Accreting protoplanets in the LkCa 15 transition disk
Nature 527, 7578 (2015). doi:10.1038/nature15761
Authors: S. Sallum, K. B. Follette, J. A. Eisner, L. M. Close, P. Hinz, K. Kratter, J. Males, A. Skemer, B. Macintosh, P. Tuthill, V. Bailey, D. Defrère, K. Morzinski, T. Rodigas, E. Spalding, A. Vaz & A. J. Weinberger
Exoplanet detections have revolutionized astronomy, offering new insights into solar system architecture and planet demographics. While nearly 1,900 exoplanets have now been discovered and confirmed, none are still in the process of formation. Transition disks, protoplanetary disks with inner clearings best explained by the influence of accreting planets, are natural laboratories for the study of planet formation. Some transition disks show evidence for the presence of young planets in the form of disk asymmetries or infrared sources detected within their clearings, as in the case of LkCa 15 (refs 8, 9). Attempts to observe directly signatures of accretion onto protoplanets have hitherto proven unsuccessful. Here we report adaptive optics observations of LkCa 15 that probe within the disk clearing. With accurate source positions over multiple epochs spanning 2009–2015, we infer the presence of multiple companions on Keplerian orbits. We directly detect Hα emission from the innermost companion, LkCa 15 b, evincing hot (about 10,000 kelvin) gas falling deep into the potential well of an accreting protoplanet.
Astrophysics: Growing planet brought to light
Nature 527, 7578 (2015). doi:10.1038/527310a
Authors: Zhaohuan Zhu
Thousands of extrasolar planets have been discovered, but none is a planet in its infancy. Observations have finally been made of a young planet growing in its birthplace — opening the way to many more such discoveries. See Letter p.342
The exoplanet files
Nature 527, 7578 (2015). http://www.nature.com/doifinder/10.1038/527288a
Author: Alexandra Witze
What we know about alien worlds — and what’s coming next.
Wayward satellites repurposed to test general relativity
Nature 527, 7578 (2015). http://www.nature.com/doifinder/10.1038/nature.2015.18780
Author: Elizabeth Gibney
Scientists will use wonky orbit to test Einstein’s theories.
Freefall space cubes are test for gravitational wave spotter
Nature 527, 7578 (2015). http://www.nature.com/doifinder/10.1038/527284a
Author: Elizabeth Gibney
Europe’s long-awaited LISA Pathfinder spacecraft has two metal cubes at its heart, which it will attempt to isolate from every force except for gravity.
Arecibo observatory director quits after funding row
Nature 527, 7577 (2015). http://www.nature.com/doifinder/10.1038/nature.2015.18745
Author: Traci Watson
Departure of long-term advocate adds to woes of the financially troubled radio telescope.
Nature 527, 7577 (2015). doi:10.1038/527134a
Conflict at the Arecibo Observatory highlights the need for funders to become more flexible.
Astronomy: A small star with an Earth-like planet
Nature 527, 7577 (2015). doi:10.1038/527169a
Authors: Drake Deming
A rocky planet close in size to Earth has been discovered in the cosmic vicinity of our Sun. The small size and proximity of the associated star bode well for studies of the planet's atmosphere. See Letter p.204
A rocky planet transiting a nearby low-mass star
Nature 527, 7577 (2015). doi:10.1038/nature15762
Authors: Zachory K. Berta-Thompson, Jonathan Irwin, David Charbonneau, Elisabeth R. Newton, Jason A. Dittmann, Nicola Astudillo-Defru, Xavier Bonfils, Michaël Gillon, Emmanuël Jehin, Antony A. Stark, Brian Stalder, Francois Bouchy, Xavier Delfosse, Thierry Forveille, Christophe Lovis, Michel Mayor, Vasco Neves, Francesco Pepe, Nuno C. Santos, Stéphane Udry & Anaël Wünsche
M-dwarf stars—hydrogen-burning stars that are smaller than 60 per cent of the size of the Sun—are the most common class of star in our Galaxy and outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M dwarfs host Earth-sized planets in great numbers: the average number of M-dwarf planets that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per star. The nearest such planets known to transit their star are 39 parsecs away, too distant for detailed follow-up observations to measure the planetary masses or to study their atmospheres. Here we report observations of GJ 1132b, a planet with a size of 1.2 Earth radii that is transiting a small star 12 parsecs away. Our Doppler mass measurement of GJ 1132b yields a density consistent with an Earth-like bulk composition, similar to the compositions of the six known exoplanets with masses less than six times that of the Earth and precisely measured densities. Receiving 19 times more stellar radiation than the Earth, the planet is too hot to be habitable but is cool enough to support a substantial atmosphere, one that has probably been considerably depleted of hydrogen. Because the host star is nearby and only 21 per cent the radius of the Sun, existing and upcoming telescopes will be able to observe the composition and dynamics of the planetary atmosphere.