cosmos
First Earth-sized planets netted
The newest exo-apples of the planet-hunting Kepler space telescope’s unblinking eye are two rocky, Earth-sized planets hovering around Kepler-20, a sunlike star 950 light-years away.
Though snuggled too close to their star to be habitable, these first Earth-sized worlds confirmed by the Kepler team are another big step forward for the planet hunters, who recently found a planet somewhat larger than Earth orbiting a sunlike star at a distance hospitable to life. Finding habitable distant worlds — Earth-sized planets at the right distance from their stars to allow the presence of liquid water — is the team’s ultimate goal.
“The hunt is on to find a planet that combines the best of both of these worlds — a true Earth twin,” says David Charbonneau, an cosmos astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and a coauthor of a study describing the small planets that appears online December 20 in Nature.
One of the planets, the pragmatically named Kepler-20e, is a bit smaller than Venus — 0.87 times as wide as Earth — and completes a trip around the star every 6.1 days. The other, Kepler-20f, is 1.03 times as wide as Earth, and a year on that planet would last just 19.6 days. Because the planets are so small, they’re probably made of ingredients similar to Earth’s.
Depending on where and how it formed, Kepler-20f could even have developed a water vapor atmosphere, says planetary scientist Jonathan Fortney of the University of California, Santa Cruz. “If it started out with the amount of water we had on Earth and Venus, it’s probably long gone — just like it is on Venus,” he says. “But if that planet had a tremendous amount more water, then it might have some left over.”
The Kepler-20 system is a quintet comprising three large planets (Kepler-20b, c and d) and the two Earth-sized ones, all tucked in nearer to their star than Mercury is to the sun. Moving out from Kepler-20, the five spheres alternate in size, with the runts of the planetary litter bracketed on either side by their bigger siblings.
“It’s one of the most shocking architectures we’ve seen,” Charbonneau says. “Exoplanets have had a lot of surprises, but this is going to be very difficult to explain.”
The strange — but stable — configuration is encoded in the blips and blinks the planets produce as they pass in front of their sun, which is one of more than 150,000 in a field of stars the telescope stares at. Different-sized blips correspond to different-sized cosmos planets, and watching the star for long enough reveals how frequently each planet completes its journey.
Currently set to wrap up at the end of 2012, the mission could be extended for several more years if limited budgets allow. More observing time will let scientists monitor Kepler’s starry patch for long enough to detect Earth-sized planets in longer, habitable orbits.
“The spacecraft doesn’t know about politics and financial difficulties — it will continue to beam data back to Earth until at least 2015, even if no one is listening,” says astronomer Debra Fischer of Yale University. “You just have to keep the lights on, and keep the science team intact. The next three years are where they’re going to detect the Earths at habitable distances.”
HIGGS IN THE SPOTLIGHT
Colliding protons create a splash of particles streaking outward along paths (yellow) reconstructed here from data collected by the CMS detector at CERN’s Large Hadron Collider. A pair of photons emerging from this smash-up (red bars) qualify this event as a potential Higgs sighting.
Arctic ozone loss in 2011 unprecedented-Cosmos
Record ozone depletion over the Arctic early this year rivals what was observed in the Antarctic when holes in the protective atmospheric layer first appeared there during the 1980s.
The observation raises concerns that portions of the Northern Hemisphere might periodically begin experiencing potentially harmful levels of ultraviolet radiation during early spring, an international team of scientists reports online October 2 in Nature.
“It was significantly worse than anything we have ever seen,” says Geir Braathen of the World Meteorological Organization in Geneva, who was not one of the authors of the Nature paper. Typically, spring Arctic ozone depletion has maxed out at a drop of between 20 and 30 percent, the atmospheric chemist notes. “But in 2011, we had a loss of around 40 percent.”
In Antarctica, 70 percent of the ozone can disappear in springtime, Braathen says. Within a 5- to 7-kilometer–thick band of the stratosphere, ozone concentrations actually plummet to zero, he says.
Arctic conditions have not gotten nearly that bad, says Michelle Santee of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., one of 29 authors of the new Arctic ozone analysis.
Although ozone can be found at any altitude over the Arctic, most accumulates between 14 to 21 kilometers up. There, concentrations hover around 4.5 parts per million much of the year. But in late March, “there was an approximately 2-kilometer altitude region where ozone fell to around 0.7 ppm,” Santee says — “meaning the ozone was pretty much gone.” In small regions, she adds, patches of the Arctic stratosphere saw ozone drop to 0.5 ppm.
It takes four things to destroy much of the stratosphere’s ozone: sunlight; very prolonged cold temperatures; a stable vortex of winds that prevents ozone losses inside it from being replenished with more from outside; and the presence of special clouds that foster the transformation of benign chlorine molecules into ozone-vanquishing types. For the first time in the Arctic, all of these conditions aligned for months, says JPL atmospheric scientist and coauthor Nathaniel Livesey, “making it the perfect storm.”
Although clearly anomalous, this year’s Arctic ozone loss could be the harbinger of worse things to come, comments Ross Salawitch of the University of Maryland in College Park. Although prolonged cold spells in the stratosphere hit only every few years, those in recent winters have been increasingly extreme, he says. There’s some concern that a progressive warming at Earth’s surface is responsible for cooling of the stratosphere, he says. The new Nature paper “sets the stage for asking: Is climate change playing a role?”
Travels with the Sun
When three astronomers discovered a small Sun-orbiting object far beyond the orbit of Pluto in 2003, they called it Sedna, for an Inuit goddess living at the bottom of the Arctic Ocean.
A very fitting name, it turns out, for Sedna has since been telling tales of visits to the deep: to the inner reaches of the Milky Way galaxy. Her ride: the whole Solar System, according to an article in this month’s issue of the journal of planetary science Icarus.
The travels of Sedna around the Sun, and of the Sun around the centre of the galaxy cosmos, can be combined nicely to solve a pair of puzzles in celestial dynamics. For Sedna itself, the riddle is the shape of her orbit. When the Solar System was formed, a dusty disk around the young sun clumped into planets, going around her in roughly circular orbits.
Sedna is presumably one of them, a dwarf planet cosmos, but her orbit is elongated. This suggests that one of the large planets, probably Neptune, once gave her a gravitational push.
The physics of such encounters predicts that the resulting orbit should bring Sedna regularly near Neptune again. But calculations show that she will give the god of the seas a wide berth forever. That means some heavenly body must have pushed her around some more. And rather than some planet, another star is generally thought to be the most likely culprit.
To this picture, now add another emerging view of the Sun’s past and present environment: that she may not always have followed the same path within the disk of the Milky Way galaxy. In this disk, most of its stars are born, after which they are supposed to go around the center of gravity of the whole thing in roughly circular orbits.
For years, cosmos astronomers have struggled with a contradiction here. If stars at a certain distance of the centre of the galaxy always stay at this distance, this ring of stars forms a distinct family. The stars convert hydrogen and helium into heavier elements – ‘metals’ in astronomical parlance. Because they eventually explode, the mix of gas from which each next generation of stars is made becomes steadily more ‘metal-rich’.
Analysis of the colours of starlight will tell you how ‘metallic’ a star is. And for the Sun’s local neighbourhood this is where the puzzle appears: old stars should have relatively low metallicity, because they formed from virgin interstellar material. And young stars should appear to be formed from older gas that contains more star-leftovers and is thus more ‘metallic’. But the actual picture is far more jumbled.
One explanation could be that stellar mixing occurs: stars might move inward or outward from their original level into regions of the galaxy where the metallicity of stars and gas is different, with a different history, thus spoiling the tidy picture the astronomers expected to see.
This migration in the radial direction could be accomplished by close encounters between stars or by the passage of one of the galaxy’s spiral arms – in fact a wave that ripples through the stars, temporarily packing them closer together like a sound wave does with air molecules.
Until recently, that solution, attractive as it is, had a snag of its own: stars that were thrown off course in that way should have elongated orbits – just like Sedna’s is around the Sun. Elongated stellar orbits do exist, but they are not common enough to provide all the stellar mixing that seems to be going on.
