On April 13, 2029, a “god of chaos” will pass just 32.000 kilometers from Earth. The asteroid Apophis, 340 meters long and shaped like a peanut, will graze our planet in a close encounter that could change its features forever.
An unprecedented cosmic encounter
When Apophis was discovered in 2004, astronomers calculated that it could pass extremely close to Earth in 2029. More detailed observations in 2021 have allowed us to determine its trajectory with greater precision, revealing that the probability of impact were lower than initially estimated.
The planned distance of 32.000 kilometers may seem enormous, but in space it's a breath: some of our artificial satellites orbit further away. While this passage does not pose a danger to Earth, it could have significant consequences for the asteroid itself.
Asteroid Apophis “against” Earth: poor him
Ronald Louis Ballouz, scientist and asteroid researcher at the Johns Hopkins University Applied Physics Laboratory, asked himself an intriguing question: what will happen to Apophis during this close encounter? He tries to explain it himself:
Tiny meteorites constantly bombard the surfaces of asteroids in a process called space weathering. The traces of this bombardment, however, are erased.
That’s right: Astronomers have noticed that asteroids passing close to planets often lack “aged” surfaces. The exact mechanism that removes traces of this aging is not well understood.
The simulation of chaos
To test their hypotheses, Ballouz and a team of international researchers created computational models of Apophis. Because many of the asteroid's physical characteristics are still unknown, the researchers based their models on a similar asteroid, Itokawa, studied in more detail.
I study (I link it here) revealed that two physical processes triggered by the Earth's gravity (we will see them in detail in the next paragraph) will likely sculpt the surface of Apophis during the 2029 encounter:
- Tremors which will begin one hour before the point of closest approach;
- Change in its “somersault” rotation movement.
As Ballouz points out:
Apophis's gravity is about 250.000 times less than Earth's. So we think earthquakes, even those of much lower magnitude, could plausibly shake things up on its surface.
Asteroid Apophis, a Space Domino Effect
The tremors could be strong enough to lift boulders off Apophis's surface. Some might escape its weak gravity, but most will fall back onto the asteroid, creating distinctive surface patterns that a passing spacecraft could identify.
The second process concerns the change in the asteroid's rotation. Apophis does not rotate on a fixed axis or with a regular period; instead, it moves through space. like a badly thrown football. This “somersault” movement will be influenced by the Earth’s gravity, which will cause potential landslides on its surface.
The mission that will verify the predictions
NASA already has a plan to test these hypotheses. The mission OSIRIS-APEX, a reconversion of the probe OSIRIS-REx which collected samples from the asteroid Bennu, will study Apophis during its passage in 2029. The probe will spend 18 months studying the asteroid's chemical composition and mapping its surface.
A broader lesson
According to Ballouz, these results not only predict the fate of Apophis, but “introduce a new mechanism for asteroid surface renewal that could provide an answer to a decades-old puzzle of how close encounters with planets might modify the surfaces of small bodies.”
It will be an unprecedented close encounter, that's for sure: the asteroid Apophis will offer us a unique celestial spectacle and an extraordinary scientific opportunity.
