<p>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."</p>

<p>NASA is currently developing or considering three space telescopes that would be able to directly image Earth-like exoplanets:</p>

<ul>
<li><p>The WFIRST space telescope (if it’s equipped with a starshade).</p></li>
<li><p>The HabEx space telescope, which would be equipped with both a starshade and
a coronagraph.</p></li>
<li><p>The LUVOIR space telescope, which would use a coronagraph to block the light 
of an exoplanet’s star.</p></li>
</ul>

<p>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:</p>

<ul>
<li><p>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. </p>

<p>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.</p></li>
<li><p>Reason 2: Maybe the type of coronagraphs planned for the LUVOIR and HabEx 
         telescopes wouldn’t work for a ground-based telescope.</p></li>
<li><p>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.</p></li>
</ul>

<p>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?</p>

CC BY-SA 4.0
2019-11-21T08:14:03.390Z
Check https://www.eso.org/sci/facilities/eelt/science/ and you will see that the prospects from ground for the next generation of giant telescopes is not great for what you want. Direct Imaging so close in needs next-gen coronography and image stability that can only be provided in space. For your point 3.) taking a spectrum requires vastly different equipment and is in a way simpler, particularly now that high-resolution radial velocity spectrographic techniques are being developed. Those can give you an atmospheric spectrum from the ground that's RV-separated from the stars, if strong enough
AtmosphericPrisonEscape
CC BY-SA 4.0
2019-11-21T16:37:57.750Z
How much money do you have?  In seriousness - large effective aperture scopes with high-density adaptive optic systems, plus all the blocking and filtering you refer to are technologically possible but at a cost (I believe) exceeding that of a space-based system including launch.
Carl Witthoft
<telescope><exoplanet>
Is it possible to build a ground-based telescope that can directly image Earth-like planets orbiting in the habitable zone of sunlike stars?
John Bowman
# Is it possible to build a ground-based telescope that can directly image Earth-like planets orbiting in the habitable zone of sunlike stars?

(Asked by: username_0 on 2019-11-21)

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?

**Tags:** telescope, exoplanet
> **Comments:**
> **username_1**: Check https://www.eso.org/sci/facilities/eelt/science/ and you will see that the prospects from ground for the next generation of giant telescopes is not great for what you want. Direct Imaging so close in needs next-gen coronography and image stability that can only be provided in space. For your point 3.) taking a spectrum requires vastly different equipment and is in a way simpler, particularly now that high-resolution radial velocity spectrographic techniques are being developed. Those can give you an atmospheric spectrum from the ground that's RV-separated from the stars, if strong enough  
> **username_2**: How much money do you have?  In seriousness - large effective aperture scopes with high-density adaptive optic systems, plus all the blocking and filtering you refer to are technologically possible but at a cost (I believe) exceeding that of a space-based system including launch.  

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## 0 answers

