Asteroid Apophis' path near Earth in 2029 offers rare lessons in defending planet

In April 2029, a 20-million ton asteroid once thought to pose a potentially catastrophic collision risk with the Earth will fly by our home.

Apophis, named for the Egyptian god of chaos and evil and currently hurtling through space at an average speed of roughly 19 miles per second, will come within about 20,000 miles of earth. That distance is, astronomically speaking, vanishingly small, smaller than the distance at which some satellites orbit our planet. Apophis will be closer, according to NASA, than any similarly sized potentially hazardous object has ever been in recorded history.

From certain vantage points — alas, not Long Island, but Australia and parts of Asia, Europe and Africa — "you’ll be able to look up in the sky and see this thing," Hofstra University astronomer Stephen Lawrence said.

"It will not be a bright star, but it will be easily visible, moving across the sky at 40 degrees per hour, and it will take a few hours to cross the entire sky. No one alive has seen that, an asteroid that close to the Earth, with the naked eye," Lawrence said.

According to the space and astronomy website EarthSky, Apophis also will be visible on April 13, 2029, with a telescope from the east coast of North America located in a part of the sky about 15 degrees north of the Pleiades star cluster. `

Possible Apophis impacts 

In 2004, when astronomers first detected Apophis orbiting the sun, they calculated two possible "impact possibilities" for Earth for 2029 and 2036. The risk of a 2029 impact was as high as 2.7% — the highest ever on the Torino scale, a method used to evaluate the threat that an asteroid poses to Earth, according to the European Space Agency. Additional observations ruled those out.

In 2021, observations from radio telescopes at Deep Space Network’s Goldstone Deep Space Communications Complex and the Green Bank Telescope in West Virginia ruled out another impact possibility for Apophis in 2068.

Astronomers have now ruled out any Apophis impact for the next century. They say the 2029 visit will present a rare opportunity to investigate an asteroid up close, perhaps learning clues about the origin of our solar system, and to hone planetary defense strategies for tracking and deflecting or destroying potentially hazardous objects flying toward the Earth in the future. 

Apophis, which measures about 1,100 feet across, originated about 4.6 billion years ago in the asteroid belt between Mars and Jupiter. It is an S-class asteroid, characterized by silicate material, metallic nickel and iron. 

Asteroids like Apophis are "fossil remnants of planetary formation," said Bruce Betts, chief scientist for the Planetary Society, a Pasadena, California, group that works to connect the public with space science and exploration. "It’s the stuff that didn’t get swept up into a planet. Things like this, we think, are what formed the Earth. These are still out there, and they haven’t been modified by the many things that affect rocks on the Earth: erosion, plate tectonics, chemical processes."

Early studies of samples of another ancient asteroid, Bennu, showed evidence of high carbon content and water, essential building blocks for life on earth, NASA has said. 

In June 2029, after Apophis’ close encounter with Earth, NASA’s OSIRIS-APEX spacecraft will attempt a rendezvous, allowing scientists to observe how earth’s gravitational pull alters the asteroid’s orbit, any changes to the asteroid’s spin and possible quakes or landslides on the asteroid’s surface, according to NASA.

The spacecraft also will dip toward the asteroid’s surface, firing its engines to churn loose rocks and dust and exposing subsurface material for observation. Apophis’ close approach "represents a significant opportunity for international collaboration to achieve major scientific benefits, at relatively low cost," NASA officials wrote in the agency’s 2023 Planetary Defense Strategy and Action Plan.

The European Space Agency’s Ramses spacecraft may also observe, though that agency has not gotten final approval for its mission.

Lessons in planetary defense

Close observation is important because "there’s only so much we can tell by remote sensing or using telescopes," said Stony Brook University planetary scientist Timothy Glotch, who participated in an earlier NASA mission that returned a sample from a different asteroid. "By visiting, learning about [asteroids’] physical properties, their density, their structure, we get a better understanding of what these asteroids are, and that could help inform planetary defense."

In 2023, NASA allotted $137.8 million for that mission.

There are tens of millions of near-Earth objects, the agency's term for asteroids and comets trailing debris that come close to or pass across Earth’s orbit around the sun.

The planet is buffeted daily by about 50 tons of dust and sand-sized objects with little adverse effect on its inhabitants. According to NASA, there are 230,000 objects near the Earth at least 164 feet across that could destroy an urban area in an impact and 25,000 objects 460 feet or larger capable of causing regional devastation. Less than half those larger objects have been detected and tracked. There are also around 1,000 objects about six-tenths of a mile across or larger "potentially capable of causing global impact effects."

None of these objects are currently considered to be an immediate threat to the planet.

The impact of a very large object on the Earth would release the equivalent of more than 100,000 megatons of TNT and cause sudden global climate change, according to ESA. The roughly 125-mile Chicxulub impact crater, formed 66 million years ago near what is now Mexico's Yucatán Peninsula and the Gulf of Mexico, is an example of such an event, thought to have been caused by the crash of a six-mile-wide object into the Earth. That impact ended the Cretaceous period, eliminating 65% of all species, including most dinosaurs.

The impact of one of those very large objects "throws enough stuff into the atmosphere that it blocks the sun." In those conditions, Glotch said, "You can’t farm crops. It’s the equivalent of nuclear winter. It could lead to mass death. It’s not stuff that is fun to think about."

NASA says it will dramatically improve its near-Earth object survey capacity with the launch, no later than 2028, of the space-based NEO Surveyor Mission, which will use two heat-sensitive infrared imaging channels to detect more than 90% of objects 460 feet or larger within a decade of launch, roughly tripling current capability.

Once an object has been identified and tracked, there are three defense options, Betts said. The first is a "kinetic impactor. You slam a spacecraft or multiple craft into it in the correct direction." Even a tiny alteration to an object’s trajectory, done at sufficient distance from the Earth, can have a significant effect because the change will keep propagating. We know this works because we’ve done it: in 2022, NASA’s half-ton DART spacecraft, traveling at 14,000 mph, struck a 492-foot asteroid nearly head-on 7 million miles from Earth, changing the object’s speed and path.

Another option would use the tiny gravity of a spacecraft, or remove a portion of an asteroid to reduce its mass, to create a "gravity tractor" effect, Betts said. The third option is to "use nuclear devices to break up the asteroid or deflect it by detonating near it and pushing it" off course, he said. "That’s if you have a big asteroid, or not as many years."

"We can’t stop hurricanes or earthquakes, but we can actually stop this," Betts said. But, he said, "It’s going to take continued work over the coming years to be prepared."