Two asteroids, two comets heading our way

Celestial flybys to thrill this year


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 closely tracking an asteroid called 99942 Apophis. Named after the god of evil and darkness in Egyptian mythology, Apophis measures around 270 meters across and would 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, “there is still a tiny chance of an impact” on April 13, 2036, said NASA’s Jet Propulsion Laboratory, which puts the risk at about 1 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 is heated on the illuminated side, which then cools as it turns away from the sun. This alternate heating and cooling can produce a little momentum, depending on the body’s spin and amount of area that warms. The question is whether, over time, the Yarkovsky effect is accelerating Apophis, thus skewing estimates for future approaches.

Seeking clues, NASA’s deep-space radars will be scanning Apophis, which on Wednesday will pass by Earth at a distance of 14.5 million km.

On Feb. 15, a 57-meter asteroid, 2012 DA14, will skim the planet at just 34,500 km. In other words, it will spookily fly by inside the orbit of geostationary satellites.

“It’s going to be the closest predicted flyby of an asteroid,” said Mark Bailey, director of the Armagh Observatory in Northern Ireland.

Comets — seen by the superstitious as harbingers of great events — could make 2013 a memorable year.

Lonely travelers of the cosmos, comets are giant clumps of primeval ice and dust, formed in the infancy of the solar system, which loop around the sun at intervals that can vary from years to eons. As they get closer to our star, solar heat warms the surface, causing it to spew gases and dust that shine as twin “tails” in the sun’s rays.

First up is Comet 2011 L4 (PANSTARRS), whose name comes from the University of Hawaii telescope that spotted it in 2011. PANSTARRS could be at its brightest from March 8 to 12.

The biggest excitement is being reserved for Comet ISON, named after the International Scientific Optical Network, whose telescope was used by Russian astronomers Vitaly Nevski and Artyom Novichonok to make the find last September.

Right now, it is unclear how bright ISON will be, but by some calculations it could become visible to the naked eye by late November and maybe linger brilliantly for months, becoming a once-a-century event. ISON is an extraordinary beast, for it last returned to Earth 10 million years ago or more, Bailey says.