Pluto snow forecast poses atmospheric conundrum
Nature 525, 7567 (2015). http://www.nature.com/doifinder/10.1038/525013a
Author: Alexandra Witze
Discrepancy arises between New Horizons and Earth-based measurements.
Astrophysics: Galaxy γ-ray signal was not oversold
Nature 525, 7567 (2015). doi:10.1038/525033d
Author: Alex Geringer-Sameth
We argue that Jan Conrad's depiction of our preprint (http://arxiv.org/abs/1503.02320; 2015) as a case study in 'crying wolf' lacks accuracy and credibility (Nature523, 27–28;10.1038/523027a2015).Based on public data from NASA's Fermi Large Area Telescope
Quasars are the light fantastic. These brilliant cores of active galaxies blaze with the radiance of a hundred billion stars compressed into a region of space not much larger than our solar system. Supermassive black holes, with millions or billions of times the mass of our sun, are the only imaginable powerhouse behind these tsunamis of raw energy.
The disruption of multiplanet systems through resonance with a binary orbit
Nature 524, 7566 (2015). doi:10.1038/nature14873
Authors: Jihad R. Touma & S. Sridhar
Most exoplanetary systems in binary stars are of S-type, and consist of one or more planets orbiting a primary star with a wide binary stellar companion. Planetary eccentricities and mutual inclinations can be large, perhaps forced gravitationally by the binary companion. Earlier work on single planet systems appealed to the Kozai–Lidov instability wherein a sufficiently inclined binary orbit excites large-amplitude oscillations in the planet’s eccentricity and inclination. The instability, however, can be quenched by many agents that induce fast orbital precession, including mutual gravitational forces in a multiplanet system. Here we report that orbital precession, which inhibits Kozai–Lidov cycling in a multiplanet system, can become fast enough to resonate with the orbital motion of a distant binary companion. Resonant binary forcing results in dramatic outcomes ranging from the excitation of large planetary eccentricities and mutual inclinations to total disruption. Processes such as planetary migration can bring an initially non-resonant system into resonance. As it does not require special physical or initial conditions, binary resonant driving is generic and may have altered the architecture of many multiplanet systems. It can also weaken the multiplanet occurrence rate in wide binaries, and affect planet formation in close binaries.
Astrophysics: Dark-energy search narrows
Nature 524, 7566 (2015). doi:10.1038/524390d
Two groups have tightened the limits on the search for elusive dark matter and dark energy, the mysterious force accelerating the expansion of the Universe.Physicists have proposed that dark energy could come from a 'chameleon' field: a force that would act in the low
Astrophysics: Cosmic neutrinos abound
Nature 524, 7566 (2015). doi:10.1038/524391e
Super-high-energy neutrinos from outside the Milky Way pepper Earth from all directions.Neutrinos are created in the Universe's most violent environments and travel through it almost unimpeded, providing a way to study distant astronomical objects. A team at the IceCube Neutrino Observatory at the South
The Gaia satellite, which orbits the sun at a distance of 1.5million km from the earth, was launched by the European Space Agency in December 2013 with the aim of observing a billion stars and revolutionising our understanding of the Milky Way.
The unique mission is reliant on the work of Cambridge researchers who collect the vast quantities of data transmitted by Gaia to a data processing centre at the university, overseen by a team at the Institute of Astronomy.
Since the start of its observations in August 2014, Gaia has recorded 272 billion positional (or astrometric) measurements and 54.4 billion brightness (or photometric) data points.
Gaia surveys stars and many other astronomical objects as it spins, observing circular swathes of the sky. By repeatedly measuring the positions of the stars with extraordinary accuracy, Gaia can tease out their distances and motions throughout the Milky Way galaxy.
Dr Francesca de Angeli, lead scientist at the Cambridge data centre, said: “The huge Gaia photometric data flow is being processed successfully into scientific information at our processing centre and has already led to many exciting discoveries.”
The Gaia team have spent a busy year processing and analysing data, with the aim of developing enormous public catalogues of the positions, distances, motions and other properties of more than a billion stars. Because of the immense volumes of data and their complex nature, this requires a huge effort from expert scientists and software developers distributed across Europe, combined in Gaia’s Data Processing and Analysis Consortium (DPAC).
“The past twelve months have been very intense, but we are getting to grips with the data, and are looking forward to the next four years of operations,” said Timo Prusti, Gaia project scientist at ESA.
“We are just a year away from Gaia's first scheduled data release, an intermediate catalogue planned for the summer of 2016. With the first year of data in our hands, we are now halfway to this milestone, and we’re able to present a few preliminary snapshots to show that the spacecraft is working well and that the data processing is on the right track.”
As Gaia has been conducting its repeated scans of the sky to measure the motions of stars, it has also been able to detect whether any of them have changed their brightness, and in doing so, has started to discover some very interesting astronomical objects.
Gaia has detected hundreds of transient sources so far, with a supernova being the very first on August 30, 2014. These detections are routinely shared with the community at large as soon as they are spotted in the form of ‘Science Alerts’, enabling rapid follow-up observations to be made using ground-based telescopes in order to determine their nature.
One transient source was seen undergoing a sudden and dramatic outburst that increased its brightness by a factor of five. It turned out that Gaia had discovered a so-called ‘cataclysmic variable’, a system of two stars in which one, a hot white dwarf, is devouring mass from a normal stellar companion, leading to outbursts of light as the material is swallowed. The system also turned out to be an eclipsing binary, in which the relatively larger normal star passes directly in front of the smaller, but brighter white dwarf, periodically obscuring the latter from view as seen from Earth.
Unusually, both stars in this system seem to have plenty of helium and little hydrogen. Gaia’s discovery data and follow-up observations may help astronomers to understand how the two stars lost their hydrogen.
Gaia has also discovered a multitude of stars whose brightness undergoes more regular changes over time. Many of these discoveries were made between July and August 2014, as Gaia performed many subsequent observations of a few patches of the sky.
Closer to home, Gaia has detected a wealth of asteroids, the small rocky bodies that populate our solar system, mainly between the orbits of Mars and Jupiter. Because they are relatively nearby and orbiting the Sun, asteroids appear to move against the stars in astronomical images, appearing in one snapshot of a given field, but not in images of the same field taken at later times.
Gaia scientists have developed special software to look for these ‘outliers’, matching them with the orbits of known asteroids in order to remove them from the data being used to study stars. But in turn, this information will be used to characterise known asteroids and to discover thousands of new ones.
Gerry Gilmore, Professor of Experimental Philosophy, and the Gaia UK Principal Investigator, said: “The early science from Gaia is already supporting major education activity involving UK school children and amateur astronomers across Europe and has established the huge discovery potential of Gaia’s data.
"We are entering a new era of big-data astrophysics, with a revolution in our knowledge of what we see in the sky. We are moving beyond just seeing to knowing about the galaxy in which we live.”
A space mission to create the largest, most-accurate, three-dimensional map of the Milky Way is celebrating its first completed year of observations.We are moving beyond just seeing to knowing about the galaxy in which we live.Gerry Gilmore Credit: Marisa Grove/Institute of AstronomyArtist’s impression of Gaia14aae
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Astrophysics: Mystery survivor of a supermassive black hole
Nature 524, 7565 (2015). doi:10.1038/524301a
Authors: John Bally
The G2 cloud in our Galaxy's core has survived an encounter with the central black hole and failed to trigger a major flare-up in the black hole's activity. A promising theory endeavours to explain the cloud's nature.
Growing the gas-giant planets by the gradual accumulation of pebbles
Nature 524, 7565 (2015). doi:10.1038/nature14675
Authors: Harold F. Levison, Katherine A. Kretke & Martin J. Duncan
It is widely held that the first step in forming gas-giant planets, such as Jupiter and Saturn, was the production of solid ‘cores’ each with a mass roughly ten times that of the Earth. Getting the cores to form before the solar nebula dissipates (in about one to ten million years; ref. 3) has been a major challenge for planet formation models. Recently models have emerged in which ‘pebbles’ (centimetre-to-metre-sized objects) are first concentrated by aerodynamic drag and then gravitationally collapse to form objects 100 to 1,000 kilometres in size. These ‘planetesimals’ can then efficiently accrete left-over pebbles and directly form the cores of giant planets. This model is known as ‘pebble accretion’; theoretically, it can produce cores of ten Earth masses in only a few thousand years. Unfortunately, full simulations of this process show that, rather than creating a few such cores, it produces a population of hundreds of Earth-mass objects that are inconsistent with the structure of the Solar System. Here we report that this difficulty can be overcome if pebbles form slowly enough to allow the planetesimals to gravitationally interact with one another. In this situation, the largest planetesimals have time to scatter their smaller siblings out of the disk of pebbles, thereby stifling their growth. Our models show that, for a large and physically reasonable region of parameter space, this typically leads to the formation of one to four gas giants between 5 and 15 astronomical units from the Sun, in agreement with the observed structure of the Solar System.