It is April 26, 2016, and a team of NASA scientists are observing unusual signals emanating from the distant moon of Europa – just one of dozens of mysterious satellites orbiting the Red Giant of Jupiter. The signals have traveled more than 390 million miles across the Solar System, but they are unmistakable: a vast plume appears to have burst forth from Europa’s surface.
The team conducted the observations at W. M. Keck Observatory in Hawaii, which is home to some of the largest telescopes on Earth. The observatory is stationed at the summit of dormant Maunakea volcano. At an altitude of 13,796 feet, it enjoys unobstructed views of the night sky, free from light pollution and other atmospheric distortions.
The discovery is spurring excited speculation. And its implications, both for science and for wider humanity, could be immense. Indeed, Europa could be hiding something that has the potential to completely transform our world. But first we will need to know more. And that will involve sending a probe to the distant Jupiter system – and perhaps even landing on Europa’s surface.
Jupiter is the fifth-most distant planet from the Sun and is the Solar System’s largest planetary body. In fact, the Red Giant has a mass that is approximately 2.5 times greater than every other planet put together. Composed mainly of hydrogen and helium, it is a gaseous, tempestuous planet ravaged by storms and vortices, poisonous ammonia clouds and ferocious winds.
Naturally, Jupiter’s toxic, volatile and highly pressurized environment is highly inhospitable. It is extremely unlikely to be harboring carbon-based life. Likewise, it is a poor candidate for terraforming or colonization, and there are no plans to send humans to visit it. That said, it is quite possible that scientists might one day send a probe through its atmosphere to see if it has any surface at all, or just a core.
Clearly visible to the naked eye, the giant planet was known as “Marduk” to the Babylonians and “Zeus” to the Greeks. Jupiter, of course, is its Roman name. As one of the most radiant points in the night sky, the planet has long featured in human imaginations, both as an abstract mythical God and as a scientifically observed physical phenomenon.
However, it was not observed in any detail until 1610. Galileo Galilei, a pioneering astronomer, was the first person to glimpse it with a telescope. His observations included the discovery of four moons – the so-called Galilean moons – which include Ganymede, Io, Callisto and Europa. 50 years later, Giovanni Cassini discovered the planet was covered in pastel-shaded bands. And roughly 14 years after that, its famous Great Red Spot was first observed.
But it was not until the late-20th century that a spacecraft ventured close enough to the planet to give us a really thorough look. In 1973 the Pioneer 10 space probe completed the first flyby of Jupiter and gathered groundbreaking data about its physical properties. Since then, a total of nine different craft have ventured into Jupiter’s celestial neighborhood.
However, the first craft to enter Jupiter’s actual orbit was the aptly named Galileo probe. Galileo was perfectly placed to observe the death of a comet, Shoemaker-Levy 9, which bowled headfirst into Jupiter in 1994. And on December 7, 1995, it commenced a seven-year orbit of the huge planet, providing scientists with a wealth of data about its planetary systems – and its moons.
There are at least 79 moons orbiting Jupiter, and there could well be more. The majority are less than six miles in diameter and appear to be mere dust specks relative to the giant planet. But the four Galilean moons are some of the largest moons in the Solar System. The smallest of the quartet, Europa, has a diameter of 1,900 miles. It is larger than Pluto but not quite as big as the Earth’s moon.
Named after a lover of Zeus, Europa has an iron-nickel core, a body of silicon-heavy rock and an exceptionally smooth surface crusted with ice. Oxygen is the main component of its atmosphere, which is known to be very thin. Due to the predominance of cracks and lines on its surface, scientists have hypothesized that there may vast and powerful oceans beneath its encasement of ice.
In fact, the Galileo probe located evidence for this hypothesis during its pioneering flybys at the turn of the millennium. Specifically, it detected disturbances in Jupiter’s magnetic field close to the orbit of Europa. The data indicated that an electrically conductive fluid could be responsible, such as a briny sea. Then in 2012 NASA’s Hubble Space Telescope acquired dramatic evidence of Europan oceans.
Led by Lorenz Roth of the KTH Royal Institute of Technology in Stockholm, the Hubble study identified hydrogen and oxygen atoms – that is, the constituent elements of water – within a mysterious atmospheric plume near the moon’s south pole. Approximately 20 times the height of Mount Everest, the formation was vast by earthly standards, and the scientists deduced that it must be partly composed of water vapor.
Then in September 2016 Hubble provided images of what appeared to be the silhouettes of plumes. And in May 2018, scientists revisited the original Galileo probe data and found convincing evidence that Europa might be ejecting water vapor. Finally, in November 2019, the science journal Nature Astronomy published the findings of Dr. Lucas Paganini and his team – the NASA Goddard Space Flight Center scientists who had received signals from Europa at the mountaintop Keck Observatory in Hawaii.
Using a spectrograph, the team identified the chemical composition of Europa’s atmosphere by measuring the infrared light emanating from it. In fact, water molecules emit certain frequencies of infrared when they interact with solar radiation, providing a distinctive and identifiable signature. The NASA team observed the Europan atmosphere on 17 separate occasions from February 2016 to May 2017 and detected a plume of water vapor on just one of them.
The event took place on Europa’s so-called leading hemisphere – that is, the part of the moon that continuously faces Jupiter. According to Paganini and his team, Europa ejected some 5,202 pounds of water per second, or the equivalent volume of an Olympic swimming pool over the course of a few minutes. Nonetheless, it was barely sufficient water to be detected millions of miles away on Earth.
So while the scientists think that such enormous plumes are relatively infrequent, they are unable to determine if Europa ejects smaller plumes more regularly. Paganini said, “For me, the interesting thing about this work is not only the first direct detection of water above Europa, but also the lack thereof within the limits of our detection method.”
Meanwhile, the findings provide compelling evidence for the claim that there is a vast ocean beneath Europa’s ice sheets: the probable source of the detected plumes. That said, some scientists have speculated that the plumes emanate from reservoirs of melted ice water below its surface. Others have advanced a less probable theory that radiation from Jupiter is causing the moon to release water.
The detection of water molecules on Europa represents a groundbreaking discovery, but the findings suggest an even more thrilling possibility: the presence of biological life. Because where Jupiter is almost certainly too inhospitable to host carbon-based life, Europa possesses all the vital ingredients. In fact, it is one of the few places in our planetary vicinity to have them.
Paganini said, “Essential chemical elements (carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur) and sources of energy, two of three requirements for life, are found all over the solar system. But the third — liquid water — is somewhat hard to find beyond Earth… While scientists have not yet detected liquid water directly, we’ve found the next best thing: water in vapor form.”
In recent years, NASA has significantly stepped up its search for extraterrestrial life, asking the question, is humanity alone? With the development of powerful new probes and telescopes, our knowledge of alien exoplanets is expanding exponentially. And thanks to improvements in our scientific understanding of so-called biosignatures – that is, the physical signs of carbon-based life – we are now able to determine which exoplanets might be likely candidates for life.
Indeed, NASA have long regarded the Jovian moon as one of the Solar system’s most likely harbors of alien life forms. As such, the agency has prioritized Europa for investigation. But if Europa does contain life – and if humans are able to locate it – what kind of form might it take, hidden beneath the ice and trapped in the moon’s vast and gloomy oceans?
This was the question asked by the 2013 science fiction movie Europa Report, in which six astronauts travel to Europa to search for life. Dramatically, the organisms they encounter turn out to be monstrous, bioluminescent sea creatures with giant tentacles. However, it seems more likely that Europa would harbor only simple, single-celled life, if any at all.
Beyond the speculation of science fiction, our most advanced exploration of the Jupiter system is being conducted by Juno, a NASA probe launched from Cape Canaveral in 2011. After a five-year journey across the solar system, Juno entered the planet’s orbit on July 5, 2016 – the second probe after Galileo to do so. Immediately, it began beaming back incredible data and images.
To reduce contact with the hazardous radiation belts encircling the Red Giant, Juno was placed in an elliptical orbit. The orbit lasts 53.5 days and it carries the probe some five million miles away from the planet at its furthest point. At its closest point, known as the perijove, Juno flies within 2,600 miles of Jupiter. That stretch of the flyby lasts for several hours and provides the probe with its most detailed data.
The main purpose of Juno is to enhance our knowledge of how Jupiter formed and evolved, thus expanding our understanding of giant planets and their role within solar systems. Its onboard devices are capable of measuring many of the planet’s atmospheric properties, such as temperature, chemical composition, magnetic fields, water content, cloud movements and ammonia levels.
Best of all, the probe is equipped with a high-resolution camera, which has so far snapped some genuinely mind-blowing images. Previously, the Hubble Space Telescope had managed to capture a crown of colorful auroras at the planet’s north pole, but those images are nothing compared to the close-ups of psychedelic storms snapped by Juno.
Scott Bolton, a Juno project leader from Southwest Research Institute in San Antonio, said, “First glimpse of Jupiter’s north pole, and it looks like nothing we have seen or imagined before. It’s bluer in color up there than other parts of the planet, and there are a lot of storms. There is no sign of the latitudinal bands or zone and belts that we are used to – this image is hardly recognizable as Jupiter.”
In fact, both of Jupiter’s poles are engulfed in massive cyclones, each the size of the United States. Never seen before – or even predicted – the storms intrigued the scientists. Naturally, they invited comparisons with earthly tempests, but how similar were they? Were the Jovian hurricanes short-term phenomena? Or, like Jupiter’s Red Spot, had the cyclones raged for hundreds of years or more?
Cheng Li from the University of California, Berkeley, said, “Nature is revealing new physics regarding fluid motions and how giant planet atmosphere’s work. We are beginning to grasp it through observations and computer simulations. Future Juno flybys will help us further refine our understanding by revealing how the cyclones evolve over time.”
Indeed, on November 3, 2019, during Juno’s 22nd flyby, the probe recorded an incredible development: the formation of a new cyclone at the south pole. Previously, the probe had sent images of five apparently stable storms organized in a pentagon around a central cyclone. Bolton said, “It almost appeared like the polar cycles were part of a private club that seemed to resist new members.”
Even more incredibly, the images of the new cyclone were obtained only after a nerve-wracking navigational procedure that could have ended in mission failure. Juno very nearly flew into Jupiter’s shadow, which would have caused its solar-powered onboard systems to shut down and fail. It was only thanks to the quick thinking of NASA engineers that disaster was avoided.
Bolton said, “No sunlight means no power, so there was real risk we might freeze to death… The engineers came up with a completely new way out of the problem: Jump Jupiter’s shadow. It was nothing less than a navigation stroke of genius. Lo and behold, first thing out of the gate on the other side, we make another fundamental discovery.”
To complete the maneuver, NASA used the probe’s reaction control system in a novel and unintended way. Their calculations indicated that Juno could avoid the shadow if they modified its trajectory weeks ahead of its perijove. Practically speaking, they needed to perform a controlled thruster burn at the point of Juno’s orbit that is furthest from Jupiter. All credit due, the plan worked.
Meanwhile, a dedicated Europa probe known as the Europa Clipper is set to travel to the Jupiter system later this decade, possibly launching as soon as 2023. It will conduct no fewer than 45 flybys of the watery moon, traveling within just 16 miles of its surface. The probe will gather a range of data using an onboard suite of instruments and, in the process, determine the likelihood of Europa harboring life.
Specifically, the spacecraft’s instruments will include radars capable of sensing beneath Europa’s icy crust, a magnetometer for detecting gravity and, potentially, tidal movements, and high-resolution cameras and spectrometers for creating maps of its surface. The 20-feet-high probe will be powered by solar arrays measuring 72 feet from end to end.
To protect its onboard instruments from the high-energy radiation emanating from Jupiter, the Europa Clipper will also be fitted with thick metallic “armor” made of titanium and aluminum. Without such protective measures, the probe would age rapidly and eventually malfunction. Of course, a prototype “radiation vault” is currently being road-tested with Juno. So far so good.
Part of the probe’s mission will include measuring Europa’s surface temperature using a thermal sensor. This may enable NASA scientists to locate its mysterious plumes and examine them in greater detail. By analyzing the water vapor and other particles in the surrounding atmosphere, they should glean groundbreaking new information concerning the moon’s chemical composition.
And concerning the search for extraterrestrial life, the Europa Clipper could well succeed. While the remote moon may be considerably colder and darker than our home planet, our knowledge of the Earth’s biosphere proves that life is hardy and quite capable of flourishing in the toughest of places. For example, complex ecosystems have been identified near hydrothermal vents at the bottom of the ocean, where temperatures and pressures are extraordinarily extreme.
Of course, identifying life on Europa may require one final, audacious step: landing on its surface, drilling through the ice and extracting physical samples from its oceans, if they exist. Even then, there is no guarantee of success. But if Europa does turn out to be barren, the search will go on. After all, according to the famous Drake equation, there are likely to billions of planets in the universe that harbor life, just waiting to be discovered.