Mysterious Substances Observed In Europa’s Cracks

Realistic-color Galileo mosaic of Europa's anti-Jovian hemisphere showing numerous lineae by NASA/JPL/SETI

Jupiter’s moon Europa is one of the potential places where scientists think we could find life in the Solar System. The moon is believed to have a deep and active ocean below an icy surface. The water movements and internal heat are deemed responsible for the formation of cracks on the otherwise smooth exterior. Scientists have now discovered mysterious substances within these cracks, which they think are probably salts brought up by the ocean.

Astronomers from CalTech used observations by the W. M. Keck Observatory in 2011 to better understand the composition of Europa's surface; it was first mapped by NASA's Galileo mission in the 90s. The data was collected using the OSIRIS spectrograph, an instrument that separates light into its constituent frequencies, just like a prism creating a rainbow from white light. Different substances absorb light at different frequencies, so by using a spectrograph astronomers can tell which elements are present on a celestial body.

Europa is the fourth largest moon of Jupiter. It is slightly smaller than our Moon and it has a tenuous oxygen atmosphere. Jupiter, Europa and Io (another of Jupiter’s moons) have a strong gravitational interaction between them, which makes both moons very active. Io has volcanos and Europa has water ice geysers, similar to Saturn’s Enceladus. 

The OSIRIS observations produced spectral analysis from 1,600 individual spots on Europa. They have found three main components on the surface of the Jovian moon, and to better understand the origin of these substances, lead author Patrick Fischer developed software that matched the spectroscopic observation with the Galileo mission's maps.

Unsurprisingly, the most common and diffuse component on Europa is water ice. The second component is a mixture of chemicals formed by ionized sulfur, oxygen, and ice. The sulfur comes from Io, whose eruption plumes can escape its weak gravity and rain on Europa.

The third component is puzzling. It was not related to ice or sulfuric substances, and it doesn’t match molecules that were expected to be seen on Europa. The research suggests that the substances could be chlorine or carbonate-based salts, but it couldn’t identify the exact components.

A more surprising discovery is that the third component is found in and around Europa’s cracks. "I was looking at the maps of the third grouping of spectra, and I noticed that it generally matched the chaos regions mapped with images from Galileo. It was a stunning moment," Fischer said in a statement. "The most important result of this research was understanding that these materials are native to Europa, because they are clearly related to areas with recent geological activity." 

Currently, there are two planned missions that aim to study Europa in great detail: ESA’s Jupiter Icy moon Explorer (JUICE) is due to launch in 2022, and NASA is planning a Europa flyby mission for the mid-2020s. 

The research has been accepted to The Astronomical Journal.

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