Can humanity live on the moons of the solar system?
As part of NASA’s Apollo program, 12 astronauts visited the Moon between 1969 and 1972. Since then, humans have not returned, and the Moon remains the only planet humans have ever visited. The Moon does not have an atmosphere similar to Earth’s, and there is no wind or water to wash away the Apollo astronauts’ footprints. The Moon also lacks tectonic activity, unlike Earth and Venus, hence its well-preserved internal structure since its formation. Scientists now have the chance to understand how the interiors of planets form. Our Moon is a historical encyclopedia containing information about ancient Earth. Likewise, exploring our solar system and understanding the planets around us involves taking a close look at the multiple moons that surround them. Jupiter, the largest planet in the Milky Way, holds many unexplored mysteries. His moon or shall we say moons hold the answer.
Jupiter and its many moons
Jupiter has 53 named moons and over 20 more awaiting formal identification. Currently, Jupiter is believed to have 79 moons in total. There are many fascinating moons around the globe, but the Galilean satellites – the first four moons identified outside Earth – hold the greatest scientific curiosity.
The Galilean satellites are named after Italian scientist Galileo Galilei, who first observed Jupiter’s four largest moons in 1610. Simon Marius, a German astronomer, claimed to have spotted the moons around the same time, but because that he did not record his findings, Galileo is credited with making the discovery. Each of these large moons – Io, Europa, Ganymede and Callisto – are unique worlds.
The most volcanically active body in the solar system is Io. Sulfur is present on the surface of Io in a variety of vibrant forms. Io’s slightly elliptical orbit around Jupiter causes surface “tides” to rise 100 meters high, creating enough heat to sustain volcanic activity and evaporate any remaining water. Hot silicate magma powers the volcanoes of Io.
Ganymede is the largest moon in the solar system (larger than the planet Mercury) and the only known moon to have its own internally generated magnetic field.
Callisto’s surface is heavily cratered and ancient, providing a visible record of events in the solar system’s early past. The very small tiny craters on Callisto, on the other hand, imply a low level of current surface activity.
Europa’s surface is mostly water ice, and there is evidence that it may cover an ocean of water or melting ice below. Europa is thought to have twice as much water as Earth. Astrobiologists are intrigued by this moon’s potential for a “habitable zone.” On Earth, life forms have been found thriving near underground volcanoes and in other harsh environments that may parallel what may exist on Europa.
The Europa Clipper Mission
Europa is named after a woman who was kidnapped by Zeus in Greek mythology. Europa is about 90% the size of Earth’s Moon, with an equatorial diameter of 1,940 miles (3,100 kilometers). Because its surface is made up of water ice, it reflects 5.5 times more sunlight than our Moon. Sunlight takes about 45 minutes to reach Europa. Due to the distance, sunlight is about 25 times weaker on Jupiter and Europa than on Earth. Europa orbits Jupiter every 3.5 days and is held in place by Jupiter’s gravity, so the same hemisphere of the moon constantly faces the planet.
With a particular interest in Europa and its potential life forms, NASA is planning a mission called Europa Clipper. It will also look for organic materials such as sulfates and carbonates. Europa Clipper will help us understand the potential for life on other ocean worlds in our solar system and beyond by establishing whether Europa has the appropriate conditions for life. One of NASA’s most expensive missions, the Clipper will explore everything from the depth and salinity of the ocean to the thickness of the ice crust.
Europa Clipper: construction and assembly
The spacecraft’s main body is a massive 10-foot-tall (3-meter-tall) propulsion module designed and built by the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland. The nine scientific instruments that Europa Clipper will carry are: Plasma Instrument for Magnetic Sounding (PIMS), Europa Clipper Magnetometer, Mapping Imaging Spectrometer for Europa (MISE), Europa Imaging System (EIS), a radar for Europa Assessment and Sounding: Ocean to Near surface (REASON), Europa Thermal Emission Imaging System (E-THEMIS), MAss SPectrometer for Planetary Exploration/Europa (MASPEX), Europa Ultraviolet Spectrograph and a surface dust analyzer (SUDA).
The radar device will map the ice of Europe, while a magnetometer will estimate the depth and salinity of the ocean. Color and infrared cameras will map the surface and look for warm areas where the ocean could leak through the ice shell. Spectrometers will assess the composition of the surface and analyze any plumes projecting water into space. The mission also has the capability to directly sample Europa’s atmosphere, including potential seawater and surface particles ejected into space by radiation from Jupiter.
To what end?
Once all the data has been collected, NASA could continue with an extended mission, possibly focusing on particularly fascinating sites with repeated close flybys. After four years of scientific flybys, the goal is to plant the spacecraft in a place less astrobiologically intriguing than Europa. Scientists don’t want to risk contaminating Europa with terrestrial bacteria that escaped NASA’s clean rooms. Thus, NASA’s official goal is to crash Clipper into Ganymede, the largest known natural satellite in our solar system.
By then, Clipper should have returned enough Europan surface data to Earth for NASA to select a landing site for a subsequent lander mission. NASA cannot rule out the possibility that Clipper was extremely lucky and detected signs of life during one of its close flybys of Europe. Clipper, however, is primarily a survey expedition. A follow-on surface lander will likely be needed to find biosignatures on Europa’s surface.
Other missions targeting Europa: JUICE
JUICE, or Jupiter ICy moons Explorer, will provide information on the evolution and habitability of icy worlds near Jupiter and Jupiter-like exoplanets. JUICE will most certainly broaden our search for life in the universe.
JUICE is scheduled to launch in August 2023 and land on Jupiter in 2031. It will orbit Jupiter for 2.5 years, often flying within 200 to 1,000 kilometers (120 to 620 miles) of icy moons. During the initial phase of the mission, the solar-powered spacecraft will pass Europa twice and Ganymede and Callisto 12 times each, enabling unprecedented close investigations of these moons. JUICE will orbit Ganymede for at least nine months during the next and final phase of the mission. It would be the first time that a spacecraft has orbited a moon other than ours.
Jupiter is also being studied as part of the JUICE expedition as it impacts icy moons and their circumstances. Jupiter has a huge magnetic field that is 20 times stronger than Earth’s; Europa and Ganymede, in particular, are covered in high-radiation particles flying along Jupiter’s magnetic field lines due to their proximity to Jupiter. JUICE’s magnetometer, particle detector and plasma instrument will map and measure Jupiter’s magnetic field, detect particles passing through it and study how they affect the material of the moons’ surfaces.
JUICE and Clipper will land around Jupiter at the same time. China is also considering a trip to Jupiter’s moons, with a Callisto orbiter and lander being one of its best options. All of these missions will tell us not only about the habitability of Jupiter’s icy moons, but also about the icy worlds orbiting other massive planets in the universe.
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