There are a lot of photos of diffrent astronomial objects such as galaxies, nebulae and stars of which some are very far away.

However there are no real photos of exoplanets (by “real photos” I mean pictures that actually show something more than a blob of light). Why is that?

Distances of galaxies are by many orders of magnitude larger than distances to exoplanets and yet we have a lot of very detailed (and beautiful) pictures of them. Meanwhile, everything we got on exoplanets is limited to a few pictures with blurred blobs of light.


Galaxies are far away but very big. Planets are nearer but very small.

Even for planets that are not completely swamped by the much brighter light of their host star, their angular size is much, much smaller than even quite distant galaxies and certainly smaller than the best achievable angular resolution by any telescopes on Earth or in space.

A quick example will suffice.

The angular resolution of the Hubble Space Telescope (HST) is about 0.1 arcseconds. That is, unless something subtends an angle of much more than 0.1 arcseconds then you are never going to get a good resolved image of it.

A big spiral galaxy is about 50 kpc in diameter. Such a galaxy will still have an angular diameter of 0.1 arcseconds when it is at a distance of $10^{11}$ pc. i.e. We can get images of such things (if they exist and if they are bright enough) right across the observable universe.

A planet the size of Jupiter subtends an angle of 0.1 arcseconds at a distance of 0.01 pc. i.e. We could not resolve the surface of Jupiter even at only a hundredth of the distance to the nearest star.


The reason is that an exoplanet only shines by the light of its parent star, and this reflected light is not only very, very faint, but often obscured by the dazzling light of the nearby star. Exoplanets are seldom if ever detected directly, for the reasons I've just explained, so we can never hope to have the sort of photographs we have of planets in our own solar system. However, there are some amazing new, state-of-the-art telescopes coming on line in the next few years, and they will probably be able to get photographs of planets which aren't too close to their stars. By analysing their spectra, astronomers will be able to find out quite a lot about them. The other things you mention are easily photographed because they are trillions of times as large and trillions of times as bright as an exoplanet.


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