Probabilistic Forecasting of the Masses and Radii of Other Worlds

Abstract

Mass and radius are two of the most fundamental properties of an astronomical object. Increasingly, new planet discoveries are being announced with a measurement of one of these terms, but not both. This has led to a growing need to forecast the missing quantity using the other, especially when predicting the detectability of certain follow-up observations. We present am unbiased forecasting model built upon a probabilistic mass-radius relation conditioned on a sample of 316 well-constrained objects. Our publicly available code, Forecaster, accounts for observational errors, hyper-parameter uncertainties and the intrinsic dispersions observed in the calibration sample. By conditioning our model upon a sample spanning dwarf planets to late-type stars, Forecaster can predict the mass (or radius) from the radius (or mass) for objects covering nine orders-of-magnitude in mass. Classification is naturally performed by our model, which uses four classes we label as Terran worlds, Neptunian worlds, Jovian worlds and stars. Our classification identifies dwarf planets as merely low-mass Terrans (like the Earth), and brown dwarfs as merely high-mass Jovians (like Jupiter). We detect a transition in the mass-radius relation at 2.0 +0.7 −0.6 M ⊕ , which we associate with the divide between solid, Terran worlds and Neptunian worlds. This independent analysis adds further weight to the emerging consensus that rocky Super-Earths represent a narrower region of parameter space than originally thought. Effectively, then, the Earth is the Super-Earth we have been looking for.

The California-Kepler Survey. V. Peas in a Pod: Planets in a Kepler Multi-planet System Are Similar in Size and Regularly Spaced*

“…Although there is large scatter in the planet masses with respect to these mean empirical relations Weiss & Marcy 2014;Rogers 2015;Wolfgang & Lopez 2015;Chen & Kipping 2017), we have no reliable basis for deciding which planet masses should be higher or lower than the mean, and so we adopt a simple one-to-one mapping of radius to mass. Furthermore, as the Hill radius scales as m 1/3 , uncertainties in the mass of order a few do not seriously affect the estimated mutual Hill radius.…”

The Dehydration of Water Worlds via Atmospheric Losses

“…Recent studies indicate that most super-Earths with radii 1.6R ⊕ are not typically rocky since they are volatile-rich planets (Rogers 2015); a stringent upper bound on the radius was also identified by Chen & Kipping (2017). The habitability of ocean planets has been extensively investigated, such as their interior structure and dynamics (Nettelmann et al 2011), mass-radius relationships (Benneke & Seager 2013), and atmospheric chemistry (Kaltenegger et al 2013;Goldblatt 2015).…”

The Moon Meets All Requirements of the IAU Definition for “Planet”

“…Star-like gas collapse mechanisms can form bodies below the deuterium burning limit, and bodies formed in a proto-planetary disk can exceed the deuterium burning limit [25]- [30]. Mass-radius and mass-density relationships from 0.3 to 60 Jupiter masses lack any distinguishing feature at 13 Jupiter masses to indicate any physical significance to deuterium burning [31] [32].…”