With its latest space mission successfully launched, NASA is set to return for a close-up investigation of Jupiter’s moon Europa. Yesterday at 12:06 p.m. EDT, the Europa Clipper lifted off via SpaceX Falcon Heavy rocket on a mission that will take a close look at Europa’s icy surface. Five years from now, the spacecraft will visit the moon, which hosts a water ocean covered by a water-ice shell. The spacecraft’s mission is to learn more about the composition and geology of the moon’s surface and interior and to assess its astrobiological potential. Because of Jupiter’s intense radiation environment, Europa Clipper will conduct a series of flybys, with its closest approach bringing it within just 16 miles of Europa’s surface.
MIT Department of Earth, Atmospheric and Planetary Sciences (EAPS) Senior Research Scientist Jason Soderblom is a co-investigator on two of the spacecraft’s instruments: the Europa Imaging System and the Mapping Imaging Spectrometer for Europa. Over the past nine years, he and his fellow team members have been building imaging and mapping instruments to study Europa’s surface in detail to gain a better understanding of previously seen geologic features, as well as the chemical composition of the materials that are present. Here, he describes the mission's primary plans and goals.
Q: What do we currently know about Europa’s surface?
A: We know from NASA Galileo mission data that the surface crust is relatively thin, but we don’t know how thin it is. One of the goals of the Europa Clipper mission is to measure the thickness of that ice shell. The surface is riddled with fractures that indicate tectonism is actively resurfacing the moon. Its crust is primarily composed of water ice, but there are also exposures of non-ice material along these fractures and ridges that we believe include material coming up from within Europa.
One of the things that makes investigating the materials on the surface more difficult is the environment. Jupiter is a significant source of radiation, and Europa is relatively close to Jupiter. That radiation modifies the materials on the surface; understanding that radiation damage is a key component to understanding the composition.
This is also what drives the clipper-style mission and gives the mission its name: we clip by Europa, collect data, and then spend the majority of our time outside of the radiation environment. That allows us time to download the data, analyze it, and make plans for the next flyby.
Q: Did that pose a significant challenge when it came to instrument design?
A: Yes, and this is one of the reasons that we're just now returning to do this mission. The concept of this mission came about around the time of the Galileo mission in the late 1990s, so it's been roughly 25 years since scientists first wanted to carry out this mission. A lot of that time has been figuring out how to deal with the radiation environment.
There's a lot of tricks that we've been developing over the years. The instruments are heavily shielded, and lots of modeling has gone into figuring exactly where to put that shielding. We've also developed very specific techniques to collect data. For example, by taking a whole bunch of short observations, we can look for the signature of this radiation noise, remove it from the little bits of data here and there, add the good data together, and end up with a low-radiation-noise observation.
Q: You're involved with the two different imaging and mapping instruments: the Europa Imaging System (EIS) and the Mapping Imaging Spectrometer for Europa (MISE). How are they different from each other?
A: The camera system [EIS] is primarily focused on understanding the physics and the geology that's driving processes on the surface, looking for: fractured zones; regions that we refer to as chaos terrain, where it looks like icebergs have been suspended in a slurry of water and have jumbled around and mixed and twisted; regions where we believe the surface is colliding and subduction is occurring, so one section of the surface is going beneath the other; and other regions that are spreading, so new surface is being created like our mid-ocean ridges on Earth.
The spectrometer’s [MISE] primary function is to constrain the composition of the surface. In particular, we're really interested in sections where we think liquid water might have come to the surface. Understanding what material is from within Europa and what material is being deposited from external sources is also important, and separating that is necessary to understand the composition of those coming from Europa and using that to learn about the composition of the subsurface ocean.
There is an intersection between those two, and that's my interest in the mission. We have color imaging with our imaging system that can provide some crude understanding of the composition, and there is a mapping component to our spectrometer that allows us to understand how the materials that we're detecting are physically distributed and correlate with the geology. So there's a way to examine the intersection of those two disciplines — to extrapolate the compositional information derived from the spectrometer to much higher resolutions using the camera, and to extrapolate the geological information that we learn from the camera to the compositional constraints from the spectrometer.
Q: How do those mission goals align with the research that you've been doing here at MIT?
A: One of the other major missions that I've been involved with was the Cassini mission, primarily working with the Visual and Infrared Spectrometer team to understand the geology and composition of Saturn's moon Titan. That instrument is very similar to the MISE instrument, both in function and in science objective, and so there's a very strong connection between that and the Europa Clipper mission. For another mission, for which I’m leading the camera team, is working to retrieve a sample of a comet, and my primary function on that mission is understanding the geology of the cometary surface.
Q: What are you most excited about learning from the Europa Clipper mission?
A: I'm most fascinated with some of these very unique geologic features that we see on the surface of Europa, understanding the composition of the material that is involved, and the processes that are driving those features. In particular, the chaos terrains and the fractures that we see on the surface.
Q: It's going to be a while before the spacecraft finally reaches Europa. What work needs to be done in the meantime?
A: A key component of this mission will be the laboratory work here on Earth, expanding our spectral libraries so that when we collect a spectrum of Europa's surface, we can compare that to laboratory measurements. We are also in the process of developing a number of models to allow us to, for example, understand how a material might process and change starting in the ocean and working its way up through fractures and eventually to the surface. Developing these models now is an important piece before we collect these data, then we can make corrections and get improved observations as the mission progresses. Making the best and most efficient use of the spacecraft resources requires an ability to reprogram and refine observations in real-time.
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