A NASA spacecraft, recently returned from a mission to asteroid Bennu, has been relaunched to study another asteroid as it approaches Earth’s orbit: Apophis, named after the Egyptian god of Chaos. The space rock is expected to pass within 32,000 kilometres of the Earth's surface on April 13, 2029.
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On December 22, NASA announced it had relaunched its OSIRIS-REx spacecraft to study a 370-metre-diameter asteroid approaching Earth's orbit named Apophis.
In Egyptian mythology, Apophis is a serpent-shaped god and an embodiment of darkness and disorder which seeks to eradicate the world. Thankfully, the asteroid bearing its name has no such intention.
Like Earth, Apophis orbits the sun and now and again, it almost comes into contact with our planet. On April 13, 2029, the 40-50 million ton asteroid is expected to get within 32,000 kilometres of Earth, closer than some artificial satellites – something that has never occurred in recorded history.
Weather permitting, five years from now, Apophis’s passage may be visible to the naked eye in Asia, the Indian Ocean, Australia, most of Africa and Europe, and part of the Pacific Ocean.
Old spacecraft, new mission
After a seven-year journey to the Bennu asteroid, the OSIRIS-REx returned to Earth in September. After the 4 billion kilometre journey, the spacecraft still had a quarter of its fuel left and was thus sent off to intercept Apophis.
Several other destinations, including Venus, were considered though the voyage to Apophis won out. For its new mission, the spacecraft was renamed OSIRIS-APEX (Origins, Spectral Interpretation, Resource Identification, and Security – Apophis Explorer).
The mission will cost an estimated $200 million, according to NASA.
Apophis is an “S-type” asteroid composed of silicate and nickel-iron materials, distinguishing it from “C-type” asteroids, rich in carbon, like Bennu.
When the asteroid gets closer to Earth, OSIRIS-APEX will get within 25 metres of Apophis’s surface to extract as much information as possible. Of particular interest to scientists is "how the surface changes when interacting with Earth's gravity", said Amy Simon, the mission's principal investigator at NASA's Goddard Space Flight Center, in the NASA press release announcing the mission.
Coming into contact with Earth’s gravitational field could trigger earthquakes and landslides on the asteroid, which would then stir up matter. "Apophis’s close encounter with Earth will change the asteroid’s orbit and the length of its 30.6-hour day,” said NASA.
"We know that tidal forces and the accumulation of rubble pile material are foundational processes that could play a role in planet formation," said Dani Mendoza DellaGiustina, principal investigator of the OSIRIS-APEX mission at the University of Arizona. "They could shed light on how we evolved from the debris of the early solar system to full-blown planets."
While most known potentially hazardous asteroids (whose orbits approach within 4.6 million kilometres of Earth) are S-type, Apophis’s proximity to Earth allows NASA to research planetary defence, one of the organisation’s top priorities.
Collision with Earth ruled out
The discovery of the Apophis at Arizona’s Kitt Peak Observatory in 2004 raised concerns and still fuels theories about a potential collision with Earth. "Apophis is coming, that's why they're building their bunkers," reads a post from a user on X.
In the early stages of discovery, the asteroid was classed as a level 4 on the Torino Scale (used to categorise the risks of impacts from near-Earth objects, such as asteroids or comets, on a scale from 0 to 10), the highest-ever classification.
But in December 2004, just a few months after the asteroid's discovery, updated modelling demonstrated the possibility of impact with Earth was nearly zero.
Furthermore, in June 2021, Apophis passed 17 million kilometres from Earth, allowing NASA to adjust calculations and definitively rule out the possibility of a collision.
Dismissing a "Don't Look Up" scenario, NASA officially removed Apophis from its Earth Close Approaches list.
After the asteroid passes, OSIRIS-APEX will operate near it for 18 months to study the changes caused to Aophis by its proximity to the Earth.
This article has been translated from the original in French.
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