Paris, June 17: In a technical feat, astronomers measured the size of a small rock six billion kilometres away to an accuracy of a few kilometres and found its surface to be a mysterious ice-like white.
Years of planning combined with a network of telescopes to grab the first pictures of the Kuiper Belt Object (KBO) through a method of celestial alignment, they reported on Wednesday in the British science journal Nature.
KBOs are a population of rocks that orbit the Sun at a distance of between 4.95 – 8.25 billion kilometres and are believed to be rubble left over from the building of the planets.
Their lonely journey takes them out beyond Neptune, the farthest acknowledged planet, and into a vast region that touches on the deeply chilled fringes of the Solar System.
The rock, KBO 55636, had been tracked by an astronomer in the US, Massachusetts Institute of Technology (MIT) professor James Elliot, for five years.
Lucky
Elliot suddenly realised that on October 9 2009 that his coveted 55636 would pass between a bright star and Earth, an event known as occultation.
When a rock or planet passes between a star and the observer, it causes changes in starlight that can reveal its size and temperature and indicate whether it has an atmosphere, and if so, what kind. But the occultation on October 9 faced a problem.
The KPO 55636 is small, and this massively complicated the task of predicting exactly where its tiny shadow would fall on Earth.
Hedging their bets, Elliot and colleagues assembled a network of 21 telescopes at 18 stations along a 5 900km track where, with luck, the occultation could be snared.
On the great day, nine of the stations were found to be outside the occultation and missed it, and seven could not see it because of bad weather. But two stations in Hawaii, manned by professional and amateur sky gazers, struck gold.
Using telescopes with mirrors of only 2.4 metres and 0.34 metres – modest affairs compared with today’s behemoths – they got excellent images of 55636 as it whizzed past at 91 000km/h.
To get this achievement in perspective, it was equal to getting a photo of a one-euro coin from a distance of 500km, with the target visible for just 10 seconds.
–Agencies