The asteroid 99942 Apophis, first discovered in 2004, caused a bit of a panic and was briefly considered a risk-impact object. In 2021, the risk was ruled out by new observations — although the asteroid will pass close to Earth, it won’t cause any real problems. But it could give us a good chance to study it.

In a study conducted by astronomers from the Orbital Dynamics Group from the Universidade Estadual de São Paulo (UNESP), Brazil, and from the Universidad Carlos III de Madrid in Spain, researchers suggest that Apophis’ 2029 fly-by offer a learning opportunity, enabling researchers to get an unprecedented view of what’s happening on the asteroid’s surface. 

The distance between us and Apophis is currently about 38,000 kilometers, as tracked by the NASA Jet Propulsion Laboratory (JPL)’s Horizons — about 10 times closer than the Moon is to the Earth. The asteroid’s estimated size is about 340 meters wide, thanks to observations from the Arecibo Observatory data, but its size is not completely clear. 

In the present study, the team simulated what they believe is the approximate size and shape of Apophis to understand what happens in it. It turns out, Apophis is in trouble: the Earth and the Sun are a threat to small particles around the rock because of gravity and the pressure caused by the Sun’s radiation.

Because the asteroid is not a spherical object and has an irregular shape, some particles will be more tilted than others. As it moves about, parts of the asteroid surface with a high slope will face more pressure than the other which sets the course of some particle floating above the surface. It is like the wind on our faces — the air passes on our cheeks, contouring them and applying pressure as it tries to move to behind our heads.

The researchers considered how Earth’s gravity could affect Apophis and they concluded that nothing drastic will change the shape of the asteroid — at most, Earth’s gravitational field will trigger small landslides on the asteroid. Solar radiation, on the other hand, will change things for the particles surrounding Apophis – like tiny moons. Particles with 15 centimeters considering Apophis’ density is low, survive the solar radiation, smaller than that won’t live to tell the story. With a higher density, the surviving chances increase for 5-centimeter particles.

The encounter will provide more information regarding the shape and composition of the asteroid in future studies. Until then, we just keep calendars marked for the closest approach in 2029 where we’ll definitely learn more about Apophis and other asteroids like it.

The study was published in Monthly Notices of the Royal Astronomical Society (MNRAS).