The search for signs and conditions for life beyond Earth is one of the primary tasks of modern cosmology. The next breakthrough step will be taken in October 2024 when the Europa Clipper spacecraft, equipped with scientific instruments, will be sent to the Jupiter system. Let’s delve into its goals and capabilities further.
In Search of Life
When searching for signs of life beyond Earth, it is worth highlighting several areas of interest and the corresponding tools. Firstly, the search around other stars. Currently, humanity does not possess sufficient technical capabilities to definitively determine if there is life on exoplanets. We are in the stage of accumulating knowledge, observing from afar, and improving our telescopes to probabilistically speculate about the conditions that may exist on different planets. However, even the discovery of an Earth-like rocky exoplanet in the so-called habitable zone does not guarantee a conducive environment for the development and sustenance of familiar life forms. Therefore, the search for life beyond the Solar System remains a distant dream, perhaps even unattainable.
Secondly, the search in the nearby vicinity. In this case, the closest realms are Venus and Mars. Earthly science has strained relations with Venus. The hostile environment of Venus seems to immediately reject any suspicions of the presence of life. Incredible winds, pressure, temperature, and acidic conditions—only someone with a very vivid imagination can envision life thriving in such circumstances. However, occasional studies reporting the discovery of certain organic compounds in Venus’s atmosphere may spark a glimmer of hope for some. Yet, subsequent research carefully dampens such hope. Nevertheless, research missions to Venus are planned, albeit with no particular expectations regarding the search for signs of life. Their aim is rather to attempt to understand what happened to Earth’s twin, turning it into this infernal world.
As for Mars, it has long been the prime candidate for hosting life, if not current, then at least past, even in its most primitive forms. However, in recent decades, the Red Planet has been diligently populated only by robots equipped with increasingly sophisticated instruments, attempting to find traces of past life. Yet, nothing of the sort has been discovered so far. Although it is now certain that Mars was once a world with water and a milder climate. Martian exploration is now shifting focus from attempts to find traces of living organisms to ideas of colonizing the planet in the future, resettling part of humanity and making our species multi-planetary.
There is also an intermediate option. Not quite the backwaters of Earth, but also not another planetary system. These are the moons of gas giants. In addition to Jupiter’s moon Europa, Enceladus and Titan, orbiting Saturn, are considered candidates for hosting forms of life. The Cassini probe has collected intriguing information about them, determining that the miniature Enceladus definitely has a subsurface ocean, from which peculiar geysers erupt. Titan, on the other hand, could easily be mistaken for Earth because of its atmosphere and terrain. Except that the more familiar gases and minerals are replaced there with hydrocarbons, and the temperatures are extremely low. Nevertheless, it is a quite dynamic and changing world, with a multitude of diverse organic compounds.
It is not surprising that NASA is preparing the Dragonfly mission to Titan, and Enceladus has been named the primary target for one of the European Space Agency’s forthcoming costly projects. They will also search for signs of life there.
Read also this interesting article: Why do we explore space?
The Three Pillars of Life
But the main character of this story will be Europa, Jupiter’s moon, which has all the necessary conditions to sustain life in a broad sense. Of course, there are many minor factors. But everything ultimately comes down to three indicators: the presence of liquid water, the availability of an energy source, and the six chemical elements that constitute the basic building blocks of life: nitrogen, oxygen, sulfur, carbon, hydrogen, and phosphorus. Let’s go through them in order.
The first detailed images of Europa were taken back in the 1960s. At that time, scientists concluded that this moon was likely composed of ice. Solid evidence of this was obtained in 1979 when Voyager 1 and Voyager 2 photographed Europa as they flew through the Jupiter system. It was noted then that there were fractures and ridges on the moon’s surface, but there were no craters. This indicated that Europa’s surface is extremely young in astronomical terms.
The arrangement of relief features on Europa’s surface indicated that it rotates with a shift that could provide a liquid layer between the surface and the core. Everything pointed to the presence of an ocean. And when the Galileo probe explored the system in the late 1990s, with a special focus on Europa during its extended mission, the thesis of a subsurface ocean already seemed proven.
Surface details demonstrated recent geological activity, and changes in the magnetic field around Europa could indicate the presence of a salty ocean, which induced these deviations. Further research only found new evidence that there is an ocean about 100 kilometers deep beneath a 20-kilometer layer of ice. And there is more water in it than in all the oceans of Earth combined.
About 98 percent of living matter on Earth consists of various compounds of carbon, oxygen, hydrogen, nitrogen, sulfur, and phosphorus. It is logical to assume that the presence of these elements greatly increases the likelihood of sustaining life. However, it is quite difficult to determine the exact chemical composition of materials on Europa without on-site exploration. Nevertheless, data collected by various spectrometers, including observations from Earth, allowed the determination of the presence of all mentioned components in the form of various compounds in ejecta on Europa’s surface and in its tenuous atmosphere. So formally, Europa meets this criterion as well.
As for the energy source, it is partly hidden within the moon and partly in its surroundings. We are, of course, talking about the giant Jupiter. The tidal forces of the planet compress and release Europa. This action generates internal heat. Factors such as proximity to Jupiter, the planet’s powerful gravity, and the moon’s slight orbital eccentricity have contributed to this effect. At the closest point to the giant, Europa is about 664,000 kilometers away, and at the farthest, about 677,000 kilometers. This difference is sufficient for certain segments of the moon’s orbit to experience stronger compression.
The effect created by tidal compression and stretching is familiar to everyone. Think about how hot a wire becomes when you try to break it by quickly bending it back and forth. The interiors of Europa, presumed to be rocky or even metallic, are subject to a similar influence. They exchange heat with the ocean, preventing it from freezing far from the Sun. Thus, distant moons of gas giants gain internal energy necessary to sustain life. Even on Earth, organisms are known to survive without a trace of sunlight, relying solely on geothermal energy from the depths and chemical compounds.
By the way, the degree of compression of Europa will be assessable by the Europa Clipper. This will provide an understanding of the moon’s structure even without looking inside. For example, if Jupiter’s moon indeed has a 100-kilometer subsurface ocean, the deformation will be about 30 meters, but if it is completely frozen, then only about a meter. But we will get to that when we start describing the probe’s instruments.
Production Torment
When the idea itself of sending a dedicated research mission to Europa emerged, the primary focus was on a lander that could take material samples and analyze them. However, sending a mission solely to the surface seemed too risky, expensive, and not very beneficial: landing in the wrong place, years of waiting, and millions of dollars would be spent in vain.
Therefore, the decision was made to focus on an orbital mission after all. NASA’s Jet Propulsion Laboratory (JPL) proposed several concepts of varying costs. There was even an idea to collaborate with other space agencies and create a large-scale program. However, the cost of such a project seemed unreasonable. And even then, NASA understood that no matter what cost estimate they included, the final price would still end up higher.
And that’s exactly what happened, by the way. Despite the initial cost of 2 billion dollars, the final mission cost exceeded 4 billion. The project had to endure several significant changes. For example, the team really wanted to combine the orbital probe with other spacecraft. Various schemes were proposed: from sending small cubesats along to placing impactors on board that could crash into Europa’s surface so that the Europa Clipper instruments could study the plumes.
In 2016, they even revisited the idea of a combined lander and orbiter. It was approved. But then they remembered why they initially rejected this idea several years ago: cost escalation and risk. Therefore, it was agreed that the Europa lander mission would be postponed until better times.
There were also doubts about the energy source for the probe. During the design phase, engineers calculated two power options: from plutonium-238 thermoelectric generators to solar panels. In 2014, it was decided to use the latter. It turned out to be cheaper, and the risk of energy shortage was not so high, despite the shortage of sunlight in Jupiter’s orbit. The Juno spacecraft, currently operating there, proves that tasks can be performed smoothly even with solar panels. However, during production, their area on the Europa Clipper had to be increased from 18 square meters to 22.
One of the most crucial points for politicians and engineers was the method of launching the Europa Clipper. The U.S. Congress really wanted to boast about the super-powerful SLS launcher, which was then only preparing for its first launch. It was planned that this rocket could “throw” a 6-ton probe to Jupiter on a direct trajectory in just over three years. And even in the project’s funding requirements, it was stipulated that the spacecraft must be launched on the SLS without fail.
But NASA cautiously urged politicians to be prudent. Agency representatives emphasized that SLS launchers were necessary for the Artemis lunar missions, and if any rocket were given for Europa Clipper needs, it could lead to delays in the lunar program. Additionally, there was a question of cost. The price of one SLS launch approached truly astronomical figures—up to 1 billion dollars. Alternatives such as Falcon Heavy and Delta IV Heavy looked much cheaper. In a situation of budget overruns, this was an important argument.
Moreover, a later analysis of the structure showed that launching Europa Clipper on SLS would be associated with a high risk due to strong vibrational loads during liftoff. Solid rocket boosters create more vibrations, which would require a redesign of the probe’s structure. Thus, abandoning SLS saved nearly 2 billion dollars. As a result, Falcon Heavy was chosen, albeit with a longer route.
Now, the journey to Jupiter will take five and a half years. The three-week launch window will open on October 10, 2024. To reach the gas giant, two gravitational maneuvers will be needed. In February 2025, Europa Clipper will use Mars’s assistance, and in December 2026, Earth’s. The spacecraft should enter Jupiter’s system by April 11, 2030, with this flight plan.
Scientific Equipment
Changes also affected the valuable payload that Europa Clipper carries on board. And it didn’t go without drama. Initially, a total of 33 scientific instruments from various research institutes and groups were proposed. Careful selection allowed for settling on ten instruments.
However, during the production phase, NASA had to “cut off” one instrument due to budget overruns. The agency decided to forego the Interior Characterization of Europa using Magnetometry (ICEMAG) magnetometer. It was supposed to study Europa’s internal structure by precisely determining the thickness of the icy crust and subsurface ocean.
This powerful instrument was abandoned because the spacecraft already had a cheaper standard magnetometer, the Europa Clipper Magnetometer (ECM). Essentially, it offers the same capabilities as ICEMAG but with lower resolution. Critics of the instrument replacement deemed the use of ECM pointless. Allegedly, its low accuracy wouldn’t reveal anything new about Europa’s structure. However, the remaining instruments will compensate for it.
Other initially selected instruments remained unchanged. Let’s go through their functions and characteristics.
The Europa Thermal Emission Imaging System (E-THEMIS) is an infrared camera with high spatial resolution. It will provide imaging of the surface of Europa in the near, mid and far infrared, which will help identify geologically active areas and places where ocean waters reach the surface. Above such areas it is especially promising to catch the smallest ice particles for analysis by other devices.
The Mapping Imaging Spectrometer for Europa (MISE) instrument is already an infrared spectrometer that will allow us to study the chemical composition of Europa’s surface, identifying organic compounds, salts and other substances there. Again, studying emissions from the deep ocean will give an indication of their possible habitability.
Europa Ultraviolet Spectrograph (Europa-UVS) is another spectrograph, but already operating in the ultraviolet range. With its help, it will be possible to analyze the composition of the plumes ejected into the thinnest exosphere of Europe. Interestingly, the device was based on research carried out using the Hubble telescope. A similar spectrometer was able to determine that Europe is still erupting peculiar geysers.
The Europa Imaging System (EIS) is a set of narrow and wide-angle cameras that will help produce a detailed optical map of Europa’s surface with a resolution of 50 to 0.5 meters per pixel. Scientists and lovers of spectacular space photography are guaranteed terabytes of highly detailed images.
Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON) is a dual-band radar that is critical to building Europa’s surface structure. He will be able to look deep into the icy crust of the moon. Scientists hope that its power will be enough to “enlighten” the surface to the ocean. But it will also be used to search for so-called water pockets that should be present on Europa. These are peculiar lakes, hidden by a relatively thin ice crust, which can be connected to the internal ocean through channels. They, along with geysers, should play an important role in the geochemical exchange on Europa.
Plasma Instrument for Magnetic Sounding (PIMS) – with the help of this instrument, scientists will obtain information about the dynamics of magnetic fields around Europa and the distribution of plasma. In conjunction with a magnetometer, PISM will help determine the thickness of the moon’s ice crust, the dynamics and volume of its ocean, as well as interaction with Jupiter’s powerful magnetic field. This affects the weathering of matter from the surface of Europa and the ionization of the material.
The Mass Spectrometer for Planetary Exploration (MASPEX) is a versatile mass spectrometer that has high hopes for determining the chemical composition of both Europa’s thin atmosphere and any materials on its surface. Partly duplicates, partly complements and double-checks data from other spectrometers. These are important and, in fact, basic tools for determining the chemistry of the moon and any other cosmic bodies.
Surface Dust Analyzer (SUDA) – finally, the last device on the list, but not the least important. Remember this name, perhaps it is destined to find the first signs of life beyond the Earth. This is also a mass spectrometer, but it is aimed at analyzing the chemical composition of those tiny particles of dust and ice that it can catch during Europa Clipper’s approach to Europe. That is, they will directly capture fragments of the substance on the spot.
The resolution of this device is intriguing. During its tests, engineers achieved such accuracy that it can even recognize particles of a living cell. And if by some miracle one gets into the analyzer, then we will have at our disposal not just indirect evidence of conditions suitable for life on Europa, but direct arguments in favor of the fact that it exists there.
As the mission progresses, Europa Clipper will have a suitable distance for collecting such samples. The trajectory involves 49 approaches to Europe at different distances. In the closest attempt, there will be only 25 kilometers between the device and the surface of the moon. These flybys will also allow the probe’s transmitting communications antenna to be used as a scientific instrument. By measuring the Doppler shift of the signal, scientists will be able to assess the subtle fluctuations in Europa’s gravitational field caused by deformation due to Jupiter’s tidal forces.
On board the probe, there is also a purely symbolic payload. It was decided to use the plate that covers the instrument compartment as a message board. This is similar to the messages to extraterrestrial civilizations placed aboard the Pioneer and Voyager probes, but with one key difference: the “note” on Europa Clipper will not leave the boundaries of the Solar System and is rather addressed to humanity itself, urging it to intensify efforts to explore other worlds.
Engraved on the plate is a poem by American poet Ada Limón, dedicated to Europa. Also depicted there is a portrait of planetary scientist Ron Greeley, who inspired this mission. There’s also a place for the famous Drake Equation and a symbolic depiction of the hydroxyl group, spectral lines of atomic hydrogen. On the reverse side, the word “water” is written in a graphical waveform in 103 languages. Attached to the plate is a microchip containing the names of 2.6 million people who signed up on a special NASA website, securing their own kind of tickets.
The primary mission of Europa Clipper is slated to conclude in October 2033. However, it has significant potential for extension. As demonstrated by the practice of similar projects, spacecraft often have plenty of fuel left to continue operating in orbit for several more years. So, a wealth of data about Europa and possibly the entire Jupiter system will be obtained. These data could revolutionize our understanding of what oceanic ice worlds around gas giants entail.
Interestingly, for much of Europa Clipper’s mission, it won’t be alone in the vicinity of Jupiter. In 2031, the ESA’s JUICE spacecraft will arrive there, also dedicated to studying icy moons but with a focus on Ganymede and Callisto.
Watching their collaboration will be incredibly interesting. Moreover, the teams behind both missions have an idea that Europa Clipper will conclude its mission by impacting the surface of Ganymede. JUICE will be tasked with observing this event, allowing it to gather additional information about this moon and study the resulting ejecta. Why not impact Europa? Scientists are very reluctant to potentially contaminate this world, which promises many more discoveries.
