Scientists Delve Into Inner Structure Of An Asteroid: Anatomy of 'Itokawa' Asteroid Yields Surprising Insights

By Ajit Jha on February 5, 2014 12:01 PM EST

Milky Way Shines over Snowy La Silla
Data gathered at the La Silla Observatory (shown here) has yielded brand new insights into the anatomy of asteroids. (Photo: ESO/José Francisco Salgado (jo)

For everything we hear about asteroids, scientists know surprisingly little about their anatomy. That's why Dr. Stephen Lowry and his team at the University of Kent decided to probe inside a peanut-shaped, near-Earth asteroid nicknamed "Itokawa." It was named by a Japanese team aboard the spacecraft Hayabusa, who discovered the asteroid's strange shape in 2005.

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Lowry and colleagues combined the measurements involving the spinning rate and changing rate of this asteroid to theoretically determine how asteroids radiate heat. They analyzed a large number of images obtained from La Silla Observatory in Chile to measure variation and change in the brightness of the rotating asteroid. The images used in the study were captured by ESO's New Technology Telescope at La Silla Observatory in addition to several more observatories from 2001 to 2013.

By combining accurate data about the asteroid's spin period with the information on the shape of the asteroid, the scientists were able to better understand the complex interior of the asteroid. The researchers found the interior density of the asteroid to measure between 1.75 and 2.85 grams per cubic centimeter.  

"This is the first time we have ever been able to determine what it is like inside an asteroid," explained Lowry in a press release. "We can see that Itokawa has a highly varied structure — this finding is a significant step forward in our understanding of rocky bodies in the Solar System."

The scientists also found that something called the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) had an effect on the asteroid.  The YORP effect is a phenomenon where sunlight affects the spin of small heavenly bodies - including asteroids. It occurs when the surface of the object that absorbs sunlight re-emits it as heat. The irregular surface of an asteroid, however, does not radiate heat evenly, leading to the formation of tiny but continuous torque on the body, which in turn actually changes its spin rate. In an earlier study, Lowry and colleagues observed this effect for the first time on a small asteroid called 2005 PH5 (later renamed 54509 YORP).

In the current study, the researchers observed that the rate of spin of Itokawa was slowly accelerating due to the YORP effect. The miniscule change in rotation of just 0.045 seconds per year is explained by different densities of the two parts of the peanut shape asteroid.

The study for the first time has shown that the internal structure of asteroid is highly varied. All previous speculations on the internal structure of asteroids were based on rough overall density measurements. In the study, the researchers hypothesize that Itokawa formed from two fused and merged components of a double asteroid.  

"Finding that asteroids don't have homogeneous interiors has far reaching implications, particularly for models of binary asteroid formation. It could also help with work on reducing the danger of asteroid collisions with Earth, or with plans for future trips to these rocky bodies," Lowry said.

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