For thousands of years, humans have recorded sightings of mysterious comets sweeping across the nighttime skies. These celestial wanderers, "snowballs" of dust and ice, are swift-moving visitors from the cold depths of space. Some of them periodically visit the inner solar system during their journeys around the sun.
Temperate Earth-sized planets transiting a nearby ultracool dwarf star
Nature 533, 7602 (2016). doi:10.1038/nature17448
Authors: Michaël Gillon, Emmanuël Jehin, Susan M. Lederer, Laetitia Delrez, Julien de Wit, Artem Burdanov, Valérie Van Grootel, Adam J. Burgasser, Amaury H. M. J. Triaud, Cyrielle Opitom, Brice-Olivier Demory, Devendra K. Sahu, Daniella Bardalez Gagliuffi, Pierre Magain & Didier Queloz
Star-like objects with effective temperatures of less than 2,700 kelvin are referred to as ‘ultracool dwarfs’. This heterogeneous group includes stars of extremely low mass as well as brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion), and represents about 15 per cent of the population of astronomical objects near the Sun. Core-accretion theory predicts that, given the small masses of these ultracool dwarfs, and the small sizes of their protoplanetary disks, there should be a large but hitherto undetected population of terrestrial planets orbiting them—ranging from metal-rich Mercury-sized planets to more hospitable volatile-rich Earth-sized planets. Here we report observations of three short-period Earth-sized planets transiting an ultracool dwarf star only 12 parsecs away. The inner two planets receive four times and two times the irradiation of Earth, respectively, placing them close to the inner edge of the habitable zone of the star. Our data suggest that 11 orbits remain possible for the third planet, the most likely resulting in irradiation significantly less than that received by Earth. The infrared brightness of the host star, combined with its Jupiter-like size, offers the possibility of thoroughly characterizing the components of this nearby planetary system.
Celestial mechanics: Fresh solutions to the four-body problem
Nature 533, 7602 (2016). doi:10.1038/nature17896
Authors: Douglas P. Hamilton
Describing the motion of three or more bodies under the influence of gravity is one of the toughest problems in astronomy. The report of solutions to a large subclass of the four-body problem is truly remarkable.
No Sun-like dynamo on the active star ζ Andromedae from starspot asymmetry
Nature 533, 7602 (2016). doi:10.1038/nature17444
Authors: R. M. Roettenbacher, J. D. Monnier, H. Korhonen, A. N. Aarnio, F. Baron, X. Che, R. O. Harmon, Zs. Kővári, S. Kraus, G. H. Schaefer, G. Torres, M. Zhao, T. A. ten Brummelaar, J. Sturmann & L. Sturmann
Sunspots are cool areas caused by strong surface magnetic fields that inhibit convection. Moreover, strong magnetic fields can alter the average atmospheric structure, degrading our ability to measure stellar masses and ages. Stars that are more active than the Sun have more and stronger dark spots than does the Sun, including on the rotational pole. Doppler imaging, which has so far produced the most detailed images of surface structures on other stars, cannot always distinguish the hemisphere in which the starspots are located, especially in the equatorial region and if the data quality is not optimal. This leads to problems in investigating the north–south distribution of starspot active latitudes (those latitudes with more starspot activity); this distribution is a crucial constraint of dynamo theory. Polar spots, whose existence is inferred from Doppler tomography, could plausibly be observational artefacts. Here we report imaging of the old, magnetically active star ζ Andromedae using long-baseline infrared interferometry. In our data, a dark polar spot is seen in each of two observation epochs, whereas lower-latitude spot structures in both hemispheres do not persist between observations, revealing global starspot asymmetries. The north–south symmetry of active latitudes observed on the Sun is absent on ζ And, which hosts global spot patterns that cannot be produced by solar-type dynamos.
Planetary science: Solar wind hits Pluto hard
Nature 533, 7602 (2016). doi:10.1038/533148a
The solar wind is diverted by Pluto, suggesting that, like some larger planets, the dwarf planet has a shield against the stream of energized particles emanating from the Sun.Before NASA's New Horizons spacecraft visited the dwarf planet (pictured) in 2015, most scientists thought that
Planetary science: Planet 9 may glow from within
Nature 533, 7602 (2016). doi:10.1038/533149d
The hypothetical ninth planet of the Solar System could shine brightly.Planet 9, if it exists, is thought to be an ice planet that is slightly smaller than Neptune, orbiting in the far outer Solar System. Esther Linder and Christoph Mordasini of the University of