Transit surveys for Earths in the habitable zones of white dwarfs

TL;DR

This paper proposes expanding the search for habitable Earth-like planets to white dwarfs, highlighting their potential for detection via transits and outlining a survey strategy using ground-based and LSST telescopes.

Contribution

It introduces the concept of habitable zones around white dwarfs and suggests a feasible survey method for detecting Earth-like planets in these zones.

Findings

White dwarf habitable zones extend from ~0.005 to 0.02 AU.

White dwarf transits by terrestrial planets are detectable with ground-based telescopes.

A survey could constrain the frequency of habitable Earths around white dwarfs.

Abstract

To date the search for habitable Earth-like planets has primarily focused on nuclear burning stars. I propose that this search should be expanded to cool white dwarf stars that have expended their nuclear fuel. I define the continuously habitable zone of white dwarfs, and show that it extends from ~0.005 to 0.02 AU for white dwarfs with masses from 0.4 to 0.9 solar masses, temperatures less than 10,000 K, and habitable durations of at least 3 Gyr. As they are similar in size to Earth, white dwarfs may be deeply eclipsed by terrestrial planets that orbit edge-on, which can easily be detected with ground-based telescopes. If planets can migrate inward or reform near white dwarfs, I show that a global robotic telescope network could carry out a transit survey of nearby white dwarfs placing interesting constraints on the presence of habitable Earths. If planets were detected, I show that the survey would favor detection of planets similar to Earth: similar size, temperature, rotation period, and host star temperatures similar to the Sun. The Large Synoptic Survey Telescope could place even tighter constraints on the frequency of habitable Earths around white dwarfs. The confirmation and characterization of these planets might be carried out with large ground and space telescopes.