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Arthur C. Clarke, creator of 2001: A Space Odyssey, once stated, “Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying.” For many years, we have defended the thesis that we are, indeed, alone. Yet, in the past years, we have seen evidence that may lead us to believe that we are not that unique across the universe. Here is some of the most compelling evidence:

APOLLO 12: MOON BACTERIA

In November 1969, astronauts Pete Conrad and Alan Bean performed the second manned lunar landing in human history. Contrary to the plan of Apollo 11, the objective of this landing was to demonstrate the ability of the Space Program to perform a “pinpoint landing." In this landing, the Lunar Module lands on a very small area, like a Helipad. This spot was humorously called “Pete’s Parking Lot,” and had a big particularity. The spot was on the border of a crater where two years before, the probe Surveyor 3 landed.��

The astronauts performed the best landing in history in terms of accuracy and fuel margin, and were even able to recover instruments from the dead probe. These instruments (including a TV camera) were sealed in plastic bags and after the mission splashed down in the Pacific Ocean, the instruments were sent to Houston for analysis.��

The scientists could not believe their eyes. All the instruments were completely contaminated by the bacteria Streptococcus Mitis, a common bacterium on Earth. It contaminated the probe before liftoff and against all odds, thrived in the lunar environment without air, water, and food and withstood extreme temperatures in complete vacuum and radiation.��

From that moment on, a very strict sterilization protocol was applied to any spacecraft sent to other worlds because if we were ever going to find life on another planet, how would we be sure that it was not brought by us?

MOON TARDIGRATES

A few years ago, a spacecraft broke that rule. On April 11th, 2019, Israel was monitoring their Beresheet probe that was about to make the first soft landing in its history. Aboard, there was a box full of tardigrades: tiny organisms that were known for being extremophiles, able to survive in the hardest environments imaginable. Everything in the mission control was going well. The spacecraft approached its landing site in the Sea of Serenity flawlessly, but a malfunction in one of the inertial measurement units (gyroscopes) made it crash against the surface, losing contact with mission control. As for today, we do not know the state of the probe and the container of the tardigrades. There is reason to believe that it opened upon crash and that the tardigrades are now on the Moon. Did they survive the crash? If so, are they still thriving in the harsh lunar environment? These questions are not answered, but if they are as resilient as we have seen them to be, we have reason to believe that they are still there. Are they a problem for future visits? Not for now.

LIFE ON MARS?

Mars is a fascinating environment for astrobiologists. In 1976, the Viking orbiters found evidence of erosion by liquid in some areas of the Martian northern hemisphere, suggesting the existence of an ancient sea that covered the whole north pole. This Paleo-Ocean was called Oceanus Borealis (Ocean of the North) and disappeared over the years due to the loss of the magnetic field and the continuous leaking of Mars’ atmosphere into outer space, leaving the inhospitable arid planet we know today.��

Mars is the only planet (outside of Earth) that orbits inside the known Habitable Zone, which is an imaginary ring where planets can orbit around a star far enough to keep water from boiling, but close enough to keep it in a liquid state. Scientists see that this region is the one that has the biggest potential to harbor life. So, in the last couple of decades, we have sent several probes and rovers to the planet to search for those traces of ancient life.

The last and most famous case is the Perseverance Rover, which in July 2024 found traces of chemicals such as clay and silt, which are known to be excellent energy sources for microbial life on Earth. This finding, along with the location of the minerals, proved that this is one of the places where the water once covered Mars’ surface. This leads us a step closer to finding biosignatures in other worlds.

THE FUTURE

But the quest goes on. CU Boulder’s LASP (Laboratory for Atmospheric and Space Physics) is currently working with JPL (Jet Propulsion Laboratory) in one of the most ambitious scientific missions in human history: Europa Clipper. This mission, launched in October of 2024, is expected to arrive at Europa (one of Jupiter’s four Galilean moons) in 2030. Europa is yet another paradise for astrobiologists. The Galileo probe found in 1995 that Jupiter’s magnetic field was disrupted around that moon, implying that below the crust there might be an electrically conductive fluid capable of creating that disturbance. Since Europa’s crust is made from water and ice, that ocean would most likely be a salt water ocean, just like ours. It is kept liquid thanks to the strong geothermal activity of the moon, the same activity found in other moons such as Io.

Once the probe arrives at Europa, it will make use of CU Boulder LASP’s SUDA instrument (Surface Dust Analyzer) to analyze the traces of dust emitted by the plumes and surface of the moon. This instrument, supervised by Dr. Sascha Kempf, can identify the traces of both inorganic and organic substances found in the samples.

ARE WE ALONE?

For decades, the scientific community has dismissed the question, “Is anybody (intelligent) out there?” The search for intelligent life outside of Earth has been treated as a joke, qualifying any scientific investigation into the issue as a chimera. But science’s primordial job is to find evidence to support or deny a hypothesis.

Humanity’s quest for intelligent extraterrestrial life has drawn us to send probes such as the Pioneers 10 and 11 or Voyager 1 and 2 to the vast infinity of space. These probes had messages attached to them in the hopes of being found in a distant future by a technologically advanced civilization. All of these probes have barely left our solar system but remain a symbol of our endeavor to find someone out there.

OUMUAMUA, OUR FIRST VISITOR

In 2017, the Pan-STARRS telescope in Hawaii found the first object ever recorded to reach our solar system from interstellar space. We called it 1I/’Oumuamua, Hawaiian for “explorer." This object sparked people’s curiosity. Nothing like this had ever been seen before. However, our first visitor from another star was behaving quite oddly. As it approached the Sun, it did not accelerate as expected, and when it crossed it, it began accelerating more than the observations predicted. This anomaly, seemingly linked to an unusual brightness produced by the sunlight, raised many questions. Abraham Loeb, head of the astronomy department at Harvard, suggested that ‘Oumuamua could be a solar sail developed by an alien civilization, or a Voyager made by another civilization, just like a bottle with a message thrown to the sea.

Loeb and other scientists proposed sending a probe to study the interstellar object, but at the time this meeting took place, ‘Oumuamua was out of reach. ‘Oumuamua kept its trajectory and is abandoning our cosmic neighborhood forever. In 2019, an amateur Russian astronomer discovered a second interstellar object, the comet 2I/Borisov, reactivating our interest in ‘Oumuamua. But Borisov was nothing like ‘Oumuamua: it was just a comet that behaved like one. Our hope of finding another cosmic “buoy” vanished.

3I/ATLAS: THE MYSTERY CONTINUES

But on July 1st, 2025, the observatory ATLAS at Río Hurtado, Chile, found the third of these objects. 3I/ATLAS was expected to be another object like Borisov, but its composition and trajectory raised alarms.

The comet approached our solar system in a trajectory very close to the ecliptic plane (the plane in our solar system where all the planets lie). This meant that the comet could make use of the planets in our solar system to perform a gravitational assist. Just as we do to send our probes to the outer solar system, an extra push could be added to the already high velocity of 61 km/s relative to the Sun. Abraham Loeb once again drew his attention to this object.

Apart from the already odd trajectory, Loeb reported the presence of an anti-tail in the comet. This was an elongation of jetted material going towards the Sun instead of away from it. These kinds of anti-tails are usually optical illusions generated when Earth crosses the orbital plane of a comet. The data gathered by the Hubble Space Telescope on the 21st of July 2025, seems to differ from that hypothesis. By August 6th, the James Webb Space Telescope used its NearInfrared Spectrograph to analyze the components of the material emitted by the comet, and the findings add mystery to the issue. The jetted material is composed of an unusual mix of volatile substances such as CO2 and water, making the chemical signature of this comet unique.

3I ATLAS will continue its hyperbolic trajectory and get lost in the infinity of space, but before it leaves us forever, just as ‘Oumuamua did, will we be able to solve all of its mysteries? Is this fake evidence that we have created to believe that there is someone out there? Or are we not alone, and all these signals are evidence that indeed life finds a way?