One of the big arguments against habitable planets around low mass stars like red dwarfs is the likelihood of tidal effects. An Earth-sized planet close enough to a red dwarf to be in its habitable zone should. the thinking goes, become tidally locked, so that it keeps one face toward its star at all times. The question then becomes, what kind of mechanisms might keep such a planet habitable at least on its day side, and could these negate the effects of a thick dark-side ice pack? Various solutions have been proposed, but the question remains open. A new paper from Jérémy Leconte (Canadian Institute for Theoretical Astrophysics, University of Toronto) and colleagues now suggests that tidal effects may not be the game-changer we assumed them to be. In fact, by developing a three-dimensional climate model that predicts the effects of a planet's atmosphere on the speed of its rotation, the authors now argue that the very presence of an atmosphere can overcome tidal...

A small satellite designed to study and characterize exoplanet atmospheres is being developed by University College London (UCL) and Surrey Satellite Technology Ltd (SSTL) in the UK. Given the engaging name Twinkle, the satellite is to be launched within four years into a polar low-Earth orbit for three years of observations, with the potential for an extended mission of another five years. SSTL, based in Guildford, Surrey and an experienced hand in satellite development, is to build the spacecraft, with scientific instrumentation in the hands of UCL. The method here is transmission spectroscopy, which can be employed when planets transit in front of their star as seen from Earth. Starlight passing through the atmosphere of the transiting world as it moves in front of and then behind the star offers a spectrum that can carry the signatures of the various molecules there, a method that has been used on a variety of worlds like the Neptune-class HAT-P-11b and the hot Jupiter HD...

The fascination with finding habitable planets -- and perhaps someday, a planet much like Earth -- drives media coverage of each new, tantalizing discovery in this direction. We have a number of candidates for habitability, but as Andrew LePage points out in this fine essay, few of these stand up to detailed examination. We're learning more all the time about how likely worlds of a given size are to be rocky, but much more goes into the mix, as Drew explains. He also points us to several planets that do remain intriguing. LePage is Senior Project Scientist at Visidyne, Inc., and also finds time to maintain Drew ex Machina, where these issues are frequently discussed. by Andrew LePage The past couple of years have been eventful ones for those with an interest in habitable extrasolar planets. The media have been filled with stories about the discovery of many new extrasolar planets that have been billed as being "potentially habitable". Unfortunately follow-up observations and new...

Not long ago we looked at a paper from Rodrigo Luger and Rory Barnes (University of Washington) making the case that planets now in a red dwarf’s habitable zone may have gone through a tortured history. Because of tidal forces causing surface volcanism and intense stellar activity in young stars, a planet’s supply of surface water may be lost entirely. As the red dwarf slowly settles into the main sequence, the upper atmosphere of a planet in what will eventually become its habitable zone can be heated enough to cause its hydrogen to escape into space. Remember that M-dwarfs have a long, slow contraction phase, one that can last as long as a billion years. That exposes planets formed in what will ultimately become the habitable zone to extreme radiation, with hydrogen loss leading to a dessicated surface inimical to life. In such worlds, a dense oxygen envelope could remain, in which case we might detect oxygen and mistakenly take it for a bio-signature (see Enter the ‘Mirage Earth’...

Finding planets around stars that are two and a half times older than our own Solar System causes a certain frisson. Our star is four and a half billion years old, evidently old enough to produce beings like us, who wonder about other civilizations in the cosmos. Could there be truly ancient civilizations that grew up around stars as old as Kepler-444, a K-class star in the constellation Lyra that is estimated to be fully 11.8 billion years old? It's a tantalizing speculation, and of course, nothing more than that. But the discovery of planets here still catches the eye. The just announced discovery and accompanying paper are the work of Tiago Campante (University of Birmingham, UK), who led a large team in the investigation. What we learn is that five planets have been discovered using Kepler data around a star that is 117 light years from Earth. These are not habitable worlds by our standards -- all five planets complete their orbits in less than ten days, making them hotter than...

Might there be gas giant planets somewhere with moons as large as the Earth, or at least Mars? Projects like the Hunt for Exomoons with Kepler (HEK) are on the prowl for exomoons, and the possibility of large moons leads to astrobiological speculation when a gas giant is in its star's habitable zone. Interestingly, we may be looking at evidence of an extremely young -- and very large -- moon in formation around a planet that circles the young star J1407. That would be intriguing in itself, but what researchers at Leiden Observatory (The Netherlands) and the University of Rochester have found is an enormous ring structure that eclipses the young star in an epic way. The diameter of the ring system, based on the lightcurve the astronomers are getting, is nearly 120 million kilometers, which makes it more than two hundred times larger than the rings of Saturn. This is a ring system that contains about an Earth's mass of dust particles, with a marked gap that signals the possibility of...

About a year ago we looked at a young star called HD 142527 in the constellation Lupus (see HD 142527: An Unusual Circumstellar Disk). A T Tauri star about five million years old, HD 142527 has drawn attention because it shows evidence of both an inner and an outer disk, each of which may be capable of producing planets. These are disks with a twist, as astronomers at the Millennium ALMA Disk Nucleus project at the Universidad de Chile demonstrate in a new paper that explains the three-dimensional geometry of this unusual system. HD 142527's two disks are striking because no other star shows a gap this large between an inner and outer disk, a gap that spans a region from 10 AU out to 120 AU. Two dark regions stand out in observations of the outer disk that break its continuity. The new study reveals these outer disk features to be caused by the shadow of the inner disk. The shape and orientation of the shadows thus become a measure of the inner disk's orientation. Using radiative...