The term 'destruction radius' around a star sounds like something out of a generic science fiction movie, probably one with lots of laser battles and starship crews dressed in capes. It's a descriptive phrase as used in this University of Warwick (UK) news release, but let's go with 'Roche radius' instead. Dimitri Veras, a physicist at the university, probes the term in the context of white dwarfs in a new paper for Monthly Notices of the Royal Astronomical Society. Veras and collaborators are looking at what happens after the challenging transition between red giant and white dwarf, a time when planets will be in high turmoil. The idea is to model the tidal forces that occur once a star collapses into a super-dense white dwarf, blowing away its outer layers in the process. We see the clear potential for dragging planets into new orbits, with some pushed out of their stellar systems entirely. The Roche radius, or limit, is the distance from the star where a self-gravitating object...

Interdisciplinary approaches to new data offer a robust way to see past the conventions of a specialized field, noting connections that provide perspective and deepen understanding. That idea is sound across many disciplines, but it is getting new emphasis with an essay in Science asking whether we have not been too blinkered in our approach to astrobiology. After all, reams have been written about studying exoplanet atmospheres for biomarkers, but shouldn't we be studying how atmospheres couple to planetary interiors? "We need a better understanding of how a planet's composition and interior influence its habitability, starting with Earth," says Anat Shahar (Carnegie Institution for Science), one of the paper's four authors. "This can be used to guide the search for exoplanets and star systems where life could thrive, signatures of which could be detected by telescopes." Thus the paper's call for merging data from astronomical observations, mathematical modeling and simulations, and...

If Kepler's task was to give us a first statistical cut at the distribution of exoplanets in the galaxy, TESS (Transiting Exoplanet Survey Satellite) has a significantly different brief, to use its four cameras to study stars that are near and bright. Among these we may hope to find the first small, rocky planets close enough that their atmospheres may be examined by space telescopes and the coming generation of extremely large telescopes (ELTs) on Earth. Thus the news that TESS has found its first planet of Earth size is heartening, even if the newly found world orbiting HD 21749 is in a tight 7.8 day orbit, making it anything but clement for life. What counts, of course, is the demonstrated ability of this mission to locate the small worlds we had hoped to find. Diana Dragomir is a postdoc at MIT's Kavli Institute for Astrophysics and Space Research, as well as lead author on the paper describing the latest TESS planet: "Because TESS monitors stars that are much closer and...

The transit method has proven invaluable for exoplanet detection, as the runaway success of the Kepler/K2 mission demonstrates. But stars where planets have been detected with this method are still capable of revealing further secrets. Consider Kepler-47. Here we have a circumbinary system some 3340 light years away in the direction of the constellation Cygnus, and as we are now learning about circumbinaries -- planets that orbit two stars -- the alignment of the orbital plane of the planet is likely to change with time. Let's pause for a moment on the value of the detection method. Transits detected in the lightcurve have helped us identify 10 transiting circumbinary planets, with the benefit of allowing astronomers to measure the planets' radius even as variations in the duration of transits and deviations from the expected timing of the transits establish the circumbinary orbit. At Kepler-47, we're looking at the only known multi-planet circumbinary system. Moreover, the orbital...

Seven planets of roughly Earth-size make TRAPPIST-1 a continuing speculative delight, as witness the colorful art it generates below. And with three of the planets arguably in the star's habitable zone, this diminutive star attracts the attention of astrobiologists anxious to examine the possible parameters under which they orbit. One thing that is only now receiving attention is the question of planet-to-planet tidal effects, as opposed to the star's tidal effects on its planets. Image: An artist's impression of the perpetual sunrise that might greet visitors on the surface of planet TRAPPIST-1f. If the planet is tidally locked, the "terminator region" dividing the night side and day side of the planet could be a place where life might take hold, even if the day side is bombarded by energetic protons. In this image, TRAPPIST-1e can be seen as a crescent in the upper left of the image, d is the middle crescent, and c is a bright dot next to the star. Credit: NASA/JPL-Caltech. In our...