Objectives of the Exploration of Jovian System
Jupiter is a giant gas planet whose diameter is 11 times larger than that of the Earth, and weighs 320 times heavier. Surrounding are four moons discovered by Galileo Galilei, namely Io, Europa, Ganymede, and Calisto. The mass of each moon is comparable to that of Mercury, and the surfaces of Europa, Ganymede, and Calisto are covered by thick ice shells. These icy bodies are fascinating planetary scientists now more than ever, because an existence of global subsurface water ocean became possible after the exploration of the Galileo spacecraft. While the sunlight is blocked by the thick ice crust, hydro-thermal activity at the bottom of the subsurface ocean might provide an energy as well as nutrient salts, such as phosphorous and potassium, necessary for sustaining life. Thus we may encounter a new world of habitable environment inside of the icy moons.
Outline of the JUICE
The JUpiter ICy moons Explorer (JUICE) is led by European Space Agency (ESA) with a collaboration of Japan and USA (Figure 1). The JUICE will be launched in 2022 and will arrive at Jupiter in 2030 investigating atmosphere and magnetosphere of the gas giant. The JUICE mission will address two fundamental issues of the planetary science: What are the conditions for planet formation and emergence of life? and How does the Solar System work?
Understanding the Jovian system and unravelling its history, from its origin to the possible emergence of habitable environments, will give us a better insight into how gas giant planets and their satellites form and evolve. In addition, new light should be shed on the potential for the emergence of life in Jupiter-like exoplanetary systems.
Laser Altimeter (GALA)
The principle of laser altimeter is straightforward. The time of flight between the emission of a photon and the receipt of reflected photon is measured. This time of flight is then converted to a distance using the well-known speed of light. By subtracting the distance from the orbit of the spacecraft with respect to the center of mass of the body, topography is derived.
Laser altimeter data reveal periodic tidal signatures in topography caused by dynamic response of ice shell to tidal forces exerted by Jupiter along Ganymede’s eccentric orbit. Surface deformations are an order of magnitude larger in the presence of subsurface oceans, as compared to a completely solid interior.
GALA is currently under development with an international corporation among Germany, Switzerland, Spain, and Japan.