A candidate giant planet imaged in the habitable zone of α Cen A

119•pinewurst•6mo ago

Comments

Qem•6mo ago

> 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•6mo ago

225K = -48C

So not exactly cozy. I'm not sure what the other measurements mean.

ch4s3•6mo ago

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.

JumpCrisscross•6mo ago

> 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

floxy•6mo ago

Radial Velocity

https://www.planetary.org/articles/color-shifting-stars-the-...

mkl•6mo ago

1 MEarth is 1 Earth mass. Even our sun is only a third of a million Earth masses. Jupiter is about 318 Earth masses.

samplatt•6mo ago

...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.

Teever•6mo ago

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."

ch4s3•6mo ago

I made a mistake here on MEarth and didn't notice the correction until well after the update window on my comment, oops!

jaredhallen•6mo ago

I don't either, but if its radius is the size of Jupiter, I imagine the gravity's a real buzz kill.

alanbernstein•6mo ago

For that range of mass values, the surface gravity would be relatively close to that of earth, even lower at 90x.

fc417fc802•6mo ago

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.

Tuna-Fish•6mo ago

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.

exe34•6mo ago

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.

fc417fc802•6mo ago

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?

exe34•6mo ago

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.

nkrisc•6mo ago

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.

andrewflnr•6mo ago

What are the numbers for the temperature Earth would have without any greenhouse gases? The right atmosphere might make it work.

dvh•6mo ago

-19°C

AlecSchueler•6mo ago

Huh that's surprisingly warm!

SJC_Hacker•6mo ago

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

kristianc•6mo ago

It would be warmer than Mars I think, which is c. 210K. Still frozen, barren and hostile, but slightly warmer than Mars.

davedx•6mo ago

Depends on its atmosphere, if it has one

m4rtink•6mo ago

Well, heating is still easier than cooling - if there are suitable resources at hand, heated habitats could be easy to setup.

yafinder•6mo ago

Let's call it Polyphemus and its interesting moon Pandora.

axblount•6mo ago

I was curious about the acceleration due to gravity at the surface:

    G * (120 Earth masses) / (radius of Jupiter ^ 2)

Comes out to 9.7 m/s. Not bad!

addaon•6mo ago

> gravity at the surface

Unfortunately that "surface" is gaseous…

microtherion•6mo ago

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•6mo ago

> 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.

balamatom•6mo ago

>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

pas•5mo ago

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

balamatom•5mo ago

It makes us do things like take Zizek seriously. Been there.

lloeki•6mo ago

nitpick: 9.7 m/s^2 ;)

koakuma-chan•6mo ago

minus one mark

azalemeth•6mo ago

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•6mo ago

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•6mo ago

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...

itsalotoffun•6mo ago

https://www.projecthyperion.org

TMEHpodcast•6mo ago

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…

reactordev•6mo ago

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•6mo ago

> There’s faster methods of traveling long distances than just pointing your nose at it.

Maybe there is. More likely, there isn't.

defyonce•6mo ago

Unless we learn how to live for billions of years.

vikingerik•6mo ago

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•6mo ago

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.

kjkjadksj•6mo ago

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.

OpenCiv3: Open-source, cross-platform reimagining of Civilization III

The Waymo World Model

How we made geo joins 400× faster with H3 indexes

What Is Ruliology?

Unseen Footage of Atari Battlezone Arcade Cabinet Production

Show HN: Look Ma, No Linux: Shell, App Installer, Vi, Cc on ESP32-S3 / BreezyBox

Monty: A minimal, secure Python interpreter written in Rust for use by AI

Show HN: I spent 4 years building a UI design tool with only the features I use

Microsoft open-sources LiteBox, a security-focused library OS

Sheldon Brown's Bicycle Technical Info

Delimited Continuations vs. Lwt for Threads

Hackers (1995) Animated Experience

Dark Alley Mathematics

PC Floppy Copy Protection: Vault Prolok

Show HN: If you lose your memory, how to regain access to your computer?

An Update on Heroku

Zlob.h 100% POSIX and glibc compatible globbing lib that is faste and better

How to effectively write quality code with AI

Show HN: R3forth, a ColorForth-inspired language with a tiny VM

Why I Joined OpenAI

I spent 5 years in DevOps – Solutions engineering gave me what I was missing

Female Asian Elephant Calf Born at the Smithsonian National Zoo

Introducing the Developer Knowledge API and MCP Server

Understanding Neural Network, Visually

Learning from context is harder than we thought

I now assume that all ads on Apple news are scams

Show HN: ARM64 Android Dev Kit

FORTH? Really!?

Show HN: Smooth CLI – Token-efficient browser for AI agents

WebView performance significantly slower than PWA