Understand the surfaces of asteroids

May 10, 2013

A fly your thesis! experience explained how behave in gravel and rocks on the surface of an asteroid. The results will be useful in explaining the asteroid geology, interpreting images of the asteroid surfaces and design missions future lander asteroids.

Asteroids are quickly progressing to the top of the scientific agenda. They contain information about the origin of the solar system, and they contain molecules that could tell us about the origin of life on Earth. Sometimes they can also present a danger to the Earth threatening to collide with our planet.

Discover their secrets, many scientists would like to collect samples from the surface of the nearby asteroids for analysis. But in the microgravity of the asteroid surface, how the gravel and pebbles, called regolith, have?

This is the question that AstEx team studied during fly your thesis of the ESA 2009! Program, coordinated by ESA's education Office. The team was composed of students of The Open University, United Kingdom and the University of Nice-Sophia Antipolis, France.

In results recently published in Physical Review Letters and soon to be published in the Monthly Notices of the Royal Astronomical Society, reporte§d students find both similarities and differences in the behavior of granular materials in microgravity compared to Earth's gravity.

The team of AstEx defining their experience

Almost 1 million glass beads with a diameter of three or four millimetres were loaded in the experience. They have been placed between two cylinders and the inner cylinder has been in rotation. This created a shear force, swirling beads. Two cameras recorded the subsequent movement for further analysis.

The experience was first run on the ground under conditions of ordinary gravity. Then it was loaded in the Airbus A300 Zero-G, operated and maintained by Novespace originating from Bordeaux, France.

The special flies aircraft maneuvers in loop that generate conditions of microgravity for about 20 seconds at a time. AstEx students had the unique opportunity to discover the weightlessness and exploit their experience periods of microgravity 90.

As beads rub against each other, they put in place of the strings of power. These are the critical support connections in a collection of granular material. On a larger scale, it's like having a bunch of oranges. Some may be removed without the stack collapse, while other trigger an avalanche. Those who cause a collapse are weight-bearing oranges, intended to be part of a chain of strength.

The UK-French team in microgravity

The popular game of Jenga also relies on the strings of power. Players carefully remove the wood of a tower blocks, hoping that the Tower remains standing. If they choose a block that is part of a chain of strength, however, the Tower will fall.

In the regolith, force these chains are more complex. They will be implemented by a probe landing or material trying to dig the surface. The behavior of the regolith under different regimes of gravity is therefore essential to know when designing these missions.

The team found a surprising result.

' When we analyzed the images later, we have seen no difference in the main flow of grains in conditions of different severity in response to a shear force,' says Naomi Murdoch, who was studying her doctorate at the University of Nice - Sophia Antipolis, France, at the time of the experience.

The students did, however, see a major difference in a secondary type of movement called granular convection. Certain types of granular convection are common to us all. They occur when the smaller grains fall at the bottom of a mixture during agitation. This is what causes the breakfast cereals to settle in their packages during transport.

It can also occur as a separate application in the grains of the same size. The team found that this convection granules did not microgravity, indicating that gravity is an important factor.

The results will assist in the design of effective anchors and basement of mechanisms of sampling missions to the asteroids, or any device to interact with the surface of the covered body of regolith, including the Moon and Mars.

More useful, however, the results will help astronomers better understand the asteroid geology and what processes take place on an asteroid.

Notes for editors:

Granular convection in microgravity by N. Murdoch et al. Is published in Physical Review Letters, PRL 110, 018307 (2013)

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