Uncovering the Secrets of the Underglacial Ocean: Europa Clipper Exploration Journey

Author | Feng Ziyang

Audit | Huang Jian

Editor | Zhao Jingyuan

Artistic image of Europa Clipper (Image courtesy of NASA)

At 00:06 on October 15, 2024, Beijing time, the Europa Clipper developed by NASA was successfully launched at the Kennedy Space Center via a heavy Falcon rocket, marking the beginning of the Europa Clipper interplanetary mission. The mission aims to launch the Europa Clipper probe to a predetermined orbit near Jupiter, and conduct about 50 flybys of Jupiter's satellite Europa, to explore the geological conditions and habitability of this Jupiter satellite, and is expected to arrive in Jupiter orbit in 2030. The Europa Clipper carries 9 major scientific instruments. It is not only NASA's largest planetary probe in history, but also NASA's largest planetary exploration mission to date. The entire mission is expected to cost about $5.2 billion. So, what is the value of this satellite? What can attract people to make such a huge investment? This has to start with the environment of Europa.

Europa Clipper was successfully launched (Image from SpaceX)

Europa was discovered by Italian astronomer Galileo Galilei and German astronomer Simon Marius in January 1610. It is the sixth closest to Jupiter among the 95 known satellites of Jupiter. Among the four Galilean satellites (Io, Europa, Ganymede, and Callisto), Europa has the smallest mass and diameter, with a diameter of only 3,121.6 kilometers, slightly smaller than the moon. Since the distance between Europa and the sun is five times the distance between the sun and the earth, the solar radiation it receives is only 1/25 of that of the earth.

Four Galileo satellites (Image courtesy of NASA)

Prior to this, probes such as Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, Galileo and Juno have conducted a general survey of this satellite. These surveys show that Europa is rich in organic elements such as carbon, hydrogen, oxygen, nitrogen, etc. Its surface is mainly composed of water ice and rocks. There may be a huge ocean of liquid water under these ice layers, which can reshape the surface of Europa. There is evidence that this subglacial ocean has existed for 4.5 billion years and contains elements necessary for life, so it may be a place for the birth of life. There may also be magma movement under the ocean of Europa, just like on Earth. Under the action of tidal heating, the deep liquid water of Europa will occasionally eject from the surface like a volcanic eruption, forming intense hydrothermal activity. These movements have profoundly affected the surface and even the internal structure of Europa, and this warm environment may be suitable for the survival of microorganisms.

Europa's subicidal ocean (artistic image) (Image courtesy of NASA)

There are countless black and reddish-brown cracks on the surface of Europa, which may be unique landforms formed by the movement of ice layers similar to that of the Earth's plates, which may contain salts and sulfur compounds. Some double ridge structures on the surface are related to the ejection of liquid water.

The mysterious icy satellite Europa (Image courtesy of NASA)

The Europa Clipper mission has three major scientific goals: first, to detect the thickness of Europa's ice shell and confirm the interaction between the surface ice and the subglacial ocean; second, to study the chemical properties of the main compounds in the water ice structure and their relationship with the chemical composition of the subglacial ocean; in addition, to investigate the geological characteristics of the satellite. Through these explorations, scientists can better understand the internal structure and environment of Europa and confirm whether its underground ocean has the conditions to nurture life.

The flight path of Europa Clipper (Image courtesy of NASA)

To achieve these goals, Europa Clipper has set off. However, there are still great risks and challenges on the way to Europa. In late February/early March 2025, it will reach a distance of 500 to 1000 kilometers from the surface of Mars, using the gravity of Mars to help it accelerate forward; in December 2026, Europa Clipper will return to the vicinity of the Earth, fly by the Earth at an altitude of about 3200 kilometers, and use the gravity of the Earth to further accelerate, so that the probe has enough energy to fly to Jupiter, about 500 million kilometers from the Earth. In April 2030, Europa Clipper will brake and decelerate for 6 hours to enter orbit around Jupiter. After this, Europa Clipper will change orbits several times to reach the planned orbit. It is expected that Europa Clipper will make its first flyby of Europa in the spring of 2031, and will fly by this fascinating satellite many times in more than 3 years. It will fly by Europa at a distance of only 25 kilometers from its surface in order to conduct a detailed scientific investigation and collect data on its thin atmosphere, surface, ice shell and sub-ice ocean. When the mission is completed in September 2034, Europa Clipper will crash into the surface of Ganymede, another satellite of Jupiter, to end its mission.

Europa Clipper's orbit (Image courtesy of NASA)

In order to ensure that Europa Clipper can perform its mission normally in extreme environments, NASA has used countless "black technologies". The most attractive of these is its pair of long solar panels, which can reach a length of 30.5 meters after being unfolded. They are the largest solar panels currently developed by NASA. They will provide a large amount of electricity for Europa Clipper in the extremely low temperature of Jupiter's orbit. The spacecraft platform is composed of an aluminum cylindrical propulsion module and a 5-meter-long rectangular box. The box contains a 150-kilogram titanium, zinc and aluminum shielding room that protects electronic components from radiation from Jupiter.

Europa Clipper is slightly longer than a standard basketball court (Image courtesy of NASA)

Europa Clipper carries nine high-precision scientific instruments, including the Europa Thermal Emission Imaging System (E-THEMIS) for detecting geologically active areas, the Europa Mapping Imaging Spectrometer (MISE) for analyzing the chemical composition of collected samples, the Europa Imaging System (EIS) for geological mapping, the Europa Ultraviolet Spectrometer for detecting eruption plumes, the Europa Assessment and Sounding Radar (REASON) for detecting ocean and near-surface structure, the Europa Clipper Magnetometer (ECM) for measuring Europa's magnetic field, the Plasma Magnetic Sounder (PIMS) for measuring Jupiter's magnetosphere and Europa's ionosphere, the Planetary Probe Mass Spectrometer (MASPEX) for determining various compounds in complex mixtures, and the Surface Dust Mass Analyzer (SUDA), etc. These scientific equipment will play a key role in Europa Clipper's scientific expedition.

Schematic diagram of the structure of Europa Clipper (picture from Wikipedia)

The Europa Clipper mission is one of the largest planetary exploration missions in NASA's history. It will also be an important milestone in the human exploration of planets and the exploration of extraterrestrial life. Through this expedition, scientists hope to uncover the secrets of Europa's sub-icy ocean and explore the possibility of habitability. We look forward to the valuable data sent back by Europa Clipper to reveal more mysteries about the universe and life.

References

1. Li Chunhui, Chapter 13: Planetary Rings and Satellites of Jupiter and Saturn, Introduction to Planetary Science, Guangxi Normal University Press

2. Europa Facts, NASA, https://science.nasa.gov/jupiter/moons/europa/europa-facts/#h-structure

3. EuropaClipperMission, NASA, https://europa.nasa.gov/mission/about/

4. Mission Timeline, NASA, https://europa.nasa.gov/mission/timeline/

5. Europa(moon), Wikipedia, https://en.wikipedia.org/wiki/Europa_(moon)

6. Europa Clipper, Wikipedia, https://en.wikipedia.org/wiki/Europa_Clipper

7. Europa Clipper Cost Chart, The Planetary Society, https://www.planetary.org/charts/europa-clipper-cost-chart

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