The geek stirs

It's been known for a long time that light has force, that even though photons are regarded as having zero mass, their energy can interact with mass and produce an effect. An obvious example is the chemical reaction between light and silver halides that makes modern photography possible.

But light can also affect motion and not just in a Crookes radiometer. As photons strike a surface, they heat it very slightly. The surface then re-emits that heat, causing a tiny recoil. Ultimately, the constant stream of photons from the Sun can make the force large enough to affect the motion of celestial bodies such as asteroids. The Yarkovsky-O'Keefe-Radzievskii-Paddack (or YORP) effect uses that to explain the spin of a cluster of objects in the asteroid belt between Mars and Jupiter. But while the mechanism has been conjectured for some time, it has never been directly observed - until now, as the BBC informed last week.

[S]eparate studies published in the journals Nature and Science have observed and measured the tiny stellar shoves on two spinning asteroids.

They reveal that both are gradually starting to spin faster and faster, which could eventually create new Solar System landmarks.

"If we can spin up an asteroid so fast, there's a really good chance that these objects will fly apart," said Dr Stephen Lowry, a planetary astronomer at Queen's University Belfast and lead author of one of two Science papers.

In this case, the fragments could form a binary asteroid where two objects orbit each other, he said.

Lowry noted that while the effect is tiny, "it's acting over millions of years."

A key result of this observation is proof that gravity is not the only force directing the past and future evolution of the solar system. So better understanding the impact of light on the motion of astronomical bodies opens the way for a new set of studies to better understand how the solar system came to be how it is.