by AOP Astronomer Gavin Ramsay

Today the European Space Agency (ESA) successfully launched its Jupiter Icy Moons Explorer (JUICE) mission from Kourou in French Guiana on an Ariane 5 launcher after it was delayed for a day due to a weather forecast of potential storms. In the planning stage for several decades, it was formally approved by ESA in 2014. After a series of flybys around Venus and Earth to give it a gravitational `push’ it will eventually reach Jupiter in mid 2031. Many scientific endeavours require a lot of patience on behalf of the many scientists involved and this is one good example!

The main objective of the mission is to search for possible signatures of life from three of Jupiter’s big “Galilean” satellites: Ganymede, Callisto and Europa. Io, the fourth of the big Jovian moons is the most volcanically active object system in the Solar System and does not have an ice layer at its surface. This might seem an odd place to search for life in the Universe (and the Solar System) but we’ll come back to why we think these moons might conceal life.

The four Galilean satellites of Jupiter. From the left: Io, Europa, Ganymede and Callisto.

Observations of astronomical objects (including the discovery of the four biggest moons of Jupiter) by Galileo in the early 17th century captured the imagination of Europe. Novels, including The Discovery of a World in the Moone written in 1638 by the Bishop of Chester John Wilkins, imagined the Moon being inhabited by human-like beings. Moving a few centuries ahead, the American Percival Lowell made observations of Mars in the late 19th century and made drawings which appeared to show canal like structures. Today these features are now regarded as optical illusions. However, Lowell’s work inspired H G Wells novel War of the Worlds (1897) about an invasion of the Earth by Martian’s. The radio adaption by Orson Wells in 1938 caused panic in America when listeners thought it was a real-life news report. Since then, various missions to Mars such as the Viking 1 and 2 in the mid 1970’s, has demonstrated there is no obvious signs of life. However, it’s still possible life may have existed on Mars in the past and ESA’s ExoMars Trace Gas Orbiter and NASA’s Mars 2020 Perseverance Rover are still performing experiments which might find evidence for life under the Martian surface.

Anyway, back to Juice! NASA’s Voyager missions to Jupiter (and Saturn) transformed our understanding of these planets and their moons. Although primitive compared to more recent probes, Voyager showed evidence that Ganymede, Callisto and Europa had surfaces which were made largely of ice. It wasn’t until the ESA Galileo probe visited the Jovian system in the mid to late 1990’s that evidence was found that a combination of the interaction of Jupiter’s magnetic field and gravitational field may heat up the interior of these moons causing liquid oceans beneath the moons surface. We know that life can occur in the Earth’s deep oceans where volcanic vents release complex molecules and heat. Does life exist beneath the surfaces of these Jovian planets? That is one the question which Juice aims to answer.

An image of Ganymede taken using NASA’s Juno mission which shows a mixture of craters and long features which may be linked to faults in the ice surface. Credit: NASA/JPL-Caltech/SwRI


The JUICE spacecraft hosts ten instruments on-board which will be able to study the gravitational fields of the moons; an optical camera to obtain unprecedented resolution of surface features; magnetometers to study magnetic fields; instruments to measure plasma in the local environments and radar which will be able to penetrate surface ice. It is a comprehensive suite of instruments which cover a large range of wavelength and be able to study a range of physical processes which will help answer key questions including are the conditions below the surface of these three moons favourable for harbouring life.

ESA is funded by the Governments of 22 nations including the UK and Ireland. The UK led the development of the J-MAG magnetometer and Ireland is involved in the Radio and Plasma Wave Instrument whose team includes Prof Caitriona Jackman from DIAS who is a member of AOP’s Management Committee.

Still images taken from ESA Live TV.


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