Image: Trojan orbit
Paul Wiegert / University of Western Ontario
Asteroid 2010 TK7 remains ahead of Earth as they both orbit the sun. However, at the same time the asteroid dances a spiral (in green) back and forth in front of our planet.
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updated 7/27/2011 3:15:17 PM ET 2011-07-27T19:15:17

The first in a long-sought type of asteroid companion to Earth has now been discovered, a space rock that always dances in front of the planet along its orbital path, just beyond its reach.

The asteroid, called 2010 TK7, is nearly 1,000 feet across and currently leading the Earth by about 50 million miles.

The asteroid is the first in a category known as Earth's Trojans, a family of space rocks that could potentially be easier to reach than the moon, even though its member asteroids can be dozens of times more distant, researchers said. Such asteroids, which have long been suspected but not confirmed until now, could one day be valuable destinations for missions, especially loaded as they might be with elements rare on Earth's surface, they added.

To imagine where Trojan asteroids are, picture the sun and Earth as being two points in a triangle whose sides are equal in length. The other point of such a triangle is known as a Trojan point, or a Lagrangian point after the mathematician who discovered them. The sun and Earth have two such points, one leading ahead of Earth, known as its L-4 point, and one trailing behind, its L-5 point.

The sun and other planets have Lagrangian points as well, and asteroids have been seen at those the sun shares with Jupiter, Neptune and Mars. Scientists had long suspected the sun and Earth had Trojans as well, but these companions would dwell mostly in the daytime sky as seen from Earth, making them largely hidden in the sunlight.

Now, with the aid of the Wide-field Infrared Survey Explorer, a satellite launched in 2009, astronomers have discovered Earth's first probable Trojan, a rock that spends its time at the sun-Earth L-4 point.

Earth's first Trojan asteroid
Asteroid 2010 TK7 has a bizarre, chaotic orbit.

Trojan asteroids typically do not orbit right at the Lagrangian points but in tadpole-shaped loops around them, due to the gravitational attraction of other bodies in the solar system. However, 2010 TK7's tadpole orbit is unusually large, at times taking it nearly as far as the opposite side of the sun from the Earth.

"This one has behavior much more interesting than I thought we would find," study co-author Martin Connors, an astronomer at Athabasca University in Canada, told Space.com. "It seems to do things not seen for Trojans before. Still, it had to have some kind of extreme behavior to move it far enough from its Lagrangian point to get within our view."

Connors and his team began their search for an Earth Trojan using data from WISE's asteroid- and comet-hunting project, called NEOWISE, named after Near-Earth Objects and WISE.

NASA
NASA's WISE satellite has spotted Earth's first Trojan asteroid. The object, asteroid 2010 TK7, orbits ahead about 50 million miles ahead of Earth in the planet's orbit and is about 1,000 feet wide.

The WISE telescope scanned the whole sky in infrared light from January 2010 to February 2011, a hunt that resulted in two candidates, one of which, 2010 TK7, was confirmed to be an Earth Trojan after follow-up observations at the Canada-France-Hawaii Telescope on Mauna Kea, Hawaii.

The researchers have calculated the asteroid's orbit well enough to understand where it will be over the next 10,000 years — 2010 TK7 will not approach Earth any closer than 12.4 million miles, which is more than 50 times the distance from Earth to the moon.

"It's as though the Earth is playing follow the leader," said Amy Mainzer, the principal investigator of NEOWISE at NASA's Jet Propulsion Laboratory, who was not a part of the study. "Earth is always chasing this asteroid around."

The fact that 2010 TK7's behavior is chaotic enough to take it quite far from its rather stable Trojan point suggests it is only marginally trapped there, having perhaps only recently been disturbed from its original position. The researchers will run more computer models of its orbit to find out what happened, Connors said.

Asteroid 2010 TK7 may be the first confirmed Earth Trojan asteroid, but there are several space rocks known to exist in relatively stable orbits in our planet's neighborhoods. They include asteroids Cruithne and 2010 SO16, which have vast horseshoe-shaped orbits, and at least two others. But none of these other asteroids have been conformed to be Earth Trojans.

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Still much unknown
So far 2010 TK7 does not have a formal name. "Its orbit needs to be nailed down before a name is considered, so it'll take a couple of years more observations before the WISE team can give it one," Connors said.

No color information of it is at yet available of 2010 TK7 to shed light on its composition. In principle asteroids could have a similar makeup to Earth's, but since they are smaller they would have cooled down faster, meaning that heavier substances would not have had time to sink to their centers as they did on our planet.

As such, elements that are uncommon on Earth's surface might be more accessible on asteroids.

"We could be mining these things one day," Connors said.

Unfortunately, 2010 TK7 is not a good target because it travels above and below the plane of Earth's orbit, which means it would require large amounts of propellant to reach. However, if other Earth Trojans do exist, they could prove more accessible.

Now that the researchers have found one, "it makes you want to wonder if there are any more," Connors said. He noted hopefully the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) array of telescopes and cameras aimed at detecting near-Earth objects could turn more up.

The scientists detailed their findings in the July 28 issue of the journal Nature.

Follow Space.com contributor Charles Q. Choi on Twitter @cqchoi. Visit Space.com for the latest in space science and exploration news on Twitter @Spacedotcom and on Facebook.

© 2013 Space.com. All rights reserved. More from Space.com.

Gallery: The new solar system

Get the facts about dwarfs, giants, terrestrials and other denizens of our planetary realm.

  1. Image: Eris
    NASA / JPL-Caltech
    Above: Gallery The new solar system
  2. Interactive Below the belt

Photos: Month in Space: January 2014

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  1. Southern stargazing

    Stars, galaxies and nebulas dot the skies over the European Southern Observatory's La Silla Paranal Observatory in Chile, in a picture released on Jan. 7. This image also shows three of the four movable units that feed light into the Very Large Telescope Interferometer, the world's most advanced optical instrument. Combining to form one larger telescope, they are greater than the sum of their parts: They reveal details that would otherwise be visible only through a telescope as large as the distance between them. (Y. Beletsky / ESO) Back to slideshow navigation
  2. A balloon's view

    Cameras captured the Grandville High School RoboDawgs' balloon floating through Earth's upper atmosphere during its ascent on Dec. 28, 2013. The Grandville RoboDawgs’ first winter balloon launch reached an estimated altitude of 130,000 feet, or about 25 miles, according to coaches Mike Evele and Doug Hepfer. It skyrocketed past the team’s previous 100,000-feet record set in June. The RoboDawgs started with just one robotics team in 1998, but they've grown to support more than 30 teams at public schools in Grandville, Mich. (Kyle Moroney / AP) Back to slideshow navigation
  3. Spacemen at work

    Russian cosmonauts Oleg Kotov, right, and Sergey Ryazanskiy perform maintenance on the International Space Station on Jan. 27. During the six-hour, eight-minute spacewalk, Kotov and Ryazanskiy completed the installation of a pair of high-fidelity cameras that experienced connectivity issues during a Dec. 27 spacewalk. The cosmonauts also retrieved scientific gear outside the station's Russian segment. (NASA) Back to slideshow navigation
  4. Special delivery

    The International Space Station's Canadian-built robotic arm moves toward Orbital Sciences Corp.'s Cygnus autonomous cargo craft as it approaches the station for a Jan. 12 delivery. The mountains below are the southwestern Alps. (NASA) Back to slideshow navigation
  5. Accidental art

    A piece of art? A time-lapse photo? A flickering light show? At first glance, this image looks nothing like the images we're used to seeing from the Hubble Space Telescope. But it's a genuine Hubble frame that was released on Jan. 27. Hubble's team suspects that the telescope's Fine Guidance System locked onto a bad guide star, potentially a double star or binary. This caused an error in the tracking system, resulting in a remarkable picture of brightly colored stellar streaks. The prominent red streaks are from stars in the globular cluster NGC 288. (NASA / ESA) Back to slideshow navigation
  6. Supersonic test flight

    A camera looking back over Virgin Galactic's SpaceShipTwo's fuselage shows the rocket burn with a Mojave Desert vista in the background during a test flight of the rocket plane on Jan. 10. Cameras were mounted on the exterior of SpaceShipTwo as well as its carrier airplane, WhiteKnightTwo, to monitor the rocket engine's performance. The test was aimed at setting the stage for honest-to-goodness flights into outer space later this year, and eventual commercial space tours.

    More about SpaceShipTwo on PhotoBlog (Virgin Galactic) Back to slideshow navigation
  7. Red lagoon

    The VLT Survey Telescope at the European Southern Observatory's Paranal Observatory in Chile captured this richly detailed new image of the Lagoon Nebula, released on Jan. 22. This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. This image is a tiny part of just one of 11 public surveys of the sky now in progress using ESO telescopes. (ESO/VPHAS team) Back to slideshow navigation
  8. Fire on the mountain

    This image provided by NASA shows a satellite view of smoke from the Colby Fire, taken by the Multi-angle Imaging SpectroRadiometer aboard NASA's Terra spacecraft as it passed over Southern California on Jan. 16. The fire burned more than 1,863 acres and forced the evacuation of 3,700 people. (NASA via AP) Back to slideshow navigation
  9. Where stars are born

    An image captured by NASA's Spitzer Space Telescope shows the Orion Nebula, an immense stellar nursery some 1,500 light-years away. This false-color infrared view, released on Jan. 15, spans about 40 light-years across the region. The brightest portion of the nebula is centered on Orion's young, massive, hot stars, known as the Trapezium Cluster. But Spitzer also can detect stars still in the process of formation, seen here in red hues. (NASA / JPL-Caltech) Back to slideshow navigation
  10. Cygnus takes flight

    Orbital Sciences Corp.'s Antares rocket rises from NASA's Wallops Flight Facility on Wallops Island, Va, on Jan. 9. The rocket sent Orbital's Cygnus cargo capsule on its first official resupply mission to the International Space Station. (Chris Perry / NASA) Back to slideshow navigation
  11. A long, long time ago...

    This long-exposure picture from the Hubble Space Telescope, released Jan. 8, is the deepest image ever made of any cluster of galaxies. The cluster known as Abell 2744 appears in the foreground. It contains several hundred galaxies as they looked 3.5 billion years ago. Abell 2744 acts as a gravitational lens to warp space, brightening and magnifying images of nearly 3,000 distant background galaxies. The more distant galaxies appear as they did more than 12 billion years ago, not long after the Big Bang. (NASA / NASA via AFP - Getty Images) Back to slideshow navigation
  12. Frosty halo

    Sun dogs are bright spots that appear in the sky around the sun when light is refracted through ice crystals in the atmosphere. These sun dogs appeared on Jan. 5 amid brutally cold temperatures along Highway 83, north of Bismarck, N.D. The temperature was about 22 degrees below zero Fahrenheit, with a 50-below-zero wind chill.

    Slideshow: The Year in Space (Brian Peterson / The Bismarck Tribune via AP) Back to slideshow navigation
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Explainer: Out-of-this-world destinations

  • NASA

    We are headed to Mars ... eventually. But first we need the rocket technology and human spaceflight savvy to get us there safely and efficiently. And the best way to do that is to visit places such as asteroids, our moon, a Martian moon and even no man's lands in space called "Lagrange points," NASA administrator Charles Bolden explained during the unveiling of the agency's revised vision for space exploration.

    The vision shifts focus away from a return to the moon as part of a steppingstone to Mars in favor of what experts call a "flexible path" to space exploration, pushing humans ever deeper into the cosmos.

    Click the "Next" label to check out six other potential destinations astronauts may visit in the years and decades to come en route to Mars.

    — John Roach, msnbc.com contributor

  • Lessons to learn on the space station

    NASA

    The cooperation required to build and maintain the International Space Station will be a key to propelling humans on to Mars, according to Louis Friedman, co-founder of The Planetary Society. The society is a space advocacy organization that supports the flexible path to space exploration. In fact, the space station itself could be a training ground for Mars-bound astronauts.

    Astronauts can spend ever longer blocks of time on the station to gain experience in long-duration flights, for example. They could also practice extravehicular activities akin to those expected on a Mars mission, Friedman noted.

  • Lunar orbit, a test of new technology

    NASA

    Lunar orbit, too, is a familiar destination for human spaceflight, but a return to the familiar with new technology would allow astronauts to test the engineering of systems designed to go deeper into space, according to Friedman.

    A return to the moon is still in the cards on the flexible path, but going to lunar orbit first defers the cost of developing the landing and surface systems needed to get in and out of the lunar gravity well, according to experts.

    The famous "Earthrise" image shown here was made in 1968 during Apollo 8, the first human voyage to orbit the moon.

  • Stable no man's lands in space

    NASA / WMAP Science Team

    There are places in space where the gravitational pulls of Earth and the moon, or Earth and the sun, have a balancing effect on a third body in orbit. Those five locations, known as Lagrange points, could offer relatively stable parking spots for astronomical facilities such as space telescopes or satellites. Human spaceflights to these points would allow astronauts to service these instruments.

    In addition, space experts believe a trip to a Lagrange point could serve as a training mission for astronauts headed to points deeper in space, such as an asteroid. Nevertheless, reaching a Lagrange point would be more of a technical achievement than a scientific achievement, according to Friedman. "It is an empty spot in space," he said.

  • Visit an asteroid near you?

    Image: Paraffin candles
    Dan Durda  /  FIAAA

    The first stop astronauts may make in interplanetary space is one of the asteroids that cross near Earth's orbit. Scientists have a keen interest in the space rocks because of the threat that one of them could strike Earth with devastating consequences. An asteroid mission would allow scientists to better understand what makes the rocks tick, and thus how to best divert one that threatens to smack our planet.

    Humans have also never been to an asteroid, which would make such a visit an exciting first, noted Friedman. "Imagine how interesting it will be to see an astronaut step out of a spacecraft and down onto an asteroid and perform scientific experiments," he said. What's more, since asteroids have almost no gravity, an asteroid encounter would be like docking with the space station, which doesn't require a heavy-lift rocket for the return. That makes an asteroid a potentially less expensive destination than the surface of the moon.

  • Back to the moon?

    NASA via Getty Images

    The moon-Mars path of human space exploration originally envisioned the moon as a training ground for a mission to the Red Planet. While the flexible-path strategy broadens the training field, the moon remains a candidate destination, according to NASA.

    Several other nations also have the moon's surface in their sights, including Japan, India and China. Some experts fear the dedicated lunar programs of these nations will eventually leave the United States in the dust as it focuses on an ambiguous flexible path.

    Friedman, of The Planetary Society, said NASA should support the lunar programs of Japan, India and China as part of team building for an international Mars mission, but sees no reason for NASA to focus on the moon. "We've done that already and that was Apollo," he said.

  • Martian moon a final pit stop?

    NASA / JPL-Caltech / UA

    Before astronauts go all the way to Mars, there's reason to make a final stop at one of its moons, Phobos or Deimos. The two moons are less than 20 miles across at their widest, which means landing on them would be less expensive than the Red Planet itself.

    Friedman used to consider a mission to a Martian moon nonsensical - akin to going to the base camp of Mount Everest instead of going to the top of the mountain. "I've now turned myself around on that, because you do go to the base camp and you do actually conduct training activities there before you attempt the summit," he said.

    "By all means go there," he added. "Test out your rendezvous and docking at Mars, conduct your three-year, round-trip mission, maybe tele-operate some rovers of the surface (of Mars). That will all be interesting and then the next mission will finally go down to the surface."

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