Temperate Earth-sized planets transiting a nearby ultracool dwarf star

Abstract

Stellar-like objects with effective temperatures of 2700K and below are referred to as “ultracool dwarfs”1. This heterogeneous group includes both extremely low-mass stars and brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion), and represents about 15% of the stellar-like objects in the vicinity of the Sun2. Based on the small masses and sizes of their protoplanetary disks3,4, core-accretion theory for ultracool dwarfs predicts a large, but heretofore undetected population of close-in terrestrial planets5, ranging from metal-rich Mercury-sized planets6 to more hospitable volatile-rich Earth-sized planets7. Here we report the discovery of three short-period Earth-sized planets transiting an ultracool dwarf star 12 parsecs away using data collected by the TRAPPIST8 telescope as part of an ongoing prototype transit survey9. The inner two planets receive four and two times the irradiation of Earth, respectively, placing them close to the inner edge of the habitable zone of the star10. Eleven orbits remain possible for the third planet based on our data, the most likely resulting in an irradiation significantly smaller than Earth's. The infrared brightness of the host star combined with its Jupiter-like size offer the possibility of thoroughly characterizing the components of this nearby planetary system.

Fast Litho-panspermia in the Habitable Zone of the TRAPPIST-1 System

“…The recently discovered TRAPPIST-1 system is particularly intriguing in this regard, as it consists of seven, nearly Earth-massed planets orbiting an M-type dwarf star. Three of those planets are believed to be within the habitable zone (HZ) and have rocky compositions (e.g., Gillon et al 2016Gillon et al , 2017. With orbital periods on order of days and orbital separations <0.01 AU, the transport of material between these planets may be more rapid and efficient than in the Earth-Mars case.…”

PREDICTIONS OF THE ATMOSPHERIC COMPOSITION OF GJ 1132b

“…For instance, water loss from the recently discovered TRAPPIST-1 system (Gillon et al 2016) was modeled by Bolmont et al (2016). As the host star is an ultra-cool dwarf and the planets therefore receive less total XUV flux, they may retain both massive water vapor and O 2 atmospheres, although conclusions must await both planet mass determinations, as well as detailed application of our model.…”

Astrometric Constraints on the Masses of Long-period Gas Giant Planets in the TRAPPIST-1 Planetary System

“…The detection of at first three (Gillon et al 2016), and then a total of at least seven exoplanets (Gillon et al 2017) orbiting the M8V dwarf TRAPPIST-1 (2M2306-05, 2MASS J23062928-0502285) has only added fuel to this race to discover and characterize potentially habitable exoplanets. Transit photometry has revealed that five of the seven known TRAPPIST-1 planets have radii and masses within factors of ∼ 1.1 and ∼ 2, respectively, of that of the Earth, and three of these appear to have stellar irradiation levels that might permit the existence of oceans of surface water, assuming Earth-like atmospheres (Gillon et al 2017).…”