An astrobiologist suggests possible types of landing sites that would allow the detection of signs of life if these exist in the subsurface oceans

A new study, using spectrographic data, shows which deposits may originate from the subsurface ocean to the chaotic ground in areas where cracks in the ice have formed

It is widely believed that the fair moon Europa contains a large salty ocean beneath its icy surface, and that this ocean has the potential to support life.
In a mission recently proposed by NASA, a spacecraft would land on the surface of Europa to study them and detect signs of life, if any. But the question is where is the best place to look? A new study by Mike Brown of Caltech, professor of physics and astronomy, and Kevin Hand, an astrobiologist and planetary scientist at JPL, indicates that it is worthwhile to land in the scarred areas that make up the area known as "the land of chaos".

"We have known for a long time that the surface of 'Europa' contains fresh ice, which is covered with cracks, ridges and ice fragments," Brown said. "These areas of chaotic land showed signs of the ice sheets breaking, moving and refreezing. These areas are particularly interesting because it is estimated that water from the ocean below may rise to the surface through the cracks and leave deposits there."

"Direct examination of the ocean will be a serious technological challenge and it can be carried out in the distant future" says Fisher. "However, if we can sample the areas of chaos, we can reveal the composition of the ocean and its dynamics. "The ocean is supposed to be 100 kilometers deep. "This can tell us a lot about the activity at the boundary of the rocky core and the ocean," says Brown. In searching for these deposits, the researchers were aided by observations made in 2011 at the Keck telescope in Hawaii using the Osiris spectrograph.

The spectrographs break down the light into its components and then measure their frequencies. Each chemical element has a unique signature of light absorption known as the "spectral band" or "absorption band". The spectral patterns coming from the light emitted, or in the case of a planetary body reflected from the surface, is used to identify the chemical composition of minerals on the surface of Europa in the sunlight reflected from the moon.

The Osiris instrument measures the spectrum in the infrared range. "The minerals we expected to find on 'Europa' leave their mark in the infrared light," said Fisher. "Combined with the extraordinary capabilities of the Keck telescope, we have a powerful tool." Adapted optics mechanisms reduce the blur caused by the turbulence in the Earth's atmosphere by measuring the interference to the light of a bright star and correcting the image accordingly.

The Osiris observations provided data on the spectrum of 1,600 points on the surface of 'Europa'. To organize the data collection, the researchers developed a method for sorting and identifying groups of spectral signatures.

"We have developed a powerful mathematical tool that allows us to take a collection of spectral measurements and automatically, without human intervention, classify them according to the signature of the materials in the spectrum emitted from them. The points were marked on a map provided by the Galileo spacecraft that orbited Jupiter in the late XNUMXs. The combination of the two maps provided a visual guide to the composition of the areas the team was interested in."
It turns out that on the surface of 'Europe' there are three types of spectrum, i.e. three types of materials. The first is of course water ice, which is also the substance that dominates most of the moon. The second category is substances created when sulfur and oxygen are ionized, the presumed origin of which is volcanic activity. So much for substances that were known until now, but the third group of chemical markers is more mysterious. It does not fit any pattern of water or sulfur, but easily identifiable salts. It is estimated that there are magnesium deposits on the surface of 'Europa', but its spectral signature is weak and therefore has not been detected until now. "In fact, this is not consistent with any salt mineral observed so far on 'Europa,'" says Brown.
When the researchers checked where the magnesium deposits were they identified them in the chaotic soil. "The map of the third group of the spectrum seems to match the chaos regions photographed by 'Galileo'."
The most important finding of the research was the understanding that these materials originate from 'Europe' because they belong to areas where there was geological activity in the recent past.
The composition of these deposits is still unclear "a unique identification will be difficult" says Brown. "We think it's worth looking at salts left after a large amount of ocean water has flowed out to the surface and evaporated." "If you're looking for an area on the surface where the ocean water floated up and left its chemical imprint on the surface, this would be the place. If a spacecraft lands there, it will be able to locate the materials that came from the ocean floor and the interface between it and the 'Europa' core, and maybe even find organic compounds there, and this will be very exciting."

For the announcement on the Caltech website