On April 13, 2029, the "big guy" asteroid Apophis will pass by the earth and stage a "shock encounter" without any danger. Apophis is a near-Earth asteroid that orbits between Venus and Mars. Its name comes from the god of destruction and chaos in Egyptian mythology, Apep, so it is also called the "Destroyed God Star".

　　This asteroid, once listed as a "potential threatening celestial body", was initially caused scientists to sweat, just like the recently discovered asteroid 2024 YR4. But as observations increased, researchers finally confirmed that the possibility of it colliding with the Earth was slim.

RAMSES mission art drawing. Image source: ESA official website

OSIRIS-APEX will use its thruster to stir the rock and dust on the surface of Apophis so that scientists can see what is below its surface (video screenshot). Image source: NASA official website

　　The British website of "New Scientist" pointed out in a report on April 17 that although the collision alarm has been lifted, the astronomical incident has still attracted the attention of space agencies in many countries. NASA, the European Space Agency (ESA) and the Japan Aerospace Research and Development Agency (JAXA) are preparing to send probes to conduct research on it. These probes will not only unveil the mystery of Apophis, but also hope to help humans master the technology of deflecting dangerous asteroids.

　　A good observation opportunity is rare in a thousand years

　　Apophis caused quite a lot of panic in 2004. Early orbital calculations show that the probability of this asteroid, about 450 meters long and about 340 meters in diameter, hitting the earth in 2029 is 2.7%. Fortunately, subsequent observations corrected this prediction: on April 13, 2029, Apophis will fly over the earth at close range without any danger.

　　By then, the asteroid will be only 32,000 kilometers away from the Earth, which is closer than a stationary orbit satellite (36,000 kilometers away from the Earth). If the weather is good, observers in Europe and Africa can even see it with their naked eyes. Richard Binzel, a researcher at the MIT Institute, described that when Apophis is brightest, it can even "light up the dusk of the earth."

　　ESA said that such a huge celestial body flew over the earth at such a close distance, its scientific research value is self-evident. To this end, the United Nations has designated 2029 as the "International Year of Asteroid Consciousness and Planetary Defense."

　　Scientists plan to use observation methods such as ground radar to accurately measure the size, shape and trajectory of Apophis. In addition, space agencies in many countries have launched or are preparing to launch probes to observe the entire process in the front, middle and late stages of Apophis flying over the earth to obtain the most complete data.

　　OSIRIS-APEX detector departure

　　Asteroids are rare "space visitors" that can help scientists unravel the mysteries of planet formation and the origin of life. Many researchers believe that the early water and life on Earth are likely to have come from the impact of these asteroids and comets rich in water and organic matter. Detection of such asteroids not only helps understand the early component information and evolutionary processes of the solar system, but also may find clues to the origin of life on Earth.

　　NASA's OSIRIS-APEX detector is already on the way to "meet" Apophis. In fact, this mission is the "sequel" of NASA's first asteroid sampling return mission OSIRIS-REx. The OSIRIS-REx was launched on September 8, 2016 and collected samples from the near-Earth asteroid "Benu" and sent back to Earth. This time, OSIRIS-REx was renamed OSIRIS-APEX and headed towards Apophis again.

　　Dany Mendoza Drajustina, the team's lead researcher, said that although the mission cannot collect samples as it did last time, it carries a high-precision camera and various scientific instruments that can deeply explore Apophis.

　　According to the plan, the detector will arrive at a place 5 million kilometers away from Apophis on April 2, 2029 and start long-distance observation. When Apophis is closest to Earth on April 13, the probe will closely observe the impact of Earth's gravity on Apophis' rotation; on June 5, the probe will enter orbit around Apophis and start an 18-month close-up journey; finally, the probe also plans to launch a propulsion system to disturb the asteroid and even try to land on its surface.

　　Japanese and European space missions are ready to be launched

　　ESA recently announced the "Quick Apophis Space Security Mission" (RAMSES) to explore Apophis. Whether this task can be implemented will be finalized by the ESA Council of Ministers in November 2025. If approved, the detector will set off in April 2028 and is expected to "successfully meet" with Apophis before February 2029 and conduct at least half a year of companion flight observations.

　　RAMSES project manager Paul Martino explained that they expect the Earth's tidal forces to change the rotation state of the asteroid and could trigger earthquakes and landslides. To monitor these changes comprehensively, RAMSES is equipped with a high-definition camera and will release two cube satellites with different functions: one carries ground penetrating radar to scan the internal structure of the asteroid; the other may install seismometers on the surface of the asteroid to detect its surface activity.

　　JAXA's DESTINY+ mission is scheduled to be launched in 2028, with its main goal being to study the active asteroid "Faeton". DESTINY+ will arrive at "Faeton" in 2030, but will "visit" Apophis in early 2029.

　　In addition, at a seminar held in Tokyo in April, Kevin Walsh and others from the Southwest Institute of the United States proposed the Apophis crater experiment (ACE), that is, impacting Apophis, and then let OSIRIS-APEX observe the impact of the impact and the impact on the Apophis orbit.

　　Although this reminds of the first human asteroid orbit deflection experiment - a double-asteroid steering test, the purpose of ACE is not to significantly change the orbit, but to observe the asteroid's response to collisions and reveal its internal structural and mechanical properties. (Reporter Liu Xia)

[Editor in charge: Zhu Jiaqi]