Different Is More: The Value of Finding an Inhabited Planet That Is Far from Earth2.0

Abstract

The search for an inhabited planet, other than our own, is a driver of planetary exploration in our solar system and beyond. Using information from our own planet to inform search strategies allows for a targeted search. It is, however, worth considering some span in the strategy and in a priori expectation. An inhabited, Earth-like planet is one that would be similar to Earth in ways that extend beyond having biota. To facilitate analysis, we employ a metric akin to the Earth-similarity index of Schulze-Makuch et al. [2011]. The metric extends from zero, for an inhabited planet that is like Earth in all other regards (i.e., zero differences), toward end-member values for planets that differ from Earth but maintain life potential. The analysis shows how finding inhabited planets that do not share all other Earth characteristics could improve our ability to assess galactic life potential without a large increase in time-commitment costs. Search strategies that acknowledge the possibility of such planets can also minimize the potential of exploration losses (e.g., searching for long durations to reach conclusions that are search strategy biased). Discovering such planets could additionally provide a test of the Gaia hypothesis -a test that has proved difficult using only the Earth as a laboratory. Lastly, we discuss how an Earth2.0 narrative that has been presented to the public as a search strategy comes with nostalgia-laden philosophical baggage that does not best serve exploration.

Habitability: a process versus a state variable framework with observational tests and theoretical implications

“…We have argued that future observations of exoplanets can discriminate between competing hypotheses as to the type of variable habitability is. This will require search strategies that come with higher, but not inordinate, cost (Bean et al 2017; Walker et al 2018; Checlair et al 2019; Lenardic and Seales 2019). The goal is to map distributions.…”

“…Discriminating between a state versus a process hypothesis of habitability will require determining if the population of such planets follows a unimodal or a bimodal distribution in terms of observables that connect to temperate surface conditions. The number of observations needed is difficult to pre-specify but, as a rule of thumb, a minimum of 30 planets would need to be characterized (Hogg and Tanis 1997; Lenardic and Seales 2019). In terms of assessing the number of observations needed, the distinction between a bimodal distribution and a unimodal distribution with outliers should be kept in mind.…”

Assessing the Intrinsic Uncertainty and Structural Stability of Planetary Models: 1. Parameterized Thermal‐Tectonic History Models

“…If probability distributions are determined for observations and for models, this opens the path to use, for example, Bayesian analysis to provide well‐defined confidence levels for planetary life potential under a range of potential scenarios (e.g., Walker et al, ). This approach becomes most effective if exoplanet search strategies are designed with statistical analysis in mind (e.g., Lenardic & Seales, ).…”

On the Rate of Abiogenesis from a Bayesian Informatics Perspective

“…This is because for certain choices of the prior, the early start to life on Earth leads to a expectation that all Earth-like planets are inhabited, thus new detections don't significantly affect the posterior. As highlighted earlier though, clearly such a result could be greatly informative if the sample is extended beyond Earth-like worlds to include more exotic locations, echoing the conclusion of Lenardic et al (2018) but for different reasons. Second, we have ignored the possibility of a successful laboratory abiogenesis in this work and instead assumed they only yield null-results and thus an upper limit on λ.…”