Protecting the Solar System

When the Martian Moons eXploration (MMX) mission reaches Phobos and Deimos, it will probe the development of habitability in the Solar System. But searching for the origins of life requires extreme caution to ensure what we find is not contaminated by our own planet’s versatile population.

PPOSS tutorial attendees at ISAS. (Credit: PPOSS)

Exactly how the Martian moons formed remains a mystery. The two small satellites may be captured asteroids or the agglomeration of debris from an impact with Mars. However, both scenarios would reveal information on how the early Earth became habitable. The discovery of hydrated minerals or organic molecules could provide clues to how water and the ingredients for life filter through to terrestrial worlds. Combined with current and future missions to the icy moons of the gas giants or Mars itself, ISAS plans to build up a map of the beginnings of planet habitability.

But investigating the beginnings of life raises an important concern: how can we protect celestial bodies from being contaminated with microbes from Earth? Such contamination might not only endanger any life we find, but a false positive result would invalidate the science we have travelled across space to obtain.

While Phobos and Deimos are not thought to harbour environments suitable for life, the story is different for Mars. Below the surface of the red planet may exist conditions suitable to support water and microbial life. With the orbit of Phobos taking it within 6,000km of Mars’s sensitive surface, the risk of contamination is taken very seriously by our mission team.

The prospect of cross-contamination between Earth and other Solar System worlds is a subject of international importance. Japan is one of 110 countries that has signed the ‘Outer Space Treaty’ to take appropriate measures to prevent contamination of other celestial bodies.

On May 11 – 12, ISAS hosted members of the Planetary Protection of the Outer Solar System Project (PPOSS) from Europe and the USA to discuss the precautions missions must take to avoid contaminating other worlds.

“Spores are everywhere,” warned Petra Rettberg from the German Aerospace Center (DLR). “and they are very resistant against many extremes.”

A concern for the Martian Moons eXploration spacecraft is whether a failure during its journey could result in a crash-landing on Mars. Mission specialists must prepare a detailed analysis of the probability of such an occurrence before launch, considering the possible sources for failure and the resulting trajectory.

For the Hayabusa2 mission to the asteroids, ISAS scientists and engineers had to present a similar detailed plan. Considering both system failure and possible damage from an asteroid impact, it was concluded the probability of Hayabusa2 hitting the Martian surface was just 0.0000000000001; far below the required threshold for contamination risk of 0.0001.

Before the anticipated launch in 2024, the Martian Moons eXploration mission will be assigned a category for both the outward and return journey, depending on the likelihood of contamination. The category choice will determine the requirements that the mission team will need to fulfil to guard against contamination. As ISAS continues to trace the history of water and other volatiles essential for life through our Solar System, such planetary protection measures will continue to be high on our agenda.

Slides from the PPOSS workshop at ISAS can be found here