As we continue to search for signs of life in the universe, how will we know we’ve found credible proof?
For many scientists, they use the Sagan standard: Extraordinary claims require extraordinary evidence.
If there was ever a finding that could prove we’re not alone, the Sagan standard would require proof that was equally as strong to back it up.
When it comes to finding proof of that extraordinary claim, one mission just launched to push us closer to gathering the required extraordinary evidence.
On the morning of Aug. 30, SpaceX’s Falcon Heavy rocket roared to life from the Kennedy Space Center in Florida. On top of the rocket was NASA’s Nancy Grace Roman Space Telescope – called Roman for short. Twenty-seven engines launched the tourbus-sized telescope on a three-month trip to its new home a million miles from Earth. And from there, scientists hope, it will fundamentally alter our understanding of the cosmos.
“Roman is going to change the way we look at the universe. It is going to discover tens of thousands, maybe even a hundred thousand new exoplanets,” said NASA’s head of science Nicky Fox just hours after liftoff.
The telescope is on the hunt for dark matter and energy. It’s also searching for exoplanets – planets that orbit stars other than our own sun. And it’s going to find a lot of them.
“Why do we care so much about exoplanets? Because one of our main goals at NASA is answering the question, are we alone in the universe?,” Fox said. “Whether you like space, whether you like technology, whatever it is, people look up at the sky, and they think ‘you know, am I alone? Are we alone? Is there another Earth 2.0 looking back at me?’ And with Roman, we are going to make this giant leap forward.”
Exoplanets are just one avenue scientists are using to answer that question. Scientists like astrophysicist Josh Colwell say in finding that answer – through exoplanets or other methods – it’s not a matter of if, but when.
“It's hard for me to think of a more important scientific question to be answering, because I think the implications are so profound and far-reaching that I think it's an essential and necessary search,” he said.
When that day comes, it will be an extraordinary claim – that humans are not the only living beings in the cosmos. As astronomer and science communicator Carl Sagan said – extraordinary claims require extraordinary evidence.
When it comes to life in the universe, what extraordinary evidence are we looking for?
Exoplanets
Let’s be clear — the search for life isn’t monolithic. There is not one thing scientists are looking for. Instead there are three parallel and distinct efforts underway that make up this quote unquote search.
Scientists are looking for chemical signs of life on far-off exoplanets, more physical traces of life on planetary surfaces closer to us, and a deep scan of the skies for evidence of alien technology.
We’re going to take a look at each of those efforts. And we’ll start with searching for chemical signs of life on planets outside our own solar system. They’re called exoplanets.
Bill Diamond is the CEO of the SETI Institute, a non-profit research organization. He said exoplanets are one of the most consequential findings in SETI. When Frank Drake was writing his equation, the only variable he really knew the value of was the first — the rate of star formation. But he had no idea what the second variable could even be. Until exoplanets came along.
“That's the discovery, which is quite recent, that planets are ubiquitous, that every star in the sky is essentially a solar system,” he said. “That's shockingly recent information.”
What does shockingly recent mean in the world of astronomy? 1995.
Coolio is topping the Billboard chart with Hootie and the Blowfish, Mariah Carey, Seal and TLC. I was in the third grade. And a pair of scientists announced the first discovery of a planet orbiting a sun-like star — 51 Pegasi b.
What was just considered a hypothesis — that other stars had planetary systems like our own — was now proven true.
(51 Pegasi b technically isn’t the first exoplanet discovered. That happened in 1992 when scientists found planets orbiting a pulsar – a dead star. The discovery in 1995 was the first to find planets orbiting a living, Sun-like star.)
Since that finding in 1995, many more efforts are underway to count these planets. NASA has confirmed over 6,000. It’s now understood that pretty much every star that we see in our night sky has planets orbiting it.
“We also have ascertained that a sizable fraction – like 30% of these planetary systems – are likely to be potentially habitable environments based on their size and and distance from their star and other characteristics,” Diamond said. “This statistically suggests the possibility that in the Milky Way galaxy alone there may be tens of billions of potentially habitable environments. That kind of new knowledge and information compels us to keep looking.”
What exactly are we looking for? Astronomers are using a technique called spectroscopy to peer inside the atmosphere of these planets. It breaks light apart — like a prism takes a beam of sunlight and turns it into a rainbow.
Through that breakdown, scientists can uncover specific chemical signatures. Different gasses absorb light in different and unique ways. So by looking at starlight passing through a far-off planet, we can know what that atmosphere is made of.
“We are trying to understand what life on planets that we cannot visit in person, what that life would do that would reveal itself to us if we are looking from a distance,” said Jennifer Wiseman, a NASA astronomer.
“If there were bacteria or microbial life, what would it do that might change the atmosphere of its planet, such that we, from a distance, could see that that atmosphere is in disequilibrium, or in some way give a sign that there's biological activity going on? We call these biosignatures.”
If an alien civilization pointed its telescope at us, it would see our own atmosphere interacting with our sun’s light revealing things like water vapor and oxygen.
That’s exactly what powerful telescopes like the James Webb Space Telescope are doing now. While it hasn’t found a smoking gun just yet, it’s opening new doors to potential plants that could harbor life.
But other efforts to find life are happening closer to home.
Life in our solar system
NASA’s Perseverance rover landed on Mars in 2021. Since then it has traversed over 28 miles with the goal of hunting for evidence of ancient life. It’s looking for that evidence in the rocks on the planet’s surface, and collecting samples to hopefully one day send back to Earth.
Scientists now know that Mars once had liquid water — oceans like our own. So why wouldn’t it have life just like us?
Mars ends up being a really great environment in framing our questions about the search for life beyond Earth, in part, because it is very Earth-like, or at least was in an ancient past,” said Amy Williams, an astrobiologist at the University of Florida and a scientist on the two Mars rovers.
“There's different parts of the community for Mars astrobiology that are looking at whether there was life in the past on Mars, and then there's also a contingent that are interested in whether, if there were life on Mars in the past, if it could have survived to the present,” she said. “There are a lot of assumptions that have to go into those kinds of searches, but the more that we learn about Mars, the more we have to ask the question, if life started on Earth, why not also on Mars?”
What Williams and her astrobiology colleagues hope they may one day find is evidence that microbes lived there. Not active life. Still, the findings would be profound indeed, and prove that life, at least in the past, existed on more than one planet.
Other missions are planned within our own solar system to look for places that might be able to sustain life. NASA’s Europa Clipper is on its way to explore a moon of Jupiter with that same name, hoping to peer beneath its icy surface to see if there are places that can sustain life — scientists think there could be a salt water ocean down there. A moon of Saturn called Encelodus could have a similar ocean beneath its icy surface. The European Space Agency is planning a mission that would arrive there in 2050.
Both exoplanet surveys and planetary missions are looking for signs of worlds that could sustain life — or evidence of past life. But one search for life in the universe is looking for something more alive.
A sign of intelligent life
A techno signature is like the next tier up, something that we could confidently attribute to some kind of technology, which would require not just life but technologically advanced life,” said Washington University in St. Louis planetary scientist Paul Byrne.
Ideas as to what this could actually be run the gamut, but the thought is that they are a sign of technology developed by an intelligent civilization that was either sent out intentionally or accidentally — and we are able to pick them up. There are three categories as to what technisignatures might be, as SETI Institute’s Bill Diamond explains
"The first way,” he said, “and what has been historically associated with SETI as an endeavor, is the use of radio telescopes to interrogate the radio spectrum to look for engineered signals”
Electromagnetic radiation is common in the universe. But very narrow band radio waves are not As we know them, they are intentionally created by us humans and used to transmit information, communication, data. These engineered signals would show up as narrow band signals or modulated waves. The Wow! signal we talked about last episode was in the narrow band.
Diamond says SETI scientists are also looking at optical waves, too, as a sign of a technosignature. “We now have programs called Laser SETI, where we use sensitive camera systems with gradings on them to look for laser pulses, short duration monochromatic, meaning signal wavelength or color that again nature doesn't produce.”
And finally, Diamond says, you can also look at what’s happening in an exoplanet’s atmosphere – but not for signs of a habitable planet like discussed earlier. Instead, one that has inhabitants.
That search includes “finding a chemical compound in those atmospheres that we pretty well understand nature doesn't produce, that is a byproduct of industry and or technology,” he said. “We would say that looks like a technological civilization based on what we're seeing in their atmosphere.”
If we find a planet with pollution, chances are pretty good we’ve found another civilization. We assume that aliens would pollute their planet just like ours.
We are actually sending out our own technosignatures. Alien civilizations, at the right distance from us, and pointing their telescope at the right spot would pick up the radio signal of I Love Lucy episodes.
As radio astronomer Emma Chapman explains, this is known as the I Love Lucy radius.
“This was seen as one of the first concentrated, strong radio signals that humanity sent, and that was [about] 75 years ago,” she said. “So the I Love Lucy sitcom is just about arriving at a planet 75 light years away.”
That signal travels at the speed of light. So civilizations some 75 light years away are just now hearing it for the first time. It’s the boundary of how far we might be detected.
But it’s not just ‘I Love Lucy’ episodes that might tell a civilization where we are. Any electromagnetic signal that’s engineered or artificial could give us away.
However, that signal is getting quieter. We’re no longer beaming out episodes of ‘I Love Lucy’ over broadcast transmitters. And we’re transmitting data differently than before. That means our radio footprint is getting smaller
“As humanity has evolved in terms of technology, we've gone from using these few really strong antennas to communicate radio stations to the kind of like Wi-Fi lower power but everywhere satellites, and that kind of quieter but wider over the frequency,” she said. “There's lots of people looking for that kind of signal too, but it's harder because it's quieter.
But we’re still listening for those signals from someone else out there. Maybe it’s an alien version of ‘I Love Lucy’ or E.T.’s Wifi. So if we hear something, how will we know it’s actually coming from another civilization?
Confirmation
In her book “The Possibility of Life,” Science writer Jaime Green explained the process this way: The detection of alien life won’t be obvious. It’ll be partial and inconclusive, a perfect task for the scientific method.
The scientific method takes an observation, forms a hypothesis for why it happened, tests that hypothesis, analyzes the data to draw conclusions and then shares the results — with the goal of other scientists to prove – or disprove – the results. It’s applied to all fields of science. And for that reason, Diamond says the scientific method should work in the case of searching for life, too.
“This process of hypotheses, experimental undertakings, and observations, verification, and repetition by other recognized individuals and institutions is what the scientific method is all about, so I think in that sense there is a self-governing validation for discoveries. It's inherent in the process,” he said. “That's not to say that people will, including in the scientific community, will sometimes, bypass that process, or make claims that are extraordinary without the extraordinary evidence.”
There are some guardrails in place to prevent just that. The closest thing to a formal plan for if and when we find something is a document: The Declaration of Principles Concerning the Successful Detection of Extraterrestrial Intelligence. It’s maintained by the International Academy of Astronautics.
They have at regular intervals put out this document, which we call informally the protocols,” Chelsea Haramia is a senior research fellow at the Center for Science and Thought at the University of Bonn in Germany, and co-director of the Discovery and Futures Lab at the SETI Institute. “It's basically how do the people who are involved in the search, how do they agree to act in the event of a meaningful detection.”
The protocols were first created in 1989, then updated in 2010, and most recently revised this year.
“They just put out a much more comprehensive and robust set of principles to help guide the scientists and those involved in the search when and if there is a successful discovery,” she said. “Here's how we've agreed to follow it up, and here's how we've agreed to act during the confirmation process.”
That includes guidance on how to verify a signal, how much transparency to maintain during the very likely long verification process, and whether we — as humans — should respond.
It charges the person or group that finds the evidence to do all that they can to authenticate and substantiate the finding using all the resources available. That might be using other tools or telescopes to replicate the results. It says the results should be scrutinized by other scientists. And if it is indeed found to be credible, that should be shared with everyone – the public, the science community and the Secretary General of the United Nations. A sub-committee will decide what to do next.
And at first, the guidelines advise, we’re not to respond directly to whatever signal we might have found. The protocols argue that any response needs to be fully representative of humanity. That will take time, and coordination through some international body, like the U.N. Until we can all agree on what to say, we should stay quiet.
Measuring the credibility of a finding is hard because there’s no governing body that oversees these findings. But there are tools scientists can use. The Rio Scale – is like what the Richter scale is to Earthquakes but measures – or tries to measure – just how consequential a potential extraterrestrial signature might be. It is an evolving scale that looks at the consequences of a finding and its credibility. Not everyone is convinced it works.
Another scale proposed by NASA scientists – the Confidence of Life Detection Scale, or CoLD – aims to categorize the confidence in a set of observations being actual alien life. There are seven steps, from detection to confirmation…and in between guidelines to rule out things like contamination or things that might not be biological in the first place.
There are also critics of this method, too.
And again, there’s no “SETI Czar” telling scientists what to do or how to measure evidence.
This uncertainty and challenging of ways to measure how important or credible a find is underscores the importance of what may come after.
The search for life is so vast — from finding fossilized microbes on Mars to discovering a planet with industrial pollution. Within the science community, there isn’t consensus on what even counts as a discovery. There’s no “if you find this, then you’ve proven that”” rule.
That’s something I asked Britney Schmidt, astrobiologist and Planetary Society board member: What evidence would she need to know that we're not alone?
“We ask ourselves that all the time in many different ways in the scientific community,” she told me. “I have an unsatisfying answer, which is I'll know it when I see it.”
The scientific community operates under a high bar of certainty, for good reason. University of Central Florida physicist Josh Colwell explains a confirmed finding would have an unprecedented impact on humanity.
“I can't even predict all of the different impacts that such a discovery would have, but I think that the long term ramifications for how humans interact with each other and. Our environment would be dramatically affected,” he said
