Exploring the Solar System

ESA's science missions are what most people mean when they think of the agency at its best: a probe flying through the tail of a comet, a lander touching down on a moon of Saturn, a spacecraft circling Mars for more than twenty years. This chapter follows the best-known missions in order and includes the story of Beagle 2, a small British lander that rode with ESA to Mars and did not do what was hoped. Mission details are given from general knowledge and flagged where they should be checked, and the chapter stops at a stated cut-off, since some missions are still under way.

Giotto and Halley's Comet (1986)

Giotto was ESA's first deep-space mission. Launched on an Ariane rocket in 1985 (Chapter 4), it flew close to Halley's Comet in March 1986 and returned the first close pictures of a comet's nucleus, the solid core inside the cloud of gas and dust. It passed within a few hundred kilometres of the nucleus at very high speed. Dust damaged the spacecraft and its camera, but it survived, and it was later sent to a second comet. It matters because it showed that Europe could carry out a difficult deep-space mission at a time when the larger agencies were also sending probes to Halley, and the choice to approach so close was a bold one.

Huygens on Titan (2005)

The Cassini–Huygens mission was a joint project of NASA, ESA and the Italian space agency. NASA's Cassini orbited Saturn. ESA supplied the Huygens probe, which separated from Cassini and descended through the thick atmosphere of Titan, Saturn's largest moon, in January 2005. It is generally described as the first landing on a body in the outer Solar System. It sent data back for a short time, and revealed a landscape with channels and what appear to be dry riverbeds. Because the probe was carried and relayed by Cassini, the mission is a good example of how ESA and NASA divide the work (see Partners later in the course).

Mars Express (2003 onward)

Mars Express was ESA's first mission to another planet. The orbiter was launched in June 2003 and entered orbit around Mars in December of that year, and is generally reported to have kept working for more than two decades (check the current status). Its cameras produced detailed pictures of the surface, and its instruments looked for water ice and studied the atmosphere. It was built quickly and at a modest cost, using designs developed for another mission, which is part of why it was seen as a success.

Beagle 2: A British Lander on a European Ride

Mars Express also carried a small lander, Beagle 2, named after the ship that carried Charles Darwin. It was a British project, led by Colin Pillinger of the Open University (a point of interest for anyone who has studied there). Its aim was to land a compact laboratory on the surface and search for signs of life, in particular chemical clues that might have a biological origin. It was not an ESA lander in the way Huygens was: ESA provided the ride to Mars, and the lander itself was developed in Britain, with funding that came from several sources.

The ending is the most interesting part. For more than a decade Beagle 2 was assumed to have crashed. Then, in 2015, high-resolution images from NASA's Mars Reconnaissance Orbiter showed that it had in fact landed safely. It appeared that it had opened only partly, and the unopened panels probably blocked its antenna, so it could not call home. Pillinger had died in 2014, before the discovery. The fate of the lander was therefore a case of an almost-success: it reached the surface and failed to function, probably through a problem in the final stage, and not through the landing.

Rosetta and Philae (2014)

Rosetta was one of ESA's best-known missions. Launched in 2004, it travelled for ten years and in 2014 became the first spacecraft to go into orbit around a comet, 67P/Churyumov–Gerasimenko. It released a small lander, Philae, which in November 2014 touched down on the comet's surface, the first soft landing on a comet. The landing did not go to plan: the lander bounced and came to rest in a shadowed spot, with too little sunlight for its solar panels, and contact was brief. It was located in photographs only in 2016. Rosetta itself ended the mission by landing on the comet in 2016. Even with the problems, the mission was widely described as a major success for the science.

Further Out

• BepiColombo. A joint mission with Japan to Mercury, launched in 2018 and due to enter orbit around the planet in the late 2020s (check the dates).
• JUICE. A mission to study Jupiter's large icy moons, launched in 2023 and due to arrive in the early 2030s (check).
• Solar Orbiter. A mission to study the Sun from close range, run jointly with NASA.
• ExoMars. A Mars programme whose first part, an orbiter, reached Mars in 2016, while the rover has been delayed repeatedly; Chapter 9 returns to its connection with Russia.

What the Missions Have in Common

Most ESA science missions are built through the mandatory science programme (Chapter 3), which gives them a more stable budget than the optional programmes. Many rely on partnerships with NASA, and many have ridden on Europe's own launchers. They are also usually selected through a competitive process among scientists, and then built by industry in the contributing countries. The result is that Europe has been strongest where it picks missions carefully and works with others, and has tended to be less visible than the larger agencies.

Exercises

Next chapter: Telescopes and Looking Back at Earth, which turns from the planets to the stars and to our own planet.