asteroidAsteroids have collided with Earth in the past and may do so again, which is why NASA is keen on tracking them, learning as much as they can about their orbits, mass, and other properties.

Now research is showing that even sunlight can alter an asteroid’s path and must be taken into consideration.

NASA has a mission that specifically targets one asteroid in particular — 1999 RQ36. The mission, OSIRIS-REx, is intended to rendezvous with the space rock and take a sample before returning to Earth.

Members of the OSIRIS-REx team are already learning new things about 1999 RQ36 from a distance — not just determining its mass, but also its orbit, including a slight drift resulting from the absorption and re-emission of heat from the sun. Steve Chesley of NASA’s Jet Propulsion Lab reported his findings in May at a conference in Japan.

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In order to calculate the precise mass of 1999 RQ36, Chesley needed to factor in its orbit and anything that might affect that orbit, such as nearby objects or propulsive force, however minute. That meant taking into account the effects of sunlight.

As unlikely as it may seem, photons carry momentum just like any other particle. That means that when light strikes something, its photons transfer energy just like hitting the object with tiny pellets, producing a recoil effect.

Solar sail propulsion for spacecraft exploits this fundamental principle.

It’s also at the heart of the “Yarkovsky effect,” proposed by a Russian engineer named Ivan Yarkovsky over 100 years ago. He hypothesized that rotating asteroids could experience tiny changes in their orbits as they absorbed heat from the sun’s light on one side, radiating it back as they turned around.

The effect would be small, just a slight imbalance, but over time it would add up, significantly altering the orbit. And it would act more strongly on smaller objects as opposed to larger ones.

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