How do scientists know so much about planets so far away?
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We don’t *know* anything with certainty, but we *infer* a lot through observation of the effects they (the exoplanets) have on other things (like a gravitational interaction with a host star, or the light it reflects from that host star).
Amazing ability we have to progress as a civilization to see and interpret things further and further out in the universe. Imagine the advances we could make if the world was acting in unison instead of war and bickering all the time.
Because of light. It sounds oversimplified, but really it’s incredibly fascinating to me.
Light is generated by energy output by stars. Different stars output different kinds and amounts of light, including light we can’t see with our eyes. This is the electromagnetic spectrum and includes radio waves, gamma rays, and all the fancy rays. We can call all of that just **light**, and the lucky thing is that we know *exactly* how fast any kind of light should travel. Because we know this speed very precisely and under pretty much any condition, it is actually quite easy to know how far away a star is.*
But if you stare at a star long enough, you’ll notice that every so often the star gets slightly dimmer in certain parts. This means something is partially blocking its light. The thing blocking its light periodically must be *orbitting* the star, so it must probably be a planet. We can tell how big it is by how much light it blocks, and how fast it moves by how quickly it moves across the star, and many other fascinating things can be deduced just by looking at how a star’s light is blocked by objects.
Then there’s the fact that planets reflect light coming from other stars around them. At the right angle, we can see light from a star in one direction bounce off the planet and shine towards us. Again, if we estimate the time that takes, we can know how far away the planet is. Furthermore, because different elements reflect different *parts* of light, which we interpret as colours, we can compare the parts we see to our own catalogue of chemical elements and compounds and deduce what the planets are made of.
For eg, we have iron here on earth, and we know that iron *absorbs* a lot of colours but mostly *reflects* red light, which is why iron is red. If we see a planet out there, and it absorbs and reflects the same parts of the light spectrum as iron does on earth, we can be pretty confident that there’s iron on the planet’s surface. Then we ask people who study rocks to tell us more details about *how* iron could have formed on the planet, because there’s only a few ways we know of that explain it.
The last really cool thing, and this really blew my mind, is that we learned recently that light interacts with gravity, meaning objects that are really big and heavy that have a lot of gravity, actually *bend* light around them. So even if light isn’t reflecting off of a planet, and the planet isn’t obscuring a star’s light, It could still be possible to “see” things out there because they are *affecting* the light around them. If we see a lot of heavy things bending light, this just gives us more interesting ways to deduce what’s happening out in the cosmos. All because of light.
*Note, astrophysics is not “easy”, but once we figured out the principle we’re trying to identify, a lot of stuff becomes easy to learn. That’s why you hear about scientists all of a sudden “discovering” a dozen interesting things a week
Exoplanets are observed with very good telescopes (Kepler is an orbital telescope especially made for this task)
We can check what kind of light this planet reflects to see what kind of elements are in the atmosphere. Size and distance to their star can be measured by checking how much light of their star they block when passing in front, or how much the star “wobbles” from it’s gravity.
We know a lot for a tiny fraction of the planets that are out there because they happen to be in well observable places. There are billions of planets we can’t see at all because their orbit is not aligned in a way they move in front of their star from our view.
They can tell by how much they “wobble” a star what the mass is, they can tell about the interval between dimming the star they orbit around how long it takes them to complete an orbit, they can tell about the light passing through the atmosphere what that might contain. Combining these factors and others allows you to make some assumptions about the planet. https://youtu.be/AnYye_c8rI4
By looking at them with large telescopes in the entire EM spectrum and corresponding that data with the knowledge of celestial+classical+quantum physics and then drawing conclusions from those correspondences.
* they are virgins? i did not mean .any disrespect towards, the scientist. they may have a better looking wife than the average wife. in the future. they also know that they are are smarter. than all of us.
Technically the science of distant bodies is “the history of”.
We don’t know anything about the current state of stars that are 100 light years away, we see what they were like 100 years ago since it took that long for the light to reach us.
We actually don’t know very much at all about exoplanets. A huge amount of what you read in articles about them is exaggerated or sometimes outright made up. At uni I did a project on exoplanets and my supervisor was keen to point out how unreliable science journalism is when it comes to exoplanets.
What we can work out about them is roughly how big they are and what their mass is, and maybe how far away from the star it is.
You can work out its size by observing the star over long periods and looking for a drop in the amount of light from the star. The light is dimmed by a fraction of a percent, so you need a good telescope to observe this, and you need repeated observations to make sure it’s not caused by some other factor.
You can work out its mass using the ‘Doppler wobble’ method. If a large enough planet is orbiting a star, it causes it to wobble back and forth in its orbit slight, and you can observe this as a doppler shift in the light from the star. Again, the change is a fraction of a percentage point, so you need a good telescope and careful observation.
This gives you its mass and size, from which you can work out its density, and with all of that information you have a pretty good idea of what sort of planet it is (and by that I mean ‘is it a terrestrial planet or a gas giant’) and how far from the host star it is, and that’s about it.
If you want to learn anything about its atmosphere, you need spectroscopy. This means you look at the light that has passed through the planet’s atmosphere, and you compare it to white light to see which part of the spectrum have been absorbed. From this, you can tell roughly what elements make up the atmosphere. This is a fairly recent method so we haven’t done it for a ton of exoplanets yet.
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