The key to life on Europa? – NASA’s Europa Clipper


Over the past four billion years, the ice-covered moon of Jupiter, Europe, has been stretched and squeezed like taffy. For all potential life, that’s a good thing.

European kneading is caused by gravity and is known as tidal warming. The giant mother planet tugs, with the help of the moons Io and Ganymede, warm the interior of Europe.

“Just like with a rubber bullet, by crushing and shooting it, the bullet will get hot,” says Cynthia Phillips, project staff scientist for the Europa Clipper mission at NASA’s Jet Propulsion Laboratory in Southern California.

Warming tides have likely allowed a vast ocean beneath Europe’s icy shell to remain liquid throughout the history of our solar system. This means that the same forces that paved the way for the development of life on Earth – a constant source of heat, liquid water, and a lot of life-friendly chemistry – could also have existed on Europe during the same amount of time. of time.

“The chemicals plus the heat – that energy can be used as fuel for the biospheres,” Phillips said. “If tidal heating is in place in the bedrock of Europe, it is possible that hydrothermal systems exist there as well. “

It’s time to find out. In 2024, Europa Clipper will be launched on Jupiter, equipped with a suite of sensitive instruments. Once it reaches orbit around the largest planet in our system, Europa Clipper will embark on a series of overflights beyond Europe, rotating its array of cameras and detectors on the ice-covered moon.

In a sense, revealing the ins and outs of warming tides – and how it affects Europa’s ice shell, rocky seabed, and the ocean sandwiched in between – is Europa Clipper’s primary mission. . These details will tell us whether or not Europa might have suitable habitats for life.

“Without tidal heat, we wouldn’t send Europa Clipper,” Phillips said.

This color image of Europe was acquired by Voyager 2 during its close encounter on July 9, 1979. The intricate network of streaks indicates that the crust has been fractured and filled with material from the interior. The absence of relief, mountains or visible craters corresponds to a thick crust of ice. Unlike its icy neighbors, Ganymede and Callisto, Europe has very few impact craters. The relative lack of features and the shallow topography suggest that the crust is young and warm a few kilometers below the surface. The suggested tidal heating process for Io can heat the interior of Europe at a lower rate.

Scientists began to speculate that the tidal warming process could warm the interior of Europe even before Voyager 2’s close encounter with the moon in 1979. Images received from Voyager 2 showed that Europe, unlike its icy neighbors Ganymede and Callisto, has few impact craters. The relative lack of features and the low topography suggest a relatively young and warm crust.

While scientists largely agree that this “push-and-pull” heating is probably happening on Europa, how exactly it works could be critical in determining whether life exists there today.

“Where is the vast majority of tidal heating located? Phillips asks. “Is it mainly in the surface ice cover or at the ice-water interface? Is it mostly at the top of the ocean, or mostly at the bottom of the ocean, in the rock layer? “

The answer will have to come from Europa Clipper. Computer models, or mathematical simulations, are increasingly powerful means of discovering the inner workings of planets and moons. In this case, however, the data collected so far is not yet sufficiently nuanced to properly inform the models.

“Current models can’t prove which one is right,” Phillips said. And in the search for life beyond Earth, the answer is not trivial.

If the warming occurs in the rocky layer of the ocean floor of Europe, it could give rise to hydrothermal vents in deep water. We have hydrothermal vents on Earth at the bottom of our own ocean; scientists have proposed that they may well have been the chemical cauldrons that billions of years ago produced some of the first experiments on the origin of life on our planet.

Such vents, typically located in mid-ocean ridges – the seams between continental plates – remain active sites for thriving ecosystems.

“There is abundant life deep in the Earth’s oceans, almost independent of sunlight,” Phillips said. “There’s enough heat and some interesting chemistry going on, with chemical gradients as seawater flows through hot rock and then is ejected at high temperatures.”

Research and computer modeling show that volcanic activity may have occurred on Europe's seabed in the recent past - and may still occur.  Computer modeling shows how the internal heat produced by the tides - distorting the shape of Europe as it changes its distance from Jupiter during its orbit - could partially melt its rock layer, a process that could fuel volcanoes at the bottom of the ocean.

Research and computer modeling show that volcanic activity may have occurred on the seabed of Europe in the recent past – and may still occur. Computer modeling shows how the internal heat produced by the tides – distorting the shape of Europe as it changes its distance from Jupiter during its orbit – could partially melt its rock layer, a process that could fuel volcanoes at the bottom of the ocean.

Something similar could have happened over Europe, whose ocean is completely cut off from the Sun by its thick, icy shell – even from the relatively faint sunlight hitting its surface. Like some deep-sea organisms on Earth, all European life is said to be completely dependent on chemical and other sources of energy, and not on photosynthesis caused by sunlight.

“It could be a story in which, either through warming tides or intense internal heating during the formation of Europe, volcanic activity occurred at some point,” said Steve Vance, astrobiologist and geophysicist. at JPL which studies ocean worlds and creates computer models of their interiors.

If so, then “high temperature hydrothermalism has played a role in the evolution of the ocean, potentially supporting sustenance or the origin of life over Europe,” he said.

The modeling to which Vance contributed showed that the main heating locations would be in the high latitude polar regions of Europe, where volcanic activity could still continue.

“We don’t know how much Europa flexes, or how much energy in the Jupiter-Europa satellite system is dissipated in the form of warming tides,” he said. “We need a lot more information about Europa, what it is made of and its internal structure.”

To this end, Vance will be particularly interested in data from Europa Clipper’s geophysical instruments, which will remotely measure the structural features of the moon. Radar combined with gravitational measurements, for example, could tell us how warm the interior is, if there are seamounts (seamounts), how thick the ice is and at how spongy it is, he said.

Europa Clipper’s entire suite of instruments will work together to capture a full picture of the effects of warming tides, Phillips said. This includes the Europa Thermal Emission Imaging System (E-THEMIS).

“The E-THEMIS thermal imager will be able to search for hot spots, study surface and near-surface properties at thermal wavelengths,” she said. “If there are places where the ice layer is thinner, or if there is liquid water in the frozen crust, it is possible that the E-THEMIS instrument is able to detect these places. “

The Europa Thermal Emission Imaging System (E-THEMIS) uses infrared light to distinguish warmer regions of Europe where hot liquid water may be near the surface or have burst on the surface.  It will also measure the texture of the surface to understand the small-scale properties of the surface.

The Europa Thermal Emission Imaging System (E-THEMIS) uses infrared light to distinguish warmer regions of Europe where hot liquid water may be near the surface or have burst on the surface. It will also measure the texture of the surface to understand the small-scale properties of the surface.

A frozen ocean world with hot spots below is probably more likely to be habitable for microorganisms than for large multicellular creatures – things like whales, giant squids, or fish – Phillips said. But even that would be extraordinary.

“If we found one-celled organisms over Europe, it would be mind-boggling – overwhelming – in terms of importance,” she said. “It would be a second origin of life. In our insignificant little solar system, if life has started not once but twice, it is revolutionary. It means that life is abundant – life is everywhere. It gives me shivers. “

By Pat Brennan


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