Renowned deep sea explorer and film maker James Cameron made the deepest ocean dive today in a one-man submarine. Journeying 7 miles down into the Pacific Ocean’s Mariana Trench, his exploit illustrated the adage that anything that can go wrong will go wrong. For planetary scientists, it may also foretell some of the challenges of returning samples from a destination that is much further away — Mars.

National Geographic explained the problems that beset the mission after Cameron successfully returned to the surface. The mission duration was cut in half because of a hydraulic fluid leak. Expected to explore the area for about six hours, he decided to resurface after three as the fluid interfered with his efforts. “I saw a lot of hydraulic fluid come up in front of the port. The port got coated with it.” he told National Geographic News. The leak also prevented him from picking up any rock or animal samples with a robot arm, and he “lost a lot of thrusters. I lost the whole starboard side.”

The goal of returning rock and animal samples was hampered before the dive began when the submarine’s sonar system malfunctioned. The original plan was to send down a baited “lander” to attract deep sea animals, but since the sonar on the submarine was not working, the team decided there was no point in launching the lander because Cameron would not be able to find it. The location where he arrived was devoid of life. “It was bleak….It looked like the Moon,” he was quoted as saying.

Planetary scientists have discussed for years the fact that returning samples from Mars is not only a technical and cost challenge, but relies on not simply returning any samples, but the right samples to provide the information they seek. Plans to launch a series of missions to collect and store (“cache”) samples from a variety of locations for eventual return to Earth are on hold indefinitely because of budget decisions.

Cameron is not deterred, however. His parting comment to National Geographic News was: “Next dive. Gotta leave something for the next dive.” That will be a lot easier for him than sending more Mars probes if failures are initially encountered. Not only are Mars probes very expensive, but Mars and Earth are correctly aligned in their orbits about the Sun only once every 26 months.