On December 19, 2025, 3I/ATLAS reached its closest distance to Earth, at 1.7 AU (167 million miles). To obtain optimum sensitivity, we observed 3I/ATLAS with the largest steerable single-dish radio telescope in the world, the 100-meter Green Bank Telescope, less than 24 hours before the closest approach of 3I/ATLAS, on December 18, 2025. We used four receivers (L, S, C, and X) spanning frequencies of 1 – 12 GHz. At closest approach, the GBT is sensitive to transmitters with an EIRP of approximately 0.1 W, more sensitive than all previous observations. No artificial radio emission localized to 3I/ATLAS was detected.

In summary, 3I/ATLAS continues to behave as expected from natural astrophysical processes. That said, it remains an extremely interesting target for observation given the overall rarity of interstellar objects. We will continue to observe 3I/ATLAS as a part of a broader strategy to thoroughly investigate all interstellar objects, consistent with our goal of conducting humanity’s most sensitive, intensive and comprehensive search for technosignatures.

Public data

Data from our radio observations require specialist software to analyze, including blimpy (loads data into Python) and turboSETI (searches the data for narrowband signals). Our data paper (Lebofsky et al. 2019) provides more information on the data format and contents for Green Bank and Parkes.

Data from the ATA are available here.

A 90 MB gzipped JSON file containing metadata for just over 2 million hits found during observations at MeerKAT in November is available.

Data from our three Murriyang observing sessions are publicly available (in subdirectories beginning “PKS”). Each session consists of a single cadence, consisting of three repeats of a Source/Reference cycle with 5 minutes on-target per pointing. Three data products are recorded by the Breakthrough Listen backend at Murriyang, a high spectral resolution SETI product, a high time resolution pulsar product, and an intermediate (spectral line) product. Data from the first observing session is recorded in full polarization whereas subsequent observations include total intensity only.

Spectrogram data (HDF5 format) from the GBT observations are publicly available (also in SETI, pulsar, and intermediate resolution products, total intensity only). One six-scan cadence (5 minutes per pointing) is available at each of L (scans numbered 0013 – 0018), S (scans 0029 – 0034), C (scans 0045 – 0050), and X (scans 0061 – 0066) bands. Raw voltage data are in the process of being transferred from Green Bank. Analysis of the GBT data with turboSETI showed no candidate technosignatures; a technical paper is available here.

Media inquiries

Email [email protected]

Originally published at https://www.physics.ox.ac.uk/research/group/breakthrough-listen/breakthrough-listen-observations-3iatlas and https://seti.berkeley.edu/atlas/