Zahlen, bitte! Jupiter's Moon Europa: Exciting Candidate in the Search for Life

A total of 97 moons are currently known to orbit Jupiter, but none of its numerous companions sparks scientists' imagination as much as Europa. This is due to its special characteristics: the icy crust, cold at -160 degrees Celsius, doesn't seem particularly inviting at first glance, but it may conceal a vast ocean where researchers hope to find life. Both NASA- and ESA probes are on their way to unlock more of the moon's secrets.

Its appearance alone is remarkable. With a diameter of 3121 kilometers, Europa is only slightly smaller than Earth's moon (3475 kilometers) and thus the sixth-largest moon in the solar system. It was officially discovered around January 7, 1610, by Galileo Galilei, along with the Jovian moons Io, Ganymede, and Callisto, which later became known as the “Galilean moons.”

Zahlen, bitte!

In this section, we present amazing, impressive, informative and funny figures ("Zahlen") from the fields of IT, science, art, business, politics and, of course, mathematics every Tuesday. The wordplay "Zahlen, bitte!" for a section about numbers is based on the ambiguity of the German word "Zahlen." On one hand, "Zahlen" can be understood as a noun in the sense of digits and numerical values, which fits the theme of the section. On the other hand, the phrase "Zahlen, bitte!" is reminiscent of a waiter's request in a restaurant or bar when they are asked to bring the bill. Through this association, the section acquires a playful and slightly humorous undertone that catches the readers' attention and makes them curious about the presented numbers and facts.

• Alle Artikel zu "Zahlen, bitte!"

In the same period, the German astronomer Simon Marius independently discovered the four moons and later claimed to have observed them as early as 1609. However, he used the old Julian calendar, while Galilei used the modern Gregorian calendar, resulting in Marius discovering the moons on January 8, 1610. Nevertheless, Marius became the namesake for the moons. Europa's name originates from Greek mythology and refers to the daughter of the Phoenician king Agenor and a lover of Zeus, who was called Jupiter in Roman religion.

First Images from the Voyager Missions

When Voyager I and Voyager II flew past Jupiter on their “Grand Tour” in March and April 1979, they also sent the first detailed images of Europa back to Earth. These were astonishing: with an albedo of 0.68, meaning it reflects 68 percent of the incident sunlight, Europa is one of the brightest moons in the solar system. Yet, its ice shell is quite cold: at up to -130 degrees Celsius, the ice is partly as hard as granite.

Its surface is also a peculiarity compared to other celestial bodies: the icy surface is interspersed with only a few impact craters. This indicates that geological activity alters the surface's composition. Furthermore, ice volcanism has been discovered in images, where water vapor rises to 200 kilometers from erupting geysers, then likely freezes and snows onto the surface as ice particles.

The surface is crisscrossed by many fissures (called lineae) and ridges. These are caused by the strong tidal forces from Jupiter and the resonant forces of the other moons, Io and Ganymede, which significantly influence the moon, causing its crust to lift to 60 meters during its orbits. Particularly fractured areas like the Conamara Chaos region are called “chaos terrains” by researchers.

Jupiter Orbit in 3.5 Days

Jupiter's gravitational influence also ensures that Europa, like the other inner moons, has a synchronous rotation and always shows the same side to the giant planet as it orbits. It's also moving fast: one orbit around Jupiter at an average distance of 671,100 kilometers takes 3 days, 13 hours, and 14 minutes. For comparison, the average distance from the Moon to Earth is 384,400 kilometers.

With measurements from the Galileo space probe around the turn of the millennium, Europa became an interesting candidate for life; the data provided evidence of a vast ocean beneath Europa's ice crust. It is suspected that more liquid water exists on Europa than in all the world's oceans. Beneath this, a silicate mantle and an iron core are presumed, which generates a magnetic field. It is believed that the ocean is kept liquid by tidal forces, volcanic activity, and a high salt content. The ice shell is thought to be up to 18 kilometers thick, covering an ocean up to 100 kilometers deep.

Researchers hope to find life forms in the ocean similar to those found in Earth's deep sea at hydrothermal vents (like black smokers). There are also indications that Europa's ocean has existed for longer than Earth's. To investigate this question and explore Europa further, two space probes are on their way: “JUICE” (Jupiter Icy Moons Explorer) from the European Space Agency ESA, which has been en route since April 14, 2023, and “Europa Clipper” from NASA, which launched into space on October 14, 2024.

While JUICE is set to explore Ganymede and Callisto in addition to Europa, Europa Clipper's sole main target is the Jovian moon itself. The latter mission plans at least 49 flybys, ranging from an altitude of 2700 kilometers down to 49 kilometers. The DLR explained that Europa Clipper and JUICE complement each other ideally, and the DLR are involved in two of the 10 Europa Clipper experiments. Starting in 2030, both space probes, weighing around 6 tons, are expected to explore Europa over several years.

Among other things, they aim to collect data for potential follow-up missions that also aim to penetrate the oceans, which is expected to be a challenge given the extreme conditions. More will be known in five years.

(mawi)