Arizona Astronomers Characterize Smallest Known Asteroid

A team of astronomers have obtained observations of the smallest asteroid – with a diameter of only two meters (six feet) – ever characterized in detail. The asteroid, named 2015 TC25, is also one of the brightest near-Earth asteroids ever discovered, reflecting 60 percent of the sunlight that falls on it.

Discovered by the University of Arizona’s Catalina Sky Survey last October, 2015 TC25 was studied extensively by a team led by Vishnu Reddy, an assistant professor at the University of Arizona’s Lunar and Planetary Laboratory. Other participating institutions include Lowell Observatory and Northern Arizona University. The team used four Earth-based telescopes for the study, published this month in The Astronomical Journal.

Reddy argues that new observations from the NASA Infrared Telescope Facility and Arecibo Planetary Radar show that 2015 TC25’s surface is similar to a rare type of highly reflective meteorite called aubrites. ¬†Aubrites consist of very bright minerals, mostly silicates, that formed in an oxygen-free, basaltic environment at very high temperatures. Only one out of every 1,000 meteorites that fall to Earth belong to this class.

“This is the first time we have optical, infrared, and radar data on such a small asteroid, which is essentially a meteoroid,” said Reddy. “You can think of it as a meteorite floating in space that hasn’t hit the atmosphere and made it to the ground – yet.”

“2015 TC25 is one of the five smallest Near-Earth Objects ever observed to measure rotation rate” says Audrey Thirouin from Lowell Observatory. Thanks to coordinated observations with Lowell’s 4.3-meter Discovery Channel Telescope, the NASA Infrared Telescope Facility, and the Magdalena Ridge Observatory 2.4-meter telescope, the team found that 2015 TC25 is a fast rotator with a rotational period of only 2.23 minutes and an irregular shape.

Small near-Earth asteroids such as 2015 TC25 are in the same size range as meteorites that fall to Earth. Astronomers discover them frequently, but not very much is known about them as they are difficult to characterize. By studying such objects in more detail, astronomers hope to better understand the parent bodies from which these meteorites originate.

Asteroids are remaining fragments from the formation of the solar system that mostly orbit the Sun between the orbits of Mars and Jupiter today. Near-Earth asteroids are a subset that cross Earth’s path. So far, more than 15,000 near-Earth asteroids have been discovered.

As far as the little asteroid’s origin is concerned, Reddy believes it likely was chipped off by another impacting rock from its parent, 44 Nysa, a main belt asteroid large enough to cover most of Los Angeles.

“Being able to observe small asteroids like this one is like looking at samples in space before they hit the atmosphere and make it to the ground,” Reddy say. “It also gives us a first look at their surfaces in pristine condition before they fall through the atmosphere.”

“It’s especially important to study the physical properties of small near-Earth asteroids because of the threats these objects pose to us,” says Stephen Tegler, co-author of the study and a professor in the Department of Physics and Astronomy at Northern Arizona University “The meteoroid that caused injuries and damage in Chelyabinsk, Russia in 2013 was less than 20 meters in diameter.”

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