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When an asteroid the size of a cruise ship comes within 20,000 miles of Earth on April 13, 2029, it won’t be alone.
The European Space Agency (ESA) has announced that its new Ramses spacecraft may accompany the asteroid Apophis before and after its safe, albeit relatively close, pass by Earth.
The space rock, 1,230 feet (375 meters) in diameter, will come closer to our planet than any satellite in its orbit and 10 times closer than the moon. Apophis will come so close to Earth that it will be visible to the naked eye of about 2 billion people living in most of Europe, Africa and parts of Asia.
To arrive at Apophis in February 2029, Ramses is scheduled for launch in April 2028. According to the agency, preparatory work for the mission has already begun, using existing resources to achieve this ambitious goal. However, the final decision to commit to the mission will be taken at the ESA Council of Ministers meeting in November 2025.
First discovered in 2004, Apophis is named after the Egyptian god of chaos and darkness. It is believed to be shaped like a peanut. Astronomers initially worried that the space rock could hit Earth in 2029 and 2068, but subsequent observations have ruled out any risk of Apophis posing a threat to Earth for the next century, according to NASA’s Center for Near-Earth Object Studies.
Scientists at the center use radar and telescopes to study near-Earth objects and understand the dangers they pose to the planet. They maintain a risk list and track asteroids with orbits that bring them close to our world — close enough to raise concerns about a potential impact.
Although Apophis is not currently a threat, the close flyby offers a rare opportunity. Astronomers believe an asteroid of this size would only come this close to Earth once every 5,000 to 10,000 years.
ESA and NASA plan to use this unique cosmic event to further our understanding of what happens when space rocks interact with Earth’s gravity by studying Apophis from the closest possible vantage point. Each agency will send a spacecraft to fly by the asteroid and track it.
“There is still so much we have 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 surfaces,” said Patrick Michelastrophysicist and research director at the National Center for Scientific Research in France, in a statement. “For the first time ever, nature is bringing one to us and doing the experiment itself.”
Up close a rocky asteroid
Apophis is interesting because it is an S-type, or rocky, asteroid. It differs from other space rocks visited by NASA missions, including Bennu, which is a C-type, or carbonaceous, asteroid.
C-type asteroids are composed of clay and silicate rock, while S-types are composed of silicate materials and nickel-iron.
Rocky asteroids are among the most common class of potentially hazardous asteroids that pose a threat to our planet. Understanding their composition and other details that can only be obtained by close flybys can help space agencies determine how best to deflect such asteroids if they are expected to be on a collision course with Earth.
The Ramses mission is unique because it would arrive at Apophis before the space rock passes our planet and then essentially ride along to record observations. This data would allow astronomers to see how the asteroid is being altered by our planet’s gravity.
“All we need to do is watch as Apophis is stretched and compressed by strong tidal forces that could trigger landslides and other disruptions and reveal new material from beneath the surface,” Michel said.
The forces exerted by Earth’s gravity can also cause earthquakes on the asteroid.
The spacecraft would carry a suite of instruments to measure the asteroid’s shape, surface, orientation, and orbit. In addition, changes in the asteroid observed during the flyby could shed light on Apophis’ composition, mass, density, porosity, and internal structure.
By monitoring Apophis during and after its approach to Earth, scientists can see if there are any shifts in the asteroid’s orbit that could affect its chances of hitting Earth in the future. They can also see if there are any changes in the asteroid’s rotation rate or on its surface.
“Ramses will demonstrate that humanity can conduct a reconnaissance mission to encounter an incoming asteroid within a few years,” Richard Moissl, head of ESA’s Planetary Defence Office, said in a statement. “This type of mission is a cornerstone of humanity’s response to a hazardous 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.”
When spaceships work together
While Ramses still needs to be designed, built and ultimately approved by ESA next year, NASA’s OSIRIS-APEX mission, formerly known as OSIRIS-REx, is on its way to catch up with the asteroid just after its close approach to Earth. Together, the two spacecraft will be able to collect valuable data that will paint a complete picture of how Apophis will change in response to its close approach to Earth.
Called OSIRIS-REx, the spacecraft made a seven-year return trip to the Earth-grazer Bennu, spending time studying, landing and collecting samples from the space rock.
The mission successfully returned to Earth in September, when NASA collected the first asteroid sample in space, and was renamed to honor its new purpose: Origins, Spectral Interpretation, Resource Identification and Security-APophis Explorer.
The spacecraft will not be able to collect a sample from Apophis, since the sample collection head was in the capsule that carried the Bennu sample back to Earth. But OSIRIS-APEX will use its gas engines in an attempt to kick up dust and small rocks on and below the surface of Apophis to study.
“Apophis offers a great opportunity to show the world the best of international cooperation, with two multi-agency missions working together for the best of science and planetary defense,” said Michel.
NASA and ESA have previously collaborated on other asteroid missions.
In September 2022, NASA’s DART mission intentionally crashed a spacecraft into Dimorphos, a moon-asteroid orbiting a larger parent asteroid known as Didymos. The historic test was the first to successfully alter the motion of a celestial body. Neither space rock posed a threat to Earth, but the binary asteroid system was a perfect target to test deflection technology because Dimorphos is comparable in size to asteroids that could endanger our planet.
ESA’s Hera mission will launch a spacecraft in October to study the aftermath of the DART impact. The spacecraft will reach the asteroid pair by the end of 2026. Together with two CubeSats, the mission will study the composition and mass of Dimorphos and determine how it was transformed by the impact. It will also determine how much momentum was transferred from the spacecraft to the asteroid.
“The Ramses mission concept reuses much of the technology, expertise and industrial and scientific communities developed for the Hera mission,” said Paolo Martino, Hera space manager who will also work on the Ramses mission, in a statement. “Hera showed how ESA and European industry can meet strict deadlines and Ramses will follow its example.”
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