Moons of our Solar System
Moons of our Solar System

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Moons of our Solar System

2.3 Lessons from Earth

Life on Earth started about 3.5 billion years ago. Think about how many species live on Earth today and how great is their variety.

To understand what life forms might be on Mars and on some of the moons of the Solar System, we need to focus on the earliest forms of life known on Earth – the very primitive forms. Archaea, for example, are very simple organisms that reproduce by cell division and can undergo evolution by changes in their genetic information. Being simple gives them a great advantage: they can be found in the most extreme environments, those that are hostile to more evolved forms of life. (The Life Marker Chip, mentioned near the end of the video, will no longer be included on the ExoMars Rover.)

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Millions of years before humans appeared, microbes were thriving here on Earth. Yet less than half of 1% of the estimated two to three billion microbial species have ever been identified. Today, the search for new microbes - able to survive in the world’s most extreme conditions - is helping us to address one of the last remaining challenges. Is there life beyond Earth?
Microbes thrive in an extraordinary range of habitats, and often where no other life forms could exist. These include freezing conditions very similar to the permafrost of Mars. This could help us prove that life may have been possible on Mars and on other planets too.
The search for life on Mars is essentially a detective story. It’s about looking for those telltale signatures of life - maybe changes to rocks, maybe parts of microbes left over. Those parts of the evidence that all come together and tell us that Mars once had life, or maybe even has life.
Mars and the Earth share many physical similarities. For example, Mars has deserts, glaciers, and polar caps. To help us, we’re looking on the Earth for the most new and different microbes living in the most extreme environments, which are similar to the environments on Mars. This way, we can study the signatures the microbes leave behind.
Scientists have found many rocks on Mars that looked like they were in contact with water. And that tells us that there were environments on Mars that may have been like environments on Earth. Environments that we know contain microorganisms. And this provides us with some compelling evidence that this is a planet might once have harboured life.
We’re looking for signs of subsurface microbes living there now, or in the past. We’re looking for key indicators associated with life. And these are the building blocks of the cell.
Once we know where to look on Earth, we can design and build instruments which can search similar environments on Mars. In fact, scientists testing equipment in similar geological conditions to Mars recently discovered a rare and complex microbial community living in blue ice vents inside the remote and frozen one million year old Sverrefjellet volcano in Norway.
We know that Mars once had water because we can see evidence of old river valleys. But the atmosphere on Mars is much thinner than Earth. So it doesn’t protect the surface from radiation from space, and makes life there impossible today. The only place where microbes might still survive, perhaps in pockets of water, is deep underground. So drilling is the only option. But it might mean going several metres below the surface.
Studying rocks that have been in contact with water, or studying rocks that contain microorganisms on Earth, helps us develop instrumentation to go look for this life on Mars. So it’s really about gaining an understanding of where microbes are on Earth to help us look for life on Mars.
This information is helping the development of a Life Marker Chip as part of the ExoMars Rover expedition in 2018. It’s an instrument incorporated into the rover, travelling across the surface of the planet, collecting and analysing soil and rock samples, and looking for specific molecules associated with life.
People get terribly excited about the possibility of life on Mars. But we have to remember, it’s just testing a hypothesis. It may be that we’ll find no evidence of life on Mars in the most compelling places that we think it might have grown. It would be just as remarkable to find no life on Mars as to find life on Mars, because that would tell us that, despite the fact that Mars was very similar to Earth in its early history, something was missing for life.
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