Introducing Ramses, ESA’s mission to asteroid Apophis

Today, ESA’s Space Safety program takes another step towards answering this question. The program has received permission to begin preparatory work for its next planetary defense mission – the Apophis Fast Space Security Mission (Ramses).

Ramses will rendezvous with asteroid 99942 Apophis and accompany it on its safe but extremely close flyby in 2029. Researchers will study the asteroid as Earth’s gravity changes its physical characteristics. Their findings will improve our ability to protect our planet from any similar objects found on a collision course in the future.

Apophis

About 375 mi across, roughly the size of a nautical line, asteroid Apophis will pass within 32,000 km of Earth’s surface on April 13, 2029. For a short time, it will be visible to the naked eye in clear skies and dark for about two billion people in most of Europe and Africa and parts of Asia.

Apophis will miss Earth: astronomers have ruled out any possibility of the asteroid colliding with our planet for at least the next 100 years. But the flyby of Apophis in April 2029 is an extremely rare natural phenomenon.

By analyzing the sizes and orbits of all known asteroids, astronomers believe that such a large object approaches Earth only once every 5,000 to 10,000 years. By comparison, a total solar eclipse occurs somewhere on Earth about once every 18 months, and Halley’s comet returns to Earth’s sky every 76 years.

Flyby Apophis 2029 will attract the attention of the whole world and represents a unique opportunity for science, planetary protection and public engagement.

Ramses

ESA’s Ramses spacecraft will rendezvous with Apophis before it passes Earth and accompany the asteroid during the flyby to observe how it is warped and changed by our planet’s gravity.

Patrick Michel Director of Research at the CNRS at the Observatoire de la Côte d’Azur in Nice, comments: “There is still so much to learn about asteroids but, until now, we have had to travel deep into the Solar System to study. and we conduct our own experiments to interact with their surface.”

“For the first time, nature is bringing us one and conducting the experiment itself. All we have to do is watch as Apophis is stretched and squeezed by strong tidal forces that can cause landslides and other disturbances and reveal new material from below the surface.”

Ramses should launch in April 2028 to allow for an Apophis arrival in February 2029, two months before close. To meet this deadline, ESA requested permission to begin preparatory work for the mission as soon as possible using existing resources. This permission was granted by the space safety program board. A decision on whether to fully commit to the mission will be made at the ESA Ministerial Council Meeting in November 2025.

Using an array of science instruments, the spacecraft will conduct a thorough before-and-after study of the asteroid’s shape, surface, orbit, rotation and orientation. By analyzing how Apophis changes during flyby, scientists will learn a lot about an asteroid’s response to external forces, as well as the asteroid’s composition, internal structure, cohesion, mass, density and porosity.

All of these are very important properties for evaluating the best way to knock a dangerous asteroid off a collision course with Earth. Since asteroids are also time capsules formed over four billion years ago, data from Ramses will also provide new scientific insights into the formation and evolution of the Solar System.

NASA, meanwhile, has redirected its OSIRIS-REx spacecraft to Apophis. Due to the limits of orbital mechanics, the newly renamed OSIRIS-APEX will reach Apophis approximately one month after the asteroid’s flyby from Earth.

Researchers predict that Earth’s tidal forces will alter the asteroid’s spin state and possibly trigger earthquakes and landslides. Having Ramses there beforehand will provide a detailed ‘before and after’ view of how Apophis has been changed by his close encounter. Then, after that, having two highly capable spacecraft at Apophis after the flyby will enable additional scientific investigations and measurement of long-term effects.

Rapid detection: a cornerstone of planetary defense

The international collaboration between NASA’s DART asteroid impactor and ESA’s Hera asteroid probe is demonstrating that, in principle, humanity can redirect an asteroid if necessary. But to react to a real threat, we need to be able to build and deploy a response quickly.

Richard Moissl, who heads ESA’s Planetary Defense Office, explains: “Ramses will demonstrate that humanity can deploy a reconnaissance mission to rendezvous with an incoming asteroid in just a few years. This type of mission is a cornerstone of humanity’s response to a dangerous asteroid. First a reconnaissance mission would be launched to analyze the orbit and structure of the incoming asteroid. The results will be used to determine how best to redirect the asteroid or rule out non-impacts before an expensive deflector mission is conducted.

Paolo Martino, leader of ESA’s Ramses effort, adds: “The Ramses mission concept reuses much of the technology, expertise and industrial and scientific communities developed for the Hera mission. Hera demonstrated how ESA and European industry can meet tight deadlines and Ramses will follow her example.”