It may be Friday the 13th, but for astronomers it will be a lucky day. On April 13, 2029, a speck of light will streak across the sky, getting brighter and faster. At one point it will travel more than the width of the full moon within a minute and get as magnitude 3.7, equal to the stars in the bucket of the Little Dipper. But don’t expect a satellite or an airplane. Instead, if we’re all still lucky enough to still be around, we’ll witness the dramatic flyby of the asteroid 99942 Apophis.
The 1,100-foot-wide (340 meters) near-Earth asteroid will zip harmlessly by Earth only 19,000 miles (31,000 km) above the surface. That’s within the distance that some of our spacecraft that orbit Earth. Hoping to make the most of the opportunity, scientists at the 2019 Planetary Defense Conference in College Park, Maryland, sat down to talk over options — from telescopic observing to sending a spacecraft to intercept the asteroid.
“The Apophis close approach in 2029 will be an incredible opportunity for science,” said Marina Brozović, a radar scientist at NASA’s Jet Propulsion Laboratory, who works on radar observations of near-Earth objects. “We’ll observe the asteroid with both optical and radar telescopes. With radar observations, we might be able to see surface details that are only a few meters in size.”
Lots of small asteroids fly past Earth with 15 objects ranging from 30-200 feet (9-162 meters) expected this month alone. But it’s rare for an asteroid the size of Apophis to pass so close. Astronomers at Kitt Peak National Observatory in Tucson discovered Apophis in June 2004 but were only able to track it for two days before technical issues and poor weather prevented further observations. Fortunately, another team in Australia rediscovered it later that year.
As soon as an orbit was determined, Apophis hit the news because calculations revealed it had a 2.7 percent chance of hitting the Earth in 2029. That’s significant! As often happens, additional observations refined the orbit and reduced the risk of impact. Current calculations show that it has a 1 in 100,000 chance of hitting Earth many decades into the future.
Since 2004, we’ve kept our eye on Apophis with optical and radar telescopes, so we know its trajectory with precision. In 2029, there will be a coordinated effort to study its size, shape and composition — and maybe even its interior — with the biggest and best telescopes on Earth. We already know that Earth’s gravity will change the object’s orbit during the close flyby, but it may also alter how fast it spins. Right now it rotates once every 1.3 days. Most exciting is the possibility of sending a spacecraft mission to Apophis.
“Apophis is a representative of about 2,000 currently known Potentially Hazardous Asteroids (PHAs),” said Paul Chodas, director of CNEOS. “By observing Apophis during its 2029 flyby, we will gain important scientific knowledge that could one day be used for planetary defense.”
The asteroid will first become visible to the naked eye in the night sky over the southern hemisphere, flying above Earth from the east coast to the west coast of Australia. It will then cross the Indian Ocean, and by the afternoon in the eastern U.S. it will have crossed the equator, still moving west, above Africa. At closest approach, just before 5 p.m. CDT, Apophis will be over the Atlantic Ocean and will move so fast that it will cross the Atlantic in just an hour. By 6 p.m. CDT, the asteroid will have crossed over the U.S.
Larger telescopes on the ground should show the asteroid’s shape during closest approach, a rare treat. Most asteroids are so small and distant they only appear as points of light.
Apophis will shine brightest around magnitude 3.7 on April 13 during the afternoon hours for the U.S., making Europe and points east the best places to see it in a dark sky. By the time darkness falls over the U.S., the asteroid will have faded to around 14th magnitude! For U.S. observers, the best viewing time will be night before (April 12), when Apophis will shine around magnitude 7.5 low in the southern sky from the tip of Hydra the water snake’s tail. I promise updates if I’m still around!