Sixty Six million years ago a 14-kilometer long, Mount-Everest sized asteroid blasted a hole in the ground, when at the moment of impact, “the top of it might have still towered more than a mile above the cruising altitude of a 747,” writes Peter Brannen in Ends of the World. “In its nearly instantaneous descent, it compressed the air below it so violently that it briefly became several times hotter than the surface of the sun, hitting Earth with enough force enough to lift a mountain back into space at escape velocity, releasing the equivalent of 100 million megatons of TNT creating a 20-mile deep, 110-mile hole and sterilizing the remaining 170 million square miles of the ancient continent of Pangaea, killing virtually every species on Earth and, oddly, paving the way for the emergence of the human species.”
Magnified Preview of a Coming Attraction?
“It would have felt like the ground beneath your feet had become a ship in the middle of the ocean,” says earth and space science professor Mark Richards at the University of Washington. “Then rocks would have bombarded you from a boiling sky that was beginning to take on a hazy glow. It would have seemed like the end of the world.”
“The pressure of the atmosphere in front of the asteroid started excavating the crater before it even got there,” geophysicist Mario Rebolledo at the Centro de Investigación Científica de Yucatán, told Brannen. “Then, when the meteorite touched ground zero, it was totally intact. It was so massive that the atmosphere didn’t even make a scratch on it. It would have been a pleasant day one second and the world was already over by the next. —all within a second or two of impact.”
Fast Forward to Earth 2068
New observations of asteroid Apophis –noteworthy because of its extremely close approach to the Earth on Friday, April 13, 2029, when the 300 meter-sized asteroid will become visible to the unaided eye as it passes within the belt of communications satellites orbiting the Earth–obtained with the Subaru telescope earlier this year revealed the effect of what’s known as Yarkovsky acceleration.
“The results show that the asteroid is drifting away from a purely gravitational orbit by about 170 meters per year, which is enough to keep the 2068 impact scenario in play,” said Dave Tholen at the University of Hawaiʻi Institute for Astronomy (IfA) about the acceleration phenomenon that arises from an extremely weak force on an object due to non-uniform thermal radiation. This force is particularly important for the asteroid Apophis, as it affects the probability of an Earth impact in 2068.
Effect of the Yarkovsky Acceleration
All asteroids need to reradiate as heat the energy they absorb from sunlight in order to maintain thermal equilibrium, a process that slightly changes the orbit of the asteroid. The orbit calculations were performed by Davide Farnocchia of the Jet Propulsion Laboratory, who is a co-author on the paper that was presented at the 2020 virtual meeting of the Division for Planetary Sciences of the American Astronomical Society.
Prior to the detection of Yarkovsky acceleration on Apophis, astronomers had concluded that a potential impact with Earth in 2068 was impossible. The detection of this effect acting on Apophis means that the 2068 impact scenario is still a possibility.
“We have known for some time that an impact with Earth is not possible during the 2029 close approach,” said Tholen, who has been accurately tracking the motion of Apophis in the sky since his team discovered it in 2004.
Further observations to refine the amplitude of the Yarkovksy effect and how it affects Apophis’ orbit are underway. Astronomers will know well before 2068 if there is any chance of an impact.
The Daily Galaxy, Sam Cabot, via University of Hawaii at Manoa