ESO: The anatomy of an asteroid

This is a schematic view of the strange peanut-shaped asteroid Itokawa. 

By making exquisitely precise timing measurements using ESO's New Technology Telescope (NTT), and combining them with a model of the asteroid's surface topography, a team of astronomers has found that different parts of this asteroid have different densities. 

As well as revealing secrets about the asteroid's formation, finding out what lies below the surface of asteroids may also shed light on what happens when bodies collide in the Solar System, and provide clues about how planets form. 

The shape model used for this view is based on the images collected by JAXA's Hayabusa spacecraft. 

Credit: ESO. Acknowledgement: JAXA

ESO's New Technology Telescope (NTT) has been used to find the first evidence that asteroids can have a highly varied internal structure.

By making measurements astronomers have found that different parts of the asteroid Itokawa have different densities.

As well as revealing secrets about the asteroid's formation, finding out what lies below the surface may also shed light on what happens when bodies collide in the Solar System, and provide clues about how planets form.

Stephen Lowry

Using very precise ground-based observations, Stephen Lowry (University of Kent, UK) and colleagues have measured the speed at which the near-Earth asteroid (25143) Itokawa spins and how that spin rate is changing over time.

They have combined these delicate observations with new theoretical work on how asteroids radiate heat.

This small asteroid is an intriguing subject as it has a strange peanut shape, as revealed by the Japanese spacecraft Hayabusa in 2005.

To probe its internal structure, Lowry's team used images gathered from 2001 to 2013, by ESO's New Technology Telescope (NTT) at the La Silla Observatory in Chile among others, to measure its brightness variation as it rotates.

This timing data was then used to deduce the asteroid's spin period very accurately and determine how it is changing over time.

When combined with knowledge of the asteroid's shape this allowed them to explore its interior—revealing the complexity within its core for the first time.

"This is the first time we have ever been able to to determine what it is like inside an asteroid," explains Lowry.

"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 spin of an asteroid and other small bodies in space can be affected by sunlight. This phenomenon, known as the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, occurs when absorbed light from the Sun is re-emitted from the surface of the object in the form of heat.

When the shape of the asteroid is very irregular the heat is not radiated evenly and this creates a tiny, but continuous, torque on the body and changes its spin rate.

Lowry's team measured that the YORP effect was slowly accelerating the rate at which Itokawa spins. The change in rotation period is tiny—a mere 0.045 seconds per year.

But this was very different from what was expected and can only be explained if the two parts of the asteroid's peanut shape have different densities.

This is the first time that astronomers have found evidence for the highly varied internal structure of asteroids.

Up until now, the properties of asteroid interiors could only be inferred using rough overall density measurements.

This rare glimpse into the diverse innards of Itokawa has led to much speculation regarding its formation.

One possibility is that it formed from the two components of a double asteroid after they bumped together and merged.

Lowry added, "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."

This new ability to probe the interior of an asteroid is a significant step forward, and may help to unlock many secrets of these mysterious objects.

More information: This research was presented in a paper "The Internal Structure of Asteroid (25143) Itokawa as Revealed by Detection of YORP Spin-up", by Lowry et al., to appear in the journal Astronomy & Astrophysics.

Japan JAXA Hayabusa-2 Mission: Commercial Exploitation of Space rocks and Asteroids

In 2013 the Japanese Aerospace Exploration Agency (JAXA) are sending the space probe, Hayabusa 2, on a long journey to an asteroid named 1999 JU3 (Image by Japan Aerospace Exploration Agency).

A unique space cannon developed for Japan's Hayabusa 2 spacecraft has successfully test-fired on Earth in preparation for a 2014 mission.

During its upcoming journey into space, the cannon will blast an asteroid and mine samples of its soil.

The test took place in the Japanese prefecture of Gifu, paving the way for the Hayabusa 2 spacecraft to extract soil samples from the asteroid, the Japan Aerospace Exploration Agency (JAXA) announced on Monday.

During the mission of Hayabusa 2, scheduled to begin in December 2014, the space probe will extract soil from inside the asteroid.

To do this, it will be equipped with a collision device designed to shoot at the surface of the asteroid from a distance of 100 meters with metal shell ammunition moving at a speed of two kilometers per second.

JAXA hopes to create a small (a few meters in diameter), artificial crater from which Japanese scientists can extract valuable samples capable of revealing the history of the formation of cosmic bodies of this type.

"A new function, [a] 'collision device,' is considered to be [on board] to create a crater artificially," JAXA explained on its website, adding that collecting samples from the surface that is exposed by a collision will ensure acquiring "fresh samples that are less weathered by the space environment or heat."

In order to calibrate the precision of the cannon, JAXA engineers had to overcome a number of challenges. However, the agency assures that all problems have already been solved.

"We were able to solve several problems associated with the development of the device. During the tests, the projectile hit right on target, and with the expected speed," JAXA engineer Takanao Saiki said.

Japanese scientists actively began exploring asteroids with the Hayabusa mission, which returned to earth in June 2010 after exploring a 500-meter-long rock-rich S-type Itokawa asteroid.

Hayabusa 2 is a successor of the first spacecraft and is scheduled to be launched in 2014 to conduct research of a C-type asteroid temporally called '1999 JU3.'

It is believed to contain a higher concentration of organic matters and water.

"Minerals and seawater which form the Earth as well as materials for life are believed to be strongly connected in the primitive solar nebula in the early solar system"

"Thus, we expect to clarify the origin of life by analyzing samples acquired from a primordial celestial body, such as a C-type asteroid, to study organic matter and water in the solar system and how they coexist while affecting each other," JAXA posted on its website.

So far, research into '1999 JU3' revealed that it is a sphere approximately 920 meters in diameter with an albedo on the surface of about 0.06. The rotation period of the celestial object is approximately 7.6 hours.

Hayabusa 2 is expected to reach its target in the middle of 2018 before departing back to Earth in 2019.