16/07/2024
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Thirty years ago, on July 16, 1994, astronomers watched in awe as the first of many pieces of the Shoemaker-Levy 9 comet slammed into Jupiter with incredible force. The event sparked intense interest in the field of planetary defense, as people wondered, “Is there anything we can do to prevent this from happening on Earth?”
Today, ESA’s Space Safety Programme is taking another step towards answering this question. The programme has been given permission to begin preparatory work for its next planetary defence mission: the Rapid Apophis Mission for Space Safety (Ramses).
Ramses will encounter and accompany asteroid 99942 Apophis during its safe but exceptionally close flyby of Earth in 2029. Researchers will study the asteroid as Earth’s gravity alters its physical characteristics. Their findings will improve our ability to defend our planet from any similar object on a collision course in the future.
Apophis
The asteroid Apophis has a diameter of about 375 meters, about the size of a cruise ship, and will pass at a distance of 32,000 kilometers from the Earth’s surface on April 13, 2029. About two billion people in large parts of Europe, Africa and parts of Asia will be able to see the asteroid briefly with the naked eye under clear, dark skies.
Apophis will miss Earth: Astronomers have ruled out the chance of the asteroid colliding with our planet in the next 100 years. But the Apophis flyby in April 2029 is an extremely rare natural phenomenon.
By analyzing the sizes and orbits of all known asteroids, astronomers believe that an object of this size would only pass this close to Earth once every 5,000 to 10,000 years. For comparison, a total solar eclipse occurs somewhere on Earth about once every 18 months, and Halley’s Comet returns to Earth’s skies every 76 years.
The 2029 flyby of Apophis will capture the world’s attention and represents a unique opportunity for science, planetary defense, and public engagement.
Apophis orbit inferred by Earth’s gravity – NEO Toolkit
Ramses
ESA’s Ramses spacecraft will rendezvous with Apophis before it passes Earth, accompanying the asteroid during the flyby to observe how it is deformed and warped by our planet’s gravity.
Patrick Michel, director of research at the CNRS at the Observatoire de la Côte d’Azur in Nice, notes: “There is still so much we have to learn about asteroids, but until now we had to travel deep into the solar system to study them and perform experiments ourselves to interact with their surfaces.”
“For the first time ever, nature is bringing one to us and running the experiment itself. All we have to do is watch as Apophis is stretched and squeezed by powerful tidal forces that can trigger landslides and other disruptions and reveal new material from beneath the surface.”
ESA’s Ramses mission to asteroid Apophis
Ramses is scheduled to launch in April 2028, with an arrival at Apophis in February 2029, two months before the approach. In order to meet this deadline, ESA has requested permission to start the mission preparation work as soon as possible using existing resources. This permission has been granted by the Space Safety Programme Board. The decision on whether to fully implement the mission will be taken at the ESA Ministerial Council meeting in November 2025.
Using a suite of scientific instruments, the spacecraft will perform a thorough before-and-after study of the asteroid’s shape, surface, orbit, rotation, and orientation. By analyzing how Apophis changes during the flyby, scientists will learn a great deal about an asteroid’s response to external forces, as well as its composition, internal structure, cohesion, mass, density, and porosity.
These are all very important properties for judging how best to divert a dangerous asteroid from a collision course with Earth. Because asteroids are also time capsules that formed more than four billion years ago, data from Ramses will also provide new scientific insights into the formation and evolution of the solar system.
Radar observations of Apophis rule out future impact
NASA, meanwhile, has rerouted its OSIRIS-REx spacecraft to Apophis. Due to the limitations of orbital mechanics, the newly renamed OSIRIS-APEX will arrive at Apophis about a month after the asteroid’s Earth flyby.
Researchers expect that Earth’s tidal forces will change the asteroid’s spin, potentially triggering earthquakes and landslides. Having Ramses there in advance will provide a detailed “before and after” view of how Apophis is changed by the close encounter. Then, after the flyby, two highly capable spacecraft will fly by Apophis to allow for additional science and measurement of long-term effects.
Rapid reconnaissance: a cornerstone of planetary defense
The international collaboration between NASA’s DART asteroid impactor and ESA’s Hera asteroid detective shows that humanity can, in principle, divert an asteroid if necessary. But to respond to a real threat, we need to be able to quickly build and deploy a response.
Richard Moissl, Head of ESA’s Planetary Defence Office, explains: “Ramses will demonstrate that humanity can deploy a reconnaissance mission to encounter an incoming asteroid within a few years. This type of mission is a cornerstone of humanity’s response to a dangerous asteroid. A reconnaissance mission would be launched first to analyse the orbit and structure of the incoming asteroid. The results would be used to determine how best to redirect the asteroid or to rule out non-impacts before developing an expensive deflector mission.”
Paolo Martino, who leads ESA’s Ramses effort, added: “The Ramses mission concept reuses much of the technology, expertise and industrial and scientific communities developed for the Hera mission. Hera showed how ESA and European industry can meet tight deadlines and Ramses will follow its example.”
Hera approaches the asteroids of Didymos