It’s been a long time coming, and I apologise greatly for that. Life finds a way, as Ian Malcolm says. What he doesn’t say is that what life finds a way to do is scupper all your best laid plans. Nevertheless, Science Burrito now ends its short hiatus with The Martian Blog!
The first EXOMARS mission is off and on its way to the red planet to look for signs of life. This is tremendously exciting (especially if it finds something) but by no means our first attempt. So I wanted to give a little bit of a run-down of what we’ve done so far, and what we’ve found so far, to answer one of science’s most interest and allusive questions. The question is, of course…
Is There Life On Mars?
There have been over fifty attempts to get space craft onto or around Mars, only about half of which have been successful. This tells us straight away that getting to and working on Mars is difficult, despite all our technological advances, and that the current Exomars mission is far from out of the woods.
The first successful mission to Mars was Mariner 4 as far back as 1964. Before we’d even put a man on the moon, we had our sights set on loftier goals. This was shortly followed by Mariners 6, 7 and 9. These early missions were strongly focussed on photographing Mars, but also included atmospheric measurements and studies of Mars’s two moons, Deimos and Phobos. These early results were not particularly hopeful for scientists looking to discover little green men, revealing a thin atmosphere over a dry rock, pockmarked with craters. The search for life now had to shift from the macro- to the microscopic.
Following on very swiftly from this, in the mid 70s, not content with merely orbiting the planet, NASA sent landers to Mars to explore the surface up close and personal with the hugely successful Viking missions. These early surface missions (coupled with orbiters of their own) were static, limited to a single place on the planet, but nevertheless presented science with a wealth of new information. Very little of this information was positive in terms of life. But there was a small ray of hope…
Before we go on, a quick word about life. We’ve probably all seen the old mnemonic, MRS GREN, or something like it in biology lessons for how to identify if something is alive. These letters stand for:
Movement – for something to be alive, it must be able to move in some way. We move around in our legs, plants move towards the sun. Respiration – living things breathe. We breathe in oxygen and out carbon dioxide (CO2). Plants do the opposite. Sensitivity – living things respond to stimuli. Your eyes respond to light, as do plants, which grow towards the sun. Growth – All living things start small and get bigger. Reproduction – Evolution works by passing things on to the next generation, which means there needs to be a next generation. Excretion & Nutrition – I lumped the last two together because they are strongly linked. To grow you need to eat, and when you eat you produce waste. Simple.
The important one for us of these is respiration. One experiment on the Viking landers was designed to “see” the respiration of life in the Martian soil. It did this by doping the soil with special radioactive carbon. If anything in the soil was breathing oxygen, it would produce CO2 using this special carbon and Viking would be able to detect it, which indeed it did. This was the first ever evidence for life on the surface of Mars. Unfortunately, if there is life, there must be organic molecules (we mean organic as in molecules that make up living matter, such as fats, amino acids, DNA etc, rather than the way your local supermarket means organic, as in expensive) but none were found. This has led to a lot debate since as to exactly what the Viking results were telling us. Whatever the case, you would have thought that this would be enough to fuel a lot more investigation into the Martian question, but in fact, the next successful missions to Mars were not for another 20 years!
In 1996 we sent three missions to the red planet, including the first successful rover, Sojourner. These missions were not geared up with the specific objective of discovering life, but led the way to a huge increase in the number of successful Martian missions, and the Global Mars Surveyor did discover evidence of water ice on the surface of Mars, water being essential for all life found on this planet, and a huge step forward in finding life, past or present, on our neighbour.
Since the missions in ’96 there have been nine successful Mars missions, seven of which are still operational. The most famous and most successful of these, in terms of the richness of data retrieved, is without a doubt the Mars Science Laboratory, better known as the Curiosity rover. Something else that life produces on this planet is methane, most famously by large herbivorous creatures… like cows. Methane is made of hydrogen and carbon. These elements, together with oxygen are the most abundant in life on Earth, and so are likely essential for life on Mars.
And Curiosity found methane. In fact, it found a lot it and all at once. On December 16th 2014, the Curiosity rover measured a ten-fold increase in methane levels. Not only that, but drilling down into the rocks on Mars, Curiosity found organic molecules. This is, so far, the most compelling evidence we have had that life might not just have once existed, but may still presently exist in some limited, microscopic form on the red planet. There are a few possible explanations for these chemicals being present, and suddenly appearing all at once, not all of which involve life, but the key point is that some of those explanations do.
Cue EXOMARS! This is a two stage mission, the first of which will send an orbiter to Mars to fly around it in space, 400 km above the surface, and make super sensitive measurements (1000 times more sensitive than ever before) of where in the atmosphere methane and other important gases are present. The orbiter will also map out the hydrogen present 1 meter under the surface of Mars. How it does this is very cool.
We are constantly being bombarded with radiation from space. This radiation has the very cool sounding name Cosmic Rays. The vast majority of these pass straight through us without interacting whatsoever. But occasionally, one of these rays can hit an atom and make part if it fly off with very high energy.
This part is the neutrally charged neutron. We’ve talked about atoms before. If you need a refresher, go here. So these neutrons fly off when they get hit by, and absorb, a cosmic ray, and some of them fly off into space. That is where they are detected by the EXOMARS orbiter. When there is hydrogen nearby, though, collisions between the hydrogen and the neutron slow the neutron down, and so fewer very fast neutrons are detected.
To understand how that happens, you need to think about pool balls. If you roll a ball against the cushion of the pool table, the ball bounces off without losing much speed. That’s because the total amount of speed has to stay the same (this is called the conservation of energy), but the small pool ball can’t make the heavy pool table go very fast. If you roll the pool ball against another ball, however, the first ball stops and the second starts moving. This is because they are the same weight so the first ball is heavy enough to move the second one. So when the neutron hits heavy atoms it bounces off without slowing down.
Hydrogen is the lightest atom there is, so when the neutron hits it, speed is transferred from one to the other, just like the pool balls, and the neutron slows down. So fewer fast neutrons means more hydrogen is present.
Why is all this important? Because water is made of hydrogen and oxygen, so where there is hydrogen, there might be water, and where there is water, there might be life!
The idea is to use this information to inform where the best place to land the second mission will be in 2018. This mission will land a new rover on Mars with a huge drill capable of drilling 2 meters under the surface of Mars, much further than previous missions which have literally only scratched the surface. With such immense ground penetrating abilities, it is hoped that EXOMARS 2018 can finally answer the question of whether all this methane is biological or geological. And who knows, maybe by 2020 we will have actually, definitively found life on Mars (albeit in the form of tiny microbes). I’m not normally one for wild speculation, but this time, I think there might actually be a chance.