac.es/proyecto/exoatmospheres/table.php

GJ 1252b: A Hot Terrestrial Super-Earth with No Atmosphere, https://iopscience.iop.org/article/10.3847/2041-8213/ac886b

"Abstract In recent years, the discovery of increasing numbers of rocky, terrestrial exoplanets orbiting nearby stars has drawn increased attention to the possibility of studying these planets' atmospheric and surface properties. This is especially true for planets orbiting M dwarfs, whose properties can best be studied with existing observatories. In particular, the minerological composition of these planets and the extent to which they can retain their atmospheres in the face of intense stellar irradiation both remain unresolved. Here, we report the detection of the secondary eclipse of the terrestrial exoplanet GJ 1252b, obtained via 10 eclipse observations using the Spitzer Space Telescope's IRAC2 4.5 μm channel...This measurement is consistent with the prediction for a bare rock surface..."

Most exoplanets documented today have little or no information determined about what type of atmosphere they have or if they even contain atmospheres. GJ 1252 b apparently does not have an atmosphere.

 

[Unclear Engineer]

I am not surprised that rocky planets very close to stars lose their atmospheres. What would really narrow the search for life would be a determination that certain star types have no overlap in the orbital distances that can (a) retain atmosphere for billions of years, and (b) maintain surface temperatures compatible with liquid water.

This particular planet does not show much about the potential for overlap of those conditions. It is so close to its star that its surface temperature is over 2,000 F. Any atmosphere would just make it hotter. It is more like Mercury than Venus or Earth in its orbit and surface conditions.

And, that should be no surprise at all, given its proximity to its star. So, I do not really see any justification for the main premise of the article what says this bodes poorly for other planets around similar stars having potential for life on their surfaces at greater orbital distances.

If there were intelligent life on the third rocky planet from that star looking at our solar system, it would be like them detecting Mercury and postulating that there is no life on any other planets in our solar system.

Similar conclusions from detecting Venus would also be inappropriate.

In fact, I have read that Earth is either just inside or just beyond the calculated habitable zone for our Sun, depending on how atmospheric factors are assumed to affect surface temperatures.

So, I think we have a lot to learn about planetary atmospheres vs orbital distance vs star type before we can reliably start putting probabilities on the parameters for Drake's Equation. Webb should help us do that for the stars in our neighborhood.

 

[rod]

"So, I think we have a lot to learn about planetary atmospheres vs orbital distance vs star type before we can reliably start putting probabilities on the parameters for Drake's Equation. Webb should help us do that for the stars in our neighborhood."

This is a more conservative approach I feel Some of the TRAPPIST-1 system planets are listed in the atmosphere site, Exoplanet atmospheres (iac.es)

Some show featureless spectra like GJ 1252 b listed and now known to have no atmosphere. Some of the others show no He and nothing else it seems.

 

[Helio]

Given it orbits about 700 times per year, it is likely migrating outward due to tidal action. So, how did it get there? Perhaps it got tossed into the fiery tantrums known for M-dwarfs, thus getting a serious sand-blasting, causing the loss of its atmosphere.

If so, perhaps we’ll find a more massive “bully”, or two, lurking farther out.

It’s too early to say most or all red dwarfs offer no real HZs, IMO. However, odds aren’t favorable for life near one of these fisty, fussy fellers!

 

[billslugg]

Wiki article on Red dwarfs says the habitable zone is so close to the star that planets there would be tidally locked. The night side would be so cold it would freeze out the atmosphere.

Also, it says Red dwarfs are prone to outbursts, which would not be good for life.

Three fourths of the stars in the Milky Way are Red dwarfs, yet not one is close enough and bright enough to be seen from Earth with the naked eye.

 

[Unclear Engineer]

It is not clear to me that a tidally locked planet that is frozen on one side and scorching on the other side can't have life if it has an atmosphere and water. There might be a temperate zone in between. And the radiation could be shielded by planetary mass in some temperate locations if it is tidally locked.

I think the key parameter for climate is the atmosphere's existence and longevity.

If the stellar outbursts strip the atmosphere of any planet that is close enough to a red dwarf so as to maintain liquid water on its star-facing side, then I think that would pretty much rule out the opportunity for life to develop.

 

[billslugg]

Yes, a tidally locked planet could have life if it had an atmosphere. Except that it can't. The dark side is so cold it freezes out all the gasses.
And yes, life might exist in shielded areas but would limit the planet to lower forms of life.

 

[Unclear Engineer]

Bill, I would think a tidally locked planet with an atmosphere would have a strong circulation pattern that takes heat from the star on one side and circulates it to the dark side for radiation back to space. And maybe liquids flowing from the dark side to the sunny side to evaporate, again. Should be easy with a lot of ocean surface, but maybe not so much with a desert planet.

So, I don't think that all of a planets atmospheric gases are going to freeze onto the surface like on Pluto when a planet is closer to its star than Mercury.

 

[billslugg]

Yes, there are alternate theories that a thick atmosphere or planet wide ocean might circulate heat around the planet to be radiated off the back side. Such a strong circulation would likely cause near supersonic winds in the narrow habitable zone. This would not be conducive to the development of intellingent life.

The planet will need interior convection to maintain a sufficient magnetic field to protect against solar wind which will strip the atmosphere as has happened on Mars.