An international team of astronomers have found evidence of ice and comets orbiting a nearby sun-like star, which could give a glimpse into how our own solar system developed.
Using data from the Atacama Large Millimeter Array (ALMA), the researchers, led by the University of Cambridge, detected very low levels of carbon monoxide gas around the star, in amounts that are consistent with the comets in our own solar system.
The results, which will be presented today at the ‘Resolving Planet Formation in the era of ALMA and extreme AO’ conference in Santiago, Chile, are a first step in establishing the properties of comet clouds around sun-like stars just after the time of their birth.
Comets are essentially ‘dirty snowballs’ of ice and rock, sometimes with a tail of dust and evaporating ice trailing behind them, and are formed early in the development of stellar systems. They are typically found in the outer reaches of our solar system, but become most clearly visible when they visit the inner regions. For example, Halley’s Comet visits the inner solar system every 75 years, some take as long as 100,000 years between visits, and others only visit once before being thrown out into interstellar space.
It’s believed that when our solar system was first formed, the Earth was a rocky wasteland, similar to how Mars is today, and that as comets collided with the young planet, they brought many elements and compounds, including water, along with them.
The star in this study, HD 181327, has a mass about 30% greater than the sun and is located 160 light years away in the Painter constellation. The system is about 23 million years old, whereas our solar system is 4.6 billion years old.
“Young systems such as this one are very active, with comets and asteroids slamming into each other and into planets,” said Sebastián Marino, a PhD student from Cambridge’s Institute of Astronomy and the paper’s lead author. “The system has a similar ice composition to our own, so it’s a good one to study in order to learn what our solar system looked like early in its existence.”
Using ALMA, the astronomers observed the star, which is surrounded by a ring of dust caused by the collisions of comets, asteroids and other bodies. It’s likely that this star has planets in orbit around it, but they are impossible to detect using current telescopes.
“Assuming there are planets orbiting this star, they would likely have already formed, but the only way to see them would be through direct imaging, which at the moment can only be used for very large planets like Jupiter,” said co-author Luca Matrà, also a PhD student at Cambridge’s Institute of Astronomy.
In order to detect the possible presence of comets, the researchers used ALMA to search for signatures of gas, since the same collisions which caused the dust ring to form should also cause the release of gas. Until now, such gas has only been detected around a few stars, all substantially more massive than the sun. Using simulations to model the composition of the system, they were able to increase the signal to noise ratio in the ALMA data, and detect very low levels of carbon monoxide gas.
“This is the lowest gas concentration ever detected in a belt of asteroids and comets – we’re really pushing ALMA to its limits,” said Marino.
“The amount of gas we detected is analogous to a 200 kilometre diameter ice ball, which is impressive considering how far away the star is,” said Matrà. “It’s amazing that we can do this with exoplanetary systems now.”
The results have been accepted for publication in the Monthly Notices of the Royal Astronomical Society.
S. Marino et al. ‘Exocometary gas in the HD 181327 debris ring.’ Paper presented to the Resolving Planet Formation in the era of ALMA and extreme AO conference, Santiago, May 16-20, 2016. http://www.eso.org/sci/meetings/2016/Planet-Formation2016/program.html
Inset image: ALMA image of the ring of comets around HD 181327 (colours have been changed). The white contours represent the size of the Kuiper Belt in the Solar System. Credit: Amanda Smith, University of Cambridge.
Astronomers have found the first evidence of comets around a star similar to the sun, providing an opportunity to study what our solar system was like as a ‘baby’.The system has a similar ice composition to our own, so it’s a good one to study in order to learn what our solar system looked like early in its existence.Sebastián MarinoAmanda Smith, University of CambridgeIllustration of the dust ring surrounding HD 181327
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Astrophysics: Illuminating brown dwarfs
Nature 533, 7603 (2016). doi:10.1038/533330a
Authors: Adam P. Showman
Objects known as brown dwarfs are midway between stars and planets in mass. Observations of a hot brown dwarf irradiated by a nearby star will help to fill a gap in our knowledge of the atmospheres of fluid planetary objects. See Letter p.366
Astronomy: Black hole weighed with precision
Nature 533, 7603 (2016). doi:10.1038/533294e
Astronomers have made precise measurements of the mass of a supermassive black hole.Aaron Barth of the University of California in Irvine focused the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile on the black hole at the heart of NGC 1332, a galaxy that is
An irradiated brown-dwarf companion to an accreting white dwarf
Nature 533, 7603 (2016). doi:10.1038/nature17952
Authors: Juan V. Hernández Santisteban, Christian Knigge, Stuart P. Littlefair, Rene P. Breton, Vikram S. Dhillon, Boris T. Gänsicke, Thomas R. Marsh, Magaretha L. Pretorius, John Southworth & Peter H. Hauschildt
Interacting compact binary systems provide a natural laboratory in which to study irradiated substellar objects. As the mass-losing secondary (donor) in these systems makes a transition from the stellar to the substellar regime, it is also irradiated by the primary (compact accretor). The internal and external energy fluxes are both expected to be comparable in these objects, providing access to an unexplored irradiation regime. The atmospheric properties of donors are largely unknown, but could be modified by the irradiation. To constrain models of donor atmospheres, it is necessary to obtain accurate observational estimates of their physical properties (masses, radii, temperatures and albedos). Here we report the spectroscopic detection and characterization of an irradiated substellar donor in an accreting white-dwarf binary system. Our near-infrared observations allow us to determine a model-independent mass estimate for the donor of 0.055 ± 0.008 solar masses and an average spectral type of L1 ± 1, supporting both theoretical predictions and model-dependent observational constraints that suggest that the donor is a brown dwarf. Our time-resolved data also allow us to estimate the average irradiation-induced temperature difference between the dayside and nightside of the substellar donor (57 kelvin) and the maximum difference between the hottest and coolest parts of its surface (200 kelvin). The observations are well described by a simple geometric reprocessing model with a bolometric (Bond) albedo of less than 0.54 at the 2σ confidence level, consistent with high reprocessing efficiency, but poor lateral heat redistribution in the atmosphere of the brown-dwarf donor. These results add to our knowledge of binary evolution, in that the donor has survived the transition from the stellar to the substellar regime, and of substellar atmospheres, in that we have been able to test a regime in which the irradiation and the internal energy of a brown dwarf are comparable.
Astrophysics: Model predicts neutron-star signal
Nature 533, 7603 (2016). doi:10.1038/533294c
Physicists have devised a fast, accurate model that recreates the gravitational-wave signals produced by spiralling and colliding neutron stars. The model could help researchers to work out the stars' properties.The US Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) is looking for gravitational waves — ripples
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