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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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.

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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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.

"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, Sébastien 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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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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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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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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An uncertain future for solar system exploration

In less than two weeks, an Atlas V rocket is slated to lift off from Cape Canaveral, propelling NASA’s Mars Science Laboratory (MSL) spacecraft towards the Red Planet. MSL—aka Curiosity—is one of the most ambitious, and expensive, Mars missions ever flown: a rover roughly the size of a Mini Cooper automobile and equipped with a suite of instruments to study Mars and learn about when it was warmer, wetter, and perhaps more hospitable to life. Its landing in August 2012 will be the capstone to what NASA calls the “Year of the Solar System”, a Martian-year-long period that includes milestones ranging from the arrival of MESSENGER at Mercury and Dawn at Vesta to the launches of Juno to Jupiter and GRAIL to the Moon.

While this is something of a golden age for planetary exploration, with a dozen active NASA planetary missions today, there is growing unease in the planetary science community about the future. There were concerns earlier this year with the release of the decadal survey of planetary science missions, which warned of a mismatch between the highest-priority missions—a Mars rover to collect samples for later return to Earth, and a Europa orbiter—and projected budgets ExoMars estrangement

The future of Mars exploration, beyond MSL, had been intended to be one of enhanced collaboration between NASA and ESA. The two agencies had agreed in 2009 to effectively merge NASA’s long-term Mars exploration program with ESA’s ExoMars effort. In 2016 NASA would launch a European Mars orbiter carrying some US instruments, to be followed two years later by the NASA launch of what was originally planned to be separate NASA and ESA Mars rovers, later merged into a single, jointly-developed rover that would cache samples for return to Earth on later missions. That would fulfill the mission of the Mars Astrobiology Explorer-Cacher (MAX-C) that the decadal survey identified earlier this year as the highest priority large, or flagship, planetary science mission in the next decade.
“The Europeans are as mad as hell,” said Hubbard of NASA’s decision not to launch ESA’s 2016 Mars orbiter.

There is evidence, though, that NASA may be backing out of that commitment. In September it informed ESA it would not be able to launch the 2016 European Mars orbiter as planned, forcing ESA officials to scramble to find an alternative approach, one that may have Russia become a partner by launching the orbiter on a Proton rocket. That decision reportedly came at the behest of the Office of Management and Budget (OMB), which also seeks to put the brakes on a joint 2018 mission.

“The Europeans are as mad as hell,” said Scott Hubbard, former director of NASA’s Ames Research Center, at a November 3 Capitol Hill forum on the future of planetary exploration jointly organized by The Mars Society and The Planetary Society. “When I talk to my European colleagues, they’re really, really upset. They feel like they’ve been swindled.”

That frustration comes after NASA and ESA had worked to lower the cost of the 2018 mission. Hubbard said the NASA cost of the mission has been reduced to $1.4 billion, more in line with a midrange New Frontiers mission. “It’s no longer a flagship-class mission,” he said, thanks to $1.2 billion provided by ESA for its role on the mission.

Hubbard believes that OMB may be misinterpreting the “decision rules” included in the planetary science decadal report on how to accommodate reduced budgets. Citing an email from someone who had met with OMB officials about the budget, MAX-C was deemed a “non-starter” by the office under current budgets even with its reduced cost, as it considers flagship missions the lowest priority of all classes of missions.

Hubbard noted that “programmatic balance”—a mix of small, medium-sized, and large missions—was a key aspect of the planetary decadal. That report, moreover, did not place flagship missions as the lowest priority. Instead, it recommended that if costs exceeded projected budgets, flagship missions should be descoped or delayed, followed by changes to the New Frontiers and Discovery programs for smaller missions.

That’s exactly what NASA has done, reducing the cost of MAX-C from its original estimate of $3.5 billion to the new estimate of $1.4 billion. “I would argue that NASA has been extremely responsive to the decadal survey and to budgetary pressure,” Hubbard said.

NASA has said little publicly about the future of its Mars exploration program and cooperation with ESA. At a news briefing last week about the upcoming MSL launch, Doug McCuistion, director of NASA’s Mars program, talked briefly about the issue. “The US and ESA realize we may have some budget concerns in the future, so ESA has approached Russia about potentially providing a launch vehicle and being involved,” he said. He declined to go into more detail because both the fiscal year 2012 budget has yet to be approved by Congress—although that may happen this week—while the 2013 budget proposal won’t be released until early next year. The subject may also come up at a hearing Tuesday on NASA’s planetary science plans by the House Science Committee.

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Solar System May Have Lost Fifth Giant Planet

Astronomer David Nesvorny from the Southwest Research Institute in Texas believes that the solar system might have once contained a fifth gigantic planet, which was ejected deep into the galaxy in a moment of cosmic turmoil.

By looking at the population of the Kuiper belt — the icy-cold ring of asteroids beyond Neptune — and by studying the historical fingerprints left on the craters of the Moon, Nesvorny was able to piece together clues about our solar system’s adolescence.

He found that a dynamic instability, which occurred about 600 million years into the solar system’s life, greatly affected the orbit of our giant planets and scattered smaller bodies. Some moved into the Kuiper belt and others traveled inwards, marking their course as impacts on the Moon and planets.

But that scenario has a flaw. Slow changes in Jupiter’s orbit would have had a large effect on the orbits of the terrestrial planets. All hell would have broken lose, and the Earth could have collided with Mars or Venus. Something had to change.

“Colleagues suggested a clever way around this problem,” says Nesvorny in a press release. Instead of a slow movement, Jupiter’s orbit could have quickly changed, which would have altered the outer solar system but been less harmful to the inner planets.

Unfortunately, this too caused problems. Computer simulations, ran thousands of times, showed that Jupiter’s quick jump had the intended effect, but Uranus or Neptune was always knocked out of the solar system. “Something was clearly wrong,” Nesvorny explains.

So perhaps, instead, the early solar system could have had five giant planets instead of four. By plopping an additional giant planet with a mass similar to that of Uranus or Neptune the simulation worked as planned. Jupiter jumped into place, the inner planets remained unharmed and the outer planets stayed behind.

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How death gave birth to our solar system

Our solar system was born thanks to the death of a nearby star in a spectacular supernova event, say researchers.

The findings are based on new computer simulations developed by Dr Matthias Gritschneder, from Beijing's Peking University, and colleagues, and published on the pre-press website ArXiv.org.

Gritschneder and colleagues found shock waves generated by a supernova could have caused the collapse of a molecular gas and dust cloud, eventually leading to the formation of the Sun and planets.

The model also explains unusual isotope readings in some of the oldest bodies of the solar system.

Stars and solar systems are created in the collapse of molecular gas and dust clouds.

Scientists say this is what happened to our solar system about 4.6 billion years ago, but until now they didn't know what triggered that collapse.

Clues have been found in the ratio of aluminium isotopes found in meteorites formed during the molecular cloud collapse.

Ancient meteorites
The isotope aluminium-26 usually has a half life of 700,000 years, eventually changing in to aluminium-24.

However the ratio of aluminium isotopes in ancient carbonaceous chondrite meteorites, called CV-chondrites, is unusually high.

CV-chondrites are thought to have formed directly out of the collapse of the molecular cloud that gave birth to our solar system.

The unusual isotope measurements suggest fresh aluminium-26 was being fed into this molecular cloud as it collapsed, either by stellar winds from a local star, or by the blast of a nearby supernova explosion, caused by the death of a star.

Gritschneder and colleagues say their model shows a supernova event 15 light years away was the most likely trigger.

"The blast's shock wave and hot gases travelled through space eventually colliding with a molecular cloud of cold gas and dust, causing it to quickly collapse, forming the Sun and solar system," says Gritschneder.

"It also provides the right ratios of aluminium isotopes to explain the levels found in CV meteorites."

"The CV-chondrites probably formed when the temperature of gas cloud dropped below about 1800°C," says Gritschneder.

"The model also shows how this would have occurred over a period of just 20,000 years, matching isotope measurements which act like time stamps marking the formation of these meteorites to within 20,000 years of each other."

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City Lights Could Reveal ET, Researchers Say

If you look at the Earth from space, it's pretty clear that there's intelligent life here because you can pick out cities on the night side. Abraham Loeb, of Harvard University and Edwin Turner, from Princeton University, are saying that we might find other civilizations the same way.

The reason is that the way we usually listen for aliens -- via radio signals -- may not work that well. One issue is that contrary to popular belief, TV transmissions don't travel all that far. (It would actually be near-impossible to pick up old shows from more than a few light years away).

ANALYSIS: The Search For Extraterrestrial Polluters
Our own civilization is actually generating less residual energy as time goes on as communications move to optical fiber. Other civilizations may have done the same, so picking them up actually gets harder as their technology gets better.

The trick is to look for a certain kind of light that would be different from natural starlight. The two note the spectrum of LEDs and streetlights is different from that of the sun. An alien looking at Earth with a sufficiently sensitive telescope would notice that.

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Moon and planets offer triple treat on Friday

Look toward the southwestern horizon just after sunset on Friday night and you’ll see a triple feature of Venus, Mercury, and the two-day old moon. And there's another planet treat in time for the pre-Halloween weekend, too.

You'll need a good low horizon and a clear sky to see the first three objects since they will be very low in the sky, less than 10 degrees up. Binoculars may help. For reference, a closed first held out at arm's length covers about 10 degrees of the night sky.

The accompanying sky map of the moon and planets here shows their locations on Friday evening.

The moon will be a razor-thin crescent, and the so-called "dark" side of the moon — actually its far side facing away from Earth, which is not always dark — should be well lit by sunlight reflecting off the Earth.

Venus should appear very bright, weather permitting. This may be the first glimpse you get of it this season, but it will soon be blazing bright every evening. Mercury will be directly under Venus.

All three objects will be very low because of the shallow angle the ecliptic — the path the sun takes across the sky — makes with the horizon on Friday. Notice that the sun is setting well to the south of the west point on the horizon, now that we're more than a month past the fall equinox.

The only days the sun sets due west is right on the equinoxes, which were March 20 and Sept. 23 this year.

A few minutes after sunset, turn around and look at the eastern horizon. You will see Jupiter rising there slightly north of due east, the brightest object in that part of the sky.

At 10 p.m. EDT on Friday, Jupiter will be opposition, exactly opposite the sun in the sky. On this night, Jupiter rises at sunset and sets at sunrise, so is visible all night long.

Binoculars or a small telescope can reveal Jupiter's four bright moons, allowing you to follow them as they constantly shift position, orbiting around the giant planet.

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Dwarf planet Eris surprises astronomers

Eris, the dwarf planet whose 2005 discovery led to Pluto losing its status as a planet, has passed in front of a star, providing astronomers with the clearest view of it since it was identified.

It is about the same size as Pluto and is one of the brightest objects in the solar system, according to the new analysis, released Wednesday by the journal Nature.

Scientists' picture of Eris had remained fuzzy because its distance from Earth is so vast: It is about three times farther out from the sun than Pluto. Some estimates pegged Eris as about 25% larger than Pluto, but it was too far away to tell for sure.

"It's very difficult, because it's so small in the sky," said lead author Bruno Sicardy, a planetary scientist at Pierre and Marie Curie University and Observatory in Paris.

With such small, far-off objects, astronomers wait for what's known as a stellar occultation, in which the object will cross over a star, essentially casting a shadow over the Earth. The amount of starlight blocked by the object allows scientists to calculate the object's size.

Witnessing this stellar occultation last year required being in the right place at exactly the right moment during the brief time window that Eris was scheduled to block the star.

To spot the star-crossing, Sicardy's team asked telescope operators at 26 different sites around the world to make observations. Just three telescopes at two of those sites, both in Chile, managed to catch the event.

From the data, the researchers were able to calculate that the dwarf planet's diameter is about 1,445 miles — on a par with Pluto, which is somewhere between 1,429 and 1,491 miles across.

The fact that Eris is smaller than previously estimated means that the amount of light scientists had detected coming from it originated from a smaller-than-anticipated surface area — and therefore its surface is brighter than anyone had thought.

In fact, the new calculations make Eris one of the brightest objects in the solar system, even though its surface should have been darkened from bombardment by cosmic rays and micrometeorites.

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Doomsday comet makes closest approach to Earth

ANTICIPATED by doomsayers as a potentially catastrophic event, Comet Elenin traversed the closest point in its trajectory around Earth (35,000km) early Sunday morning just before sunrise. But save for a few keen observers and astronomers, this went largely unnoticed.

When discovered by astronomer Leonid Elenin in December 2010, the passing of the 3-5 km wide chunk of space ice was predicted to be the astronomical event of the year, which in turn inspired an overkill of apocalyptic theories.

Amateur astronomers and conspiracy theorists put forth the idea that Comet Elenin was responsible for a variety of anomalous events seen throughout 2011; from the scattered outbursts of political uprisings to the earthquake in Japan.

Others extrapolated these prophecies to Comet Elenin representing the end of the world.
However, sometime during the middle of August, Comet Elenin began disintegrating as it crossed the solar system and traveled through the sun’s solar flares. And so at around 4 am Sunday morning, the comet passed within view of ground telescopes in an event that astronomers described as “largely uneventful.”

“I could see a hazy group of dim chunks of rock sitting in the sky, moving very slowly,” said Samir Nawar, a professor at the National Research Institute of Astronomy and Geophysics (NRIAG) in Helwan.

“But it was far less interesting than looking at the sun or the moon on any other day of the year, and a lot less noticeable,” he joked, referring to the Earth’s temperate climate and tides.
On the issue of conspiracy theories, Nawar went on to say that there is an obsession with space phenomena, which are far away and little understood; and that even if Comet Elenin had not disintegrated, the event would have still passed largely unnoticed. –AA

“People like to play on the fact that there are a lot of ‘maybes’ with these ‘unknown’ phenomena,” he continued. “But the truth is there are few maybes; there is a lot of accuracy with understanding space science, more than there is an understanding of what’s at the bottom of the oceans. If there was any issue of concern, NASA or any professional astronomer would be the first to raise the issue.”

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New Proof That Comets Watered the Earth

By rights, the earth should not be the cosmic garden it is. In a solar system of planets and moons that are solid rock or mostly gas, shrouded in clouds or atmosphere-free, scorchingly hot or bitterly cold, there's only one that's dripping wet. Earthlings like to refer to our home planet as the solar system's water world, and it's a jolly good thing it's as wet as it is, because without plenty of water, life (at least as we know it) would be impossible.

All the same, it's likely our planet was once a far drier, dustier place. You need only look at two of our nearby rocky neighbors — Mercury and Venus — for a reminder of what living so close to the blast furnace of the sun can do to you. Our atmosphere helps us retain the abundant water we do have, but how did it get to us in the first place?

One popular theory has long been comets. The solar system swarms with these little rogue bodies — perhaps a trillion of them, according to astronomers' back-of-the-envelope estimates — and shortly after the sun and planets formed, they were everywhere, flying randomly and free to collide with anything in their way. Since comets are essentially dirty snowballs made of rock, gas and water ice, a few crash landings on earth could have provided all the water we needed quite nicely.

But there was a problem with that theory. All of the comets astronomers observed were indeed packed with water ice, but a lot of it was what's known as heavy water, in which the hydrogen in the H2O mix is an isotope known as deuterium, with one proton and one neutron in its nucleus. The hydrogen found in ordinary water has no neutron. Since the overwhelming share of the water in earth's oceans is made with the light hydrogen atom, astronomers calculated that comets could have accounted for only about 10% of what's there. Now, according to a new paper published in the journal Nature, it appears that those scientists may have been wrong — and the reason for their error is that they were simply looking at the wrong comets.

The paper, co-authored by researchers at the California Institute of Technology, is based on observations conducted by the Herschel Space Observatory, a spacecraft launched by the European Space Agency in 2009. Herschel looked specifically at comet Hartley 2, a small comet discovered in 1986 with an estimated diameter of .75 to .99 mi. (1.2 to 1.6 km). Analyzing the chemical composition of Hartley 2's corona — or the gassy veil surrounding the main comet body — Herschel discovered that its concentration of heavy water was only about half that of any comets observed before. While that wouldn't entirely explain earth's particular heavy- and light-water mix, it does bring the chemistry a lot more into line — and gives the cometary explanation for earthly water a big boost.

"Our results with Herschel suggest that comets could have played a major role in bringing vast amounts of water to an early earth," says physicist Dariusz Lis of Caltech, a co-author of the paper.

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2 Small Asteroids Zoom Between Earth and Moon's Orbit

A small asteroid zipped by Earth well inside the orbit of the moon today (Sept. 30), the second space rock encounter for our planet this week. Both asteroids posed no threat to Earth, scientists say.

"Small asteroid 2011 SM173 just passed Earth at a safe distance of 180,000 miles (290,000 km or .8 lunar distance)," scientists with NASA's Asteroid Watch program announced in a Twitter post today.

Asteroid 2011 SM173 was discovered yesterday by astronomers and is about 56 feet (17 meters) wide, making it about the size of a house. Its flyby came just four days after the pass of another space rock — the asteroid 2011 SE58 —which actually came even closer to Earth.

The 33-foot (10-m) wide asteroid 2011 SE58 slipped within 147,000 miles (236,573 km) of Earth during an evening flyby on Monday (Sept. 26), according to Asteroid Watch scientists.

The average distance between Earth and the moon is about 238,900 miles (384,402 km).

No threat to Earth
Both asteroids were too small to threaten Earth with a serious impact. If they had barreled into Earth, they likely would have burned up completely in Earth's atmosphere, the researchers said.

"Rocky asteroids the size of 2011 SE58 are not considered hazardous as they break up in the atmosphere & cause no ground damage," Asteroid Watch scientists wrote.

Asteroid 2011 SE58 was discovered by skywatchers on Sept. 21, according to database maintained by NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.

By coincidence, the asteroid flybys this week occurred just as NASA announced the latest results from its efforts to find the largest near-Earth asteroids, objects that could potentially endanger Earth.

NASA's asteroid census has discovered about 90 percent of the largest near-Earth asteroids and revealed that the population of mid-size space rocks (asteroids about 3,300 feet, or 1,006 m, wide) is far lower than previously thought.

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NASA Space Telescope Finds Fewer Asteroids Near Earth

PASADENA, Calif. -- New observations by NASA's Wide-field Infrared Survey Explorer, or WISE, show there are significantly fewer near-Earth asteroids in the mid-size range than previously thought. The findings also indicate NASA has found more than 90 percent of the largest near-Earth asteroids, meeting a goal agreed to with Congress in 1998.

Astronomers now estimate there are roughly 19,500 -- not 35,000 -- mid-size near-Earth asteroids. Scientists say this improved understanding of the population may indicate the hazard to Earth could be somewhat less than previously thought. However, the majority of these mid-size asteroids remain to be discovered. More research also is needed to determine if fewer mid-size objects (between 330 and 3,300-feet wide) also mean fewer potentially hazardous asteroids, those that come closest to Earth.

The results come from the most accurate census to date of near-Earth asteroids, the space rocks that orbit within 120 million miles (195 million kilometers) of the sun into Earth's orbital vicinity. WISE observed infrared light from those in the middle to large-size category. The survey project, called NEOWISE, is the asteroid-hunting portion of the WISE mission. Study results appear in the Astrophysical Journal.

"NEOWISE allowed us to take a look at a more representative slice of the near-Earth asteroid numbers and make better estimates about the whole population," said Amy Mainzer, lead author of the new study and principal investigator for the NEOWISE project at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "It's like a population census, where you poll a small group of people to draw conclusions about the entire country."

WISE scanned the entire celestial sky twice in infrared light between January 2010 and February 2011, continuously snapping pictures of everything from distant galaxies to near-Earth asteroids and comets. NEOWISE observed more than 100 thousand asteroids in the main belt between Mars and Jupiter, in addition to at least 585 near Earth.

WISE captured a more accurate sample of the asteroid population than previous visible-light surveys because its infrared detectors could see both dark and light objects. It is difficult for visible-light telescopes to see the dim amounts of visible-light reflected by dark asteroids. Infrared-sensing telescopes detect an object's heat, which is dependent on size and not reflective properties.

Though the WISE data reveal only a small decline in the estimated numbers for the largest near-Earth asteroids, which are 3,300 feet (1 kilometer) and larger, they show 93 percent of the estimated population have been found. This fulfills the initial "Spaceguard" goal agreed to with Congress. These large asteroids are about the size of a small mountain and would have global consequences if they were to strike Earth. The new data revise their total numbers from about 1,000 down to 981, of which 911 already have been found. None of them represents a threat to Earth in the next few centuries. It is believed that all near-Earth asteroids approximately 6 miles (10 kilometers) across, as big as the one thought to have wiped out the dinosaurs, have been found.

"The risk of a really large asteroid impacting the Earth before we could find and warn of it has been substantially reduced," said Tim Spahr, the director of the Minor Planet Center at the Harvard Smithsonian Center for Astrophysics in Cambridge, Mass.

The situation is different for the mid-size asteroids, which could destroy a metropolitan area if they were to impact in the wrong place. The NEOWISE results find a larger decline in the estimated population for these bodies than what was observed for the largest asteroids. So far, the Spaceguard effort has found and is tracking more than 5,200 near-Earth asteroids 330 feet or larger, leaving more than an estimated 15,000 still to discover. In addition, scientists estimate there are more than a million unknown smaller near-Earth asteroids that could cause damage if they were to impact Earth.

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Obscure Full Moon Names of 2011

Jan. 19, 4:21 p.m. EST – Full Wolf Moon: Amid the zero cold and deep snows of midwinter, the wolf packs howled hungrily outside Indian villages. The Full Wolf Moon was also known as the Old Moon or the Moon After Yule. In some tribes, this was also known as the Full Snow Moon; most applied that name to the next moon.

Feb. 18, 3:36 a.m. EST – Full Snow Moon: Usually the heaviest snows fall in this month. Hunting becomes very difficult, and hence to some tribes this was known as the Full Hunger Moon.

Mar. 19, 2:10 p.m. EDT – Full Worm Moon: In this month, the ground softens and the earthworm casts reappear, inviting the return of the robins.

The more northern tribes knew this as the Full Crow Moon, when the cawing of crows signals the end of winter, or the Full Crust Moon because the snow cover becomes crusted from thawing by day and freezing at night. TheFull Sap Moon, marking the time of tapping maple trees, is another variation.

The moon will also arrive at perigee only 50 minutes later at 3:00 p.m. EDT at a distance of 221,565 miles (356,575 kilometers) from Earth. So this is the biggest full moon of 2011. Very high ocean tides can be expected during the next two or three days, thanks to the coincidence of perigee with full moon.

Apr. 17, 10:44 p.m. EDT – Full Pink Moon: The grass pink or wild ground phlox is one of the earliest widespread flowers of the spring. Other names were the Full Sprouting Grass Moon, the Egg Moon and – among coastal tribes – the Full Fish Moon, when the shad come upstream to spawn.

In 2011, this is also the Paschal Full Moon; the first full moon of the spring season. The first Sunday following the Paschal Moon is Easter Sunday, which indeed will be observed one week later on Sunday, April 24. This, incidentally, is just one day shy of the latest date that Easter can fall.

May 17, 7:09 a.m. EDT – Full Flower Moon: Flowers are now abundant everywhere. This moon was also known as the Full Corn Planting Moon or the Milk Moon.

Jun. 15, 4:14 p.m. EDT – Full Strawberry Moon: Strawberry picking season peaks during this month. Europeans called this the Rose Moon. There will be also be a total lunar eclipse that will be visible across much of South America, Europe, Africa and Asia. Totality will last an unusually long length of time: 1 hour 40 minutes.

Jul. 15, 2:40 a.m. EDT – Full Buck Moon: when the new antlers of buck deer push out from their foreheads in coatings of velvety fur. It was also often called the Full Thunder Moon, thunderstorms being now most frequent. Sometimes it's also called the Full Hay Moon.

Aug. 13, 2:57 p.m. EDT – Full Sturgeon Moon: When this large fish of the Great Lakes and other major bodies of water like Lake Champlain is most readily caught. A few tribes knew it as the Full Red Moon because when the moon rises it looks reddish through sultry haze, or the Green Corn Moon or Grain Moon.

The occurrence of this full moon on this particular date is rather poor timing for those who enjoy the annual performance of the Perseid meteor shower; this display will peak on this very same day and the brilliant light of the moon will likely wash out all but the very brightest of these swift streaks of light.

Sep. 12, 5:27 a.m. EDT – Full Harvest Moon: Traditionally, this designation goes to the full moon that occurs closest to the autumnal (fall) equinox. The Harvest Moon usually comes in September in the Northern Hemisphere, but (on average) once or twice a decade it will fall in early October.

At the peak of the harvest, farmers can work into the night by the light of this moon. Usually the moon rises an average of 50 minutes later each night, but for the few nights around the Harvest Moon, the moon seems to rise at nearly the same time each night – just 25 to 30 minutes later across the U.S., and only 10 to 20 minutes later for much of Canada and Europe. Corn, pumpkins, squash, beans and wild rice – the chief Indian staples – are now ready for gathering.

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Messenger findings may 'revolutionize' views of Mercury

A spacecraft sent to the least explored rocky planet in the solar system is providing surprising new information that may rewrite what scientists believe about the growth of planets.

Mercury, the tiny planet closest to the sun, has a lopsided magnetic field, much more sulfur than expected and strange "hollows" across its surface that may hint at present-day geologic activity, according to data gleaned by the Messenger spacecraft.

The results, published in a package of seven papers in Friday's edition of the journal Science, may force scientists to throw out many ideas about how Mercury formed.

When Mariner 10 flew by in 1974 and 1975, planetary scientists got a tantalizing glimpse at Mercury's moon-like features — craters, flat plains of ancient lava — and discovered it had a magnetic field. The Messenger mission, armed with a suite of instruments including cameras, element-sensing spectrometers and a magnetic field detector, was designed to answer questions dangled by that decades-old snapshot.

Launched in 2004, the spacecraft flew by the planet three times before entering orbit in March of this year, when it sent the first close-up images back to Earth. It will continue to send data as it circles the planet for about a year.

Mercury, planetary scientists knew, is uncommonly dense — most likely because its inner core of iron is very large relative to the rest of the planet. This led some scientists to theorize that Mercury had once been perhaps two to three times larger and its outer layers had been stripped away, either from the sun's fierce glare or major impacts from asteroids.

As molten balls of rock coalesce to form a planet, the heavier elements such as iron tend to sink toward the center while lighter elements such as sulfur or phosphorus, which are more likely to evaporate, drift in the opposite direction. This, scientists had reasoned, would make those volatile lighter elements the first to get stripped away, leaving the planet comparatively dense.

But when scientists used Messenger's gamma-ray and X-ray spectrometers to analyze elements on Mercury's surface, they found that the planet was rich in phosphorus and that sulfur was 10 times more abundant on the surface than on the Earth or moon.

"At this point, the origin of Mercury's large core is still a mystery," said Larry Nittler, a cosmochemist at the Carnegie Institution of Washington who led the X-ray spectrometer study.

Another paper found that the vast flat plains on Mercury were not caused by eruptions from volcanoes but were fashioned from large amounts of lava that seeped up from cracks in the ground and flooded the surface. The scorching-hot lava also carved teardrop-shaped islands into the surface, which are visible near the edges of these plains.

Mercury is "essentially wallpapered by huge volumes of lava," said James Head, a planetary geoscientist at Brown University and lead author of that study.

"Volcanism is important because it represents the pulse of the planets," he added. "It's like the blood of the interior: Is it not doing much inside, or is it really active?"

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"Dark" Supermoon Tomorrow: New Moon Gets Closest to Earth

Tomorrow night the new moon will make a close approach to Earth, giving rise to the second supermoon of the year—but this one will have the power of invisibility.

Because the moon's orbit is egg shaped, there are times in the roughly monthlong lunar cycle when the moon is at perigee—its closest distance to Earth—or at apogee, its farthest distance from Earth.

"A supermoon occurs when the moon is at perigee and it's in either a full or new phase," said Raminder Singh Samra, an astronomer at the H.R. MacMillan Space Centre in Vancouver, Canada.

In March sky-watchers were treated to a full moon at perigee, which made for the biggest full moon seen in 18 years.

A new moon happens when the lunar orb positions itself between Earth and the sun, so that the side of the moon that faces Earth is unlighted.

"The upcoming moon on September 27, 2011, is set to be at perigee and at the new phase," Samra said, "so we won't be able to witness the event, as the moon and sun will be in the same region of the sky" and the lunar disk will be entirely dark.

Supermoon to Affect Earth's Tides?

Because the size of the moon's orbit also varies slightly, each perigee is not always the same distance from Earth.

When at perigee, the moon is about 18,640 miles (30,000 kilometers) closer to Earth than its average distance of roughly 240,000 miles (385,000 kilometers). When perigee occurs during a full moon, the lunar disk can appear about 14 percent bigger in the sky, Samra said.

Tuesday's dark supermoon will be just 222,175 miles (357,557 kilometers) away from Earth.

Some people have speculated that this lunar proximity can have unusual gravitational effects on Earth, triggering dramatic events such as earthquakes.

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