#3 | Proof of extraterrestrial life
Single-celled bacteria on faraway planets
Door Marit Bonne
By Marit Bonne
Marit Bonne
Biking home on a clear night, all you have to do is look up at the sky to see millions of stars. Some of them come together to form constellations, while others look like paint drops on a dark background. What’s hiding between those stars so far outside our own solar system?
Whether it’s grey aliens from Mars, a bacteria colony, or something in between, Floris van der Tak cannot say. But the honorary professor of astrochemistry is certain that extraterrestrial life exists. ‘Earth really isn’t that special.’
Unfortunately, there is no hard proof for extraterrestrial life – one of the holy grails of astronomy. Van der Tak hopes to change this.
Such a discovery will turn the way we think about life on its head, he thinks, not to mention the new avenues of research it opens up. Will that alien life resemble life on earth? If not, what will it look like? ‘The answer to the question of whether extraterrestrial life exists only raises more questions.’
Space telescopes
While physicists have made great strides in the field over the past few decades, technology has yet to catch up. The current telescopes deployed in space, such as the James Webb telescope, aren’t sensitive enough to find traces of life outside our solar system.
Earth really isn’t that special
But that doesn’t mean no one is looking for alien life. Late next year will see the launch of the PLATO satellite, which will inventory more exoplanets than ever before. His big brother LIFE will be given the resulting treasure map. This space telescope will be launched in 2045 to look at the atmosphere of earth-like planets in solar systems similar to our own. And yes, it will be looking for signs of life.
Van der Tak is involved in LIFE. He and his team are working on the optics in the telescope, which will enable it to take a closer look at the – relatively small – earth-like planets. The telescope will be scanning the atmospheres of these exoplanets for unnatural circumstances: a cocktail of molecules that, at first glance, wouldn’t make sense.
Biosignals
There’s a good example of what it will be looking for right here on earth. ‘Methane and oxygen both occur in the earth’s atmosphere’, says Van der Tak. ‘That’s weird, because they are highly reactive.’ In theory, scientists would expect a different cocktail to what they’re actually seeing. That means there is something that’s disrupting this molecular balance – something living.
Because Van der Tak’s team can’t go and visit these exoplanets themselves, they use space telescopes like LIFE to detect the materials that make up the atmosphere of earth-like planets, as well as whether there are any signs of life, known as biosignals.
While it may sound simple, it is anything but. Planets with a similar temperature to the one on earth, are close to their own star, the way earth is relatively close to the sun. ‘These stars tend to be so bright that the planet becomes overexposed’, says Van der Tak. All he can see is the star, when what he wants to look at is the closest planet.
Eye patches and funhouse mirrors
‘If you want to study the planet, you have to find a way to dim the sun’s light’, he explains. Engineers in Groningen and Dwingeloo, among other places, are therefore working on smart technical gadgets that can change the way a telescope’s lens works, allowing them to see the planet.
If you want to study the planet, you have to dim the sun’s light
The scientists actually came up with a little eye patch for the telescope, which covers up the bright star. Other gadgets include bendable mirrors that can distort once a second, not unlike funhouse mirrors. When the scientists tune the mirrors just right, they will reflect the star’s overbearing light.
‘Then you can cover the star’s light and measure the light coming from the planet’, says Van der Tak. ‘Once you turn that into a light spectrum, you can extrapolate exactly which molecules are in the atmosphere.’
Life
Some of these molecules could show that the planet contains life. There are for instance specific gases that are produced by single-celled microbes, like phosphine or dimethyl sulphate. But, says Van der Tak, these chemicals do not denote signs of life on every planet.
Sometimes, they are found on earth-like planets, which can lead to misunderstandings in the media. ‘A while ago, newspapers wrote that scientists had found life on Venus. It was a whole thing’, he explains.
It turned out that scientists had indeed found phosphine in the atmosphere of the white planet close to us. ‘But phosphine naturally occurs in Venus’ atmosphere.’ In other words, it was a false alarm. The context in which these findings are done is very important, Van der Tak emphasises.
Water
Not every planet can sustain life. One important factor is the temperature: it has to be similar to that on earth. At these temperatures, water tends to be liquid, which creates favourable circumstances for potential extraterrestrial life.
Human life started on a single continent here on earth
Water is highly beneficial to the chemical processes that are essential to living organisms, because they are ideal solvents and a means of transport – much better than solid chemicals or gases. ‘Water is liquid at a wide range of temperatures and therefore a very suitable building block of life.’
Alien life ‘does not necessarily have to look like life on earth’, says Van der Tak. But looking for similar life does make the search much easier. ‘At least then we know what we’re looking for.’
We don’t even have to leave our solar system to learn about other forms of life. The professor says that Titan, one of Saturn’s moons, can tell us a lot about extraterrestrial life and what it might look like. ‘Titan has an atmosphere, just like earth, but it’s much colder. It’s even possible to penetrate that atmosphere, which makes the moon very easy to study.’
Single-celled bacteria
Will we be finding signs of extraterrestrial life in our lifetime? Van der Tak thinks it’s likely. Scientists are slowly getting closer to this particular holy grail, but it’s more likely that they’ll find single-celled bacteria than grey aliens with long fingers and big black eyes.
It’s not that strange that we haven’t found any proof of alien civilisation, he says: a lot of evolution can be chalked up to chance. ‘Human life started on a single continent here on earth, which shows just how selective it is.’
Does that mean there is humanoid life out there somewhere? Van der Tak: ‘Who knows? Maybe there are organisms many light years away wondering the same thing.’