2013년 10월 16일 수요일

Black Holes May Have 'Hair'

Black holes may not be bald after all.
In a challenge to traditional models of the universe's gravitational monsters, new research suggests black holes could be quite "hairy," with more tangled features than previously believed.

The gravitational attraction of black holes is so strong that even light cannot escape their pull, making these super-dense objects invisible to outside observers and almost indistinguishable from one another.

"The accepted picture is that black holes are very simple objects that can be fully characterized by only 3 quantities: their mass, their angular momentum (how fast they spin) and their electric charge," Thomas Sotiriou, a physicist at the International School for Advanced Studies of Trieste, told SPACE.com in an email.

The electric charge, however, is usually negligibly small, and researchers typically throw it out when describing a black hole.

Astronomer John Wheeler, who coined the term "black hole" nearly 50 years ago, famously said that "black holes have no hair" because of their simplicity. Now "hair" is used as a colloquial term among physicists as a stand-in for any other measure needed to describe a black hole that departs from the traditional three-quantity model.
For their study, Sotiriou and his colleagues looked at black holes in the context of the equations of scalar-tensor theories of gravity.

"These are theories different than Einstein's theory, general relativity," Sotiriou wrote in an email. "They also describe the gravitational field in term of curvature of spacetime and predict the existence of black holes. However, they include also a different kind of field — a scalar field — to participate to the mediation of the gravitational interaction."
The researchers found that black holes develop scalar "hair" when ordinary matter surrounds them.

"This does not happen in the standard picture," Sotiriou said.
It's not clear from the study if these strands of scalar "hair" make black holes look much different from the standard picture, and it's not clear how observable the effect is with current technology, Sotiriou explained.

Not only would the existence of "hair" help researchers understand the structure of black holes themselves, proof of "hairy" black holes could represent a paradigm shift, Sotiriou said, since Einstein's theory does not include a scalar field.

Source of Article: Space.com

Does Mercury Hold Clues to Birth of Earth's Moon?

Mercury, the smallest planet in our solar system, may hold clues to understanding how the Earth's moon was born, a scientist studying the planet says.

Just like the moon, Mercury is a desolate, rocky and airless body, albeit a bit bigger than Earth's satellite, said Sean Solomon, the principal investigator for NASA's Messenger mission to Mercury. He presented the idea of using Mercury to glean insights into Earth's moon at the recent Origin of the Moon conference held here at the Royal Society.

There is currently no theory that can successfully tick all the boxes answering the question how the moon formed. The most popular theory is that it was produced after a planet-size body nick-named Theia smashed into the infant Earth some 4.5 billion years ago, with the moon coalescing from material blasted out from the catastrophic impact.

But this Great Impact theory has shortcomings, and researchers are trying numerous angles to find fresh clues, including the studies on the origins of Mercury by Solomon and his colleagues.

In March this year, the $446 million Messenger spacecraft successfully finished mapping the small planet’s entire surface. The spacecraft launched in 2004 and arrived in orbit around Mercury in 2011. Scientists are now sifting through the heap of data beamed back by Messenger.  

Volcanic twins?

One of the most remarkable findings so far are the astonishing similarities between moon and Mercury, particularly with regards to their geological history.

"Mercury and the moon [seem to] have followed very similar tracks," said Solomon, who is also director of the Lamont-Doherty Earth Observatory of Columbia University in New York.

It is striking, given that Mercury is thought to have formed from the material that made up the early disk of gas and dust spinning around the sun, and not due to a giant impact like the moon, Solomon added.

Just like the moon, a part of Mercury's surface is relatively smooth terrain. On Mercury, these plains cover 27 per cent of the surface, on the moon around 16 per cent. Scientists think that the plains of both bodies formed billions of years ago from volcanic eruptions that covered the surface with low-viscosity lava, effectively flooding low-lying regions and partially filling or burying old craters.

Although Mercury's ancient cratered uplands and younger volcanic plains are differently composed than their lunar equivalent, they are very similar in their topography and also about the same age.

It means that "both bodies also had explosive volcanic eruptions that produced what are known as pyroclastic deposits, the pyroclastic glasses," Solomon said. Volcanic glasses are molten rocks that cooled and solidified on a space body’s surface.

The moon's volcanic glasses, however, are primarily basaltic in chemistry and darker than their surroundings. Those on Mercury are brighter and redder than the rest of the surface.
Despite the differences, it is significant that "in volcanic eruptions there was a sufficient content of volatiles in the magma to drive the fire fountain eruptions that produced the glasses," Solomon said, explaining that "volatiles" are gases that can escape extremely easily.

The similarities between the moon and Mercury don't stop there.
Both bodies have polar ice deposits formed in regions of permanent shade and preserved for eons because of the resonance between the planet's spin rate and orbital period. And finally, Solomon said, Mercury and the moon have strong hemispherical differences, meaning that each has two sides that are markedly different from each other.

While basaltic plains prevail on the side of the moon that permanently faces the Earth, the moon's far side is almost completely covered in craters.
"The moon also has a remarkable concentration of heat-producing elements on the near side, and the presumption is that this side was hotter for a longer period of time. It differs perhaps even chemically from the far side," Solomon said.
Mercury also has important hemispherical differences: Most of its volcanic plains are in the northern hemisphere.

Mercurial rocks

So what can all this tell scientists about the origin of the moon? After all, the two bodies have significant differences: unlike the moon, Mercury has a global magnetic field; its density is higher; there is an abundance of volatile elements such as sulfur; its surface contains much less iron, particularly in its crustal silicates — which indicates that the processes deep inside both bodies have been very different.

But Solomon says we should look at the many commonalities of their geological evolution.
"It means that many aspects of the moon are common to rocky bodies that are similar in size despite being different in bulk composition," he said. "Therefore, we have to focus on those aspects of the moon that are special, if we want to gain traction on the question of what made the moon as opposed to what made the planets."

One stumbling block of the giant impact theory of moon formation has been the incredible isotopic similarities between the Earth and the moon.
Indeed, if a large object that hit the Earth was different from it, why then are the planet and its satellite so isotopically alike?

One thing that could really help solve this riddle, is a sample from Mercury — from a meteorite or a future mission, Solomon said.

If Mercury happens to be isotopically similar to Earth, it would mean that most of the material in the early disk spinning around the Sun shared isotopic characteristics — and that the objects that collided to grow the final stages of the Earth and created the moon started out with a similar composition.

However, such a scenario would leave an odd one out: Mars.
Mars is isotopically different from Earth. If Theia had had Mars' isotopic composition, the oxygen isotopes on Earth and moon would be quite distinct.
But if Mercury turns out to be similar to Earth, it could imply that there was some process that homogenized the isotopes of all planets between the sun and Mars — and this is "the big question right now," said Jay Melosh, Distinguished Professor of Earth, Atmospheric and Planetary Sciences at Purdue University.

"If there was [such a process] then Theia might have had a nearly identical isotopic composition to Earth and all our puzzles about why the Moon and Earth are so similar isotopically then evaporate," he added. "The process obviously did not affect Mars, but it did affect the planets closer to the sun."

Source of Article: Space.com

Superbright Supernovas' Cause Potentially Revealed

The cause of a mysterious, long-lasting, superbright form of supernova, the most energetic stellar explosion in the universe, may now have been discovered, astronomers say.

Surprisingly, these outbursts may be driven by the birth of magnetars, dead stars that rank among the most powerful magnets in the cosmos, according to a study published online today (Oct. 16) in the journal Nature.

Supernovas result from the deaths of stars. These explosions can briefly outshine all of the other stars in their galaxies.

More than a decade ago, scientists first detected a new, extremely rare class of supernova. These incredibly bright explosions, known as superluminous supernovas, are up to 100 times brighter than other types of stellar outbursts.

A number of these explosions fade very slowly, matching theoretical models of what are called pair-instability supernovas. Astrophysicists suspected that within the extremely massive stars thought to give rise to pair-instability supernovas — ones more than 140 times the mass of the sun — conditions are just right for gamma-rays, the highest-energy form of light, to convert into pairs of electrons and their antimatter counterparts, known as positrons.

These gamma-rays normally exert pressure that helps support the star against the crushing effects of its own gravity. However, as gamma-rays get converted to matter, the star loses this support and collapses in on itself. This, in turn, causes a runaway explosion that completely obliterates the star.

Scientists had suggested these slow-fading explosions generate huge amounts of radioactive matter, enough to equal several times the mass of the sun. This debris produces superluminous supernovas' slowly dimming light through radioactive decay, according to the idea.

Now, however, researchers have discovered two superluminous supernovas whose slow-fading light was apparently not generated by radioactive decay. Instead, these supernovas may be caused by a type of explosion that creates extremely magnetic neutron stars known as magnetars.

Astronomers discovered two superluminous supernovas named PTF 12dam and PS1-11ap, which lie about 1.6 billion light-years and nearly 10 billion light-years from Earth, respectively. The light from these explosions was blue in color and increased rapidly to their peaks over the course of about two months, whereas pair-instability supernovas should be redder and increase more slowly.

Computer models suggest explosions that create magnetars could generate the light patterns seen from these newfound supernovas. Magnetars are a kind of neutron star, remnants of dead stars that are only about as large as a city but contain at least as much mass as the sun.

Magnetars possess magnetic fields up to 5,000 trillion times more powerful than that of the Earth. Magnetars that expel glowing matter in vast amounts more than 10 to 16 times the mass of the sun during their births could explain these newfound supernovas, researchers said.

"It was exciting to find such a great match to the predictions of the magnetar model, which also fits most of the fast-declining superluminous supernovas," study lead author Matt Nicholl, an astronomer at Queen's University Belfast in Northern Ireland, told SPACE.com. "Two types of supernova which previously looked very different can actually both be explained quite nicely by this model."

The brightness and colors of PTF 12dam and PS1-11ap are similar to another recently observed superluminous supernova, SN 2007bi, originally suggested to be a pair-instability explosion. This suggests that pair-instability explosions may be even rarer than before thought, accounting for less than one out every 100,000 supernovas.

SN 2007bi was only thought to be one of a handful of pair-instability supernovas. These new findings could banish pair-instability supernovas back to the realm of theoretical possibility, although they do not rule them out, Nicholl said.

Source of Article: Space.com

Huge Chunk of Russia Meteorite Pulled from Lake

Divers raised a coffee-table-size chunk of the Chelyabinsk meteorite from its muddy home at the bottom of Russia's Lake Chebarkul on Wednesday (Oct. 16).

The massive boulder is the largest fragment recovered so far from the Feb. 15 Russian meteor explosion over the city of Chelyabinsk that injured more than 1,000 people.

The blast scattered meteor shards across the region and left holes in the ice-covered Lake Chebarkul, so it was assumed that big lumps fell into the lake. Later surveys revealed possible extraterrestrial rocks buried beneath the bottom mud.

Recovery crews have since pulled five meteorite chunks from the lake, RT.com reported.
The 5-foot-long (1.5 meters) rock dragged from the depths Wednesday was 65 feet (20 m) below the surface. After it was pulled to the surface with cables, the meteorite fragment fractured into three pieces, shown live on Russian television.

Together, the dark, craggy stones weighed more than the scale brought to the lake could read, tipping in at more than 1,250 lbs. (570 kilograms), AFP reported. Preliminary tests confirmed the rocks are from the Chelyabinsk meteorite.

Pictures and video from the retrieval effort show telltale signs of the meteorite's fiery trip through the atmosphere. There's a fusion crust — a shiny, glassy layer of black material that forms when the outer portions of the rock melt. The rock also appears to have regmaglypts, shallow surface indentations that look like thumbprints.  

The Chelyabinsk meteorite is a mix of different types of ordinary chondrites, the stony meteorites that crash into Earth most often, researchers have found. The mélange inside the fragments suggests the meteorite may have collided with another asteroid early in its history.

Researchers have estimated that the asteroid that caused the Chelyabinsk fireball was about 55 feet (17 m) wide and weighed 10,000 tons when it streaked into Earth's atmosphere.

It hit on Feb. 15, the same day a 130-foot (40 m) asteroid called 2012 DA14 gave Earth a close shave, missing our planet by just 17,200 miles (27,000 kilometers). But the two space rocks are unrelated, experts say.

Source of Article: Space.com

2013년 10월 13일 일요일

Scientists Cook Up Mars-Like Clouds On Earth In Former Nuclear Reactor

Scientists have created Mars-like clouds in a former nuclear reactor here on Earth.
Clouds formed under Mars atmosphere conditions in a three-story-tall chamber in Germany after researchers cranked up the humidity to 190 percent — nearly double the threshold required for clouds on our own planet.

This discovery should help improve weather predictions on Mars, which previously were hampered by assumptions based on what we know from Earth, researchers said.

"A lot of atmospheric models for Mars are very simple," lead author Dan Cziczo, an atmospheric chemistry professor at the Massachusetts Institute of Technology, said in a statement. "They have to make gross assumptions about how clouds form: As soon as it hits 100 percent humidity, boom, you get a cloud to form. But we found you need more to kick-start the process."

NASA's Opportunity rover was the first to spot high-altitude wispy clouds on Mars in 2004. From the rover's vantage point in Meridiani Planum, the clouds looked surprisingly like cirrus clouds on Earth and were likely made up of water ice, researchers said at the time.

Cziczo's team hoped to better understand the conditions under which such clouds come to be. Most of the experiments took place in a former nuclear reactor in Karlsruhe, Germany that is now used as the world's largest cloud chamber. The facility, called the Aerosol Interaction and Dynamics in the Atmosphere (AIDA), has only done simulations of Earth environments before.

To make the chamber more Mars-centric, Cziczo's team removed all the oxygen from the chamber and replaced it with nitrogen and carbon dioxide, which make up most of the Red Planet's atmosphere. Because Mars is extremely dusty, they added particles that are similar in size and makeup to those found on the Red Planet. The dust is important because, as on Earth, water vapor gloms onto these particles and forms clouds.

As a control, the researchers moved the temperature dial down to minus 81 degrees Fahrenheit (minus 63 Celsius), which is the coldest temperature at which clouds occur on Earth. They were able to form clouds under Earth's climate conditions. Gradually, the researchers then moved the temperatures to a low of minus 120 Fahrenheit (minus 84 Celsius) — a balmy summer day on Mars.

The team created 10 Martian-like clouds in a week of experiments, analyzing the clouds' composition, numbers and size with laser beams that scattered within the cloud. They then performed six months of analysis, during which they uncovered the need for Martian clouds to have high humidity.

No one knows why such high humidity is the crucial ingredient, but it's a ripe area for further study. The cloud chamber will soon be renovated to accommodate colder temperatures that are more representative of Mars conditions. Cziczo said he hopes to start new experiments next fall.

Source of Article: Space.com

Sunjammer, World's Largest Solar Sail, Passes Key Test for 2015 Launch

A NASA plan to launch the world's largest solar sail into space and unfurl it like a giant parasol has passed a major test as the mission moves closer to a planned January 2015 launch. Sunjammer mission successfully deployed part of its huge solar sail in a test on Sept. 30, revealing the craft should be ready to function successfully following its January 2015 launch.

The giant Sunjammer solar sail, cleared a successful design test that required the deploying beam to stretch a quarter of the sail completely open. Because the Sept. 30 test took place on Earth, gravity and atmosphere made conditions more challenging than they would be in the vacuum of space, the sail's designers said.

"If this test succeeded under these stressing conditions, we certainly anticipate it will work exceedingly well in space," Nathan Barnes, President of lead contractor L'Garde Inc, said in a statement.

When Sunjammer launches in 2015, it will be the largest solar sail ever flown. Covering an area of almost 13,000 square feet (1,200 square meters), the full sail will span approximately a third the length of a football field. Despite its size, the enormous sail will be only about five millionths of a meter thick, keeping its weight down to 70 pounds (31 kilograms).

The lightweight, reflective material will rely on the pressure generated by sunlight to maneuver it through space. Smaller sails at the end of each of four booms will act as rudders to help the craft navigate.

Sunjammer will monitor solar activity as it demonstrates the validity of relying solely on low-cost, propellantless solar winds for spacecraft navigation. Ultimately, Sunjammer could form a part of a fleet of solar sail crafts providing an early warning system for space weather. Other sun-powered craft could travel completely out of the solar system.
The successful deployment of Sunjammer's solar sail is a key step for the success of the mission.

"We are very pleased by these results, as they bring us one step closer to realizing NASA's vision of a propellantless spacecraft and introduce the exciting potential of solar sails to the world," L'Garde's Space Services CEO Charles Chafer said in the same statement.

Soure of Article: Space.com

Europe's Gravity-Mapping GOCE Satellite Faces Big Fall from Space

A European-built satellite built to map Earth's gravity like never before is about to fall victim to the planet's ever-present gravitational pull.

The European Space Agency's Gravity field and steady-state Ocean Circulation Explorer, or GOCE for short, is nearly out of fuel and will make a nosedive to Earth this month after more than four successful years studying the planet's gravitational field.
The doomed GOCE satellite launched in 2009 into a Sun-synchronous, near-circular polar orbit by a Russian Rockot vehicle from the Plesetsk Cosmodrome. In today’s dollars, the mission is a $475 million effort, including launcher and operations.

The sleek 1.2-ton (1,100 kilograms) GOCE satellite is outfitted with an Xenon-fueled ion engine that compensated for any drag by generating carefully calculated thrusts. It skimmed above Earth at a low orbit of about 139 miles (224 kilometers).

GOCE runs out of fuel in the mid- to end of October time period. Two or three weeks after that, the spacecraft is expected to tumble to Earth.

When the uncontrolled GOCE spacecraft plunges through the atmosphere, several pieces of the satellite will likely survive the ensuing fireball and reach the Earth's surface. But when and where that space debris will fall is not yet known.

GOCE satellite fragments to reach Earth

The debris zone area for GOCE's fall from space will be narrowed down closer to the time of spacecraft demise, ESA officials say. According to ESA estimates, up to 40 to 50 pieces of GOCE — making up about 500 pounds (250 kilograms) of the satellite's full mass — may survive the skyfall.

But given that two thirds of Earth is covered by oceans, and vast areas are thinly populated, the risk to life or property is gauged as very low, ESA officials have said. As has been the case in the past, an international campaign of space debris analysts will monitor the descent and provide updates as to the debris fallout location.

Recent examples of uncontrolled reentries that stirred up media, public and analytical attention were the 2011 re-entries of NASA's Upper Atmosphere Research Satellite (UARS), the German Röntgensatellit ROSAT satellite, followed by Russia's failed Phobos-Grunt mission to Mars in 2012.

Global GOCE-watch campaign

A global campaign of space groups will monitor the GOCE descent, a wait-and-watch group of 12 member agencies within the Inter-Agency Space Debris Coordination Committee (IADC). ESA's Space Debris Office will issue re-entry predictions and risk assessments regarding the fall of GOCE, updating its Member States and also relevant safety authorities.

Re-entry experts in Europe use a computer modeling tool, Space Craft Atmospheric Re-entry and Aero-thermal Breakup, or SCARAB. As an integrated system for destructive re-entry analysis, SCARAB can forecast the aerodynamic and aero-heating loads on GOCE, down to what pieces of the spacecraft might reach the Earth's surface.

Holger Krag of ESA's Space Debris Office located at the European Space Operations Center in Darmstadt, Germany said that a detailed break-up analysis on GOCE using SCARAB has been performed.

GOCE satellite leftovers

"GOCE is a precise gravity measurement experiment, hence, there are no particularly critical components onboard … neither heat-resistant optics nor any toxic materials, Krag told SPACE.com.

GOCE has an electric propulsion system, hence the tanks are rather small.
"The Scarab results reveal that the GOCE reentry does not show any particularities with respect to other uncontrolled re-entries," Krag said. "Typical spacecraft in the one-ton class have 20 percent to 30 percent of their mass surviving the re-entry. You may assume that also GOCE operates in the same range, but there were no exotic findings among the fragments."

Krag said that GOCE components that are the typical suspects for surviving re-entry are a tank and magnetotorquers, as the spacecraft has no reaction wheels. "The rest of the components are ‘unrecognizable’ incomplete, irregular fragments," he added.

Remaining fuel uncertain

Rune Floberghagen, GOCE mission manager, told SPACE.com that the best engineering estimates point to the spacecraft running out of fuel around Oct. 19 or 20, followed by two to three weeks before re-entry.

"However, we do have uncertainties in the estimate of the remaining fuel," as well as other uncertainties that can influence the longevity of GOCE's stay in space," Floberghagen said. "In other words, the flight period might be a bit shorter or a bit longer."
GOCE spacecraft operations manager Christoph Steiger said that once GOCE runs out of fuel, its orbit will start decaying.

"We will initially keep operating the spacecraft, switching it off when its subsystems stop working due to the harsh environmental conditions at lower altitudes," Floberghagen said.This will mark the end of activities for the GOCE flight control team, he added.

Wealth of data

"We have collected a wealth of science data over the last four and a half years," Steiger told SPACE.com. The spacecraft has lasted much longer than the originally planned 20 months thanks to the low solar activity in the last few years," he said.
Steiger said that to get even more precise gravity measurements, in its last year of life the orbit of GOCE was lowered from 158 miles (255 km) down to an extremely low altitude of only 139 miles (224 km).
"The results are fantastic … we have obtained the most accurate gravity data ever available to scientists," Steiger added.

The looming doom of GOCE has some mission scientists like Steiger reflecting back on what has been a successful space science flight.

"Personally, I do feel sorry to see GOCE come to an end, a project on which I have spent seven intense years. Then again, it is also a good feeling to know that we have really gotten the most out of this mission before its natural end … much more than what we could have hoped for," Steiger said.

Source of Article: Space.com

Massive Star Explosion Seeded the Early Solar System, Meteorite Study Suggests

The explosive death of a star seeded matter into the solar system soon after its birth, analysis of a meteorite now reveals.

Earth and the rest of the solar system coalesced from a giant cloud of gas and dust more than 4.5 billion years ago. Many of the details about the galactic neighborhood in which the solar system arose still remain a mystery.

Meteorites contain some of the oldest material in the solar system, dating back to its formation. As such, researchers often analyze these objects in order to discover what materials were present when the sun, Earth and other planets were born. This study sheds light on where these solar system bodies might have come from.

All elements heavier than nickel are ultimately created by supernovas, giant explosions resulting from the deaths of stars. These explosions are bright enough to momentarily outshine their entire galaxies. Now, scientists analyzing meteorites have found that a supernova may have injected matter into the solar system within a small window of time after the solar system's first solids formed.

"This is evidence for supernova addition at the very start of our solar system, over 4.5 billion years ago," said the meteorite study's lead author,Gregory Brennecka, a cosmochemist at Lawrence Livermore National Laboratory.

Brennecka and his colleagues investigated the Allende meteorite, which fell to Earth as a fireball in Mexico in 1969. Theyfocused on lumps within this meteorite known as calcium-aluminum-rich inclusions. These particles are some of the oldest objects in the solar system — they were the first solids to form in the protoplanetary disk that eventually gave rise to Earth and the other planets.

The scientists focused on a wide range of isotopes within the inclusions. In general, elements come in a variety of isotopes that differ in how many neutrons they possess in their atomic nuclei; carbon-12 has six neutrons, while carbon-13 has seven. (Both have six protons.)

Brennecka and his colleagues discovered these inclusions all had similar concentrations of isotopes. However, the concentrations were distinct from the average composition of the materials that make up the bulk of meteorites and the Earth.

The researchers propose the inclusions formed close to the young sun, possibly within a span as short as 20,000 to 50,000 years. As such, matter from a nearby supernova did not pollute these inclusions, as it did the outer regions of the protoplanetary disk. The inclusions later mixed with the material that went on to make the Allende meteorite and other rocks.

"Not only do we know that the supernova happened, we can see what material was injected and how it changed the elemental and isotopic composition of our solar system," Brennecka told SPACE.com.

These findings are consistent with the notion that the solar system developed in an active star-forming region of the galaxy. Stellar nurseries are often home to stars that go supernova.

Future research can aim to better understand the fingerprints of this supernova in other samples "and how much influence it and possible other supernovae had on the development of our solar system," Brennecka said.

Source of Article: Space.com

2013년 10월 9일 수요일

Huge Collision Likely Caused Pluto Moons’ Weird Orbits

The odd orbits of Pluto’s five known moons may be the result of a gigantic impact that occurred about four billion years ago, a new study reports.

The huge collision that formed Pluto’s largest moon, Charon, likely led to the creation and destruction of numerous smaller satellites shortly thereafter, researchers said. This series of events eventually culminated in the strange configuration seen today, in which Pluto’s four tiny moons — Styx, Nix, Kerberos and Hydra — have orbital periods almost exactly 3, 4, 5 and 6 times longer than that of Charon, respectively.

"The implications for this result are that the current small satellites are the last generation of many previous generations of satellites," study co-author Kevin Walsh, of the Southwest Research Institute (SwRI) in Boulder, Colo., said in a statement. "They were probably first formed around four billion years ago, and after an eventful million years of breaking and rebuilding, have survived in their current configuration ever since." 

At 750 miles (1,207 kilometers) wide, Charon is by far the largest of Pluto’s moons (and about half as wide as Pluto itself). The other four satellites range from a few miles across to a few dozen miles in diameter, though their sizes are tough to pin down precisely.

Scientists have long been puzzled by the orbital arrangement of these five moons. Previous models of Charon’s formation have successfully predicted the concomitant creation of smaller satellites as well but could not explain how these minuscule moons moved outward from Pluto without exiting the dwarf planet system or crashing into Charon, researchers said.
"This configuration suggests that we have been missing some important mechanism to transport material around in this system,” lead author Hal Levison, also of SwRI, said in a statement.

The new study, which modeled the early days of the newly formed Pluto/Charon system, may have identified such a mechanism.
Levison and his team found that newly created small moons could be slingshotted outward from Pluto by Charon’s substantial gravity. Further, the frequent collisions among these tiny bodies could have changed their orbits, keeping them away from the system’s largest moon. 
In the aftermath of the huge Charon-forming collision, then, multiple generations of smaller satellites were likely created and destroyed, their pieces moving outward and coming together once again to form new moons of Pluto.

Levison presented the findings today (Oct. 9) at the American Astronomical Society's Division for Planetary Sciences 45th annual meeting in Denver.

Source of Article: Space.com

2013년 10월 7일 월요일

Life on Alien Planets Trickier to Find Than Previously Thought

Finding alien life on habitable planets around distant stars may be harder to identify than scientists have previously thought, a new study suggests.

The search for inhabited and habitable exoplanets is focused on M dwarf stars — stars that are smaller than the sun but make up more than 75 percent of the stars in the sun's vicinity, scientists have said.  

But these small stars have different ultraviolet properties from the sun, however, which could further complicate the search for alien life, researchers with the new study, which was unveiled today (Oct. 7).

"Before we can claim the discovery of life on exoplanets, we have to examine the stars harboring these planets more carefully," study leader Feng Tian, a professor at the Center for Earth System Science at Tsinghua University in Beijing, China, said in a statement. He presented the research today in Denver, Colo., at the 45th annual meeting of the American Astronomical Society's Division for Planetary Sciences.

The buildup of high levels of oxygen in the atmosphere of an exoplanet is the most promising indicatory for life on alien planets, officials from Tsinghua University said. The new study shows that oxygen can still build up in the atmospheres of lifeless planets, they added.

Feng Tian and his research team used the idea of a hypothetical habitable planet orbiting GJ 876 to test this in an earlier study. 

"In this case the atmosphere of a lifeless planet can be close to that of the Earth's 2.2 billion years ago, after the so called Great Oxidation Event in Earth's geological history," he said.

The new study also suggests that these earlier findings can be extrapolated out to other alien planets circling M dwarf stars, researchers said. The team collected ultraviolet data from GJ 667C — a star that plays host to three possibly habitable planets — and three other M dwarfs for the new work.

"Prof. Feng Tian's research addresses one of the most important questions of contemporary astrophysics and indeed of great interest to the general public: Are there other habitable planets near Earth, and is there any evidence that they are indeed inhabited?" Jeffrey Linsky of the University of Colorado at Boulder, said in a statement.

Source of Article: Space.com

Incredible Technology: How to Use 'Shells' to Terraform a Planet

One day, humans could re-make a world in Earth's image.
Engineering an inhospitable world into a livable one, a process known as terraforming, could be a successful way to colonize another world after a long, interstellar journey, said Ken Roy, an engineer and presenter at last week's Starship Congress in Dallas, Tex.

Roy's terraforming vision hinges upon what he calls "shell worlds." Upon arrival at an ideal planet, humans would literally encase the alien world inside of a protective shell made from Kevlar, dirt and steel.

"We have a central world. We put an atmosphere on it," Roy said. We can have the "composition, temperature, pressure of our choosing. Let's assume we want 'Earth-normal,' and we put a shell around the central world to contain this atmosphere. The atmosphere then exists between the shell and the central world. The outer part of the shell is essentially a vacuum."

While the planet's gravity would remain unchanged, the rest of the world could be made very similar to Earth after importing vital materials, Roy said. The new world could even have some benefits not afforded on Earth, such as:
  • Industry and facilities that could benefit from access to a vacuum could use a port that connects to the outside of the shell.
  • Ultraviolet radiation from a star would not be a problem since the world would be fully encased in the shell.
  • The heating, cooling and the length of a day on the world would not be dependent upon the orbit of the planet around a star.
  • The shell would provide radiation protection.
  • The world would provide an almost limitless playground for design. For example, cities could hang down from the interior of the shell.
A small planetary body like Mars or even Pluto would be a great candidate for the shell world treatment, Roy said.
Martian gravity is about one third that of Earth's, and the surface area of the Red Planet is equal to the land area of Earth. Mars has no magnetic field; plate tectonics seem to be non-existent, and the planet's core is frozen, Roy said.
While all of these factors might seem to add up into an inhospitable world, they actually make a Martian-type planet a great candidate for shelling.
"That is not a bad thing," Roy said. "It means you don’t have to deal with volcanoes and earthquakes. I'd say that's a good thing."

Roy admits that these kinds of worlds wouldn't be perfect. The creation of a habitable shell world would be an intensive process; large amounts of nitrogen and water would need to be imported or produced on the planet, and the construction of a shell itself would be a vast undertaking. But it might be preferable to other ways of terraforming, he said.
Traditional terraforming methods used on a Mars-like body would require mirrors that reflect sunlight down onto the planet's surface, simulating a greenhouse effect for a small planet.

If the world's manufactured atmosphere is designed to provide Earth-like conditions on the surface of the traditionally terraformed home, then engineers would need the equivalent of about half of the mass of the Earth's atmosphere imported to Mars, Roy said. That atmosphere would also bleed off into space eventually.

A Mars-sized shell world would only require about 6.6 percent of the mass of Earth's atmosphere, a much more manageable amount of material.
Shells could provide the next step once humans actually reached a Mars-sized planet orbiting another star, Roy said.

"Getting [to another star] is half the battle, but you also have to give thought to what you do once you get there," he said. "One of the objectives of traveling to another star … is colonization. It's unlikely that once we get to an alien star system, we'll find a world that we can move into."

Source of Article: Space.com

Quick Fusion-Powered Trips to Mars No Fantasy, Scientists Say

Sending astronauts to Mars aboard a superfast spacecraft powered by nuclear fusion may seem like a sci-fi dream, but it's entirely attainable, scientists say.

The physics behind a fusion-driven rocket have been demonstrated in the laboratory, so such a device may well be propelling people on 90-day trips to the Red Planet in a matter of decades, according to a team of researchers working on the technology.

"This is a reality, basically," Anthony Pancotti, of the space-propulsion company MSNW, said Sept. 25 during a presentation with NASA's Future In-Space Operations working group. "Fusion occurs in the sun, and also in our labs."

Fast track to Mars

A trip to Mars and back takes about 500 days using traditional chemical propulsion systems. Spending so much time in deep space poses serious health risks for astronauts, who would be exposed to lots of radiation and would have to exercise like mad to minimize bone and muscle loss.

Developing a faster propulsion system is thus a chief goal of NASA, which aims to get people to the vicinity of the Red Planet by the mid-2030s. The space agency has funded Pancotti's fusion-rocket team — led by John Slough of the University of Washington — through its NASA Innovative Advanced Concepts program, or NIAC.

The researchers are designing their work around a potential manned Mars mission that would last a total of 210 days — 83 days for the trip out, 30 days on the surface of the Red Planet and 97 days to get back home to Earth.

"We feel we've defined a very good problem, a very good mission, and we're focused on the fusion device to fit this mission," he said.

Because nuclear fusion is an extremely efficient and powerful energy source, this mission could be accomplished in a single launch of the most powerful version of NASA's Space Launch System mega-rocket, which is in development. It would take perhaps nine launches to mount such an effort with chemical propulsion, Pancotti said.

How it would work

Fusion occurs when the nuclei of two or more atoms combine, releasing energy. The sun and other stars convert this energy to light, and the phenomenon also gives hydrogen bombs their enormous destructive power.

The team's fusion-driven rocket would rely on a plasma created using deuterium and tritium, "heavy" isotopes of hydrogen. ("Normal" hydrogen contains no neutrons, while deuterium has one and tritium contains two.)

Bubbles of this plasma would be injected into a chamber, where a magnetic field would collapse metal rings around them, briefly compressing the bubbles into a fusion state. The energy released by the fusion reactions would vaporize and ionize the metal, which would be accelerated out the back of the spacecraft through a nozzle, creating thrust.
Solar panels would generate the energy necessary onboard the spacecraft to put all of this in motion.

There is no reason to doubt the feasibility of such a concept, Pancotti said.
"This is probably the most simple and straightforward, lowest-cost fusion propulsion system you can think of," he said. "The fundamental physics have been proven in the laboratory with hardware, and fusion yields, neutrons, have been produced. So what I'm talking about is building a device with known physics and with a proven method."

Further, that device can be built using commercial off-the-shelf components, so no engineering leaps should be required, Pancotti added.
Slough and his team are building hardware and conducting experiments to help bring the technology closer to implementation. They hope to check off a big milestone sometime in 2014.

"We're in the lab, we're building the coils, we're showing the scaling and we'll be producing the neutrons within the next year to show that fusion is occurring, and it's occurring at the scales required to build a fusion-driven rocket," Pancotti said.

Source of Article: Space.com