Tuesday, March 20, 2012

The planetary pileups of popular solar system orbits


Some orbits are apparently more popular than others in young solar systems emerging around baby stars - which often results in "planet pileups" and "planet deserts."


Sophisticated computer simulations have revealed a rather plausible explanation for a phenomenon that has long puzzled astronomers. 

Essentially, rather than occupying orbits at regular distances from a star, giant gas planets similar to Jupiter and Saturn appear to prefer residing within certain regions of mature solar systems while staying clear of others.

The planet pileups of popular solar system orbits"Our results show that the final distribution of planets does not vary smoothly with distance from the star," explained Ilaria Pascucci, an assistant professor at the University of Arizona's Lunar and Planetary Laboratory. "Instead, it has clear 'deserts' - deficits of planets - and 'pileups' of planets at particular locations."


Pascucci and Richard Alexander of the University of Leicester identified high-energy radiation from baby sun-like stars as the likely force that carves gaps in protoplanetary disks, the clouds of gas and dust that swirl around young stars and provide the raw materials for planets. The gaps then act as barricades, corralling planets into certain orbits.

Of course, the exact locations of those gaps depend on the planets' mass, but they generally occur in an area between 1 and 2 astronomical units from the star. One astronomical unit, or AU, marks the average distance from the Earth to the sun. 

According to conventional wisdom, a solar system starts out from a cloud of gas and dust. At the center of the prospective solar system, material clumps together, forming a young star. As the baby star grows, its gravitational force increases as well, and it attracts dust and gas from the surrounding cloud.

Accelerated by the growing gravitation of its star, the cloud spins faster and faster, and eventually flattens into what is called a protoplanetary disk. Once the bulk of the star's mass has formed, it is still fed material by its protoplanetary disk, but at a significantly lower rate.

"For a long time, it was assumed that the process of accreting material from the disk onto the star was enough to explain the thinning of the protoplanetary disk over time," said Pascucci. "Our new results suggest that there is another process at work that takes material out of the disk."

That process, called photo-evaporation, works by high-energy photons streaming out of the star and heating the dust and gas on the surface of the protoplanetary disk.

"The disk material that is very close to the star is very hot, but it is held in place by the star's strong gravity," Alexander noted. "Further out in the disk where gravity is much weaker, the heated gas evaporates into space."

However, even further out in the disk, the radiation emanating from the star is not intense enough to heat the gas sufficiently to cause much evaporation. Yet at a distance between 1 and 2 AU, the balancing effects of gravitation and heat clear a gap.

While studying protoplanetary disks, Pascucci also discovered that gas on the surface of the disk was gravitationally unbound and leaving the disk system via photoevaporation. These were the first observations proving that photoevaporation does occur in real systems.

Encouraged by those findings, Alexander and Pascucci subsequently used the ALICE High Performance Computing Facility at the University of Leicester to simulate protoplanetary discs undergoing accretion of material to the central star that took the effects of photo-evaporation into account.

"We don't yet know exactly where and when planets form around young stars, so our models considered developing solar systems with various combinations of giant planets at different locations and different stages in time," Alexander said.

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Monday, March 12, 2012

A Strong Backhand Slap from End of Solar Storm


The solar storm that seemed to be more fizzle than fury got much stronger early Friday before fading again.

At its peak, it was the most potent solar storm since 2004, space weather forecasters said.

No power Relevant Products/Services outages or other technological disturbances were reported from the solar storm that started to peter out late Friday morning.

Solar storms, which can't hurt people, can disturb electric Relevant Products/Services grids, GPS systems, and satellites. They can also spread colorful Northern Lights further south than usual, as the latest storm did early Friday.

And more storms are coming. The federal government's Space Weather Prediction Center says the same area of the sun erupted again Thursday night, with a milder storm expected to reach Earth early Sunday.

The latest storm started with a flare on Tuesday, and had been forecast to be strong and direct, with one scientist predicting it would blast Earth directly like a punch in the nose. But it arrived Thursday morning at mild levels -- at the bottom of the government's 1-5 scale of severity. It strengthened to a level 3 for several hours early Friday as the storm neared its end. Scientists say that's because the magnetic part of the storm flipped direction.

"We were watching the boxer, expecting the punch. It didn't come," said physicist Terry Onsager at the National Oceanic and Atmospheric Administration's space weather center Relevant Products/Services in Boulder, Colo. "It hit us with the back of the hand as it was retreating."

Forecasters can predict a solar storm's speed and strength, but not the direction of its magnetic field. If it is northward, like Earth's, the jolt of energy flows harmlessly around the planet, Onsager said. A southerly direction can cause power outages and other problems.
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Thursday's storm came in northerly, but early Friday switched to the fierce southerly direction. The magnetic part of the storm spent several hours at that strong level, so combined with strong radiation and radio levels, it turned out to be the strongest solar storm since November 2004, said NOAA lead forecaster Bob Rutledge.

Skywatchers reported to NOAA shimmering colorful auroras in Michigan, Wisconsin and Seattle -- areas that don't normally see the Northern Lights -- Rutledge said. Other space weather enthusiasts reported auroras in Alaska, Minnesota, and North Dakota and in the southern hemisphere in Australia and New Zealand.

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Wednesday, February 01, 2012

Solar Storm Blasts Electrons from Earth's Van Allen Belts

Scientists say they have solved the mystery of why electrically-charged particles intent in radiation belts thousands of kilometers above the Earth suddenly vanish and then reappear during periods of heightened solar activity.

NASA-funded researchers at the University of California, Los Angeles (UCLA) tracked the electrons using data collected at once with 11 different spacecraft.

Their findings show that when bursts of solar energy released by storms on the sun strike Earth’s magnetic field, they send electrons in the so-called Van Allen radiation belts hurtling into external space. Within a few days, the depleted radiation rings once again swell with a whole new crop of the sun’s highly-charged electrons, which are so active that they move at almost the speed of light.

The UCLA researchers note that the highly charged particles that escape the Van Allen belts forever stream outward, rather than raining down into Earth’s atmosphere as some theories suggest.
The Van Allen belts are a method of bubble-shaped rings of radiation that encircle the planet. Earth's protective magnetic field holds the Van Allen belts in their spot several tens of thousands of kilometers above its surface, and protects the planet from deadly solar, cosmic and other types of space radiation.

The Van Allen belts are named after late NASA astrophysicist James Van Allen, who confirmed occurrence of the radiation rings in 1958. The revolutionary scientist died in 2006 at the age of 91.

Tuesday, January 17, 2012

"Earth's Twin" May Be in Our Solar System: Saturn's Moon, Titan --Hosts a Layered Atmosphere


Saturn's moon Titan may be more similar to an Earth-like world than previously thought, possessing a layered atmosphere just like our planet. Titan has long held interest for scientists because of its promise, as the only known moon in the solar system that has a dense atmosphere, there has been hope that it might host some form of life. Information provided by three separate spacecraft missions sent to the area has created more speculation about the moon, which is roughly twice the size of our own (which, quite inexplicably, still has no name) but is nine times farther away from the sun and a freezzing -180°C.

The first mission was Voyager 1, which flew by in 1981, followed by Cassini in 2004, and the next year by the Huygens probe, which actually landed on its surface. Despite the massive amounts of data collected by all three vehicles and the dense athmosphere, scientists have still not been able to get conclusive evidence on what is going on with Titan’s atmosphere.

To clear up some of the mystery, the two researchers --Benjamin Charnay, a planetary scientist at France's National Center of Scientific Research and colleague, S├ębastien Lebonnois-- put together a three dimensional computer model that incorporates information collected from all three space vehicles that includes among other things, chemical compositions, dune movement and measurements of wind and cloud formations and were able to conclude that Titan’s atmosphere very clearly has at least one boundary, which is the part of an atmosphere that is impacted by the surface (friction, heat, etc.) and vice-versa.

But they also found evidence that there appears to be a second boundary as well that is likely caused by changes in seasonal air circulation. The lowest layer is most influenced by a planet or moon's surface, and has greatest influence on the surface with clouds and winds, as well as by sculpting dunes found on Titan.

Earth's boundary layer, which is between 1,650 feet and 1.8 miles (500 meters and 3 kilometers) thick, is controlled mostly by solar heat warming the planet's surface. Since Titan is more distnat from the sun, its boundary layer might behave quite differently. Titan's atmosphere is thick and opaque, obscuring our knowledge about its lower layers. "This layer is very important for the climate and weather — we live in the terrestrial boundary layer," said Charnay.

Their simulations revealed the lower atmosphere of Titan appears separated into two layers that are both distinct from the upper atmosphere in terms of temperature. The lowermost boundary layer is shallow, only about 2,600 feet (800 meters) deep and, like Earth's, changes on a daily basis. The layer above, which is 1.2 miles (2 kilometers) deep, changes seasonally.

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Tuesday, December 06, 2011

Scientists find monster black holes, biggest yet


CAPE CANAVERAL, Fla. (AP) — Scientists have found the biggest black holes known to exist — each one 10 billion times the size of our sun.

A team led by astronomers at the University of California, Berkeley, discovered the two gigantic black holes in clusters of elliptical galaxies more than 300 million light years away. That's relatively close on the galactic scale.

"They are monstrous," Berkeley astrophysicist Chung-Pei Ma told reporters. "We did not expect to find such massive black holes because they are more massive than indicated by their galaxy properties. They're kind of extraordinary."

The previous black hole record-holder is as large as 6 billion suns.

In research released Monday by the journal Nature, the scientists suggest these black holes may be the leftovers of quasars that crammed the early universe. They are similar in mass to young quasars, they said, and have been well hidden until now.

The scientists used ground-based telescopes as well as the Hubble Space Telescope and Texas supercomputers, observing stars near the black holes and measuring the stellar velocities to uncover these vast, invisible regions.

Black holes are objects so dense that nothing, not even light, can escape. Some are formed by the collapse of a super-size star. It's uncertain how these two newly discovered whoppers originated, said Nicholas McConnell, a Berkeley graduate student who is the study's lead author. To be so massive now means they must have grown considerably since their formation, he said.

Most if not all galaxies are believed to have black holes at their center. The bigger the galaxy, it seems, the bigger the black hole.

Quasars are some of the most energized and distant of galactic centers.

The researchers said their findings suggest differences in the way black holes grow, depending on the size of the galaxy.

Ma speculates these two black holes remained hidden for so long because they are living in quiet retirement — much quieter and more boring than their boisterous youth powering quasars billions of years ago.

"For an astronomer, finding these insatiable black holes is like finally encountering people nine feet tall whose great height had only been inferred from fossilized bones. How did they grow so large?" Ma said in a news release. "This rare find will help us understand whether these black holes had very tall parents or ate a lot of spinach."

Oxford University astrophysicist Michele Cappellari, who wrote an accompanying commentary in the journal, agreed that the two newly discovered black holes "probably represent the missing dormant relics of the giant black holes that powered the brightest quasars in the early universe."

One of the newly detected black holes weighs 9.7 billion times the mass of the sun. The second, slightly farther from Earth, is as big or even bigger.

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Monday, November 28, 2011

New Earth-like planet may have water, life


Scientists claim to have discovered a potentially habitable planet which has an environment much similar to that of the Earth and may contain water and even life.

The exoplanet, called Gliese 581g, is located around 123 trillion miles away from the Earth and orbits a star at a distance that places it squarely in the habitable or the Goldilocks zone, the scientists said.

The research, published in the Astrophysical Journal, suggests that the planet could contain liquid water on its surface, meaning it tops the league of planets and moons rated as being most like Earth, they said.

Compelling case
“Our findings offer a very compelling case for a potentially habitable planet,” said lead researcher Steven Vogt, a professor of astronomy and astrophysics at the University of California, Santa Cruz.

“The fact that we were able to detect this planet so quickly and so nearby tells us that planets like this must be really common,” Prof. Vogt was quoted as saying byDaily Mail.

The new findings are based on 11 years of observations of the nearby red dwarf star Gliese 581 using the HIRES spectrometer on the Keck I Telescope by a team from UC Santa Cruz and the Carnegie Institution of Washington.

The team reported the discovery of two new planets around Gliese 581. This brings the total number of known planets around this star to six, the most yet discovered in a planetary system outside of our own.

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Thursday, November 24, 2011

Europa’s “Great Lake”


In a significant finding in the search for life beyond Earth, scientists from The University of Texas at Austin and elsewhere have discovered what appears to be a body of liquid water the volume of the North American Great Lakes locked inside the icy shell of Jupiter’s moon Europa.

The water could represent a potential habitat for life, and many more such lakes might exist throughout the shallow regions of Europa’s shell, lead author Britney Schmidt, a postdoctoral fellow at The University of Texas at Austin’s Institute for Geophysics, writes in the journal Nature.

Further increasing the potential for life, the newly discovered lake is covered by floating ice shelves that seem to be collapsing, providing a mechanism for transferring nutrients and energy between the surface and a vast ocean already inferred to exist below the thick ice shell.

“One opinion in the scientific community has been, ‘If the ice shell is thick, that’s bad for biology -- that it might mean the surface isn’t communicating with the underlying ocean,’” said Schmidt. “Now we see evidence that even though the ice shell is thick, it can mix vigorously. That could make Europa and its ocean more habitable.”

The scientists focused on Galileo spacecraft images of two roughly circular, bumpy features on Europa’s surface called chaos terrains. Based on similar processes seen here on Earth -- on ice shelves and under glaciers overlaying volcanoes -- the researchers developed a four-step model to explain how the features form on Europa. It resolves several conflicting observations, some of which seemed to suggest that the ice shell is thick and others that it is thin.

“I read the paper and immediately thought, yes, that’s it, that makes sense,” said Robert Pappalardo, senior research scientist at NASA’s Planetary Science Section who did not participate in the study. “It’s the only convincing model that fits the full range of observations. To me, that says yes, that’s the right answer.”

The scientists have good reason to believe their model is correct, based on observations of Europa from the Galileo spacecraft and of Earth. Still, because the inferred lakes are several kilometers below the surface, the only true confirmation of their presence would come from a future spacecraft mission designed to probe the ice shell. Such a mission was rated as the second-highest priority flagship mission by the National Research Council’s recent Planetary Science Decadal Survey and is currently being studied by NASA. On Earth, radar instruments are used to image similar features within the ice, and are among the instruments being considered for a future Europa mission.

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