news20100611nn1

[naturenews] from [nature.com]

[nature.com > naturenews]
Published online 10 June 2010 | Nature | doi:10.1038/news.2010.291
News
Asteroid probe begins return from rendezvous
｛小惑星探査機、”イトカワ”とランデブーし、帰還開始｝

But is Japan's Hayabusa capsule carrying any precious asteroid dust?
By David Cyranoski
｛しかし、日本の「はやぶさ」のカブセルに貴重な小惑星の微粒子が採取されているか？｝

{{Japan's Hayabusa is on its way home after its rendezvous with Itokawa.}
Akihiro Ikeshita / Japanese Aerospace Exploration Agency}

Yesterday in the south central Australian village of Woomera, Japanese scientists, with US and Australian colleagues, celebrated news from their Hayabusa spacecraft — the first round-trip space mission to an asteroid. Successful manoeuvres that day had put the spacecraft on course to parachute its recovery capsule into the nearby desert on 13 June. Anticipation will continue to build until the capsule's lid is opened, offering, they hope, the first peek at asteroid dust.

Scientists anticipate that such samples will provide greater knowledge of these 'little planets', shedding light on the beginnings of the Solar System, the origins of life on Earth (see 'Asteroid ice hints at rocky start to life on Earth') and the connection between asteroids and the tens of thousands of meteorites that have been found on Earth. "It could establish a bridge for the first time," says Michael Zolensky, a NASA scientist who will analyse some of the Hayabusa samples.

The original aim of Hayabusa was as a technical mission to test various engineering technologies, such as ion-thrust engines and autonomous navigation systems, needed for landing on an asteroid and returning to Earth. The spacecraft, launched in May 2003, landed on the 535-metre-long Itokawa asteroid twice in November 2005.

The mission is lucky to get this far, says Hajime Yano, a Hayabusa project scientist with the Japan Aerospace Exploration Agency (JAXA). After the spacecraft landed on Itokawa a second and final time, a massive fuel leak resulted in loss of communication for several months. Hayabusa's engines also experienced a range of problems, and its return was uncertain until 8 June, when its faltering thrusters completed the last necessary trajectory correction. "It's like a critical patient who can't walk well," says Yano. "Up until yesterday, anything could have happened."

Mission accomplished

Although three years behind schedule, the mission has achieved its major goals, and has already yielded scientific data about Itokawa's dimensions and composition, which will provide a benchmark for future asteroid studies.

The remaining mission goals are retrieving the sample-return capsule from the desert and analysing any samples within it. The capsule is a disk-shaped aluminium container about 40 centimetres in diameter, and is scheduled to separate from the craft on 13 June before entering Earth's atmosphere. "From their perspective, it's all gravy," says Scott Sandford, another NASA scientist working on the project. "Everything we're getting now is a bonus, but to me it's the most interesting part."

{“From their perspective, it's all gravy.”}

The incoming capsule has a radio beacon to signal its location, and infrared-detection devices on helicopters will also be used to find it. Even if these fail, monitoring stations will track the burning wreckage of Hayabusa through the atmosphere as a guide to the trajectory of the nearby capsule.

JAXA scientists will retrieve the capsule on 14 June, and by the end of the week, they hope to have it back in their laboratory in Sagamihara, just south of Tokyo. There they will first take X-ray images to estimate the amount of dust picked up — if any.

High hopes

Zolensky says they were originally hoping to have "spoonfuls, several grams of sample", made up of "chips like peanut-size grains". But sample collection didn't go as planned. Pellets designed to hit Itokawa to dislodge loose fragments seem not to have fired. "It's very likely we won't be able to see anything with the naked eye," says Makoto Yoshikawa, also a Hayabusa project scientist at JAXA.

Still, the scientists have high hopes. A hard impact on Hayabusa's first landing attempt on the asteroid is likely to have kicked up dust, says Yoshikawa. Hayabusa sat on the surface for 30 minutes after that. Zolensky agrees: "Just the fact that it landed should cover it in dust. The astronauts on the Moon got covered with dust just walking around. The mission team might not get grams, but they'll have something. With today's technologies, even microbe-sized particles should be enough."

On the basis of the X-ray results, the researchers will decide when and how to open the lid and distribute the contents between analysis and storage. Any dust that is found will be analysed over the next six months as scientists look at oxygen isotopes, helium content, water traces, and other clues that might provide insight into Itokawa's history. "We want to look at its elemental composition and structure," says Yoshikawa. "When this asteroid was born, what kind of matter was around? This will tell us about Earth and the Solar System."

news20100611nn2

[naturenews] from [nature.com]

[nature.com > naturenews]
Published online 10 June 2010 | Nature | doi:10.1038/news.2010.292
News
Global warming's impact on Asia's rivers overblown
｛地球温暖化の影響論、アジアの河川を誇大問題化｝

Freshwater flow dominated by monsoon rains rather than glacier run-off.
｛淡水の流量は、氷河からの流出よりもモンスーンの雨量によって左右される｝
By Richard A. Lovett

{Meltwater from glaciers makes a large contribution to the Indus river but not to all Asian rivers.}World Pictures/Photoshot}

Although global warming is expected to shrink glaciers in the Himalayas and other high mountains in Central Asia, the declining ice will have less overall impact on the region's water supplies than previously believed, a study concludes.

It's an important finding, says Richard Armstrong, a climatologist at the US National Snow and Ice Data Center in Boulder, Colorado, who notes that the Intergovernmental Panel on Climate Change had previously predicted dire restrictions on water supplies in Asia. "There clearly were some misunderstandings," he says.

The researchers behind the latest study began by calculating the importance of meltwater in the overall hydrology of five rivers: the Indus, the Ganges and the Brahmaputra in India, Pakistan and Bangladesh, and the Yellow River and the Yangtze in China¹. The authors found that meltwater is most important to the Indus, with a contribution roughly 1.5 times that from lowland rains. In the Brahmaputra, meltwater flow is equivalent to only one-quarter of the volume supplied by lowland rainfall, and, in the other rivers, it forms no more than one-tenth of the input.

Furthermore, the study found that in the Indus and Ganges basins, glacial ice contributes only about 40% of the total meltwater, with the rest coming from seasonal snows. In the other three rivers its contribution is even lower.

High and dry?

That's important, says Walter Immerzeel, a hydrologist at FutureWater in Wageningen, The Netherlands, and lead author of the study¹, because Asian rivers are fed by three sources: rain, snow melt and melting glaciers.

The first two are driven by current weather patterns, because rains fall either as water or as snow that will later melt. The last is a carry-over from the build-up of glaciers in prior centuries. As the glaciers shrink, their contribution will also decline until the glaciers have either melted entirely, or stabilized at smaller sizes.

{“The glaciers are tiny, compared with the monsoon.”}

Climate change will therefore have two effects, Immerzeel says. One will be to reduce the contribution of glaciers to total run-off. The other will be to change weather patterns, including rain and snowfall. Combining these and looking at averages from five climate models, Immerzeel and colleagues concluded that the change in upstream water inputs will range from a decrease of 19.6% for the Brahmaputra to a 9.5% increase for the Yellow River. The latter, he notes, is due to increased winter rains. "The Yellow River depends only marginally on meltwater," he says, "and, on average, the models project an increase in winter precipitation in the Yellow River basin."

What this means, Armstrong says, is that river flows are dominated by seasonal rains. "The glaciers are tiny, compared with the monsoon," he says.

Nevertheless, the study concludes that climate change will reduce water supplies enough that by 2050, declines in irrigation water are likely to reduce the number of people the region's agriculture can support by about 60 million — 4.5% of the region's present population.

Model uncertainty

One caveat, Immerzeel notes, is that climate models don't fare well at simulating the effect of warming on Asian rainfall. "There's still a lot of research going into the effect of climate change on the behaviour of the monsoon," he says.

Further refinements will also come from improved mapping of the area's glaciers, something that Armstrong's team has recently started, using remote-sensing data from satellites. That's an important next step, he says, although he adds, "I don't think we'll have a substantially different result."

The findings are important for policy-makers, says Jeffrey Kargel, a glaciologist at the University of Arizona in Tucson. "This paper adds to mounting evidence that the Indus Basin [between India and Pakistan] is particularly vulnerable to climate change," says Kargel. "This is a matter that obviously concerns India and Pakistan very much."

"The two nations must talk to one another and see that it is in their mutual best interests to arrive at an equitable means of sharing and utilizing water," he adds.

References
1. Immerzeel, W. W. , van Beek, L. P. H. & Bierkens, M. F. P. Science 328, 1382-1385 (2010).


[nature.com > naturenews]
Published online 10 June 2010 | Nature | doi:10.1038/news.2010.290
News
The Sun as comet snatcher
｛太陽、誘拐犯？｝

Most of the Solar System's comets may have been stolen from other stars.
｛太陽系の彗星のほとんどが、他の系外の星から侵入したものか？｝
By Lucas Laursen

{{Comets in the Sun's Oort cloud may be stolen goods.}
DR SETH SHOSTAK / SCIENCE PHOTO LIBRARY}

New simulations suggest that the Sun may have captured more than its fair share of comets from the primordial star-forming soup. The study, led by Harold Levison of the Southwest Research Institute in Boulder, Colorado, seeks to account for the abundance of comets in the outer reaches of the Solar System.

Our Solar System's comets spend most of their time between roughly 5,000 and 100,000 times further away from the Sun than the Earth, in a little-understood region beyond the planets known as the Oort cloud. Occasionally, some zip past the inner Solar System, and a rare few, such as Halley's Comet, return on a regular basis. But the origin of even the most well known comets is something of a mystery.

An influential model of how the Solar System formed predicts that around 6 billion comets in the Oort cloud are home-grown¹. But some astronomers estimate that there are as many as 400 billion comets surrounding the Solar System — a discrepancy that researchers have struggled to explain.

Now the Levison study suggests that these mystery comets may actually have formed around other stars during the first moments of star formation. "Our Sun is a relatively heavy star," explains Ramon Brasser, a co-author of the study, which appears online in Science today². When material such as gas, dust and ice began to find gravitational dancing partners, our Sun may have been massive enough to skim spare comets from its more lightweight neighbours.

Stolen goods

Levinson and colleagues are not the first to suggest that some comets may be from beyond the Solar System. A team examined the possibility in a 1990 study, but concluded that the Sun's pull was not sufficient to attract enough comets³. "They did not have the computing power to do the simulation we have done," Brasser says.

Brasser and his colleagues built a computer model in which many stars form near one another in a stellar cluster. In the simulation, each star spawns planetary objects including comets, some of which settle into orbits occupying an extended scattered disk around the star and others of which are ejected into the wider gas cloud enveloping the cluster. About 3 million years into the simulation, the gas surrounding the newly formed stars collapses into each solar system, and most of the free-floating comets find homes around one of the stars. During subsequent flybys with other stars, the simulation shows the Sun snags enough comets to account for its present collection.

However, running such a detailed simulation required the astronomers to make many assumptions about solar system formation, which introduce large uncertainties into the picture. "The most vulnerable assumption is that extended scattered disks would actually exist at the early time considered," says Hans Rickman of Uppsala Astronomical Observatory in Sweden. Extended scattered disks, a hypothetical home for comets in orbit around stars, have not been directly observed, nor do theorists agree on how they form, Rickman says. In one recent model, the disk does not form until 1 billion years after the beginning of a solar system.

Brasser says the simulation also had to assume that all stars have the same number of comets because solid numbers are not available. "People will have difficulty with this assumption," he admits. And for lack of more information, the authors write in the paper that they assumed that other solar systems have a distribution of large planets (whose mass influence cometary orbits) similar to our own.

Even the more widely accepted estimates of the number of comets in the Oort cloud could be too high, Rickman says, and a later formation of the cloud could make it easier to fill with home-grown comets. All the uncertainty, he says, "makes me think there does not have to be any problem at all".

References
1. Levison, H. F. & Duncan, M. J. Icarus 127, 13 (1997).
2. Levison, H. F. , Duncan, M. J. , Brasser, R. & Kaufmann, D. E. Science published online, doi: 10.1126/science.1187535 (10 June 2010).
3. Zheng, J-Q. , Valtonen, M. J. & Valtaoja, L. Celest. Mech. Dyn. Astr. 49, 265 (1990).

news20100611bbc1

[One-Minute World News] from [BBC NEWS]

[bbc.co.uk > Science & Environment]
Page last updated at 09:46 GMT, Friday, 11 June 2010 10:46 UK
Japan unfurls solar sail in orbit
｛日本、軌道上で太陽光を受ける帆を展開｝

{An image of the deployment is sent back to Earth}

Japanese scientists are celebrating the successful deployment of their solar sail Ikaros.
｛日本の科学者、宇宙ヨット「イカロス」の帆の展開の成功を祝う｝

The 200-sq-m (2,100-sq-ft) membrane is attached to a small disc-shaped spacecraft that was put in orbit last month by an H-IIA rocket.

Ikaros will demonstrate the principle of using sunlight as a simple and efficient means of propulsion.

The technique has long been touted as a way of moving spacecraft around the Solar System using no chemical fuels.

The mission team will be watching to see if Ikaros produces a measurable acceleration, and how well its systems are able to steer the craft through space.

The Japan Aerospace Exploration Agency (Jaxa) said in a statement that its scientists and engineers had begun to deploy the solar sail on 3 June (JST). On 10 June, Jaxa said, confirmation was received that the sail had expanded successfully and was generating power through the thin film solar cells embedded in the membrane

The deployment occurred about seven million km from Earth.

Ikaros was a piggy-back payload to Japan's Venus orbiter Akatsuki. The pair were boosted in to space on 21 May (JST) from the Tanegashima Space Center.

Akatsuki will arrive at Venus in December. Key goals include finding definitive evidence for lightning and for active volcanoes.

{{SAILING TO VENUS - HOW IKAROS UNFURLS ITS SOLAR SAIL}
(1) For the deployment, the disc-shaped Ikaros spacecraft was first spun up
(2) The four weighted corners of the sail were then released and flew outwards
(3) Finally, the packed sail membrane was released and pulled flat by the rotating tips}


[bbc.co.uk > Science & Environment]
Page last updated at 08:16 GMT, Friday, 11 June 2010 09:16 UK
By Mark Kinver
Science and environment reporter, BBC News
Himalayan climate impacts 'cannot be generalised'
｛ヒマラヤの気候温暖化の影響は総括的に述べれない｝

{Mountain glaciers provide vital lifeblood for some of Asia's major rivers}
｛アジアの大河には、山の氷河が極めて重要な活力源になっているものがある｝

Melting glaciers in the Himalayas will have varying impacts on the region's five major river basins, a study says.
｛調査報告書によると、ヒマヤラの氷山の溶解が５大河川流域に種々の影響を及ぼしている｝

Changes to the flow of meltwater as a result of global warming is likely to have a "severe" impact on food security in some area, say scientists.

Yet people living elsewhere are likely to see food productivity increase, they added in a paper published in Science.

Overall, the food security of 4.5% of 1.4bn people in the region is threatened, the researchers conclude.

More than 1.4bn people depend on water from the Indus, Ganges, Brahmaputra, Yangtze and Yellow rivers.

"We show that meltwater is extremely important in the Indus basin and important for the Brahmanputra basin, but only plays a modest role for the Ganges, Yangtze and Yellow rivers," the team from the Netherlands wrote.

"The Brahmaputra and Indus basins are most susceptible to reductions of flow, threatening the food security of an estimated 60m people."

The researchers described mountains as the "water towers of the world".

"Snow and glacial melt are important hydrological processes... and changes in temperature and precipitation are expected to seriously affect the melt characteristics," they explained.

Summer rains

The team used data to assess a number of factors to reach their conclusions, including: the current importance of meltwater in overall river basin hydrology; observed cyrospheric changes; and the effects of climate change on the water supply from the upstream basins and on food security.

"The Yellow River, in particular, shows a consistent increase in early spring discharge, " they said.

"This is highly beneficial because most reservoirs are empty at the beginning of the growing season.

"An accelerated melt peak may thus alleviate a shortage of irrigation water in the drought-prone early stages of the growing season."

However, despite the projected compensating effects of increased rainfall in the Indus and Brahmaputra basins, the team predicted that summer and late spring discharges would eventually be reduced "consistently and considerably by 2046 to 2065 after a period with increase flows as a result of accelerated glacial melt".

"These anticipated changes will also have considerable effects on food security," they warned.

"By relating changes in upstream water availability to net irrigation requirements, observed crop yields, calorific value of the crops and required human energy consumption, one can estimate the change in the number of people that can be fed."

The team estimates that about 34.5m fewer people could be fed in the Brahmaputra basin; 26.3m fewer in the Indus basin; 7.1m in the Yangtze region and about 2.1m fewer around the Ganges.

However, they suggested that the changes could see an increase in food production in the Yellow River basin, enough to feed a further 3m people.

"In total, we estimate that the food security of 4.5% of the total population will be threatened as a result of reduced water availability," they concluded.

"The strong need for prioritising adaptation options and further increasing water productivity is therefore ever more eminent.

"We conclude that Asia's water towers are threatened by climate change, but the effects of climate change on water availability and food security in Asia differ substantially among basins and cannot be generalised.

"The effects in the Indus and Brahmaputra basins are likely to be severe owing to the large population and the high dependence on irrigated land and meltwater.

"In the Yellow River, climate change may even yield a positive benefit as the dependence on meltwater is low and a projected increased upstream precipitation, when retained in reservoirs, would enhance water availability for irrigated agriculture and food security."

news20100611bbc2

[One-Minute World News] from [BBC NEWS]

[bbc.co.uk > Science & Environment]
Page last updated at 08:40 GMT, Friday, 11 June 2010 09:40 UK
By Katia Moskvitch
Science reporter, BBC News
Most comets may have extra-solar origin
｛ほとんどの彗星は太陽系外の起源｝

{Hale-Bopp comet is believed to have formed in the Oort cloud}
｛ヘールボップ彗星はオールトの雲で形成されたものと思われる｝

Many famous comets may have formed in other Solar Systems, a new theory proposes.
｛新理論によると、有名な彗星の多くは他の太陽系で形成されている。｝

Astronomers now believe that when our Sun was still a young star, it may have gravitationally captured the "dusty" Oort cloud comets formed elsewhere in the galaxy.

This contradicts the earlier theory that most comets were born in the Sun's protoplanetary disk.

The scientists described their findings in the journal Science.

The formation of the Oort cloud has long been a mystery.

Up until now, astronomers thought that this spherical cloud of comets lying at the outermost edge of the Solar System might have formed in the Sun's protoplanetary disk - a cloud of gas and matter that gave birth to planets, some 4.6 billion years ago.

But this hypothesis has been challenged by an international group of astronomers led by Dr Harold Levison from the Southwest Research Institute in Colorado, US.

Sun's cluster

A member of the team, Dr Ramon Brasser from the University of Nice-Sophia Antipolis, explained to BBC News that the Sun was not born alone.

{For 60 years we did not know how the Oort cloud had formed and we have been looking for an answer}
Dr Roman Brasser
University of Nice-Sophia Antipolis}

Instead, he said, it is believed to have formed in a cluster of about a thousand of other stars, all packed together.

"Imagine that you have a very large cloud of gas composed of mostly hydrogen that is sitting around in our galaxy.

"From some disturbances inside it, the cloud slowly starts to collapse, it shrinks, becoming more compact.

"It then forms lumps and those lumps compress even further - that is how stars are born," said Dr Brasser.

He explained that each young star then creates a huge number of small icy bodies around it in a disk from which planets gradually form.

In our galaxy's early times, many of these icy objects got "ejected" from the planetary systems and eventually became comets.

But a few stayed near the Sun, affected by strong interstellar forces. They formed, astronomers used to believe, what became known as the peculiar "dusty" Oort cloud, about a light-year from the Sun.

It was assumed to be the birthplace of the majority of the famous comets, including Halley, Hale-bopp and McNaught.

Mystery 'solved'

When the Sun's cluster dispersed, exploding from inside out, the star was left all alone.

The Oort cloud was thought to have formed around the Sun And the new study showed that its gravitational field may have been so strong that it pulled in a large cloud of comets originally formed in other solar systems.

The idea of the Oort cloud comets being extra-solar was suggested before, in the early 1990s. But back then, the methods used were not precise enough to prove the theory and it was abandoned.

Dr Levinson said that his team picked up on the same thought and used computer simulations to construct a model of a star cluster and comets - and had some interesting results.

"If we assume that the Sun's observed proto-planetary disk can be used to estimate the indigenous population of the Oort cloud, we can conclude that more than 90% of the observed Oort cloud comets have an extra-solar origin," commented the astronomer.

His colleague Martin Duncan from the Queen's University in Ontario, Canada, said that the findings lead "to the exciting possibility that the [Oort] cloud contains a potpourri that samples material from a large number of stellar siblings of the Sun".

Dr Brasser concluded that the recent findings may be an important missing link to explain the formation of the Universe.

"For 60 years we have not known how the Oort cloud formed and for 60 years people have been looking for an answer. It has been a missing piece and it might help understand the evolution and the formation of our Solar System," he said.