Working from the current uncertainty in the asteroid’s orbit and using just gravity, astronomers calculated that encounters later this century would also be harmless. However, in 2015, David Vokrouhlický (Charles University in Prague) and his colleagues predicted that Apophis should experience a tiny orbital change due to the Yarkovsky effect, leading to a possible impact in 2068.
The Yarkovsky effect is a subtle, net force on a small, rotating body caused by asymmetric heating. Tholen and his colleagues have now measured the strength of this effect on Apophis by making extremely precise positional observations using the Japanese 8.3-meter Subaru telescope on Mauna Kea, Hawai‘i. Their results indicate that the semi-major axis of the asteroid’s orbit is decreasing by 170 meters per year – in very good agreement with Vokrouhlický’s prediction.
The upshot: there’s indeed a small chance (currently about 1 in 150,000) of an actual impact in April 2068, a little more than 47 years from now.
Govert Schilling
Speaking of possible impacts by near-Earth asteroids, Apophis is one of the most talked about because of its size and several close approaches to Earth over the next century. It has recently returned in the news following refinements of its orbit that slightly increase the chances of collision with our planet. They remain minuscule fortunately, because considering our poor results in dealing with a pandemic and global warming, I would not give humanity very good odds of averting an asteroid impact, even one discovered decades in advance such as this one.
On a brighter note, during the approach on April 13th 2029 (a Friday no less), the asteroid will be visible as a fast-moving naked-eye object from Europe and Africa. With a peak magnitude of 3.1, it will look as bright as one of the Big Dipper stars, which should make for a rare astronomical sight!
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