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Assessing planetary complexity and potential agnostic biosignatures using epsilon machines

Bartlett, Stuart and Li, Jiazheng and Gu, Lixiang and Sinapayen, Lana and Fan, Siteng and Natraj, Vijay and Jiang, Jonathan H. and Crisp, David and Yung, Yuk L. (2022) Assessing planetary complexity and potential agnostic biosignatures using epsilon machines. Nature Astronomy, 6 (3). pp. 387-392. ISSN 2397-3366. doi:10.1038/s41550-021-01559-x.

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We present a new approach to exoplanet characterization using techniques from complexity science, with potential applications to biosignature detection. This agnostic method makes use of the temporal variability of light reflected or emitted from a planet. We use a technique known as epsilon machine reconstruction to compute the statistical complexity, a measure of the minimal model size for time series data. We demonstrate that statistical complexity is an effective measure of the complexity of planetary features. Increasing levels of qualitative planetary complexity correlate with increases in statistical complexity and Shannon entropy, demonstrating that our approach can identify planets with the richest dynamics. We also compare Earth time series with Jupiter data, and find that for the three wavelengths considered Earth’s average complexity and entropy rate are approximately 50% and 43% higher than Jupiter’s, respectively. The majority of schemes for the detection of extraterrestrial life rely upon biochemical signatures and planetary context. However, it is increasingly recognized that extraterrestrial life could be very different from life on Earth. Under the hypothesis that there is a correlation between the presence of a biosphere and observable planetary complexity, our technique offers an agnostic and quantitative method for the measurement thereof.

Item Type:Article
Related URLs:
URLURL TypeDescription ReadCube access ItemC++ code for the EMR process Paper
Bartlett, Stuart0000-0001-5680-476X
Li, Jiazheng0000-0002-2563-6289
Gu, Lixiang0000-0002-3089-3706
Sinapayen, Lana0000-0003-2270-2954
Fan, Siteng0000-0002-3041-4680
Natraj, Vijay0000-0003-3154-9429
Jiang, Jonathan H.0000-0002-5929-8951
Crisp, David0000-0002-4573-9998
Yung, Yuk L.0000-0002-4263-2562
Additional Information:© The Author(s), under exclusive licence to Springer Nature Limited 2022. Received 26 December 2020. Accepted 12 November 2021. Published 07 February 2022. We acknowledge partial funding support from the NASA Exoplanet Research Program NNH18ZDA001N-2XRP. A portion of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA (80NM0018D0004). Y.L.Y. was supported in part by an NAI Virtual Planetary Laboratory grant from the University of Washington. We thank the members of the Caltech GPS ‘Astrobiothermoevoinfo’ reading group for the various inspiring discussions that have helped catalyse ideas such as those presented here. We also thank T. Ewald at Caltech for valuable help with the processing of Jupiter data from Cassini. Finally, S.B. thanks S. Bullock for being his guide into the world of complexity. Contributions. S.B. conceived of the idea of using EMR to analyse planetary complexity and the hypothesized correlation between planetary complexity and the presence of life. He performed the complexity analysis, produced the figures and wrote the manuscript. J.L. provided the Jupiter Cassini data. L.G. and S.F. produced the synthetic Earth and recomposed datasets. L.S. assisted with the complexity analysis, results interpretation, literature review and manuscript editing. V.N. assisted with results interpretation and manuscript editing. J.H.J., D.C. and Y.L.Y. provided essential guidance, assistance with data provision, results interpretation and manuscript editing. Data availability. Source data for all time series as well as the data points in the figures in the main text are provided with this paper. Code availability. C++ code for the EMR process used in this study can be accessed here: The authors declare no competing interests. Peer review information. Nature Astronomy thanks Cole Mathis and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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University of WashingtonUNSPECIFIED
Subject Keywords:Astrobiology; Exoplanets; Information theory and computation; Time-domain astronomy
Issue or Number:3
Record Number:CaltechAUTHORS:20220208-948270000
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Official Citation:Bartlett, S., Li, J., Gu, L. et al. Assessing planetary complexity and potential agnostic biosignatures using epsilon machines. Nat Astron 6, 387-392 (2022).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113335
Deposited By: George Porter
Deposited On:08 Feb 2022 20:21
Last Modified:17 May 2022 17:57

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