After a relatively low-profile year, October 2024 was a good month for planetary exploration with the launch of two missions. On the 14th, with a slight delay to avoid getting caught in the trajectory of hurricane Milton, the ambitious Europa Clipper left Earth to reach its namesake destination. Clipper is a mission with a long legacy, as is often the case for spacecrafts with multi-billion dollar price tags. First discussed in the late 1990s, it went through several iterations before settling on its final multi-flyby architecture. Given the well-known astrobiological potential of Europa, it is not surprising that NASA has had its eyes set on this moon of Jupiter for a long time, and that it insisted on sending this mission despite the various drawbacks. Clipper will reach Jupiter in April 2030 and is planned to last for four years in Europa’s harsh radiation environment.

In the early 2030s we will therefore have the luxury of two spacecrafts in the Jovian system dedicated to the study of its large moons. In July 2031, the European Jupiter Icy Moons Explorer (Juice) will join Clipper by performing a series of flybys of Europa, Ganymede and Callisto before settling in an orbit around Ganymede, the largest moon of the Solar System, in December 2034. In a curious twist of fate, we will in some sense get a scaled version of the defunct ESA/NASA joint mission Europa Jupiter System Mission–Laplace (EJSM–Laplace), which planned to have two independent but coordinated orbiters — NASA’s around Europa and ESA’s around Ganymede — before its death-by-budget in 2009.

A week before Europa Clipper, it was ESA’s turn with the launch of the Hera spacecraft. Hera is a rather unique concept as it is a follow-up of another mission, NASA’s Double Asteroid Redirection Test (DART), which impacted near-Earth asteroid Dimorphos and changed its orbit around its bigger companion Didymos. The main purpose of the DART mission was to explore how an artificial impactor could change the trajectory of an asteroid in the frame of planetary defence, whereas Hera will look at the long-term structural changes of Dimorphos itself, with some hypotheses suggesting it underwent a full restructuring with resurfacing material from the interior. Hera is planned to arrive at the end of 2026, four years after DART’s impact, when Dimorphos will probably be stable in its new state.

DART and Hera represent the first concrete steps to engage in the active protection of Earth from hazardous objects after many theoretical projects and proofs of concept. Planetary defence is ramping up its efforts, with 2029 as the next pivotal date due to the expected Earth flyby of near-Earth asteroid 99942 Apophis in April of that year. For some time after this asteroid’s discovery in 2004, there was a non-negligible probability (2.7%) that it would hit Earth in its 2029 flyby. Though further calculations have excluded the possibility of an impact, Apophis has remained the poster child of hazardous objects and its passage will be an unprecedented occasion to raise global awareness on the risk of asteroid impacts. For this purpose, a proposal was submitted at the UN to designate 2029 as the International Year of Planetary Defence.

Apophis will still pass within 32,000 km of Earth’s surface (closer than the orbit of geosynchronous satellites), and represents a unique opportunity to study near-Earth asteroids up close. The space agencies are thus gearing up to reach the asteroid during its passage. NASA has converted the sample return spacecraft OSIRIS-REx into OSIRIS-APEX, which will reach Apophis one month after closest approach and will accompany it for 18 months. Unlike OSIRIS-REx, OSIRIS-APEX will not extract any samples from Apophis, but at a certain point during its mission will expose Apophis’s subsurface for analysis by firing its thrusters to remove the surficial regolith. ESA will probably join the efforts with its Rapid Apophis Mission for Space Safety (Ramses) spacecraft, but the timing is tight: the mission will not be officially approved until the Ministerial Council Meeting of November 2025 and will need to be launched at the latest in April 2028. For this reason, and to demonstrate its engagement in the mission, ESA has already approved funds for preparatory work in July 2024 and assigned them in October, ten days after Hera’s launch. Due to these time constraints, Ramses will also probably rely heavily on the existing Hera design — a procedure that ESA has used successfully once before with Venus Express, which was put together in just 4 years from proposal to launch by repurposing the design of Mars Express. Ramses is planned to arrive at Apophis two months before the closest approach and follow it for part of its orbit. OSIRIS-APEX and Ramses will thus be highly complementary, highlighting the synergy between ESA and NASA that is also displayed by the Juice/Europa Clipper and the DART/Hera combinations.

“OSIRIS-APEX and Ramses will thus be highly complementary, highlighting the synergy between ESA and NASA that is also displayed by the Juice/Europa Clipper and the DART/Hera combinations.”