June 24th of this year marked the 74th anniversary of Kenneth Arnold’s alleged sighting of the first flying saucers to grace the American consciousness. Since 1947, UFOs and aliens have become so embedded in our culture, invading living rooms through television screens, magazine covers, radio programs, Halloween costumes and action figures, that we often forget how distant they actually are, if they exist at all.
“Space is a lot bigger than people realize,” says Andrew Fraknoi, Professor of Astronomy, Fromm Institute at the University of San Francisco. “The fastest spacecraft we have devised so far would take over 70,000 years to get to the nearest star. And presuming the aliens could go faster, it would be extremely expensive. The amount of energy it takes to travel near the speed of light and make space travel reasonable is astronomically large. So, most astronomers don’t believe that space travel is the way information will travel between civilizations. It is much more likely to travel at the speed of light using some messaging system.”
Proxima Centauri, one of three stars in the Alpha Centauri star system, is the closest to Earth. Invisible to the naked eye, it sits 4.22 lightyears away, meaning a spacecraft traveling at the speed of light (186,282 miles per second) would take 4.22 years to reach it from Earth. In 2016, the European Southern Observatory announced the discovery of Proxima Centauri b, a planet orbiting Proxima Centauri that happens to lie within what astronomers call “the Goldilocks zone,” a region just the right distance from its star to potentially contain liquid water, and therefore life.
Recent studies suggest, however, that Proxima b may not be able to keep a grip on its atmosphere, leaving the surface exposed to harmful radiation. This may be due to intense solar flares that strip away its atmosphere thousands of times faster than on Earth. Despite the excitement from the scientific community when it was discovered, the planet is an unlikely candidate for visitors from outer space.
“At the minimum, about 30% of Sun-like stars in our galaxy are potentially habitable,” says Dr. Ravi Kumar Kopparapu, a research scientist at NASA Goddard Space Flight Center. “That translates to something like two billion potentially habitable planets.”
Those habitable planets are much further from Earth than Proxima Centauri b, though. Barring the invention of warp drives like those dreamed up in Star Trek, closing the distance between us and them looks all but impossible. Interstellar communication may be humanity’s best bet at finding a friend somewhere in the galaxy, and in that, we are just getting started.
“Is there within 100 lightyears a habitable planet with life on it? Perhaps,” Fraknoi says. “Is there a planet with life on it somewhere in the galaxy? Almost certainly. But again, we are counting angels on the head of a pin. What we need to do is identify them. And what we have done so far in searching for radio messages is roughly equivalent to one glass of water out of the ocean.”
Radio waves were long seen as the most effective way to search for extraterrestrial life because they are relatively cheap and penetrate easily through objects and atmospheres. But astronomers are considering other methods. The SETI Institute, for example, is building a network of cameras in sites like California, Hawaii, Puerto Rico, Chile and the Canary Islands to monitor the night sky for laser flashes it believes advanced civilizations could use to send encoded messages.
Because lasers are monochromatic, they are more easily distinguished from false positives like cosmic rays, and they can, in principle, convey about half a million more bits per second than radio waves, allowing more information to be transmitted. During the initial phase of development, LaserSETI, as the program is called, will capture half of the western hemisphere. The institute expects the final network to cover the entire globe and cost five million dollars.
Wide-field astronomical telescopes similarly capture large swaths of the sky. Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) is a system of telescopes in Hawaii that takes periodic snapshots of the night sky and compares one image to another to calculate the position, trajectory and brightness of objects. If a near-Earth object is detected, the data is reported to the Minor Planet Center, and a worldwide network of telescopes are activated to determine if it poses a threat to Earth.
In 2017, Pan-STARRS caught sight of a long, thin, cigar-shaped object tumbling through our solar system. ‘Oumuamua, as the astronomers named it, became the first known interstellar object to visit. But Avi Loeb, professor of science at Harvard University, suggested it was something even more extraordinary: the first known sign of intelligent extraterrestrial life.
In his book, Extraterrestrial, Loeb made the case that ‘Oumuamua was in fact alien technology. Dismissing alternative explanations such as an asteroid, a comet or a lost planetary fragment, he argued that its abnormal acceleration could be due to a LightSail, a machine that speeds up as solar radiation pushes it. Since then, he has become one of the world’s celebrity astronomers, making the rounds with hundreds of top publications.
Most scientists, however, disagree. One research team hypothesized that solid hydrogen was blasting invisibly off ‘Oumuamua’s surface, causing it to accelerate. Another group of researchers found that “in all cases the observations are consistent with a purely natural origin.”
Analysis of ‘Oumuamua is limited, though, by a lack of data. Future telescopes are expected to detect similar objects sooner and with more detail. Chile’s Vera C. Rubin Observatory, which is purported to become operational by 2023, will point a 3,200-megapixel camera at the sky. Its surveys will produce a dataset of unprecedented size and complexity, and it will study phenomena as diverse as dark matter, the history of the Milky Way Galaxy and the nature of the solar system’s outer regions.
“Because of the Vera C. Rubin Observatory, we will be much more sensitive than Pan-STARRS to discover objects like ‘Oumuamua,” Loeb says. “Roughly speaking, we expect a new object every month as compared to every few years with Pan-STARRS. The only caveat is that SpaceX and other companies are launching constellations of communications satellites that could compromise the sensitivity of the observatory because they reflect sunlight at night.”
If more advanced telescopes detect anomalous objects further in advance, Loeb says, then rockets can be sent to intercept them, take pictures and even land on them. An example of how this could be done occurred in 2018 when NASA’s OSIRIS-REx spacecraft touched down on the near-Earth asteroid Bennu. It departed last May and is scheduled to return to Earth on September 24, 2023 with samples of rocks and dust from Bennu.
However, perusing the galaxy for radio waves, laser flashes and habitable planets can only tell scientists so much. Without a method to analyze the data, it will be difficult to distinguish non-life from life, nature from artifice, and spontaneity from intelligent design. Researchers look for technosignatures — signs of advanced technology made by extraterrestrial life — in different ways. One indicator that has become popular in recent years is pollution in a planet’s atmosphere, which suggests industrial activity.
“During the last year of COVID, the nitrogen dioxide concentration on Earth decreased because of lockdowns,” said Kopparapu. “So we thought, what if we could use this to find extraterrestrial civilizations? That’s one way to do it. The other way is, if they are so advanced, they might build some structures on the planet. They may also be emitting enough heat for us to detect.”
Once NASA’s James Webb Space Telescope (JWST), scheduled to launch later this year, settles into orbit above Earth, astronomers will be able to detect chlorofluorocarbons (CFC) in the atmospheres of distant planets. CFCs are artificial compounds most commonly used as refrigerants, propellants, and solvents. “If any civilization is using them for refrigerants and emitting CFCs, even in the tiniest amounts, then James Webb will be able to detect it in a nearby system,” says Kopparapu.
The possibility remains that any existing extraterrestrial life finds us before we find them. Whether one of the Voyager space probes captivates a far-off alien species like ‘Oumuamua did on Earth, or a curious telescope uncovers our terribly polluted planet, one civilization must lay eyes on another eventually. As Kopparapu put it, “no matter what we do, we will be discovered.”