The Breakthrough Listen Search for Intelligent Life: A 3.95-8.00 GHz Search for Radio Technosignatures in the Restricted Earth Transit Zone
Sofia Z. Sheikh · Andrew Siemion · J. Emilio Enriquez · Danny C. Price · Howard Isaacson · Matt Lebofsky · Vishal Gajjar · Paul Kalas
The Astronomical Journal · 2020
A 3.95–8.00 GHz narrowband search of 20 stars in the restricted Earth Transit Zone with the Green Bank Telescope found no technosignatures, constraining that at least 8% of rETZ systems within 150 pc lack transmitters detectable at this sensitivity.
Brief
Sheikh et al. (2020) used the Robert C. Byrd Green Bank Telescope under the Breakthrough Listen program to conduct 288-second ABABAB on-off observations of 20 K and G dwarf stars lying within the restricted Earth Transit Zone (rETZ), the 0.262°-wide band from which an observer would see Earth transit the Sun with an impact parameter under 0.5 solar radii. The turboSETI pipeline searched ±20 Hz/s drift rates at SNR ≥ 10 across 3.95–8.00 GHz, producing 425,168 raw hits that were filtered to 2,986 event-related hits for visual inspection. One candidate cluster on exoplanet host HIP 109656 survived initial cuts but was identified as anthropogenic RFI. The minimum detectable EIRP ranged from 47 GW at 7.4 pc (HIP 3765) to 18 TW at 143 pc (HIP 19054), bracketing 10⁻³ to 0.88 Arecibo-radar equivalents.
Metadata
- Category
- Search
- Venue
- The Astronomical Journal
- Type
- Peer-reviewed
- Year
- 2020
- Authors
- Sofia Z. Sheikh, Andrew Siemion, J. Emilio Enriquez, Danny C. Price, Howard Isaacson, Matt Lebofsky, Vishal Gajjar, Paul Kalas
- arXiv
- 2002.06162
- Access
- Open access
- Length
- 3.7 M
- Programs
- Breakthrough Listen
- Instruments
- Robert C. Byrd Green Bank Telescope, VEGAS spectrometer, turboSETI, BLIMPY
- Data sources
- Breakthrough Listen Public Data Archive (BLDR2), Gaia DR2
- Tags
- SETI, technosignature, radio astronomy, narrowband search, Earth Transit Zone, astrobiology
Key points
- First dedicated targeted SETI search of the restricted Earth Transit Zone, per authors' knowledge.p.1
- Sample: 20 main-sequence K and G dwarfs at distances 7.4–143 pc, selected from Heller & Pudritz (2016) to minimize distance while excluding confirmed binaries and a red giant.p.4
- Minimum detectable flux: 7.14 × 10⁻²⁶ W m⁻², derived using SNR threshold 10, 288 s integration, and 2.7 Hz frequency resolution on the GBT C-band receiver.p.4
- EIRP sensitivity span: 47 GW (nearest target, HIP 3765 at 7.4 pc) to 18 TW (furthest target, HIP 65642 at 137 pc), i.e., 0.001–0.88 × Arecibo radar EIRP.p.5
- turboSETI generated 425,168 hits above SNR 10; event filtering reduced these to 2,986 event-related hits, of which only 103 plots in four groups required detailed follow-up.p.8
- Sole candidate signal on HIP 109656, the only exoplanet host in the sample (1.6 R⊕ planet, 13-day period), was consistent with known anthropogenic RFI properties.p.1
- Statistical constraint: at least 8% of rETZ systems within 150 pc do not host high-duty-cycle narrowband transmitters at C-band detectable at this sensitivity.p.1
- Eight of 20 targets suffered shifted tunings during observation, reducing recorded bandwidth to ~5–8 GHz rather than the full 4–8 GHz.p.6
Verbatim
“We find no evidence for radio technosignatures from extraterrestrial intelligence in our observations.”
p.1“To our knowledge, this is the first targeted search for extraterrestrial intelligence of the restricted Earth Transit Zone.”
p.1“We conclude that at least 8% of the systems in the restricted Earth Transit Zone within 150 pc do not possess the type of transmitters searched in this survey.”
p.1“We find that a minimum transmitter EIRP of 47 GW would be required for a detection from the nearest star in the target list (HIP 3765) and a minimum of 18 TW would be required for a detection from the furthest star in the target list (HIP 65642).”
p.5“Once completed, this process created a list of 425168 detections above the SNR threshold, or "hits".”
p.8“The restricted Earth Transit Zone (rETZ) further limits this swath of the sky to a width of 0.262 ◦ to only include stars that see Earth transit less than 0.5 solar radii from the Sun's center”
p.2
Most interesting
- The only exoplanet host in the sample, HIP 109656, was also the only star to generate a candidate signal, a coincidence that did not survive RFI vetting.
- Ten of the 20 targets were close enough in angular separation to serve as each other's RFI off-sources, effectively doubling SETI yield per slew.
- The rETZ is geometrically motivated by game theory: ETIs residing there could detect Earth transits, observe humanity's ecliptic-directed radar, and also guess that we would preferentially transmit toward the ETZ.
- The C-band receiver was selected partly because it is comparatively underexplored in prior SETI programs relative to lower-frequency bands such as L and S.
- The drift-rate search range of ±20 Hz/s at these frequencies corresponds to normalized drift rates of 2.5–5 nHz, sufficient to detect a transmitter on any solar-system body including Io (2.39 nHz normalized).
- A luminosity-limited survey design, observing each target to the same transmitter-power threshold, would have required roughly 400 times more telescope time for the most distant stars than the nearest, making it operationally infeasible.