Scientists question possible signs of life on exoplanet K2-18b in new study: 'We never saw more than insignificant hints

[Admin]

The skepticism continues over recent claims of possible hints of alien life on exoplanet K2-18b.

Scientists question possible signs of life on exoplanet K2-18b in new study: 'We never saw more than insignificant hints : Read more

 

[Helio]

This comes with little surprise to those who, like me, are pessimistic for life on exoplanets hosted by red dwarf stars.

It is in the calculated HZ (Habitable Zone) but it's only 0.14 AU from its star. It's a little large at over 2x the Earth's radius and has a surface gravity of about 3g (1.66g). The size, however, doesn't disqualify it.

There are several other concerns I have for this exo:
1) It is so close to the star, thus it is likely in a tidal lock -- one side always sees the light of day, the other side only sees the light of night.
2) Red dwarfs are notorious at spewing flares and CMEs, including monster versions of both. The planets proximity to the star only makes their impact even worse.
3) Red dwarfs are called red for a reason. The emissions of higher energy photons of violet and blue, and ultraviolet are greatly diminished which may, or may not, impact the chance for the emergence of sustained life.

As a result, FWIW, K2-18 b isn't in my Top 10 list. My favorite is KOI-4878 b.

 

[rod]

Others are reporting a bit more skeptical thinking about life on K2-18 b now. Hopes for alien life dim as doubts emerge over exoplanet K2-18b chemical signals, https://phys.org/news/2025-05-alien-life-dim-emerge-exoplanet.html

My note, exoplanet properties for K2-18 b can be seen here, https://exoplanet.eu/catalog/k2_18_b--3953/

The mass is about 8.921 earth mass and radius about 2.365 earth radii. The surface gravity would be some 1.59 g. I have seen no reports that show abiogenesis creates life from non-living matter in higher surface gravity than Earth's surface gravity. This is an assumption introduced into astrobiology *science* it appears. Higher gravity suggests more bombardments too when the exoplanet formed from a solar nebula type model.

 

[Helio]

The mass is about 8.921 earth mass and radius about 2.365 earth radii. The surface gravity would be some 1.59 g.

Oops, I see my revised program ignored the given radius of the exoplanet, thus it calculated its radius based on a rough density table. I'm further off than I would like to see. But, I did correct my code hiccup. Thanks!

We are in agreement, but we are off only a little on the radius. I use 10.937x as the size difference, in lieu of 11.2. The 10.937 is the radius based on the volumetric mean, so it's a little more accurate.

I have seen no reports that show abiogenesis creates life from non-living matter in higher surface gravity than Earth's surface gravity. This is an assumption introduced into astrobiology *science* it appears.

Where do you see such assumptions that favor higher surface gravities are more favorable for abiogenesis? I haven't seen that idea, though it wouldn't surprise me.

Higher gravity suggests more bombardments too when the exoplanet formed from a solar nebula type model.

That's a good point. This might, however, have the advantage of a faster rotating iron core, thus granting far greater protection from the heavy hits likely from a fisty red dwarf.

 

[Helio]

One other thing worth noting, the original public presentation for DMS came with the optimistic statement of "I kid you not."

 

[rod]

Helio et al. When it comes to publishing a top ten list of exoplanets that are earth-like or perhaps support biological life, the last list I read was back in January 2022 at space.com. The 10 most Earth-like exoplanets, https://www.space.com/30172-six-most-earth-like-alien-planets.html

I am still waiting for ET to phone home here

 

[Helio]

Helio et al. When it comes to publishing a top ten list of exoplanets that are earth-like or perhaps support biological life, the last list I read was back in January 2022 at space.com. The 10 most Earth-like exoplanets, https://www.space.com/30172-six-most-earth-like-alien-planets.html

I am still waiting for ET to phone home here

I like three of those 10 listed: Kepler-22 b, Kepler-442-b and Kepler-452 b.

GJ 667 c orbits an M3.5 V red dwarf. I suspect all red dwarf stars could easily be too violent. Then there is the issue of how much tidal locking will hurt chances for life forms.

Kepler-186 f, Kepler-1649 c, Proxima Cen. b, and Trappist-1 e all have red dwarf hosts. None are in the sweetest HZ spot, though the latter two are close.

Kepler-69 c orbits a G4 V star, which is nice. But it has the equivalent orbit essentially that of Venus. I suspect this is too hot, but optimistic stretches of the HZ do allow this zone. But there are better chances in my top 10, of course IMO.

Kepler-62 f orbits a K2V, which is likely pretty favorable, but it's orbital equivalent is a little farther out than Mars, so perhaps too cold.

My Favorties haven't changed in a while...

				Sol Eq.,
Rank	Name	Radius	Star Class	AU
1	KOI-4878 b	1.02	F (9?)	0.98
2	Kepler-452 b	1.59	G2	0.95
3	Kepler-22 b	2.05	G5V	1
4	Kepler-283 c	1.78	K (6?)	1.06
5	Kepler-442 b	1.32	K (6?)	1.17
6	HD 191939 g	2.21?	G8V	0.97
7	Kepler-443 b	2.3	K (3.5?)	1.04
8	Kepler-1653 Ab	2.13	K (2.5?)	0.99
9	BD-11 4672 c	2.19	K7V	0.96
10	Kepler-1341 Ab	2.46	K5V	0.94

 

[rod]

Helio, I checked out your Top Ten list, nice The .eu site now has filters showing exoplanets of different sizes you can filter on. For the Mercury or so group, 228 show up. Your radius are all large than earth size, the 228 radii range 0.285 earth to 0.996 earth. https://exoplanet.eu/home/

If I use TESS 629 exoplanets, the top ten do not show up there either radii sizes range 0.566 earth to 25 earth radii size. https://exoplanetarchive.ipac.caltech.edu/index.html

Perhaps space.com will update their favorite *most earth-like* exoplanet list

 

[rod]

FYI. IMO, K2-18 b is the media grabbing exoplanet with possible life like we see on Earth according to a variety of claims published and now rebuttals. IMO, this indicates to me there should be a SOR or System Of Record that shows and tracks all of these claims and the authoritative top ten list for earth like exoplanet claims.

 

[billslugg]

An authoritative list can be generated with anyone with sufficient cred. Cred comes from doing something right, over a very long period, better than anyone else. I have several areas in my personal life, locally, on a small scale, where I am "Da Man" and no one would care in the slightest to challenge it. The positions are overwhelmingly by orders of magnitude, off the charts bigger, better than what anyone ever did before in that tiny arena.
Do it better than anyone else, do it often, never miss a beat. Make it not worth the effort to challenge you. Then no one will challenge you. But don't slip. One slip and all that cred is gone. I go to extreme lengths not "to slip". For example, I keep a daily, detailed diary of my movements around town. Names, dates places and times to the nearest minute. Every call logged. I never need to "guess" where I was at a particular moment and what I was doing. I simply applied more rigor to a "thing" that most all people do but not on the scale I have. Twelve years, every Fri and every Mon I drive ten miles, meet some people, do some counseling. Twice a week for 13 years and never missed one. When I tell one of them I am going to do something, they take it as absolute gospel truth that I will follow through. This gives me tremendous power. I can leverage assets using nothing but my word.

Pick a field, find a tiny niche no one else ever exploited, do it better than good, do it incredibly good. Then, get on the record with it but don't toot your horn. Everyone toots their horn and no one believes it. Let some other person, interested in the subject, stumble upon your work. They will be surprised. Embarassed they weren't aware of it. Everyone will believe the same words you uttered, because they come from a disinterested party. Do it, but let the world discover it. This is how overnight successes occur.

 

[Helio]

Rod, the big decision in making a “most favorable” list is to accept or not accept red dwarf exos.

After that, then it’s just a matter of their HZ locations and size. At least until more info can be gleaned (eg atmospheres).

If I were a professional astronomer, I would be inclined to allow red dwarf prospects since we need more studies on their behavior and how much tidal locking hurts life’s probability. One limited study shows some hope that their violent flares may have inclinations away from their equatorial regions. Call it sharks and lawyers— professional courtesy.

So, I’m an example contra to Bill’s Totem pole top. When knowledge is available, an expert can arise and build a great reputation. [ I just left a highly reputable surgeon’s office, where his knowledge and experience are well-established.]. But, where grains of salt must be taken constantly, some room for amateur contribution exist.

iPhone

 

[rod]

Helio et al. When it comes to exoplanets with atmospheres documented, I use this site, https://research.iac.es/proyecto/exoatmospheres/index.php

"As of today, 269 different planets have been analyzed and 64 different molecules have been detected."

 

[Helio]

Helio et al. When it comes to exoplanets with atmospheres documented, I use this site, https://research.iac.es/proyecto/exoatmospheres/index.php

"As of today, 269 different planets have been analyzed and 64 different molecules have been detected."

Very nice site. Thanks. It's not one I've seen.

At some point, I expect that the molecular detections will be added to the main databases (NASA and exoplanet.eu).

Methane, CO, DMS, phosphine, H2O and other molecules I suspect offer the greatest optimism for life forms. These findings will enhance the "Most Favored" list, when such information is available. Of course, the advanced scopes are coming on-line in the near future and will therefore be adding those enhancements.

At this site, however, their list only has two exos that are "Temperate Earth-size" exos. This is not surprising this early in the hunt since the low-hanging fruit (hot, large exos) always comes first.

Also, their CSV download doesn't work for me. Is there a way I can force the download to use semicolons for delimiters? [I could, I suppose, write a quick VBA program to convert it, but why bother if I'm simply doing something wrong.]

 

[billslugg]

For us amateurs without academic contacts we can sometimes succeed by looking at old, available, data in new ways. AI comes to mind. Why not take whatever list you can get ahold of and ask an AI program to show relationships we may have missed to date, using conventional analysis?

 

[rod]

Very nice site. Thanks. It's not one I've seen.

At some point, I expect that the molecular detections will be added to the main databases (NASA and exoplanet.eu).

Methane, CO, DMS, phosphine, H2O and other molecules I suspect offer the greatest optimism for life forms. These findings will enhance the "Most Favored" list, when such information is available. Of course, the advanced scopes are coming on-line in the near future and will therefore be adding those enhancements.

At this site, however, their list only has two exos that are "Temperate Earth-size" exos. This is not surprising this early in the hunt since the low-hanging fruit (hot, large exos) always comes first.

Also, their CSV download doesn't work for me. Is there a way I can force the download to use semicolons for delimiters? [I could, I suppose, write a quick VBA program to convert it, but why bother if I'm simply doing something wrong.]

Helio, I use MS Office 365 and MS Excel. I opened with no problem into Excel using Data and importing using From Text/CSV option. Imports and save nicely to Excel file with column headings. Multiple rows for some exoplanets due to variations in some properties reported like molecules.

 

[rod]

Helio, when it comes to the exoatmospheres site, these are the exoplanets listed as temperate type. Still waiting to see Earth 2.0 and life out there confirmed

Iac_exoplanet_atmospheres unique type QueryIac_exoplanet_atmospheres unique type Query

name	type	mass	radius	mass_earth	radius_earth
beta Pic b	Temperate Jupiter	11.9000000​	1.6500000​	3782.06​	18.49​
HD 80606 b	Temperate Jupiter	4.1641000​	1.0320000​	1323.43​	11.57​
HIP 41378 f	Temperate Jupiter	0.0380000​	0.8210000​	12.08​	9.20​
K2-18 b	Temperate	0.0280700​	0.2110000​	8.92​	2.37​
K2-25 b	Temperate	0.0771000​	0.3060000​	24.50​	3.43​
Kepler-51 d	Temperate Jupiter	0.0240000​	0.8650000​	7.63​	9.70​
Kepler-62 e	Temperate	0.1130000​	0.1440000​	35.91​	1.61​
LHS 1140 b	Temperate	0.0219600​	0.1540700​	6.98​	1.73​
LTT 3780 c	Temperate	0.0267000​	0.2050000​	8.49​	2.30​
TOI-2136 b	Temperate	0.0148000​	0.1865000​	4.70​	2.09​
TOI-270 d	Temperate	0.0132000​	0.1900000​	4.20​	2.13​
TRAPPIST-1 c	Temperate	0.0043400​	0.0942100​	1.38​	1.06​
TRAPPIST-1 e	Temperate	0.0020000​	0.0819000​	0.64​	0.92​
TRAPPIST-1 f	Temperate	0.0021000​	0.0932300​	0.67​	1.05​
TRAPPIST-1 g	Temperate	0.0042200​	0.1005000​	1.34​	1.13​
TRAPPIST-1 h	Temperate	0.0010410​	0.0674000​	0.33​	0.76​
WD 1856+534 b	Temperate Jupiter	13.8000000​	0.9280000​	4385.92​	10.40​

 

[Helio]

Helio, I use MS Office 365 and MS Excel. I opened with no problem into Excel using Data and importing using From Text/CSV option. Imports and save nicely to Excel file with column headings. Multiple rows for some exoplanets due to variations in some properties reported like molecules.

Ah. That solves it nicely, and colorfully. Thanks.

 

[Helio]

Their "Temperate" term seems to be broad but not fully.

They show five of the Trappist exos, but they ignore Trappist-1 d, which has a sol. equivalent of 0.93 AU. I show Trappist-1 d in the warm to hot HZ area; Trappist-1 e as being in the normal HZ area; Trappist-1 f at sol. eq. of 1.62 in the cold area; Trappist-1 g in the very cold extreme area of the HZ with a sol. eq. of 1.97 AU.

Worse is that Trappist-1 is an M8 red dwarf, about as cool as you can get and likely fisty.

I do like, however, their table for its molecular findings. Perhaps the PH info as well.