Millimetre/Sub-Millimetre SETI: Expanding the Radio Technosignature Parameter Space with ALMA2040
Abstract
The search for extraterrestrial intelligence (SETI) has been largely concentrated at centimetre wavelengths, and in particular in the 'water hole' (1.42-1.66 GHz) range. The millimetre and sub-millimetre sky is, by contrast, almost entirely unsearched. It also offers some natural advantages: above 35 GHz, the interstellar and interplanetary media are effectively transparent and non-dispersive, terrestrial interference is sparse, and interferometry suppresses what interference remains. Both antenna gain and usable fractional bandwidth increase with frequency, so a civilisation optimising directed, high-data-rate links has advantageous reasons to operate in this regime, as illustrated by the ongoing migration of our own telecommunications systems to much higher frequencies. Building on the first ALMA technosignature survey (Mason et al. 2025), we identify four searches ALMA2040 is uniquely placed to make: (i) narrowband searches using a phased-up, beamformed array, extending the commensal model pioneered for the VLA and MeerKAT into a regime where drift rates reach ~ 103 Hz s^-1; (ii) broadband aggregate leakage (BRaTs) from Kardashev Type I civilisations, for which 128-512 GHz of instantaneous bandwidth places a ~ 60 pc horizon within an integration time of one hour on source; (iii) Dysonian searches for the cold waste heat of computation - Slysh haloes - whose arcsecond and subarcsecond angular scales around M dwarfs are well matched to ALMA2040's array configuration; and (iv) geometric discontinuities imprinted by occulting megastructures, detectable as ringing in the visibility function with a phased ALMA operating in a mm/sub-mm VLBI array. We set out the corresponding requirements: bandwidth, beamforming, commensal access, spectral resolution and sub-second time resolution.
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BibTeX
@misc{mason2026millimetresubmillimetre,
title = {{Millimetre/Sub-Millimetre SETI: Expanding the Radio Technosignature Parameter Space with ALMA2040}},
author = {Louisa A. Mason and Michael A. Garrett and Sofia Z. Sheikh and Kelvin Wandia and Anita M. S. Richards and Vishal Gajjar and Chenoa D. Tremblay and Andrew P. V. Siemion},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.22266},
eprint = {2610.22266},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.22266},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Millimetre/Sub-Millimetre SETI: Expanding the Radio Technosignature Parameter Space with ALMA2040
AU - Louisa A. Mason
AU - Michael A. Garrett
AU - Sofia Z. Sheikh
AU - Kelvin Wandia
AU - Anita M. S. Richards
AU - Vishal Gajjar
AU - Chenoa D. Tremblay
AU - Andrew P. V. Siemion
PY - 2026
DA - 2026/10/15
PB - arXiv
DO - 10.48550/arxiv.2610.22266
UR - https://arxiv.org/abs/2610.22266
AB - The search for extraterrestrial intelligence (SETI) has been largely concentrated at centimetre wavelengths, and in particular in the 'water hole' (1.42-1.66 GHz) range. The millimetre and sub-millimetre sky is, by contrast, almost entirely unsearched. It also offers some natural advantages: above 35 GHz, the interstellar and interplanetary media are effectively transparent and non-dispersive, terrestrial interference is sparse, and interferometry suppresses what interference remains. Both antenna gain and usable fractional bandwidth increase with frequency, so a civilisation optimising directed, high-data-rate links has advantageous reasons to operate in this regime, as illustrated by the ongoing migration of our own telecommunications systems to much higher frequencies. Building on the first ALMA technosignature survey (Mason et al. 2025), we identify four searches ALMA2040 is uniquely placed to make: (i) narrowband searches using a phased-up, beamformed array, extending the commensal model pioneered for the VLA and MeerKAT into a regime where drift rates reach ~ 103 Hz s^-1; (ii) broadband aggregate leakage (BRaTs) from Kardashev Type I civilisations, for which 128-512 GHz of instantaneous bandwidth places a ~ 60 pc horizon within an integration time of one hour on source; (iii) Dysonian searches for the cold waste heat of computation - Slysh haloes - whose arcsecond and subarcsecond angular scales around M dwarfs are well matched to ALMA2040's array configuration; and (iv) geometric discontinuities imprinted by occulting megastructures, detectable as ringing in the visibility function with a phased ALMA operating in a mm/sub-mm VLBI array. We set out the corresponding requirements: bandwidth, beamforming, commensal access, spectral resolution and sub-second time resolution.
ER -