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★ボイジャー1号太陽系を脱出


NASA12日「Voyager 1が太陽系の外へ昨年の825日頃脱出したと見られる。太陽系外の恒星間空間 ”interstellar space”に到達した初の人工物である。」と米科学誌サイエンス電子版に発表した事を13日付各メディアは報じている。

そのボイジャー1号は1977年に打ち上げられ「はやぶさ」の総飛行距離の3倍以上を36年かけて旅し現在太陽から約187km付近(恒星間空間)を時速約6kmの速度で飛行中である。次の恒星との出会いは約4万年後(但しボイジャー1号の電源寿命は2020年頃迄で通信は途絶える)であるが、果たしてその頃人類が存続しているかの保証はない・・・との事だそうである。

ボイジャー1号は197980年にかけて木星の表面の「大赤斑、”
Great red spot」と言われる模様(地球の直径の2倍以上もある大きな水素とヘリュームから成る大気の渦)や、土星の輪の鮮明なデータを送信して来た事で有名で、我々に驚きと感動を与えてくれた。



NASA: Voyager 1 has left the solar system

Sep. 13, 2013 - Updated 03:09 UTC
 NHK WORLD 

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The US space agency NASA says its spacecraft

Voyager 1 has become the first artificial object to leave the solar system. NASA hails the achievement as a historic event.

NASA announced on Thursday that the unmanned spacecraft launched in 1977 is about 19 billion kilometers from the Sun. The probe is cruising in interstellar space --- the space between the stars.

After analyzing data sent from Voyager 1 earlier this year, scientists at NASA and the University of Iowa concluded that it exited the solar system in August last year.

The data showed a decrease in the density of charged particles emanating from the Sun and a spike in the number of cosmic rays from outside the solar system.

Voyager 1 was launched 36 years ago to survey the outer planets.

It transmitted clear images of Jupiter's surface patterns and Saturn's rings.

The spacecraft is travelling at a speed of 60,000 kilometers per hour and is expected to send data back to Earth until around 2020, when it will run out of fuel.

Scientists have high hopes that Voyager 1 will help them to make new discoveries about the universe.  
  



ボイジャー太陽系脱出
朝日新聞 913日朝刊

 

ボイジャー1号太陽系離脱001.jpg ボイジャー1号太陽系離脱002.jpg

ボイジャー1号太陽系離脱003.jpg




■ボイジャー
1号、太陽圏脱出を確認 恒星間空間を航行中


2013年
0913 0855分
提供元:ITmedia ニュース


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太陽圏を脱出したボイジャー
1号のイラスト=NASA


米航空宇宙局(NASA)は912日(現地時間)、1977年に打ち上げた探査船「ボイジャー1号」が太陽圏(heliosphere)を昨年8月に脱出したことを確認したと発表した。恒星間空間に到達した初の人工物となる。

ボイジャー1号は2004年、太陽風が星間物質との相互作用で減速する「末端衝撃波面」を通過。現在は地球から190億キロの地点を秒速約17キロで航行している。

アイオワ大学の研究チームがデータを調べたところ、ボイジャー1号周辺のプラズマ密度は、太陽圏の外側の層で検知した密度の40倍に上っていた。太陽風と星間物質が混ざり合う「ヘリオポーズ」を脱し、恒星間空間に到達したと考えられるという。

ボイジャー計画の科学者であるエドワード・ストーン元JPL所長は、分析結果について「これは恒星間空間への人類の歴史的跳躍だと信じている」と述べている。研究結果は米科学誌「Science」に掲載された。

データの分析から、ボイジャー1号が恒星間空間に到達したのは2012825日だったと特定した。太陽から183億キロの距離だった。

ボイジャー1号は197795日に打ち上げられ、1979年に再接近した木星表面の鮮明な写真を送信するなど、ボイジャー2号とともにさまざまなデータを送った。1990214日、最後の写真として撮影された「太陽系の家族写真」には6惑星が写っている。

原子力電池で動作しているが、NASAによると2020年ごろから限界に達し始め、科学的観測機器を1つずつオフにする作業を開始する。最後の観測機器は25年ごろまで動作し、工学的データはさらにその後数年は取得できると考えられている。

ボイジャー2号は1号より34億キロ太陽に近い位置を航行中で、まだ太陽圏を脱していないと考えられている。

ボイジャー1号はへびつかい座の方向に向かって航行しており、約38000年後には1.7光年の位置にあるこぐま座の星に近づくという。

NASA
によると、ボイジャー1号と2号にかかったコストは9月の時点で約98800万ドルだという。



米探査機ボイジャーついに太陽系外へ 打ち上げから36年、人工物で初

2013.9.13 09:11産経ニュース

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太陽系外に広がる星間空間を飛行する米探査機「ボイジャー1号」の想像図(NASA提供・共同)

米航空宇宙局(NASA)は36年前に打ち上げられた米探査機「ボイジャー1号」が太陽系の端の領域を越え、人工物体として初めて太陽系外に広がる星間空間に旅立ったことが確認されたと、米科学誌サイエンス電子版に発表した。

太陽系の最も端に達したことは分かっていたが、データ分析の結果、出ていたことが判明した。NASAの研究者は「星間空間に人類が踏み出した歴史的な出来事だ」としている。

NASAのチームは、ボイジャー1号が今年春に観測したデータを使い、太陽から送り出される「太陽風」と呼ばれる粒子の流れと太陽系外から飛来する宇宙線の変化を分析。太陽風が衰える一方で、宇宙線に由来する電子の密度が高くなっていることから、星間空間にあると結論付けた。太陽系を出た時期は昨年8月25日ごろとみられる。

ボイジャー1号は1977年に打ち上げられ木星や土星に接近、写真を撮影。現在は太陽から約190億キロ離れたところを時速約6万キロで飛行中。(共同)



■木星の模様、土星の輪…成果残したボイジャー「36年の旅」

2013.9.13 14:30 産経ニュース



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ボイジャーに搭載された世界のあいさつなどを記録した銅製のレコード。

金張りでゴールデンレコードと呼ばれる(NASA提供)


太陽系から旅立ったことが確認されたボイジャー1号。打ち上げから36年にわたる旅の間、木星の模様や土星の輪の詳細な写真を撮影するなど2号とともに輝かしい成果を挙げてきた。


1977年夏、ボイジャー1、2号が米フロリダ州のケネディ宇宙センターから打ち上げられた。1号は79年3月、太陽系最大の惑星の木星に最接近し、2号も同年7月に到達した。観測で木星の表面にある「大赤斑」という模様が、反時計回りに動く複雑な大気の流れであることが判明。木星の衛星3個を新たに発見した

80~81年には太陽系で2番目に大きい土星に到達。岩石が集まってできた土星の輪を撮影、新たな衛星を発見した。1号はその後、太陽系外を目指し、2号は86年に天王星、88~89年に海王星を探査した。

地球外の知的生命体に遭遇した場合にも備え「ゴールデンレコード」という金を張った銅製レコードと再生用の針を搭載。波や風、雷の音や動物の鳴き声、クラシック音楽や日本の尺八の音色も収められた。



scn13091314330003-p1木星表面.jpg
ボイジャー1号が木星に接近して撮影した表面の斑点(NASA提供)


scn13091314330003-p3ボイジャー1号.jpg
太陽系外に広がる星間空間を飛行する米探査機「ボイジャー1号」の想像図(NASA提供)


scn13091314330003-p4土星.jpg
1980年にボイジャー1号が撮影した土星(NASA提供)



NASA HP

Voyager Embarks on Journey Into Interstellar Space

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NASA's Voyager 1 spacecraft officially is the first human-made object to venture into interstellar space.

The 36-year-old probe is about 12 billion miles (19 billion km) from our sun. New and unexpected data indicate Voyager 1 has been traveling for about one year through plasma, or ionized gas, present in the space between stars.

> Voyager Mission Page



How Do We Know When Voyager Reaches Interstellar Space?

Sept 12, 2013

pia17046red-full_1少.jpg

You Are Here, Voyager: This artist's concept puts huge solar system distances in perspective. The scale bar is measured in astronomical units (AU), with each set distance beyond 1 AU representing 10 times the previous distance. Each AU is equal to the distance from the sun to the Earth. It took from 1977 to 2013 for Voyager 1 to reach the edge of interstellar space.

Image Credit: NASA/JPL-Caltech

Image Token: Feature Link: 



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Layers of Intrigue: This illustration shows the outer layers of our solar bubble, or heliosphere, and the interstellar space that Voyager 1 is currently investigating.

Image Credit: NASA/JPL-Caltech

Image Token: Feature Link: 



Whether and when NASA's Voyager 1 spacecraft, humankind's most distant object, broke through to interstellar space, the space between stars, has been a thorny issue. For the last year, claims have surfaced every few months that Voyager 1 has "left our solar system." Why has the Voyager team held off from saying the craft reached interstellar space until now?


"We have been cautious because we're dealing with one of the most important milestones in the history of exploration,” said Voyager Project Scientist Ed Stone of the California Institute of Technology in Pasadena.  “Only now do we have the data -- and the analysis -- we needed."


Basically, the team needed more data on plasma, which is ionized gas, the densest and slowest moving of charged particles in space. (The glow of neon in a storefront sign is an example of plasma.) Plasma is the most important marker that distinguishes whether Voyager 1 is inside the solar bubble, known as the heliosphere, which is inflated by plasma that streams outward from our sun, or in interstellar space and surrounded by material ejected by the explosion of nearby giant stars millions of years ago. Adding to the challenge: they didn't know how they'd be able to detect it.


"We looked for the signs predicted by the models that use the best available data, but until now we had no measurements of the plasma from Voyager 1," said Stone.

 

Scientific debates can take years, even decades to settle, especially when more data are needed. It took decades, for instance, for scientists to understand the idea of plate tectonics, the theory that explains the shape of Earth's continents and the structure of its sea floors. First introduced in the 1910s, continental drift and related ideas were controversial for years. A mature theory of plate tectonics didn't emerge until the 1950s and 1960s. Only after scientists gathered data showing that sea floors slowly spread out from mid-ocean ridges did they finally start accepting the theory. Most active geophysicists accepted plate tectonics by the late 1960s, though some never did.


Voyager 1 is exploring an even more unfamiliar place than our Earth's sea floors -- a place more than 11 billion miles (17 billion kilometers) away from our sun. It has been sending back so much unexpected data that the science team has been grappling with the question of how to explain all the information. None of the handful of models the Voyager team uses as blueprints have accounted for the observations about the transition between our heliosphere and the interstellar medium in detail. The team has known it might take months, or longer, to understand the data fully and draw their conclusions.


"No one has been to interstellar space before, and it's like traveling with guidebooks that are incomplete," said Stone. "Still, uncertainty is part of exploration. We wouldn't go exploring if we knew exactly what we'd find."


The two Voyager spacecraft were launched in 1977 and, between them, had visited Jupiter, Saturn, Uranus and Neptune by 1989. Voyager 1's plasma instrument, which measures the density, temperature and speed of plasma, stopped working in 1980, right after its last planetary flyby. When Voyager 1 detected the pressure of interstellar space on our heliosphere in 2004, the science team didn't have the instrument that would provide the most direct measurements of plasma. Instead, they focused on the direction of the magnetic field as a proxy for source of the plasma. Since solar plasma carries the magnetic field lines emanating from the sun and interstellar plasma carries interstellar magnetic field lines, the directions of the solar and interstellar magnetic fields were expected to differ.


Most models told the Voyager science team to expect an abrupt change in the magnetic field direction as Voyager switched from the solar magnetic field lines inside our solar bubble to those in interstellar space. The models also said to expect the levels of charged particles originating from inside the heliosphere to drop and the levels of galactic cosmic rays, which originate outside the heliosphere, to jump.


In May 2012, the number of galactic cosmic rays made its first significant jump, while some of the inside particles made their first significant dip. The pace of change quickened dramatically on July 28, 2012. After five days, the intensities returned to what they had been.  This was the first taste of a new region, and at the time Voyager scientists thought the spacecraft might have briefly touched the edge of interstellar space.


By Aug. 25, when, as we now know, Voyager 1 entered this new region for good, all the lower-energy particles from inside zipped away. Some inside particles dropped by more than a factor of 1,000 compared to 2004. The levels of galactic cosmic rays jumped to the highest of the entire mission.  These would be the expected changes if Voyager 1 had crossed the heliopause, which is the boundary between the heliosphere and interstellar space. However, subsequent analysis of the magnetic field data revealed that even though the magnetic field strength jumped by 60 percent at the boundary, the direction changed less than 2 degrees. This suggested that Voyager 1 had not left the solar magnetic field and had only entered a new region, still inside our solar bubble, that had been depleted of inside particles.


Then, in April 2013, scientists got another piece of the puzzle by chance. For the first eight years of exploring the heliosheath, which is the outer layer of the heliosphere, Voyager's plasma wave instrument had heard nothing. But the plasma wave science team, led by Don Gurnett and Bill Kurth at the University of Iowa, Iowa City, had observed bursts of radio waves in 1983 to 1984 and again in 1992 to 1993. They deduced these bursts were produced by the interstellar plasma when a large outburst of solar material would plow into it and cause it to oscillate.  It took about 400 days for such solar outbursts to reach interstellar space, leading to an estimated distance of 117 to 177 AU (117 to 177 times the distance from the sun to the Earth) to the heliopause. They knew, though, that they would be able to observe plasma oscillations directly once Voyager 1 was surrounded by interstellar plasma.


Then on April 9, 2013, it happened: Voyager 1's plasma wave instrument picked up local plasma oscillations. Scientists think they probably stemmed from a burst of solar activity from a year before, a burst that has become known as the St. Patrick's Day Solar Storms. The oscillations increased in pitch through May 22 and indicated that Voyager was moving into an increasingly dense region of plasma. This plasma had the signatures of interstellar plasma, with a density more than 40 times that observed by Voyager 2 in the heliosheath.


Gurnett and Kurth began going through the recent data and found a fainter, lower-frequency set of oscillations from Oct. 23 to Nov. 27, 2012. When they extrapolated back, they deduced that Voyager had first encountered this dense interstellar plasma in August 2012, consistent with the sharp boundaries in the charged particle and magnetic field data on August 25.


Stone called three meetings of the Voyager team. They had to decide how to define the boundary between our solar bubble and interstellar space and how to interpret all the data Voyager 1 had been sending back. There was general agreement Voyager 1 was seeing interstellar plasma, based on the results from Gurnett and Kurth, but the sun still had influence. One persisting sign of solar influence, for example, was the detection of outside particles hitting Voyager from some directions more than others. In interstellar space, these particles would be expected to hit Voyager uniformly from all directions.


"Now that we had actual measurements of the plasma environment – by way of an unexpected outburst from the sun – we had to reconsider why there was still solar influence on the magnetic field and plasma in interstellar space," Stone said.

 

"The path to interstellar space has been a lot more complicated than we imagined."


Stone discussed with the Voyager science group whether they thought Voyager 1 had crossed the heliopause. What should they call the region were Voyager 1 is?

 

"In the end, there was general agreement that Voyager 1 was indeed outside in interstellar space," Stone said. "But that location comes with some disclaimers – we're in a mixed, transitional region of interstellar space. We don't know when we'll reach interstellar space free from the influence of our solar bubble."

 

So, would the team say Voyager 1 has left the solar system? Not exactly – and that's part of the confusion. Since the 1960s, most scientists have defined our solar system as going out to the Oort Cloud, where the comets that swing by our sun on long timescales originate. That area is where the gravity of other stars begins to dominate that of the sun. It will take about 300 years for Voyager 1 to reach the inner edge of the Oort Cloud and possibly about 30,000 years to fly beyond it. Informally, of course, "solar system" typically means the planetary neighborhood around our sun. Because of this ambiguity, the Voyager team has lately favored talking about interstellar space, which is specifically the space between each star's realm of plasma influence.

 

"What we can say is Voyager 1 is bathed in matter from other stars," Stone said. "What we can't say is what exact discoveries await Voyager's continued journey. No one was able to predict all of the details that Voyager 1 has seen. So we expect more surprises."

 

Voyager 1, which is working with a finite power supply, has enough electrical power to keep operating the fields and particles science instruments through at least 2020, which will mark 43 years of continual operation. At that point, mission managers will have to start turning off these instruments one by one to conserve power, with the last one turning off around 2025.

 

Voyager 1 will continue sending engineering data for a few more years after the last science instrument is turned off, but after that it will be sailing on as a silent ambassador. In about 40,000 years, it will be closer to the star AC +79 3888 than our own sun. (AC +79 3888 is traveling toward us faster than we are traveling towards it, so while Alpha Centauri is the next closest star now, it won't be in 40,000 years.) And for the rest of time, Voyager 1 will continue orbiting around the heart of the Milky Way galaxy, with our sun but a tiny point of light among many.

 

The Voyager spacecraft were built and continue to be operated by NASA's Jet Propulsion Laboratory, in Pasadena, Calif. Caltech manages JPL for NASA. The Voyager missions are a part of NASA's Heliophysics System Observatory, sponsored by the Heliophysics Division of the Science Mission Directorate at NASA Headquarters in Washington.

 

For more information about Voyager, visit: http://www.nasa.gov/voyager and http://voyager.jpl.nasa.gov .

 

Jia-Rui Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov

2013-278       




 
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