In a new report to NASA released this week, a 21-member team of scientists assess the scientific value and engineering design of a future mission to the surface of Europa.
This artist’s rendering illustrates a conceptual design for a potential future mission to land a robotic probe on the surface of Europa. The lander is 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 for this mission concept. Image credit: NASA / JPL-Caltech / M. Carroll.
Jupiter’s moon Europa, which is approximately the size of Earth’s moon, very likely harbors a global, deep, liquid water ocean beneath its relatively thin ice shell. This ocean exists today and it has possibly persisted for much of the history of the Solar System.
Europa’s ocean is probably in contact with a rocky, silicate seafloor, which may lead to an ocean rich in the elements and energy needed for the emergence of life, and for potentially sustaining life through time.
This rare circumstance makes Europa one of the highest priority targets in the search for present-day life beyond our planet.
The surface of Europa looms large in this newly-reprocessed color view; image scale is 1.6 km per pixel; north on Europa is at right. Image credit: NASA / JPL-Caltech / SETI Institute.
In June 2016, in response to a congressional directive, NASA initiated a Pre-Phase A mission concept study for a robotic lander to the surface of Europa for the purpose of in situ analyses of samples of the surface and shallow subsurface.
As part of this effort, NASA convened a Science Definition Team (SDT) to provide scientific guidance to the mission study.
The co-chairs selected for leadership of the SDT were Dr. James Garvin of NASA Goddard Spaceflight Center, Dr. Alison Murray of the Desert Research Institute, and Dr. Kevin Hand of NASA’s Jet Propulsion Laboratory.
Working with Dr. Curt Niebur and Joan Salute of NASA Headquarters, a group of 18 additional scientists were selected to join 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, 2017.
“The Europa Lander Science Definition Team Report presents the integrated results of an intensive science and engineering team effort to develop and optimize a mission concept that would follow the Europa Multiple Flyby Mission and conduct the first in situ search for evidence of life on another world since the Viking spacecraft on Mars in the 1970s,” the researchers explained.
The report lists three science goals for the mission:
(i) to search for evidence of life on Europa;
(ii) to assess the habitability of Europa by directly analyzing material from the surface;
(iii) to characterize the surface and subsurface to support future robotic exploration of Europa and its ocean.
This mosaic of images includes the most detailed view of the surface of 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 m) per pixel. The other seven images in this observation were obtained at a resolution of 38 feet (12 m) per pixel, thus the mosaic, including the top image, has been projected at the higher image scale. 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. Image credit: NASA / JPL-Caltech.
“The Europa Lander mission would be a pathfinder for characterizing the biological potential of Europa’s ocean through direct study of any chemical, geological, and possibly biological, signatures as expressed on, and just below, the surface of Europa,” the authors said in the report.
“The search for signs of life on Europa’s surface requires an analytical payload that performs quantitative organic compositional, microscopic, and spectroscopic analysis on five samples acquired from at least 10 cm beneath the surface, with supporting context imaging observations.”
“This mission would significantly advance our understanding of Europa as an ocean world, even in the absence of any definitive signs of life, and would provide the foundation for the future robotic exploration of Europa.”
“This is a very real step toward a signs of life mission,” said Dr. Murray, who is best known for her work discovering the existence of microbial life within an Antarctica’s ice-sealed, anoxic, dark, and negative 13-degree Celsius brines of Lake Vida, the largest of several unique lakes found in the McMurdo Dry Valleys.
“There was a lot of deliberation on the best ways to accomplish such a monumental set of tasks,” she added. “Since the Viking mission we’ve learned a lot more about the search for life and how to answer the tough questions.”
Artistic representation of Europa in cross-section showing processes from the seafloor to the surface. Boxes indicate potentially habitable sites such as hydrothermal vents, and regions on and within the ice shell that could harbor biosignatures. This diagram shows an integrated perspective pf how the seafloor, ocean, and ice shell could yield biosignatures detectable on the surface by a landed spacecraft. Image credit: K.P. Hand et al / NASA.
The report also describes some of the notional instruments that could be expected to perform measurements in support of these goals.
“The Europa Lander mission concept provides 42.5 kg for the baseline science instrument payload,” the authors said. “With the exception of the Context Remote Sensing Instrument (CRSI), all instruments are held within a vault that provides radiation shielding.”
“The centerpiece instruments for characterizing any potential signs of life are:
(i) an Organic Compositional Analyzer (OCA), which in the baseline model payload is a Gas Chromatograph-Mass Spectrometer (GC-MS) capable of achieving a 1 picomole per gram of sample limit of detection for organics;
(ii) a microscope system (referred to as the Microscope for Life Detection, MLD) capable of distinguishing microbial cells as small as 0.2 microns in diameter, and as dilute as 100 cells per cubic centimeter (cc, or equivalently 1 mL) of ice. In the baseline model payload this capability is to be addressed by a combination of spectroscopy and atomic force microscopy (AFM) or optical light microscopy (OM);
(iii) a Vibrational Spectrometer (VS), which in the baseline model payload is a Raman and Deep UV fluorescence spectrometer capable of characterizing both organic and inorganic compounds down to a level of parts per thousand by mass.
Along with the analytical suite for detailed analyses of samples, the Europa Lander model payload also includes a pair of color stereo imagers for examining the landing site in 3D (including capabilities for characterizing surface composition), and a seismic package for determining Europa’s ice shell and ocean thickness through acoustic monitoring of cracking events in the ice shell.”
The SDT 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.
Key features of Europa Lander mission design, from launch to landing: the mission would require a single launch on a SLS (Space Launch System) and could be launched as early as 2024. An Earth gravity assist would be used, resulting in a 5-year cruise to Jupiter Orbit Insertion. A series of jovian moon flybys over the course of 1.5 years would set up the trajectory required for Deorbit, Descent, and Landing (DDL). The deorbit vehicle would separate from the carrier (also known as the Carrier Relay Orbiter, or CRO) and execute a guided deorbit burn. After jettisoning the deorbit stage with its solid rocket, the Powered Descent Vehicle liquid propulsion system would cancel out relative velocity and lower the lander to the surface via tethers with an MSL-derived Sky Crane system. The CRO would establish an orbit around Europa and serve as a communications relay for the 20+ day surface mission, during which five samples would be acquired and analyzed by the science instruments. Image credit: K.P. Hand et al / NASA.
The concept lander is separate from NASA’s 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 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, and also will lay the foundation for a future landing by performing detailed reconnaissance using its powerful cameras.
NASA has announced two upcoming town hall meetings to discuss the Europa Lander Science Definition Team Report and receive feedback from the science community.
The first will be on March 19, in conjunction with the 2017 Lunar and Planetary Science Conference (LPSC) at The Woodlands, Texas. The second event will be on April 23 at the Astrobiology Science Conference (AbSciCon) in Mesa, Arizona.
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Hand, K.P., Murray, A.E., Garvin, J.B., Brinckerhoff, W.B., Christner, B.C, Edgett, K.S, Ehlmann, B.L., German, C.R., Hayes, A.G., Hoehler, T.M., Horst, S.M., Lunine, J.I., Nealson, K.H., Paranicas, C., Schmidt, B.E., Smith, D.E., Rhoden, A.R., Russell, M.J., Templeton, A.S., Willis, P.A., Yingst, R.A., Phillips, C.B, Cable, M.L., Craft., K.L., Hofmann, A.E., Nordheim, T.A., Pappalardo, R.P., and the Project Engineering Team. Report of the Europa Lander Science Definition Team. Posted February, 2017
