Strict rules around contamination hamper exploration for life beyond Earth

June 27, 2017 by David Rothery, The Conversation
Artist’s impression of Cassini ending its life as a fireball in Saturn’s atmosphere. Credit: NASA/JPL-Caltech

NASA's orbiter Cassini will make a series of decreasing orbits that will end in a fiery death dive into Saturn's atmosphere in September. This deliberate termination of a still serviceable spacecraft is to comply with "planetary protection" protocols, designed to minimise the risk of depositing stowaway Earth microbes into an environment where they might be able to reproduce.

The particular fear in this case is that if Cassini were allowed to become derelict in orbit it might eventually crash into Enceladus – a moon of Saturn now realised to have a watery interior that is eminently habitable for microbes. By similar reasoning, NASA's first Jupiter orbiter Galileo was made to burn up in the planet's atmosphere in 2003 rather than risk a future crash into its microbially habitable moon Europa. The same fate awaits Juno in February 2018.

This makes sense. When we eventually send landers capable of detecting life, it would be frustrating and potentially misleading if all they found was the descendants of microbes that we'd accidentally sent there ourselves. Apart from the science, there is the ethical question of whether we ought to "contaminate" alien ecosystems with bugs from Earth.

Cleanliness is next to impossible

You might think this risk could be eliminated by ensuring that the relevant spacecraft are scrupulously clean to begin with. However, despite using plasma (matter composed of electrically charged particles), intense radiation and heat to sterilise the components, and using special "clean rooms" to assemble them, it has proved impossible to construct a microbe-free spacecraft. The heat, cold, vacuum and harsh radiation encountered during spaceflight will kill most of them, but some will probably remain alive long enough to reach the destination. Experiments on the International Space Station have proved that spore-forming bacteria can remain viable in space for at least as long as it takes to get to Mars.

Beagle2, which crashed on Mars in 2003, during assembly in an clean room at the Open University. Credit: Beagle2

The international regulatory body COSPAR (Committee on Space Research) recognises the problem, and has protocols governing missions travelling from the surface of one planetary body to another. These accept that the risk of accidental contamination cannot be entirely eliminated, and specify a maximum risk that can be tolerated in each circumstance. NASA adheres to these rules and other space-faring nations, including China, are signatories too.

The rules say that no Mars lander may carry more than 300,000 spores on its surface. A lander sent to a "special region", where organisms might be able to feed and reproduce, has a much smaller permissible maximum of just 30. The logic is that 30 spores adhering to a spacecraft's surface would be too few to cause contamination.

For missions to Europa, which is thought to be the most habitable place in the solar system, the requirements are framed differently. They stipulate that the chances of inadvertent contamination of its internal ocean must be less than one in 10,000 per mission.

Strict rules around contamination hamper exploration for life beyond Earth
Artist’s concept of a lander on Jupiter’s moon Europa. Should this even be allowed? Credit: NASA/JPL-Caltech

Unrealistic standards?

None of these rules have any force in law, and there are fears that they are liable to be be bent or broken on cost-saving grounds. Rather than leave them in place to be broken accidentally or deliberately breached by a "rogue" space agency, it would be better to have less stringent but more practicable protocols.

Certainly, as soon as you start sending humans to the surface of Mars, even the 300,000 spores rule goes (almost literally) out of the window. There are billions of microbes living on your skin, and also on the skin of even the best-scrubbed Mars astronaut. As soon as an airlock is flushed, or a spacesuit that has been handled by a human touches the martian soil, some of these bugs will be out there, released into the atmosphere. Don't forget also that these humans will be going to the toilet. Although they will be recycling their urine, their solid wastes will almost certainly be left on the planet to lighten the load for take-off back to space.

‘Mark Watney’ on Mars. He survived by ruining Mars for future searches for life.

The COSPAR policy recognises these issues, in a hand-wringy sort of way. It requires humans to avoid "special regions" of Mars (including where liquid water is suspected at or near the surface), until a "comprehensive planetary protection protocol for human missions" has been developed. However, any human mission to Mars – whether it goes to plan or miscarries as in the recent book and film The Martian – would almost certainly have to break the rules.

What's more, it is possible that much of the caution, at least where Mars is concerned, is unnecessary. There may already be Mars microbes on Earth, and also microbes from Earth on Mars. Though landers are unlikely to have caused this, these two planets orbit sufficiently close to each other that debris thrown up by asteroid impacts can make the journey from one to the other and then rain down as meteorites, carrying potentially viable .

Could microbes travel naturally from Earth to Mars (and vice versa) on meteorites?

If we do eventually find life on Mars, we will want to be able to distinguish between the alternative possibilities of a common origin versus two independent origins. This means we must try to avoid accidental contamination that might confuse the evidence.

But we have to ask ourselves whether the current rules are too strict. Eventual contamination is inevitable, unless we give up completely.

Explore further: OPINION: Why we need a human mission to Mars

Related Stories

OPINION: Why we need a human mission to Mars

June 16, 2017

If we want to know whether there is life beyond Earth then the quickest way to answer that question is to explore Mars. That exploration is currently being done by remote space probes sent from Earth.

Mars missions: Past, Present and Future

October 18, 2016

Long before the space age, Earthlings were already in hot pursuit of life on Mars, using primitive telescopes and even psychic mediums to seek evidence of sentient beings.

What does Earth look like from Mars?

October 3, 2016

Modern astronomy and space exploration has blessed us with a plethora of wonderful images. Whether they were images of distant planets, stars and galaxies taken by Earth-based telescopes, or close-ups of planets or moons ...

Recommended for you

Hunting molecules to find new planets

June 19, 2018

It's impossible to obtain direct images of exoplanets as they are masked by the high luminous intensity of their stars. However, astronomers led by UNIGE propose detecting molecules present in the exoplanet's atmosphere in ...

Exploring planetary plasma environments from your laptop

June 15, 2018

A new database of plasma simulations, combined with observational data and powerful visualisation tools, is providing planetary scientists with an unprecedented way to explore some of the Solar System's most interesting plasma ...

NASA encounters the perfect storm for science

June 14, 2018

One of the thickest dust storms ever observed on Mars has been spreading for the past week and a half. The storm has caused NASA's Opportunity rover to suspend science operations, but also offers a window for four other spacecraft ...


Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Jun 27, 2017
So contaminate Saturn instead of it's moona.
Da Schneib
not rated yet Jun 27, 2017
So contaminate Saturn instead of it's moona.
The chances of contamination of Saturn by Cassini after it burns up in Saturn's atmosphere are extremely low due to the very high temperatures of the reentry. And in any case, Saturn isn't a good candidate for life due to its conditions.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.