Thursday, 31 October 2024

Eclipse observed on Mars.

NASA's Perseverance Rover has observed an eclipse from the surface of Mars, caused by the moon Phobos passing in front of the Sun. Phobos is significantly smaller than our Moon, only 17 km in diameter compared to 3475 km, but orbits much closer to Mars than the Moon does to Earth, an average of 9376 km compared to 384 400 km, which combined with the smaller apparent size of the Sun seen from Mars, which is roughly 1½ times as far from the Sun as the Earth is, means that eclipses are still an observable phenomenon. 

Solar eclipse on Mars, caused by the moon Phobos passing in front of the Sun, recorded by the Perseverance Rover. Images are at 10 second intervals, with the whole event lasting much less time than an eclipse on Earth, due to the closer orbit of Phobos, and the correspondingly higher speed of the Martian moon, which takes only 7.6 hours to orbit the planet. NASA.

The eclipse, which occurred on 30 September 2024, was the second such eclipse observed by Perseverance this year, with the Curiosity and Opportunity rovers also having Martian eclipses. These eclipses are common because, unlike that of our Moon, the orbit of Phobos has very little tilt, effectively remaining above the planet's equator at all times.

An eclipse caused by the passage of Phobos in front of the Sun recorded by the Perseverance Rover on 8 February 2024. NASA.

Mars's second moon, Deimos, does not cause such obvious eclipses, as it is only 6.2 km in diameter, and orbits at an altitude of 23 460 km, making it almost invisible from the planet's surface.

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Wednesday, 30 October 2024

Murina yushuensis: A new species of Tube-nosed Bat from a high altitude cave on the Tibetan Plateau.

Tube-nosed Bats, Murina spp., are a large group of Vespertilionid Bats found from northeastern Russia to Papua New Guinea. There are currently 40 described species in the genus about half of which have been described in the past decade, largely from genetic studies which have uncovered many cryptic species, predominantly in South and Southeast China. These Bats are insectivorous, and generally found in lowland forests, with the maximum known diversity in South China and Southeast Asia, although this may be due to a lack of sampling in more northerly parts of China.

In a paper published in the Journal of Mammalogy on 23 October 2024, Xiaoyun Wang of the Key Laboratory of Conservation and Application in Biodiversity of South China at Guangzhou University, Xuesong Han of the Shan Shui Conservation Center and the Center for Nature and Society at Peking University, Gábor Csorba of the Department of Zoology at the Hungarian Natural History Museum, Yi Wu, also of the Key Laboratory of Conservation and Application in Biodiversity of South China at Guangzhou University, Huaiqing Chen also of the Center for Nature and Society at Peking University, Xiang Zhao and  Zhengyi Dong, also of the Shan Shui Conservation Center, Wenhua Yu,again of the Key Laboratory of Conservation and Application in Biodiversity of South China at Guangzhou University, and Zhi Lu, again of the Center for Nature and Society at Peking University, describe a new species of Murina from a high altitude cave on the Tibetan Plateau in Qinghai Province in Northeast China.

On 15 March 2018, a Bat roosting in the entrance to a cave on the bank of the Batang River about 8 km from the city of Yushu and 3770 m above sealevel was disturbed, responding by making a long, high-pitched noise. At the time the significance of this was not realised, but when the significance was realised, several repeat visits were made, with the Bat being found again on 25 December 2018.

The new species is described from this single male specimen, and is named Murina yushuensis, where 'yushuensis' means 'from Yushu'. The single specimen is 30.44 mm long (small for a member of the genus). with dark skin and small round ears, lacking the notch seen in some members of the genus. The fur of the dorsal surface is about 10 mm in length, with the basal 7 mm being black in colour, and the 3 mm at the tip being a golden brown. The fur of the ventral surface is slightly shorter, which the basal black portion being about 6 mm, and the 3 mm of the tip being pale. 

Holotype specimen of Murina yushuensis, GZHU 20077. Wang et al. (2024).

The Batang River is a tributary of the Yangtze running across the Tibetan Plateau, at altitudes of between 3860 m and 3530 m above sealevel. The area where Murina yushuensis was discovered has a mean annual temperature of only 2.9°C, and an annual average precipitation of 487 mm. The vegetation is largely meadows of Feathergrass with scattered shrubs and patches of Juniper woodland. This is a distinctly unusual environment for a member of a genus usually found in lowland tropical and subtropical forests. Murina yushuensis was discovered at the highest altitude any member of the genus has ever been recorded at, with the previous record being a specimen of the Little Tube-nosed But, Murina aurata, found at 2500 m. However, Wang et al. consider that while Murina yushuensis may seem exceptional, it is also potentially an indicator that other species of the genus may be living at high and intermediate altitudes, and not yet discovered due to a lack of sampling.

Surrounding environment of the cave where Murina yushuensis was discovered in March 2018. Wang et al. (2024).

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Sunday, 27 October 2024

What abandoned grinding stones can tell us about the medieval town of Handoga in Djibouti.

The abandoned town of Handoga in southern Djibouti covers an area of about 600 m north-to-south and 300 m east-to-west, and is located about 13 km from the border with Ethiopia. Archaeological investigations have suggested that the site was initially used in the twelfth century as an occasional campsite by nomadic herders passing through the region, becoming a permanent settlement in the thirteenth century, from when it evolved into a town, with buildings with stone-built lower portions and wattle-and-daub upper portions coming to replace earlier temporary structures. The town was abruptly abandoned in the sixteenth century, with no sign of any violent upheaval preceding this event. As well as dwellings, the town had a range of open spaces which may have been squares, junctions of streets, or other public spaces, as well as two mosques, both at the northern end of the settlement, and a cemetery, at its southern end.

In a paper published in the journal World Archaeology on 30 September 2024, Jorge de Torres Rodríguez of the Instituto de Ciencias del Patrimonio in Santiago de Compostela, Spain;, and Valeria Franco Salvi of the Instituto de Humanidades at the Universidad Nacional de Córdoba in Argentina present the results of an analysis of grinding stones recovered from C-6000, the first structure at the northern end of Handoga to be the subject of archaeological investigations.

Location of Handoga in the Horn of Africa. De Torres Rodríguez & Salvi (2024).

The C-6000 site comprises two circular stone structures, linked by a series of walls enclosing a central open area, interpreted as having been used for food preparation and other domestic activities. The remains unearthed within this area resemble those found within courtyards excavated towards the southern end of the settlement, with two notable exceptions. Firstly, the site has yielded a quantity of well-preserved charred fruits, seeds, and wood fragments, which are currently under study, and which it is hoped will yield radiocarbon dates which will enable a chronology of the site to be built up. Secondly, excavations at the site have produced 88 fragments of grinding stone stones of different types, the largest collection of such stones not just from Handoga, but from any medieval Islamic site excavated to date, providing a rare opportunity to analyse how these objects were made and used, and any changes in their use over time.

Compound C-600 with main rooms and areas. De Torres Rodríguez & Salvi (2024).

Grinding stones were found across the site, with roughly two thirds coming from collapse layers, while about one third were found on original occupation layers. Grinding stones were found in all areas, with 47% coming from Room A, identified as the principal occupation site, 11% from Room B, identified as a storage area, and 34% from the central area. The stones can be split into two types, passive grinding stones, upon which grains would have been ground, and handstones, which would have been used to grind grains upon the grinding stones. Of the two, passive grinding stones are more common (55, compared to 33 handstones).

Handstones (upper rows) and one of the passive grinding stones (bottom) found at C-6000. De Torres Rodríguez & Salvi (2024).

Many of the passive grinding stones were highly fragmented, with 17 deemed intact enough for study. All were made from a vesicular-textured basalt, which probably came from an outcrop about 500 m from the settlement. Such a rock would have been ideal for grinding dehydrated or floury products, as it would be relatively easy to clean, and would have maintained a rough surface through use. These grinding stones appear to have been made from nodules or similar, with most made from approximately spherical or approximately cylindrical pieces of rock, with minimal shaping to achieve the desired shape. Despite the fragmentary nature of the grinding stones. about 60% still weighed between 2 kg and 5 kg, with the remaining 40% weighing under 2 kg. Twelve of the grinding stones are thought to have been portable, while the remaining five would have been large objects, presumably immobile during their working lives. The average grinding surface of these stones is 373 cm², with the largest having a surface area of 495 cm².

(1) Outcrop where the material for grinding stones was likely collected. (2) Compound C-6000. De Torres Rodríguez & Salvi (2024).

A much lower number of handstones (32) were recovered, these being largely fragmented, and scattered about with no sign of having been stored. They were apparently left where they lay between uses, and then abandoned once they became to worn for use.  Few showed any signs of maintenance during use, and none of any attempts to prolong their lives. Many of the handstones had been worn-down to the point of uselessness. The often had two wear-facets, showing their users had attempted to gain the maximum utility from them. All the handstones weighed less than 1 kg, with about 40% weighing less than 500 g. The handstones were made from rock which could be collected from within less than a kilometre, with the majority being made from basalt, although granite examples were also present, and one was made from quartzite.

While there appears to have been some variation in the way in which grinding stones were made and used at Handoga, the defining feature that appears to link all of them is an apparent lack of care. Only a minimal amount of work appears to have been put into modifying stones from their natural state to make them into tools, and little investment in their upkeep has been made during their lifetimes. There was no apparent standardized way to make these tools, which suggests that they were not manufactured by specialist craftspeople.

One consistent pattern which can be seen throughout the sample is the division into handstones and passive grinding stones, with grinding stones being larger and made from a single material, vesicular basalt, while handstones are smaller and made from denser and smoother material, with more variation in the selection of that material. A similar pattern has been seen at sites in Cameroon and Mali. There was also a difference in the distribution of these two elements, although the significance of this is unclear.

Large passive grinding stone found during a survey in Handoga. De Torres Rodríguez & Salvi (2024).

De Torres Rodríguez and Salvi suggest that this apparent lack of importance placed upon the manufacture and conservation of grinding stones suggests that these objects were not particularly valued by the people of Handoga. They further suggest that this lack of importance has implications for how we understand the settlement itself. Handoga was initially interpreted as an agricultural settlement, likely deriving water from the nearby Wadi Chekheiti, and trading Sorghum and Millet with the surrounding nomadic groups. However, no archaeobotanical studies have been carried out at Handoga, so there has been no evidence to date to either support or counter this hypothesis. 

In agricultural societies, grinding stones are typically high value items, of considerable economic significance, whereas at Handoga they appear to have been poorly valued, and used within domestic settings. This leads de Torres Rodríguez and Salvi to conclude that while agriculture was probably caried out at Handoga, it was likely a low-status activity, not having the same prestige as traditional nomadic activities such as herding and trade.

This in turn has implications for the history of Handoga. The settlement appears to have been initially used on a temporary camp by nomads in the twelfth century, gradually becoming more permanent, and transitioning to a town with stone buildings sometime in the fourteenth century. De Torres Rodríguez and Salvi reason that the low importance given to the processing of agricultural products suggests that despite becoming a permanent settlement, Handoga never really lost it's nomadic emphasis, something which is also reflected in the design of its buildings.

This in turn helps to explain why Handoga was abandoned so easily in the mid-sixteenth century. During the sixteenth century the Sultanate of Barr Saʿd al-Dīn, which ruled over much of the Red Sea coast of the Horn of Africa, collapsed following a series of disastrous wars with Abyssinia, severely disrupting trade routes, and causing many settlements to be abandoned. For peoples who had become truly sedentary in nature, this would have been a difficult process, either abandoning practices such as agriculture and having to relearn nomadic ways or relocate to other settlements, possibly some distance away. However, if the inhabitants of Handoga had retained an essentially nomadic nature with their main income deriving from pastoralism, the abandonment of the town may have been a less painful process than for more settled communities.

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Tuesday, 22 October 2024

Yunfuconcha bimenta: A Heteroconch Bivalve from the Middle Ordovician of Guangdong Province, China.

Molecular clock studies have suggested that major modern Bivalve lineages are likely to have diverged early in the Phanerozoic, although the poor fossil record of early Bivalves makes this difficult to assess. Notably, the Archiheterodonta and Palaeotaxodonta have been predicted to have diverged from one-another during the Cambrian, although there is little evidence of this; perhaps unsurprisingly, given the rarity of Cambrian and Early Ordovician Bivalves.

In a paper published in the Journal of Molluscan Studies on 15 October 2024, Ren-jie Zhang of the Hubei Key Laboratory of Paleontology and Geological Environment Evolution and the Wuhan Center of the China Geological SurveyPaul Johnston of the Department of Earth and Environmental Sciences at Mount Royal University, Zhi-jun Niu, also of the Hubei Key Laboratory of Paleontology and Geological Environment Evolution and the Wuhan Center of the China Geological Survey, Chu-an Li of the Guangdong Marine Geologic Survey, Zhi-hong Wang, again of the Hubei Key Laboratory of Paleontology and Geological Environment Evolution and the Wuhan Center of the China Geological Survey, Kun Hu of the Guangdong Geologic Survey Institute, Fang Song, Yao-yan He, and Jin-lan He, again of the Hubei Key Laboratory of Paleontology and Geological Environment Evolution and the Wuhan Center of the China Geological Survey, Xiao-ming Lin, again of the Guangdong Geologic Survey Institute, and Wen-qiang Yang, once again of the Hubei Key Laboratory of Paleontology and Geological Environment Evolution and the Wuhan Center of the China Geological Survey, describe a new species of Heteroconch Bivalve from the Middle Ordovician Dongchong Formation of Guangdong Province, China.

The new species is named Yunfuconcha bimenta, where 'Yunfuconcha' means 'Yunfu-shell', in reference to the city of Yunfu in Guangdong Province, and 'bimenta' means 'double-state', in reference to the combination of Archiheterodont-like and Palaeotaxodont-like features seen in the species.

Yunfuconcha bimenta, Ordovician, Dongchong Formation, near Gankeng Village, Yunan County, Guangdong Province, China. (A)–(E) Holotype, Ng525, right valve. (A) Incomplete internal mould. (B)–(D) Latex cast. (B) Internal view; arrow marks possible inner edge of posterior adductor scar. (C) Dorsal oblique view showing subdued umbo. Arrows mark short opisthocline ridges, better seen in (E). (D) Ventral oblique view showing angular contact of ligament area and anterior hinge plate. Long arrow marks prominent ligament ridge. An apparent second prominent ridge to the right may be owing to breakage developed on the mould during casting. Short arrow indicates one of several short oblique ridges on anterior portion of ligament area. (E) Close-up of hinge area on internal mould of holotype. Arrows show short opisthocline ridges (grooves on mould). Vertical white lines show inferred lateral extent of ligament area. (F)–(H) Paratype, Ng526, right valve. (F) Silicone rubber cast; ventral oblique view; long arrow marks ligament ridge; short arrows mark short opisthocline ridges near boundary of the ligament area. (G), (H( Incomplete internal mould. (G) Anterodorsal portion of valve. White box is detailed in (H). (H) Detail from (G); arrows mark subtle radial ornament (this portion of mould is composite). (A), (E), (G), and (H), unwhitened. Scale bars are 5 mm. Abbreviations: la, ligament area; pa, posterior adductor scar. Zhang et al. (2024).

Yunfuconcha bimenta has a subequilateral shell with a distinctive dentition on the anterior  part of the hinge plate (in Bivalves 'dentition' refers to protrusions on the articulations of the shells, which generally fit into sockets on the opposing shell, rather than actual teeth). 

Zhang et al. note that Yunfuconcha bimenta shows some similarities to the Early Ordovician Palaeotaxodont Afghanodesma, although, curiously, they also challenge the validity of Afghanodesma on the basis that the type material for the species is a series of wax casts made in the field, rather that the actual fossil material, in breach of the rules of the International Commission on Zoological Nomenclature. This is technically correct, but seems unhelpful in this instance, and seems a strange point to raise given that they describe their own material as 'moulds were with latex or silicone rubber for study'.

Zhang et al. suggest that Yunfuconcha bimenta is either a stem-group Heteroconch (i.e. a species more closely related to the Heterochomchia than any other group, but not decended from the last common ancestor of all extant members of the group) or an early member of the Archiheterodonta, thought to be one of the earliest branching groups within the Heterochomchia.

Hypothesized phylogenetic relationships of Yunfuconcha as a stem Archiheterodont or a stem Heteroconch. Solid vertical lines denote known paleontological ranges of lineages. Dashed vertical lines denote inferred ranges. Horizontal grey lines mark late, middle and early intervals of respective period. The relative width of the Ordovician Period is expanded. Images from left to right: Yuexiconcha duplicataPraeleda subtilisYunfuconcha bimentaCrassatellopsis yongeiCarminodonta crossiParacyclas alleniCypricardella inflata, and Sanguinolites? concentrirugosa. Zhang et al. (2024).

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Sunday, 20 October 2024

The Orionid Meteor Shower.

The Orionid Meteors are a prolific meteor shower appearing between 2 October and 7 November each year and peaking on the nights of 20-22 October, when the shower can produce 50-70 meteors per hour, originating in the constellation of Orion (above and to the right of Orion's right shoulder). This makes them both one of the more prolific meteor showers, and one of the easiest for an amateur enthusiast to locate the radiant of (apparent point of origin). The peak of this year's display falls slightly before the Third Quarter Moon (the Half Moon after a Full Moon), which is not ideal for viewing, but better than closer to the Full Moon. The best viewing this year should be just before dawn on Monday 21 October, from anywhere on Earth, although viewing will be better from the Northern Hemisphere.

The radiant point of the Orionid Meteor Shower. EarthSky.

Meteor streams are thought to come from dust shed by comets as they come close to the Sun and their icy surfaces begin to evaporate away. Although the dust is separated from the comet, it continues to orbit the Sun on roughly the same orbital path, creating a visible meteor shower when the Earth crosses that path, and flecks of dust burn in the upper atmosphere, due to friction with the atmosphere.

The Earth passing through a stream of comet dust, resulting in a meteor shower. Not to scale. Astro Bob.

The Orionid Meteor Shower is caused by the Earth passing through the trail of Halley's Comet (technically Comet P1/Halley), and encountering dust from the tail of this comet. The dust particles strike the atmosphere at speeds of over 200 000 km per hour, burning up in the upper atmosphere and producing a light show in the process. The Earth does not need to pass close to Halley's Comet for the meteor shower to occur, it simply passes through a trail of dust from the comet's tail that is following the same orbital path. Halley's Comet only visits the Inner Solar System once every 75 years, last doing so in 1986. 

How the passage of the Earth through a meteor shower creates a radiant point from which they can be observed. In The Sky.

Halley's Comet has been observed repeatedly and recognised as the same recurring object since at least 240 BC. However, it takes its modern name from the eighteenth century English Astronomer Edmund Halley, who determined the comet's periodicity in 1705.

Halley's Comet completes one orbit every 75.32 years (27 509 days) on an eccentric, orbit tilted at 162° to the plane of the Solar System (i.e. a retrograde orbit, at an angle of18° to the plane of the Solar System, but travelling in the opposite direction to the majority of the objects in the Solar System), that takes it from 0.56 AU from the Sun (59% of the average distance at which the Earth orbits the Sun, and inside the orbit of the planet Venus) to 35.1 AU from the Sun (35.1 times as far from the Sun as the Earth, and outside the orbit of the planet Neptune). As a comet with a period of more than 20 years but less than 200 years, Halley's Comet is considered to be a Periodic Comet, and a Halley-type Comet.

The current position and orbit of Halley's Comet. JPL Small Body Database.

Halley's Comet was visited by the European Space Agency's Giotto Probe and the Soviet Vega 1 and Vega 2 probes in March 1986, which were able to determine that the nucleus of the comet was only 15 km across, although it was surrounded by a coma about 100 000 km in diameter, made up of fragments of dust and ice released from the surface as it was heated by the Sun, causing the ices on its surface to sublimate (turn directly from solids to gasses), and that this material comprised 80% water, 10% carbon monoxide, 2.5% methane and ammonia, as well as trace amounts of more complex hydrocarbons, iron and sodium.

Image of Halley's Comet taken by the Giotto Space Probe in 1986 - the first ever photograph of the nucleus of a comet. Halley Multicolour Camera Team/Giotto Project/European Space Agency.

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