This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: While astronomers have found thousands of exoplanets over the last few decades, the true prize continues to elude them—they have yet to find an Earth-mass, rocky planet orbiting in the habitable zone of a sun-like star. That's partially due to cosmic geography—around half of all sun-like stars near us aren't alone.
They have one or more companion stars that complicate their orbital dynamics, as well as those of any planets they might host. But a new paper, available as a preprint on arXiv, suggests a new NASA Small Explorer mission called Searching for Habitable Exoplanets with Relative Astrometry (SHERA), which aims to use those complex dynamics to help find Earth-sized worlds in these multistar systems. Currently, there are three main ways astronomers hunt for exoplanets, and while we've covered them all in great detail here at UT, it's worth a recap to show how SHERA fits into the mix.
Missions like Kepler and the Transiting Exoplanet Survey Satellite (TESS) use a technique called transiting—they watch for slight dips in a star's light as a planet passes in front of it. While the technique has been wildly successful, it requires a significant amount of luck, as a planet's orbit has to align with Earth for the technique to be most effective. A second method, practiced by many ground-based spectrographs, is known as radial velocity (RV) measurements.
These measure the "wobble" in a star caused by a planet orbiting it. But an Earth-like planet tugging on a sun-like star from one astronomical unit (AU) moves its star only around 9 cm/s—and the limit of our current suite of instrumentation is around 50 cm/s due to activity on the star's surface—so this technique is out for finding an Earth analog. That leaves one other option—astrometry.
This technique measures the exact position of stars against a background field of, you guessed it, other stars. But again, astronomers have run into problems with sensitivity. For an Earth twin orbiting a sun-like star 33 light-years away, the "wobble" the planet would induce would show up as a movement of around 0.3 microarcseconds (uas).
Our most powerful astrometry mission—GAIA—currently has a precision of around 100 uas, several orders of magnitude above what would be needed to find this type of planet. SHERA takes a page from GAIA's book, but with a twist. Instead of mapping a star against the faint background of stars, which can add a baseline level of "noise" that's hard to overcome, SHERA focuses on bright but closely separated binary pairs of stars.
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