I have read that immensley powerful telescopes such as the European Extremley Large Telescope will be able to directly image the atmospheres of exoplanets, and even determine their rotation rates.

I am wondering, what are the obstacles that prevent current telescopes from achieving this; how will these obstacles be overcome exactly by the new telescopes such as the EELT; and tentativley when can we expect these kinds of telescopes to come online?

Also, is it theoretically possible to build a telescope (earth or space based) that can discern fine structures such as clouds, or surface features of exoplanets (or is this in fact the level of detail that will be achieved by telescopes such as the EELT)?

  • $\begingroup$ Where have you read that direct imaging of atmospheres will be possible? Even stellar atmospheres cannot be imaged given the current technology and planets will require you to go 10 times sharper in resolution. I think you are mixing up two different things - (1) direct imaging of planets (a way to detect planets around stars) and (2) characterization of atmospheres, which is done using spectroscopic techniques (for example, transmission spectroscopy) or by studying the dips in the light curves of an object (this, for example, is how we detect star-spots on other stars) $\endgroup$
    – Takku
    Commented Feb 11, 2015 at 22:23
  • $\begingroup$ I heard the EELT will be able to do both. $\endgroup$
    – math_lover
    Commented Feb 12, 2015 at 20:53
  • $\begingroup$ The James Webb, coming to a sky near you in 2018 ! $\endgroup$ Commented Feb 15, 2015 at 23:54
  • $\begingroup$ Interstellar spacecraft? $\endgroup$ Commented Feb 16, 2015 at 19:39
  • $\begingroup$ no, it is ensentially a replacement for Hubble. $\endgroup$ Commented Mar 18, 2015 at 7:02

1 Answer 1


When the light from two telescopes is combined to make an interferometer, the resolution of the combined instrument is equal to the resolution of a single telescope with a diameter equal the the distance between the two (or more) smaller telescopes. This is the technology you need to view exo-planets to any resolution you want.

This has been incredibly successful in radio astronomy. Long baseline radio astronomy gives the resolution of a radio telescope the size of the diameter of the Earth. Optical telescopes in space can be even bigger. Arrays of relatively small telescopes with specially calculated spacings can do even better. Big mirrors are still better in order to get enough light on a sensor to be useful.

The twin Keck telescopes in Hawaii can form an interferometer but funding has dried up at the moment. It has an effective size of 280 feet. I don't know why there is no funding, but at this point it may be likely that a space-based interferometer would work so well that finishing the ground based instrument is not cost effective. Or the time required to set up and get data is a poor trade-off compared to other demands for telescope time. Also, longer IR is better for the planet imaging and space is a lot better place for that.

For some reason, this is a hot topic among PhD candidates, but a delay in getting pictures of these objects is not going to mean much for the rest of us.


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