While partial melting occurring near mid-ocean ridges due to high temperatures can produce such anomalous conditions, it fails to account for the sharp and large drops in the velocity of seismic waves observed at the LAB far from mid-ocean ridges. Understanding the origin of this seismic wave velocity drop and attenuation at the oceanic LAB is crucial for deciphering the asthenosphere’s low viscosity and how it facilitates the movement of tectonic plates over the Earth’s surface, giving rise to mountain-building processes, earthquakes, and volcanism.

In this regard, a team of researchers from Japan, led by Professor Takashi Yoshino from the Institute for Planetary Materials at Okayama University, has recently investigated the effect of water on the seismic properties of titanium-free olivine rocks, similar to those found in the asthenosphere. Their study was published in Volume 120, Issue 32 of the journal Proceedings of the National Academy of Sciences on 31 July 2023.

“We experimentally determined the seismic wave attenuation characteristics, parameters for ascertaining the softness of the lithosphere and asthenosphere, under high temperature and pressure using our short-period oscillation generation technology,” explains Prof. Yoshino.

The team studied the anelastic properties of the olivine rocks under conditions which resemble the LAB beneath the old oceanic floor — 3 GPa pressure and temperatures ranging from 1,223 to 1,373 K. They employed in situ X-ray monitoring and subjected the olivine rocks to mechanical testing by generating forced vibrations over a wide range of seismic frequencies — 0.5 to 1,000 seconds — through their unique short-period oscillation technology.

The experiments revealed that water had a significant effect, enhancing the energy dispersion and reducing the elastic moduli of the rocks across a wide range of frequencies. Additionally, the researchers observed a seismic attenuation peak at higher frequencies of 1 to 5 seconds, which became more pronounced with increasing water content. “The presence of water induces attenuation at higher frequencies, leading to a decrease in the velocity of seismic waves. The presence of water also weakens the asthenosphere, which allows the lithosphere to move smoothly over it,” says Prof. Yoshino.

These observations suggest that the oceanic asthenosphere must contain water. This difference in water content between the two layers constituting the LAB can explain the sharp velocity drops as well as the near constant attenuation observed over a wide frequency range in the asthenosphere.

Notably, the researchers acknowledge that their conclusion assumes a negligible effect of iron on hydrogen-related defects in the rocks, indicating the need for further research to explore the anelastic properties of iron-bearing olivine rocks.

Prof. Yoshino highlights the long-term implications of their findings. “The presence of water in the asthenosphere can provide important insights into volcanic and seismic activities, thus facilitating their prediction and detection,” he speculates.

Overall, this study contributes to our understanding of tectonic plate movement, paving the way for better comprehension of various tectonic activities.

A new study by researchers at Queen Mary University of London, Imperial College London and The University of Melbourne has found that people can learn to use supernumerary robotic arms as effectively as working with a partner in just one hour of training.

The study, published in the journal IEEE Open Journal of Engineering in Medicine and Biology, investigated the potential of supernumerary robotic arms to help people perform tasks that require more than two hands. The idea of human augmentation with additional artificial limbs has long been in science fiction, like in Doctor Octopus in The Amazing Spider-Man (1963).

“Many tasks in daily life, such as opening a door while carrying a big package, require more than two hands,” said Dr Ekaterina Ivanova, lead author of the study from Queen Mary University of London. “Supernumerary robotic arms have been proposed as a way to allow people to do these tasks more easily, but until now, it was not clear how easy they would be to use.”

The study involved 24 participants who were asked to perform a variety of tasks with a supernumerary robotic arm. The participants were either given one hour of training in how to use the arm, or they were asked to work with a partner.

The results showed that the participants who had received training on the supernumerary arm performed the tasks just as well as the participants who were working with a partner. This suggests that supernumerary robotic arms can be a viable alternative to working with a partner, and that they can be learned to use effectively in a relatively short amount of time.

“Our findings are promising for the development of supernumerary robotic arms,” said Dr Ivanova. “They suggest that these arms could be used to help people with a variety of tasks, such as surgery, industrial work, or rehabilitation.”

The study was funded by the EU H2020 NIMA (FETOPEN 899626), TRIMANUAL (MSCA 843408) and CONBOTS (ICT 871803) grants.

“Our findings support the idea that large-diameter fuel build-up is a strong contributor to fire severity,” said Audrey Odwuor, a Ph.D. candidate in the UCI Department of Earth System Science and the lead author of the new study.

Researchers have known for decades that an increasing number of trees and an increasing abundance of dead plant matter on forest floors are the things making California wildfires more severe — but until now it was unclear what kinds of plant debris contribute most to a fire.

To tackle the question, Odwuor and two of the study’s co-authors — James Randerson, professor of Earth system science at UCI, and Alondra Moreno from the California Air Resources Board — drove a mobile lab owned and operated by the lab of study co-author and UCI alumna Francesca Hopkins at UC Riverside, to the southern Sierra Nevada mountains during 2021’s KNP Complex Fire.

The KNP Complex Fire burned almost 90,000 acres in California’s Sequoia and Kings Canyon National Parks. In the fire’s smoke, the team took samples of particulate matter-laden air and analyzed the samples for their radiocarbon content at UCI’s W.M. Keck Accelerator Mass Spectrometer facility with co-author and UCI Earth system science professor Claudia Czimczik.

Different fuel types, explained Czimczik, have different radiocarbon signatures, such that when they analyzed the smoke they discovered radiocarbon values associated with large fuel sources like fallen tree logs.

“What we did was pretty distinctive, as we were able to identify fuel sources by measuring the wildfire smoke,” said Czimczik. “Our approach provides what we think of as an integrated picture of the fire because we’re sampling smoke produced over the course of the fire that has been transported downwind.”

The team also saw elevated levels of particulate matter that is 2.5 microns in diameter or less, which includes particles that, if inhaled, are small enough to absorb into the bloodstream.

The preponderance of large-diameter fuels is new in western forests. “We’re really in a situation that’s a consequence of both management strategies and climate warming since European-American settlement began in California,” Odwuor said. “These fuels are building up on the forest floor over periods of decades, which is not typically how these forests were maintained.”

It’s information that, according to Odwuor, could help California better manage its wildfires.

“The knowledge that large-diameter fuels drive fires and fire emissions — at least in the KNP Complex Fire — can be useful for knowing which fuels to target with fuel treatments and what might end up in the smoke from both wildfires and prescribed fire,” said Odwuor. “The idea is that because we can’t control the climate, we can only do our best to manage the fuels, which will theoretically have an impact on fire severity and the composition of the smoke.”

But the solution isn’t as straightforward as removing trees from forest floors, because, among other things, they provide habitat for wildlife. That, and “once you get them out, where do you send them? There are only so many mills in California that can handle all the wood,” Odwuor said.

Where the new knowledge could be helpful is with prescribed burns, wherein teams burn tracks of forest in a planned fashion with the aim of reducing the amount of fuel available for future wildfires.

“We’re hoping to build some urgency for these management strategies,” said Odwuor.

Not only does the new research shed light on the nature of TRAPPIST-1 b, the exoplanet orbiting closest to the system’s star, it has also shown the importance of parent stars when studying exoplanets.

Published in Astrophysical Journal Letters, the findings by astronomers at UdeM’s Trottier Institute for Research on Exoplanets (iREx) and colleagues in Canada, the U.K. and U.S. shed light on the complex interplay between stellar activity and exoplanet characteristics.

Captured the attention

TRAPPIST-1, a star much smaller and cooler than our sun located approximately 40 light-years away from Earth, has captured the attention of scientists and space enthusiasts alike since the discovery of its seven Earth-sized exoplanets seven years ago. These worlds, tightly packed around their star with three of them within its habitable zone, have fueled hopes of finding potentially habitable environments beyond our solar system.

Led by iREx doctoral student Olivia Lim, the researchers employed the powerful James Webb Space Telescope (JWST) to observe TRAPPIST-1 b. Their observations were collected as part of the largest Canadian-led General Observers (GO) program during the JWST’s first year of operations. (This program also included observations of three other planets in the system, TRAPPIST-1 c, g and h.) TRAPPIST-1 b was observed during two transits — the moment when the planet passes in front of its star — using the Canadian-made NIRISS instrument aboard the JWST.

“These are the very first spectroscopic observations of any TRAPPIST-1 planet obtained by the JWST, and we’ve been waiting for them for years” said Lim, the GO program’s principal Investigator.

She and her colleagues used the technique of transmission spectroscopy to peer deeper into the distant world. By analysing the central star’s light after it has passed through the exoplanet’s atmosphere during a transit, astronomers can see the unique fingerprint left behind by the molecules and atoms found within that atmosphere.

‘Just a small subset’

“This is just a small subset of many more observations of this unique planetary system yet to come and to be analysed,” adds René Doyon, Principal Investigator of the NIRISS instrument and co-author on the study. “These first observations highlight the power of NIRISS and the JWST in general to probe the thin atmospheres around rocky planets.”

The astronomers’ key finding was just how significant stellar activity and contamination are when trying to determine the nature of an exoplanet. Stellar contamination refers to the influence of the star’s own features, such as dark spots and bright faculae, on the measurements of the exoplanet’s atmosphere.

The team found compelling evidence that stellar contamination plays a crucial role in shaping the transmission spectra of TRAPPIST-1 b and, likely, the other planets in the system. The central star’s activity can create “ghost signals” that may fool the observer into thinking they have detected a particular molecule in the exoplanet’s atmosphere.

This result underscores the importance of considering stellar contamination when planning future observations of all exoplanetary systems, the sceintists say. This is especially true for systems like TRAPPIST-1, since the system is centred around a red dwarf star which can be particularly active with starspots and frequent flare events.

“In addition to the contamination from stellar spots and faculae, we saw a stellar flare, an unpredictable event during which the star looks brighter for several minutes or hours,” said Lim. “This flare affected our measurement of the amount of light blocked by the planet. Such signatures of stellar activity are difficult to model but we need to account for them to ensure that we interpret the data correctly.”

A range of models explored

Based on their collected JWST observations, Lim and her team explored a range of atmospheric models for TRAPPIST-1 b, examining various possible compositions and scenarios.

They found they could confidently rule out the existence of cloud-free, hydrogen-rich atmospheres — in other words, there appears to be no clear, extended atmosphere around TRAPPIST-1 b. However, the data could not confidently exclude thinner atmospheres, such as those composed of pure water, carbon dioxide, or methane, nor an atmosphere similar to that of Titan, a moon of Saturn and the only moon in the Solar System with its own atmosphere.

These results are generally consistent with previous (photometric, and not spectroscopic) JWST observations of TRAPPIST-1 b with the MIRI instrument. The new study also proves that Canada’s NIRISS instrument is a highly performing, sensitive tool able to probe for atmospheres on Earth-sized exoplanets at impressive levels.