[astro-ph.EP] Binary relative astrometry is a technique to search for rocky planets in the habitable zone of nearby binary stars using 1D relative astrometry at the microarcsecond level.
This unprecedented precision would allow a custom-designed space telescope to directly measure the occurrence rate of these planets. The success of such a mission depends on our ability to recover and characterize planets from the unique format of extreme precision binary relative astrometry data.
We present MARA, the Microarcsecond Astrometric Retrieval Algorithm, specifically designed for these data. We describe the design and format of the MARA pipeline, and demonstrate its accuracy and performance with a series of validation tests on simulated data, using the SHERA SMEx mission concept as an example.
Our injection/recovery tests show that with these data, MARA is able to detect and characterize rocky planets in the habitable zone of alpha Cen A, down to a coplanar mass of about 1 Earth mass in 1 year orbits.
Expanding to a range of input planet masses and periods for the same example mission, we find that the results from these injection/recovery tests generally agree with the analytic predictions of binary relative astrometry sensitivity.
We use MARA to map out the expected completeness as a function of planet mass and period, which in this case reaches down to about 0.5 M Earth masses at 3 year orbits around alpha Cen A. These depth-of-search calculations will be a vital ingredient in demographics calculations from the final data from a binary relative astrometry mission.
Completeness to planets for α Cen A, assuming 3 years of SHERA observations with 3.8 µas uncertainties with 149 total epochs. The white dashed line shows the analytic prediction (Equations 6 and 7), with the symbols showing Venus, Earth, and Neptune for comparison. Shaded contours give the results from 10,000 injection/recovery tests using the periodogram portion of the MARA pipeline, while circles and crosses are from a random subset of 400 injections. The shaded green region corresponds to the conservative habitable zone following (R. K. Kopparapu et al. 2013). There is generally good agreement between the two methods, with deviations largely due to combinations of orbital phase and the Solar Keepout gaps either making a planet more or less detectable than predicted by the analytic approximation. From this analysis SHERA observations would be about 87% complete to a planet with mass between 0.9 and 1.1 M⊕ and period between 1.85-2.05 years, corresponding to the center of the habitable zone for α Cen A. — [astro-ph.EP]
William Roberson, Eric L. Nielsen, Jessie L. Christiansen, Gautam Vasisht, Eduardo Bendek, Alex Davis, Eric E. Mamajek, Catherine A. Clark, Kaitlin M. Kratter, Juliette Becker, Michael R. Meyer
Comments: 21 pages, 13 figures. Submitted to AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2608.19444 [astro-ph.EP] (or arXiv:2608.19444v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2608.19444
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Submission history
From: Eric Nielsen
[v1] Wed, 19 Aug 2026 20:56:31 UTC (4,670 KB)
https://arxiv.org/abs/2608.19444
Astrobiology, exoplanet,
