<p>One of the <a href="https://en.wikipedia.org/wiki/STEREO" rel="nofollow">STEREO</a> satellites has been at the earth-sun L4 point, so we have "looked behind the sun", and verified that there is no counter-earth there.
That was not the purpose of their mission though.</p>

CC BY-SA 3.0
2014-10-10T14:39:50.160Z
2014-10-11T18:26:37.803Z
2014-10-11T18:26:37.803Z
usethedeathstar
<p>It would be detectable due to its gravity effect on other planets, comets and the Sun. Check these sites for further info:</p>

<p><a href="http://en.wikipedia.org/wiki/Counter-Earth#Scientific_analysis" rel="nofollow">http://en.wikipedia.org/wiki/Counter-Earth#Scientific_analysis</a></p>

<p><a href="http://en.wikipedia.org/wiki/Lagrangian_point#L3" rel="nofollow">http://en.wikipedia.org/wiki/Lagrangian_point#L3</a></p>

CC BY-SA 3.0
2014-10-09T08:56:06.250Z
2014-10-09T08:56:06.250Z
Joan.bdm
<p>Let's assume hypothetically that Earth has a twin planet on the opposite side of Earth's orbit. Its orbital period would be exactly the same as Earth's and it would always be behind the Sun so directly observing it from Earth would not be possible.</p>

<p>How would we detect the planet's existence short of sending out a spacecraft that could look "behind" the sun and observe it visually? Have we confirmed that there is no such planet?</p>

<planet><observational-astronomy>
How would we detect a planet behind the Sun?
Moyli
# How would we detect a planet behind the Sun?

(Asked by: username_0 on 2014-10-09)

Let's assume hypothetically that Earth has a twin planet on the opposite side of Earth's orbit. Its orbital period would be exactly the same as Earth's and it would always be behind the Sun so directly observing it from Earth would not be possible.

How would we detect the planet's existence short of sending out a spacecraft that could look "behind" the sun and observe it visually? Have we confirmed that there is no such planet?

**Tags:** planet, observational-astronomy

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## 2 answers

### Answer by username_1 on 2014-10-10. Score: 2

One of the [STEREO](https://en.wikipedia.org/wiki/STEREO) satellites has been at the earth-sun L4 point, so we have "looked behind the sun", and verified that there is no counter-earth there.
That was not the purpose of their mission though.


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### Answer by username_2 on 2014-10-09. Score: 1

It would be detectable due to its gravity effect on other planets, comets and the Sun. Check these sites for further info:

<http://en.wikipedia.org/wiki/Counter-Earth#Scientific_analysis>

<http://en.wikipedia.org/wiki/Lagrangian_point#L3>


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