O asteroide 2010 TK7 está circulado em verde, nesta singela foto tirada pelo Explorador de Campo Amplo em Infravermelho da NASA, ou WISE. A maioria dos demais pontos são galáxias muito além do nosso Sistema Solar Imagem: NASA/JPL-Caltech/UCLA
O primeiro asteroide Trojan da Terra
Luiz Leitão
Astrônomos que estudam observações da missão WISE descobriram o primeiro asteroide "Trojan" (Cavalo de Troia) orbitando o Sol em companhia da Terra.
Trojans são asteroides que compartilham e orbitam em pontos estáveis de órbita defronte ou atrás de um planeta. Por constantemente estarem à frente ou atrás na mesma órbita do planeta, eles jamais podem colidir com ele. Em nosso Sistema Solar, Trojans também compartilham órbitas com Netuno, Marte e Júpiter. Duas das luas de Saturno compartilham órbitas com Trojans.
Cientistas previram que a terra deveria ter Trojans, mas têm dificuldade em encontrá-los porque eles são relativamente pequenos e parecem próximos ao Sol, do ponto de vista da Terra.
"Estes asteroides se mostram geralmente durante a luz do dia, o que torna muito difícil vê-los," disse Martin Connors da Universidade Atabasca, no Canadá, principal autor de um novo artigo sobre a descoberta na edição de 28 de Julho da revista Nature. "Mas nós finalmente encontramos um deles, porque o objeto tem uma órbita incomum que o leva mais distante do Sol do que os Trojans típicos. O WISE virou o jogo, dando-nos um ponto de visão difícil de obter da superfície da Terra."
O telescópio WISE varreu todo o céu em luz infravermelha de janeiro de 2010 a Fevereiro de 2011. Connors e equipe iniciaram sua busca por um Trojan da Terra com dados do NEOWISE, um complemento à missão WISE que se concentra em parte dos objetos próximos à Terra (near-Earth objects), ou NEOs, como asteroides e cometas.
NEOs are são corpos que passam dentro de 45 milhões que quilômetro do trajeto da Terra em torno do Sol. O projeto NEOWISE observou mais de 155.000 asteroides nos principais cinturões entre Marte e Júpiter, e mais de 500 NEOs, descobrindo 132 anteriormente desconhecidos.
A busca da equipe resultou em dois candidatos a Trojan. Um, designado 2010 TK7 foi confirmado como Trojan da Terra após observações posteriores com o telescópio Franco-Canadense- Havaiano em Mauna Kea, no Havaí.
O asteroide tem cerca de 300 metros de diâmetro. Tem uma órbita incomum que traça um movimento complexo próximo a um ponto estável no plano orbital da Terra, embora ele também se mova acima e abaixo do plano. O objeto está a cerca de 80 milhões de quilômetros da Terra. Sua órbita é bem definida, e pelo menos nos próximos 100 anos, ele não chegará mais perto da Terra do que 24 milhões de quilômetros.
"É como se a Terra estivesse jogando 'siga o líder," disse Amy Mainzer, principal pesquisadora do NEOWISE no Laboratório de Propulsão a Jato da Nasa (Jetlab), em Pasadena, Califórnia. "A Terra está sempre no encalço desse asteroide por aí."
Uma porção de outros asteroides têm também órbitas semelhantes à da Terra. Tais objetos poderiam ser excelentes candidatos à futura exploração robótica ou humana. O asteroide 2010 TK7 não é um bom alvo porque viaja muito longe acima e abaixo do plano orbital terrestre, o que demandaria grandes quantidades de combustível para alcançá-lo.
"Esta observação mostra por que o programa de observação NEO da NASA financiou o processo de aprimoramento da missão para processar os dados coletados pelo WISE," disse Lindley Johnson, do programa NEOWISE no quartel general da NASA em Washington. "Nós acreditávamos que havia um grande potencial de encontrar objeto no espaço próximo à Terra que nunca haviam sido vistos antes."
Luiz Leitão da Cunha é jornalista luizmleitao@gmail.com
Astronomers studying observations taken by NASA's Wide-field Infrared Survey Explorer (WISE) mission have discovered the first known "Trojan" asteroid orbiting the sun along with Earth.
Trojans are asteroids that share an orbit with a planet near stable points in front of or behind the planet. Because they constantly lead or follow in the same orbit as the planet, they never can collide with it. In our solar system, Trojans also share orbits with Neptune, Mars and Jupiter. Two of Saturn's moons share orbits with Trojans.
Scientists had predicted Earth should have Trojans, but they have been difficult to find because they are relatively small and appear near the sun from Earth's point of view.
"These asteroids dwell mostly in the daylight, making them very hard to see," said Martin Connors of Athabasca University in Canada, lead author of a new paper on the discovery in the July 28 issue of the journal Nature. "But we finally found one, because the object has an unusual orbit that takes it farther away from the sun than what is typical for Trojans. WISE was a game-changer, giving us a point of view difficult to have at Earth's surface."
The WISE telescope scanned the entire sky in infrared light from January 2010 to February 2011. Connors and his team began their search for an Earth Trojan using data from NEOWISE, an addition to the WISE mission that focused in part on near-Earth objects, or NEOs, such as asteroids and comets. NEOs are bodies that pass within 28 million miles (45 million kilometers) of Earth's path around the sun. The NEOWISE project observed more than 155,000 asteroids in the main belt between Mars and Jupiter, and more than 500 NEOs, discovering 132 that were previously unknown.
The team's hunt resulted in two Trojan candidates. One called 2010 TK7 was confirmed as an Earth Trojan after follow-up observations with the Canada-France-Hawaii Telescope on Mauna Kea in Hawaii.
The asteroid is roughly 1,000 feet (300 meters) in diameter. It has an unusual orbit that traces a complex motion near a stable point in the plane of Earth's orbit, although the asteroid also moves above and below the plane. The object is about 50 million miles (80 million kilometers) from Earth. The asteroid's orbit is well-defined and for at least the next 100 years, it will not come closer to Earth than 15 million miles (24 million kilometers). An animation showing the orbit is available at: http://www.nasa.gov/multimedia/videogallery/index.html?media_id=103550791 .
"It's as though Earth is playing follow the leader," said Amy Mainzer, the principal investigator of NEOWISE at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Earth always is chasing this asteroid around."
A handful of other asteroids also have orbits similar to Earth. Such objects could make excellent candidates for future robotic or human exploration. Asteroid 2010 TK7 is not a good target because it travels too far above and below the plane of Earth's orbit, which would require large amounts of fuel to reach it.
"This observation illustrates why NASA's NEO Observation program funded the mission enhancement to process data collected by WISE," said Lindley Johnson, NEOWISE program executive at NASA Headquarters in Washington. "We believed there was great potential to find objects in near-Earth space that had not been seen before."
Trojans are asteroids that share an orbit with a planet near stable points in front of or behind the planet. Because they constantly lead or follow in the same orbit as the planet, they never can collide with it. In our solar system, Trojans also share orbits with Neptune, Mars and Jupiter. Two of Saturn's moons share orbits with Trojans.
Scientists had predicted Earth should have Trojans, but they have been difficult to find because they are relatively small and appear near the sun from Earth's point of view.
"These asteroids dwell mostly in the daylight, making them very hard to see," said Martin Connors of Athabasca University in Canada, lead author of a new paper on the discovery in the July 28 issue of the journal Nature. "But we finally found one, because the object has an unusual orbit that takes it farther away from the sun than what is typical for Trojans. WISE was a game-changer, giving us a point of view difficult to have at Earth's surface."
The WISE telescope scanned the entire sky in infrared light from January 2010 to February 2011. Connors and his team began their search for an Earth Trojan using data from NEOWISE, an addition to the WISE mission that focused in part on near-Earth objects, or NEOs, such as asteroids and comets. NEOs are bodies that pass within 28 million miles (45 million kilometers) of Earth's path around the sun. The NEOWISE project observed more than 155,000 asteroids in the main belt between Mars and Jupiter, and more than 500 NEOs, discovering 132 that were previously unknown.
The team's hunt resulted in two Trojan candidates. One called 2010 TK7 was confirmed as an Earth Trojan after follow-up observations with the Canada-France-Hawaii Telescope on Mauna Kea in Hawaii.
The asteroid is roughly 1,000 feet (300 meters) in diameter. It has an unusual orbit that traces a complex motion near a stable point in the plane of Earth's orbit, although the asteroid also moves above and below the plane. The object is about 50 million miles (80 million kilometers) from Earth. The asteroid's orbit is well-defined and for at least the next 100 years, it will not come closer to Earth than 15 million miles (24 million kilometers). An animation showing the orbit is available at: http://www.nasa.gov/multimedia/videogallery/index.html?media_id=103550791 .
"It's as though Earth is playing follow the leader," said Amy Mainzer, the principal investigator of NEOWISE at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Earth always is chasing this asteroid around."
A handful of other asteroids also have orbits similar to Earth. Such objects could make excellent candidates for future robotic or human exploration. Asteroid 2010 TK7 is not a good target because it travels too far above and below the plane of Earth's orbit, which would require large amounts of fuel to reach it.
"This observation illustrates why NASA's NEO Observation program funded the mission enhancement to process data collected by WISE," said Lindley Johnson, NEOWISE program executive at NASA Headquarters in Washington. "We believed there was great potential to find objects in near-Earth space that had not been seen before."
Asteroid 2010 TK7 is circled in green, in this single frame taken by NASA's Wide-field Infrared Survey Explorer, or WISE. The majority of the other dots are stars or galaxies far beyond our solar system. Image credit: NASA/JPL-Caltech/UCLA
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