Carl Sagan once said “somewhere, something incredible is waiting to be known.” It’s that desire to know what is not already known that drives humanity beyond the stars. We push beyond our own world to the reaches of space to see what’s out there. And what we’ve found is literally beyond comprehension. The James Webb telescope has sent back images of the universe stretching back over 13 billion years, almost to its very creation.
We’ve seen thousands of galaxies which hold billions of stars and potentially hundreds of billions of worlds. All out there in space, just like us. And the question remains, are any of them like us? Are there other people out there? Or things that draw breath and live and grow? The search continues, and it involves more methods than you might think.
10. Monitoring Starlight
The vast space between here and literally anywhere makes searching for alien life a little harder than searching for a lost pair of socks. In many cases it seems easier not to look for aliens per se, but signs that they exist. That’s why we’ve started monitoring starlight.
Light from distant stars is often one of the few things we can see from a faraway galaxy. Even with the James Webb telescope, we’re not going to be peeping into the windows of alien houses. But a star can tell us a lot about a particular solar system just by analyzing the light that reaches us.
Starlight is also searched for signs of alien technology, not just their worlds. If you have a massive space station, for instance, it’s going to cast a shadow and we might be able to see that blocking starlight as well. The idea is that a suitably advanced race will have created amazing technological feats, like star-sized power plants or computers that take up whole solar systems.
Stars like the distant Boyajian’s star are prone to periodic dimming which has led scientists to wonder if there are alien mega-structures that could be interfering with the transmission of light from there to here.
9. Tracking Biosignatures in Alien Atmospheres
Planets pass in front of stars. Using a technique called spectroscopy, we can analyze the spectrum of light that comes from a star when a planet passes in front of it. There will be a color shift that lets us see the spectrum of the planet itself and the gasses that must exist in that planet’s atmosphere to filter out certain frequencies of light.
Methane is a gas produced by living things in our experience, and conducive to life. If a planet has methane in the atmosphere, it’s a possible host for life. So we can analyze the light spectrum, filter out the light from the star which won’t change, and determine what gasses are present in a planet’s atmosphere and perhaps whether it holds life.
With thousands of exoplanets already discovered and now, thanks to the Webb telescope, tens of thousands more likely on the horizon, there will be a lot of ground to cover in terms of looking for life. Narrowing the search means looking for specific things like biosignatures, those signs that a planet does or at least can host life.
We search atmospheres for gasses like oxygen and methane, the things we know are conducive to life because our own atmosphere has them and living things need or produce them. While oxygen is an obvious one, it’s not an all or nothing proposition, especially since we know oxygen has only existed on Earth for a fraction of its life. Instead, scientists have identified thousands of potential compounds that could indicate life that we can search for. Things like carbon dioxide but not carbon monoxide are also potential indicators of life or, at least, habitability.
8. Technosignatures In an Alien Atmosphere
So we’ve seen how biosignatures and technology are both targets for the search for alien life. But with a little modification to those search techniques, we can also hone in on technosignatures.
What we’ve described so far is searching for markers of life or the possibility for life. Technosignature hunting is the search for signs of industry. More specifically, pollution. A species able to build is able to pollute. That means we can search the atmosphere for nitrogen dioxide, for instance. Though it comes from natural sources, it also comes from burning fuel.
Solar panels are another potential technosignature we could detect. Because every planet has to orbit a star for life to exist, it is not unreasonable to assume an intelligent species would harness their sun’s power just like we have. Solar panels reflect a lot of light and that light would have a specific spectral signature. If we detect that, it could indicate life.
7. Radio Signals
One of the oldest and still most popular ways to search for alien life is to search for radio signals. Researchers at MIT discovered a repeating signal likened to a heartbeat in July 2022 that comes from billions of light years from earth. The exact location hasn’t been identified, but it joins the list of many signals, some mysterious and others naturally occurring, that we’ve detected over the years.
Just before that signal, Chinese scientists claimed they too had detected an alien signal, possibly from an alien intelligence, using their massive Sky Eye telescope.
SETI, the Search for Extraterrestrial Intelligence, began searching for radio signals as far back as 1960 with their Project Ozma. One of the big problems with this method is narrowing down where to look in the vastness of space and the fact that many natural sources of radio waves exist. Stars and numerous other celestial bodies produce radio frequencies and need to be investigated and ruled out in the search. The hope is to one day find a signal that’s more than just background noise and offers a clear sign of intelligent intent.
6. Telescopes
Arguably the most obvious way to search for planets is still at the forefront of the effort. Using a telescope is not as simple as it sounds, but it’s how we get those amazing images that come back to us thanks to things like Hubble and then the Webb telescope. The hard part is figuring out where to look.
There are many telltale signs that can be relied on to determine where to point a telescope. One method is the wobble method. You find a distant star and observe the light. If the star looks like it’s wobbling, it means something might be orbiting it and so you train the telescope on that area.
We have already filled the sky with numerous satellites and probes to aid in our search. Webb and Hubble are two but there’s also Spitzer, Kepler, Tess, and Cheops with many more on the way. The European Space Agency plans to launch PLATO in 2024 with the ability to observe 1 million stars and search for planets around them
5. Quantum Communications
The average person is not super familiar with the idea of quantum communications but it’s of interest to those searching for alien life. Signals could be sent across galaxies using photons without losing any information in the signal. Instead of using standard bits like our computers use now, with their ones and zeroes, quantum communications use something called qubits. Humans are still playing with this idea to develop secure communications networks that we believe will offer unprecedented security for a potential quantum internet.
While we’re just getting the hang of it, the idea is that a more sophisticated species would have mastered it and could be using it already. This could also account for why our search for signals is getting us nowhere. Looking for radio signals in a quantum universe would be like trying to track dinosaurs at the zoo. You’re just late to the party and what you want to find doesn’t exist anymore. But if we tweak what we’re searching for, we may start to find better results.
4. Life-Hunting Robot Probes
Closer to home, the moons of Saturn and Mars are still ripe with possibility. While we haven’t discovered signs of life yet it doesn’t mean there’s nothing yet to be discovered. And more efficient means of discovery will improve our chances.
NASA has been looking into the idea of sending probes to moons like Europa and Enceladus which can be sent below the ice we know is there ro search for signs of life. A team of robots could be inserted into liquid water below the ice and allowed to swim far and wide to see what they can see.
This would be just one kind of future smart probe that is able to search and then determine for itself if it’s found anything useful. Because signals from space take a long time to travel to Earth, they could use AI to help them search and analyze, only reporting back when they believe they have found something of note.
3. Gravitational Lensing
If you recall Star Trek IV (the one with the whales) then you may know there’s precedent for things being whipped around the sun. And as fantastically fictional as that movie was, there is science behind the idea of using the sun’s gravity to make things move. It’s called gravitational lensing and it might help us intercept alien signals.
If something is big enough, then its gravitational pull can even bend light. It will also focus and magnify that light as a result. Researchers have posited that communications signals can be bent and focused in the same way. That means stars like our sun could be used like terrestrial satellite networks, transmitting and looping signals across the galaxy. If another race of beings used stars in this way, and we set up a satellite relay, we could listen in.
Communications aren’t all, though. The effect of the sun on light is also being pursued. If we get a spacecraft or satellite into a position where the light from it is bent and then focused by our sun, we can get a much clearer look at alien worlds. The sun would effectively become a natural telescope, magnifying the view for us. At least one researcher thinks the effect would be stunning – the ability to achieve a resolution of 20km per pixel. Clear enough to make out continents and even weather patterns on other worlds.
2. Wet Chemistry
Offputting though it may sound, wet chemistry holds the possibility of finding life on other worlds. This one works on planets closer to home, like Mars, rather than in distant galaxies.
Using something called Sample Analysis at Mars, or SAM, the Curiosity Rover has been searching Martian soil for the building blocks of life. This includes any organic compounds that may contain things like oxygen and nitrogen. Soil samples are analyzed in three different chambers where they can be subjected to a variety of solvents and others where they can be baked. The result was the discovery of various organic molecules that normal sample analysis would have missed. We didn’t discover life, of course, but it gave us a much clearer picture of what was there and could definitely help in the future.
This technique can be applied again elsewhere, on moons of Saturn like Titan, for instance.
1. Auroral Radio Waves
Have you ever heard of auroral radio waves? There’s not something that pop up often in casual conversation but they are a definite point of interest in the search for alien life.
Here on Earth, the Northern Lights occur when charged particles from the sun collide with gasses in our atmosphere. They occur over both poles, not just the North. It’s most often green but different gasses produce different colors. And Earth is not the only planet where these occur.
An aurora produces radio waves and those radio signals can give us information about the planet they come from, including what kind of magnetic field it has. This is important because a magnetic field is essential to a planet harboring life as we know it. Our magnetic field is the reason our atmosphere stays put and harmful particles from space can’t reach us and wipe out all life on the surface.
If an exoplanet is discovered and has an aurora, we can analyze those radio waves. If they indicate a strong magnetic field, then that could be a strong indicator that the planet is a suitable host for life. Likewise, the signals themselves could lead us back to planets we might otherwise overlook.