Amsterdam, Feb 5 : A team of French and Italian astronomers has devised a new method for measuring the size and shape of asteroids, which would increase the number of asteroids that can be measured by a factor of several hundred.

This method takes advantage of the unique capabilities of ESO's Very Large Telescope Interferometer (VLTI).

"Knowledge of the sizes and shapes of asteroids is crucial to understanding how, in the early days of our Solar System, dust and pebbles collected together to form larger bodies and how collisions and re-accumulation have since modified them," said Marco Delbo from the Observatoire de la Cote d'Azur, France, who led the study.

Direct imaging with adaptive optics on the largest ground-based telescopes such as the Very Large Telescope (VLT) in Chile, and space telescopes, or radar measurements are the currently favored methods of asteroid measurement.

However, direct imaging, even with adaptive optics, is generally limited to the one hundred largest asteroids of the main belt, while radar measurements are mostly constrained to observations of near-Earth asteroids that experience close encounters with our planet.

Delbo and his colleagues have devised a new method that uses interferometry to resolve asteroids as small as about 15 km in diameter located in the main asteroid belt, 
200 million kilometres away.

This is equivalent to being able to measure the size of a tennis ball a distance of a thousand kilometers.

This technique will not only increase the number of objects that can be measured dramatically, but, more importantly, bring small asteroids that are physically very different from the well studied larger ones into reach.

The interferometric technique combines the light from two or more telescopes.

Astronomers proved their method using ESO's VLTI, combining the light of two of the VLT's 8.2-metre Unit Telescopes.

"This is equivalent to having vision as sharp as that of a telescope with a diameter equal to the separation between the two VLT Unit Telescopes used, in this case, 47 meters," said co-author Sebastiano Ligori, from INAF-Torino, Italy.

The researchers applied their technique to the main belt asteroid (234) Barbara. Although it is so far away, the VLTI observations also revealed that this object has a peculiar shape.

"The two parts appear to overlap," said Delbo. "So, the object could be shaped like a gigantic peanut or, it could be two separate bodies orbiting each other," he added.

Having proven the validity of their new and powerful technique, the team can now start a large observing campaign to study small asteroids. (ANI)