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submitted 11 months ago by The_Picard_Maneuver@startrek.website to c/science_memes@mander.xyz

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[-] callyral@pawb.social 14 points 11 months ago

It could just be that they're just so far that we're looking at these planets millions/billion of years in the past, meaning there may may be life there but we can't see it yet.

Earth looked pretty icy when it was "snowball Earth" and early Earth's surface was full of molten rocks.

[-] Thorry84@feddit.nl 22 points 11 months ago* (last edited 11 months ago)

The Milky Way galaxy is "only" 100.000 light years across, so any planets we see around stars in our galaxy we would only see about at most 100.000 years in the past. So it would be very unlikely there would be detectable life now, where there wasn't 100.000 years ago. And even if there were, it wouldn't be complex life.

The most distant exoplanet we've found to date is 27.710 light years away, so we see that planet as it was 27.710 years ago. We've had humans running round for at least a 100.000 year on Earth, so if there are any aliens on that planet we would see them.

Almost forgot the mandatory XKCD reference: https://xkcd.com/1342/

[-] themeatbridge@lemmy.world 11 points 11 months ago

It's worth mentioning that we can't "see" any exoplanets at all. We know they are there by the gravitational lensing that occurs when a planet passes in front of the star it orbits. Once we calculate the position and orbit, we can track the planets and listen for any radio waves or radiation that would indicate life. We are also getting better as guessing the chemical composition of the planets, but it's not like we can scan the surface for plants and animals.

[-] Thorry84@feddit.nl 6 points 11 months ago

That's one way of detecting exoplanets, but not the most common one.

There are a couple of ways we can detect exoplanets:

We can see a wobble in the position of the star, as the star and the planet orbit around their common center of mass, which is offset from the center of mass of the star due to the mass of the planet.

Another way is to observe the light from a star, as the planet passes in front of the star some of the light gets blocked by the planet. By measuring the time and amount of light blocked, we can tell a lot about what is doing the blocking. The benefit of this method is some light passes through the atmosphere of the planet (if it has a significant atmosphere), by analyzing the spectrum we can tell what the atmosphere is made from.

We can also literally see a planet by direct observation, by blocking out the light of the central star, we can see light bouncing off the planet and observe that directly. This is hard, but has been done with several exoplanets.

There are more ways, see this Wikipedia article as a jumping off point for learning all about it: https://en.wikipedia.org/wiki/Methods_of_detecting_exoplanets

[-] callyral@pawb.social 3 points 11 months ago

There's always a relevant xkcd!

Yeah I didn't know we were mostly looking at planets in the Milky Way, but it makes sense. Rocky planets are very tiny compared to other stuff in the universe so it's gotta be hard detecting them millions of light years out.