Sunlight puts asteroid in a spin

An asteroid washed in sunlight has gone into a spin cycle, scientists have discovered. The pressure of the sun’s rays is causing the space rock, named 2000 PH5, to turn one millisecond faster each year.

Radar images of asteroid 2000 PH5Over the next 15-40 million years that will change its spin rate from once every 12 minutes to once in 20 seconds.

The discovery was jointly made by astronomers Stephen Lowry and Alan Fitzsimmons, of Queen’s University Belfast, and Jean-Luc Margot and Patrick Taylor of Cornell University in the US.

It is the first time the so-called Yarkovsky-O’Keefe-Radzievskii-Paddack or YORP effect, named after the scientists who predicted it, has been observed working in the solar system.

Asteroid 2000 PH5 is one of the so-called Near-Earth Objects that cross our own orbit and so pose a potential impact threat. It comes within 1.1 million miles of Earth and is thought to be about 175 yards wide. Like most asteroids, it has an uneven shape and it is this which allows the sunlight to affect its spin.

The scientists used a powerful radio telescope at Arecibo, Puerto Rico, to bounce radar signals off the asteroid and produce images such as shown here. These helped them to measure its speed of rotation. Visual observation with giant optical telescopes around the world provided confirmation by checking how the asteroid’s brightness varies as it spins.

Dr Lowry said: “The warming caused by sunlight hitting the surfaces of asteroids and meteoroids leads to a gentle recoil effect as the heat is released. In the same way, if one were to shine light on a propeller over a long enough period, it would start spinning. It’s a tiny, tiny effect but it’s acting over millions of years.”

The team believe the increasing spin speed may eventually cause the asteroid to break up into two or more smaller space rocks.

Although the YORP effect sounds immeasurably weak, the scientists say it plays an important role in changing the orbits of asteroids between Mars and Jupiter and could put some into orbits crossing the Earth’s.

Earth still faces a small but real risk of impact by an asteroid called Apophis in 2036.

Picture: European Southern Observatory.

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Paul Sutherland

Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.
Paul Sutherland

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Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.

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