The properties of a six-meter near-Earth object

Jun 27, 2014
The properties of a six-meter near-Earth object
An image of the rubble-pile asteroid 25143 Itokawa as seen by the Japanese Hayabusa spacecraft during a flyby. Astronomers have just detected a nearby rubble-pile asteroid only about six meters in size, and which may be suitable for a NASA capture and recovery mission. Credit: ISAS/JAXA

( —Near Earth Objects (NEOs) are asteroids (or comets) whose orbits sometimes bring them close to the earth's orbit. Thus they could potentially collide with the Earth, giving them considerably more parochial interest than most objects in astronomy. The 1908 Tunguska event, for example, that flattened over 2000 square kilometers in Russia was by some basic estimates caused by an asteroid about 60 meters in diameter. The asteroid that struck Siberia last spring (the Chelyabinsk meteor) was only about 40 meters in diameter. While it is relatively easy to detect an NEO in visible light by watching its movement across the sky from night to night, determining its size is more difficult. This is because the optical brightness of an NEO is the result of two factors, its size and its reflectivity. CfA astronomers have for several years been using the IRAC infrared camera on Spitzer to measure the infrared light emitted from NEOs, and modeling the flux to determine the reflectivity and thus the sizes of NEOs.

NASA has decided to support a human mission to an asteroid, with the first step likely being the robotic recovery of an NEO. The current Asteroid Recovery Mission (ARM) concept proposes to robotically grab a smallish NEO (between five and ten meters in diameter) and tow it into an orbit around the Earth where a crew of astronauts would rendezvous with it and retrieve samples. Finding a suitable one is tough, however: the sizes of some smallish NEOs have only recently been determined (by infrared techniques), and a suitable one needs to be in an orbit close enough now for remote characterization but then returning to the immediate neighborhood in a few years for the recovery mission itself.

CfA astronomers Joe Hora, Howard Smith and Giovanni Fazio, together with their team, used the Spitzer Space Telescope to observe the NEO 2011MD. It turns out to be the smallest object ever seen with Spitzer, and was extremely faint, taking 19.9 hours to spot. The object is small enough that non-gravitational forces (that is, effects of radiation) can alter its path, and so knowing where to point the telescope required some complex calculations. Since it might have been even smaller, a non-detection would have been inconclusive since Spitzer might have pointed in the wrong direction.

As it happens a faint detection was made right in the expected location in the sky. Modeling of the emission, combined with earlier optical results, find that the object is about six meters in size (plus four or minus two meters). From its size, the astronomers conclude that its density is a tad more than water, about 1.1 grams per cubic centimeter, and that its composition is probably a rubble-pile with high macroporosity. The information will be used by NASA to decide whether or not to go after it - we'll keep you posted.

Explore further: Spitzer spies an odd, tiny asteroid

More information: "Physical Properties of Near-Earth Asteroid 2011 MD," M. Mommert, D. Farnocchia, J. L. Hora, S. R. Chesley, D. E. Trilling, P. W. Chodas, M. Mueller, A. W. Harris, H. A. Smith, G. G. Fazio, ApJLett, 789, L22, 2014.

Related Stories

Retrieving an asteroid

Dec 27, 2013

( —Asteroids (or comets) whose orbits bring them close to the earth's orbit are called near Earth objects. Some of them are old, dating from the origins of the solar system about four and one-half ...

Sizes for potentially dangerous asteroids

Aug 27, 2010

Near Earth Objects (NEOs) are asteroids or comets whose orbits sometimes take them close to the earth's orbit. An NEO could therefore someday collide with the earth -- and there are almost 7000 of them known, ...

Spitzer spies an odd, tiny asteroid

Jun 19, 2014

( —Astronomers using NASA's Spitzer Space Telescope have measured the size of an asteroid candidate for NASA's Asteroid Redirect Mission (ARM), a proposed spacecraft concept to capture either a ...

Visiting an asteroid

Dec 17, 2010

Asteroids (or comets) whose orbits bring them close to the earth's orbit are called Near Earth Objects (NEOs). Some asteroids are old, dating from the origins of the solar system about four and one-half billion ...

Asteroid discovered by NASA to pass Earth safely

Jun 09, 2014

( —A newfound asteroid will safely pass Earth on June 8 from a distance of about 777,000 miles (1.25 million kilometers), more than three times farther away than our moon.

Rendezvous with a near Earth object

Oct 25, 2011

( -- One of the most accessible goals for human spaceflight is a rendezvous with a Near Earth Object (NEO). NEOs are asteroids or comets whose orbits take them close to the earth's orbit. An NEO ...

Recommended for you

Cassini: Return to Rhea

12 hours ago

After a couple of years in high-inclination orbits that limited its ability to encounter Saturn's moons, NASA's Cassini spacecraft returned to Saturn's equatorial plane in March 2015.

Comet dust—planet Mercury's 'invisible paint'

19 hours ago

A team of scientists has a new explanation for the planet Mercury's dark, barely reflective surface. In a paper published in Nature Geoscience, the researchers suggest that a steady dusting of carbon from p ...

It's 'full spin ahead' for NASA soil moisture mapper

22 hours ago

The 20-foot (6-meter) "golden lasso" reflector antenna atop NASA's new Soil Moisture Active Passive (SMAP) observatory is now ready to wrangle up high-resolution global soil moisture data, following the successful ...

What drives the solar cycle?

22 hours ago

You can be thankful that we bask in the glow of a relatively placid star. Currently about halfway along its 10 billion year career on the Main Sequence, our sun fuses hydrogen into helium in a battle against ...

MESSENGER completes 4,000th orbit of Mercury

22 hours ago

On March 25, the MESSENGER spacecraft completed its 4,000th orbit of Mercury, and the lowest point in its orbit continues to move closer to the planet than ever before. The orbital phase of the MESSENGER ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.