After A Long Nap, NEOWISE Springs Into Action With Asteroid Discoveries

If anything, NASA’s asteroid-hunting spacecraft seems to be refreshed after going into forced hibernation for 2.5 years. In the first 25 days since it started seeking small solar system bodies in earnest again, the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) found three new objects and detected an additional 854, NASA said Thursday (Jan. 23).

Luckily for people interested in this field, Amy Mainzer (the principal investigator for this mission) has been tweeting out discoveries as they come — and other observations besides. “Just passed our @WISE_Mission post-restart review. I believe the technical term is “Yee haw!!” she wrote Jan. 21. Below are a couple of illustrated examples of discoveries from her Twitter feed. Click on the pictures for larger versions.

2014 AA53 NEOWISE

2014 AQ46 NEOWISE

In a release, NASA added that NEOWISE is “observing and characterizing” one NEO a day, which means not only looking at the object, but probing its size and composition. Astronomers know of about 10,500 NEOs, but of those only 10% (or about 1,500) have physical measurements cataloged as well. NEOWISE investigators aim to make hundreds of more of these measurements.

The mission (originally called WISE) launched in December 2009 to examine the universe in infrared light. After completely mapping the sky, it ran out of coolant it needed to do this work in 2010. It then shifted to examining comets and asteroids before being put into hibernation in February 2011. Read more about its mission history in this past Universe Today article.

How A New Family Tree of Space Rocks Could Better Protect Earth

An artist's conception of an asteroid collision, which leads to how "families" of these space rocks are made in the belt between Mars and Jupiter. Credit: NASA/JPL-Caltech

In perhaps the neatest astronomical application of geneology yet, astronomers found 28 “hidden” families of asteroids that could eventually show them how some rocks get into orbits that skirt the Earth’s path in space.

From scanning millions of snapshots of asteroid heat signatures in the infrared, these groups popped out in an all-sky survey of asteroids undertaken by NASA’s orbiting Wide-Field Infrared Survey Explorer. This survey took place in the belt of asteroids between Mars and Jupiter, where most near-Earth objects (NEOs) come from.

NEOs, to back up for a second, are asteroids and comets that approach Earth’s orbit from within 28 million miles (45 million kilometers). Sometimes, a gravitational push can send a previously unthreatening rock closer to the planet’s direction. The dinosaurs’ extinction roughly 65 million years ago, for example, is widely attributed to a massive rock collision on Earth.

Part of NASA’s job is to keep an eye out for potentially hazardous asteroids and consider approaches to lessen the threat.

Artist concept of the asteroid belt. Credit: NASA
Artist concept of the asteroid belt between Mars and Jupiter. Credit: NASA

There are about 600,000 known asteroids between Mars and Jupiter, and the survey looked at about 120,000 of them. Astronomers then attempted to group some of them into “families”, which are best determined by the mineral composition of an asteroid and how much light it reflects.

While it’s hard to measure reflectivity in visible light — a big, dark asteroid reflects a similar amount of light as a small shiny one — infrared observations are harder to fool. Bigger objects give off more heat.

This allowed astronomers to reclassify some previously studied asteroids (which were previously grouped by their orbits), and come up with 28 new families.

“This will help us trace the NEOs back to their sources and understand how some of them have migrated to orbits hazardous to the Earth,” stated Lindley Johnson, NASA’s program executive for the Near-Earth Object Observation Program.

This diagram illustrates the differences between orbits of a typical near-Earth asteroid (blue) and a potentially hazardous asteroid, or PHA (orange). Image credit: NASA/JPL-Caltech
This diagram illustrates the differences between orbits of a typical near-Earth asteroid (blue) and a potentially hazardous asteroid, or PHA (orange). Image credit: NASA/JPL-Caltech

The astronomers next hope to study these different families to figure out their parent bodies. Astronomers believe that many asteroids we see today broke off from something much larger, most likely through a collision at some point in the past.

While Earthlings will be most interested in how NEOs came from these larger bodies and threaten the planet today, astronomers are also interested in learning how the asteroid belt formed and why the rocks did not coalesce into a planet.

The prevailing theory today says that was due to influences from giant Jupiter’s strong gravity, which to this day pulls many incoming comets and asteroids into different orbits if they swing too close. (Just look at what happened to Shoemaker-Levy 9 in 1994, for example.)

Source: NASA

Earth’s First Trojan Asteroid Discovered

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The first known “Trojan” asteroid in Earth’s orbit has been discovered. A Trojan asteroid shares an orbit with a larger planet or moon, but does not collide with it because it orbits around one of two Lagrangian points. Trojans sharing an orbit with Earth have been predicted but never found until now. Astronomers analyzing data from the asteroid-hunting WISE telescope – which ceased operations in February 2011 – found the asteroid, named 2010 TK7, and followup observations with the Canada-France-Hawaii Telescope on Mauna Kea in Hawaii confirmed the discovery and the object’s stealthy orbit.

In our solar system, we know of Trojans that share orbits with Neptune, Mars and Jupiter. Two of Saturn’s moons share orbits with Trojans. Astronomers have known that Earth Trojans would be difficult to find because they are relatively small and appear near the sun from Earth’s point of view.

But 2010 TK7 proves that Trojans associated to Earth can be found, and astronomers predict that since one has been found, perhaps they’ll find more, as we’ll learn more about their dynamics and characteristics of their population from this first one.

“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 animation below shows the orbit of 2010 TK7 (green dots).

The asteroid is roughly 1,000 feet (300 meters) in diameter. It has an unusual orbit that traces a complex motion near the L4 point. However, 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).

“It’s as though Earth is playing follow the leader,” said Amy Mainzer, the principal investigator of WISE’s extended mission called NEOWISE that looked especially for Near Earth Object “Earth always is chasing this asteroid around.”

Asteroid 2010 TK7 is circled in green, in this single frame taken by NASA's Wide-field Infrared Survey Explorer, or WISE. Image credit: NASA/JPL-Caltech/UCLA

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.”

The WISE telescope scanned the entire sky in infrared light from January 2010 to February 2011. 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.

Sources: Canada-France-Hawaii Telescope, NASA

Mission Complete: NEOWISE Concludes Hunt for Near-Earth Objects

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The WISE spacecraft has completed a special mission called NEOWISE, looking for small bodies in the solar system, and has discovered a plethora of previously unknown objects. The NEOWISE mission found 20 comets, more than 33,000 asteroids in the main belt between Mars and Jupiter, and 134 near-Earth objects (NEOs). More data from NEOWISE also have the potential to reveal a brown dwarf even closer to us than our closest known star, Proxima Centauri, if such an object does exist. Likewise, if there is a hidden gas-giant planet in the outer reaches of our solar system, data from WISE and NEOWISE could detect it.

“WISE has unearthed a mother lode of amazing sources, and we’re having a great time figuring out their nature,” said Edward (Ned) Wright, the principal investigator of WISE at UCLA.

“Even just one year of observations from the NEOWISE project has significantly increased our catalog of data on NEOs and the other small bodies of the solar systems,” said Lindley Johnson, NASA’s program executive for the NEO Observation Program.

The NEOs are asteroids and comets with orbits that come within 45 million kilometers (28 million miles) of Earth’s path around the sun.

The NEOWISE mission made use of the the WISE spacecraft, the Wide-field Infrared Survey Explorer that launched in December 2009. WISE scanned the entire celestial sky in infrared light about 1.5 times. It captured more than 2.7 million images of objects in space, ranging from faraway galaxies to asteroids and comets close to Earth.

However, in early October 2010, after completing its prime science mission, the spacecraft ran out of the frozen coolant that keeps its instrumentation cold. But two of its four infrared cameras remained operational, which were still optimal for asteroid hunting, so NASA extended the NEOWISE portion of the WISE mission by four months, with the primary purpose of hunting for more asteroids and comets, and to finish one complete scan of the main asteroid belt.

Now that NEOWISE has successfully completed a full sweep of the main asteroid belt, the WISE spacecraft will go into hibernation mode and remain in polar orbit around Earth, where it could be called back into service in the future.

In addition to discovering new asteroids and comets, NEOWISE also confirmed the presence of objects in the main belt that had already been detected. In just one year, it observed about 153,000 rocky bodies out of approximately 500,000 known objects. Those include the 33,000 that NEOWISE discovered.

NEOWISE also observed known objects closer and farther to us than the main belt, including roughly 2,000 asteroids that orbit along with Jupiter, hundreds of NEOs and more than 100 comets.

These observations will be key to determining the objects’ sizes and compositions. Visible-light data alone reveal how much sunlight reflects off an asteroid, whereas infrared data is much more directly related to the object’s size. By combining visible and infrared measurements, astronomers also can learn about the compositions of the rocky bodies — for example, whether they are solid or crumbly. The findings will lead to a much-improved picture of the various asteroid populations.

NEOWISE took longer to survey the whole asteroid belt than WISE took to scan the entire sky because most of the asteroids are moving in the same direction around the sun as the spacecraft moves while it orbits Earth. The spacecraft field of view had to catch up to, and lap, the movement of the asteroids in order to see them all.

“You can think of Earth and the asteroids as racehorses moving along in a track,” said Amy Mainzer, the principal investigator of NEOWISE at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “We’re moving along together around the sun, but the main belt asteroids are like horses on the outer part of the track. They take longer to orbit than us, so we eventually lap them.”

NEOWISE data on the asteroid and comet orbits are catalogued at the NASA-funded International Astronomical Union’s Minor Planet Center, a clearinghouse for information about all solar system bodies at the Smithsonian Astrophysical Observatory in Cambridge, Mass. The science team is analyzing the infrared observations now and will publish new findings in the coming months.

The first batch of observations from the WISE mission will be available to the public and astronomical community in April.

Source: NASA