2012년 11월 22일 목요일

Super-Earths Get Magnetic 'Shield' from Liquid Metal

Within supersized alien versions of Earth, a common transparent ceramic may become a flowing liquid metal, perhaps granting those distant worlds magnetic fields to shield life from harmful radiation, researchers say.
Among the hundreds of extrasolar planets, or exoplanets, that astronomers have discovered in recent years are so-called "super-Earths," which are rocky planets like Earth but larger, at up to 10 times its mass. Scientists have discovered super-Earths that may support oceans of water on their surfaces on their surfaces, and others that may even be planets made of diamond.
The increased mass of super-Earths would bring about internal pressures much greater than Earth's. Such high pressures would lead to large viscosities and high melting temperatures, meaning the interiors of super-Earths might not separate into rocky mantles and metallic cores like Earth's does.
Earth's magnetic field results from its flowing liquid metallic core. If super-Earths lack such dynamic cores, investigators suggested they might lack magnetic fields as well.
Now, researchers find that magnesium oxide, a common rocky mineral on Earth, can transform into liquid metal at the extreme pressures and temperatures found in super-Earths. This fluid metal could help generate magnetic dynamos in super-Earths, they say.
Magnesium oxide is a transparent ceramic found from Earth's surface to its deepest mantle. To see how this rocky material might behave in alien planets, researchers fired powerful lasers at small pieces of magnesium oxide, in just 1 billionth of a second, heating and squeezing this mineral to conditions found inside super-Earths, such as pressures up to 14 million times normal Earth atmospheric pressure and temperatures as high as 90,000 degrees Fahrenheit (50,000 Celsius). They watched this rocky substance change to a solid with a new crystal structure, and finally into a liquid metal.
"What was most surprising was how well-behaved magnesium oxide is in the laboratory," said lead study author R. Stewart McWilliams, a geophysicist at the Carnegie Institution of Washington. "The physical properties of magnesium oxide look very similar to what has been predicted for decades by theorists. As scientists, we can't ask for much better."
These findings might blur the distinction between planetary cores and mantles.
"For many decades we have usually imagined terrestrial planets — the Earth, its neighbors such as Mars, and distant super-Earths — as all having Earth-like properties: that is, they have a outer shell or mantle composed of nonmetallic oxides, and an iron rich core which is metallic and from which planetary magnetic fields originate," McWilliams told.
 "This rule is central to our thinking about super-Earths, yet it is clearly anthropocentric — that is, we are applying what we know from our own observations on Earth to remote planets for which we can observe very little — and, as for many anthropocentric ideas, we are finding that more imagination is needed to understand such alien worlds.
"Our results show that the usual assumption that planetary magnetic fields originate exclusively in iron cores is too limiting," McWilliams said. "Magnetic fields might also form within planetary mantles. In fact, this idea has been speculated on for decades, but now we have hard data to show that, indeed, such a 'mantle-dynamo' is plausible."
Earth's magnetic field helps protect it from hazardous electrically charged particles from space.
"It is often said that life on planets may require the presence of a strong magnetic field to protect organisms from dangerous radiation from space such as cosmic rays — at least this may be true for certain types of life, similar to humans, that live on a planet's surface," McWilliams said. "We find that magnetic fields may occur on a wider range of planets than previously thought, possibly creating unexpected environments for life in the universe."
McWilliams noted that much remains unknown about the physics of super-Earths, and that researchers need to generate computer models to see where and how this liquid metal might exist in nature.
"Everyone, both scientists and the public, should keep in mind that super-Earths are, and probably will remain for some time, a big mystery," McWilliams said. "It is easy to speculate as to their properties — to draw a picture of one, for example — but quite difficult to make certain conclusions such as we have for our own Earth. This is both exciting and daunting — there are many possibilities to explore, but scientists have much work to do. We hope the public has a lot of patience."

Source of Article : space.com

Dwarf Planet Beyond Pluto Lacks Atmosphere

Distant starlight has given astronomers the best look yet at a distant icy sibling of Pluto, a dwarf planet called Makemake that appears to be missing its atmosphere, researchers say.
Although this icy world currently lacks an atmosphere, there is still a chance it could form one like a comet when it approaches the point in its orbit that is closest to the sun, scientists added.
In the past decade, astronomers have discovered a slew of "dwarf planets" that dwell with Pluto beyond the orbit of Neptune. Makemake was a world nicknamed "Easterbunny" by its discoverers before officially getting named after the Polynesian creator of humanity and the god of fertility.

The dwarf planet's red-tinged surface is apparently covered by a layer of frozen methane, and is bright enough to be seen by a high-end amateur telescope, despite its current distance of nearly 53 times the distance between the Earth and the sun.
Makemake: A plutoid revealed
Makemake is a type of icy dwarf planet known as a plutoid, as are Pluto and the newfound trans-Neptunian worlds Erisand Haumea.
Whereas Pluto has a tenuous atmosphere surrounding it, its near-twin Eris does not, most likely due to Eris's greater distance from the sun and colder surface temperature. Makemake orbits at an intermediate distance from the sun between Pluto and Eris, raising the question of whether it might possess an atmosphere.
In 2011, Makemake passed directly in front of the distant star NOMAD 1181-0235723. This eclipse or occultation helped backlight the icy world, and researchers now reveal data from seven telescopes of this eclipse has helped them pin down Makemake's size, shape and surface properties better than ever. 
"For me it is extremely remarkable that we can get an accurate knowledge of important properties of these mysterious dwarf planets even though they are so far away from the Earth," said lead study author Jose Ortiz, a planetary scientist at the Institute of Astrophysics of Andalucía in Granada, Spain. "Only three years ago we had never observed a single occultation by a trans-Neptunian object, and now we have managed to observe 12 such events, nine of them by our international team."
Such occultations are extremely difficult to predict and observe. For comparison, these worlds are so distant they appear about the same size "as that of a coin seen at a distance of 30 miles (50 kilometers) or smaller," Ortiz told SPACE.com. "But thanks to our hard work and to an important international collaboration, we were able to beat all the difficulties."
Makemake is about 890 miles (1,430 km) wide, making it about two-thirds the diameter of Pluto. Light from this distant star appeared and disappeared quickly as Makemake passed in front of it. This suggests there was no significant atmosphere around it to smear out the star's light.
At most, Makemake's atmosphere is 80 million to 250 million times thinner than Earth's at sea level, the researchers calculate. Still, there might be patches of atmosphere overlying warmer regions on its surface, such as dark patches that absorb more sunlight.
"We suspect that these dark patches might be concentrated near the latitude of the subsolar point of the planet — the subsolar point is the point of the planet where the solar rays reach the surface perpendicularly, and therefore cause the maximum heating possible," Ortiz said. "These dark patches might form sort of a dark band in the planet."

Wispy atmosphere still possible
Other bodies with patchy atmospheres include Jupiter's moon Io and Saturn's moon Enceladus, which arise "mostly from gas released by volcanoes or the so-called cryovolcanoes, 'volcanoes' which instead of releasing magma release liquid water or a liquid mix," Ortiz said. "Even Mars has areas with a locally denser atmosphere, which in this case arises from sublimation of carbon dioxide ice."
Makemake might very well behave like a comet and grow an atmosphere during the parts of its year when it approaches the sun.
"We suspect that this is the case," Ortiz said. "But comets are usually so small and have so little mass that their gravity does not allow them to retain the atmospheres, which escape to space giving rise to the comets' tails. In the case of Makemake, its gravity is much higher and therefore the escape of the gases is not as dramatic as that of the comets."
Future research can focus on looking for other stellar occultations by large trans-Neptunian objects.
"We can now investigate trans-Neptunian objects with far more in depth than we could a few years ago, thanks to the stellar occultation technique," Ortiz said. "This will not only shed light on atmospheric phenomena, but also on important physics of these bodies. We would also like to explain and understand the similarities and differences in composition of the trans-Neptunian objects in general, which requires theoretical developments, models of different physical phenomena and plenty of work in many fields."
The scientists detailed their findings Nov. 22 in the journal Nature.

Source of Article : space.com

2012년 11월 12일 월요일

Comet Collisions Fuel Star's Oddly Young Look

A cosmic mystery around the star named 46 CETI has puzzled astronomers nearly two decades, but it may finally be solved. At 40 million years old, the star is quite ancient, and yet it's surrounded by a tremendous amount of gas — a signature feature of young stars that usually fades within 10 million years, scientist say.
So what keeps 49 CETI looking young? A new study suggests that a prolific number of comet collisions are rejuvenating the star's fresh appearance. So many comet collisions, in fact, that the crashes have occurred every six seconds for the past 10 million years.
A team of astronomers reports that gas surrounding 49 CETI can be explained by a massive disk-shaped region around star that is similar to our solar system's Kuiper Belt. The belt around 49 CETI is 4,000 times more massive than our solar system's Kuiper Belt, which lies beyond the orbit of Neptune, and is packed with more objects constantly crashing into each other.

"Imagine so many trillions of comets, each the size of the UCLA campus — approximately 1 mile in diameter — orbiting around 49 CETI and bashing into one another," study researcher Benjamin Zuckerman, a UCLA professor of physics and astronomy, said in a statement. "These young comets likely contain more carbon monoxide than typical comets in our solar system. When they collide, the carbon monoxide escapes as a gas."
Zuckerman and his colleagues calculated that these comets crash into each other around 49 CETI about every six seconds. What's more, they estimate this has been going on for a long time.
"I was absolutely amazed when we calculated this rapid rate," Zuckerman. "I would not have dreamt it in a million years. We think these collisions have been occurring for 10 million years or so."
Zuckerman and his colleagues had discovered the gas that orbits 49 CETI back in 1995 using a radio telescope in the Sierra Nevada Mountains of southern Spain and had been trying to explain its origins ever since. The group says they only know of one other old star that's surrounded by so much gas, but it's considerably younger than 49 CETI at 30 million years old.
The new research was detailed in the Sept. 27 edition of the Astrophysical Journal.

Source of Article : space.com

Inside NASA's New Spaceship for Asteroid Missions

The re-election of President Barack Obama has kept NASA on track to send human explorers to an asteroid, and that means work on a 21st-century spacecraft to fly astronauts to the target space rock and hover nearby — or maybe even pogo off its surface — will go ahead as well.
As of 2010, Obama has challenged NASA to get astronauts to an asteroid by 2025, and on to Mars by the mid-2030s. Whether or not the space agency can stick to that schedule largely depends on its future budget, experts say, but regardless of the pace, work on the asteroid mission is already under way.
The Multi-Mission Space Exploration Vehicle (SEV) is a prototype that began its design life as a wheeled moon rover. When the president shifted NASA's focus from the moon-oriented Constellation program set up by the Bush administration, the space agency adapted the SEV to meet the needs of an asteroid mission instead.

That meant taking off the wheels and converting the vehicle into two parts: a robotic sled that will be used for propulsion and guidance, and a detachable crew cabin that can be fitted on top.
Floating tests
Prototype versions of the sled and crew cabin are being built and tested at NASA's Johnson Space Center in Houston. There, engineers have set up a surface that resembles an air hockey table for the vehicles to float on to simulate frictionless motion in microgravity.
"We're just trying to simulate the feeling of weightlessness in two dimensions to simulate what three dimensions will be like," said Hugo Martinez, project manager for the SEV's sled at Johnson Space Center.
Transitioning the SEV from a moon-bound craft to an asteroid-targeted vehicle require significant changes. Not only can the spacecraft not drive around on the surface of an asteroid — it probably can't event land there.
"It won't land like it would on the moon or any other planet because asteroids are so small there's no gravity to speak of," Martinez told SPACE.com during a September interview. "So we're kind of docking with it."
SEV Sled Worker
A NASA engineer works on a mockup of the sled component of the SEV spacecraft, attaching wiring onto this preliminary prototype.
CREDIT: Clara Moskowitz/SPACE.com
The engineers have fitted the prototype SEV with robotic arms that may be able to grab onto the surface of an asteroid. "Alternatively, we're carrying enough propellant onboard that if you can't dock, you're going to have to maintain relative attitude to it going around it. It's got to be sized to basically hover over the surface in a lot of different positions. That drives a completely different design than a conventional lander."
Space pogo stick
Furthermore, if neither of these "docking" systems works with the asteroid in question, the scientists are thinking of another option: a pogo stick.
A "stinger" protruding from the front of the spacecraft could be used to spring around the surface of the space rock. "When you get to an asteroid, instead of having to hover all the time, you'd kind of softly bounce off of it. It's pulling you in with a wimpy amount of gravity and then you can just kind of balance on top of it."
This idea needs some testing out, so the engineers plan to barricade the trial sled inside a small area with a model asteroid, and use the air hockey floor to try out pogo-ing.
And the stinger isn't the only element of the SEV that needs work. Many of the design features of the vehicle are in the early stages, and the details still need to be tested. If the current schedule holds, NASA could test-drive a version of the SEV at the International Space Station in 2017. Although pogo-ing off the station is not in the offing.
"We would take just the sled, maybe with a cabin, up to the space station," Martinez said. "We would do stuff there to build our confidence" with the design.
Although there are many unresolved details, the basic technology required to build the SEV is within reach, he said. The political and funding future for the program is much more of a risk than the technology itself.
"The biggest problem is political, is not knowing which way you're going," Martinez said. "Technically, I think we really don’t have any big challenges. If we're given a goal and enough money to do it, I think we can do it."
The plan would be to send an unmanned precursor mission to an asteroid first, with the sled component of the SEV alone, equipped with scientific instruments to do preliminary studies. If that went well, humans would follow in a cabin-sled combination.
Astronauts will likely launch on a new heavy-lift rocket being developed called the Space Launch System, inside a capsule under construction called Orion. Once in space, Orion could dock with the SEV to allow astronauts to transfer over.
Another real challenge for such a manned mission to an asteroid is the issue of protecting humans from radiation. No technology currently exists to adequately shield a spacecraft from the harmful radiation in space without weighing a space vehicle down prohibitively.
"That continues to be the biggest hurdle to really going to an asteroid," Martinez said. The unmanned precursor mission, at least, shouldn't be too hard.
"We've got the technology to do it. It'll take money and it'll take time," he said.

Source of Article : space.com

2012년 11월 6일 화요일

Pristine Moon Crater Could Help Unlock Impacts' Secrets

Scientists trying to understand the evolution of impact craters on Earth and other rocky bodies have found a good case study on the moon.
Researchers are focusing on Linne Crater, which lies in the moon's Mare Serenitatis region. Linne is just 1.4 miles (2.2 kilometers) wide, but it's extremely young — having formed just 10 million years or so ago — and beautifully preserved.
Craters don't erode nearly as quickly on the moon as they do on Earth, where wind and water reshape and fill in craters at a rapid clip. But Linne is pristine even for a lunar crater, researchers said; it shows no signs of any subsequent major impacts, retaining its original shape more or less intact.
And that shape is a bit of surprise. Scientists had thought simple lunar craters such as Linne should be bowl-shaped. But observations by NASA's Lunar Reconnaissance Orbiter spacecraft (LRO) show that Linne is actually an inverted cone.

Linne's shape and the way rocks are scattered around its rim could help shed light on how craters start out on Earth and Mars, and how weathering wears them down, a new NASA video explains.
"Without craters like Linne on the moon, we wouldn't know how landforms evolve over time in the presence of weather, climate change and other factors," the video's narrator says.
NASA launched the $504 million Lunar Reconnaissance Orbiter in June 2009 to map the moon in unprecedented detail with seven different instruments.
The spacecraft, which is about the size of a small car, is studying the lunar surface for scientific and exploration purposes. Its maps will help researchers identify safe landing sites for future human missions, assess lunar resources such as water ice and better understand how the moon's radiation environment may affect humans, NASA officials say.
LRO has already gathered as much data as all other planetary missions combined, officials say.

Source of Article : space.com