Would existing or upcoming telescopes (such as James Webb) be powerful enough to perform spectroscopy on an extra solar planet?

Or would this require technology that is far beyond our current or imminent technological capabilities e.g. optical interferometry.

To constrain the answer further imagine we find an earth sized planet around alpha centauri b in the habitable zone - what would we need to see if free oxygen is present on the surface of the planet?

Thanks for your time!

  • 2
    $\begingroup$ IIRC this is already being done by comparing the star's spectrum during a planet transit with the spectrum after the transit. $\endgroup$
    – Hobbes
    May 10, 2016 at 19:27
  • $\begingroup$ if that is the case is there any evidence of finding oxygen, co2, nitrogen or other common atmospheric gases on any extra solar planets? $\endgroup$ May 10, 2016 at 19:40
  • $\begingroup$ The problem is actually a very simple one. One needs to directly observe the planet to be able to detect the make up of the planet. Once you can image the planet, you can apply spectroscopy to it. So the answer to your question is, "you need a [very] powerful telescope". $\endgroup$
    – Aron
    May 11, 2016 at 5:36
  • $\begingroup$ Look for the ESO's HARPS spectrometer - I believe these measurements have already been done in some cases, as @Hobbes said. $\endgroup$
    – Andy
    May 11, 2016 at 7:39

2 Answers 2


Ok, I've done some more research and found a good review article by Sara Seager:


Here is my understanding:

Near future: The TESS (transiting exoplanet surveying satellite) will discover a large number of exoplanets using the transiting technique (like kepler). Some of these may be good candidates for observation with the James Webb telescope. If we get really really really lucky we might find enough exoplanets that happen to transit their suns in a convenient way for us to image and do atmospheric spectroscopy. Its unlikely that enough/any data will be forthcoming to get any reasonable probability that biosignature gases are present.

Many decades from now: If this doesn't work (and it probably wont) then some form of direct imaging is required. Two technologies are discussed:

Internal coronography - special optics in the space telescope which blank out the light from the star but not the planet.

Starshade designs - a shade is flown tens of thousands of km away from a telescope and positioned very accurately to block the light from the star but not the planet. If this type of thing sounds difficult, expensive and time consuming its because it is.

Far future: Build a massive telescope that can directly image an exoplanet. Not going to happen any time soon.

The issue with this type of work is that a large number of sample planets are needed to be able to overcome the large number of false positives that are undoubtedly going to be discovered.

So to answer my question, yes the JWST can perform exoplanet spectroscopy but its unlikely that it will give us any definitive answers. Optical interferometry will not be needed and the above descriptions of future technology should give us the answers we need.


JWST is designed to do that.

Kepler is biased towards large planets close to their star. Those are (thought thought) not suitable for life, thus TESS and WFIRST are designed specifically to look for smaller worlds that in the habitable zone.

JWST and TESS are scheduled to be launched just a year apart (2018 & 2017 respectively) with WFIRST scheduled for mid 2020s which will hopefully overlap JWST for a few years.


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