Could the ocean beneath Europa's icy surface harbor life? Europa Clipper sets out to find out

Artist's impression of the Europa Clipper probe flying over Europa

The moment the Europa Clipper probe was launched

Introduction

Jupiter's moon Europa is considered one of the most likely objects in the solar system to harbor life, and now a probe has just set sail to explore the planet's potentially habitable environment.

At 0:06 a.m. Beijing time on October 15, after being delayed for many days due to the impact of hurricanes, the Europa Clipper probe of the National Aeronautics and Space Administration (NASA) was launched from the Kennedy Space Center in Florida, USA, on a SpaceX Falcon 9 heavy rocket, heading for Europa, Jupiter's second moon, to look for an environment on this Jupiter satellite that may support life.

As the largest planetary probe built by NASA so far, Europa Clipper weighs about 6 tons, equivalent to the weight of an African elephant . When its solar sail is unfolded, its maximum width reaches about 30.5 meters, which is wider than a standard basketball court. According to the plan, it will arrive in the Jupiter system in about 5 and a half years and begin the exploration of Europa.

Solar panels on the Europa Clipper

The deep ocean beneath the ice

The entire crust of Europa is composed of an ice layer 15 to 25 kilometers thick. The salt water ocean below is deep and boundless, with a depth of 60 to 150 kilometers, and the amount of water is twice as much as the total of the Earth's oceans.

Since the late 1990s, various signs have continuously confirmed the existence of this ocean, inspiring humans to imagine its mysteries. Therefore, the Europa Clipper carries nine precision instruments to detect whether this ocean world has habitable conditions suitable for life.

You may ask

What kind of environment is suitable for the existence of life?

Within the scope of currently known life, a place has the potential to become the cradle of life if it has liquid water, an energy source and carbon-containing compounds (i.e. organic matter) at the same time.

On Earth, water and organic matter are everywhere, and sunlight is the energy source that drives plants to perform photosynthesis, injecting vitality into the entire biosphere. However, in the dark and deep salt water ocean of Europa, sunlight cannot penetrate hundreds of meters of darkness, and photosynthesis cannot be carried out here. Is it possible for life to exist in such an environment?

In 1977, scientists witnessed another miracle of life in the underwater world of nearly 2,500 meters near a volcanic hotspot on the Pacific Ocean floor. They were surprised to find that there was a rich ecosystem around the deep-sea hydrothermal vents, and the life in it did not rely on photosynthesis, but on chemosynthesis, that is, obtaining energy through chemical reactions.

This discovery completely overturned scientists' traditional understanding of the conditions for the habitability of life. At this point, scientists also realized that sunlight is not a necessary condition for the existence of life.

The transition zone between two different terrains on Europa

Heat source from Jupiter's gravity

So why can the sea water under Europa's thick ice shell remain liquid?

This is thanks to the frictional heating effect of Jupiter's powerful gravity. As Europa moves in its orbit, its surface is stretched and relaxed by Jupiter's gravity, generating heat.

However, for Europa's ocean to be habitable to life, a continuous supply of raw materials to support some form of chemosynthesis would be required, either from hydrothermal vents on Europa's rocky seafloor or from seepage from the icy crust (the "ceiling" of the seafloor).

Unfortunately, the specific operation of these mechanisms is still unclear, and scientists still need to collect more data from different angles to reveal its mysteries. However, there is increasing evidence that there are jets of material from the surface of Europa into space. If these materials do come from the ocean, then measuring their composition will help understand the habitability of this ocean for life.

The moment the Europa Clipper probe was launched

A tortuous road of exploration

Looking back, the exploration mission to Europa can be traced back to at least the 1990s. NASA's "Europa Orbiter" project was canceled in 2002, and the ambitious "Jupiter Icy Moons Orbiter" (Jimo) plan was also aborted in 2005. However, human beings' enthusiasm for exploring Europa has not been extinguished.

In 2008, NASA and the European Space Agency (ESA) jointly proposed the "Europa-Jupiter System Mission - Laplace" (EJSM-Laplace), which aims to launch orbiters to Europa and Ganymede. Although these two projects were cancelled in 2011, the subsequent launch of ESA's "Jupiter Icy Moons Explorer" (Juice) and NASA's "Europa Clipper" has injected new vitality into human exploration of the mysteries of Europa.

Juice will be launched in April 2023 and is expected to arrive at its destination in July 2031, while Europa Clipper will set off on October 10. The two spacecraft will work side by side in the Jovian system for three years, and are expected to eventually achieve a grand blueprint similar to the 2008 EJSM-Laplace plan.

A circuitous journey into space

However, it is not so easy to fly to Jupiter . Jupiter and the Earth both orbit the sun in their own orbits, with an average distance of about 770 million kilometers between them, and the amount of fuel that a spacecraft can carry is limited. In order to save fuel, mission planners plan to have the Europa Clipper fly by Mars first and then by the Earth, using the gravity of the two planets as a "slingshot" to accelerate the probe.

Europa Clipper's circuitous route to Jupiter

After five and a half years and 2.9 billion kilometers of flight, Europa Clipper will start its engines and enter Jupiter's orbit in April 2030. When it arrives at Jupiter, the probe will not orbit Europa directly, but will cleverly fly around Jupiter. During this period, it will fly over Europa nearly 50 times and gradually build a global scan of Europa.

During the flyby, a magnetic field instrument on board will accurately determine the depth and salinity of the ocean; a mass spectrometer will be able to "taste" the jet material and analyze its composition; a ground-penetrating radar will penetrate the ice shell to detect the presence of water; and an infrared instrument will scan the surface for traces of organic matter and perform thermal imaging.

The nine scientific instruments will provide strong support for scientists to fully reveal Europa's ocean, geological structure and current activity status, thereby determining whether there is an environment that may support life underground in Jupiter's icy moon Europa, which is also the core goal of NASA's mission.

For decades, planetary scientists have believed that ocean worlds like Europa could be potential habitats for life. While Europa Clipper cannot directly detect the presence of life, it marks the first time that an ocean world has been studied in depth specifically to search for signs of habitability.

If any signs of life are found on Europa in the future, a subsequent lander may be launched to conduct more in-depth exploration. The surface observation data collected by Clipper during this mission will be crucial in planning this follow-up mission.

In this fantastic journey of searching for extraterrestrial life, Europa is undoubtedly a destination full of mystery and hope. With the setting sail of the Europa Clipper, mankind has taken another solid step towards uncovering the truth of the mystery of life in the universe.

References

1. https://theconversation.com/nasas-europa-clipper-spacecraft-will-investigate-whether-an-icy-moon-of-jupiter-can-support-alien-life-240371

Compiled by: Liu Yun

Planning: Liu Kun, Zhang Chao, Yang Liu

Reviewer: Liu Yong, Researcher at the National Space Science Center of the Chinese Academy of Sciences, Ambassador of China's Space Science Popularization