A candidate giant planet imaged in the habitable zone of α Cen A
43 comments
·August 7, 2025TMEHpodcast
vikingerik
Note that the "Earth-sized" condition in there is doing some heavy lifting. Earth is a factor of 40x more massive than the largest moon in our solar system. A body needs to be fairly close to Earth's mass to have enough gravity to retain liquid water on its surface. Not that it couldn't happen, but we currently don't have any known precedent for a moon that large.
spartanatreyu
Why limit ourselves to liquid water on its surface?
It'd be easy to have a world covered in ice with underwater oceans kept liquid by volcanic vents.
defyonce
Unless we learn how to live for billions of years.
reactordev
We would need to master gravity as a manipulating force instead of a constant. There’s faster methods of traveling long distances than just pointing your nose at it.
pbmonster
> There’s faster methods of traveling long distances than just pointing your nose at it.
Maybe there is. More likely, there isn't.
kjkjadksj
Sometime this week there was an article talking about using lasers to send 1cm probes at 0.25c to alpha centauri. Estimates are 30 years for arrival of a swarm of these.
Qem
> Based on the photometry and orbital properties, the planet candidate could have a temperature of 225 K, a radius of ≈1-1.1 RJup and a mass between 90-150 MEarth, consistent with RV limits.
Hope it has some interesting moons.
UI_at_80x24
225K = -48C
So not exactly cozy. I'm not sure what the other measurements mean.
andrewflnr
What are the numbers for the temperature Earth would have without any greenhouse gases? The right atmosphere might make it work.
SJC_Hacker
Keep in mind these calcs discard the the greenhouse effect, but not the albedo, which reality can’t happen since the same factor is causing both
dvh
-19°C
jaredhallen
I don't either, but if its radius is the size of Jupiter, I imagine the gravity's a real buzz kill.
alanbernstein
For that range of mass values, the surface gravity would be relatively close to that of earth, even lower at 90x.
nkrisc
If those units mean what I think they mean, then the planet seems to be far less dense than Jupiter, which is a little more then 300x Earth mass.
kristianc
It would be warmer than Mars I think, which is c. 210K. Still frozen, barren and hostile, but slightly warmer than Mars.
davedx
Depends on its atmosphere, if it has one
m4rtink
Well, heating is still easier than cooling - if there are suitable resources at hand, heated habitats could be easy to setup.
ch4s3
RJup is the radius of Jupiter. 1 MEarth is equal to one million times the mass of the Earth. I’m not sure about RV limits.
mkl
1 MEarth is 1 Earth mass. Even our sun is only a third of a million Earth masses. Jupiter is about 318 Earth masses.
JumpCrisscross
> not sure about RV limits
Radial velocity, how quickly a planet moves “back and forth towards an observer” as it revolved about its star [1]. Its amplitude suggests planetary mass, its spectral shape orbital eccentricity.
ch4s3
I made a mistake here on MEarth and didn't notice the correction until well after the update window on my comment, oops!
yafinder
Let's call it Polyphemus and its interesting moon Pandora.
axblount
I was curious about the acceleration due to gravity at the surface:
G * (120 Earth masses) / (radius of Jupiter ^ 2)
addaon
> gravity at the surface
Unfortunately that "surface" is gaseous…
microtherion
That's what I (as a layperson) would think. The size of Jupiter, with half to a third of the mass would make it even more gas gianty than Jupiter.
… or it has a massive shell that is hollow inside /s.
Do any of the other measurements suggest anything about the nature of the surface?
pas
> a massive shell that is hollow inside /s
aren't we all? /?
> nature of the surface?
so Jupiter is 317.8 M⊕, this thing is around 80-150, but ... Saturn is right there at 80 ... so unlikely to have a solid surface, but likely has a rocky core, and wild winds at this temperature. (Saturn's average temp is -178C, -138C "surface", and this candidate seems to have -48C.)
https://arxiv.org/html/2508.03814v1/MR_relation.jpg
It seems that all of this is based on 2 data points, and they only provide some examples that are consistent with that, but the models are also very low-confidence (as we don't have a lot of data about cold and small orbiting things - as they are hard to detect).
see section 5.2 https://arxiv.org/html/2508.03814v1#S5
but also consistent with the data is that it has ring(s):
Alternate explanations for the F1550C brightness include (1) a knot of exozodiacal emission; or (2) a smaller planet with a circumplanetary ring.
azalemeth
Perhaps worth stating that although proxima centauri is the closest star to us at 4.25 LYr, Centauri A is the closest solar-type star to the Sun and isn't exactly far behind at 4.34 LYr.
Bring on the ion thruster visitor spacecraft!
metalman
chemical launch, on starship in full expenditure mode(500000lbs+payload],ion thrust, solar sail, "accelerator module" that sacrifices itself in an aero braking manouver to then release an in system observation ship
m4rtink
If you can also make the probe survive a close flyby by the star (that should ideally require just a good sun shield & robust orientation control) you could the so called solar Oberth manuever - basically this[0] but to slow down an incoming interstellar probe, not to launch one. A simple storable high thrust solid rocket motor would be ideal for this.
[0] https://www.centauri-dreams.org/2021/10/06/assessing-the-obe...
The detection of a potential giant planet in the habitable zone of Alpha Centauri A is compelling, not because we could live on the planet (likely a gas giant), but because it could host moons with the right conditions for life. If even one of those moons is Earth-sized and water-rich, it might be our nearest shot at finding another habitable world.
Still, getting there with something like David Kipping’s proposed TARS propulsion system (a solar-powered launcher that can fling tiny probes at ~40 km/s) we’d be looking at 30,000+ years to reach the star system. It’s a step forward, but for now, our best hope is to keep watching. Until someone develops fusion propulsion…