Sampling the Surface of Europa

For the better part of a quarter of a century, Jupiter’s ice-covered moon Europa has caught the attention of scientists and the lay public alike. Although it is the smallest of Jupiter’s four Galilean satellites, NASA’s Galileo mission returned data that strongly suggests that Europa hosts a tidally heated ocean of liquid water rivalling Earth’s oceans in total volume beneath a protective icy veneer up to tens of kilometers thick. The presence of this ocean of water and tidally-driven chemical energy sources makes Europa a prime target for scientists looking for extraterrestrial life. Still unconfirmed observations in 2012 by the Hubble Space Telescope that could indicate the presence occasional plume activity have only heightened interest in this tempting astrobiological target.

This graphic shows the location of water vapor detected over Europa’s south pole by NASA’s Hubble Space Telescope in December 2012. Although the observation remains unconfirmed, this is the first strong evidence of water plumes erupting off Europa’s surface. (NASA/ESA/L. Roth/SWRI/University of Cologne)

Since before the end of NASA’s Galileo mission in September 2003, the scientific community has studied a range of mission options to return and study Europa and its potential to host life. Unfortunately the multi-billion dollar price tags for these proposed flagship-class missions as well as commitments to other expensive programs such as NASA’s James Web Space Telescope and the ongoing Mars exploration program have hampered any progress towards a Europa mission for well over a decade. That has finally changed in recent years as support for a dedicated mission to Europa to be launched in the early 2020s has materialized in the Administration and Congress

NASA’s currently envisioned Europa mission would send a solar-powered spacecraft into a long, looping orbit around Jupiter to perform repeated close flybys of Europa over a three-year period. In total, the mission would perform 45 flybys at altitudes ranging from 25 kilometers to 2,700 kilometers. Presumably if the spacecraft exceeds its design life and its systems survive the repeated exposure to Jupiter’s intense radiation environment, even more flybys would be possible during an extended mission.

This color image mosaic of the reddish regions Thera and Thrace acquired by Galileo on September 26, 1998 are examples of some of the structure present on the icy surface of Europa that overlays its ocean of liquid water. (NASA/JPL/University of Arizona)

In 2014, NASA invited researchers to submit proposals for instruments to study Europa. Thirty-three were reviewed and, of those, nine were selected for the upcoming Europa mission. These instruments are:

 

Plasma Instrument for Magnetic Sounding (PIMS) – Principal investigator Dr. Joseph Westlake of Johns Hopkins Applied Physics Laboratory (APL), Laurel, Maryland. This instrument works in conjunction with a magnetometer and is key to determining Europa’s ice shell thickness, ocean depth, and salinity by correcting the magnetic induction signal for plasma currents around Europa.

Interior Characterization of Europa using Magnetometry (ICEMAG) – Principal investigator Dr. Carol Raymond of NASA’s Jet Propulsion Laboratory (JPL), Pasadena, California. This magnetometer will measure the magnetic field near Europa and – in conjunction with the PIMS instrument – infer the location, thickness and salinity of Europa’s subsurface ocean using multi-frequency electromagnetic sounding.

Mapping Imaging Spectrometer for Europa (MISE) – Principal investigator Dr. Diana Blaney of JPL. This instrument will probe the composition of Europa, identifying and mapping the distributions of organics, salts, acid hydrates, water ice phases, and other materials to determine the habitability of Europa’s ocean.

Europa Imaging System (EIS) – Principal investigator Dr. Elizabeth Turtle of APL. The wide and narrow angle cameras on this instrument will map most of Europa at 50-meter resolution, and will provide images of areas of Europa’s surface at up to 100 times higher resolution.

Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON) – Principal investigator Dr. Donald Blankenship of the University of Texas, Austin. This dual-frequency ice penetrating radar instrument is designed to characterize and sound Europa’s icy crust from the near-surface to the ocean, revealing the hidden structure of Europa’s ice shell and potential water within.

Europa Thermal Emission Imaging System (E-THEMIS) – Principal investigator Dr. Philip Christensen of Arizona State University, Tempe. This “heat detector” will provide high spatial resolution, multi-spectral thermal imaging of Europa to help detect active sites, such as potential vents erupting plumes of water into space.

MAss SPectrometer for Planetary EXploration/Europa (MASPEX) – Principal investigator Dr. Jack (Hunter) Waite of the Southwest Research Institute (SwRI), San Antonio. This instrument will determine the composition of the surface and subsurface ocean by measuring Europa’s extremely tenuous atmosphere and any surface material ejected into space.

Ultraviolet Spectrograph/Europa (UVS) – Principal investigator Dr. Kurt Retherford of SwRI. This instrument will adopt the same technique used by the Hubble Space Telescope to detect the likely presence of water plumes erupting from Europa’s surface. UVS will be able to detect small plumes and will provide valuable data about the composition and dynamics of the moon’s rarefied atmosphere.

SUrface Dust Mass Analyzer (SUDA) – Principal investigator Dr. Sascha Kempf of the University of Colorado, Boulder. This instrument will measure the composition of small, solid particles ejected from Europa, providing the opportunity to directly sample the surface and potential plumes on low-altitude flybys.

 

This proposed suite of instruments will add greatly to our knowledge of Europa and allow detailed planning for more in depth missions of exploration in the future. While all of these instruments would contribute important pieces to the overall picture of Europa, I am especially intrigued by SUDA which promises to make direct measurements of any dust particles from the putative Europan plumes or launched from the surface as a result of micrometeorite impacts.

SUDA is a four-kilogram device whose heritage can be traced to earlier instruments like the Cometary and Interstellar Dust Analyzer (CIDA) flown on NASA’s Stardust mission launched in 1999 and the Cosmic Dust Analyzer (CDA) which, among other things, has been used to analyze plume particles from Saturn’s moon, Enceladus, as part of the ongoing Cassini mission. A prototype for SUDA has already been built and tested by the PI, Sascha Kempf, and his team at the University of Colorado – Boulder.

Cutaway diagram of SUDA (SUrface Dust Mass Analyzer) which will analyze the composition of Europan dust particles. Click on image to enlarge. (Kempf et al.)

With a collecting area of 220 square centimeters, dust particles would enter SUDA’s aperture and pass a series of electrical grids to impact a ring-shaped target inside the instrument’s main chamber. Here even a slow moving dust particle would be vaporized and the resulting ions analyzed to determine their masses. In this way, the composition of the dust particle is determined for molecular weights in the 1 to 250 amu range with a mass resolution of 2%. As a result, the composition of the surface of Europa and the ocean beneath can be indirectly sampled using SUDA. And if it proves that the Europan plumes actually exist and NASA’s Europa spacecraft can be directed through them, the subsurface ocean of Europa can be more directly sampled just as Cassini has recently sampled the subsurface water of Enceladus by analyzing this moon’s plume particles.

The results from SUDA as well as other searches for plumes or concentrations of dust particles in the vicinity of Europa using instruments like MASPEX and EIS also raises an intriguing possibility for future missions to Europa. If the plumes or other concentrations of dust prove to be present in sufficient quantities near Europa, it should prove possible to gather these particles during multiple flybys using aerogel collectors of the sort used during NASA’s Stardust mission to Comet Wild 2 in 2004 and return them to Earth for a much more detailed analysis than would be possible using any space borne instrument (see “A Europa-Io Sample Return Mission” for more details). A similar mission has been proposed to return samples of plume particles from Enceladus called LIFE (Life Investigations For Enceladus). Although the mission concept has continued to evolve over the last several years and the proposed launch date has now been pushed out to possibly 2030, similar hardware from this New Frontier-class mission could be used for a Europa sample return mission for a tiny fraction of the cost of a conventional sample return mission involving a lander.

Particles from Europa’s plumes or from dust launched from its surface by micrometeoroid impacts (as well as Io’s volcanic plumes shown in the distance) could be gathered using aerogel collectors and returned to Earth for detailed analysis as part of a low-cost sample return mission. (NASA/JPL)

Of course, all of these plans depend on NASA getting this proposed mission off the ground and to Europa. While at the moment there seems to be support in Congress and the Administration to fly a mission to Europa, the various factions involved seem to have conflicting visions for that mission and its goals. And even if some consensus is reached, the multi-billion dollar price tag for this mission will make it a target for cancellation by a future Congress and Administration if Federal budget priorities change. This would be especially true if the goals of this mission become too ambitious and its costs begin to rise too much as happens too often with NASA’s large space projects including their flagship-class planetary missions. With luck, however, the long awaited mission to Europa will finally be on its way within a decade.

 

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Related Reading

“A Europa-Io Sample Return Mission”, Drew Ex Machina, March 27, 2014 [Post]

 

General References

Bruce Dorminey, “NASA May Plumb for Signs of Life in Enceladus Plumes”, Forbes (on line), April 29, 2015 [Article]

S. Kempf et al., “SUDA: A Dust Mass Spectrometer for Compositional Surface Mapping for a Mission to Europa”, European Planetary Science Congress 2014, Vol. 9, ESPSC2014-229, 2014 [Paper]

P. Tsou, D.E. Brownlee, C.P. McKay, A. Anbar, H. Yano, Nathan Strange, Richard Dissly and I Kanik, “Low Cost Enceladus Sample Return Mission Concept”, Low Cost Planetary Mission Conference – 10 (Pasadena, CA; June 18 – 20, 2013), 2013 [Presentation]

“NASA’s Europa Mission Begins with Selection of Science Instruments”, NASA Press Release 15-104, May 26, 2015 [Press Release]