It seems like a couple times a year I see a story about a planet or group of newly discovered planets relatively close to Earth. How is this possible? Haven’t we had telescopes trained on the surrounding universe for decades now? Where are these planets hiding such that we are still finding them today?
In: Earth Science
We’ve only had telescopes good enough to detect exoplanets for a couple of decades now.
A star is way, way bigger than any of its planets and any light bounced off the planet towards us is totally drowned out by light directly from the star. To detect them we have to either measure the dimming of a star as a planet goes in front of it, or measure as the planet’s gravity tugs the star a tiny bit closer and farther to us.
This is a tiny, tiny amount – an alien looking at the sun would see a dimming of 0.008% when the earth passes between them and the sun. Jupiter makes the sun move by about 13m/s back and forth over the course of a jupiter year.
So, those are absurdly tiny changes to detect. Thats why the first ones found are really huge planets in really tight orbits. Telescopes and methods have been getting better since then and recently gotten good enough to start turning up huge numbers in the last few years.
For most methods it takes quite a while to take enough pictures to find a planet and even longer to process the data and confirm it
Finding planets around distant stars isn’t like looking at Jupiter and seeing the Galilean moons beside it, the distance to the star is soooo big and the planet is so faint so we generally can’t see them even with large telescopes
We’re generally taking a long series of pictures and checking for changes in the star.
If the planet passes between us and that star then we’ll see the star dim but this *only* works if the planet passes in front of it’s star and you have to watch for a long time to find something with an orbit like Jupiter.
If we’re looking down on the top of the star then you can look for wobbles in the star as it’s planets orbit. This takes a lot more processing to both confirm that it is wobbling and the parameters of planets that would cause that
There’s a lot of sky and we’ve really only looked at a small area
I think you’re underestimating how vast the outer space is. Even our own solar system is 36 billion times bigger than the Earth. Consider how many telescopes it’d take to cover such space, let alone the rest of observable universe. So think of it as playing Where’s Waldo at giant scales.
The colors we see through telescopes from other planets actually tell us about the planet’s atmospheric composition.
It’s a big effing sky. Decades aren’t that much time in the grand scheme of things. We are still constantly finding out things about our own solar system let alone the rest of the galaxy.
It’s a slow process because there are so many stars, but new star systems are surveyed via telescope. Planets within a certain distance of their star are said to lie in the “Goldilocks zone” (not too warm, not too cold). These planets are looked at with special scrutiny to see what their atmospheric composition is.
When I was a space-loving child in the eighties, all the books and magazines said we’d probably never be able to see foreign planets at all, since the light from their parent star was so bright it completely overwhelmed anything reflected from the planets.
It’s really a miracle of modern technology, with specialized optics and computer processing that can either measure the position of a star so precisely that we can detect its planets from their gravitational influence, or “cancel” the light of the parent star in a way that reveals just the light of its planets, well enough to detect them in the first place.
It’s a new, and somewhat slow process that requires staring at a star for a long time and analyzing the heck out of the data. So, bit by bit, we get enough data from enough stars to find one planet at a time. [Seems like the most recent numbers I could find were from 2014, where we jumped up to finding about 2 a day.](https://cdn.arstechnica.net/wp-content/uploads/2014/02/exoplanetdiscoverieshistogram.jpg)
Planets in other solar systems are too small to see with even our largest telescopes on Earth. Even the planets out at the edge of our solar system can’t be imaged clearly from telescopes on Earth or in Earth orbit. Prior to around 2009, we didn’t have any evidence that there were planets around other suns.
In 2009, NASA launched the Kepler Space Telescope, which wasn’t a particularly powerful telescope, but it used a new method of hunting for planets. Instead of trying to actually take a picture of a planet around another sun, it looked for planets passing in front of their stars. When this happens, the star gets briefly dimmer. Kepler would pay attention to a bunch of stars, and look for changes in how bright they were.
Using this method, we suddenly started finding not only one or two, but thousands of planets around other stars. Plus, this method only detects a planet if it happens to pass between the star and the telescope, and this means there are many more planets out there that aren’t detectable this way.
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