미국 우주탐사선 보이저 1호가 인류 역사상 최초로 태양계의 끝에 도착했다.
미 항공우주국(NASA)의 과학자들은 보이저 1호가 태양풍이 불고 있는 ‘말단충격(Termination shock)’ 지대를 지나 태양계 외부 우주공간과의 경계지대인 ‘헬리오스히스(Heliosheath)’에 진입했다고 24일 밝혔다.
보이저 1호가 태양계의 마지막 관문인 이 지대를 통과해 태양풍이 거의 소멸되는 경계면인 ‘헬리오포즈(Heliopause)’와 ‘바우충격(Bow Shock)’ 지대를 빠져나가면 태양계를 완전히 벗어나게 되는 것이다. 보이저 1호가 헬리오스히스를 지나는데는 10년이 걸린다.
과학자들은 “보이저1호가 포착한 태양풍의 속도가 시속 240만km에서 갑자기 제로에 가까운 수준으로 줄어 들었기 때문에 헬리오스히스에 도달했다는 결론을 내렸다”며 “2020년까지는 플루토늄 동력원이 유지되기 때문에 외부 우주공간인 ‘항성간 우주공간(Interstellar Space)’에 무난히 진입할 수 있을 것”이라고 예상했다.
보이저 1호는 보이저 2호보다 2주 정도 늦은 1977년 9월 5일에 발사된 후 81년까지 목성, 토성 탐사를 마치고 당초 계획인 5년을 훨씬 넘어 28년째 미지의 영역을 향해 탐사를 계속하고 있다.
보이저 1호와 2호는 목성, 토성까지는 차례로 탐사한 뒤 1호는 태양계 끝으로 향했고 2호는 천왕성과 해왕성을 지나 다른 방향 태양계 끝으로 선회했다. 이들 쌍둥이 탐사선은 또 총 22개의 위성을 탐사했다. 보이저 1호는 현재 지구에서 약 140억km 떨어진 헬리오스히스에 진입해 시속 7만 3,600km 속도로 항해하고 있으며, 보이저 2호는 지구에서 104억km 떨어진 곳을 지나고 있다.
이들 탐사선은 외계생명체와 만났을 때를 대비해 55개국 언어로 된 인사말 등 인류에 대한 각종 정보를 담은 골든디스크를 탑재하고 있다.
Voyager sails to edge of solar system
by Peter N. Spotts | Staff writer of The Christian Science Monitor
A century after the Wright brothers briefly piloted an ungainly aircraft 12 feet above the dunes of North Carolina, humanity is reaching another milestone: getting a craft to the threshold between the solar system and interstellar space.
NASA's Voyager 1 spacecraft may have already entered the inner portion of that boundary. Scientists this week reported readings that suggest the craft had entered a shock wave typical of this region. The shock wave is generated as the solar wind - charged particles that race off the sun at supersonic speeds - slams into the dust and gas of interstellar space.
Not everyone agrees the craft is there yet. The scientists' conclusion has been challenged by other members of the Voyager team, who suggest that the 27-year-old spacecraft has seen only the foothills, not the mountains of this important frontier.
But the dueling sets of data are welcome, notes Voyager's chief scientist Edward Stone.
"We've been inside the bubble for 40 years," he says, referring to an envelope of solar wind and magnetic fields surrounding the solar system. "Now we're in a totally new region."
What they learn here, researchers say, will give them insights into the factors that determine the extended shape of the solar system and the processes that govern how much cosmic radiation the solar system receives from the rest of the galaxy.
Some scientists also suggest that the information gleaned at the solar system's edge could help improve "space weather" forecasts on Earth.
It could provide more data on the interplay between charged particles from the sun and magnetic fields in and beyond the shock wave, which astronomers call the sun's termination shock. This interplay near Earth generates auroras and can silence radio communications, knock out satellites, and trigger electrical blackouts. It also can expose airliners flying over the polar route to relatively high levels of radiation.
For astronomers and astrophysicists, this region of space 10 billion miles from Earth (give or take a few billion miles) represents a milestone. They've seen Hubble Space Telescope images of other stars plowing through dust and gas dubbed the interstellar medium. Now they anticipate the chance to study the process directly.
For some, Voyager crossed the threshold unambiguously, if briefly. Measurements from an instrument designed to detect low-energy charged particles recorded a big jump in particle density that began roughly Aug. 1, 2002. This jump would be expected as the particles get squeezed in a region known as the heliosheath, between the terminal shock and the final boundary known as the bow shock. Voyager 2, some 1.7 billion miles behind, didn't see the jump.
In addition, the particles streamed by in a different direction from those from the solar wind, says Stamatios Krimigis, head of the space department at The Johns Hopkins University's Applied Physics Laboratory. Moreover, indirect measurements suggested the solar wind had dropped dramatically.
By February, however, the measurements returned to previous levels, suggesting that Voyager 1 had reentered the solar wind. Mr. Krimigis and other scientists suggest that the shock boundary may shift with solar activity. Thus Voyager pierced the veil, only to have an energetic blast of solar wind push the veil farther spaceward again.
The second team, which includes Dr. Stone, is less convinced. It notes that the spacecraft's magnetometer failed to detect the shifts in magnetic fields researchers expected to see had Voyager entered the heliosheath. Nor were other indicators present with the characteristics theories predicted should exist.
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