Along for the Ride: The Trojan asteroid that shares Earth's orbit

NASA's WISE Mission Finds First Trojan Asteroid Sharing Earth's Orbit

Earth’s Trojan asteroid
Martin Connors, Paul Wiegert & Christian Veillet
Nature 475, 481–483 (28 July 2011) | doi:10.1038/nature10233
Received 11 April 2011 | Accepted 27 May 2011 | Published online 27 July 2011

It was realized in 1772 that small bodies can stably share the same orbit as a planet if they remain near ‘triangular points’ 60° ahead of or behind it in the orbit1. Such ‘Trojan asteroids’ have been found co-orbiting with Jupiter2, Mars3 and Neptune4. They have not hitherto been found associated with Earth, where the viewing geometry poses difficulties for their detection5, although other kinds of co-orbital asteroid (horseshoe orbiters6 and quasi-satellites7) have been observed8. Here we report an archival search of infrared data for possible Earth Trojans, producing the candidate 2010 TK7. We subsequently made optical observations which established that 2010 TK7 is a Trojan companion of Earth, librating around the leading Lagrange triangular point, L4. Its orbit is stable over at least ten thousand years.

Astronomers spot Earth's first orbital partner - July 27, 2011

The Earth has a very skittish dance partner. Locked ahead of the Earth’s orbit lies a 300-metre lump of rock -- Earth’s first Trojan asteroid, astronomers report today in Nature.

The points 60 degrees ahead of and behind a planet are one type of Lagrange point -- stable gravitational wells where objects can lurk, caught between the Sun’s gravity and the planet’s. Objects residing in these spots are known as Trojans. With the discovery, the Earth joins Mars, Neptune and Jupiter as planets with known Trojans.

Trojans around Earth have been difficult to find because the objects dwell mostly in the daytime sky. But Martin Connors of Athabasca University in Canada and his colleagues used data from the Wide-field Infrared Survey Explorer (WISE), which launched in 2009 and has found more than 500 near-Earth objects. The researchers confirmed that the object, called 2010 TK7, was a Trojan through follow-up observations with telescopes in Hawaii.

The authors say the object’s behavior is fairly chaotic -- it dances around the orbital plane with a tadpole-like motion. They say the asteroid might jump to other Lagrange points or orbital modes, and its stability can’t be guaranteed beyond about 7,000 years. The Earth better enjoy its pas de deux while it can.

Earth's first Trojan Asteroid discovered

Dr. Martin Connors and two colleagues have confirmed the existence of the first known Trojan Asteroid associated with earth. The discovery is highlighted in the July 28th, 2011 edition of Nature magazine.

"The discovery is important because it proves that Trojans can exist in orbit around the Sun in a very earth-like orbit," said Dr. Connors. "And since U. S. President Obama announced NASA's intentions to land a man on an asteroid by 2025, we may find Trojans or related asteroids that are the ideal candidates for that landing".

The Trojan, called 2010 TK7 was first detected by Connors and colleagues Paul Weigert and Christian Veillet using NASA's Wide-field Infrared Survey Explorer (WISE) satellite launched in 2009. The discovery was confirmed using the ground-based Canada-France-Hawaii Telescope in April, 2011.

Previously, Trojans were known to exist associated with Jupiter, Neptune and Mars. 2010 TK7 proves that they also are found in stable orbits similar to earth's. "This should make it easier for scientists to get telescope time to look for other Earth Trojans," said Connors. "I'm confident others will be found, giving the space program a number of candidates for a landing by the President's goal of 2025."

Dr. Rory McGreal, Associate Vice-president of Research at AU, is thrilled with the discovery by his colleague.

"I know that Dr. Connors has spent many nights scouring our northern skies and days trudging through the snowy fields of northern Alberta searching for meteorites. This Nature article is a clear demonstration of the importance of his work and adds to his international reputation."

Dr. Connors is the Canada Research Chair in Space Science at Athabasca University. He is in charge of the Athabasca University Geophysical Observatory in northern Alberta and is a world-renowned expert in asteroids and near-earth objects.

Obama's asteroid goal: tougher, riskier than moon

(AP) -- Landing a man on the moon was a towering achievement. Now the president has given NASA an even harder job, one with a certain Hollywood quality: sending astronauts to an asteroid, a giant speeding rock, just 15 years from now.

Space experts say such a voyage could take several months longer than a journey to the moon and entail far greater dangers.

"It is really the hardest thing we can do," NASA Administrator Charles Bolden said.

Going to an asteroid could provide vital training for an eventual mission to Mars. It might help unlock the secrets of how our solar system formed. And it could give mankind the know-how to do something that has been accomplished only in the movies by a few square-jawed, squinty-eyed heroes: saving the Earth from a collision with a killer asteroid.

"You could be saving humankind. That's worthy, isn't it?" said Bill Nye, TV's Science Guy and vice president of the Planetary Society.

President Barack Obama outlined NASA's new path during a visit to the Kennedy Space Center on Thursday.

"By 2025, we expect new spacecraft designed for long journeys to allow us to begin the first-ever crewed missions beyond the moon into deep space," he said. "We'll start by sending astronauts to an asteroid for the first time in history."

On the day the president announced the goal, a NASA task force of scientists, engineers and ex-astronauts was meeting in Boston to work on a plan to protect Earth from a cataclysmic collision with an asteroid or a comet. more »»»

Western astronomer shares discovery of first Trojan asteroid found in Earth’s orbit
Nature Article (PDF)

Studying images compiled by NASA, an astronomer from The University of Western Ontario has proved the existence of the first Trojan asteroid found to share Earth’s orbit. The findings of Paul Wiegert and his colleagues at Athabasca University and the Canada-France-Hawaii Telescope were published today as the cover story for the July 28 issue of distinguished journal, Nature.

A Trojan asteroid shares an orbit with a larger planet or moon, in this case Earth, but does not collide with it because it follows the same orbital path. Before this discovery, only the planets Jupiter, Neptune and Mars were known to harbour these asteroids named for the soldiers of the ancient war immortalized by Homer in The Iliad and The Odyssey.

“Like a pair of dancers performing a complicated tango, the asteroid moves in an elaborate path that brings it sometimes closer and sometimes farther from us,” says Wiegert, a professor in Western’s Department of Physics and Astronomy. “The Earth and the asteroid remain in sync however, with the asteroid always preceding the Earth as they both move around the Sun.”

Currently known as Asteroid 2010 TK7, the as-yet-unnamed near-Earth asteroid (NEA) was discovered by the Wide-field Infrared Survey Explorer satellite in October 2010. Following the discovery, the possible co-orbital nature of the asteroid was first deemed a possibility by Martin Connors from Athabasca.

Images of the asteroid were then taken by Christian Veillet, Executive Director of the Canada-France-Hawaii Telescope in Hawaii, to refine the asteroid’s orbit once it was favourably placed in the night sky. Based on these new images, Wiegert was able to create computer simulations of Asteroid 2010 TK7, which confirmed the Trojan character of its motion.

“These asteroids are very interesting as individual members of the near-Earth asteroid population but they also tell us a lot about how the Earth and asteroids interact gravitationally at a distance,” says Wiegert. “Because this asteroid is a Trojan asteroid, it interacts with the Earth in a very special way allowing us a unique opportunity to study near-Earth asteroids.”

Trojan Asteroid simulation videos
Trojan Asteroid Simulation 1 (above)
Trojan Asteroid Simulation 2

NASA's WISE Finds Earth's First Trojan Asteroid

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). Here is an animation showing the orbit.

"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."

Is an Earth Trojan Asteroid the Logical Target for the “Flexible Path”?

The obvious question is whether this is the logical destination for NASA’s Flexible Path manned asteroid mission? The Lagrange 4 point (SEL-4) is a logical way station on the Solar System exploration highway. Other NEO asteroids that have been identified as possible targets are few and much more difficult to reach and return than an asteroid at SEL-4. This may well be the target of opportunity that opens manned exploration of the Solar System in an “easy” mode. Unfortunately, Asteroid 2010 TK7 travels too far above and below the plane of Earth’s orbit, which would require large amounts of fuel to reach it.