Asteroid Apophis Is Swinging by This Weekend to Taunt Us

Potentially hazardous asteroid Apophis, as imaged on March 2, 2021.
Potentially hazardous asteroid Apophis, as imaged on March 2, 2021.
Image: Gianluca Masi/The Virtual Telescope Project

An asteroid with a small chance of hitting Earth in 2068 will swing past our planet in the coming days, providing a rare opportunity for astronomers to observe this potentially hazardous object.


For its current sojourn around the Sun, asteroid 99942 Apophis will make its closest approach to Earth on March 6, 2021, during which time it will come to within 10.5 million miles (16.9 million kilometers) of our planet, according to a bulletin put out by astronomers with Goldstone Solar System Radar.

That’s a reasonably big distance—about 44 times the distance to the Moon—so there’s no need to worry.

Apophis won’t be visible to the unaided eye, but the close approach is of interest to radar astronomers, who will be monitoring the large asteroid as it zips past Earth. This will be our last opportunity to study the potentially hazardous object before an even closer approach several years from now. On Friday April 13, 2029, Apophis will come to within 19,000 miles (31,000 kilometers) of Earth—that’s about one-tenth the distance of the Earth to the Moon—during which time it will be visible to the unaided eye.

Astronomers say there’s no chance that Apophis will smash into our planet in 2029, nor in 2036 when the asteroid is scheduled to make yet another close approach, but the same cannot be said for the 2068 encounter.

Apophis, discovered back in June 2004, is currently ranked third on NASA’s list of potentially hazardous near-Earth objects (NEOs). Estimates of a potential collision in 2068 vary, ranging from a 1 in 150,000 chance to 1 in 530,000. Those are exceptionally slim odds, but slim is not the same as zero.


Indeed, a collision with this 1,100-foot-wide (350 meters) object would be devastating. Apophis, with the width of three football fields, would unleash the equivalent of 1,150 megatons of TNT. For scale, imagine 3,800 Hiroshima-like atomic bombs going off at the same time. Such an event would result in both local and global devastation, including the onset of an impact winter.

Collisions of this magnitude are rare but they are expected to happen about once every 80,000 years. By comparison, asteroids similar in size to the one that caused the extinction of all non-avian dinosaurs are expected about once every 250 million to 730 million years. Known as the Chicxulub impactor, the dino-killing asteroid measured over 10 miles (16 km) wide, and it crashed into the Yucatan peninsula approximately 66 million years ago.


Which brings us back to Apophis and its upcoming close approach. Astronomers have been preparing for the upcoming close encounter, and their efforts are being coordinated through the 99942 Apophis 2021 Observing Campaign organized by the International Asteroid Warning Network (IAWN).

Astronomers at NASA’s Goldstone Deep Space Communications Complex in California will be watching, as will a group at the Green Bank Telescope in West Virginia. Regrettably, this close approach would have been a perfect opportunity for the Arecibo Observatory in Puerto Rico, but this famous radar dish collapsed late last year.


Radar observations of Apophis in the coming days “should improve knowledge of the spin state and shape” of the object, according to the Goldstone observatory. Refined measurements will expose potential changes to the asteroid when it flies by in 2029 (Earth’s gravitational tug is expected to alter the asteroid and its trajectory in various ways), and even “enable prediction of the orientation of the asteroid after the 2029 encounter,” per Goldstone. The primary objective of the 2021 campaign is to “reduce uncertainties in the orbit, spin state, and 3D shape” of the object.


This latest flyby is important, but the 2029 approach will be the real deal. Scientists and engineers are already planning for this rare opportunity, including potential missions to park spacecraft near the asteroid and send probes to the surface. We’ll learn a lot about Apophis and asteroids in general from these missions, but we’ll also get a better sense of the risk posed by the 2068 encounter.

For now, we’ll just have to glare at this menacing object from a distance.


George is a senior staff reporter at Gizmodo.


Darwinian Man

“Spin state”? Do quantum mechanics apply here?