Astronomers are conducting extensive observations to estimate how many planets in our Milky Way galaxy might be potential abodes for life. These are collectively called "Earth-like" in other words, Earth-sized worlds that are at the right distances from their stars for moderate temperatures to nurture the origin of life. The search for extraterrestrial intelligent life in the universe (SETI) is based on the hypothesis that some fraction of worlds, where life originates, go on to evolve intelligent technological civilizations. Until we ever find such evidence, Earth is the only known abode of life in the universe. But the universe is not only vastly big, it has a vast future. There is so much leftover gas from galaxy evolution available that the universe will keep cooking up stars and planets for a very long time to come. In fact, most of the potentially habitable Earth-like planets have yet to be born. This theoretical conclusion is based on an assessment of star-birth data collected by the Hubble Space Telescope and exoplanet surveys made by the planet-hunting Kepler space observatory.
Two independent and primitive envelopes of the bilobate nucleus of comet 67P
Nature 526, 7573 (2015). doi:10.1038/nature15511
Authors: Matteo Massironi, Emanuele Simioni, Francesco Marzari, Gabriele Cremonese, Lorenza Giacomini, Maurizio Pajola, Laurent Jorda, Giampiero Naletto, Stephen Lowry, Mohamed Ramy El-Maarry, Frank Preusker, Frank Scholten, Holger Sierks, Cesare Barbieri, Philippe Lamy, Rafael Rodrigo, Detlef Koschny, Hans Rickman, Horst Uwe Keller, Michael F. A’Hearn, Jessica Agarwal, Anne-Thérèse Auger, M. Antonella Barucci, Jean-Loup Bertaux, Ivano Bertini, Sebastien Besse, Dennis Bodewits, Claire Capanna, Vania Da Deppo, Björn Davidsson, Stefano Debei, Mariolino De Cecco, Francesca Ferri, Sonia Fornasier, Marco Fulle, Robert Gaskell, Olivier Groussin, Pedro J. Gutiérrez, Carsten Güttler, Stubbe F. Hviid, Wing-Huen Ip, Jörg Knollenberg, Gabor Kovacs, Rainer Kramm, Ekkehard Kührt, Michael Küppers, Fiorangela La Forgia, Luisa M. Lara, Monica Lazzarin, Zhong-Yi Lin, Josè J. Lopez Moreno, Sara Magrin, Harald Michalik, Stefano Mottola, Nilda Oklay, Antoine Pommerol, Nicolas Thomas, Cecilia Tubiana & Jean-Baptiste Vincent
The factors shaping cometary nuclei are still largely unknown, but could be the result of concurrent effects of evolutionary and primordial processes. The peculiar bilobed shape of comet 67P/Churyumov–Gerasimenko may be the result of the fusion of two objects that were once separate or the result of a localized excavation by outgassing at the interface between the two lobes. Here we report that the comet’s major lobe is enveloped by a nearly continuous set of strata, up to 650 metres thick, which are independent of an analogous stratified envelope on the minor lobe. Gravity vectors computed for the two lobes separately are closer to perpendicular to the strata than those calculated for the entire nucleus and adjacent to the neck separating the two lobes. Therefore comet 67P/Churyumov–Gerasimenko is an accreted body of two distinct objects with ‘onion-like’ stratification, which formed before they merged. We conclude that gentle, low-velocity collisions occurred between two fully formed kilometre-sized cometesimals in the early stages of the Solar System. The notable structural similarities between the two lobes of comet 67P/Churyumov–Gerasimenko indicate that the early-forming cometesimals experienced similar primordial stratified accretion, even though they formed independently.
Scientists using NASA's Hubble Space Telescope have produced new global maps of
Jupiter the first in a series of annual portraits of the solar system's outer planets
from the Outer Planet Atmospheres Legacy program (OPAL). The two Jupiter maps,
representing nearly back-to-back rotations of the planet on Jan. 19, 2015, show
the movements of the clouds and make it possible to determine the speeds of
Jupiter's winds. The Hubble observations confirm that the Great Red Spot continues
to shrink and become more circular. In addition, an unusual wispy filament is seen, spanning almost the entire width of the vortex. These findings are described in a
new paper published online in the October 10 issue of The Astrophysical Journal.
The collection of maps to be obtained over time from the OPAL program will not only help scientists understand the atmospheres of our giant planets, but also the atmospheres of planets being discovered around other stars. For more visuals and information about this study, visit: http://www.nasa.gov/hubble .
And to learn even more about Jupiter and Hubble, join the live Hubble Hangout discussion at 3:00 pm on Thurs., Oct. 15 at http://hbbl.us/y6C .
The Barringer meteor crater is an iconic Arizona landmark, more than 1km wide and 170 metres deep, left behind by a massive 300,000 tonne meteorite that hit Earth 50,000 years ago with a force equivalent to a ten megaton nuclear bomb. The forces unleashed by such an impact are hard to comprehend, but a team of Stanford scientists has recreated the conditions experienced during the first billionths of a second as the meteor struck in order to reveal the effects it had on the rock underneath.
The sandstone rocks of Arizona were, on that day of impact 50,000 years ago, pushed beyond their limits and momentarily – for the first few trillionths and billionths of a second – transformed into a new state. The Stanford scientists, in a study published in the journal Nature Materials, recreated the conditions as the impact shockwave passed through the ground through computer models of half a million atoms of silica. Blasted by fragments of an asteroid that fell to Earth at tens of kilometres a second, the silica quartz crystals in the sandstone rocks would have experienced pressures of hundreds of thousands of atmospheres, and temperatures of thousands of degrees Celsius.
What the model reveals is that atoms form an immensely dense structure almost instantaneously as the shock wave hits at more than 7km/s. Within ten trillionths of a second the silica has reached temperatures of around 3,000℃ and pressures of more than half a million atmospheres. Then, within the next billionth of a second, the dense silica crystallises into a very rare mineral called stishovite.
The results are particularly exciting because stishovite is exactly the mineral found in shocked rocks at the Barringer Crater and similar sites across the globe. Indeed, stishovite (named after a Russian high-pressure physics researcher) was first found at the Barringer Crater in 1962. The latest simulations give an insight into the birth of mineral grains in the first moments of meteorite impact.
Simulations show how crystals form in billionths of a second
The size of the crystals that form in the impact event appears to be indicative of the size and nature of the impact. The simulations arrive at crystals of stishovite very similar to the range of sizes actually observed in geological samples of asteroid impacts.
Studying transformations of minerals such as quartz, the commonest mineral of Earth’s continental crust, under such extreme conditions of temperature and pressure is challenging. To measure what happens on such short timescales adds another degree of complexity to the problem.
These computer models point the way forward, and will guide experimentalists in the studies of shock events in the future. In the next few years we can expect to see these computer simulations backed up with further laboratory studies of impact events using the next generation of X-ray instruments, called X-ray free electron lasers, which have the potential to “see” materials transform under the same conditions and on the same sorts of timescales.
Inset image: Barringer meteor Crater, Arizona (NASA Earth Observatory).
Simon Redfern from the Department of Earth Sciences discusses a study that has recreated the conditions experienced during the meteor strike that formed the Barringer Crater in Arizona.United States Geological Survey/D. RoddyBarringer Crater aerial photo
The text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.
Astrophysics: Surprisingly fast motions in a dust disk
Nature 526, 7572 (2015). doi:10.1038/526204a
Authors: Marshall D. Perrin
A recently commissioned planet-finding instrument has been used to study a young solar system around the star AU Microscopii, leading to the discovery of rapidly moving features in the dust disk around the star. See Letter p.230
NASA narrows its list of planetary targets
Nature 526, 7572 (2015). http://www.nature.com/doifinder/10.1038/nature.2015.18482
Author: Alexandra Witze
Venus and asteroids take the spotlight as the agency chops list of Discovery-class candidates from 27 to 5.