NASA: the asteroid could still hit the Earth in 2068

Earth has been bombarded with space rocks throughout its history, but we are fortunate that none of the large ones have crashed on the planet lately. Astronomers watch the skies closely, hoping to spot potential impactors early enough that they can do something about it, and one of the most troubling objects is 99942 Apophis. This skyscraper-sized asteroid could still hit Earth in 2068, according to a new analysis from the University of Hawaii and NASA’s Jet Propulsion Laboratory.

Scientists discovered Apophis in 2004, sounding the alarm when initial observations suggested it had a disturbing 2.4% chance of hitting Earth in 2029. Fortunately, further studies have reduced that probability to zero. However, astronomers have been keeping a close eye on Apophis ever since – it is currently considered the third highest impact threat on Earth, behind 101955 Bennu and 29075 (1950 DA). However, the highest impact risks for those objects are centuries.

NASA’s Sentry Risk Table shows a one in 150,000 chance of Apophis hitting Earth in 2068, but that doesn’t take into account a phenomenon known as the Yarkovsky effect. As asteroids roll into space, they absorb energy from the sun. That energy is radiated into space in the form of heat, but the process is not uniform over the entire surface of the object. The result is a small but measurable push that alters the object’s orbit. Davide Farnocchia of NASA and Dave Tholen of the University of Hawaii used data from the Subaru Telescope to try to identify how much the Yarkovsky effect changes our probabilities.

This is our best guess on the form of Apophis.

Tholen says the true risk of impact is likely closer to 1 in 530,000, a number used by the NEODyS impact monitoring service that includes the Yarkovsky effect. The new observations will likely push NASA’s Sentry risk to an equally low level. So yes, Apophis is probably less likely to hit Earth in a few decades, but astronomers will need to monitor its orbit over time to be sure. There is still a very real, non-zero possibility that Apophis will be captured by Earth’s gravity in 2068.

You don’t want to take chances with an item like Apophis. Even if “mass extinction” isn’t big enough, an impact would be catastrophic. It’s a simple matter of physics: Apophis hitting Earth results in an explosion equivalent to 1,151 megatons of TNT. By comparison, the largest nuclear weapon ever detonated by humans was around 57 megatons. The 1883 eruption of Krakatoa recorded a speed of about 200 megatons. Apophis could wreak havoc on a small town, cause huge tsunamis and set off extensive fires. All in all, a pretty bad day for the Earth.

In case Apophis is ever on a collision course, astronomers should be able to tell us well in advance. Maybe it will even be soon enough to try out one of those pie asteroid deflection systems we always hear about.

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