Friday, September 30, 2011

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?"

Diamond stud

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Wednesday, September 28, 2011

"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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Sunday, September 25, 2011

How Common Are Earth-Moon Planetary Systems

Earth's Moon might have played an important role in the development and evolution of life on Earth. The Moon was formed via a giant impact in which a Mars-size projectile collided with the young Earth. The ejected material accumulated in orbit around our planet and formed the Moon. After its formation, the Moon was much closer to Earth than it is today, which caused high tides several times per day.

This may have helped promote the very early evolution of life. In addition, a stable climate of more than a billion years may be essential to guarantee a suitable environment for life. But without its satellite, Earth would suffer chaotic variations of the direction of its spin axis, which would in turn result in dramatic variations of the climate.

Therefore, concerning the habitability of extrasolar planets, it is reasonable to ask: How common are Earth-Moon planetary systems?

Sebastian Elser, Prof. Ben Moore and Dr. Joachim Stadel of the University of Zurich, Switzerland, along with Ryuji Morishima of NASA's Jet Propulsion Laboratory in Pasadena, California, ran a large set of N-body simulations to study the formation of the rocky planets in our solar system via the collisional growth of thousands of small rocky bodies in a disk around the Sun.

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Friday, September 23, 2011

Plenty of room on planet Earth

The world now has almost seven billion people and rising. The population may surpass nine billion by 2050. We, together with our 20 billion chickens and four billion cattle, sheep and pigs, will utterly dominate the planet. Can the planet take it? Can we take it?

Yes. Not only is such a huge population going to prove indefinitely "sustainable;" it is actually likely that the ecological impact of nine billion in 2050 will be lighter, not heavier: there will be less pollution and more space left over for nature than there is today.

Consider three startling facts. The world population quadrupled in the 20th century, but the calories available per person went up, not down. The world population doubled in the second half of the century, but the total forest area on the planet went up slightly, not down. The world population increased by a billion in the last 13 years, but the number living in absolute poverty (less than a dollar a day, adjusted for inflation) fell by around a third.

Clearly it is possible at least for a while to escape the fate forecast by Robert Malthus, the pessimistic mathematical cleric, in 1798. We've been proving Malthus wrong for more than 200 years. And now the population explosion is fading. Fertility rates are falling all over the world: in Bangladesh it's down from 6.8 children per woman in 1955 to 2.7 today; China - 5.6 to 1.7; Iran - 7 to 1.7; Nigeria - 6.5 to 5.2; Brazil 6.1 to 1.8; Yemen - 8.3 to 5.1.

The rate of growth of world population has halved since the 1960s; the absolute number added to the population each year has been falling for more than 20 years. According to the United Nations, population will probably cease growing by 2070. This miraculous collapse of fertility has not been caused by Malthusian misery or coercion (except in China), but by the opposite: enrichment, urbanization, female emancipation, education and above all the defeat of child mortality - which means women start to plan families rather than continue breeding.

Increasing prosperity means eating more food, though. Can we really feed today's let alone tomorrow's billions? In 60 years we have trebled the total harvest of the three biggest crops: wheat, rice and corn. Yet the acreage devoted to growing these crops has barely changed. This is because fertilizer, irrigation, pesticides and new varieties have greatly increased yields.

They continue to do so. Growth regulators boost the yield of wheat. Genetic modification boosts the yield of cotton (while increasing the biodiversity in fields). New enzymes promise to cut the phosphate output and increase weight gain of pigs. These technologies save rainforest by sparing land from the plow. If we went back to organic farming, the world would have to cultivate more than twice as much land as we do.

Already huge swaths of the world are being released from farming and reforested. New England is now 80 per cent woodland, where it was once 70 per cent farmland. Italy and England have more woodland than they have for centuries. Moose, coyotes, beavers and bears are back in places where they have not been for centuries. France has a wolf problem; Scotland a deer problem. It is the poor countries, not the affluent ones, that are losing forest. Haiti, with its near total dependence on renewable power (wood), is 98 per cent deforested and counting.

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Tuesday, September 20, 2011

Our solar system might have once had an extra gas planet

This solar system just doesn't work. According to a new computer simulation, the planets could never have come together in their current configuration. The only explanation is that we once had a fifth gas giant...and it's still out there somewhere.

That's a pretty big claim to make, so let's see how David Nesvorny of Colorado's Southwest Research Institute reached that particular conclusion. The key idea here is that our solar system wouldn't have formed in its present configuration — the planets would have tugged on each other as they formed, pulling each other out of their original orbits and into new ones. The solar system doesn't begin fully-formed, even once the various planets are complete. It's still a long evolutionary process.

We can't know exactly how the planets first fit together, so Nesvorny simply tried a bunch of different possible starting positions and ran simulations to find out which could conceivably result in the present solar system. The problem is that Jupiter, Saturn, Uranus, and Neptune are just so damn big that they can barely move around without violently disrupting each other's orbits.

In the vast majority of simulations, one gas giant would rip another apart. Even in simulations where all four gas giants survived, it was often at the expense of the rocky planets. According to Nesvorny's simulation, the current solar system is of astoundingly low probability, assuming we're only starting with four inner rocky planets and four outer gas planets. It's when you alter that assumption that things start to get interesting.

By adding a fifth gas planet into the mix, Nesvorny found that the odds of our current solar system emerging increased dramatically. That's obviously not proof of this fifth gas planet's existence, but if this computer simulation holds up, then it's actually more likely than not.

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Monday, September 19, 2011

Fifty New Exoplanets Discovered by HARPS

Astronomers using ESO’s world-leading exoplanet hunter HARPS have today announced a rich haul of more than 50 new exoplanets, including 16 super-Earths, one of which orbits at the edge of the habitable zone of its star. By studying the properties of all the HARPS planets found so far, the team has found that about 40% of stars similar to the Sun have at least one planet lighter than Saturn.

The HARPS spectrograph on the 3.6-metre telescope at ESO’s La Silla Observatory in Chile is the world’s most successful planet finder [1]. The HARPS team, led by Michel Mayor (University of Geneva, Switzerland), today announced the discovery of more than 50 new exoplanets orbiting nearby stars, including sixteen super-Earths [2]. This is the largest number of such planets ever announced at one time [3]. The new findings are being presented at a conference on Extreme Solar Systems where 350 exoplanet experts are meeting in Wyoming, USA.

“The harvest of discoveries from HARPS has exceeded all expectations and includes an exceptionally rich population of super-Earths and Neptune-type planets hosted by stars very similar to our Sun. And even better — the new results show that the pace of discovery is accelerating,” says Mayor.

In the eight years since it started surveying stars like the Sun using the radial velocity technique HARPS has been used to discover more than 150 new planets. About two thirds of all the known exoplanets with masses less than that of Neptune [4] were discovered by HARPS. These exceptional results are the fruit of several hundred nights of HARPS observations [5].

Working with HARPS observations of 376 Sun-like stars, astronomers have now also much improved the estimate of how likely it is that a star like the Sun is host to low-mass planets (as opposed to gaseous giants). They find that about 40% of such stars have at least one planet less massive than Saturn. The majority of exoplanets of Neptune mass or less appear to be in systems with multiple planets.

With upgrades to both hardware and software systems in progress, HARPS is being pushed to the next level of stability and sensitivity to search for rocky planets that could support life. Ten nearby stars similar to the Sun were selected for a new survey. These stars had already been observed by HARPS and are known to be suitable for extremely precise radial velocity measurements. After two years of work, the team of astronomers has discovered five new planets with masses less than five times that of Earth.

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Tuesday, September 13, 2011

16 'super-Earths' found outside solar system

It's not like aliens put up a welcome banner or anything, but scientists now have newly identified at least one planet that could potentially sustain life.

The European Southern Observatory has just announced the discovery of more than 50 new exoplanets (planets outside our solar system), including 16 super-Earths (planets whose mass is between one and 10 times that of our own planet).

One of these planets in particular could theoretically be home to life if conditions are right. It's called HD 85512 b, and scientists say it's about 3.6 times the mass of the Earth. This planet is about 35 light years from Earth. Its location with respect to its star suggests that this planet could have liquid water under certain circumstances.

Don't get too excited, though; there's a lot more work to be done to explore whether this planet is truly fit for life, in addition to whether there are alien life forms there.

The discovery comes from High Accuracy Radial Velocity Planet Searcher, or HARPS. HARPS is located at the La Silla Observatory in Chile, and is part of a telescope that's nearly 12 feet long.

Here's how it works, according to ESO: When a planet orbits a star, the star move towards and away from the person who's stargazing on Earth in a regular fashion. That's called a change in radial velocity. Because of the Doppler effect, changes in radial velocity makes the star's light spectrum move towards longer wavelengths when it's moving away, and towards shorter wavelengths as it gets closer. HARPS can detect this shift in the spectrum, and infer that there is a planet present.

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