Olivine in an unexpected location on Vesta’s surface
Nature 504, 7478 (2013). doi:10.1038/nature12665
Authors: E. Ammannito, M. C. De Sanctis, E. Palomba, A. Longobardo, D. W. Mittlefehldt, H. Y. McSween, S. Marchi, M. T. Capria, F. Capaccioni, A. Frigeri, C. M. Pieters, O. Ruesch, F. Tosi, F. Zambon, F. Carraro, S. Fonte, H. Hiesinger, G. Magni, L. A. McFadden, C. A. Raymond, C. T. Russell & J. M. Sunshine
Olivine is a major component of the mantle of differentiated bodies, including Earth. Howardite, eucrite and diogenite (HED) meteorites represent regolith, basaltic-crust, lower-crust and possibly ultramafic-mantle samples of asteroid Vesta, which is the lone surviving, large, differentiated, basaltic rocky protoplanet in the Solar System. Only a few of these meteorites, the orthopyroxene-rich diogenites, contain olivine, typically with a concentration of less than 25 per cent by volume. Olivine was tentatively identified on Vesta, on the basis of spectral and colour data, but other observations did not confirm its presence. Here we report that olivine is indeed present locally on Vesta’s surface but that, unexpectedly, it has not been found within the deep, south-pole basins, which are thought to be excavated mantle rocks. Instead, it occurs as near-surface materials in the northern hemisphere. Unlike the meteorites, the olivine-rich (more than 50 per cent by volume) material is not associated with diogenite but seems to be mixed with howardite, the most common surface material. Olivine is exposed in crater walls and in ejecta scattered diffusely over a broad area. The size of the olivine exposures and the absence of associated diogenite favour a mantle source, but the exposures are located far from the deep impact basins. The amount and distribution of observed olivine-rich material suggest a complex evolutionary history for Vesta.
Astronomy: Explosions in the young Universe
Nature 503, 7474 (2013). doi:10.1038/503009c
The biggest ever thermonuclear blasts happened in the early Universe, when primordial gas clumps collapsed and created the seeds of supermassive black holes.Arising even before many stars and galaxies had time to form, the origins of big black holes have been a puzzle. Daniel
X-rays top space agenda
Nature 503, 7474 (2013). http://www.nature.com/doifinder/10.1038/503013a
Author: Elizabeth Gibney
European agency selects mission themes, with X-ray telescope the biggest winner.
The Square Kilometre Array (SKA) is likely to revolutionise our understanding of the Universe - as it will be able to detect radio waves with unprecedented sensitivity and image fidelity - and could help unravel some of the biggest mysteries in the Universe such as the role of dark energy and dark matter.
Even in its earliest phase (SKA1), the radio telescope will be the fastest and most sensitive in the world.
SKA1 is now entering the “detailed design” stage, in which design work and concept selection will be done. The SKA1 observatory will consist of three world-beating instruments.
A total of 250 dishes will work as one machine in South Africa’s Karoo desert to detect mid-range radio frequencies. A further two instruments will be in the Western Australian desert: one being an array of many hundreds of aerial clusters working at low radio frequencies, the other a range of around 90 dishes - each equipped with a ‘Phase Array Feed’ to expand the field of view.
Construction on all three sites will commence in 2018 with completion aimed for 2023.
Cambridge is leading the 'Science Data Processor' (SDP) consortium for SKA1. The SDP work involves designing the hardware and software for the massive scale of data processing required for the project, building on decades of local expertise.
The University’s High Performance Computing service will house a laboratory to test computer implementations and scalable architectures for the enormous proportions that SKA requires.
“We are thrilled to be able to build on the decades of expertise we have in the University to contribute to the SKA project, which is the exemplar “big data” project of this generation,” said Professor Paul Alexander from the Cavendish Laboratory, who is leading the Cambridge work.
To complete the three year, €18 million detailed design project, the Cambridge team is working alongside over two dozen academic partners across the UK and the globe, including ICRAR and CSIRO (both in Australia), SKA SA (in South Africa), ASTRON (in the Netherlands) and partners in Canada, as well as representation from a number of industrial partners.
“The SKA is a complex system, with computing requirements varying greatly depending on the science modes the instruments are in: imagining these 'use scenarios' and planning for this flexibility is an exciting challenge” says SDP project scientist and Cambridge researcher Rosie Bolton.
Cambridge also leads the work developing the low frequency antennas and system design for SKA1, as part of the Low Frequency Aperture Array consortium which is led by ASTRON, with the University’s radio observatory at Lord’s Bridge being used as a test-bed for prototype low frequency antennas.
These antennas operate at long radio wavelength (up to 6 metres), and each is around 2m tall. SKA1 will require a quarter of a million such antennas, so each must be designed to be inexpensive and easily deployed - as well as meeting the stringent science criteria.
These antennas will be used to measure the very faint signals from the Epoch of Reionisation, back from the dawn of the Universe, when the first stars were switching on and beginning to ionize the hydrogen gas surrounding the galaxies.
“These low-frequency antennas are going to do the most exciting science of the first phase of the SKA,” said LFAA Project Engineer Andrew Faulkner from the Cavendish’s Astrophyics group.
“We can see the different states of the hydrogen gas and use this information to constrain our models of the early Universe.”
Inset image: Simulated hydrogen in the Epoch of Reionisation, which will be probed with SKA1. Image credit: SKA Organisation / Swinburne Astronomy Productions
This week, work begins on the next phase of development for the Square Kilometre Array radio telescope, with the University of Cambridge leading major ‘work packages’.telescopeSquare Kilometre Arrayastrophysicsradio wavesuniversedark matterRosie BoltonPaul AlexanderAndrew FaulknerScience and Technologies Facilities CouncilCavendish LaboratoryBattcock Centre for Experimental AstrophysicsWe are thrilled to be able to build on the decades of expertise we have in the University to contribute to the SKA projectPaul AlexanderSwinburne Astronomy Productions/ICRAR/ASTRONCGI graphic showing how a cluster of low frequency antennas might look when deployed in the Australian desert
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Proxima Centauri lies in the constellation of Centaurus (the Centaur), just over four light-years from Earth. Although it looks bright through the eye of the Hubble Space Telescope, as you might expect from the nearest star to the solar system, Proxima Centauri is not visible to the naked eye. Its average luminosity is very low, and it is quite small compared to other stars, at only about an eighth of the mass of the Sun. These observations were taken using Hubble's Wide Field and Planetary Camera 2 (WFPC2) in 1996. Proxima Centauri is actually part of a triple star system its two companions, Alpha Centauri A and B, lie out of frame.
An Earth-sized planet with an Earth-like density
Nature 503, 7476 (2013). doi:10.1038/nature12768
Authors: Francesco Pepe, Andrew Collier Cameron, David W. Latham, Emilio Molinari, Stéphane Udry, Aldo S. Bonomo, Lars A. Buchhave, David Charbonneau, Rosario Cosentino, Courtney D. Dressing, Xavier Dumusque, Pedro Figueira, Aldo F. M. Fiorenzano, Sara Gettel, Avet Harutyunyan, Raphaëlle D. Haywood, Keith Horne, Mercedes Lopez-Morales, Christophe Lovis, Luca Malavolta, Michel Mayor, Giusi Micela, Fatemeh Motalebi, Valerio Nascimbeni, David Phillips, Giampaolo Piotto, Don Pollacco, Didier Queloz, Ken Rice, Dimitar Sasselov, Damien Ségransan, Alessandro Sozzetti, Andrew Szentgyorgyi & Christopher A. Watson
Recent analyses of data from the NASA Kepler spacecraft have established that planets with radii within 25 per cent of the Earth’s () are commonplace throughout the Galaxy, orbiting at least 16.5 per cent of Sun-like stars. Because these studies were sensitive to the sizes of the planets but not their masses, the question remains whether these Earth-sized planets are indeed similar to the Earth in bulk composition. The smallest planets for which masses have been accurately determined are Kepler-10b (1.42) and Kepler-36b (1.49), which are both significantly larger than the Earth. Recently, the planet Kepler-78b was discovered and found to have a radius of only 1.16. Here we report that the mass of this planet is 1.86 Earth masses. The resulting mean density of the planet is 5.57 g cm−3, which is similar to that of the Earth and implies a composition of iron and rock.
A rocky composition for an Earth-sized exoplanet
Nature 503, 7476 (2013). doi:10.1038/nature12767
Authors: Andrew W. Howard, Roberto Sanchis-Ojeda, Geoffrey W. Marcy, John Asher Johnson, Joshua N. Winn, Howard Isaacson, Debra A. Fischer, Benjamin J. Fulton, Evan Sinukoff & Jonathan J. Fortney
Planets with sizes between that of Earth (with radius ) and Neptune (about 4) are now known to be common around Sun-like stars. Most such planets have been discovered through the transit technique, by which the planet’s size can be determined from the fraction of starlight blocked by the planet as it passes in front of its star. Measuring the planet’s mass—and hence its density, which is a clue to its composition—is more difficult. Planets of size 2–4 have proved to have a wide range of densities, implying a diversity of compositions, but these measurements did not extend to planets as small as Earth. Here we report Doppler spectroscopic measurements of the mass of the Earth-sized planet Kepler-78b, which orbits its host star every 8.5 hours (ref. 6). Given a radius of 1.20 ± 0.09 and a mass of 1.69 ± 0.41, the planet’s mean density of 5.3 ± 1.8 g cm−3 is similar to Earth’s, suggesting a composition of rock and iron.
Extrasolar planets: An infernal Earth
Nature 503, 7476 (2013). doi:10.1038/nature12702
Authors: Drake Deming
Orbiting less than two stellar radii above the visible surface of a Sun-like star, the Earth-sized exoplanet Kepler-78b is a hellish world. But its existence bodes well for the discovery and characterization of habitable planets. See Letters p.377 & p.381
Planetary science: Why Martian craters are flat
Nature 502, 7473 (2013). doi:10.1038/502597b
When meteorites pummelled a young Mars, they may have obliterated enough of its crust to allow the planet's mantle to well up and trigger volcano-like activity across the red planet.A team led by Christopher Edwards of the California Institute of Technology in Pasadena looked