COLLEGE PARK, Md. -- In 2010, an analysis of imagery from NASA’s Lunar Reconnaissance Orbiter (LRO) found that the moon shriveled like a raisin as its interior cooled, leaving behind thousands of cliffs called thrust faults on the moon’s surface. Now a new analysis suggests that the moon may still be shrinking and actively producing moonquakes along these thrust faults.

A team of researchers including Nicholas Schmerr, an assistant professor of geology at the University of Maryland, designed a new algorithm to re-analyze seismic data from instruments [seismometers] placed by NASA’s Apollo missions in the 1960s and ’70s. Their analysis provided more accurate epicenter location data for 28 moonquakes recorded from 1969 to 1977.

The team then superimposed this location data onto LRO imagery of the thrust faults. Based on the quakes’ proximity to the thrust faults, the researchers found that at least eight of the quakes likely resulted from true tectonic activity—the movement of crustal plates—along the thrust faults, rather than from asteroid impacts or rumblings deep within the moon’s interior.

Although the Apollo instruments recorded their last quake shortly before the instruments were retired in 1977, the researchers suggest that the moon is likely still experiencing quakes to this day. A paper describing the work, co-authored by Schmerr, was published in the journal Nature Geoscience on May 13, 2019.

“We found that a number of the quakes recorded in the Apollo data happened very close to the faults seen in the LRO imagery,” Schmerr said, noting that the LRO imagery also shows physical evidence of geologically recent fault movement, such as landslides and tumbled boulders. “It’s quite likely that the faults are still active today. You don’t often get to see active tectonics anywhere but Earth, so it’s very exciting to think these faults may still be producing moonquakes.”

During the Apollo missions astronauts placed a number of different instruments on the moon, including five seismometers on the moon’s surface during the Apollo 11, 12, 14, 15 and 16 missions. The Apollo 11 seismometer operated only for three weeks, but the four remaining instruments recorded 28 shallow moonquakes—the type produced by tectonic faults—from 1969 to 1977. On Earth, the quakes would have ranged in magnitude from about 2 to 5.

Using the revised location estimates from their new algorithm, the researchers found that the epicenters of eight of those 28 shallow quakes were within 19 miles of faults visible in the LRO images. This was close enough for the team to conclude that the faults likely caused the quakes. Schmerr led the effort to produce “shake maps” derived from models that predict where the strongest shaking should occur, given the size of the thrust faults.

The researchers also found that six of the eight quakes happened when the moon was at or near its apogee, the point in the moon’s orbit when it is farthest from Earth. This is where additional tidal stress from Earth’s gravity causes a peak in the total stress on the moon’s crust, making slippage along the thrust faults more likely.

“We think it’s very likely that these eight quakes were produced by faults slipping as stress built up when the lunar crust was compressed by global contraction and tidal forces, indicating that the Apollo seismometers recorded the shrinking moon and the moon is still tectonically active,” said Thomas Watters, lead author of the research paper and senior scientist in the Center for Earth and Planetary Studies at the Smithsonian Institution in Washington.

Much as a grape wrinkles as it dries to become a raisin, the moon also wrinkles as its interior cools and shrinks. Unlike the flexible skin on a grape, however, the moon’s crust is brittle, causing it to break as the interior shrinks. This breakage results in thrust faults, where one section of crust is pushed up over an adjacent section. These faults resemble small stair-shaped cliffs, or scarps, when seen from the lunar surface; each is roughly tens of yards high and a few miles long.

The LRO has imaged more than 3,500 fault scarps on the moon since it began operation in 2009. Some of these images show landslides or boulders at the bottom of relatively bright patches on the slopes of fault scarps or nearby terrain. Because weathering gradually darkens material on the lunar surface, brighter areas indicate regions that are freshly exposed by an event such as a moonquake.

Other LRO fault images show fresh tracks from boulder falls, suggesting that quakes sent these boulders rolling down their cliff slopes. Such tracks would be erased relatively quickly, in terms of geologic time, by the constant rain of micrometeoroid impacts on the moon. With nearly a decade of LRO imagery already available and more on the way in the coming years, the team would like to compare pictures of specific fault regions from different times to look for fresh evidence of recent moonquakes.

“For me, these findings emphasize that we need to go back to the moon,” Schmerr said. “We learned a lot from the Apollo missions, but they really only scratched the surface. With a larger network of modern seismometers, we could make huge strides in our understanding of the moon’s geology. This provides some very promising low-hanging fruit for science on a future mission to the moon.”

This release is adapted from text provided by NASA’s Goddard Space Flight Center.

The research paper, “Shallow seismic activity and young thrust faults on the Moon,” Thomas Watters, Renee Weber, Geoffrey Collins, Ian Howley, Nicholas Schmerr and Catherine Johnson, was published in the journal Nature Geoscience on May 13, 2019.

This work was supported by NASA’s Lunar Reconnaissance Orbiter Project and the Natural Sciences and Engineering Research Council of Canada. The content of this article does not necessarily reflect the views of these organizations.

COLLEGE PARK, Md. – An international team of researchers discovered a previously unknown visual system that may allow color vision in deep, dark waters where animals were presumed to be colorblind. The research appears on the cover of the May 10, 2019, issue of the journal Science.

“This is the first paper that examines a diverse set of fishes and finds how versatile and variable their visual systems can be,” said Karen Carleton, a biology professor at the University of Maryland and co-author of the paper. “The genes that determine the spectrum of light our eyes are sensitive to turn out to be a much more variable set of genes, causing greater visual system evolution much more quickly than we anticipated.”

Vertebrate eyes use two types of photoreceptor cells to see—rods and cones. Both rods and cones contain light-sensitive pigments called opsins, which absorb specific wavelengths of light and convert them into electrochemical signals that the brain interprets as color. The number and type of opsins expressed in a photoreceptor cell determine the colors an animal perceives.

Before this new study, it was accepted that cones are responsible for color vision, and rods are responsible for detecting brightness in dim conditions. 

This new work indicates that is not strictly the case. By analyzing the genomes of 101 fish, the team of researchers from the University of Maryland, the University of Queensland in Australia, Charles University in the Czech Republic and the University of Basel in Switzerland discovered that some fish contained multiple rod opsins raising the possibility they have rod-based color vision.

Cones typically contain genes for expressing multiple opsins, which is why they are used for color vision. But they are not as sensitive as rods, which can detect a single photon and are used for low-light vision. In 99% of all vertebrates, rods express just one type of light-sensitive opsin, which means the vast majority of vertebrates are colorblind in low-light conditions.

Vision in most deep-sea fish follows this same pattern, but the new research revealed some remarkable exceptions. By analyzing the genes for expressing opsins in rods and cones of fish living from the shallow surface waters down to 6,500 feet of depth, the researchers found 13 fish with rods that contained more than one opsin gene. Four of those, all deep-sea fish, contained more than three rod opsin genes.

Most remarkable was the silver spinyfin fish, which had a surprising 38 rod opsin genes. That is more opsins than the researchers found in the cones of any other fish and the highest number of opsins found in any known vertebrate. (Human vision by comparison uses four opsins). In addition, the rod opsins found in silver spinyfin fish are sensitive to different wavelengths.

“This was very surprising,” Carleton said. “It means the silver spinyfin fish have very different visual capabilities than we thought. So, the question then is, what good is that? What could these fish use these spectrally different opsins for?”                                               

Carleton believes the answer may have to do with detecting the right prey. It has long been presumed that animals living in very deep water have no need for color vision, because only blue light penetrates deeper than 600 feet. But despite the lack of sunlight, the deep sea is not devoid of color. Many animals that live in darkness generate their own light through bioluminescence.

The new study found that in fish with multiple rod opsins, the specific wavelength of light their opsins are tuned to overlap with the spectrum of light emitted by the bioluminescent creatures that share their habitat.

“It may be that their vision is highly tuned to the different colors of light emitted from the different species they prey on,” Carleton said.

It’s important to note that the four species of fish found to have more than three rod opsins are unrelated species. This suggests that rod-based color vision, which can be thought of as deep-water color vision, evolved independently multiple times and must confer some benefit to survival.  

The researchers say their next steps are to broaden the study to other deep-sea fish and to look for shallow-water relatives of silver spinyfin fish that may have evolved a large number of rod opsins.

The research paper “Vision using multiple distinct rod opsins in deep-sea fishes,” Zuzana Musilova, Fabio Cortesi1, Michael Matschiner, Wayne I. L. Davies, Jagdish Suresh Patel, Sara M. Stieb, Fanny de Busserolles, Martin Malmstrøm, Ole K. Tørresen, Celeste J. Brown11, Jessica K. Mountford, Reinhold Hanel, Deborah L. Stenkamp, Kjetill S. Jakobsen, Karen L. Carleton, Sissel Jentoft, Justin Marshall, Walter Salzburger, was published in the journal Science on May 10, 2019.

This study was supported by the Czech Science Foundation (Award No. 16-09784Y), the Swiss National Science Foundation (Award Nos. 166550, 156405, 176039, 165364), the Basler Stiftung für Experimentelle Zoologie, a UQ Development Fellowship, the Australian Research Council (Award Nos. FT110100176, LP0775179), a Discovery Project grant (Award No. DP140102117), the Research Council of Norway (Award No. 222378), the Center for Modeling Complex Interactions sponsored by the NIGMS (Award No.  P20 GM104420), the National Science Foundation (Award No. OIA1736253), the National Institutes of Health (Award Nos. 01EY012146, R01EY024639) and the European Research Council. The content of this article does not necessarily reflect the views of these organizations.