[Cosmic ‘weather’ at edge of solar system (太陽系外延の宇宙)]

U. CHICAGO—Scientists have published the first comprehensive sky maps revealing a surprising ribbon of energetic neutral atoms at the outer edge of the solar wind bubble surrounding the solar system.


The maps are based mostly on data collected from NASA’s Interstellar Boundary Explorer satellite (IBEX). Findings appear in Science Express, the advance online version of the journal Science.

マップは主として、NASAのInterstellar Boundary Explorer(星間境界探査機)(IBEX)が集めたデータに基づいている。この発見はScience誌のオンライン先行版であるScience Expressに発表された。

“Nature is full of surprises, and IBEX has been lucky to discover one of those surprises,” says Priscilla Frisch, a senior scientist in astronomy and astrophysics at the University of Chicago. “The sky maps are dominated by a giant ribbon of energetic neutral atoms extending throughout the sky in an arc that is 300 degrees long.”

「自然は驚きに満ちていて、IBEXは幸運にもそのひとつを発見した。スカイマップは、300°の広がりを持つ虚空のアークに広がる高エネルギー中性粒子の大きなリボンに占められている」とUniversity of Chicagoの天文学・宇宙物理学のシニア科学者Priscilla Frischは言う。

Energetic neutral atoms form when hot solar wind ions (charged particles) steal electrons from cool interstellar neutral atoms.


IBEX was launched Oct. 19, 2008, to produce the first all-sky maps of the sun’s domain—called the heliosphere—which reaches far beyond the solar system’s most distant planets. Extending more than 100 times farther than the distance from Earth to the sun, the heliosphere marks the region of outer space subjected to the sun’s particle emissions.


The new maps show how high-speed cosmic particle streams collide and mix at the edge of the heliosphere, says Frisch, who coauthored three of a set of IBEX articles appearing in Science Express. The outgoing solar wind blows at 900,000 miles an hour, crashing into a 60,000-mile-an-hour “breeze” of incoming interstellar gas.

「この新しいマップは、高速宇宙粒子の流れがヘリオスフィア外延で衝突・混合している様子を示している」とScience Expressに発表されたIBEX論文のうち3本の共著者であるPriscilla Frischは述べた。太陽風は毎時90万マイルで系外へ流れていて、毎時6万マイルで侵入してくる星間ガスの風と衝突している。

Revealed in the IBEX data, but not predicted in the theoretical heliosphere simulations of three different research groups, was the ribbon itself, formed where the direction of the interstellar magnetic field draping over the heliosphere is perpendicular to the viewpoint of the sun.


Energetic protons create forces as they move through the magnetic field, and when the protons are bathed in interstellar neutrals, they produce energetic neutral atoms.


“We’re still trying to understand this unexpected structure, and we believe that the interstellar magnetic forces are associated with the enhanced ENA production at the ribbon,” Frisch says.

「我々はこの予想外の構造を理解しようとしている。我々は、リボンでの増幅された高エネルギー中性原子の生成に星間磁場が関係していると考えている」とPriscilla Frischは言う。

IBEX shows that energetic neutral atoms are produced toward the north pole of the ecliptic (the plane traced by the orbit of the planets around the sun), as well as toward the heliosphere tail pointed toward the constellations of Taurus and Orion.


“The particle energies change between the poles and tail, but surprisingly not in the ribbon compared to adjacent locations,” Frisch says.

「粒子のエネルギーは極と尾部の間で変化するが、驚くべきことに、隣接領域と比べればリボンの中での変化は小さい」とPriscilla Frischは言う。

IBEX is the latest in NASA’s series of low-cost, rapidly developed Small Explorers space missions. Southwest Research Institute in San Antonio, Texas, leads and developed the mission with a team of national and international partners. NASA’s Goddard Space Flight Center in Greenbelt, Md., manages the Explorers Program for NASA’s Science Mission Directorate in Washington.

IBEXはNASA最新のローコスト・ラピッド開発の小型宇宙短期計画シリーズのひとつである。テキサス州San AntonioのSouthwest Research Instituteが、米国ないおよび国際チームとともに、ミッションの指導・開発にあたった。メリーランド州GreenbeltのNASAのGoddard Space Flight CenterはワシントンのNASAのScience Mission Directorateのために探査計画を管理している。

Heliosphere’s orientation in the Milky Way galaxy. The light blue olive-shape marks the termination shock, where solar wind slows from supersonic to subsonic speeds. The lavender area is the heliosphere’s bow shock, formed as the sun moves supersonically through the surrounding interstellar cloud. In between those two regions is the heliopause. (Credit: Priscilla Frisch, Andrew Hanson, Philip Chi-Wing Fu)


University of Chicago news: http://news.uchicago.edu/
"bow shock"は、弓型衝撃波(ボウショック)じゃなくて、船の舳先の衝撃波(バウショック)が正解だった記憶がある。

posted by Kumicit at 2009/10/29 08:45 | Comment(1) | TrackBack(0) | News | このブログの読者になる | 更新情報をチェックする
Posted by U at 2016/07/14 21:37



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