In the following discussion I will refer to Earth-like exoplanets planets orbiting in the habitable zone of sunlike stars simply as “Earth-like exoplanets."
NASA is currently developing or considering three space telescopes that would be able to directly image Earth-like exoplanets:
The WFIRST space telescope (if it’s equipped with a starshade).
The HabEx space telescope, which would be equipped with both a starshade and a coronagraph.
The LUVOIR space telescope, which would use a coronagraph to block the light of an exoplanet’s star.
I can think of three possible reasons why it might not be feasible to build a ground-based telescope that can (like the three space-based telescopes) directly image Earth-like exoplanets:
Reason 1: A starshade is one of the best technologies for blocking the light of an exoplanet’s star, and it seems very difficult to use a starshade with a ground-based telescope.
Reason 1 seems valid, but it doesn’t seem that it can be the whole story because (as discussed above) the LUVOIR telescope will only use a coronagraph to block the light of an exoplanet’s star, and the HabEx telescope will use a starshade for some observations and a coronagraph for other observations.
Reason 2: Maybe the type of coronagraphs planned for the LUVOIR and HabEx telescopes wouldn’t work for a ground-based telescope.
Reason 3: One of the main reasons why scientists want to directly image Earth-like exoplanets is to spectroscopically examine their atmospheres to look for possible signs of life such as oxygen and methane. Maybe spectroscopically examining the atmospheres of Earth-like exoplanets requires imaging in the infrared spectrum, which isn’t possible for ground-based telescopes.
Are these three reasons valid, and do they imply that it isn’t feasible to build a ground-based telescope that can directly image Earth-like exoplanets? Are there other factors that need to be considered? Or is it actually possible to build a ground-based telescope that can directly image Earth-like exoplanets?
