It all started late one night in June 2004 with a small dot that appeared in the optics of the Keith Peak National Observatory in the mountains of Arizona. Astronomer Fabrizio Bernardi and two of his colleagues noted the point as a possible newly discovered asteroid and shortly confirmed its status on a space rock. Originally referred to as the 2004 MN4, the asteroid was intriguing but inconspicuous – an object several hundred meters wide (now estimated at 340 meters) about 170 million kilometers from Earth. “It wasn’t very interesting then,” said Bernardi, now of the Italian space software company SpaceDyS.

Six months later, however, a preliminary estimate of the object’s orbit will shock the world. An analysis at NASA’s Jet Propulsion Laboratory (JPL) in California suggests that the asteroid has one in 37, or 2.7 percent, a chance to hit Earth in 2029. This was the highest probability ever found for a significant asteroid impact in recorded history, and the object was large enough that its impact could devastate entire regions. “It was the most dangerous asteroid ever discovered,” Bernardi recalled. “People were scared.” The asteroid would be called Apophis, after the Egyptian god of destruction.

To make things easier for the world, further improvements to Apophis’ orbit ruled out the possibility of it hitting Earth. for the next century. Yet the asteroid will still be extremely close to us in 2029, when it will pass only 32,000 kilometers from our planet, descending into the orbits of geostationary satellites. “This is an extraordinary meeting,” said Davide Farnokia of the JPL’s Center for Near-Earth Research. Objects of this size come so close to Earth only once “every few thousand years”. Apophis will be as bright as a satellite as it passes through our skies on April 13, 2029, visible to billions of observers with the naked eye in parts of Europe, Africa, Australia and South America – and watched closely before and after its meeting by astronomers around the world. . Asked how many stars will watch this remarkable meeting, JPL’s Marina Brozovic replied simply: “Everyone.”

Apophis’ close approach can offer more than heavenly eye candy. Scientists have eagerly suggested possible missions to meet the site on or around its passage in 2029. Now at least one visitor from our planet has been confirmed: NASA’s OSIRIS-REx spacecraft, originally launched in 2016 with a mission to collect samples from another asteroid, Benu, and bring them back to Earth. OSIRIS-REx is currently on its way home from a successful meeting with Bennu and is scheduled to leave its priceless samples in September 2023. However, the spacecraft will continue to fly through space, leading NASA to approves an extension of $ 200 million to the mission. OSIRIS-REx will now meet with Apophis, becoming OSIRIS-APEX (OSIRIS-Apophis Explorer) in the process. “It’s really exciting,” said Daniela Della Justina of the University of Arizona, who will lead OSIRIS-APEX investigations. “This will be a phenomenal step forward” in our understanding of Apophis.

OSIRIS-APEX will approach Apophis a few months after the asteroid’s close encounter with Earth, conducting initial reconnaissance before entering orbit around the object in August 2029. Mapping the surface, mission scientists will look for any interesting changes caused by the brief fall of Apophis through the gravitational grip of our planet. “Tidal forces could cause small landslides and reveal fresh material,” said Mike Nolan of the University of Arizona, who heads the research team at OSIRIS-REx. “It can be reshaped.”

Surface mapping is just one of the spacecraft’s tasks for its 1.5-year stay near the asteroid; Determining the orbital motion of an object to a scale accuracy is another important goal. This will allow researchers to work out very accurate values ​​for the future trajectory of Apophis – and thus for its future threat to Earth. “Currently, we can predict until 2116,” says Farnokia. OSIRIS-APEX measurements will significantly expand such forecasts, but it is not yet clear exactly how much in the future. Part of the uncertainty is due to the “Yarkovsky effect”, a phenomenon in which uneven heating by sunlight can change the trajectory of the asteroid through space. The spacecraft will measure this effect on Apophis, as well as any changes in the orbital’s orbital speed and rotation resulting from its encounter with Earth in 2029. In any case, Nolan said, the spacecraft’s measurements will allow scientists to “see if our ideas are right or wrong “about how asteroids react to external forces – critical information for planning possible interventions against Apophis and other potentially threatening cosmic rocks.

OSIRIS-APEX may not be the only mission to visit Apophis and it is not the only mission that involves planetary protection. There is a South Korean team also offered a trip to the asteroid with a spaceship launched in 2027 and arriving in January 2029, before flying over the Earth to Apophis to better observe structural changes. And missions with smaller spaceships, such as Apophis Pathfinder, are also presented. Maybe even some private astronauts, in a SpaceX vehicle or otherwise, might consider flying to the asteroid to see human eyes on it, Brozovic said. “I wouldn’t be surprised to fly with a crew of astronauts,” she said. “You can get someone on a space safari.” Meanwhile, NASA is exploring how to deflect an asteroid with its upcoming DART (Double Asteroid Redirection Test) mission later this year, while China hopes to carry out a similar feat around 2025. recently announced mission to divert asteroids. “China is striving to develop its own capabilities in this area,” said Andrew Jones, a space journalist who closely follows China’s space program.

At the end of the main extended mission of OSIRIS-APEX, which is currently scheduled for October 2030, the spacecraft will approach Apophis and launch its engines to the surface from a few meters away. The idea is to take material and look below the surface, revealing more about the composition and structure of the asteroid. The spacecraft also has an extensible arm used to collect samples from Bennu, but planning missions say they have no plans to work with the arm at Apophis at the moment. If NASA welcomes an additional extended mission beyond the first 18 months in Apophis, says Della Justina, using the hand or even landing OSIRIS-APEX on the surface to act as a beacon of tracking could become a viable goal for the “ultimate game” . Probably, she adds, if the spacecraft stays healthy, it could even switch to another asteroid.

So far, Apophis is not an immediate threat to Earth. But in 2029, for a brief moment, he will fire a warning shot as he splashes across our sky, followed closely by at least one curious observer. Learning as much as we can about this site now, and not later, when the situation may be much more urgent, may be the best hope for avoiding some distant future catastrophe. “Apophis is the archetype of the type of asteroid we are worried about,” says Nolan. With OSIRIS-APEX, we may just be ready for the next one.

https://www.scientificamerican.com/article/nasa-spacecraft-will-visit-apophis-once-earth-rsquo-s-deadliest-asteroid-threat/

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