Tuesday, 25 August 2015

NASA's Europa Swiss Army Knife

This week at the Applied Physics Laboratory (APL) in Maryland, the Outer Planet Assessment Group (OPAG) is meeting and sharing ideas and progress, and I'm indebted to all those tweeters who contributed to the #OPAG hashtag during the meeting to allow me to write this summary. It also provides an opportunity to discuss the newest of NASA’s missions, the as-yet-unnamed Europa mission.  The mission is expected to perform 45 flybys at altitudes ranging from 25 to 2700 km.  All of the PIs of the selected instruments were present to describe the experiments that will be onboard, described by Bob Pappalardo (mission project scientist) as sending a versatile Swiss Army knife to the outer solar system.  Although this isn’t the orbital mission that we’d originally planned when this was still part of EJSM (the Europa Jupiter System Mission prior to 2010), NASA expects that the flyby mission will still recover 90% of the intended science return.

The mission is now in Phase A, which means that it’s still in flux and being formulated, with many ideas on the table - Hubble is still searching for further evidence of plume activity from Europa’s south pole; potential contributions from ESA are being explored (such as landers, life detection, small free flyers), and about 250 kg of launch mass is being retained from the Phase A studies for more consideration in 2016.  Out of 33 submitted proposals, nine instruments have been selected to explore habitable conditions on Jupiter’s enigmatic moon:

1.  UVS - an ultraviolet spectrograph from Kurt Retherford and colleagues at Southwest Research Institute that’s a clone of the one being flown on ESA’s JUICE spacecraft, which will continue to hunt for plumes from Europa’s subsurface, determine their composition and chemistry, sources and sinks, structure and variability.  It uses a combination of UV emissions, surface reflections and transmissions (e.g., stellar and solar occultations) to detect and characterise Europa’s surface and tenuous atmosphere.

2.  EIS - the Europa dual imaging camera system led by Zibi Turtle of APL, combining both a narrow (NAC) and wide angle camera (WAC) with colour and stereo capabilities to understand the formation of landforms, the potential for current activity on the surface, and characterise the ice shell and ice-ocean interface.  The NAC has a 2-axis gimbal that allows the FOV to be moved both within and beyond the field of the WAC, achieving resolutions of 0.5 m from an altitude of 50 km above Europa’s surface.  The WAC will have a resolution of 4m from 50 km altitude, over a wider surface area.  The whole surface of the moon could potentially be mapped at a resolution of 50m.  The stereo capabilities will allow the creation of a digital terrain model (DTM) with a 4m vertical precision from the 50-km flyby altitude.  

3.  MISE - the mapping infrared spectrometer for Europa led by Diana Blaney (JPL) will be used to map the history of geologic activity on the surface, including a search for currently active areas.  Covering 0.8-5.0 µm with a 10 nm spectral resolution, this near-infrared spectrometer is a common feature of missions - Cassini, Juno and JUICE all have similar experiments (VIMS, JIRAM and MAJIS).  MISE will get resolutions of 25 m on a local scale, 300 m on a regional scale, and 10 km on a global scale, assuming 100-km altitude flybys.  Near-IR reflectance spectra will allow distinguishing between hydrate regions, sulphate regions, and even search for trace organics.

4.  E-THEMIS is the thermal instrument on board (so glad NASA chose to take a mid-infrared instrument, and I wish ESA/JUICE had one too!), provided by Phil Christensen of Arizonal State University.  The instrument will search for thermal anomalies on the surface (particular associated with any active venting), with a resolution of 5x22 m from 25 km altitude and a precision of 0.2 K for 90-K surfaces and 0.1 K for 220-K surfaces.  It has three filters, 7-14, 14-28 and 28-70 µm.

5.  REASON - the Radar for Europe Assessment and Sounding: Ocean to Near-Surface provided by Don Blankenship and team at Texas (best acronym ever), and a sister instrument for the RIME instrument on ESA/JUICE.  It’s a dual frequency radar at 60 MHz, with 15-m vertical resolution for shallow sounding to 4.5 km depth, or 150-m vertical resolution for ocean sounding below 4.5-km depth.  It will study the surface, sub-surface, using reflectometry to study near-surface roughness, porosity and composition, and search for an ice-ocean interface and evidence of exchange processes beneath Europa’s surface.  

6. PIMS - the plasma instrument for magnetic sounding provided by Joe Westlake from Johns Hopkins APL, which will work to characterise the salinity and depth of Europa’s oceans by measuring the plasma environment surrounding Europa and the magnetic induction response as conductive Europa moves through Jupiter’s magnetosphere.

7.  ICEMAG - the mission magnetometer provided by Carol Raymond of JPL to characterise Europa’s interior, thermal evolution, atmospheric sources and sinks, and the coupling between Europa and Jupiter’s ionosphere.  ICEMAG can also look at Europa’s exosphere by looking at dynamic species coming off Europa during each flyby.  

8.  MASPEX - a mass spectrometer provided by Hunter Waite and colleagues at the Southwest Research Institute (SwRI) to sniff out the exospheric (and ejected surface) composition.  Particles can be sputtered from Europa’s surface due to bombardment by energetic particles, or can simply sublimate from the surface, creating a density enhancement over the sunlit region.  Plume material would also contribute, being transported equatorward and deposited at lower latitudes to join other materials to be sputtered.

9.  SUDA - a dust experiment to characterise the surface using lofted dust detected with low-altitude flyby, provided by Sascha Kempf of University of Colorado, Boulder.  The Galileo dust detector had previously found that each of the Galilean satellites were wrapped in dust clouds of surface ejecta.  euro

More information on each of these instruments can be found here:
…and I’ll try to compare the capabilities of the Europa mission to those of JUICE (which will be performing two Europa flybys) in future blog posts.

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