I would like to know how do scientists know what other planets are like billions of light years away from us, i know there are powerful telescopes but even then the planets on the pictures are super tiny
How do they know there is water there or that it has an atmosphere,
Always wanted to ask thanks
In: Physics
In addition to the other answers we don’t know what planets are like billions of light years away. We can only really get good information about exoplanets around stars close to us as our instruments are less sensitive to them the further away they are. Pretty much all exoplanets we know anything about are within a few thousand light years which is much much less than a billion.
To answer the actual question we use spectroscopy, which means measuring the spectrum of light from an object. When light passes through the atmosphere of a planet some colours get absorbed by molecules in the atmosphere, every molecules has a unique fingerprint of wavelengths it absorbs. We can detect the light from the exoplanet either directly if it is separated enough from its host star, or we can observe the spectrum of the star before and after the exoplanet goes between us and it, then the difference in the spectra lets us work out the contribution from the planet.
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