> 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.
Is it Jupiter that's unusually dense or this planet that's unusually light? Related, any idea what the feasible range of densities is for a planet of a given size? I always assumed something as large as Jupiter would be impossible for a human to set foot on due to being crushed.
A ball of foamed rock the size of a planet is an amusing thought but I have to assume that's physically impossible.
Jupiter is a gas giant. It's near the threshold where adding more mass to it makes it smaller, not larger, as the added gravitational pull would make it denser.
But what would make it larger is if it was warmer. The radius of a planet like jupiter scales to the 1.6th power of it's temperature. Jupiter is actually slowly shrinking in size as the primordial heat of its formation is radiated away.
Jupiter has no surface to set foot on, unless you count the hypothetical earth size rock inside all the gas. What would happen is that you would sink and get crushed long before you got to the rock.
Pedantry. (Well I suppose it's at least a valid point that without a solid surface there probably isn't anything for a human to want to bother visiting in the first place.)
This one presumably doesn't have a surface either, yet an earlier commenter spoke of surface gravity. Doesn't it surprise you in the slightest that two planets of the same size could have gravity that differs by such a wide margin?
...so it's got a mass 3x that of our sun, but it's the size of Jupiter? And it's a planet? ...What? The star it orbits is about the same size as our sun, yet a planet orbits it with 3x the mass? I'm missing something massive here, or the summary is terrible.
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.
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…
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.
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.
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.
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.)
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).
Offtopic, but such an interesting civilization where the keepers of knowledges seem to relate to this statement so much, innit?
Very Zen or is it just the overwork? Maybe it's a thing installed in our childhoods so that we would not struggle for power. (I certainly remember acquiring this manner of speaking based on fundamental self-deprecation around 5th grade, some other kids not acquiring it, and then 10y later we'd have mutually incomprehensible life scenarios.)
While kinds of dark humor other than "the falsity and futility of my own existence, amirite?" don't quite resonate with people as much, for whatever reason.
I propose main character syndrome as explanation. Reading too many blogs, thinking we are one of the cognoscenti, projecting ourselves a bit too close to the big polymath plasma screen in the sky, and eventually just ending up as ash in the divertor at the bottom of the big social tokamak. We think we know better, because we likely do, but what good does that do us?
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.
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
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.
> 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.
225K = -48C
So not exactly cozy. I'm not sure what the other measurements mean.
What are the numbers for the temperature Earth would have without any greenhouse gases? The right atmosphere might make it work.
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
-19°C
Huh that's surprisingly warm!
I don't either, but if its radius is the size of Jupiter, I imagine the gravity's a real buzz kill.
For that range of mass values, the surface gravity would be relatively close to that of earth, even lower at 90x.
Is it Jupiter that's unusually dense or this planet that's unusually light? Related, any idea what the feasible range of densities is for a planet of a given size? I always assumed something as large as Jupiter would be impossible for a human to set foot on due to being crushed.
A ball of foamed rock the size of a planet is an amusing thought but I have to assume that's physically impossible.
Jupiter is a gas giant. It's near the threshold where adding more mass to it makes it smaller, not larger, as the added gravitational pull would make it denser.
But what would make it larger is if it was warmer. The radius of a planet like jupiter scales to the 1.6th power of it's temperature. Jupiter is actually slowly shrinking in size as the primordial heat of its formation is radiated away.
Jupiter has no surface to set foot on, unless you count the hypothetical earth size rock inside all the gas. What would happen is that you would sink and get crushed long before you got to the rock.
Pedantry. (Well I suppose it's at least a valid point that without a solid surface there probably isn't anything for a human to want to bother visiting in the first place.)
This one presumably doesn't have a surface either, yet an earlier commenter spoke of surface gravity. Doesn't it surprise you in the slightest that two planets of the same size could have gravity that differs by such a wide margin?
I worked in the area a long time ago, so as it happens, no, but I can see how it's unintuitive!
Surface gravity in this case would be the visible radius - the same way we talk about the surface gravity of the sun, and mean the photosphere.
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.
It would be warmer than Mars I think, which is c. 210K. Still frozen, barren and hostile, but slightly warmer than Mars.
Depends on its atmosphere, if it has one
Well, heating is still easier than cooling - if there are suitable resources at hand, heated habitats could be easy to setup.
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.
1 MEarth is 1 Earth mass. Even our sun is only a third of a million Earth masses. Jupiter is about 318 Earth masses.
...so it's got a mass 3x that of our sun, but it's the size of Jupiter? And it's a planet? ...What? The star it orbits is about the same size as our sun, yet a planet orbits it with 3x the mass? I'm missing something massive here, or the summary is terrible.
The M in this context stands for "Mass" not "Mega."
If you take a look at the linked PDF you'll see that the "Earth" portion of that term is a subscript, so it reads "90-150 Earth masses."
> 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.
[1] https://arxiv.org/pdf/2308.00701
Radial Velocity
https://www.planetary.org/articles/color-shifting-stars-the-...
I made a mistake here on MEarth and didn't notice the correction until well after the update window on my comment, oops!
Let's call it Polyphemus and its interesting moon Pandora.
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…
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.
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.
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.
Unless we learn how to live for billions of years.
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.
> There’s faster methods of traveling long distances than just pointing your nose at it.
Maybe there is. More likely, there isn't.
I was curious about the acceleration due to gravity at the surface:
Comes out to 9.7 m/s. Not bad!nitpick: 9.7 m/s^2 ;)
minus one mark
> gravity at the surface
Unfortunately that "surface" is gaseous…
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?
> 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.
>hollow inside
>aren't we all? /?
Offtopic, but such an interesting civilization where the keepers of knowledges seem to relate to this statement so much, innit?
Very Zen or is it just the overwork? Maybe it's a thing installed in our childhoods so that we would not struggle for power. (I certainly remember acquiring this manner of speaking based on fundamental self-deprecation around 5th grade, some other kids not acquiring it, and then 10y later we'd have mutually incomprehensible life scenarios.)
While kinds of dark humor other than "the falsity and futility of my own existence, amirite?" don't quite resonate with people as much, for whatever reason.
Pz https://www.youtube.com/watch?v=n-TkVH2j7gU
I propose main character syndrome as explanation. Reading too many blogs, thinking we are one of the cognoscenti, projecting ourselves a bit too close to the big polymath plasma screen in the sky, and eventually just ending up as ash in the divertor at the bottom of the big social tokamak. We think we know better, because we likely do, but what good does that do us?
https://www.youtube.com/watch?v=GLkweSiuG2E
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!
https://www.projecthyperion.org
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
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...