The ice plumes that bloom above Saturn's icy moon Enceladus are almost certainly rooted in a subsurface sea of liquid water.
The Cassini spacecraft flew through a plume on 9 October 2008 and measured the molecular weight of chemicals in the ice. Frank Postberg of the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, and colleagues, found traces of sodium in the form of salt and sodium bicarbonate. The chemicals would have originated in the rocky core of Enceladus, so to reach a plume they must have leached from the core via liquid water. Observations from Earth in 2007 spotted no sign of sodium, casting doubt on such a subsurface sea.
Although the salt could have been leached out by an ancient ocean which since froze solid, that freezing process would concentrate most of the salt very far from the surface of the moon's ice, says Julie Castillo of NASA's Jet Propulsion Laboratory in Pasadena, California. "It is easier to imagine that the salts are present in a liquid ocean below the surface," she says. "That's why this detection, if confirmed, is very important."
Science & Technology
© Martin Lee / Rex Features
Gravity works the same way on all normal matter, but might antimatter respond differently?
Gravity works the same way on all normal matter, but might antimatter respond differently?
AEGIS, a CERN experiment that has just been given the go-ahead, is designed to find out. Gravity is a relatively weak force, so the experiment will use uncharged particles to prevent electromagnetic forces drowning out gravitational effects. It will first build highly unstable pairings of electrons and positrons, known as positronium, then excite them with lasers to prevent them annihilating too quickly. Clouds of antiprotons will rip these pairs apart, stealing their positrons to create neutral antihydrogen atoms.
Pulses of these anti-atoms shot horizontally through two grids of slits will create a fine pattern of impact and shadow on a detector screen. By measuring how the position of this pattern is displaced, the strength - and direction - of the gravitational force on antimatter can be measured.
It's a clever idea, but the devil is in the detail, says AEGIS spokesman Michael Doser. "No one has ever made controlled positronium like this, nobody has ever made a positronium excited state with lasers in an environment like this and nobody has ever made an antihydrogen pulse like this."
© Q D Wang et al / UMass Amherst / CXC / NASA
The centre of the Milky Way, as seen from NASA's Chandra X-ray Observatory. New evidence strongly suggests that there is a black hole lurking in there.
The centre of the Milky Way, as seen from NASA's Chandra X-ray Observatory. New evidence strongly suggests that there is a black hole lurking in there.
Falling into a black hole is aone-way trip - once matter or light crosses a threshold called the event horizon, it can never escape. While astronomers have identified many dark, dense objects they strongly suspect are black holes, it is difficult to prove that they possess event horizons, the defining feature of such objects. Among the proposed alternatives are dense balls of exotic matter called boson stars, which don't have event horizons.
Now Avery Broderick of the Canadian Institute of Theoretical Astrophysics and his colleagues have analysed previous infrared and radio observations of the galactic centre and put forward the strongest evidence yet that an object at our galaxy's centre does indeed have an event horizon.
The team reasoned that if the object were not a black hole, it should glow in the infrared. This is because the kinetic energy of matter hitting the object would be converted into heat. Given the rate that matter appears to be falling onto the central object, it should have a temperature of at least a few hundred Kelvin, they calculate. The resulting infrared glow would be 250 times as bright as the actual glow coming from the region containing the massive object and its disc of matter, when previously measured during quieter moments when the disc is not flaring up.
© Don Davis
Artist's rendition of an Asteroid Impact
Artist's rendition of an Asteroid Impact
There are currently no known space rocks on a collision course with Earth, but with ample evidence for past impacts, researchers say it's only a matter of time before one is found to be heading our way.
A swarm of political and legal issues bedevil any national or international response, whether it's responsibility for collateral damage from deflected asteroids or the possible outcry if one country decides to unilaterally nuke the space threat.
© Mark Garlick/HELAS
Planets orbiting near their stars may not last for very long
Planets orbiting near their stars may not last for very long
A star's gravity can put a nearby planet on a 'fast track' to spiralling into the star and may also cause the planet to lose much of its atmosphere, the studies say. The research may help explain why few exoplanets have been found right next to their host stars.
More than 300 exoplanets have been catalogued to date. Many are situated close to their host stars, where it is thought to be too hot for gas and dust to collapse into planets in the first place. That implies that the planets came from farther away and migrated inwards.
Using a NASA satellite, astronomers have gotten a glimpse of the oldest object in the universe that humans have ever seen. NASA announced today that its Swift satellite and a global team of astronomers have detected a 10-second, gamma ray burst (see video) from a star that died when the universe was just a baby. The burst, called the "most distant cosmic explosion ever seen," happened when the universe was only 630 million years old.
Scientists estimate that the universe is now some 13.73 billion years old.
Scientists estimate that the universe is now some 13.73 billion years old.
© NASA / N Benitez (JHU) / T Broadhurst (Racah Institute of Physics/The Hebrew University) / H Ford (JHU) / M Clampin (STScI) / G Hartig (STScI) / G Illingworth (UCO/Lick Observatory) / the ACS Science Team and ESA
Galaxies, like Abell 1689, should not exist at all according to the standard model of physics.
Galaxies, like Abell 1689, should not exist at all according to the standard model of physics.
According to the theory, matter and antimatter were created in equal amounts at the big bang. By rights, they should have annihilated each other totally in the first second or so of the universe's existence. The cosmos should be full of light and little else.
And yet here we are. So too are planets, stars and galaxies; all, as far as we can see, made exclusively out of matter. Reality 1, theory 0.
There are two plausible solutions to this existential mystery. First, there might be some subtle difference in the physics of matter and antimatter that left the early universe with a surplus of matter. While theory predicts that the antimatter world is a perfect reflection of our own, experiments have already found suspicious scratches in the mirror. In 1998, CERN experiments showed that one particular exotic particle, the kaon, turned into its antiparticle slightly more often than the reverse happened, creating a tiny imbalance between the two.
© Laurent Guiraud / CERN
The ATHENA experiment at CERN. Antiprotons enter from the AD (left) and are captured in a trap inside the superconducting magnet (left). The positron accumulator (right) provides the positrons for producing antihydrogen.
The ATHENA experiment at CERN. Antiprotons enter from the AD (left) and are captured in a trap inside the superconducting magnet (left). The positron accumulator (right) provides the positrons for producing antihydrogen.
Two CERN experiments, ATRAP and ALPHA, are grappling with that question. Their aim is to make antihydrogen - the simplest anti-atom possible, just an antiproton and a positron bound together - in sufficient quantity and for long enough to compare the spectrum of light it emits with that of regular hydrogen. Even the slightest difference between the two would shake up the standard model.
The experiments require a near-perfect vacuum, as encountering a mere atom of air would spell the end for any antiparticle, and there must be some way of trapping the antiparticles: not in a conventional container, but using electric and magnetic fields.
A handful of drizzly days would be enough to mend a damaged bridge made of the new substance. Self-healing is possible because the material is designed to bend and crack in narrow hairlines rather than break and split in wide gaps, as traditional concrete behaves.
"It's like if you get a small cut on your hand, your body can heal itself. But if you have a large wound, your body needs help. You might need stitches. We've created a material with such tiny crack widths that it takes care of the healing by itself. Even if you overload it, the cracks stay small," said Victor Li, the E. Benjamin Wylie Collegiate Professor of Civil Engineering and a professor of Materials Science and Engineering.
© NASA/D Berry
A gamma-ray burst has been found at a distance of 13.1 billion light years from Earth - the most distant object ever confirmed to be seen.
A gamma-ray burst has been found at a distance of 13.1 billion light years from Earth - the most distant object ever confirmed to be seen.
The object is a gamma-ray burst (GRB) - the brightest type of stellar explosion. GRBs occur when massive, spinning stars collapse to form black holes and spew out jets of gas at nearly the speed of light. These jets send gamma rays our way, along with "afterglows" at other wavelengths, which are produced when the jet heats up surrounding gas.
