Wednesday, July 23, 2025

Can seismic signals detect fragmentation of a fireball meteoroid?

Seismological Society of America

The seismic signature of a fireball meteoroid event can be used to tell whether the fireball fragmented or remained intact as it fell through the atmosphere, according to new research published in Seismological Research Letters.

The 2020 return of the sample capsule from the asteroid-exploring Hayabusa2 mission to southern Australia offered a unique opportunity to test this idea, write Iona Clemente of Curtin University and colleagues in the journal.

Clemente and colleagues compared seismic signals associated with the Hayabusa2 capsule’s return with signals collected from two natural meteoroids and the re-entry of the upper stage of a 2.5-ton Russian Soyuz 2.1b rocket that all plummeted to Earth over Australia.

The researchers concluded that objects that remained intact during their fall—Hayabusa2, the Soyuz re-entry and one of the natural meteoroids—had a distinct seismic signature compared to a large natural meteoroid over North Queensland that likely fragmented with a final dramatic airburst or disintegration.

Visual evidence of fireball fragmentation is rare, making it important to have another way to identify these events, said Clemente. “Understanding fragmentation helps us model how different types of space objects might behave during atmospheric entry, informing planetary defense strategies.”

For instance, shock waves produced solely by the high-speed trajectory of the object through the atmosphere will radiate energy mostly in one direction, compared to shock waves produced by fragmentation, which will radiate energy in all directions, she explained. Fragmentation data helps researchers refine their estimates of where meteoroids fall and how large a debris field they create.

Fragmentation can also provide valuable information on the composition of a meteoroid’s parent body, as chondritic or stony meteoroids are usually weaker and more prone to fragmentation compared to iron-rich meteoroids. “This distinction helps build statistics on the types of objects entering Earth’s atmosphere and improves our understanding of the relative proportions of chondritic versus iron-type meteoroids,” Clemente noted.

Shock waves produced by fireball events are captured as seismic or acoustic waves on the ground. In the SRL study, the researchers used seismic data captured by both permanent seismic networks in Australia and two temporary high-density seismic networks that operated from 2018 to 2022 and 2020 to 2022.

Knowing exactly when and where the Hayabusa2 sample capsule was to return to Earth, the researchers could zero in on traces in the seismic record to characterize and verify the capsule’s unique re-entry signature. They confirmed that the shock wave produced by the capsule came from its ballistic trajectory, or its high-speed trajectory through the atmosphere.

“The strong observed signal for the Hayabusa2 [capsule] is largely due to the dense seismic network that happened to be positioned directly beneath the re-entry trajectory,” Clemente explained. “This level of station coverage is rare and enabled us to capture the ballistic shock wave signature with good clarity and a high signal-to-noise ratio.”

The strong similarity in signals between the Hayabusa2 capsule and a 2021 fireball that fell over Lake Torrens, South Australia “was also particularly interesting,” she added. “The strong match we get between the two events likely indicated that this object didn’t fragment. This is supported by the data we have from the Desert Fireball Network, which uses the brightness of the object—light curves—to identify fragmentation.”

Curtin University’s Desert Fireball Network is an Australian network of cameras that tracks meteoroids entering the atmosphere.

The researchers note that variations in atmospheric temperature, pressure, wind strength and other factors can impact how a shock wave travels and is recorded on the ground. Similarly, local geological conditions such as soil type and topography can also impact how a shock wave is detected by seismic sensors. “While our current approach does not explicitly model these effects, they are important factors that we aim to explore further in future work to improve the accuracy and confidence of our interpretations,” said Clemente.

“This study represents an important first step, and we see tremendous potential for developing this into an operational tool for fireball characterization,” she noted. “We also plan to apply our method to a larger set of fireball events, which will help us test its general applicability, and potentially reveal new patterns or behaviors.”

The study is one of several research papers included in SRL’s upcoming Special Focus section on the OSIRIS-REx Re-entry, a sample capsule from a mission to the near-Earth asteroid Bennu that returned to Earth in 2023. Along with Hayabusa2 and OSIRIS-Rex, there have been only two other sample return capsule re-entries monitored using seismic sensors.

Journal

Seismological Research Letters

DOI

10.1785/0220250032

Method of Research

Observational study

Subject of Research

Not applicable

Article Title

Exploring Seismic Signal Detection and Source Identification of Atmospheric Entries: The Hayabusa2 Sample Return Capsule as a Benchmark

Article Publication Date

23-Jul-2025

Study of now-submerged migration routes redraws map of how humans settled beyond Africa

University of Kansas

Known routes of migration — image:
Reference map showing natural features cited, cities, and known routes connecting the Nile River, Foul Bay, Gulf of Suez, Red Sea, and Mediterranean Sea throughout history.
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Credit: Dobson et al

LAWRENCE — A University of Kansas researcher has spent years studying “aquaterra” — his term for regions around the world once populated by ancient humans that today are submerged under water due to sea-level changes.

Jerome Dobson, KU professor emeritus of geography, believes these regions — typically extending from continental coasts and surrounding scattered islands — contain vast archaeological treasures and answers about ancient humanity, and deserve much more research attention.

Dobson and Italian colleagues Giorgio Spada of the University of Bologna and Gaia Galassi of the University of Urbino recently published a reexamination of ancient human migratory routes from Africa, where homo sapiens first evolved, based on a newly improved glacial isostatic adjustment (GIA) model of historical sea levels along with DNA and archaeological data.

An improved simulation of ancient sea levels can reveal how melting glaciers — continuing long after the Last Glacial Maximum — may have transformed migration pathways and shaped the rise of civilizations in Africa.

The new research appears in the peer-reviewed journal Comptes Rendus Géoscience, published by the Académie des sciences, heir to the Comptes Rendus des Séances hebdomadaires de l'Académie des Sciences, founded in 1835 by Arago.

“The exciting implication is that a lot of underwater landscapes have archaeological relevance, and this mapping gives scientists a better shot at finding them,” Dobson said. “We hope this enables people to see and explore the landscapes that were exposed during the last ice age — especially at the Last Glacial Maximum 21,000 years ago.”

Dobson’s study refines understanding of ocean levels, coastlines and ancient migratory corridors in Africa and West Asia, using the new sea-level data to explore alternative land and sea routes into and out of Africa. These include the Suez crossing between the Red and Mediterranean seas, the Gulf of Aqaba route to the Levant, the Bab el Mandab crossing to Saudi Arabia, the crossing from Foul Bay to the Mediterranean Sea, and the island route across the Sicily and Messina straits.

“We wanted to generate coastlines that are physically and geophysically correct,” said the KU researcher. “Researchers need to use GIA modeling because simply subtracting sea-level height from topography isn’t enough. The Earth’s crust literally warps under the weight of ice sheets.”

According to the findings, some of these important migration routes were exposed by retreating seas for much longer than was known previously, though they varied with regional sea-level fluctuations.

Dobson and his co-authors also used datasets of DNA to reconstruct how human beings migrated out of Africa — seeing where they align with possible geographical routes.

“We benefited from a newly published map of DNA centers going back 2 million years,” Dobson said. “It shows a single ancient origin in the south, near Meroe in Kush, well into Africa. The archaeological evidence is sparse, while the DNA evidence is strong and consistent.”

The team sought to trace early human migration from the first-known centers of humanity. They examined northern routes through the Sinai Peninsula and southern routes that cross the Red Sea at the Bab el-Mandeb.

“The early human haplotype center appears to be in northeast Sudan,” Dobson said. “That wasn’t a shock, somewhat expected by the DNA experts who discovered it. There were clear connections going up into the Levant. Archaeological literature often emphasizes the southern route across the Bab el-Mandeb, but the maps they produce show little connection between the western and eastern sides of that divide.”

Dobson said that although the Bab el-Mandeb is the narrowest passage geographically, it might have been a major barrier depending on the watercraft of that time.

“People who study this deeply say the northern route — through the Sinai — is well established,” said the KU researcher. “The southern one, across Bab el-Mandeb, looks much less supported by archaeology based on the new data.”

Dobson and his co-authors considered other migratory routes and crossings. Their findings show south-to-north and east-to-west directions of human occupancy in the Nile Valley and highlight the site of Berenice on Foul Bay along the Egyptian coast of the Red Sea as a port or potential point of crossing.

“Two things make Foul Bay important: First, it’s an alternative route when sea level is low,” Dobson said. “The Isthmus of Suez is over 500 kilometers across — such a long, dry crossing. We expected people would prefer going up through Foul Bay to the First Cataract of the Nile, which would only be a 300-kilometer route. Even in favorable times, people are concerned with long north-south voyages on the Red Sea, which is narrow and has tremendous coral reefs, especially on the western side. Foul Bay would be an important alternative for anyone going from the Red Sea to the Mediterranean or vice versa.”

The KU researcher asserts that with the new information about Berenice, people should reexamine migration into the Nile Valley before or during the glacial maximum. Coral reefs near Foul Bay might hold more clues, according to Dobson.

“It is well established that coral reefs, including patch coral reefs, are dependent on a solid base,” he said. “Our circumstantial evidence is intriguing, but it demands confirmation through rigorous searches for evidence of human construction.”

Because the GIA data developed by the research team is open access, it can serve future research in disciplines like geography, archaeology, migration studies, climate-change science and species conservation.

“This is a community resource,” Dobson said. “We wanted to put these reconstructions in investigators’ hands so they can explore their own regions of interest — where humans lived, what the land looked like, and how it changed.”

DOI

10.5802/crgeos.273

SPUN launches Underground Atlas: First global map of fungal biodiversity reveals 90% conservation gap

SPUN (Society for the Protection of Underground Networks)

Global ectomycorrhizal biodiversity hotspots — image:
High-resolution map of from SPUN’s Underground Atlas showing predicted ectomycorrhizal biodiversity patterns across underground ecosystems. Bright colors indicate higher richness and endemism
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Credit: SPUN

The Society for the Protection of Underground Networks (SPUN) has launched the Underground Atlas, the first digital map predicting Earth's underground mycorrhizal fungal biodiversity. The work, published in Nature on July 23 analyzed 2.8 billion DNA sequences from 130 countries revealing that over 90% of mycorrhizal biodiversity hotspots lie outside protected areas.

Mycorrhizal fungi form critical underground networks that provide plants with essential nutrients while drawing approximately 13 billion tons of CO₂ per year into soils. Despite their importance for climate regulation and ecosystem health, these "ecosystem engineers" have been largely overlooked in conservation planning.

Developed by an international, multi-disciplinary team, with our fungal data partners GlobalFungi and the Global Soil Mycobiome consortium, the Underground Atlas translates emerging scientific research into an accessible platform that allows users to explore fungal biodiversity patterns at 1km2 resolution across the planet. The team used machine learning algorithms to analyze relationships between fungal diversity and environmental factors, enabling predictions for previously unmapped regions and underground ecosystems.

Platform Features:

Interactive maps showing biodiversity richness and endemism hotspots
Species estimates for each 1km2 pixel of Earth
Uncertainty indicators highlighting areas needing additional sampling
Data downloads for research and conservation planning
Applications for restoration site prioritization and protected area designations
Tools to explore opportunities for underground conservation corridors

The tool reveals richness hotspots from Ethiopia's Simien Mountains to Brazil's Cerrado savanna, while identifying rare endemic fungi in West Africa's forests and Tasmania's temperate ecosystems. This enables decision-makers to prioritize conservation efforts and leverage mycorrhizal systems for climate mitigation, crop productivity, and ecosystem resilience.

Explore the Underground Atlas: https://www.spun.earth/underground-atlas

Watch the Underground Atlas demo: https://app.air.inc/a/cxKBgWAyl

Research published in Nature: https://www.nature.com/articles/s41586-025-09277-4

The Society for the Protection of Underground Networks (SPUN) is a science-based initiative launched in 2021 to map and protect the mycorrhizal communities that regulate Earth's climate and ecosystems. SPUN’s work is supported by Jeremy and Hannelore Grantham Environmental Trust, Allen Family Philanthropies, The Schmidt Family Foundation, Quadrature Climate Foundation, Dutch Research Council (NWO), and the Bezos Earth Fund. To explore the Underground Atlas or support SPUN’s mission, visit: https://spun.earth

High-resolution map of from SPUN’s Underground Atlas showing predicted arbuscular mycorrhizal biodiversity patterns across underground ecosystems. Bright colors indicate higher richness and endemism

Credit

SPUN

Maps show how poorly protected mycorrhizal biodiversity hotspots are globally [VIDEO]