In September of 2016, astronomers using NASA’s Hubble Space Telescope imaged what may be water vapor plumes erupting off the surface of Jupiter’s moon Europa.
“First, perhaps, it might be best to understand why anyone would want to land on Europa at all. Europa – the second of Jupiter’s four large satellites – is clearly a special place,” says Caltech’s Mike Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy. “Ever since the time of the Galileo spacecraft nearly two decades ago, we have recognized that Europa’s fresh icy surface (shown above), covered with cracks and ridges and transform faults, is the external signature of a vast internal salty ocean.
The plumes are estimated to rise about 125 miles (200 kilometers) before, presumably, raining material back down onto Europa’s surface. Europa has a huge global ocean containing twice as much water as Earth’s oceans, but it is protected by a layer of extremely cold and hard ice of unknown thickness. The plumes provide a tantalizing opportunity to gather samples originating from under the surface without having to land or drill through the ice.
“Europa provisionally is a great place to go,” said Jonathan Lunine a memeber of NASA’s Science Definition Team (SDT). “It has a very large amount of rocks, it’s got a lot of heat [at its core], so at the base of the oceans there are undoubtedly hydrothermal systems. Everything we know about it makes this a good [place] to look for life.”
“The important thing to remember is that this is intended to be a ‘bug hunt,’ this is designed to land in a place where based on the Europa flyby mission, there would be deposits from the ocean, organic materials, that sort of thing,” said Lunine. “So the intent is to use instruments that can detect the signs of life on those samples.” The team is especially interested in finding biosignatures— isotopes or molecules that suggest past or present life.
NASA’s Europa flyby mission, which is slated to take place in the early 2020s will play a key role in the later SDT lander mission, using its cameras to pinpoint plumes or cracks where material from Europa’s subterranean might surface. The lander will later visit these locations in order to take samples.
The first strong evidence for a subterranean ocean on Europa came from NASA’s Galileo mission, which explored Jupiter and its moons in the late 1990s. But samples have never been collected from the ocean itself, which is thought to be buried beneath 11 to 15 miles (19 to 27 kilometers) of ice. The ocean, comprised of liquid water and an unknown amount of salt, is an estimated 62 miles deep.
In early 2016, in response to a congressional directive, NASA’s Planetary Science Division began a pre-Phase A study to assess the science value and engineering design of a future Europa lander mission. NASA routinely conducts such studies — known as Science Definition Team (SDT) reports — long before the beginning of any mission to gain an understanding of the challenges, feasibility and science value of the potential mission. In June 2016, NASA convened a 21-member team of scientists for the SDT. Since then, the team has deliberated to define a workable and worthy set of science objectives and measurements for the mission concept, submitting a report to NASA on Feb. 7.
This artist’s illustration above is a conceptual design for the Europa lander mission, shown with a sampling arm extended, having previously excavated a small area on the surface. The circular dish on top is a dual-purpose high-gain antenna and camera mast, with stereo imaging cameras mounted on the back of the antenna. Three vertical shapes located around the top center of the lander are attachment points for cables that would lower the rover from a sky crane, which is envisioned as the landing system.
The report lists three science goals for the mission that hopes to launch as soon as 2031. The primary goal is to search for evidence of life on Europa. The other goals are to assess the habitability of Europa by directly analyzing material from the surface, and to characterize the surface and subsurface to support future robotic exploration of Europa and its ocean. The report also describes some of the notional instruments that could be expected to perform measurements in support of these goals.
Scientists agree that the evidence is quite strong that Europa, which is slightly smaller than Earth’s moon, has a global saltwater ocean beneath its icy crust. This ocean has at least twice as much water as Earth’s oceans. While recent discoveries have shown that many bodies in the solar system either have subsurface oceans now, or may have in the past, Europa is one of only two places where the ocean is understood to be in contact with a rocky seafloor (the other being Saturn’s moon Enceladus). This rare circumstance makes Europa one of the highest priority targets in the search for present-day life beyond Earth.
The SDT was tasked with developing a life-detection strategy, a first for a NASA mission since the Mars Viking mission era more than four decades ago. The report makes recommendations on the number and type of science instruments that would be required to confirm if signs of life are present in samples collected from the icy moon’s surface.
The team also worked closely with engineers to design a system capable of landing on a surface about which very little is known. Given that Europa has no atmosphere, the team developed a concept that could deliver its science payload to the icy surface without the benefit of technologies like a heat shield or parachutes.
This mosaic of images includes the most detailed view of the surface of Jupiter’s moon Europa obtained by NASA’s Galileo mission. The topmost footprint is the highest resolution image taken by Galileo at Europa. It was obtained at an original image scale of 19 feet (6 meters) per pixel.
The other seven images in this observation were obtained at a resolution of 38 feet (12 meters) per pixel, thus the mosaic, including the top image, has been projected at the higher image scale. The top image is also provided at its original resolution, as a separate image file. It includes a vertical black line that resulted from missing data that was not transmitted by Galileo.
This is the highest resolution view of Europa available until a future mission visits the icy moon. The right side of the image was previously published as PIA01180. Although this data has been publicly available in NASA’s Planetary Data System archive for many years, NASA scientists have not previously combined these images into a mosaic for public release. This observation was taken with the sun relatively high in the sky, so most of the brightness variations visible here are due to color differences in the surface material rather than shadows. Bright ridge tops are paired with darker valleys, perhaps due to a process in which small temperature variations allow bright frost to accumulate in slightly colder, higher-elevation locations.
The concept lander is separate from the solar-powered Europa multiple flyby mission, now in development for launch in the early 2020s. The spacecraft will arrive at Jupiter after a multi-year journey, orbiting the gas giant every two weeks for a series of 45 close flybys of Europa. The multiple flyby mission will investigate Europa’s habitability by mapping its composition, determining the characteristics of the ocean and ice shell, and increasing our understanding of its geology. The mission also will lay the foundation for a future landing by performing detailed reconnaissance using its powerful cameras.
Source: The Daily Galaxy
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