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A cost-effective search for extraterrestrial probes in the Solar system
Nordita SU, Stockholm University, Hannes Alfvéns väg 12, SE-106 91 Stockholm, Sweden.
Whitin Observatory, Dept. Physics & Astronomy, Wellesley College, 106 Central Street Wellesley, MA 02481, USA.
Instituto de Astrofísica de Canarias, Vía Láctea, E-38205 La Laguna, Tenerife, Spain.
Departamento de Astrofísica, Centro de Astrobiología (CSIC/INTA), P.O. Box 78, E-28691 Villanueva de la Cañada, Spain.
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2026 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 546, no 2, article id staf1158Article in journal (Refereed) Published
Abstract [en]

For centuries, astronomers have discussed the possibility of inhabited worlds-from Herschel’s 18th-century observations suggesting Mars may host life, to the systematic search for technosignatures that began in the 1960s using radio telescopes. Searching for artefacts in the Solar system has received relatively little formal scientific interest and has faced significant technical and social challenges. Automated surveys and new observational techniques developed over the past decade now enable astronomers to survey parts of the sky for anomalous objects. We briefly describe four methods for detecting extraterrestrial artefacts and probes within the Solar system and then focus on demonstrating one of these. The first makes use of pre-Sputnik images to search for flashes from glinting objects. The second method makes use of space-borne telescopes to search for artificial objects. A third approach involves examining the reflectance spectra of objects in Earth orbit, in search of the characteristic reddening that may imply long-term exposure of metallic surfaces to space weathering. We focus here on a fourth approach, which involves using Earth’s shadow as a filter when searching for optically luminous objects in near-Earth space. We demonstrate a proof-of-concept of this method by conducting two searches for transients in images acquired by the Zwicky Transient Facility, which has generated many repeated 30-s exposures of the same fields. In this way, we identified previously uncatalogued events at short angular separations from the centre of the shadow, motivating more extensive searches using this technique. We conclude that the Earth’s shadow presents a new and exciting search domain for near-Earth Searches for Extraterrestrial Intelligence.

Place, publisher, year, edition, pages
Oxford University Press (OUP) , 2026. Vol. 546, no 2, article id staf1158
Keywords [en]
extraterrestrial intelligence, minor planets, asteroids: general, surveys, Transients
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:kth:diva-377475DOI: 10.1093/mnras/staf1158ISI: 001676626100001Scopus ID: 2-s2.0-105029363292OAI: oai:DiVA.org:kth-377475DiVA, id: diva2:2042553
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QC 20260302

Available from: 2026-03-02 Created: 2026-03-02 Last updated: 2026-03-02Bibliographically approved

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Mattsson, Lars

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