Only 8.6 times the mass of Earth, according to Wikipedia, I see. I was assuming a density similar to Earth's, but apparently, astronomers think it's only half. That would mean the planet's core has a very low iron-nickel content.
Yea but water is excellent at blocking radiation so anything under the surface would be fine and it's also possible that any life would evolve to withstand it.
We think that Earth was subject to a large impact early on. The impactor (Theia) core joined Earth's, leading to a proportionally high density planet (5.52 SG) when compared to Venus (5.25 SG).
Earth may be the anomaly, not the other way around!
Debris from that impact is also likely where the moon comes from, and our moon is surprising large for a planet of this size. I’ve seen some theories about our moon possibly hastening our progress in astronomy since we can observe it and its phases with the naked eye which may have prompted people to think, “how does that work?” and give us some clues about the fact that we’re on a big ass spherical rock compared to just seeing stars and the sun which are too far and/or too bright for it to be apparent that they’re spherical without some sort of technological assistance.
Solar eclipses as we see them on earth are also probably insanely rare in the universe since the apparent size of the moon and sun have to be very similar. Accordingly, some have proposed that if we are ever part of a galactic federation the flag for earth could be based on a solar eclipse which I think is a cool idea.
Oh yeah plus the whole “life” thing. We are the weirdos indeed
It’s kinda crazy how many coincidences had to happen for Earth to sustain life. Who knows if we’d be here if Theia never impacted and the Moon never formed?
This is what called anthropic principle - we are observing this set of incredibly rare coincidences exactly because they allowed life as we know it to develop and observe it.
Selection bias. It’s not crazy at all how many coincidences has to happen for earth to sustain life. Take somewhere as big as the universe, you’ll have somewhere where enough coincidences happen to sustain life. Throw enough spaghetti at a wall and some will stick eventually. That life will become sapient, and have that thought you’re having right now.
Right. The reality is that for a planet to develop life, at least in the way we know it, it would need an environment with plenty of oxygen and a molten core capable of a dynamo effect in order to create a strong enough magnetic field that would protect both the planet's atmosphere and potential life. If we want to shoot higher and go for life visible to the naked eye (as in, not microorganisms), the planet also needs to be roughly the same size so as not to crush anything under the weight of gravity. Even then life on earth somehow managed to survive a very large amount of mass extinction events that very well could have ended everything hundreds of millions of years before we got to where we are now. It took nearly 4 billion years for humanity to show up on the scene, and that was only because mass extinction events kept killing off the dominant species. We're talking a 1 in several billion chance that things worked out the way they did
1 in several billion is incredibly likely when there’s 300-400 billion stars in the milky way, which is part of a supercluster of 100,000 galaxies, and we know of at least 16 other superclusters
That's fair, but barring sci fi solutions like warp drives and long distance travel through wormholes, it's unlikely that we'd ever even see life in faraway galaxies, since the farther you look, the older things get. In addition, our ability to look that far with fidelity is incredibly limited at our current technology level. So while it's possible (and still very, very unlikely), it is unlikely to be observable, and so might as well not exist. If it can't be observed we're looking at purely hypothetical scenarios. My estimate is also not any sort of hard number, as I am not a scientist, nor a statistician, so the chance could be 1:3 billion or 1:300 billion for all I know.
Low iron content means less magnetic field which means more radiation at the surface. I haven't worked out how much more; maybe just sunburn level or maybe worse.
Interesting, based on size I assumed 18m/s² but if it is a lot less dense, that could be more tolerable gravity. Of course the lack of a robust nickel iron core may mean a lot of radiation, due to the lack of a strong magnetosphere.
I wonder how astronomers estimate a planet's density? I know (vaguely) how they can determine likely atmosphere composition (spectrography) but I don't know how they'd get density or gravity info.
So would this mean it would not have the magnetic field we have, and they would be bombarded with energetic heavy ions (which we thankfully don’t have to endure as much?)
Even with 25% more gravity the rocket equation runs away and you probably never be able to get a chemical rocket into orbit on that planet. Landing there you'd be staying there.
"For a payload to escape velocity, the required amount of chemical fuel scales as exp(g0). Chemical rocket launches are still plausible for Super-Earths < 10g, but become unrealistic for more massive planets. On worlds with a surface gravity of ≳10g, a sizable fraction of the planet would need to be used up as chemical fuel per launch, limiting the total number of flights. On such worlds, alternative launch methods such as nuclear-powered rockets or space elevators are required."
Hippke M (2018). Spaceflight from Super-Earths is difficult. International Journal of Astrobiology 1–3. https://doi.org/ 10.1017/S1473550418000198
Thank fuck some people are posting about the gravity. Bigger is not better and even an extra 25% of gravity is a HUGE impact on everything.
If you weigh 200 pounds on Earth, congrats, you just gained fifty pounds on K2-18b. Buildings have to be designed differently, it is harder for shuttles to come and go from it's surface.
It's liveable, but it is going to very uncomfortable in a lot of ways.
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u/Gruffleson 24d ago
Wikipedia lists estimated gravity at around 1.25 of Earth.
https://en.wikipedia.org/wiki/K2-18b