If you’re a fan of asteroids, then the name 99942 Apophis will likely mean something to you. It’s an 885-foot-wide asteroid assumed to weigh around
2,727kg 2.7 x 1010kg. When it was discovered back in 2004 there was a relatively high (2.7 percent) chance this huge asteroid would hit the Earth on April 13, 2029. But later observations ruled that out, however it does remain a potential future threat.
Today, at around about 7pm EST, Apophis is set to closely pass the Earth. By close, I mean within 9 million miles. Astronomers hope this relatively close pass will allow them to take a radar ranging, which will then allow them to better predict the location of the asteroid right up to 2070.
After today’s pass things get a little more worrying, though. The 2029 pass will be much closer at just 30,000km and within range of some satellites. It’s also close enough that most people (in Europe, Africa, and western Asia) will be able to see it in the sky using binoculars.
Passing so close to Earth will also have a major impact on Apophis’ trajectory, and could allow the asteroid to pass through a half-mile-wide gravitational keyhole setting it up for an impact with Earth in 2036. The chances of that happening are tiny though, and a lot depends on the 2029 pass.
If Apophis did hit Earth the effects would depend a lot on its composition, but the impact is estimated to be the equivalent of 510 megatons. That would do significant damage to an area thousands of square kilometers in size, but would have no long term global effects.
We should know more once the pass today happens and new calculations are made. Then we’ll definitely know if an impact will happen after the 2029 pass, at which point action will have to be taken to divert it if necessary.