Astronomers are gearing up for thrills this year when Earth gets buzzed by two rogue asteroids and two comets, including a wanderer last seen by the forerunners of mankind.
The guardians who scour the heavens for dangerous space rocks are currently closely tracking an asteroid called 99942 Apophis.
Named after the god of evil and darkness in Egyptian mythology, Apophis measures around 270 metres (877 feet) across, a mass able to deliver more energy than 25,000 Hiroshima bombs if it ever smashed into Earth.
Apophis sparked some heart-stopping moments when it was first detected in 2004.
Early calculations suggested a 2.7-percent probability of a collision in 2029, the highest ever seen for an asteroid, but the risk was swiftly downgraded after more observations.
Even so, for April 13, 2036, “there is still a tiny chance of an impact,” says NASA’s fabled Jet Propulsion Laboratory (JPL), which puts the risk at about one in 250,000.
One of the big unknowns is the Yarkovsky effect, a phenomenon discovered by a Russian engineer at the start of the 20th century.
A slowly rotating body that orbits close to the Sun experiences heating on one side of its body that then cools at “night” as it turns over.
This alternate heating and cooling can cause a tiny momentum, depending on the body’s spin and amount of area that warms.