Chris Impey: Detection of life outside Earth would be one of the deepest discoveries in the history of science. The lonely galaxy of the Milky Way organizes hundreds of millions of potentially inhabited planets. Astronomers operate powerful space telescopes to search for molecular biology indicators in the atmosphere of the most earthly of these planets.
But so far no solid evidence has been found outside Earth. The article published in April 2025 claimed that it was detecting the signature of life in the atmosphere of the planet K2-18b.
And although this discovery is intriguing, most astronomers – including the authors of the newspaper – are not ready to say that this means extraterrestrial life. Detection of life would be an extraordinary development.
Carl Sagan astronomer used this expression: “Unusual claims require extraordinary evidence” in relation to the search for alien life. It will show the idea that evidence should exist a high strap to support an extraordinary claim.
I am an astronomer who wrote a book about astrobiology. During my career I saw some convincing scientific discoveries. But to achieve this threshold of finding a life outside the ground, the result must meet several vital criteria.
When is the result vital and reliable?
There are three criteria for a scientific result that represents a real discovery and are not subject to uncertainty and doubts. How is the life claim on K2-18b?
First of all, the experiment must measure a significant and vital amount. Scientists observed the atmosphere of K2-18b with the space telescope of James Webb and saw a spectral feature that they identified as a dimeth sulfide.
On earth, dimethilobus is associated with biology, in particular bacteria and plankton in the oceans. However, it can arise by other means, so this single molecule is not a decisive proof of life.
Secondly, detection must be sturdy. Each detector has some random electron movement noise. The signal should be sturdy enough to have a low probability of this buzz accidentally.
The K2-18B detection is vital, which means that it is 0.3% likely to occur by accident.
Sounds low, but most scientists believe that penniless detection. There are many molecules that can create a function in the same spectral range.
The “gold standard” for scientific detection is 5-sigma, which means that the probability of discovery is less than 0.00006%. For example, physicists in CERN collected data patiently for two years until they detected 5-sigms of the Higgs Boson particles, which led to the Nobel Prize a year later in 2013.
Third, the result must be repetitive. The results are considered credible when repeated – ideally confirmed by other researchers or confirmed using another instrument.
In the case of K2-18B, this may mean detecting other molecules that indicate biology, such as oxygen in the planet's atmosphere.
Life claims on Mars
In the past, some scientists claimed that they found their lives much closer to the house, on the planet Mars.
Over a hundred years ago, the retired merchant Boston changed the Percival Lowell astronomer, claimed that the linear features he saw on the surface of Mars were channels built by the dying civilization for transporting water from poles to the equator. Artificial waterway on Mars would certainly be a grave discovery, but this example failed the other two criteria: sturdy evidence and repetition.
Lowell was misled by his visual observations and was involved in wishful thinking. No other astronomers could confirm his findings.
In 1996, NASA organized a press conference in which a team of scientists presented evidence of biology in the Martian meteorite ALH 84001. Their evidence included a suggestive image that seemed to show microscoses in a meteorite.
However, scientists came up with explanations of the extraordinary features of meteorites that do not include biology. This extraordinary claim has dispersed.
Recently, astronomers have detected low methane levels in the atmosphere of Mars. Like dimeth sulfide and oxygen, methane on Earth is produced primarily – but not only – through life. Various space ships and rover on the Martian surface returned conflicting results in which detection with one spacecraft was not confirmed by another.
The low level and variability of methane on Mars is still a secret. And in the absence of final evidence that this very low methane level has biological origin, nobody claims that the final evidence of life on Mars.
Claims of advanced civilizations
Detection of microorganisms on Mars or exoplanets would be dramatic, but the discovery of extraterrestrial civilizations would be really spectacular.
The search for extraterrestrial intelligentsia or Seti has been going on for 75 years. No messages were received, but in 1977 a radio telescope in Ohio detected a sturdy signal that lasted only for a minute.
This signal was so unusual that the astronomer working in the telescope wrote “WOW!” on the print, giving the signal its name. Unfortunately, since then it has not been detected from this region of the sky, so WOW! The signal fails the repetition test.
In 2017, Rocky, in the shape of a cigar, the object called “Oumuamua was the first known interstellar object that visited the Solar System.” The strange shape and trajectory of Oumuamua led Harvard Astronomer Avi Loeb to argue that it was a foreign artifact. However, the object has already left the solar system, so astronomers have no chance of being able to observe it. And some researchers gathered evidence suggesting that this is just a comet.
While many scientists think that we are not alone, taking into account the huge amount of real estate to live outside Earth, no detection has settled the threshold issued by Carl Sagan.
The claims about the universe
The same criteria concern research on the entire universe. One particular problem in cosmology is the fact that, unlike the planet case, there is only one universe to learn.
A cautious story is due to attempts to show that the universe has undergone a period of extremely swift expansion, a split second after a great explosion. Cosologists call this inflation of the event and refers to explain why the universe is now sleek and flat.
In 2014, astronomers claimed that they found evidence of inflation in a subtle signal from the microwaves remaining after a great explosion. However, during the year the team withdrew the result because the signal had a mundane explanation: in our galaxy they mixed up dust with the signature of inflation.
On the other hand, the discovery of the acceleration of the universe shows the success of the scientific method. In 1929, the astronomer Edwin Hubble stated that the universe was developing. Then in 1998 there was evidence that this cosmic expansion accelerates. This result surprised physics.
Two research groups used supernova for separate expansion tracking. In amiable competition they used different sets of Supernova, but they obtained the same result. Independent confirmation increased their certainty that the universe has accelerated. They called strength for this accelerating expansion of gloomy energy and received the Nobel Prize in 2011 for its discovery.
In the scales of vast and diminutive astronomers, they try to determine the high belt of evidence before leaving.
Chris Impey, University Distinguished Professor of Astronomy, University of Arizona
This article is published from Conversation under the Creative Commons license. Read Original article.
Image Source: Pixabay.com
