OCEANS IN SPACE
With a new NASA MISSION lifting off next week to explore A WATERY MOON ORBITING jupiter, we take a look at five (probable) oceans in DEEP space
A rendering of NASA's Europa Clipper spacecraft. Credit: NASA/JPL-Caltech.
Once believed to be rare in our solar system, scientists now know that water is plentiful on the moons and planets in our cosmic neighborhood – with recent missions confirming and pinpointing ice and water deposits at the south poles of the Moon and Mars. Further out, entire oceans vaster than those on Earth might lie hidden on moons orbiting the gas giants of the outer solar system and even on Earth-like planets in distant star systems. Buried under thick crusts of ice but heated by warm cores and massive tidal forces, some of these far-off oceans could even be home to unknown extraterrestrial lifeforms. With World Space Week kicking off today and a new NASA ‘Ocean Worlds’ spacecraft set to launch on October 10, join us on a journey to five of the most likely locations for oceans in space and learn more about how we’re planning to explore them.
Credit: NASA/JPL-Caltech/SETI Institute.
Europa
Distance from Earth: 433.6 million miles
Easily visible with good binoculars or a small telescope, Europa and her three sister moons of Ganymede, Callisto and Io are among the most spectacular sights to pick out in the night sky. These four Galilean moons appear as brilliant little dots of light orbiting Jupiter and change places as the night progresses, slowly turning like a miniature solar system. Three out of the four are candidates for oceans, but of all the possible places for subsurface water and unknown life Europa is the one that has scientists most excited – with three space missions set to visit.
Due to blast off from Kennedy Space Center on October 10 and reach its destination in 2030, the Europa Clipper mission will join the American Juno probe (already in orbit) and European Jupiter Icy Moons Explorer (already en route). Beyond other mission goals, all are designed to conduct fly-bys of Europa to get a better look at its mysterious surface – which is the smoothest in the solar system and incredibly bright. The most specialized is Europa Clipper: the largest spacecraft for planetary exploration humanity has built so far.
Once in orbit around Jupiter and Europa, it will study and photograph the moon’s icy crust – thought to be 10 to 15 miles thick. As NASA’s mission team explains, “Europa's surface has signs there may be an ocean beneath it. Images of the surface show patterns of cracks and ridges that suggest a global ocean allowing for large tides that deform the surface. In addition, Europa’s surface geology suggests that warm ice has risen upward through the ice shell, likely from near an ice-ocean interface.”
Beyond the presence of this ocean, thought to contain twice as much water as all Earth’s oceans combined, scientists have detected clay-like minerals and the presence of carbon dioxide – both potential signals there might be life on Europa too. Whether this turns out to be tiny microbes, giant space whales or nothing at all, we’ll likely have to wait until 2030 and beyond to find out for sure.
Technicians at Kennedy Space Center prepare to load propellant onto NASA's Europa Clipper spacecraft. Credit: NASA/Kim Shiflett.
“Life needs a source of energy, the presence of certain chemical compounds, and temperatures that allow liquid water to exist. Jupiter’s icy moon Europa seems to be just such a place.”
NASA MISSION BRIEFING
Credit: NASA/JPL/University of Arizona.
TITAN
Distance from Earth: 812.7 million miles
One of the only known locations beyond Earth where surfing might be feasible, Titan is a vast, super strange world of methane and ethane seas. Orbiting the gas giant Saturn at a distance of over 800,000 miles, it features an atmosphere denser than ours, methane rain, cryovolcanoes, Earthlike dunes, rivers, deltas and seasonal weather patterns. Even at -290 degrees Fahrenheit, the hydrocarbon seas of Titan remain liquid and likely ripple in the wind as on Earth.
During early missions, scientists theorized that surfing on Titan might be possible if the wind whipped up waves big enough, with some estimates even suggesting they could be ten times larger than at Nazaré. More recent research, sadly, suggests these ‘swells’ might top out at 1 or 2 inches – a major bummer for science and future surf trips. Perhaps most remarkable about Titan is the fact it’s a dynamic world of shifting seasons. As a NASA mission briefing explains: “It is the sole other place in the solar system known to have an Earthlike cycle of liquids raining from clouds, flowing across its surface, filling lakes and seas and evaporating back into the sky. Titan is also thought to have a subsurface ocean of water.”
We’ll find out more when NASA’s Dragonfly mission launches in 2027 and arrives at Titan in 2034 with a drone helicopter onboard to descend into Titan’s hazy atmosphere and give us another glimpse of this enigmatic moon.
Neptune’s moon Triton. Credit: NASA/JPL/USGS.
TRITON
Distance from Earth: 2.687 billion miles
Among the many stunning photos captured by NASA’s Voyager 2 probe as it toured the outer planets, the above image of Triton, captured in 1989, stands out. It was humanity’s first close-up look at Neptune’s largest moon, and shows in detail the coldest lunar or planetary surface in our solar system. Despite temperatures of -391 degrees Fahrenheit, researchers believe Triton’s icy shell could hide a vast subsurface ocean that melted when after moon was captured by Neptune’s massive gravity well.
Because it orbits in the wrong direction around the planet compared to other moons, researchers believe Triton likely drifted in from a remote region of space known as the Kuiper Belt. Once in orbit around Neptune, the extreme tidal forces generated by the huge planet – combined with natural radiation in the moon’s core – might have generated a liquid ocean beneath the surface. It’s so far from the sun that it’s considered a less likely candidate for life, but a proposed mission named Trident could visit this distant moon the next time the planets align for a gravity assist manoeuvre, in about 14 or 15 years from now.
“The story of oceans is the story of life. Oceans define our home planet, But more profound still, the story of our oceans envelops our home in a far larger context that reaches deep into the universe and places us in a rich family of ocean worlds that span our solar system and beyond”
NASA OCEAN WORLDS INTRODUCTION
Enceladus. Credit: NASA/JPL/Space Science Institute
Enceladus above Saturn's rings. Credit: NASA/JPL/Space Science Institute.
Enceladus
Distance from Earth: 813.4 million miles
Another moon of Saturn, Enceladus stands out as an ocean world worth exploring because of its unique hydrothermal vents – which give us a glimpse at the chemistry of its subsurface ocean. As a NASA mission briefing explains, “a handful of worlds are thought to have liquid water oceans beneath their frozen shell, but Enceladus sprays its ocean out into space where spacecraft can sample it. From these samples, scientists have determined that Enceladus has most of the chemical ingredients needed for life, and likely has hydrothermal vents releasing hot, mineral-rich water into its ocean.”
First discovered by the Cassini spacecraft in 2005, the vents of Enceladus spew a mixture of water vapor, carbon dioxide, methane and ammonia, along with salts and silica – forming one of Saturn’s distinctive rings as it orbits the giant planet. The plumes are rich in organic materials, leading researchers to believe the moon’s ocean could harbor life. Because they also contain nanograins of silica formed only at specific temperatures and pressures, scientists believe Enceladus is home to subsurface thermal vents at the bottom of its ocean – similar to those found on Earth. Intriguingly, these are one of the candidate locations for the beginnings of life on our planet, meaning with similar conditions an entirely different form of life may have emerged deep in this distant, hidden ocean. We’ll need to wait awhile to learn more given the vast distance, but two new missions to Saturn and Enceladus have been proposed.
Artist's rendering of the Kepler-138 star system. Credit: NASA/JPL-Caltech/R. Hurt (IPAC).
THE OCEAN PLANETS OF Kepler-138
Distance from Earth: 1.287 quadrillion miles
Much, much, much further out in space, researchers have identified two absolutely mind-blowing exoplanets: Kepler-138c and Kepler-138d. The first true “water worlds” ever discovered, both feature vast oceans over 1,000 miles deep – that’s five hundred times deeper than ours. Both planets orbit the red dwarf star Kepler-138, named after the space telescope which first imaged it. They are slightly larger than our home planet, but less dense – a finding which led astronomers to delve deeper and publish a paper in December 2022 confirming the discovery.
As co-author Björn Benneke explains, “We previously thought that planets that were a bit larger than Earth were big balls of metal and rock, like scaled-up versions of Earth, and that’s why we called them super-Earths. However, we have now shown that these two planets, Kepler-138 c and d, are quite different in nature and that a big fraction of their entire volume is likely composed of water. It is the best evidence yet for water worlds, a type of planet that was theorized by astronomers to exist for a long time.”
Whether and what kind of strange life exists in these unbelievably deep, massive oceans may remain a mystery for years to come, given the vast distances involved – the star system is over 200 light years from us. We can’t send probes (yet) but with increasingly sophisticated telescopes researchers can analyze the atmospheres of these distant worlds and give us clues to possible life processes in their oceans. With NASA’s James Webb Space Telescope only just getting started, we may soon discover more oceans world closer to home… or further out amid the endless stars of our galaxy.
Text: Chris Hatherill | Images: NASA
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