Potentially dangerous asteroid 99942 Apophis makes a breathtaking flyby of Earth on April 13, 2029, and you can see more than 2 billion people across Africa and Western Europe crossing the night sky. Under clear skies, Space Rock appears like a faint star – as bright as a large dipper star, and is visible as unpopular as the unpopular star, but steadily glides overhead.
Richard Binsel, professor of planetary science at MIT, marks Apophis’ flyby “is visible to the naked eye for the first time in the history of the universe.” Astronomers estimate that this large asteroid’s close approach – 1,100 feet (340 meters) in diameter, or the Eiffel Tower almost height, occurs only once every 7,500 years.
For the general public, it becomes a dazzling, once-in-a-lifetime sight. For scientists, it promises even rarer. This is a natural experiment of one millenium to see in real time how Earth’s gravity forms a giant asteroid. “We don’t know,” Binzel said.
A pioneer in asteroid hazard research and inventor of the Turin Impact Hazard Scale, Binzel, is a measure of the hazard scale used to assess the impact risk of asteroids and comets, highlighting one point above all. “Apophis passes safely through the Earth. Apophis passes safely through the Earth. Apophis passes safely through the Earth.”
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However, when Apophis was first discovered in 2004, the photos were less certain. Early calculations suggested that an impact of 2.7% could occur on April 13, 2029, and were placed on the Turin scale at level 4. The scientist was named Apophis, and was nicknamed “The God of Chaos” Asteroid, after the Egyptian god of the underworld.
Over the next 20 years, serial tracking and radar observations narrowed the Apophis trajectory only a few trajectories from hundreds of miles of uncertainty. By 2021, Apophis would be officially removed from all risk lists, with scientists presuming it will not pose a threat for at least the next 100 years. However, last September, it has been pointed out that there is still a small possibility that an unknown asteroid could tweak it into the collision path before the Earth’s flyby near 2029.
“It was a lot of work by many people to ensure that Apophis could say with full and confidently that they would pass through the planet safely — undoubtedly,” Bindel said.
“The Earth doesn’t care, but Apophis will.”
The Earth itself barely notices encounters, but Apophis remains unchanged. Just over 18,600 miles (30,000 km) from the planet’s surface, it is closer to Earth’s satellites – it is mostly within the Earth’s path around that star, and is often hidden by the bright glare of the stars, and is thus reshaped into a wider Apollo-class orbit. That rotation could also change, which could send the asteroid into a fresh fall, Binzel said.
“The Earth doesn’t bother you, but Apophis does care because Apophis’ orbit changes,” he said. “It’s all about encounter physics.”
To capture these changes directly, NASA has reassigned the fresh Osiris-Rex spacecraft from its mission to the asteroid Bennu to its new role as Osiris Apex. This probe burns with an apophie before a flyby, maps its surface, monitors its spin and measures how Earth’s gravity changes the asteroid during a tight path. Among the most appetizing goals, Binzel said there is an opportunity to measure seismic vibrations within Apophis.
“In 60 years of planetary science, we only measured seismicity for two objects, the moon and Mars,” he said. “This will provide another leap in measuring earthquakes and interpreting internal properties.”
That leap could come from the rapid Apophis mission (Ramsess) for space safety. The European Space Agency (ESA) mission, if approved by the ESA’s Ministerial Council in November, will begin in spring 2028 and arrive on the asteroid by February 2029. The mission’s goal is to observe Apophis before, during and after the Earth’s flyby.
Hovering near 3 miles (5 km) from the asteroid on April 12-14, 2029, Ramses mapped Apophis’ orbit, searching for dust clouds grown by the power of the tide dal, and unfolded a small satellite called Cubesat to touch the surface to detect seismic waves.
Beyond science, Apophis is a proof of planetary defense, scientists say. This is because it supports humanity’s efforts to understand and prepare rare but realistic risks of impact on asteroids. Apophis itself does not pose any danger, but it belongs to a class of nearby asteroids that could one day threaten our planet. By studying how Earth’s tidal forces reconstruct Apophis, scientists can refine key models to deflect dangerous asteroids.
“Apophis is not a planetary defense emergency,” added Tom Staller, a planetary scientist at NASA headquarters in Washington, DC, during a Q&A session at the conference. “It’s an opportunity, an unprecedented opportunity.”
“Asteroids are not scary,” he added. “They should understand, that’s what we do.”
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