- Satellites See Evidence of One-Two Asteroid Punches on Mars
- NASA Climate Satellite Crashes After Launch
- Cosmic Rays May Not Come From Supernovas
Posted: 04 Mar 2011 11:46 AM PST
New images from two Mars-orbiting satellites capture times when the planet was pummeled by at least two meteorites at once.
The slug-shaped crater above, photographed on Aug. 4, 2010 by ESA's Mars Express spacecraft, was probably carved by a chain of projectiles coming in at a shallow angle. The 48-mile-long crater has no name, but it lies in Mars' heavily cratered southern highlands, just south of a large crater called the Huygens basin.
Astronomers have speculated that similarly oblong basins were formed by one oblique impact or by volcanic flows. But the shape of the material tossed out of this crater in the initial impact, called the ejecta blanket, suggests the unnamed scar came from a double punch. The blanket shows two distinct lobes like butterfly wings, hinting that each blob was excavated by a different incoming rock.
Three deeper areas inside the crater itself suggest that there could have been more than two impactors. Smaller craters that lie to the gouge's right probably formed later.
A photo taken Jan. 10 with NASA's HiRISE camera is even more striking. The image below shows two symmetrical, neatly overlapping craters that must have formed at the same time.
The assailing rocks could have been parts of a once-intact body that broke up on its way through Mars' thin atmosphere before slamming into the surface. Several known celestial bodies, including the rubbly asteroid Itokawa and the chicken-leg-shaped comet Hartley 2, would likely break in two and form simultaneous impact craters if they smacked into a planet.
Although planets suffer fewer slings and arrows now than they did in the solar system's youth, Mars is headed for another rough time. One of its moons, Phobos, will collide with the planet in a few tens of millions of years, breaking up in the process to form more wonky-shaped impact craters.
Images: 1) ESA/DLR/FU Berlin (G. Neukum). 2) NASA/JPL/University of Arizona
Posted: 04 Mar 2011 09:32 AM PST
By Mark Brown, Wired UK
The rocket carrying NASA's Glory satellite, an observation spacecraft designed to study the effect atmospheric particles have on the planet's climate, has failed to reach orbit due to an engineering glitch with its nose cap.
The Taurus XL rocket blasted off from the Vandenberg Air Force Base in California earlier this week, but just minutes after liftoff it suffered from a technical failure. The rocket's "fairing" — an aerodynamic cone designed to separate during the trip into space — didn't come off as planned.
"Telemetry indicated the fairing did not separate as expected about three minutes after launch," a NASA statement read. Without that crucial separation, the 1,160-pound rocket and satellite combo was too just heavy to reach its intended orbit 438 miles above Earth.
The $424 million satellite would have gone on a three-year mission to improve our understanding of how the sun and atmospheric particles called aerosols affect the planet's climate. It would have established the magnitude of aerosols in the atmosphere, and measured variations in the amount of radiation that enters Earth's atmosphere during the sun's decade-long solar cycle.
The mission was originally plagued by a computer glitch which caused a delay of more than a week. It also comes almost exactly two years after NASA's Orbiting Carbon Observatory (OCO) — another climate-tracking satellite that would have measured carbon dioxide levels — crashed into the ocean with an almost identical technical failure.
On 24 February 2009, the Taurus XL also failed to shed its protective fairing, and couldn't reach orbit. It crashed down in the ocean near Antarctica, putting the $270m satellite out of commission. At the time, NASA launch director Chuck Dovale said, "Our goal will be to find a root cause for the problem. And we won't fly Glory until we have that data known to us."
A duplicate version of Glory is now scheduled to launch from Vandenberg in 2013.
Posted: 04 Mar 2011 07:00 AM PST
The confirmed origin of ordinary cosmic rays may need to be unconfirmed.
"The mechanism for the acceleration of cosmic rays needs to be completely revised," says Piergiorgio Picozza, a physicist at the University of Rome Tor Vergata in Italy. Picozza is a co-author of a March 3 paper in Science detailing the new observations of the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics, or PAMELA, instrument.
Cosmic rays aren't actually rays. They're fast-moving particles that carry an extraordinary amount of energy and continuously bombard the Earth from every direction. The most popular explanation for the origin of these particles points to shock waves created by far-off supernovas, one of the few phenomena in the cosmos powerful enough to impart such energy.
According to that explanation, known as the diffusive shock acceleration mechanism, clouds of charged gas rush outward during a supernova and generate strong magnetic fields. These magnetic fields could accelerate charged particles to tremendous speeds and eject them into space.
Orbiting hundreds of kilometers above Earth, the PAMELA detector spent three years collecting cosmic ray particles; mostly nuclei of hydrogen and helium with energies ranging from a billion to a trillion electron volts, which is comparable to the energy of protons in the biggest particle accelerator in the United States.
Magnetic fields in a supernova should accelerate both hydrogen and helium particles in the same way: Graph the mathematical equations describing this push, and the curve for each particle should have the same slope. But in the PAMELA data, Picozza found a difference in these slopes that a single shock wave can't explain.
"The two particles seem to be accelerated by different mechanisms," he says.
Scientists should investigate other astronomical objects as possible sources of cosmic rays, Picozza says. One place to look proposed by Russian physicists is in the novas, or smaller explosions, produced when white dwarf stars belch out energy. Another option is giant superbubbles of gas blown around the universe by stellar winds, says Picozza.
But Mikhail Malkov, a plasma physicist at the University of California, San Diego, who studies supernova shock waves, isn't ready to toss out the existing cosmic ray theory. "The data look statistically significant, but it's too early to say that the supernova acceleration model is in trouble. This statement is too strong," says Malkov.
Space telescopes peering into the remnants of supernovas have found lots of evidence over the years to support the supernova shock wave theory — including gamma rays that reveal the structure of magnetic fields, and missing energy that could have been spent making cosmic rays.
Malkov says the difference between Picozza's hydrogen and helium curves is small, and it could be accounted for simply by tweaking the existing supernova model. Malkov hasn't worked out the details yet, but he suspects that PAMELA may be seeing cosmic rays created by a shock wave that wasn't completely uniform or a mishmash of particles released by two different supernovas.
Image: Illustration of a cosmic ray shower. (Cosmus/University of Chicago)
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