3.4.3 Cassini’s sacrifice
The Cassini spacecraft delivered the Huygens probe to the surface of Titan in 2004 (Figure 22). However, it was launched seven years earlier, in 1997. At that time, it was considered highly unlikely that life could survive in the extreme cold of Titan’s surface and the risk of contamination of the moon was low. For this reason, it was classified as a Category II mission (interesting for origin of life but low risk of contamination).
By the time Cassini reached the end of its mission, much more was known about the potential for water on nearby moons, such as Enceladus. With the mission initially destined to be adrift in the Saturnian system once operations had ended, the possibility of it crashing into an astrobiologically important body was therefore high. To avoid this, while Cassini was still operating, it was programmed for a controlled descent into Jupiter’s atmosphere where it was destroyed, losing contact with Earth in 2017 and avoiding a collision and contamination event elsewhere.
Cassini’s example may seem drastic, but our understanding of the Solar System is constantly changing, and planetary protection requirements need to evolve to accommodate this.