From The California Institute of Technology
4.29.24
Lori Dajose
(626) 395‑1217
ldajose@caltech.edu
Over the course of its elliptical orbit, the moon Enceladus is squeezed unevenly by Saturn’s gravitational pull and deforms from a spherical shape into a football shape and back again. This cyclic stress causes a phenomenon called “tidal heating” within Enceladus and dissipates enough energy to maintain what is believed to be a global ocean underneath the moon’s icy crust.
At Enceladus’s south pole, a large number of jets spray icy particles out from a set of jagged, 150-kilometer-long faults—known as the tiger-stripe faults—and this ejected material coalesces above the moon’s surface to form a plume. Samples of this plume material analyzed by NASA’s Cassini mission suggests that the chemical conditions believed to be necessary for life may exist in the ocean deep beneath Enceladus’s surface.
Now, new research led by graduate student Alexander Berne (MS ’22), working with Mark Simons, the John W. and Herberta M. Miles Professor of Geophysics and director of the Brinson Exploration Hub at Caltech, uses a detailed geophysical model to characterize the motion of these tiger-stripe faults and provides new insights into the geophysical processes controlling jet activity. Understanding these and other factors—such as the extent to which the jet material represents the subsurface ocean, how long jets have been active, the topography of its ice shell, and so on—is crucial for getting a detailed picture of the moon’s potential habitability over time.
The plume above Enceladus’s south pole varies in intensity, waxing and waning in strength to produce two notable bright peaks in emission during the moon’s 33-hour orbit around Saturn. It has been theorized that tidal forces cause the tiger-stripe faults to open and close like an elevator door, allowing them to emit more or less material in cycles that correspond to those tides. However, such models are not able to accurately predict the timing of peaks in plume brightness. More problematic: This fault-opening mechanism requires more energy than is expected to be available from tidal forcing alone.
The new study suggests that observed variations in Enceladus’s plume strength may be due to the tiger-stripe faults moving in a strike–slip fashion, with one side shearing past the other, similar to the style of fault motion that produces earthquakes along faults like California’s San Andreas. The energy required for such fault motion is considerably less than required by the opening/closing mechanism.
Berne and colleagues developed a sophisticated numerical model to simulate strike–slip motion along Enceladus’ faults. These models also consider the role of friction between the faults’ icy walls, which causes deformation to be sensitive to both compressional stresses that tend to clamp and unclamp the fault, and shear stresses that tend to drive slip on the fault. The numerical model is able to simulate slip along the tiger stripes in a manner which matches the variations in plume brightness variations as well as spatial variations in surface temperature, suggesting that the jets are indeed controlled by strike–slip motion over Enceladus’s orbit.
The researchers theorize that the individual jets occur at “pull-aparts” in the faults—bent sections of fault that open under regional strike–slip motion. Recent separate research from JPL also examined the tiger-stripe region and found geological evidence for pull-aparts along the faults, located right at the location of the jets. “We now appear to have both geologic and geophysical reasons to suspect that jet activity occurs at pull-aparts along Enceladus’s tiger stripes,” says Berne.
Basic diagram of a fault pull-apart. Curved sections of the fault moving in opposite parallel directions lead to openings in the fault. Credit: Caltech
In 2005, the Cassini mission flew by Enceladus, sampled the jet material, and discovered that the plume contains elements like carbon and nitrogen, indicating that the subsurface ocean currently could harbor conditions favorable for life. In addition to the presence of these and other chemical components, key geophysical conditions—such as sufficient heat production and nutrient flux between the core, the ocean, and the surface—are required for habitability.
“For life to evolve, the conditions for habitability have to be right for a long time, not just an instant,” Simons says. “On Enceladus, you need a long-lived ocean. Geophysical and geological observations can provide key constraints on the dynamics of the core and the crust as well as the extent to which these processes have been active over time.”
“Detailed measurements of motion along the tiger stripes are needed to confirm the hypotheses laid out in our work,” Berne says. “For instance, we now have the capacity to image fault slip, such as earthquakes, on Earth using radar measurements from satellites in orbit. Applying these methods at Enceladus should allow us to better understand the transport of material from the ocean to the surface, the thickness of the ice crust, and the long-term conditions which may enable life to form and evolve on Enceladus.”
The paper appears in the journal Nature Geoscience on April 29. Berne is the study’s first author. In addition to Simons, co-authors are James T. Keane, Erin J. Leonard, and Ryan S. Park of JPL. Funding was provided by NASA and JPL.
See the full article here .
Comments are invited and will be appreciated, especially if the reader finds any errors which I can correct.
five-ways-keep-your-child-safe-school-shootings
Please help promote STEM in your local schools.
The California Institute of Technology is a private research university in Pasadena, California. The university is known for its strength in science and engineering, and is one among a small group of institutes of technology in the United States which is primarily devoted to the instruction of pure and applied sciences.
The California Institute of Technology was founded as a preparatory and vocational school by Amos G. Throop in 1891 and began attracting influential scientists such as George Ellery Hale, Arthur Amos Noyes, and Robert Andrews Millikan in the early 20th century. The vocational and preparatory schools were disbanded and spun off in 1910 and the college assumed its present name in 1920. In 1934, The California Institute of Technology was elected to the Association of American Universities, and the antecedents of National Aeronautics and Space Administration ‘s Jet Propulsion Laboratory, which The California Institute of Technology continues to manage and operate, were established between 1936 and 1943 under Theodore von Kármán.
The California Institute of Technology has six academic divisions with strong emphasis on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. First-year students are required to live on campus, and 95% of undergraduates remain in the on-campus House System at The California Institute of Technology. Although The California Institute of Technology has a strong tradition of practical jokes and pranks, student life is governed by an honor code which allows faculty to assign take-home examinations. The The California Institute of Technology Beavers compete in 13 intercollegiate sports in the NCAA Division III’s Southern California Intercollegiate Athletic Conference (SCIAC).
There are many Nobel laureates who have been affiliated with The California Institute of Technology, including alumni and faculty members (Linus Pauling being the only individual in history to win two unshared prizes). In addition, Fields Medalists and Turing Award winners have been affiliated with The California Institute of Technology. Crafoord Laureates and non-emeritus faculty members (as well as many emeritus faculty members) who have been elected to one of the United States National Academies. There are or have been Chief Scientists of the U.S. Air Force and numerous United States National Medal of Science or Technology winners. Many faculty members are associated with the Howard Hughes Medical Institute as well as National Aeronautics and Space Administration. According to a Pomona College study, The California Institute of Technology ranked very highly in the U.S. for the percentage of its graduates who go on to earn a PhD.
Research
The California Institute of Technology is classified among “R1: Doctoral Universities – Very High Research Activity”. Caltech was elected to The Association of American Universities in 1934 and remains a research university with “very high” research activity, primarily in STEM fields. The largest federal agencies contributing to research are National Aeronautics and Space Administration; National Science Foundation; Department of Health and Human Services; Department of Defense, and Department of Energy.
The California Institute of Technology has over 739,000 square feet (68,700 m^2) dedicated to research: 330,000 square feet (30,700 m^2) to physical sciences, 163,000 square feet (15,100 m^2) to engineering, and 160,000 square feet (14,900 m^2) to biological sciences.
In addition to managing NASA-JPL/Caltech , The California Institute of Technology also operates the Caltech Palomar Observatory; The Owens Valley Radio Observatory along with the New Jersey Institute of Technology; the Caltech Submillimeter Observatory; the W. M. Keck Observatory at the Maunakea Observatory along with the University of California; the Laser Interferometer Gravitational-Wave Observatory at Livingston, Louisiana and Hanford, Washington along with the Massachusetts Institute of Technology; and Kerckhoff Marine Laboratory in Corona del Mar, California. The Institute launched the Kavli Nanoscience Institute at The California Institute of Technology in 2006; the Keck Institute for Space Studies in 2008; and is also the current home for the Einstein Papers Project. The Spitzer Science Center, part of the Infrared Processing and Analysis Center located on The California Institute of Technology campus, is the data analysis and community support center for NASA’s Spitzer Infrared Space Telescope [no longer in service] .
The California Institute of Technology partnered with University of California-Los Angeles to establish a Joint Center for Translational Medicine (UCLA-Caltech JCTM), which conducts experimental research into clinical applications, including the diagnosis and treatment of diseases such as cancer.
The California Institute of Technology operates several Total Carbon Column Observing Network stations as part of an international collaborative effort of measuring greenhouse gases globally. One station is on campus.
sciencesprings 