The Search for Life in the Inner Solar System

The Search for Life in the Inner Solar System. From the writer of The Terraformers’ Toolkit.
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Why?
NASA and other space agencies have been searching for life elsewhere in our solar system for over 50 years. The reason is that they would like to know if life on earth is the only sort of life in our solar system. On earth all living things use the same DNA and cellular chemistry because they are all descended from the same common ancestor.
If they discovered alien life they would like to know if it’s the same. If it is, then that means life in our solar system has some way of jumping from planet to planet.
If it’s completely different, it means there is a second origin, it appears frequently and its likely to be common in our galaxy.
One added bonus is that if it is very different, then we may be able to use its enzymes, hormones, proteins and other chemicals to help us make food, pharmaceuticals and many other products in the cold of deep space.
Panspermia
If we find that life elsewhere in the solar system uses the same chemistry and DNA as earth life, then we have to infer that it can jump from one planet to another in someway. The mechanism is probably panspermia in which bacterial spores are thrown into space inside rocks during large asteroid impacts, and are then pulled toward other planets or moons by gravity.
During the very early days of our solar system, it’s possible that all three planets Earth, Mars and Venus were habitable, and that life was spread between them by panspermia as asteroids impacted each during the late heavy bombardment about 4 billion years ago.
Mars
We have no proof that there is any life on Mars other than the occurrence of methane plumes. These might be produced by living organisms or they might be a product of Mars’ geology. We don’t know which it is, but on Earth it’s normally life.
Mars surface would sterilise anything living with a broad radiation spectrum, extreme cold and dryness, very low atmospheric pressure and an inhospitable surface chemistry.
However, there are some places defined as ‘special’, which are more likely to have liquid water and therefore life than others. At the moment rovers are avoiding these because of the risk of us introducing microorganisms from Earth by mistake, which could outcompete any Martian microbes.
If there is any life on Mars, it’s liable to be microorganisms living very deep beneath the surface. But the ‘special’ locations may serve as windows into their deep rock ecosystem. Here, warmer, wetter conditions exist and the organisms would be protected from radiation by thick rock layers.
Venus
On the face of it, Venus seems highly unlikely, place to find living organisms. It has a 92 bar atmosphere and super hot surface temperatures of 457°C (854 Fahrenheit).
However, 20 Parts Per Billion of phosphine have been found in the atmosphere, which on earth is only produced by biological human activity. This detection is still being debated, and any life in the atmosphere is controversial because of the lack of water.
Asteroid Belt
The largest of the asteroids is a spherical (dwarf planet) called Ceres. Its crust is believed to be a 30% water ice brine, and some of this erupts on the surface as cryovolcanoes. It isn’t thought to have an internal ocean, but it may host microorganisms just the same.
Additionally, once we reach the outer edge of the asteroid belt, organic molecules become a lot more common, providing many of the essential elements needed by life. In the inner solar system, most of these chemicals have been swept away over billions of years by the solar wind.
Chiral asymmetry
When it comes to working out if there is life elsewhere in the solar system there are ways to tell life from non-life. There are organic molecules in space which were produced by chemistry and radiation rather than life. The difference between these and the organics produced by life is that life has a preference for left or right handed molecules. For example life prefers to use left handed amino acids and right handed sugars.
Unstable atmospheres
Another clue about the presence of life is the oxygen in our atmosphere. This wouldn’t be there if it wasn’t for photosynthesis producing it. In the absence of photosynthesis our atmosphere would be primarily carbon dioxide.
Mars’ atmosphere is primarily carbon dioxide, which suggest there isn’t any life there, and when we look at exoplanets outside our own system solar system, we can try to detect oxygen. If we found it, that might give us an indication that there is life on the planet without having to go there to confirm it.
Summary
Finding other forms of life in our solar system would be really interesting for our understanding of our place in the cosmos, and might provide us with a host of new chemistries to help us survive in space.