Newly discovered super-Earth orbits in and out of its star's habitable zone. Could life survive its extreme climate?

[Admin]

Located less than 20 light years away, HD 20794d could potentially be one of the most Earth-like planets found so far, despite its extreme climatic variability.

Newly discovered super-Earth orbits in and out of its star's habitable zone. Could life survive its extreme climate? : Read more

 

[Helio]

Interesting planet and, as noted, close to us. It has several less eccentric sister planets, too.

The greater the eccentricity, per one paper, the greater the net luminosity impacts the planet, so it can orbit farther out beyond the outer HZ (HZo) than otherwise. [This gives our exoplanet about a 10% bump in luminosity effect.]

Here's my shot at illustrating it. The green area is the habitabile zone.

 

[Unclear Engineer]

A few comments and questions:

1. The article states both
"The planet provides a brilliant target for the next generation of telescopes to probe its atmosphere, and for scientists to test the extreme limits of planetary habitability. 'Its luminosity and proximity make it an ideal candidate for future telescopes whose mission will be to observe the atmospheres of exoplanets directly,'"
and
"astronomers have not directly observed HD 20794d, nor taken a picture of it or even seen it in transit yet."
So, I am guessing that the editors just messed-up on the proper antecedent for "its luminosity" and are referring to the star, not the planet. A G6 star certainly gives more light to work with than the red dwarfs for which we have so many exoplanet sightings.

2. With a mass of 6.6 times that of the Earth, I would expect a much thicker atmosphere than any of the inner planets in our solar system. That might help stabilize its climate a lot, compared to Earth and Mars. And a water ocean plus "dry" land areas, particularly if they are glaciated so that ice survives more than 1 of that planet's years, would also help stabilize the climate.

3. The heat and climate in which life may have evolved could be under the ocean, in some sort of heat vent such as what we see on our midocean ridges. So even if the atmosphere freezes out and heats up to steaming conditions, some deep underwater habitats might be quite stable.

4. With a gravitational mass of 6.6 times Earth's, if its density is about the same as Earth's, then it would have an gravitational acceleration about twice Earth's on its surface. So, surface pressure would probably be substantially higher than Earth's, especially if it has a higher concentration of heavier gases, such as CO2, compared to O2 and N2 such as the situation on Venus. With a potentially thick and heavy atmosphere, water at the surface might not boil even in the heat of the planet's summer, although it would obviously evaporate faster when heated.

I hope I live long enough for those "next generation telescopes" to get some real data.

 

[Helio]

So, I am guessing that the editors just messed-up on the proper antecedent for "its luminosity" and are referring to the star, not the planet. A G6 star certainly gives more light to work with than the red dwarfs for which we have so many exoplanet sightings.

Luminosity is sometimes meant as apparent luminosity, IMO. It's an oversight. That's how I took it. Planets are illuminated and aren't luminous, to your point, except in IR.

2. With a mass of 6.6 times that of the Earth, I would expect a much thicker atmosphere than any of the inner planets in our solar system. That might help stabilize its climate a lot, compared to Earth and Mars. And a water ocean plus "dry" land areas, particularly if they are glaciated so that ice survives more than 1 of that planet's years, would also help stabilize the climate.

Because it is close to us, I would bet it gets lots of study. We are entering a time when new scopes are geared to study atmospheres.

Will larger planets covered in clouds be cooler due to the increase in their albedo, assuming they aren't Venus-like? Will their atmospheres retain residual heat significantly longer. This system is, *cough", stated as being 14 Gyrs. old (give or take 5 Gyrs), though I favor "take" more than "give".

So, perhaps the great age would make this exo much cooler than a younger one.

Though it is about 10% farther out past Mars using a solar equivalent distance, per my math, it is in the habitable zone thanks in part to its eccentricity.

I wonder how it got that 0.45 eccentricity? The sister planets known are less massive. Maybe there's a big one lurking farther out that avoided migration, or something.

3. The heat and climate in which life may have evolved could be under the ocean, in some sort of heat vent such as what we see on our midocean ridges. So even if the atmosphere freezes out and heats up to steaming conditions, some deep underwater habitats might be quite stable.

Yes, I would expect its oceans might be as good as any for life, given we don't know much yet about that.

Its atmosphere, IMO, may one day be shown to avoid the extreme vaporization and freezing. Fast circulation rates would greatly help.

I hope I live long enough for those "next generation telescopes" to get some real data.

Well, don't leave too soon. *wink*

Scopes like Plato (2026) will greatly improve our studies.

Future scopes list

 

[rod]

https://exoplanetarchive.ipac.caltech.edu/overview/HD%2020794%20d#planet_HD-20794-d_collapsible

I do not see radius reported. 6.6 earth mass exoplanet with 2.0 earth radii, mean density 4.53 g cm^-3. Surface gravity compared to Earth would be about 1.65 earth g. It likely has a dense atmosphere. Need more data here before jumping to habitable and could have life

 

[Helio]

https://exoplanetarchive.ipac.caltech.edu/overview/HD%2020794%20d#planet_HD-20794-d_collapsible

I do not see radius reported. 6.6 earth mass exoplanet with 2.0 earth radii, mean density 4.53 g cm^-3. Surface gravity compared to Earth would be about 1.65 earth g. It likely has a dense atmosphere. Need more data here before jumping to habitable and could have life

Using a density table that varies with exo type, I get a radius of 1.68 earth radii. This equates to 2.1g and an escape velocity of 1.9x that of Earth.

There is a chart in a paper here.