Graduate student and astronomy writer

Entropy of planetary transits


During the Summer and Fall of 2014 I have been working with Dr. Jason Wright and Dr. Steinn Sigurdsson at PSU studying the entropy of planetary transit signals, particularly the oddball case of KIC-1255 and how it can be used to determine the SETI-like nature of these strange and varying transit signals. This work is still in progress and will be presented as a poster at the 225th AAS meeting in Seattle, WA in Jan. 2015.

Poster abstract:

This project aims to construct a robust information theoretic metric to quantify anomalous transit light curves and compare regular and irregular transits in a reproducible way. Using this metric we can distinguish natural transits from predicted extraterrestrial intelligence (ETI) communication that utilizes transiting mega-structures to alter the transit shape and depth in a measurable way. KIC-12557548b  (KIC-1255b) is such an anomalous planet, with highly variable consecutive transit depths and shapes that have been explained by Rappaport et al. (2012) and Croll et al. (2014) as due to a disintegrating sub-Mercury sized planet with a debris tail encompassing the planetary orbit. However, Arnold (2005) and later Forgan (2013) presented models showing that planet-sized, non-circular artificial structures transiting their host star could be identified as non-natural by light curves anomalous in their duration and asymmetry, as in the case of KIC-1255b. If such mega-engineering structures were able to alter their aspects on orbital timescales, the resulting transit depths could be used to transmit information at low bandwidth. We use KIC-1255b as a benchmark case for separating anomalous transit signals that resemble ETI predictions but are naturally occurring. To do this, we use the Kullback-Leibler (KL) divergence of the KIC-1255b transit depth time series to quantify the entropy of the dataset. We calibrate our relative entropy metric by calculating the KL divergence of the Kepler-5b transits, which are markedly constant compared to KIC-1255b. Artificially generated transit depth time series data using Arnold’s beacons allow us to calculate the KL divergence of predicted ETI communications and show that while the shape and depth variations of KIC-1255b might qualitatively resemble an Arnold beacon, the information content of its depth time series is far higher by our metric, consistent with a natural, turbulent origin. Thus we can use the entropy metric to test other cases of anomalous transits to separate out those transiting planets that can be explained through natural models and those for which an ETI hypothesis might be entertained.

AAS 225 Poster (not presented due to illness)


Relevant Papers:

Croll et al (2014): Multiwavelength Observations of the Candidate Disintegrating Sub-Mercury KIC 12557548b

Arnold (2005): Transit Light-curve Signatures of Artificial Objects

Forgan (2013): On the Possibility of Detecting Class A Stellar Engines using Exoplanet Transit Curves

Leave a Reply

Your email address will not be published. Required fields are marked *

Skip to toolbar