Developing a Drift Rate Distribution for Technosignature Searches of Exoplanets

Abstract:

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.