ESA Gets Go Ahead to Begin Work on Apophis Mission

To the delight of planetary defense experts, ESA is beginning work on a probe to visit the asteroid Apophis before it reaches Earth in 2029. Apophis will not impact Earth, but its very close approach presents a unique opportunity for scientific analysis not only by ground-based instruments, but spacecraft that can obtain before and after data to assess how it changes as it passes by. NASA already has a probe that will study Apophis afterwards and ESA now is leading an international team to study the before phase.

ESA announced this week that it has permission to begin preparatory work on the Rapid Apophis Mission for SpacE Safety — RAMSES. ESA formally approves new missions only at triennial Ministerial Council meetings, but the next one isn’t until November 2025 and that would be too late to start designing and building a spacecraft that needs to launch by April 2028. ESA has won approval to begin work with existing resources while awaiting a formal commitment next year.

During a meeting of NASA’s Small Bodies Assessment Group (SBAG) last week, ESA’s Paolo Martino previewed the RAMSES news and seemed confident the formal commitment will come.

Apophis will fly past Earth on April 13, 2029 coming as close as 32,000 kilometers, about the altitude where geostationary satellites orbit the Earth. Scientists are confident the roughly 375-meter diameter asteroid will not hit Earth and are eager to use this opportunity to learn more about it.

Planetary defense refers to protecting Earth from asteroids and comets that might cause regional or global devastation. Apophis was discovered in 2004 as part of efforts to locate Potentially Hazardous Asteroids (PHAs) early enough to provide warnings if any are inbound.  Scientists are certain Apophis will not hit Earth.

Apophis will be visible to the naked eye in Europe, Africa and parts of Asia. Ground-based telescopes and radars will get a really good look, but scientists want detailed data before it gets here and after it leaves so they can better understand its composition and how it’s affected by Earth’s gravity. That could help in determining methods to deflect future asteroids that might be on a collision course.

NASA is taking care of the after phase using an existing spacecraft. Known as OSIRIS-REx when it was collecting and returning samples of the asteroid Bennu to Earth, the main spacecraft is still in space and has been given a new name, OSIRIS-APophis EXplorer (OSIRIS-APEX), and a new mission to rendezvous with Apophis in June 2029, two months after its Earth flyby. It will study Apophis for 18 months, going into orbit and dipping close to the surface and firing its thrusters to stir up material and reveal what’s below.

Getting money to pay for another spacecraft to study Apophis before it gets here is a challenge that’s been taken up by the international planetary defense community. ESA is stepping forward with RAMSES.

Martino told SBAG they are targeting April 2028 for launch with arrival at Apophis in February 2029. “We expect to be able to start characterization of the asteroid no later than first of March” giving about 40 days to study it before Earth arrival. He said the timing is the “best compromise” between launching as late as possible to allow time for spacecraft development and arriving as early as possible to maximize data collection.

ESA and NASA are coordinating the OSIRIS-APEX and RAMSES observations and discussing the possibility of NASA providing one of the RAMSES instruments. The Japan Aerospace Exploration Agency, JAXA, may also provide an instrument and possibly launch on an H3 rocket. The Indian and Korean space agencies, ISRO and KASI, also have expressed interest, Martino said.

Demonstrating the ability to quickly design, build and launch a spacecraft to get a close look at an approaching asteroid was one of the recommendations of the most recent planetary science Decadal Survey from the National Academies of Sciences, Engineering, and Medicine — a “rapid response” capability.

SBAG has been urging NASA to launch its own mission, perhaps using two small spacecraft called Janus that are in storage. They were supposed to ride along with the Psyche mission, but Psyche’s launch was delayed a year and its revised trajectory was in the wrong direction for Janus to accomplish its task. Even though they are already built, NASA officials have indicated their highly constrained science budget is unlikely to accommodate retrofitting and launching them for this purpose.

This will be ESA’s second planetary defense mission. The first, Hera, is scheduled for launch in October. It will return to the double-asteroid Didymos and Dimorphos to investigate the after-effects of NASA’s DART mission in 2022.

Dimorphos is a tiny moon of Didymos. DART, the Double-Asteroid Redirection Test, rammed into the moon to determine if the kinetic impact could change its orbit as a test of how asteroids might be diverted in the future. NASA scored a bulls-eye in September 2022. Images of the resulting debris trail were captured by an Italian cubesat, LICIACube, that was along for the ride and ground-based telescopes, but Hera will get a close-up view of the aftermath two years later.

Martino is leading the RAMSES effort and also is spacecraft manager for Hera. His presentation to SBAG was the first indication RAMSES had a green light. SBAG member Richard Binzel, a planetary scientist at MIT and vigorous proponent of sending missions to Apophis, called it “terrific news” and a testament to international cooperation.

“Congratulations to all our ESA partners who put an enormous effort to get to this point. It’s really terrific news. I just want to comment [that] it’s a very nice balance because DART was NASA followed by ESA, and in this case, for Apophis, it will be the symmetry of ESA doing the pre-encounter and NASA doing the post-encounter. So there’s beautiful international collaboration symmetry here.” — Richard Binzel

Asteroids are rocks in space. When they fall through Earth’s atmosphere they are called meteors and any bits that reach the surface are meteorites. Small ones like the Perseid meteor showers create delightful displays, but slightly larger meteors like the one that exploded over Chelyabinsk, Russia in 2013 can be damaging. The real concern is those 140- meters or more in diameter that can result in regional or global catastrophe. Scientists believe a 10-15 kilometer wide asteroid hit Earth 65 million years ago and led to the extinction of the dinosaurs when massive amounts of dust spewed into the atmosphere, blocking sunlight and cooling the planet.