Talk abstracts and recordings are available here. All of our talks and posters are also available on our Zenodo Community, which provides DOIs and citations.
Monday Morning
Review: Exoplanetary SETI – Ravi Kopparapu
Detection of Industrial Compounds via Atmospheric Chemical Reaction Network Topology – Tessa Fisher
With spectral analysis of terrestrial exoplanets approaching on the near horizon, new tools are required to analyze the characteristics of these atmospheres. One approach is measuring the topology of the topology of the atmospheric chemical reaction network. Building on previous works using network topology to understand atmospheric disequilibria (Fisher et al 2022) and the interface between biospheres and atmospheres (Walker et al 2021), we propose modeling Earth-like atmospheres with and without the presence of industrial compounds. In particular, we will examine how atmospheric network topology is affected by the introduction of CFCs. This investigation may help identify spectral signatures that indicate the presence of CFCs indirectly and that are more easily detectable.
Technosignatures as a Path Towards Identifying Life Outside the Solar System – Thomas Beatty
The search for biosignatures on potentially habitable exoplanets has driven much of the recent planning in the exoplanet community for the next generation of space telescopes, and as our ability to characterize exoplanets improves, we also move closer to the direct detection of technosignatures on exoplanets. Though likely less common than biosignature signals, in many cases the clearly artificial nature of certain technosignatures would make their detection clearly indicative of life outside the Solar System. In the last few years serious thought has been given to the types of technosignatures one could reasonably expect to detect using current and next-generation observatories, giving a firm astrophysical foundation to this sub-field. I will summarize the immediate prospects for technosignature detection using JWST, and using a LUVOIR- or HabEx-like next generation space telescope. I will particularly focus on the possibilities of detecting industrial pollutants in exoplanet atmospheres, the emission from nightside city lights on exoplanets, and the spectroscopic signatures of advanced spaceflight. All three of these possible technosignatures now have detailed and physically-based expectations for their observability, and I will also discuss how non-detections can place meaningful upper limits on the frequency of technological life in the Solar Neighborhood.
An Archival Search for Technosignatures During Planet-Planet Occultations – Evan Sneed
Over the past decade, new survey programs have greatly increased the analyzed fraction of the cosmic haystack, largely by observing new target systems for longer using different frequencies of light. However, these surveys rarely consider when one should search, instead assuming that technosignatures are persistent and detectable over long time frames. Here, we present a method to search for “spillover” radio signals by identifying when two or more exoplanets are collinear with Earth. This scenario, known as a planet-planet occultation, can be modeled using N-body gravitational simulations for well-defined planetary systems. This method provides both a time and place to search for technosignatures, and is sensitive to both deliberate transmission attempts and communications not intended for Earth. Here, we present the results of an archival search of Breakthrough Listen data and introduce plans for a future observational campaign.
Monday Afternoon
Review: Laser and Radio SETI – Sofia Sheikh
Searches for electromagnetic transmissions from extraterrestrial agents (primarily in the optical and radio wavelengths) comprise the most well-developed sub-field within the SETI literature, both in theory and in observation. While the technosignature field has diversified in recent years, the rationale for radio and optical SETI remains extremely convincing, and recent projects have made huge strides in covering new parameter space. In this talk, I will cover the history of radio and optical SETI, the pros and cons of these techniques, current and near-future campaigns and instruments, and why transmission-based SETI is a necessary cornerstone of a well-rounded technosignature portfolio.
Tuesday Morning
On the Wide-Band and Broadband Radio Technosignature Searches with Breakthrough Listen – Vishal Gajjar
The search for extraterrestrial intelligence (ETI) at radio frequencies has largely been focused on continuous-wave narrowband signals. We demonstrate that different classes of wide-band and broadband pulsed beacons are energetically efficient compared to narrowband beacons over longer operational timescales. Searching for these unconventional signals enables us to constrain the existence of ETIs in proverbial multi-dimensional parameter space. These signal classes include wide-band periodic pulses akin to several powerful Earth-based air-traffic radars, 24 different types of wide-band signals with embedded modulations, and three different types of broadband signals with artificial dispersions. To scour for these 28 unique classes of signals, we have developed state-of-the-art search pipelines; leveraging advances made in the convolution/deep neural network classifiers and high-performance GPUs. We report on the first extensive survey for some of these signals towards 1883 stars in the solar neighborhood and in around half a million stars at the Galactic Center; utilizing around 250 hours of deep observations across 4 to 8 GHz using the Robert C. Byrd Green Bank Telescope as a part of the Breakthrough Listen program (Gajjar et al. 2021, 2022). Due to the absence of any signal-of-interest from our survey, we place a constraint on the existence of broadband beacons: < 1 in 1000 stars in the solar neighborhood (or in the spiral arm) and < 1 in half a million stars at the Galactic Center with broadband signal transmitter power densities of > 10^5 W/Hz and > 10^7 W/Hz, respectively. One of the major challenges in searching for these unconventional classes of signals from single dishes is the large number of false positives arising due to radio frequency interference. We will discuss how we are utilizing long-baselines of two widely-separated international LOw Frequency ARray (LOFAR) stations and band-limited spectral imaging of interferometers, such as the Giant Meterwave Radio Telescope (GMRT), to curb these challenges.
Technosignature Search with the Allen Telescope Array – Pranav Premanth – Given by Wael Farah
SETI surveys have been typically conducted at lower frequencies, i.e., less than 1.5 GHz. Utilizing the new hardware upgrades and the newly deployed Digital Signal Processing (DSP) backend of the Allen Telescope Array (ATA), we present an ongoing SETI survey of over 300 stars selected from the REsearch Consortium On Nearby Stars (RECONS) catalog, within 10 pc of the Earth. The ATA is a flexible 42-element interferometer located in Northern California, and the first instrument to be solely built to conduct SETI research. We perform observations of the selected stars between 3-10 GHz, with an instantaneous bandwidth of 1.4 GHz, using the newly commissioned beamformer. The output of the beamformer was analyzed using a high-resolution spectrometer and a de-doppler search algorithm, looking for narrow band signals over a wide range of drift-rates across all covered sub-bands. In this talk, I will present early results of the ongoing SETI survey, and the upgrades envisioned for the telescope’s frontend and backend.
Narrowband Signal Searches Towards the Galactic Plane and Center – Karen Perez
Over the last decade, discoveries of Earth-type exoplanets have extended the possibility of other life-bearing worlds. However, the question of the existence of intelligent life might remain elusive unless a dedicated attempt is made to extensively Search for Extraterrestrial Intelligence (SETI). The Breakthrough Listen (BL) program is a 10-year effort to conduct the most sensitive, comprehensive, and intensive search for advanced intelligent life on other worlds ever performed. Two of the primary targets of the BL program are the Galactic Center (GC) and a comprehensive blind survey of the entire Galactic Plane (GP) to search for artificial narrowband transmitters from ETIs. The line of sight toward the GC offers the largest integrated galactic star count of any direction in the sky, is a widely cited possible location for a beacon built by an advanced intelligence, and is the most energetic region in the Milky Way. Likewise, the GP is an ideal direction to search for such signals due to the increased likelihood that transmitters would emit toward this region as opposed to random directions. Here, I discuss our observation and narrowband search strategy, as well as results, for the Green Bank Telescope (GBT) (4-8 GHz) and Parkes Telescope (0.7-4 GHz) from our GC Survey so far. I also discuss an extension of these strategies for our GP Parkes 21cm Multibeam Receiver (1.2-1.55 GHz) Survey, which covers roughly 3000 square degrees during 1200 hours, were we have extended the multibeam coincidence rejection technique used for detecting Fast Radio Bursts to scrutinize narrowband signals detected across 13-beams. This allows us to discriminate terrestrial interferences from truly sky localized signals to help us reject large fractions of false positives. I will review our strategy and preliminary search results, as well as its applications going forward as we look towards expanding our search with other multibeam telescopes.
The SETI@home Candidate Pipeline – Eric Korpela
SETI@home observed the Arecibo sky for over 20 years looking for signs of extraterrestrial technology. We describe the SETI@home candidate selection pipeline and its use of realistic simulated signals to determine its sensitivity to real ETs. We discuss some of the best candidates. About 100 of the best candidates will be reobserved using the FAST 500-m radio telescope later this year.
Extragalactic SETI – Michael Garrett
The Breakthrough Listen Initiative has embarked on a comprehensive SETI survey of nearby stars in the Milky Way that is vastly superior to previous efforts as measured by a wide range of different metrics. SETI surveys traditionally ignore the fact that they are sensitive to many background objects, in addition to the foreground target star. In order to better appreciate and exploit the presence of extragalactic objects in the field of view, the Aladin sky atlas and NED were employed to make a rudimentary census of extragalactic objects that were serendipitously observed by the 100-m Greenbank telescope observing at 1.1-1.9 GHz. For 469 target fields (assuming a FWHM radial field-of-view of 4.2 arcminutes), NED identified a grand total of 143024 extragalactic objects, including various astrophysical exotica e.g. AGN of various type, radio galaxies, interacting galaxies, and one confirmed gravitational lens system. Several nearby galaxies, galaxy groups and galaxy clusters are identified, permitting the parameter space probed by SETI surveys to be significantly extended. New constraints are placed on the luminosity function of potential extraterrestrial transmitters and limits on the prevalence of very powerful extraterrestrial transmitters associated with these vast stellar systems are also determined. It is demonstrated that the recent Breakthrough Listen Initiative, and indeed many previous SETI radio surveys, place stronger limits on the prevalence of extraterrestrial intelligence in the distant Universe than is often fully appreciated.
Developing a Drift Rate Distribution for Technosignature Searches of Exoplanets – Megan Li
A stable-frequency transmitter with relative radial acceleration with respect to to a receiver will show a change in received frequency over time, known as a “drift rate”. If the transmitter is on an exoplanet, and the receiver on Earth, we must account for multiple components of drift rate: the orbit of the transmitter’s planet around its host star, the rotation of the transmitter’s planet, and the Earth’s planetary orbit and rotation, among other contributions. Understanding the drift rate distribution produced by planets in our galaxy, relative to Earth, can a) help us constrain which drift rates should be covered in a Search for Extraterrestrial Intelligence (SETI) project to detect radio technosignatures and b) help us determine the validity of signals-of-interest, as we can attempt to match any drifting signals that we detect with the expected distributions from the target star. In this project, we modeled the drift rate distribution for over 4000 confirmed exoplanets, using parameters from the NASA Exoplanet Archive (NEA). We find that the confirmed exoplanets have a drift rates distribution such that 99% of them fall within the ± 45 nHz range. This implies a distribution-informed maximum drift rate ∼ 4 times lower than previous work. However, we know that the planetary sample in the NEA is subject to observational biases. Therefore, we also simulated an exoplanet population built to reduce these biases, based on recent exoplanet population literature. The results suggest that, for a target star without known exoplanets, ± 1 nHz would be sufficient to account for 99% of signals. This huge reduction in recommended maximum drift rate is partially due to inclination effects, and partially due to bias from the exoplanetary period. The narrowed drift rate maxima from both the NEA and the simulated population will increase the efficiency of searches and save significant computational effort in future radio technosignature searches.
Tuesday Afternoon
Search for Extra-terrestrial intelligence (SETI) using COSMIC: An Ethernet based Multi-user Commensal Observing System with the Very Large Array (VLA) – Savin Varghese
The search for technosignatures addresses one of the most profound questions humanity has ever asked: Are we alone in this universe as an intelligent species? Searching for technosignatures is extremely challenging as it requires exploring the vast SETI parameter space and the searches so far have covered only a tiny fraction of this space. In order to explore this parameter space better, the SETI Institute is collaborating with the National Radio Astronomy Observatory (NRAO) to build a new commensal observing system with the VLA radio telescope in New Mexico. The new commensal observing system is known as COSMIC – Commensal Open Source Multimode Interferometer Cluster. COSMIC takes advantage of the multicasting Ethernet protocol allowing multiple subscribers to access the data simultaneously, and thus achieving different science goals. In the COSMIC architecture, the data streams from the VLA antennas are split before going to the VLA correlator (WIDAR) and an independent copy is sent to an FPGA hardware. The data in FPGAs are channelized and re-transmitted as ethernet packets to a CPU/GPU based compute cluster using a network switch, where further processing takes place. This will enable COSMIC access to the continuous VLA data streams and act as a parallel digital backend for SETI searches.
COSMIC is planning to conduct its first SETI survey during the third epoch of the VLA Sky Survey (VLASS) scheduled in January 2023. The VLASS is a fast sky scan survey covering the entire Northern hemisphere above a declination of -40 degrees. This will enable COSMIC to observe 40 million stars in the first 2 years of operation, with a wide range of frequencies (74 MHz – 50 GHz), and at a sensitivity good enough to detect an Arecibo-like transmitter at a distance of 25 pc from Earth. In this talk, we will focus on the recent developments of COSMIC and the planned SETI survey to conduct one of the most comprehensive searches for technosignatures.
On the Importance of Field-of-View for Detection Rate in RF SETI – Ken Houston
A recent paper [1] developed a model for detection rate in radio SETI, defined as the expected number of ET detections per year of observation, and abbreviated “DPY”. The number of detections will be proportional to the number of stars within a “detection cone” with a height defined by the detection range (a function of sensitivity, source power, and averaging parameters) and an angular breadth defined by the receiver field-of-view (FOV). While improving detection range is often difficult, FOV expansion in arrays can usually be achieved by scaling computation, and is aided by Moore’s Law. Since FOV follows an inverse square of frequency, lower frequencies should be favored in general. In the paper, DPY was compared for a wide range of existing and proposed radio telescopes, with perhaps surprising results. Large single-pixel dishes have the worst DPY values, as high sensitivity cannot make up for limited FOV.
It is important for SETI researchers to understand detection rate challenges in order to maximize their chances of success. In this talk, the detection rate model will be described. To aid understanding, a simple 2-D analog involving a lighthouse with a rotating observer will be introduced. Metrics for search quality, including a revised “Haystack Function”, will also be discussed.
[1] K.M. Houston, A.P.V. Siemion, and S. Croft , “Strategies for Maximizing Detection Rate in Radio SETI”, The Astronomical Journal, 162:151, October 2021.
Review: Social Sciences & SETI – Rebecca Charbonneau
The Drake Equation and the Search for Life in the Galaxy through Indigenist Lenses – Hilding Neilson
So much of the modern search for life in beyond our Solar System is motivated by the interpretation of the Drake Equation. However, much of this discourse has arisen with colonial and Eurocentric biases that limit the interpretation of the various terms of the equation. In this talk, I will present an Indigenist view of the Drake Equation and show that this perspective leads to a significantly different view of life in the Galaxy. I will also show that this perspective suggests that the current binary discussion of bio-signatures and techno-signatures in the search for intelligent life can be very limiting.
Is There a Moral Difference Between Messaging and Mere Detectability? – Chelsea Haramia
Messaging ExtraTerrestrial Intelligence (METI) is one way to conduct the Search for ExtraTerrestrial Intelligence (SETI). Messaging is the act of intentionally attempting communication with ETI. But other, unintentional signals—such as Earth’s biosignatures or humans’ planetary radar—may be detectable at interstellar distances and carry with them the potential to successfully communicate information to ETI. One potential justification for messaging involves the claim that it is effectively indistinguishable from, and thereby morally equivalent to, other merely-detectable signaling. We explore this reasoning alongside current scientific data on questions of detectability, and we evaluate candidate responses that appeal to the claim that there is a morally-relevant difference between messaging and mere detectability.
The Breakthrough Listen Initiative – Pete Worden
Wednesday Morning
Review: Waste Heat and Megastructures – Macy Huston
A Search for Dyson Spheres Using Space-Based Photometric Surveys – Matias Suazo
The search for intelligent life beyond Earth represents one of the most captivating quests that humanity has ever undertaken. In addition to the signal-based SETI strategy, there are strategies to search for indirect signs of extraterrestrial technology. A reasonably generic expectation is that technologically advanced civilizations would ultimately strive to overcome the resource limitations of their home planet. One way of doing this would be to tap into the radiation energy of one’s host star by constructing a so-called Dyson sphere – a structure or suite of structures that absorb some fraction of the photons that the star would otherwise radiate into interstellar space. As in any thermodynamic process, the conversion of stellar energy would involve the emission of waste heat emitted as infrared radiation that can serve as a signature of its existence. On the other hand, these “partial” Dyson spheres would block some of their host stellar light, leading to a drop in their optical fluxes. Nowadays, we count on missions that have mapped the sky in the optical and infrared, specifically Gaia, 2MASS, and WISE. We use this data to create a family of Dyson sphere models, i.e., models with different temperatures and covering factors. Then, we compare these models with stars with the best photometry in our vicinity of 300 pc to seek resemblances to create a candidates list that will undergo follow-up observations. Additionally, we compare the spectral energy distribution of our models with that of potential interlopers, such as Pre-main sequence stars
Review: Solar System SETI – Joseph Lazio
NASA has five robotic space probes on escape trajectories from the solar system (Pioneer 11, Pioneer 12, Voyager 1, Voyager 2, and New Horizons), and the Interstellar Probe is a concept likely to be submitted for consideration in the forthcoming Solar & Space Physics Decadal Survey. While none of these robotic probes will be operational on the time scale that it would take to reach another star, it is natural to ask whether another civilization might also be sending out interstellar probes. Serious consideration of such interstellar probes dates at least to R. Bracewell in the early 1960s, and the discovery of 1I/2017 ‘Oumuamua has rekindled some of that interest.
I consider what limits exist on signatures of extraterrestrial technology might be present in the Solar System, considering both objects on various orbits (“probes”) and surface artifacts, using data available from planetary exploration and astronomical sky surveys. Perhaps not surprisingly, the completeness to which the Solar System has been searched varies as a function of distance from the Sun. However, with notable exceptions, only extremely crude limits can be placed on the existence of interstellar probes. I also highlight areas that might be profitable for improving these limits considerably.
A Radio Search for Artifacts at a Focal Point of the Solar Gravitational Lens – Nick Tusay
Through gravitational lensing, stars can be used to transmit and receive signals with high gain over interstellar distances. Extraterrestrial Intelligences may be utilizing this strategy to setup an interstellar communication network, which may include our Sun. We demonstrate a wide bandwidth search using the Breakthrough Listen (BL) backend at Green Bank Telescope (GBT) for radio transmissions from a relay at the focal point of the solar gravitational lens (≥550 AU) targeting a nearby star system, Alpha Centauri. Utilizing the turboSETI software developed by BL, we found no technological signals of non-human origin within our observations in the L and S bands. Assuming a conservative gain of 1000 in L band and roughly 4 times that in S band, a directed transmitter roughly 1 meter in diameter would be detectable by our search above 7 W at 550 AU or 23 W at 1000 AU in L band, and above 2 W at 550 AU or 7 W at 1000 AU in S band. As an ancillary objective, analysis of our off-target pointing containing the star HD 13908 also yielded no positive detections. Our work concludes with a discussion on applying this search method to other targets and frequencies.
Wednesday Afternoon
Review: SETI Theory – David Kipping
How Might Technologically Advanced Civilization Spread Through the Galaxy – Jonathan Carroll-Nellenback
We model the settlement of the galaxy by space-faring civilizations of varying levels of technological sophistication in order to understand how the local density of habitable worlds (as well as mean civilization lifetimes) might effect the level of technological sophistication in various regions of the galaxy. We model the technological development of a civilization to be an Ornstein-Uhlenbeck (OU) process and tie the level of technology to the range of interstellar travel. We find that the level of technological sophistication tends to evolve (when possible) to one necessary to maintain modest levels of settlement. We interpret this as a balance of selection pressure and the tendency of the technology to revert to the mean. This might indicate more advanced civilizations to likely exist near the periphery of the galaxy where advanced technology is needed to colonize neighboring systems.
Thursday Morning
Searching the SETI Ellipsoid with Gaia and TESS – James Davenport
The SETI Ellipsoid is a geometric method for prioritizing technosignature observations, based on a strategy of receiving signals synchronized to conspicuous astronomical events. Precise distances to nearby stars from Gaia makes constraining Ellipsoid crossing times possible. We use the Gaia Catalog of Nearby Stars to identify targets intersecting the SN 1987A SETI Ellipsoid, as well the Ellipsoids defined by 278 classical novae. Less than 8% of stars within the 100 pc sample are inside the SN 1987A SETI Ellipsoid, meaning the vast majority of nearby stars are still viable targets to monitor for coordinated signals! We find an average of 734 stars per year within the 100 pc volume will intersect the Ellipsoid from SN 1987A, with ~10% of those having distance uncertainties from Gaia better than 0.1 lyr. Finally I will discuss how this framework can be implemented with surveys like TESS and eventually LSST.
Simulation of the Earth Radio-leakage from mobile towers as seen from selected nearby stellar systems – Ramiro Saide
Mobile communication towers represent a relatively new but important contributor to the total radio leakage associated with planet Earth. We investigate the overall power contribu- tion of mobile communication towers to the Earth’s radio leakage, as seen from a selection of different habitable exo-planets. We made use of publicly available Geo-location data of mobile towers from the the world’s largest Open Database of GPS Cell Towers (OpenCelliD). The free and open source Qgis software was also used to create, edit, visualize, and analyze the geo-spacial information. We created a model of the total mobile tower radio leakage by gridding the surface of the planet into small, computationally manageable regions, assuming a simple integrated transmission pattern for the mobile antennas. In this model, these mobile tower regions rise and set as the Earth rotates. In this way, a dynamic power spectrum of the Earth was determined, summed over all cellular frequency bands. We calculated this dynamic power spectrum from four different viewing points – Barnard’s star, HD 95735 star and, Alpha Centauri A. Our preliminary results demonstrate that the peak power leaking into space from mobile towers is ∼ 4GW and this is associated with Western Europe. This leaks in the direction of HD 95735 star and corresponds to LTE mobile towers technology. The second most powerful leakage emission comes from West of Asia and Central Europe, following East of Africa and Australia, with power levels of 3.5 GW. We demonstrate that the mobile tower leakage is periodic, direction dependent, and that these could not be detected by a nearby civilisation located within 10 light years of the Earth, using instrumentation with a sensitivity similar to the Green Bank Telescope. With this model, we intend to expand our simulations to include anticipated 5G mobile systems, radar installations, ground based up-links (including the Deep Space Network), and various types of satellite services, including low-Earth orbit constellations such as the Starlink and OneWeb.
Technosignatures Gap List Study – Virisha Timmaraju
Motivation and Objective: The ExEP (Exoplanet Exploration Program) is a program within NASA’s Astrophysics Division whose charter includes identification and development of key technologies to enable the discovery of habitable worlds. We are following up on the 2018 NASA Technosignatures (TS) Workshop report to inform the ExEP with a thorough survey of TS search approaches and to identify their specific technology needs. The final product will be a peer-reviewed, regularly updated database informing the ExEP and will be publicly available to the TS community.
Approach: A survey of the TS literature for a complete list of search strategies will be conducted by reaching out to experts for detailed input. We will then identify Descriptors and Assessors to characterize the TS search approaches. Descriptors provide information describing the TS search approach. Assessors are factors such as potential figures of merit and technology needs. Next, we will prioritize the TS search techniques using a set of acceptable community criteria. Finally, a complete data capture including technology needs as well as other needs such as facilities, AI/ML will be performed. A panel of community experts will be assembled to independently review and provide feedback on all of the survey milestones.
Status: We developed a list of potential users and information they might be interested in within this gap list. The purpose of this list is to aid with the development of descriptors and assessors that would benefit various kinds of users. A diverse panel of community experts has been assembled. A list of data fields and their definitions have been finalized based on reviews from the community experts. We have compiled a list of potential extraterrestrial activities and associated TS approaches.