According to the ESA’s Near-Earth Objects Coordination Center (NEOCC), 35,264 known asteroids regularly cross the orbit of Earth and the other inner planets. Of these, 1,626 have been identified as Potentially Hazardous Asteroids (PHAs), meaning that they may someday pass close enough to Earth to be caught by its gravity and impact its surface. While planetary defense has always been a concern, the comet Shoemaker-Levy 9 slamming into Jupiter in 1994 sparked intense interest in this field.
In 2022, NASA’s Double-Asteroid Redirect Test (DART) mission successfully tested the kinetic impact method when it collided with Dimorphos, the small asteroid orbiting Didymos. Today, the ESA Space Safety program is taking steps to test the next planetary defense mission – the Rapid Apophis Missin for Space Safety (RAMSES). In 2029, RAMSES will rendezvous with the Near Earth Asteroid (NEA) 99942 Apophis and accompany it as it makes a very close (but safe) flyby of Earth in 2029. The data it collects will help scientists improve our ability to protect Earth from similar objects that could pose an impact risk.
Discovered in 2004, Apophis is an irregularly shaped asteroid measuring about 375 m (410 yards) across. At the time, observations indicated there was a small risk that it would impact Earth in 2029, 2036, or 2068. Given its size and the devastating effect an impact would have, astronomers decided to name it after the Egyptian god of chaos and destruction. While astronomers have since ruled out the possibility of a collision for at least the next century, Apophis will pass within 32,000 km (~19,885 mi) of Earth’s surface on April 13th, 2029.
Radar observations of Apophis rule out future impact. Credit: NASA/JPL-Caltech and NSF/AUI/GBO
At this distance, the asteroid will be close enough to be visible to the naked eye to roughly two billion people across much of Europe, Africa, and parts of Asia. Based on analyses of the size and orbits of all known asteroids, astronomers believe that objects this large pass this close to Earth only once every 5,000 to 10,000 years. The RAMSES spacecraft will rendezvous with Apophis before it makes its closest pass to Earth and follow behind, monitoring it with a suite of scientific instruments to see how Earth’s gravity changes it.
This will consist of conducting before-and-after surveys of the asteroid’s shape, surface, orbit, rotation, and orientation. Based on this comparative analysis, scientists will learn more about how an asteroid’s fundamental characteristics – its composition, interior structure, cohesion, mass, density, and porosity – respond to external forces. These properties are vital for determining how to knock a PHA off course so it does not collide with Earth. Patrick Michel, the Director of Research at the Centre national de la recherche scientifique (CNRS) and the Observatoire de la Côte d’Azur in Nice, explained in an ESA press release:
“There is still so much we have yet to learn about asteroids but, until now, we have had to travel deep into the Solar System to study them and perform experiments ourselves to interact with their surface. For the first time ever, nature is bringing one to us and conducting the experiment itself. All we need to do is watch as Apophis is stretched and squeezed by strong tidal forces that may trigger landslides and other disturbances and reveal new material from beneath the surface.”
The ESA recently secured permission from the Space Safety Program board to begin preparatory work on the mission so it can launch by April 2028. This deadline is necessary, so the mission is to be ready to launch and rendezvous with Apophis in orbit by February 2029. The final decision to commit to the mission will be made at the ESA’s Ministerial Council Meeting in November 2025. In the meantime, NASA has redirected its newly renamed OSIRIS-APEX spacecraft towards Apophis, which will arrive one month after the asteroid makes its flyby.
Apophis orbit diverted by Earth’s gravity – NEO Toolkit Space Safety Apophis orbit diverted by Earth’s gravity, Credit: ESA
Since asteroids are leftover material from the formation of the Solar System (ca. 4.5 billion years ago), this rendezvous is also an opportunity to obtain data that could provide new insights into planetary formation and evolution. This makes the 2029 flyby an extremely rare opportunity for astronomy, asteroid science, planetary defense, and for engaging billions of people worldwide. It will also be an opportunity for international collaboration, as previously demonstrated by the DART and the ESA’s Hera missions – the former redirected Didymos while the latter confirmed a change in orbit.
Last, but not least, the RAMSES mission will test the ability of space agencies to build and deploy an asteroid response quickly. As Richard Moissl, heading ESA’s Planetary Defence Office, explained:
“Ramses will demonstrate that humankind can deploy a reconnaissance mission to rendezvous with an incoming asteroid in just a few years. This type of mission is a cornerstone of humankind’s response to a hazardous asteroid. A reconnaissance mission would be launched first to analyse the incoming asteroid’s orbit and structure. The results would be used to determine how best to redirect the asteroid or to rule out non-impacts before an expensive deflector mission is developed.”
Further Reading: ESA
