A Radio Technosignature Search of TRAPPIST-1 with the Allen Telescope Array (2409.08313v1)

Abstract: Planet-planet occultations (PPOs) occur when one exoplanet occults another exoplanet in the same system as seen from the Earth's vantage point. PPOs may provide a unique opportunity to observe radio "spillover" from extraterrestrial intelligences' (ETIs) radio transmissions or radar being transmitted from the further exoplanet towards the nearer one for the purposes of communication or scientific exploration. Planetary systems with many tightly packed, low-inclination planets, such as TRAPPIST-1, are predicted to have frequent PPOs. Here, the narrowband technosignature search code turboSETI was used in combination with the newly developed NbeamAnalysis filtering pipeline to analyze 28 hours of beamformed data taken with the Allen Telescope Array (ATA) during late October and early November 2022, from 0.9--9.3~GHz, targeting TRAPPIST-1. During this observing window, 7 possible PPO events were predicted using the NbodyGradient code. The filtering pipeline reduced the original list of 25 million candidate signals down to 6 million by rejecting signals that were not sky-localized and, from these, identified a final list of 11127 candidate signals above a power law cutoff designed to segregate signals by their attenuation and morphological similarity between beams. All signals were plotted for visual inspection, 2264 of which were found to occur during PPO windows. We report no detection of signals of non-human origin, with upper limits calculated for each PPO event exceeding EIRPs of 2.17--13.3 TW for minimally drifting signals and 40.8--421 TW in the maximally drifting case. This work constitutes the longest single-target radio SETI search of TRAPPIST-1 to date.

• The paper demonstrates a novel technosignature search by targeting narrowband emissions during planetary occultations in the TRAPPIST-1 system.
• It applies a combined methodology using the ATA, NbodyGradient predictions, and turboSETI analysis to screen over 11,000 candidate signals.
• Despite severe RFI challenges, the study establishes upper EIRP limits (2.17–421 TW) and highlights the need for improved signal-processing techniques in SETI.

A Radio Technosignature Search of TRAPPIST-1 with the Allen Telescope Array

This academic essay provides a detailed summary of the radio technosignature search conducted on the TRAPPIST-1 exoplanetary system using the Allen Telescope Array (ATA). The research focuses on the detection of narrowband radio signals, potentially indicative of extraterrestrial intelligence (ETI) within a tightly-packed planetary system exhibiting planet-planet occultations (PPOs). The outcomes and theoretical implications of these observations are discussed below.

The paper targets TRAPPIST-1, a well-characterized M-dwarf star system known to host seven transiting planets. Configured in a nearly edge-on alignment from Earth's vantage point, this system presents frequent PPO opportunities. The motivation behind focusing on PPOs is to potentially capture radio "spillover" from ETIs' communications beyond the line-of-sight, as such signals might extend beyond their intended planetary target and propagate toward Earth.

Methodology and Observations

The ATA was utilized to perform 28 hours of radio observations covering a frequency range between 0.9 and 9.3 GHz. The technosignature search involved predicting PPO events using the NbodyGradient code and analyzing the data with turboSETI, an open-source de-Doppler algorithm that searches for drifting narrowband signals in spectral data. The filtering framework incorporated an innovative approach involving NbeamAnalysis, which applies spatial filtering and evaluates the correlation of signals between beams using DOT scoring and SNR-ratio calculations.

Results and Analysis

The analysis revealed a dense environment of radio frequency interference (RFI), primarily locally sourced on Earth, complicating the identification of extraterrestrial technosignatures. The filtering process culminated in retaining approximately 11,127 candidate signals for visual inspection, of which 2,264 coincided with PPO event windows, but did not conclusively indicate non-human origin.

No narrowband radio signals attributable to ETIs were detected, leading to upper limits on detectable Equivalent Isotropic Radiated Power (EIRP) for transmissions from TRAPPIST-1, benchmarked against Earth-analogous deep space network transmissions. EIRP constraints ranged from 2.17 to 421 terawatts, depending on drift rates and other parameters.

Implications and Future Prospects

From a practical perspective, the research highlights the need for improved RFI mitigation techniques, potentially involving machine learning strategies to discern genuine extraterrestrial signals obscured by terrestrial interference. The current limitations of turboSETI in dealing with broadband RFI demonstrate potential areas for algorithm refinement, particularly in addressing frequency binning challenges at higher drift rates.

Despite the null results concerning ETI signals, the data acquired offers valuable insights into the efficacy of PPO-centric observations and the dynamic variability inherent in RFI environments. It also sets a precedent for employing predictive models in optimizing observation schedules for future radio technosignature searches, particularly with upcoming observatories like the Square Kilometer Array that promise heightened sensitivity and longer observation durations.

In conclusion, while the search using the ATA yielded no definitive technosignature detections from the TRAPPIST-1 system, it underscores the significance of refined methodologies and advanced signal-processing techniques in SETI. With advancements in computing and data analysis, further research will continue to explore the cosmic possibility of detecting interstellar communications.