Published : Dec. 6, 2011 - 10:01
WASHINGTON (AP) -- A newly discovered planet is eerily similar to Earth and is sitting outside Earth's solar system in what seems to be the ideal place for life, except for one hitch. It is a bit too big.
The planet is smack in the middle of what astronomers call the Goldilocks zone, that hard to find place that is not too hot, not too cold, where water, which is essential for life, does not freeze or boil. And it has a shopping mall-like surface temperature of near 72 degrees, scientists say.
The planet's confirmation was announced Monday by NASA along with other discoveries by its Kepler telescope, which was launched on a planet-hunting mission in 2009.
This undated handout artist rendering provided by NASA shows Kepler-22b, a planet known to comfortably circle in the habitable zone of a sun-like star. (NASA via AP)
That is the first planet confirmed in the habitable zone for Kepler, which already had found Earth-like rocky planets elsewhere. Twice before astronomers have announced a planet found in that zone, but neither has been as promising.
``This is a phenomenal discovery in the course of human history,'' Geoff Marcy of University of California, Berkeley, one of the pioneers of planet-hunting outside Earth's solar system, said in an email. ``This discovery shows that we Homo sapiens are straining our reach into the universe to find planets that remind us of home. We are almost there.''
The new planet, named Kepler-22b, has key aspects it shares with Earth. It circles a star that could be the twin of Earth's sun and at just about the same distance. The planet's year of 290 days is even close to Earth's. It probably has water and rock.
The only trouble is the planet's a bit big for life to exist on the surface. The planet is about 2.4 times the size of Earth. It could be more like the gas-and-liquid Neptune with only a rocky core and mostly ocean.
``It's so exciting to imagine the possibilities,'' said Natalie Batalha, the Kepler deputy science chief.
Floating on that ``world completely covered in water'' could be like being on an Earth ocean and ``it's not beyond the realm of possibility that life could exist in such an ocean,'' Batalha said in a phone interview.
Kepler cannot find life itself, just where the conditions might be right for it to thrive. And when astronomers look for life elsewhere, they are talking about everything ranging from microbes to advanced intelligence that can be looking back at us.
So far the Kepler telescope has spotted 2,326 candidate planets outside Earth's solar system with 139 of them potentially habitable ones. Even though the confirmed Kepler-22b is a bit big, it is smaller than most of the other candidates. It is closest to Earth in size, temperature and star than either of the two previously announced planets in the zone.
The confirmation of one of two, though, has been disputed. The latest discovery has been confirmed several ways, including by two other telescopes.
This year, a European team of astronomers said they had confirmed another planet in the habitable zone, but that one was hot and barely on the inside edge of the habitable zone.
For Marcy, who is on the Kepler team, the newest planet is a smidgen too large. But, ``that smidgen makes all the difference,'' he said.
Because its size implies that it is closer to Neptune in composition than Earth, ``I would bet my telescope that there is no hard, rocky surface to walk on,'' Marcy said.
Chief Kepler scientist William Borucki said he thinks the planet is somewhere between Earth and gas-and-liquid Neptune, but that it has a lot of rocky material. It is in a size range that scientists do not really know anything about. Measurements next summer may help astronomers have a better idea of its makeup, he said.
The planet is 600 light years away. Each light year is 5.9 trillion miles. It would take a space shuttle about 22 million years to get there.
Kepler spots a planet when it passes in front of its star. NASA requires three of those sightings before it begins to confirm it as a planet. Borucki said the third sighting for 22b happened a year ago, just before the telescope shut down for a while. It took several months to finish the confirmation.
``It's a great gift,'' Borucki said. ``We consider this sort of our Christmas planet.''
생명체 존재 가능한 '제2의 지구' 발견
물이 액체 상태로 존재할 수 있는 우주 영역에서 지구와 환경 이 비슷한 `슈퍼지구' 행성이 처음으로 확인됐다고 사이언스 데일리와 BBC 뉴스가 5 일 미항공우주국(NASA) 발표를 인용 보도했다.
NASA 과학자들이 케플러 우주망원경을 통해 발견한 케플러-22b는 지금까지 생명 체가 살 수 있는 이른바 `골디락' 영역에서 발견된 가장 작은 행성으로 지름이 지구 의 2.4배 정도이고 온도는 약 22℃이다. `골디락' 영역이란 중심별과의 거리가 적당 해 너무 뜨겁지도, 너무 차갑지도 않아 액체 상태의 물이 존재할 수 있는 온도대를 가리킨다.
지구에서 약 600광년 거리에 있는 이 행성은 지난 2009년 처음 발견됐으며 NASA 연구진은 이 행성이 중심별을 지나가는 것을 세 차례 관찰함으로써 그 존재를 확인 했다.
학자들은 이 행성을 구성하는 성분이 지구처럼 암석인지, 아니면 가스나 액체인 지 알지 못하지만 이 행성의 발견은 슈퍼지구를 찾는데 한 걸음 진전을 가져온 것이 라고 말했다.
골디락 영역에 지구와 비슷한 크기의 행성이 존재한다는 조짐은 이전 연구들에 서도 발견됐지만 실제로 확인되기는 이번이 처음이다. 케플러 망원경은 약 15만개의 별을 대상으로 그 앞을 지나가는 행성 때문에 생기는 밝기의 차이를 관찰해 간접적 으로 행성의 존재를 유추하고 있다.
케플러-22b는 지구보다 크지만 공전주기가 290일로 지구와 비슷하다. 이 행성의 중심별은 우리 태양보다 약간 작고 온도가 낮지만 같은 G형 항성이다.
NASA의 케플러 연구팀은 지난 2월 54개의 생명체 서식 가능 행성들을 보고했는 데 케플러-22b는 이 가운데 처음으로 확인된 것이다.
케플러 팀은 지난 2009년 5월부터 2010년 9월 사이 1천94개의 새 행성 후보들을 발견했다고 5일 열린 과학회의에서 보고했다. 지금까지 케플러 팀이 발견한 외부행 성의 수는 2천326개이며 이 가운데 207개가 대략 지구와 비슷한 크기이고 680개는 슈퍼 지구 크기이며 1천181개가 해왕성 크기, 203개가 목성 크기이고 55개는 목성보 다 크다.
연구진은 "지구만한 행성 후보의 수가 크게 늘어난 것은 케플러 우주망원경이 목표로 하는 `지구 크기에, 생명체가 살 수 있는' 행성 발견 기술이 점점 발전하고 있음을 말해 주는 것"이라고 강조했다.