The sharpest earth-based images of Europa and Ganymede show their icy landscape

The mix of chemicals that make up the frozen surfaces on two of Jupiter’s largest moons have been revealed in the most detailed images of them ever taken by a telescope on Earth.

Planetary scientists from the University of Leicester’s School of Physics and Astronomy have unveiled new images of Europa and Ganymede, two future targets for new missions to the giant planet’s system.

The images provide new insights into the chemical composition of the moons, including geological features such as long crack-like lines cutting through Europa’s surface.

Ganymede and Europa are two of the four largest moons orbiting Jupiter, known as the Galilean moons.

Europa is similar in size to Earth’s moon, while Ganymede is the largest moon in the entire solar system.

PhD student Oliver King, of the University of Leicester’s School of Physics and Astronomy, said: “We have mapped the distribution of the various materials on the surface, including the sulphate of frost, which is found mainly on Europe’s most heavily bombarded side of the gases, the Jupiter surround.

“The modeling indicated that a variety of different salts could be present on the surface, but suggested that infrared spectroscopy alone is generally not able to identify which specific types of salts are present.”

Researchers used the European Southern Observatory’s Very Large Telescope (VLT) in Chile to observe and map the surfaces of the moons.

They recorded the sunlight reflected from the surfaces of Europa and Ganymede at different infrared wavelengths and produced a reflectance spectrum.

This was analyzed by developing a computer model that compares the observations to different substances measured in laboratories.

Images and spectra of Europa, published in the Planetary Science Journal, show that Europa’s crust is composed mostly of frozen water ice, with non-ice materials contaminating the surface.

Observations of Ganymede, published in the journal JGR:Planets, show how the surface consists of two main types of terrain.

These are young areas with large amounts of water ice and old areas composed of an unknown dark gray material.

The icy areas – which appear blue in the images – include Ganymede’s polar caps and craters – where an impact event has exposed the fresh clean ice of Ganymede’s crust.

The researchers also mapped how the size of Ganymede’s ice grains varies across the surface, and the possible distributions of a variety of different salts, some of which may have originated from the moon itself.

The Very Large Telescope is located at high altitude in northern Chile and, with mirrors over eight meters in diameter, is one of the most powerful telescope systems in the world.

Mr King said: “This has allowed us to carry out detailed mapping of Europa and Ganymede and observe features on their surfaces less than 150 km in diameter – all at distances of over 600 million km from Earth.

“Mapping at this fine scale has only been possible until now by sending spacecraft to Jupiter to observe the moons up close.”

Professor Leigh Fletcher, who oversaw the VLT study, is a member of the science teams of the European Space Agency’s Jupiter Icy Moons Explorer (Juice) mission and NASA’s Europa Clipper mission, which will explore Ganymede and Europa up close in the early 2030s .

Juice’s launch is slated for 2023, with University of Leicester scientists playing a key role in the proposed study of Jupiter’s atmosphere, magnetosphere and moons.

Prof Fletcher said: “These ground-based observations stimulate our future exploration of Jupiter’s moons.

“Planetary missions are subject to severe operational limitations and we simply cannot cover all of the terrain we would like to have, so tough decisions must be made about which areas of the lunar surface deserve the closest scrutiny.

“150 km-scale observations, such as those provided by the VLT and ultimately its enormous successor, the ELT (Extremely Large Telescope), help provide a global context for spacecraft observations.”