A Swarm of Swimming Robots to Search for Life Under the Ice on Europa

An artist’s interpretation of liquid water on the surface of the Europa pooling beneath chaos terrain. Credit: : NASA/JPL-Caltech

When Galileo pointed his telescope at Jupiter 400 years ago, he saw three blobs of light around the giant planet, which he at first thought were fixed stars. He kept looking, and eventually, he spotted a fourth blob and noticed the blobs were moving. Galileo’s discovery of objects orbiting something other than Earth—which we call the Galilean moons in his honour—struck a blow to the Ptolemaic (geocentric) worldview of the time.

Galileo couldn’t have foreseen the age of space exploration that we’re living in now. Fast forward 400 years, and here we are. We know the Earth doesn’t occupy any central point. We’ve discovered thousands of other planets, and many of them will have their own moons. Galileo would be amazed at this.

What would he think about robotic missions to explore one of the blobs of light he spotted?

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Micrometeorites Churn up the Surface of Europa. If you Want to Find Life, You’ll Need to dig Down a Meter or So

An artist's rendering of Europa and Jupiter based on images sent by visiting spacecraft. Credit: NASA/JPL-Caltech

In the coming decade, NASA and the ESA will be sending two dedicated missions that will explore Jupiter’s moon Europa. These missions are known as the Europa Clipper and the JUpiter ICy moons Explorer (JUICE) missions, which will fulfill a dream that has been decades in the making – searching for possible evidence of life inside Europa. Since the 1970s, astronomers have theorized that this satellite contains a warm-water ocean that could support life.

The case for life in Europa has only been bolstered thanks to multiple flybys and observation campaigns that have been mounted since. According to new research led by the University of Hawaii at Manoa, the best way to look for potential signs of life (aka. biosignatures) would be to analyze small impact craters on Europa’s surface. These patches of exposed subsurface ice could point the way towards life that might exist deeper in the moon’s interior.

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There Might be Volcanoes at the Bottom of Europa’s sub-ice Oceans

Artist's concept of a Europa Clipper mission. Credit: NASA/JPL

In about three years, NASA plans to launch a robotic orbiter that will study Jupiter’s mysterious moon Europa. It’s called the Europa Clipper mission, which will spend four years orbiting Europa to learn more about its ice sheet, interior structure, chemical composition, and plume activity. In the process, NASA hopes to find evidence that will help resolve the ongoing debate as to whether or not Europa harbors life in its interior.

Naturally, scientists are especially curious about what the Clipper mission might find, especially in Europa’s interior. According to new research and modeling supported by NASA, it’s possible that volcanic activity occurred on the seafloor in the recent past – which could be happening still. This research is the most detailed and thorough 3D modeling on how internal heat is produced and transferred and what effect this will have on a moon.

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How Salty is Enceladus’ Ocean Under the ice?

An icy satellite of Saturn, Enceladus, has been a subject of increasing interest in recent years since Cassini captured jets of water and other material being ejected out of the south pole of the moon.  One particularly tantalizing hypothesis supported by the sample composition is that there might be life in the oceans under the ice shells of Enceladus. To evaluate Enceladus’ habitability and to figure out the best way to probe this icy moon, scientists need to better understand the chemical composition and dynamics of Enceladus’ ocean.

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The Same Technology Could Search for Microbes in Mars Rocks or Under the ice on Europa

Credit: NASA/JPL-Caltech

Ever since it landed in the Jezero Crater on Feb. 18th, 2021, the Perseverance rover has been prepping its scientific instruments to begin searching for signs of past life on the Red Planet. These include spectrometers that will scan Martian rocks for organics and minerals that form in the presence of water and a caching system that will store samples of Martian soil and rock for retrieval by a future mission.

These telltale indicators could be signs of past life, which would most likely take the form of fossilized microbes. In the near future, a similar instrument could be used to search for present-day extraterrestrial life. It’s known as the Wireline Analysis Tool for the Subsurface Observation of Northern ice sheets (WATSON), and could be used to find evidence of life inside “ocean worlds” like Europa, Enceladus, and Titan.

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Beyond “Fermi’s Paradox” XIII: What is the “Ocean Worlds” Hypothesis?

Credit: NASA/JPL

Welcome back to our Fermi Paradox series, where we take a look at possible resolutions to Enrico Fermi’s famous question, “Where Is Everybody?” Today, we examine the possibility that the reason for the Great Silence is that most life out there exists in warm water oceans under sheets of ice!

In 1950, Italian-American physicist Enrico Fermi sat down to lunch with some of his colleagues at the Los Alamos National Laboratory, where he had worked five years prior as part of the Manhattan Project. According to various accounts, the conversation turned to aliens and the recent spate of UFOs. Into this, Fermi issued a statement that would go down in the annals of history: “Where is everybody?

This became the basis of the Fermi Paradox, which refers to the disparity between high probability estimates for the existence of extraterrestrial intelligence (ETI) and the apparent lack of evidence. Since Fermi’s time, there have been several proposed resolutions to his question, which include the possibility that Oceans Worlds (and not rocky planets) might be the best candidates for finding life.

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Planets With Large Oceans are Probably Common in the Milky Way

Credit: NASA/JPL

Within our Solar Systems, there are several moons where astronomers believe life could be found. This includes Ceres, Callisto, Europa, Ganymede, Enceladus, Titan, and maybe Dione, Mimas, Triton, and the dwarf planet Pluto. These “ocean worlds” are believed to have abundant liquid water in their interiors, as well as organic molecules and tidal heating – the basic ingredients for life.

Which raises the all-important question: are similar moons to be found in other star systems? This is the question NASA planetary scientist Dr. Lynnae C. Quick and her team from NASA’s Goddard Space Flight Center sought to address. In a recent study, Quick and her colleagues examined a sample of exoplanet systems and found that ocean worlds are likely to be very common in our galaxy.

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An Insulating Layer of Gas Could Keep a Liquid Ocean Inside Pluto

According to a new study, the idea that Pluto is not a planet is unsupported in scientific literature. Credit: NASA

In July of 2015, NASA’s New Horizons mission made history by becoming the first spacecraft to ever conduct a flyby with Pluto. In addition to providing the world with the first up-close images of this distant world, New Horizons‘ suite of scientific instruments also provided scientists with a wealth of information about Pluto – including its surface features, composition, and atmosphere.

The images the spacecraft took of the surface also revealed unexpected features like the basin named Sputnik Planitia – which scientists saw as an indication of a subsurface ocean. In a new study led by researchers from the University of Hokkaido, the presence of a thin layer of clathrate hydrates at the base of Pluto’s ice shell would ensure that this world could support an ocean.

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NASA Wants to Send a Low-Cost Mission to Explore Neptune’s Moon Triton

Global Color Mosaic of Triton, taken by Voyager 2 in 1989. Credit: NASA/JPL/USGS

In the coming years, NASA has some bold plans to build on the success of the New Horizons mission. Not only did this spacecraft make history by conducting the first-ever flyby of Pluto in 2015, it has since followed up on that by making the first encounter in history with a Kuiper Belt Object (KBO) – 2014 MU69 (aka. Ultima Thule).

Given the wealth of data and stunning images that resulted from these events (which NASA scientists are still processing), other similarly-ambitious missions to explore the outer Solar System are being considered. For example, there is the proposal for the Trident spacecraft, a Discovery-class mission that would reveal things about Neptune’s largest moon, Triton.

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Are There Enough Chemicals on Icy Worlds to Support Life?

A montage of some of the "ocean worlds" in our Solar System. From top to bottom, left to right, these include Europa, Enceladus, TItan and Ceres. Credit: NASA/JPL

For decades, scientists have believed that there could be life beneath the icy surface of Jupiter’s moon Europa. Since that time, multiple lines of evidence have emerged that suggest that it is not alone. Indeed, within the Solar System, there are many “ocean worlds” that could potentially host life, including Ceres, Ganymede, Enceladus, Titan, Dione, Triton, and maybe even Pluto.

But what if the elements for life as we know it are not abundant enough on these worlds? In a new study, two researchers from the Harvard Smithsonian Center of Astrophysics (CfA) sought to determine if there could in fact be a scarcity of bioessential elements on ocean worlds. Their conclusions could have wide-ranging implications for the existence of life in the Solar System and beyond, not to mention our ability to study it.

The study, titled “Is extraterrestrial life suppressed on subsurface ocean worlds due to the paucity of bioessential elements?” recently appeared online. The study was led by Manasvi Lingam, a postdoctoral fellow at the Institute for Theory and Computation (ITC) at Harvard University and the CfA, with the support of Abraham Loeb – the director of the ITC and the Frank B. Baird, Jr. Professor of Science at Harvard.

Artist’s depiction of a watery exoplanet orbiting a distant red dwarf star. Credit: CfA

In previous studies, questions on the habitability of moons and other planets have tended to focus on the existence of water. This has been true when it comes to the study of planets and moons within the Solar System, and especially true when it comes the study of extra-solar planets. When they have found new exoplanets, astronomers have paid close attention to whether or not the planet in question orbits within its star’s habitable zone.

This is key to determining whether or not the planet can support liquid water on its surface. In addition, astronomers have attempted to obtain spectra from around rocky exoplanets to determine if water loss is taking place from its atmosphere, as evidenced by the presence of hydrogen gas. Meanwhile, other studies have attempted to determine the presence of energy sources, since this is also essential to life as we know it.

In contrast, Dr. Lingam and Prof. Loeb considered how the existence of life on ocean planets could be dependent on the availability of limiting nutrients (LN). For some time, there has been considerable debate as to which nutrients would be essential to extra-terrestrial life, since these elements could vary from place to place and over timescales. As Lingam told Universe Today via email:

“The mostly commonly accepted list of elements necessary for life as we know it comprises of hydrogen, oxygen, carbon, nitrogen and sulphur. In addition, certain trace metals (e.g. iron and molybdenum) may also be valuable for life as we know it, but the list of bioessential trace metals is subject to a higher degree of uncertainty and variability.”

Artist rendering showing an interior cross-section of the crust of Enceladus, which shows how hydrothermal activity may be causing the plumes of water at the moon’s surface. Credits: NASA-GSFC/SVS, NASA/JPL-Caltech/Southwest Research Institute

For their purposes, Dr. Lingam and Prof. Loeb created a model using Earth’s oceans to determine how the sources and sinks – i.e. the factors that add or deplete LN elements into oceans, respectively – could be similar to those on ocean worlds. On Earth, the sources of these nutrients include fluvial (from rivers), atmospheric and glacial sources, with energy being provided by sunlight.

Of these nutrients, they determined that the most important would be phosphorus, and examined how abundant this and other elements could be on ocean worlds, where conditions as vastly different. As Dr. Lingam explained, it is reasonable to assume that on these worlds, the potential existence of life would also come down to a balance between the net inflow (sources) and net outflow (sinks).

“If the sinks are much more dominant than the sources, it could indicate that the elements would be depleted relatively quickly. In other to estimate the magnitudes of the sources and sinks, we drew upon our knowledge of the Earth and coupled it with other basic parameters of these ocean worlds such as the pH of the ocean, the size of the world, etc. known from observations/theoretical models.”

While atmospheric sources would not be available to interior oceans, Dr. Lingam and Prof. Loeb considered the contribution played by hydrothermal vents. Already, there is abundant evidence that these exist on Europa, Enceladus, and other ocean worlds. They also considered abiotic sources, which consist of minerals leached from rocks by rain on Earth, but would consist of the weathering of rocks by these moons’ interior oceans.

Artist’s rendering of possible hydrothermal activity that may be taking place on and under the seafloor of Enceladus. Credit: NASA/JPL

Ultimately, what they found was that, unlike water and energy, limiting nutrients might be in limited supply when it comes to ocean worlds in our Solar System:

“We found that, as per the assumptions in our model, phosphorus, which is one of the bioessential elements, is depleted over fast timescales (by geological standards) on ocean worlds whose oceans are neutral or alkaline in nature, and which possess hydrothermal activity (i.e. hydrothermal vent systems at the ocean floor). Hence, our work suggests that life may exist in low concentrations globally in these ocean worlds (or be present only in local patches), and may therefore not be easily detectable.”

This naturally has implications for missions destined for Europa and other moons in the outer Solar System. These include the NASA Europa Clipper mission, which is currently scheduled to launch between 2022 and 2025. Through a series of flybys of Europa, this probe will attempt to measure biomarkers in the plume activity coming from the moon’s surface.

Similar missions have been proposed for Enceladus, and NASA is also considering a “Dragonfly” mission to explore Titan’s atmosphere, surface and methane lakes. However, if Dr. Lingam and Prof. Loeb’s study is correct, then the chances of these missions finding any signs of life on an ocean world in the Solar System are rather slim. Nevertheless, as Lingam indicated, they still believe that such missions should be mounted.

Artist’s concept of a Europa Clipper mission. Credit: NASA/JPL

“Although our model predicts that future space missions to these worlds might have low chances of success in terms of detecting extraterrestrial life, we believe that such missions are still worthy of being pursued,” he said. “This is because they will offer an excellent opportunity to: (i) test and/or falsify the key predictions of our model, and (ii) collect more data and improve our understanding of ocean worlds and their biogeochemical cycles.”

In addition, as Prof. Loeb indicated via email, this study was focused on “life as we know it”. If a mission to these worlds did find sources of extra-terrestrial life, then it would indicate that life can arise from conditions and elements that we are not familiar with. As such, the exploration of Europa and other ocean worlds is not only advisable, but necessary.

“Our paper shows that elements that are essential for the ‘chemistry-of-life-as-we-know-it’, such as phosphorous, are depleted in subsurface oceans,” he said. “As a result, life would be challenging in the oceans suspected to exist under the surface ice of Europa or Enceladus. If future missions confirm the depleted level of phosphorous but nevertheless find life in these oceans, then we would know of a new chemical path for life other than the one on Earth.”

In the end, scientists are forced to take the “low-hanging fruit” approach when it comes to searching for life in the Universe . Until such time that we find life beyond Earth, all of our educated guesses will be based on life as it exists here. I can’t imagine a better reason to get out there and explore the Universe than this!

Further Reading: arXiv