'Exocomets' Common Across Milky Way Galaxy

Comets may be as common as alien planets in star systems throughout the Milky Way galaxy, scientists say.

Astronomers have spotted likely comets around six faraway stars, bringing the total number of systems now thought to host the so-called "exocomets" to 10. It's likely that all 10 of these systems also harbor alien planets, suggesting that comets and exoplanets are often found together, as they are in our own solar system, the new study found.

The number of exocomet-hosting systems could thus number in the billions across the Milky Way, as astronomers think our galaxy harbors at least 100 billion alien planets.

"This is sort of the missing link in current planetary formation studies," lead author Barry Welsh, of the University of California, Berkeley, said in a statement.

"We see dust disks — presumably the primordial planet-forming material — around a whole load of stars, and we see planets, but we don't see much of the stuff in between: the asteroid-like planetesimals and the comets," Welsh added. "Now, I think we have nailed it. These exocomets are more common and easier to detect than people previously thought."

Welsh presented the findings today (Jan. 7) duing a meeting of the American Astronomical Society in Long Beach, Calif.

The researchers discovered the six new exocomet systems using the 2.1-meter telescope of the McDonald Observatory in Texas.

The telescope picked up faint absorption lines that varied from night to night. The astronomers determined these features were caused by large clouds of gas emanating from comets as they drew close to their host stars and heated up.

In our own solar system, comets usually stay far from the sun, only venturing close after a gravitational disturbance sends them veering off on a new course. It's likely that alien planets caused the newly discovered exocomets to plunge toward their stars, Welsh said.

The newfound exocomets all orbit very young and bright stars that are about 5 million years old, because the team's detection technique works best with such stars. But higher-resolution instruments may reveal comets around older, more sun-like stars — the type around which most exoplanets have been found to date, researchers said.

The first exocomet system was discovered in 1987, and three more were spotted over the years.

"But then, people just lost interest. They decided that exocomets were a done deal, and everybody switched to the more exciting thing, exoplanets," Welsh said. "But I came back to it last year and thought, 'Four exocomets is not all that many compared to the couple of thousand exoplanets known — perhaps I can improve on that.'"

Source of Article : space.com

Monster Black Hole Burp Surprises Scientists

Astronomers have discovered what appears to be colossal belch from a massive black hole at the heart of a distant galaxy. The outburst was 10 times as bright as the biggest star explosion, scientists say.

The potential super-sized black hole burp find came as astronomers studied the galaxy NGC 660, which is located 44 million light-years away in the constellation Pisces.

"The discovery was entirely serendipitous. Our observations were spread over a few years, and when we looked at them, we found that one galaxy had changed over that time from being placid and quiescent to undergone a hugely energetic outburst at the end," study researcher Robert Minchin of Arecibo Observatory in Puerto Rico said in a statement.

To determine whether the outburst was from a supernova — the explosive end of a star —  or the galaxy's core, the researchers used the High Sensitivity Array, a global network of telescopes that includes the Very Long Baseline Array, the Arecibo Telescope, the NSF's 100-meter Green Bank Telescope, and the 100-meter Effelsberg Radio Telescope in Germany.

Instead of an expanding ring of material suggesting a supernova event, the researchers found five locations with bright radio emissions clustered around the galaxy's core.

"The most likely explanation is that there are jets coming from the core, but they are precessing, or wobbling, and the hot spots we see are where the jets slammed into the material near the galaxy's nucleus," said Chris Salter, also of the Arecibo Observatory.

Those jets, the researchers said, would mean the outburst likely came from a supermassive black hole at the heart of galaxy NGC 660. As the black hole devours dust and mass, it pulls a whirling disk of matter into its heart that spews jets of particles as it is consumed.

Supermassive black holes are colossal structures at the cores of galaxies that are between millions and billions of times as massive as the sun. They are much larger than stellar-mass black holes, which are created from the deaths of giant stars and can contain the mass of about 10 suns.

Source of Article : space.com

17 Billion Earth-Size Alien Planets Inhabit Milky Way

The Milky Way hosts at least 17 billion Earth-size alien planets, and probably many more, a new study reveals.

Astronomers have determined that about 17 percent of stars in our galaxy harbor a roughly Earth-size exoplanet in a close orbit. Since there are 100 billion or so stars in the Milky Way, that works out to a minimum of 17 billion small, rocky alien worlds, or an Earth-size planet around one of every six stars.

And there are probably many more such planets orbiting at greater distances from their stars, some of which may even be "alien Earths" capable of supporting life as we know it.

"These kind of rocky objects are everywhere," team member Francois Fressin, of the Harvard-Smithsonian Center for Astrophysics (CfA), told reporters today (Jan. 7) during a meeting of the American Astronomical Society in Long Beach, Calif. 

Crunching the numbers

The research team conducted an analysis of data collected by NASA's planet-hunting Kepler Space Telescope. Kepler detects alien worlds by noting the telltale dips in brightness caused when planets cross the face of — or transit — their parent stars from the instrument's perspective. The telescope, which launched in March 2009, flagged more than 2,700 potential planets in its first 22 months of operation, more than 100 of which have been confirmed to date. 

The research team wanted to know how complete and accurate Kepler's survey has been — that is, what percentage of its finds are real, and how many planets is it likely missing? So they came up with a simulation that mimicked the telescope's work, finding that about 90 percent of its detections are probably the real deal.

"There is a list of astrophysical configurations that can mimic planet signals, but altogether, they can only account for one-tenth of the huge number of Kepler candidates," Fressin said in a statement. "All the other signals are bona-fide planets."

The study has been accepted for publication in The Astrophysical Journal.

Planets, planets everywhere

Using information from both the actual and simulated Kepler surveys, the team calculated some estimates about how common different types of planets are thoughout the Milky Way.

They determined, for example, that 17 percent of stars have a planet 0.8 to 1.25 times the size of Earth in tight orbits, with periods of 85 days or less. About 25 percent of stars have a so-called "super-Earth" (worlds 1.25 to 2 times as big as our own) in an orbit of 150 days or less — the same percentage that hosts a "mini-Neptune" (a planet 2 to 4 times Earth's size) with an orbital period up to 250 days.

Big planets such as Saturn or Jupiter are far less common. Only 5 percent of stars harbor a gas giant with an orbital period of 400 days or less, researchers said.

Overall, the team found that about 50 percent of all stars in the Milky Way have a planet the size of Earth or larger in a tight orbit. Extrapolation and incorporation of data from other instruments suggest that virtually all sun-like stars host planets, Fressin said.

Further, stars don't have to be sun-like to host an Earth-size world. The team also determined that small and medium-size exoplanets are commonly found around red dwarfs as well, which are smaller and cooler than our star.

"Earths and super-Earths aren’t picky," said co-author Guillermo Torres, also of the CfA. "We’re finding them in all kinds of neighborhoods."

Kepler generally requires three planetary transits to flag a potential alien world. Since more tightly orbiting planets transit more frequently, the telescope's early findings have been biased toward close-in worlds. But as Kepler continues to operate, it should find more and more planets farther from their host stars — including, perhaps, Earth-size worlds in Earthlike orbits.

Source of Article : space.com

Double-Star Systems Can Be Dangerous for Exoplanets

Alien planets born in widely separated two-star systems face a grave danger of being booted into interstellar space, a new study suggests.

Exoplanets circling a star with a far-flung stellar companion — worlds that are part of "wide binary" systems — are susceptible to violent and dramatic orbital disruptions, including outright ejection, the study found.

Such effects are generally limited to sprawling planetary systems with at least one distantly orbiting world, while more compact systems are relatively immune. This finding, which observational evidence supports, should help astronomers better understand the structure and evolution of alien solar systems across the galaxy, researchers said.

"The fact that planets observed within wide binaries tend to have more eccentric (or 'excited') orbits than those around isolated stars tells us that wide binaries do often disrupt planetary systems," lead author Nathan Kaib, of Northwestern University and the University of Toronto, told..

"Thus, we believe most planetary systems are extended, with outer planets orbiting at tens of AU from their host stars," Kaib added. (One AU, or astronomical unit, equals the distance from Earth to the sun — about 93 million miles, or 150 million kilometers.)

The study was published today (Jan. 6) in the journal Nature and will be presented by Kaib at the 221st meeting of the American Astronomical Society in Long Beach, Calif., on Monday (Jan. 7).

Shifting stellar orbits 

Two-star systems occur commonly throughout our galaxy; indeed, astronomers think the Milky Way harbors about as many binary systems as single stars. Recently, astronomers have begun discovering planets in binary systems, some of them "Tatooine" worlds with two suns in their skies, like Luke Skywalker's home planent in the "Star Wars" films.

Many double-star systems throughout the galaxy are wide binaries, in which 1,000 AU or more separate the stellar companions on average.

The distance between stars in a wide binary often changes dramatically over time, however, since their orbits around a common center of mass can be far from circular.

"The stellar orbits of wide binaries are very sensitive to disturbances from other passing stars as well as the tidal field of the Milky Way," Kaib said in a statement. "This causes their stellar orbits to constantly change their eccentricity, their degree of circularity. If a wide binary lasts long enough, it eventually will find itself with a very high orbital eccentricity at some point in its life.”

Eccentric orbits bring the two stars quite close together from time to time, even if the wide binary has a large average separation distance. And these close encounters can wreak havoc on planetary systems, the researchers found after performing about 3,000 computer simulations. 

In one set of runs, for example, the team added a wide-binary companion to our own solar system. In nearly half of the simulations, at least one giant planet — Jupiter, Saturn, Uranus or Neptune — got booted out into space.

Signficant orbital disruption generally takes hundreds of millions or billions of years to manifest, Kaib and his colleagues calculated.

"Consequently, planets in these systems initially form and evolve as if they orbited an isolated star," Kaib said. "It is only much later that they begin to feel the effects of their companion star, which often times leads to disruption of the planetary system."

Shedding light on extrasolar systems

Such destabilization, which is more dramatic in wide binaries than in more tightly orbiting two-star systems, does not always take the form of planetary ejection. Often, exoplanets just get tugged from their orginal, near-circular orbits into more eccentric ones, the simulations showed.

The researchers also looked at orbital eccentricities of actual exoplanets. The team found that planets in wide binaries have more eccentric orbits than worlds that circle single stars, suggesting the computer models are on the money.

"The eccentric planetary orbits seen in these systems are essentially scars from past disruptions caused by the companion star," co-author Sean Raymond, of the University of Bordeaux and the National Center for Scientific Research in France, said in a statement.

The team's computer simulations further suggest that these disruptions generally happen only in planetary systems that extend at least 10 AU or so from the host star.

Taken together, the observational and modeling results imply that many extrasolar systems harbor distantly orbiting worlds, though such planets are tough for astronomers to detect at the moment, researchers said.

"Given that most planet-detection campaigns cannot detect planets beyond 5-10 AU from their host stars, our results provide new clues about the characteristics of planetary systems in a regime that is poorly constrained by current observations," Kaib told. "We believe that planets orbiting at distances of 10 AU or further from their host stars are common."

Source of Article : space.com

Giant Sun Eruption Could Swallow 20 Earths

A massive eruption on the surface of the sun this week blasted out a wave of super-hot plasma so high that it could tower over 20 Earths, NASA officials say.

The New Year's Eve solar eruption occurred Monday (Dec. 31) and was captured on camera by NASA's powerful Solar Dynamics Observatory, a sun-watching spacecraft that constantly records high-definition video of our star. The result: an eye-popping video of the New Year's Eve sun storm.

Despite its size, the solar eruption was not the most powerful example of the sun's stormy wrath, NASA officials said.

"Magnetic forces drove the flow of plasma, but without sufficient force to overcome the sun's gravity much of the plasma fell back into the sun," NASA officials wrote in an image description today (Jan. 4). "The length of the eruption extends about 160,000 miles [257,495 kilometers] out from the sun. With Earth about 7,900 miles [12,714 km] in diameter, this relatively minor eruption is about 20 times the diameter of our planet."

Some NASA officials described Monday's sun eruption, which occurred over a four-hour period, as a solar ballet. The Solar Dynamics Observatory is one of several spacecraft that keep a constant watch on the sun for flare and storm activity.

The sun is currently in an active phase of its 11-year solar activity cycle  and is expected to reach its peak level later this year. However, NASA scientists have said that the peak of the current cycle, known as Solar Cycle 24, may be the lowest of its kind in a century.

Solar flares and eruptions can have a significant impact on Earth when they are aimed at the planet. The most powerful solar flares can interfere with satellite communications, pose a safety risk for astronauts in orbit and damage power system infrastructure on the planet's surface.

Minor solar storms can also trigger amazing geomagnetic storms above Earth that supercharge the planet's aurora displays above its poles.

Source of Article : space.com

Crater on Huge Asteroid Vesta Gets 3D Treatment

A new 3D photo from NASA's Dawn spacecraft reveals a stunning glimpse inside a massive crater on the huge asteroid Vesta. 

The new image shows dark streaks of carbon-rich material radiating out from the 9-mile-wide (15 kilometers) Cornelia Crater. The coal-black material speckles the rim and flanks of the crater, which is found in Vesta's southern half. Dawn captured the images that make up the 3D mosaic while orbiting Vesta from an altitude of 420 miles (680 km), researchers said.

The dark material is common around the edges of two enormous impact basins in the southern hemisphere of Vesta, which at 325 miles (523 km) wide is the second-largest body in the main asteroid belt between Mars and Jupiter.

These two basins, which are known as Veneneia and Rheasilvia, were likely formed by asteroids between 25 and 36 miles (40 to 60 km) wide, scientists have said. The Rheasilvia impact probably blasted out about 250,000 cubic miles (1.04 million cubic km) of material — enough to fill the Grand Canyon 1,000 times over.

Veneneia, which apparently formed between two and three billion years ago, is about 250 miles (400 km) across. The younger Rheasilvia is even larger; at 310 miles (500 km) wide, it spans virtually all of Vesta's diameter.

A recent analysis of the carbon-rich dark stuff suggests that much of it was delivered by the object that created Veneneia, researchers said. Some of the material was then likely covered up by the massive impact that produced Rheasilvia.

Scientists think Vesta is a protoplanet left over from the solar system's early days, a building block whose progression toward full-fledged planet was halted by Jupiter's powerful gravitational pull.

The $466 million Dawn spacecraft arrived at Vesta in July 2011 and orbited the intriguing object for more than a year. In September 2012, Dawn departed for the dwarf planet Ceres, the largest resident of the asteroid belt. Dawn is slated to arrive at Ceres in early 2015.

Source of Article : space.com

Mars Rover Curiosity Finds Martian 'Flower' and Snake-Like Rock

New photos of Mars from NASA's Curiosity rover have sparked a buzz of discussion over an odd formation that some have dubbed a "flower" embedded in a Martian rock. The rover has also found a snake-like rock formation winding across the Red Planet's surface.

The so-called Mars "flower" photo was snapped on Dec. 19 by the microscope-like Mars Hand Lends Imager at the end of Curiosity's robotic arm. At the lower left of the image is a strange, apparently transparent formation that some Internet forum users on the website claimed looked much like a flower, according to NBCNews.com's photoblog.

NASA posted a raw, unprocessed version of the photo online on the Curiosity rover’s mission website overseen by the agency's Jet Propulsion Laboratory in Pasadena, Calif. Internet forum readers on the website Above Top Secret christened the object a flower, according to NBCNews.com's Alan Boyle.

Curiosity has seen bits of clear plastic (pieces of the rover itself) on the surface of Mars before, but NASA officials said that doesn’t appear to be the case this time.

JPL spokesman Guy Webster told NBCNews.com that the object "appears to be part of the rock, not debris from the spacecraft."

On Friday (Jan. 4), NASA also unveiled a new panorama of Curiosity’s current location on Mars, a shallow depression called Yellowknife Bayinside the vast Gale Crater. The image is a mosaic of photos that is dominated by a sinewy, snake-like rock winding across its center.

NASA scientists have dubbed the rock "Snake River." It is a thin curving line of dark rock that rises above the flatter rocks of its surroundings, making it an intriguing target for Curiosity's instruments, JPL officials said.

"It's one piece of the puzzle," rover mission project scientist John Grotzinger, of the California Institute of Technology in Pasadena, said in a statement. "It has a crosscutting relationship to the surrounding rock and appears to have formed after the deposition of the layer that it transects."

The $2.5 billion Mars rover Curiosity landed on Aug. 5 to begin a two-year primary mission of determining whether the planet could have once been habitable for primitive microbial life. It is currently driving toward a 3-mile-high (5 kilometers) mountain rising up from the center of its Gale Crater landing site.

Curiosity is destined for a point called Glenelg at the base of the Martian peak, which scientists have named MountSharp. But first, mission scientists are looking over Curiosity's images of YellowknifeBay in order to pick a rock target for the rover to use as its first drill site. That drill test is expected soon, JPL officials said.

“The area the rover is in looks good for our first drilling target," rover project manager Richard Cook said.

Source of Article : space.com