Sun puts asteroids in a spin
9 March 2007
Space scientists have made an amazing discovery - a 'solar-powered' asteroid. They hope that studying the large lump of spinning space rock will reveal new ways to power spaceships or even protect the Earth from asteroid impact.
Antenna finds out more...
This research was published in Nature on 8 March 2007.
Image: NASA
Asteroids are lumps of rock that orbit the Sun. Scientists have already spotted hundreds of thousands of asteroids in our Solar System and more are being found every day. We know gravity makes asteroids move around, but now scientists think they have found another driving force.
Scientists think there are about a thousand large asteroids that regularly come close to Earth.
Image: NASA-GRC
Researchers at the University of Helsinki in Finland have been investigating one near-Earth asteroid named Apollo for 25 years. They've discovered that it's gradually spinning faster and have traced the cause to energy from the Sun.
'We found that Apollo's rotation speed is increasing as it bounces solar energy off of its surface,' says lead scientist Mikko Kaasalainen. 'Over the last 40 years the asteroid has gained one extra spin during its journey round the Sun.'
Mikko Kaasalainen, asteroid hunter, University of Helsinki
Image: Sanna Kaasalainen
The team's findings are the first direct observations of a phenomenon called the YORP effect. This says that sunlight reflecting off an asteroid with an irregular shape gives it a small uneven push, making it spin.
'We've been using mathematical models to predict what makes this particular asteroid spin,' explains Mikko. 'Models with only gravity forces don't work, but models including the YORP effect fit our observations perfectly.'
The Apollo asteroid has an irregular shape - it looks different from different angles. This is what makes it spin.
Image: Mikko Kaasalainen
How can scientists see asteroids spin?
Most asteroids are so small and so far away from Earth that we can't directly see how they move. But scientists can use telescopes to measure an asteroid's brightness. This brightness changes as the asteroid rotates, giving clues about its spinning speed.
Asteroids and other objects in space reflect light from the Sun that can be picked up by telescopes on Earth.
Image: NASA, ESA, and Y. Momany (University of Padua)
Apollo is just one of the asteroids that Mikko's team are studying. They have already analysed over a hundred other asteroids and are hoping that new telescopes will let them look at thousands more.
'We have a network of observers searching for asteroids across Europe, the USA and Australia,' says Mikko. 'Within the next decade we hope to have a good overview of all the asteroids in our solar system.'
What do these findings mean for us?
'Many asteroids have orbits that regularly bring them close to the Earth and could crash into our planet,' says asteroid expert Bill Bottke from the Southwest Research Institute in America. 'Any asteroid more than a mile long could produce global environmental damage and larger impacts could wipe us out altogether.'
Bill Bottke, asteroid expert, Southwest Research Institute, USA
Image: Bill Bottke, SWRI
Space scientists have only discovered about three-quarters of the larger asteroids that approach the Earth, and a much smaller fraction of the smaller ones. So we can't be sure when Earth's next asteroid impact will happen, and we might not have any warning time to prepare.
Bill thinks this new research will let us make better predictions about how asteroids move across the Solar System. 'The more information we have about asteroid movements, the more warning we'll have about potential impacts with Earth.'
Early warning of an asteroid impact could give us time to evacuate areas in danger.
Image: Don Davis, NASA
But that's not all. 'This information could help us to model new types of solar-powered spacecraft like solar sails,' says Mikko. 'One day we could even deflect asteroids away from the Earth by changing the amount of sunlight they reflect.'