Artist’s concept of NASA’s Europa Clipper spacecraft as it orbits Jupiter and passes over its ice-covered moon Europa. Credit: NASA/JPL-Caltech

1 Can you give a brief introduction to your background, and tell us why you joined the Clipper mission?

Christopher Glein: I’m a planetary geochemist at Southwest Research Institute in San Antonio, Texas. I study chemical processes that occur on other planets and their moons. I joined the Europa Clipper mission because I’m trying to help create a new field of extraterrestrial oceanography. Europa’s ice-covered ocean is a major focus of this mission, so it seemed like a perfect match.

Elodie Lesage: I am a research scientist at the NASA Jet Propulsion Laboratory (JPL), in California. I have been studying Europa’s surface and geophysical activity since I was a Master’s student. I am fascinated by the mystery around this moon’s surface and dedicated my career to better understand it. I naturally joined the Europa Clipper Science Team when I arrived at JPL to support this fantastic mission.

Annie Marinan: I am a Systems Engineer at the NASA Jet Propulsion Laboratory. I was on the Payload Systems Engineering team for Europa Clipper for a few years before launch and I now do Science Planning and Operations Coordination. I have an Aerospace Engineering background, and through grad school and the first part of my career I worked on very small satellites. I joined the Clipper mission because it was a really great opportunity to work on a flagship NASA mission with a whole host of different scientific instruments.

2 What instruments are onboard Clipper, how were they selected, and what types of measurements can be taken?

Christopher Glein: Europa Clipper is a flagship mission. It is equipped with a variety of advanced instruments to investigate Europa’s habitability. They were competitively selected by NASA based on an evaluation of proposals. I’m a co-investigator on MASPEX (MAss Spectrometer for Planetary EXploration) – the onboard neutral gas mass spectrometer. We are the mission’s “nose”. We will sample gases near Europa and determine what they are. We can then construct geochemical models to decode what certain molecules tell us about present processes and the history of Europa. If we get lucky, we could sniff a plume erupting out of Europa’s ocean. That would be very exciting!

Elodie Lesage: Europa Clipper is a Flagship mission, the largest NASA class of missions. The spacecraft carries nine instruments, and an additional scientific investigation. These include remote sensing and in situ instruments and investigations, with imagers in visible, IR, thermal IR and UV wavelengths, radar in two wavelengths, radio and gravity measurements, a magnetometer, neutral and charged particle detectors, and a chemistry analyser. This is a very broad range of instruments and a complete payload that will allow us to learn about many different aspects of Europa and answer the question of whether it reunites the conditions necessary to life.

Annie Marinan: There are nine different instruments (though some of those are actually two instruments in one) and one science investigation (which uses the radio to do science) on Europa Clipper. The instruments can broadly be split into two categories: in situ and remote sensing. In situ means they physically measure or interact with the dust, plasma, particles, magnetic field, or gravity field surrounding Europa. The remote sensing instruments include a radar and a suite of different imagers that are each sensitive to different wavelengths of light. All of those instruments were selected via a proposal process, and they all do slightly different, complementary things. When combined, these instruments provide the measurements that the mission needs to answer its main science questions around Europa.

3 How does Jupiter’s strong radiation complicate the mission? How does this affect instrument design, contamination control, and data interpretation?

Elodie Lesage: Because of the plasma torus around Jupiter created by Io’s volcanoes, the environment at Europa is very harsh and damaging for a spacecraft. We had to design the spacecraft to make it extra resistant to radiation by protecting all the electronics. We enclosed them into a “vault”, a protective shield made of thick metal plates. We also had to adapt our trajectory and orbit around Jupiter instead of Europa: we will conduct brief, successive flybys of Europa, returning to the safer orbit in between.

Annie Marinan: Jupiter has a really strong magnetic field that traps energetic particles from solar wind as well as galactic background radiation (just like the Earth’s Van Allen belts but much bigger and with much more radiation). This radiation can corrupt data or cause electronics and materials to degrade over time. Europa is deep within those bands of radiation, so instead of orbiting Europa directly, the spacecraft flies by Europa every few weeks, spending most time in a higher, less radiation-intense orbit around Jupiter. Even with this modified orbit the spacecraft builds up a lot of radiation. Every part on each instrument needed to be carefully selected and tested to make sure they would survive and give good science measurements for the duration of the mission.

4 Can you explain the mission’s planetary protection requirements and how they have been addressed/if they have affected your objectives?

Elodie Lesage: To ensure that we won’t contaminate Europa with an Earth life form, we had to keep the spacecraft extremely clean during its assembly and transport. The spacecraft was assembled in JPL’s clean room, and regularly swabbed and tested to make sure that the number of particles on it was under a very low limit. To make sure that the spacecraft won’t touch Europa, which is the ultimate way to protect the moon from contamination, we will dispose of it by crashing into Callisto at the end of its life. This is not a problem for our objectives, and even gives us the opportunity to study another moon of the Jovian system, which can add valuable context and data to the mission.

Annie Marinan: The goal of planetary protection is to protect other places in the solar system where we think life could form from being contaminated with biological samples from Earth. Europa Clipper had strict requirements on how clean it needed to be at launch because Europa is a place where it’s possible that life could develop on its own, and we don’t want to inadvertently interfere. The spacecraft was assembled in a controlled environment, all the parts were exposed to high temperatures and cleaned thoroughly before assembly. Throughout assembly the spacecraft was swabbed and analysed to ensure that it stayed clean. Meeting planetary protection requirements helps Clipper meet its objectives because we can be confident that the spacecraft itself doesn’t affect any of the measurements or Europa itself.

5 What do we know about Europa’s geology based on both the Galileo mission more than 20 years ago, and the ongoing Juno mission, and how will Clipper complement this?

Elodie Lesage: The Voyager and Galileo missions were path-breaking. Thanks to these missions, we are now almost certain that Europa hosts a global saltwater ocean beneath its icy crust. We also know that its surface is among the youngest in the solar system and that it presents very rich chemistry. But we lack quantitative data: we do not know how salty the ocean is, how deep it is buried, how much material is exchanged between the surface and the ocean. We also lack images to understand Europa’s geology. The Galileo spacecraft faced the failure of its high-gain antenna and returned a very limited number of images of Europa. With its multiple imagery systems, including both narrow- and wide-angle cameras in the visible spectrum, the Europa Clipper spacecraft will revolutionize our understanding of the moon’s surface and subsurface.

6 What is the question you are specifically hoping the data returned can answer? What would be your ‘wow’ signal?

Christopher Glein: Our team is interested in whether Europa has the stuff of life. Things like carbon- and nitrogen-bearing compounds, especially organic molecules. I think it would be incredible to find methane (CH4) at Europa. It looks so simple, but it’s really not. The surface environment on Europa is irradiated and strongly oxidizing (like bleach). This means it has a tendency to destroy carbon-hydrogen bonds. It is not the kind of place where we would expect to find methane, unless there are active sources delivering methane and other reduced chemicals from the interior to the surface. That’s a tantalizing possibility.

Elodie Lesage: I personally work on modelling the transport of water through Europa’s icy shell, and the data I am the most excited for are the UV spectrometer (“Europa-UVS”) images, and the radar data. Europa-UVS would be able to detect a geyser of water vapour erupting from the ice shell. We don’t know whether this is happening at Europa, or how often, so it would be a very exciting and encouraging discovery. I also am very excited for the ice-penetrating radar (REASON), that will scan the ice shell at two wavelengths. It would be able to detect water or salt layers in the ice shell, which would be immensely helpful in understanding the transport and storage of liquid water there.

7 What are the requirements for life that we already know Europa can meet, and what are the requirements that Clipper can confirm or disprove the existence of?

Christopher Glein: We often distil the search for habitable environments in terms of the presence of liquid water and the availability of CHNOPS elements and sources of energy that can drive metabolic processes. On Europa, we are pretty sure that a subsurface ocean exists, although Europa Clipper will settle any lingering uncertainty using its magnetometer (ECM) and radar (REASON) instruments. Europa’s surface has deposits of CO2 ice and sulphate (SO4) sulphur. Yet, we are not sure if these materials came from the subsurface ocean. We are also not sure if organic molecules are present and if there are sources of nitrogen and phosphorus. We need to search for them.

Europa Clipper has a powerful suite of instruments that will determine the chemical composition of Europa. These include two mass spectrometers (SUDA, MASPEX), an infrared spectrometer (MISE), and an ultraviolet spectrograph (Europa-UVS). By coordinating our observations, we will achieve a wide coverage of Europa in terms of both chemical (i.e., the types and phases of materials) and geographic space. Some of these measurements might also reveal energy sources, such as hydrothermal vents, which could provide reduced molecules (like CH4) that may be out of chemical equilibrium with oxidized molecules (O2, H2O2) found at Europa’s surface.

8 Other icy Moons, such as Saturn’s Enceladus, are thought to have a liquid ocean beneath their ice crust. Why did you choose to study Europa, and what can this mission potentially tell us about other icy satellites and exoplanets?

Christopher Glein: We need to compare Europa and Enceladus so we can get a more general understanding about the evolution of ocean worlds and the processes that may make them habitable. Based on data from the Cassini mission, Enceladus looks like a great place for potential life. We lack the same level of detail for Europa, but Europa Clipper will solve this problem. What’s beautiful is that we have all these worlds to help us understand what kinds of outcomes (including life) may be inevitable where water and rock coevolve over billions of years, and what is rarer and possibly comes down to contingency. Europa, Enceladus, and other ocean worlds (including some exoplanets) are all part of how we will find out.

Elodie Lesage: Both Europa and Enceladus present great potential for habitability. The Cassini spacecraft was able to sample and analyse material ejected from Enceladus’ interior, which is a piece of the puzzle that we lack for Europa and are hoping to get with Europa Clipper. Studying multiple icy ocean worlds of the solar system strengthens our understanding of how these worlds formed and evolved, which can then be extended to outside of the solar system. Direct detection of icy satellites outside of the solar system remains a challenge, and better characterizing their chemical signature is a first step to being able to identify them.

Annie Marinan: One of the cool things about Europa is that scientists think that there is a rocky core underneath the liquid ocean, versus other icy moons that might be made up of primarily ice and water. On Earth, there are all sorts of fascinating biomes deep on the ocean floor, and it’s possible that that rock-water interface could mean Europa might be able to support interesting biology even though it’s so much farther from the sun. Anything we learn about Europa can help us understand both our own planet as well as other moons and planets in (and outside of!) our solar system.

The interview was conducted by Sam Royle and Sebastian Mueller.