ELI5: until we flew next to Pluto this month all we had is blurry 16-pixel images. How can we get such precise data on something millions of times further?
Nearly all of the ways we detect exoplanets involve indirect observation. Most of them are based on observing the star(s) in the system of the planet. The two main ways we detect exoplanets are:
* Radial Velocity - just as the gravity of a star effects a planet's orbit, the gravity of a planet also has an impact on the star's. It's just this impact is extremely small. By measuring variations in a star's movement due to the planet's gravity we can both detect the planet and estimate its mass.
* Photometry - when a planet moves in front of a star it reduces both the brightness and spectrum of the light we perceive. By carefully measuring this we can determine not only the size of the planet, but also it's chemical make-up - light from the star travels through the atmosphere of the planet, changing its spectrum in response to the elements present.
There are several other ways we can detect and examine planets, but nearly all of them are based not on observing the planet itself but its impact on much larger, detectable things that surround it. There's a comprehensive list here - https://en.wikipedia.org/wiki/Methods_of_detecting_exoplanet...
As an aside, there is an episode of the Cosmos reboot that talked about Photometry at a mile-high level. I had never heard of it before, but it is supremely interesting.
In order to take something akin to a photograph of a planet in another solar system, you'd need to build a network of telescopes with a diameter on the order of the size of Earth's distance from the sun. And in addition to being spread apart, they'd need to be pretty huge in order to capture enough photons from the target. (though of course there could be clever ways around this)
This page contains the measurements of the planet which might be the subject of the announcement; it gives you an idea of what kinds of metrics drive such an analysis:
The similarity index measures things that can be worked out without needing a precise image of the planet. These are things like radius, density and surface temperature, which can be measured by examining its orbit and how much light from the star is blocked as it passes.
IANAAP, but I saw a similar question about how the Hubble space telescope could only get blurry pictures of Pluto. The answer was that it was akin to using a microscope as a telescope (or vice-versa), if that makes sense?
Not really. The problem isn't that Pluto is too close (Hubble has taken excellent pictures of Mars), it's that Pluto is tiny, specifically in angular size.
Distance, time, and amount of light. All these things come into effect. The reason why Pluto took so long? Imagine trying to read a magazine with a pair of binoculars vs. somebody taking a picture right next to it. Which do you think will be easier to read?
We've had a pair of binoculars up in space for a while, but it was designed to see way further than Pluto. That is why we have always had blurry images.
We've had blurry images of Pluto because of its tiny angular size. The fact that its closer than some of the things Hubble has taken better pictures of is not relevant.
