If you were worried about asteroid 99942 Apophis hitting the Earth in 2068, you can relax for at least another century. A new survey by NASA's Center for Near-Earth Object Studies (CNEOS) has confirmed that the probability of it colliding with us then is too low for it to be regarded as a threat.
First discovered on June 19, 2004 by astronomers at the Kitt Peak Observatory, Apophis soon gained notoriety when its orbit was calculated, showing that it would pass close to the Earth on several occasions over the next century. This was worrying because it would pass within the orbit of the Moon on occasion and, since it measures 1,100 ft (340 m) across and weighs an estimated 61 million tonnes, it could have an impact force roughly equivalent to a two-megaton bomb.
What didn't help was that the orbit of Apophis and the effect that a flyby of Earth would have on it were only roughly understood. This is because calculating the trajectory of an asteroid, like anything else in space, requires many observations over time. The first results are therefore a rough estimate, but as more precise measurements are made, the orbital calculations become more accurate.
For the latest survey, CNEOS waited until Apophis made a flyby of Earth on March 5, 2021. The team relied on radar observations using the 70-m (230-ft) radio antenna at the Deep Space Network’s Goldstone Deep Space Communications Complex near Barstow, California, to beam a radar signal at Apophis 10.6 million miles (17 million km) away that was reflected and recorded by the 100-m (330-ft) Green Bank Telescope in West Virginia.
As a result, the position of Apophis is now confirmed with an accuracy within 490 feet (150 m). The new orbit plot has the asteroid passing very close to the Earth on April 13, 2029, when it will come within 20,000 miles (32,000 km) of the planet's surface. This is close enough that, in the Eastern Hemisphere, it will be visible to the naked eye. However, the future path of the asteroid is now known with greater certainty and the feared impact in 2038 is no longer a probable threat.
"A 2068 impact is not in the realm of possibility anymore, and our calculations don’t show any impact risk for at least the next 100 years,” says Davide Farnocchia of CNEOS, which is managed by NASA’s Jet Propulsion Laboratory in Southern California. “With the support of recent optical observations and additional radar observations, the uncertainty in Apophis’ orbit has collapsed from hundreds of kilometers to just a handful of kilometers when projected to 2029. This greatly improved knowledge of its position in 2029 provides more certainty of its future motion, so we can now remove Apophis from the [Sentry Impact Risk Table, which lists potentially dangerous near-Earth asteroids]."
The animation below shows Apophis passing the Earth in 2029.
Source: NASA