Send signals through the ice on ocean worlds

project

Ocean Worlds Trans-Ice Signals (STI)

glimpse

The Ocean Worlds Signals Through Ice (STI) team is developing communication technologies to enable subsurface exploration of ocean worlds where conditions might be conducive to life.

Artist's concept showing a sectional view of a possible ocean world with a surface layer of ice over a thick layer of ocean water over a thinner layer of ocean floor.  3 thumbnails below showing hydrothermal vents, ice fractures and glaciers.
Figure 1: Artist’s concept of a sectional perspective of Europa depicting the exciting potentially habitable environment of the ocean world (Credit: K. Hand et al./NASA/JPL)

The discovery of extraterrestrial life would be an incredible discovery, revolutionizing humanity’s perception of life and providing us with insight into how life began and persists in different environments. Exploration of ocean worlds like Europa and Enceladus — which orbit Jupiter and Saturn, respectively — are particularly interesting, because they may harbor conditions conducive to life including liquid water, essential chemistry, heat or energy sources, and long-lived oceans.

To follow up on discoveries of habitable environments obtained by previous missions (eg, Cassini), future missions to discover life on icy ocean worlds will require more than just remote observations. Deep subsurface exploration reaching out to the moons’ oceans and/or pockets of water in the icy crust, as well as describing in detail any life that might have existed there.

Access to the subterranean ocean or pockets of melt within an ice crust would present significant challenges. From a technological perspective, a successful exploration mission would require starting in a vacuum at cryogenic (“very cold” temperatures), penetrating tens of kilometers through an ice shell for a few years, and reaching the ocean – all while maintaining communication with assets on the lunar surface to transmit data back. other down to earth. The journey through the ice will entail navigating through an ice envelope with unknown changes in temperature, strength of materials, and potential caustic compositions, and will require the ability to survive the stress of tides and movement of potential faults (such as ice quakes).

Illustration of a large gray tubular device piercing through a layer of ice at the ocean's surface
Figure 2. Artist’s concept of robotics in Europe (Image credit: Alexander Pawlusik/NASA)

To date, a powerful technical concept has emerged to effectively explore the interiors of ice shells: the ice-breaking robot, or ‘cryobot’ (see Figure 2). The cryobot cuts through ice by melting or drilling away ice (and non-ice contaminants) using the melt, cut, or hybrid method. Ground-based ice probes have been proposed and/or developed for decades, with laboratory and field tests in Antarctica and Greenland exploring the feasibility of the concept for future planetary missions. To improve the mission readiness of this icy ocean probe, the STI team is developing robust communication technologies that use optical cords and free space radio frequency units capable of transmitting data across many kilometers of ice while surviving the extreme conditions found on ocean worlds.

Europa: Extremely Cold and Extreme Loads: Submersible robots using robust optical fiber nanoropes (~1–2 mm diameters) of sufficient length and mass to support proposed Europa cryobot architectures have been successfully used on land for exploration of the Earth’s oceans. However, the ability of these systems to withstand the harsh glacial conditions over Europe has not been demonstrated. Therefore, an interdisciplinary STI team developed new protocols and tools to evaluate the capabilities of optical communication ropes under the stress and temperature conditions (100–260 K) expected in Europa’s ice cap. The team applied these temperature shear loadings to a range of loads and loading rates to simulate the ice creep and rapid-slide earthquakes expected in a global ocean ice cap environment.

A set of photographs: (left) a schematic diagram showing a hydraulic test rig; (upper right) a photograph of a test specimen of an ice block with rope on the left and mandrel on the right;  (Lower right) Illustration of a green tube with yellow inner layers and a white fiber cable running through the center.

The STI team performed these tests using a cryogenic biaxial deformation instrument at the Lamont-Doherty Earth Observatory (LDEO) (see Fig. 3a). By testing in a laboratory environment that simulates that of a relevant ocean world, the team characterizes the shearing strength of the two ropes under conditions similar to the ice crevasses of Europa. The team used a modern three-section mold to apply a claim to the rope (see Fig. 3b), around which a polycrystalline ice sample was frozen, with two plane breaks previously represented as vertical faults in the rope. may intersect (dotted lines, in Fig. 3b).

This template protocol has proven to be a reliable method for creating fully embedded, pre-stranded rope ice samples, and demonstrated a valuable new test preparation technique for the science community. Figure 3c shows one of the tested cords, High Strength Linden Rope Optical Fiber Cable (HS-STFOC), and the layers of protective material surrounding the optical fiber through which data is transmitted. The changes in visual integrity and signal strength observed during the test indicate how well the tether is capable in different regions of Europa’s ice cap.

Shear test results showed a surprisingly high level of rope toughness across the range of temperatures and ice-rift sliding velocities expected on ocean worlds such as Europa and Enceladus. The fault slip velocities were controlled by the applied loading rates. Figure 4b shows the maximum stress survived by two of the strength ropes tested: Linden Photonics Inc. 7 to 3×10-4 m / s.

Group photo (left, top) photo of a man and woman standing on a shelf of computers and consoles;  (top right) histogram with blue boxes, red triangles, and black circles indicating peak stress and temperature;  (Bottom left) A small graphic with a cracked yellow fiber cable

However, despite surviving a range of creeping slide and ice quake events in the coldest temperatures (around 100 K) and maintaining eye contact throughout the tests, the team noticed some damage to the ropes’ outer jackets and stretching of the interiors. fibers (eg, Fig. 4c), indicating the need for further tether development, which is currently being pursued under the COLDTech program of the Division of Planetary Sciences.

An STI study with incompletely fractured planar slip-ice fronts (likely similar to reinvigorated faults in Europe) across fault-slip rates, shear loads and cryospheric temperature ranges provides strong confirmation of how the frictional stability of ice depends on temperature and fault-slip velocity. . These results are important for potential application to Europe, indicating variation in slip behavior with depth. The upper and lower parts of the ice shell slide smoothly (and slowly), while in a medium range in temperature and depth, ice faults can initiate fast-slide glacial earthquake events. By characterizing data transmission in these conditions, the tests show that the tethers can serve as scientific tools for detecting ice earthquakes and determining the thermal profile of the ice crust.

These and other developments by the STI team advance tethered and free space communication technologies to eliminate technical risks for the cryobot mission to reach ocean worlds. STI’s efforts also improve the ability to investigate the temperatures, mechanical and compositional properties of dynamic ice shells, and guide future technological developments for exploring subsurface ocean worlds.

Project leaders

Kathleen Kraft, JHU Applied Physics Laboratory (JHU APL); Vishal Singh, Lamont-Doherty Earth Observatory (LDEO), Columbia University; Christine McCarthy, LDEO; Jacoba, Woods Hole Oceanographic Institution (WHOI); Matthew Sylvia, WHO

Sponsoring organizations

SESAME Planetary Science Division and COLDTech Programs

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