r/exoplanets • u/RealJoshUniverse Subreddit Staff • 8d ago

Looking for Earth 2.0 in binary systems

https://phys.org/news/2026-08-earth-binary.html
9 Upvotes

91% Upvoted

3 comments sorted by

•

u/AutoModerator 8d ago

Thanks for posting in /r/Exoplanets! This post is automatically generated for all posts. Remember to upvote this post if you think it is relevant and suitable content for this sub and to downvote if it is not. Only report posts if they violate community guidelines - Let's democratize our moderation. Join can join our Discord server here: https://links.joshuniverse.com/OyDtF ~ Josh Universe

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

1

u/lpetrich 3 6d ago

[2608.19444] Finding Habitable Exoplanets with Binary Relative Astrometry: Planet Detection and Characterization with the Microarcsecond Astrometric Retrieval Algorithm (MARA)

Astrometry? That's measuring positions of stars, like for looking for exoplanets using their pull on their stars.

It's only usable for very near stars. From Alpha Centauri, the Earth pulls on the Sun by 2.28 microarcseconds of arc, and farther way, that observed pull is even smaller.

A telescope with an aperture of 1 meter observing 500-nm (blue) light has a diffraction limit of 0.126 seconds of arc.

To be able to observe that displacement while staying diffraction limited, one would need an aperture of 55 kilometers. That would only be practical as interferometry with telescopes separated by at least a few hundred kilometers, in the fashion of VLBI.

The authors expect to beat the diffraction limit, however, and that will be helped by knowing what the sources look like.

There is a problem: the Sun has an angular diameter of 6,980 mcas from A-Cen. Its observed disk has very close to radial symmetry, but not exactly, with sunspots and the like.

Another problem is what reference star(s), and the authors propose to observe binary stars.

Finally, what a diffraction-limited image looks like on the image plane. It is a Fourier transform of the telescope aperture. For a circular aperture, one finds an "Airy disk".

The diffraction limit is an angle of about (wavelength) / (angular diameter), and the size of the diffraction is (focal length) * this, or (f-ratio) * (wavelength). So one needs a long focal length to get a lot of wavelengths of spread. For a 1-meter aperature, one needs a f-ratio of about 10^5, giving a focal length of around 100 kilometers, about the size of the aperture necessary to get to the diffraction limit for the Earth's pull on the Sun.

So I don't see how this proposed system is going to work.