Saturday, 20 October 2018

Looking for the origin of Asteroid (514107) 2015 BZ509.

The Centaurs are a population of asteroids with orbits that cross those of the Solar System’s giant planets (Jupiter, Saturn, Uranus, and Neptune). The majority of these are on somewhat chaotic pathways; they are presumed to have originated in the outer reaches of the Solar System and been knocked inwards by interaction with some other body and are now buffeted from orbit to orbit by close encounters with the giant planets. Such asteroids typically survive as Centaurs for less than a million years, and almost never survive for more than about 10 million years. Other Centaurs manage to achieve resonant orbits with one or more giant planets, finding a pathway on which they are held steady by periodic encounters with the resonant planet or planets. Such asteroids may remain in stable orbits for hundreds of millions of years, and may be in prograde or retrograde orbits (i.e. may orbit in the same direction as the planets, or in the opposite), with those in steeply inclined retrograde orbits often the most stable.

Asteroid (514107) 2015 BZ509 was discovered in January 2015 by the University of Hawaii's PANSTARRS telescope (technocally it was first captured in an image in November 2014, but not actually noticed until January 2015); the name 2015 implies that it was the 12 750th asteroid (asteroid Z509) discovered in the second half of January 2015 (period 2015 B), while the designation (514107) implies that it was the 514 107th asteroid ever discovered. (514107) 2015 BZ509 is a Jupiter-orbit crossing Centaur Asteroid with an orbit similar to those of the Jupiter Trojans (asteroids on the same orbital path as Jupiter, but within its Trojan Points, 60° ahead and behind the planet), but on a retrograde orbit inclined at 163° to the plane of the Solar System (or 17° from the plane of the Solar System, but travelling in the wrong direction).It is the first asteroid ever discovered in a 1:1 resonance with a planet, completing one orbit for every one orbit of Jupiter, and has a diameter of about 3 km.

The calculated orbit of (514107) 2015 BZ509 Minor Planet Center.

In a paper published in the journal Monthly Notices of the Royal Astronomical Society on 26 May, Fathi Namouni of the Observatoire de la Côte d’Azur at the Université Côte d’Azur and Maria Helena Morais of the Instituto de Geociências e Ciências Exatas at the Universidade Estadual Paulista, present the results of a study of (514107) 2015 BZ509, in which they attempted to use a computer model to backtrack the orbit of the asteroid, and determine its origin.

To Namouni and Morais’s surprise, the current orbit of (514107) 2015 BZ509 appears to be stable for a period of around 4.5 billion years – roughly the age of the Solar System. Based upon this they conclude that the asteroid originated outside the Solar System, and was captured during the system’s formation. This is not completely outrageous; the Solar System is thought likely to contain a number of bodies originating outside the system that have been captured, though these are by nature difficult to detect.

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Warnings issued to aviation after eruptions on Mount Sabancaya, Peru.

The Buenos Aires Volcanic Ash Advisory Center issued a warning to aviation after an eruption was seen by a webcam on the Sabancaya volcano in southern Peru by web cameras around the volcano. The webcam images showed an ash plume of uncertain size plus ongoing gaseous emissions. Volcanic ash is extremely hazardous to aircraft in a number of ways. At its most obvious it is opaque, both visually and to radar. Then it is abrasive, ash particles physically scour aircraft, damaging components and frosting windows. However the ash is most dangerous when it is sucked into jet engines, here the high temperatures can melt the tiny silica particles, forming volcanic glass which then clogs engine. When this happens the only hope the aircraft has is to dive sharply, in the hope that cold air passing through the engine during the descent will cause the glass to shatter, allowing the engine to be restarted.

The approximate location of Mount Sabancaya. Google Maps.

Sabancaya is a 5967 m stratovolcano (cone shaped volcano) located on a saddle between the older, and larger Hualca Hualca and Ampato, neither of which has been active in historic times. The three volcanoes are located in the Andes of southern Peru. Eruptions were first recorded on Sabacnya by Europeans in 1595, and the volcano is likely to have been intermittently active prior to this. The volcano erupted a number of times in the eighteenth century, then remained quiet until 1986, since when it has undergone six bouts of explosive eruption.

The volcanoes of the Peruvian Andes, and of South America in general, are fuelled by the subduction of the Nazca Plate beneath the South American Plate. The Nazca Plate underlies a large chunk of the eastern Pacific Ocean, and is being subducted along Peru-Chile Trench to the west of South America. As it sinks into the Earth, the Nazca Plate passes under South America, where it is heated by friction with the overlying South American Plate and by the heat of the planet's interior. This causes the Nazca Plate to partially melt, and some of this melted material then rises through the South American Plate as magma, fuelling the volcanoes of the Andes. The motion of one plate beneath another is not a smooth process, and the Nazca and South American Plates frequently stick together, then break apart as the pressure builds up, triggering frequent Earthquakes along the western coast of South America, and sometimes further inland.

The subduction of the Nazca Plate beneath the South American Plate, and how it causes Earthquakes and volcanoes. Pacific Earthquake Engineering Research Center.

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Friday, 19 October 2018

Arcotheres placunicola: A new species of Pea Crab from Singapore.

Pea Crabs, Pinnotheridae, are very small Crabs that often live symbiotically within the shells of Bivalves or other organisms. Members of the genus Arcotheres are often associated with Indo-Pacific Window-pane Shells of the genus Placuna, with at least three species found within the wide ranging Placuna placenta. The Singapore Window-pane Shell, Placuna ephippium, was presumed to host the same species, but such interchangeability between hosts is now considered to be rare.

In a paper published in the journal Raffles Bulletin of Zoology on 23 August 2018, Peter Ng of the Lee Kong Chian Natural History Museum at the National University of Singapore, describes a new species of Arcotheres from the Singapore Window-pane Shell, based upon examination of specimens collected around Singapore.

The new species is named Arcotheres placunicola, which appears to mean ‘Placuna-dweller’ though the derivation of this name is not given. Females of this species are subcircular and distinctly wider than long, with adults typically being a little over 10 mm in width, males are smaller, reaching only a little over 5 mm in width, and have more circular carapaces. The females are variable on colour, ranging from yellow to orange, or off-white with brown patterns, the males are greenish brown.

Two specimens of Arcotheres placunicola in situ on Placuna ephippium. Ng (2018).

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Thursday, 18 October 2018

Dynamoterror dynastes: A new species of Tyrannosaurid Dinosaur from the Late Cretaceous Menefee Formation of New Mexico.

Tyrannosaurids are a significant part of the Latest Cretaceous Dinosaur faunas of Asia and North America, and include the giant predators Tyrannosaurus rex and Tarbosaurus bataar, as well as a variety of smaller forms. However, almost all known Tyrannosaurids are known from the last ten million years of the Cretaceous, with only one older species known, the 80 million-year-old Lythronax argestes, from the Wahweap Formation of Utah. This has the effect that, while the relationship of the Tyrannosaurids to other Theropod groups is well understood, exactly how they rose to dominance is somewhat of a mystery.

In a paper published in the journal PeerJ on 9 October 2018, Andrew McDonald of the Western Science Center, Douglas Wolfe of the Zuni Dinosaur Institute for Geosciences, and Alton Dooley, also of the Western Science Center describe a new species of Tyrannosaurid from the upper part of the 84.0–78.5 million-year-old Menefee Formation of San Juan County, New Mexico.

The new species is named Dynamoterror dynastes, where ‘Dynamoterror’ means ‘powerful terror’ and ‘dynastes’ means ‘ruler’. The species is described from fragmentary remains comprising the left and right frontals, four fragmentary vertebral centra, fragments of the dorsal ribs, the right metacarpal II, the supraacetabular crest of the right ilium, several unidentifiable fragments of long bones, phalanx 2 of left pedal digit IV, and phalanx 4 of left pedal digit IV. These fragments were found as float (i.e. they were loose on the surface) and excavations at the site could find no further material. All of the fragments were found together, and are consistent in size, leading McDonald et al. to conclude that they come from a single animal, interpreted to be a medium sized Tyrannosaurid Dinosaur, about nine metres in length.

Frontals of Dynamoterror dynastes in rostral view. Photographs and 3-D models of right (A), (B) and left (C), (D). Abbreviations: bnp, basal of nasal process; cnc, caudal extent of nasal cavity; plp, prefrontolacrimal process; pnp, prefrontonasal process; rpos, rostral part of postorbital suture; vls, ventrolateral part of lacrimal suture. Scale bars equal five cm. McDonald et al. (2018). 

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The Orionid Meteors.

The Orionid Meteors are a prolific meteor shower appearing in late October 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). However, this year's display falls shortly before the Full Moon on Wednesday 24 October 2018, so that the glare of the Moon may reduce the visibility of the meteors.

The Radiant Point of the Orionid Meteors. EarthSky.

The 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. 

The calculated orbit and position of Comet P1/Halley on 18 October 2018. The Sky Live 3D Solar System Simulator.

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Tuesday, 16 October 2018

Lasius tapinomoides: A new species of Ant from Crete.

Ants of the genus Lasius are found across Eurasia, with most species being wide-ranging and dominant members of the local Ant community. The genus contains very few endemic species (species with limited distributions), with these mostly found on islands or occasionally mountains. There are currently seven members of the genus reported on Crete, one of the largest islands in the Mediterranean, with a diverse, mountainous, landscape, though the Ant fauna of the island is not well studied.

In a paper published in the journal ZooKeys on 10 October 2018, Sebastian Salata and Lech Borowiec of the Department of Biodiversity and Evolutionary Taxonomy at the University of Wrocław, describe a new species of Lasius from Crete.

The new species is named Lasius tapinomoides, for its similarity to Ants of the genus Tapinoma. These Ants are dark brown in colour, with orange antennae and legs. The head is oval, and slightly longer than wide, the eyes also oval and 25% as long as the head. The species is covered in a dense coat of hairs and is believed to be endemic to Crete.

Lasius tapinomoides, worker in lateral view. Salata and Borowiec (2018). 

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A Middle Pleistocene Acheulean Site from the Central Ethiopian Highlands.

High altitude environments provide a unique set of survival challenges for Modern Humans, and presumably also the earlier Hominins from which we are descended, including reduced oxygen levels, higher exposure to ultra-violet radiation, higher rates of water loss and higher nutrition requirements to support a stressed metabolism. For this reason, the conquest of these environments has always been assumed to be a relatively modern phenomenon, which occurred when Holocene Humans with rising populations began to fill up lowland environments, leading them to explore the less optimal highlands of Europe and Asia.

In a paper published in the Journal of Paleolithic Archaeology on 24 September 2018, Ralf Vogelsang of the Institute of Prehistoric Archaeology at the University of Cologne, Olaf Bubenzer of the Institute of Geography at Heidelberg University, Martin Kehl and Svenja Meyer of the Institute of Geography at the University of Cologne, Jürgen Richter, also of the Institute of Prehistoric Archaeology at the University of Cologne, and Bahru Zinaye of the School of Earth Sciences at Addis Ababa University, describe an Middle Pleistocene Acheulean Site from the Dendi Caldera in the Western Central Highland Plateaus of Ethiopia.

The Dendi Caldera is an extinct volcano on the Yerer-TulluWellel Volcano Tectonic Lineament, which stretches west from the Main Ethiopian Rift as far as the border with Sudan. The volcano is thought to have begun erupting in the Middle Miocene, with activity ceasing less than a million years ago. The rocks of the caldera are largely rhyolites and trachytes, overlain by lava flows with a significant proportion of obsidian (likely to have been valued by stone age tool makers), which are in turn overlain by volcanic ash deposits. The caldera is surrounded by a rim which rises 440 m above the central depression, which contains a double lake fed by springs and seeps within the caldera. The River Huluka, a tributary of the Blue Nile, originates in the caldera.

Mount Dendi. (a) View of Mount Dendi (looking west). (b) View of the two crater lakes within the caldera. (c) Map showing the location of archaeological sites. Vogelsang et al. (2018).

Archaeological material was first discovered in the caldera during a survey by the Collaborative Research Center of the University of Cologne, and two successive expeditions in 2013 and 2015 have revealed a total of 75 archaeological sites. The majority of these are Later Stone Age and Middle Stone Age sites, yielding small amounts of material, but ten of the sites yield Early Stone Age material and are dated to the Middle Pleistocene. Vogelsang et al. concentrate on one of these sites, DEN-12-A02.

DEN-12-A02 is located in the eastern Dendi Caldera, at an altitude of 3000 metres above sea level. The site has yielded both Early Stone Age and Middle Stone Age material, with a total of 65 artifacts (33 flakes, 8 cores, 5 blades, 8 large bifacial tools, 7 small facially retouched points) from two terraces exposed during road construction work. The Early Stone Age material comprises Acheulean material (a technology that appeared about 1.8 million years ago and which is associated with Homo erectus, and sometimes other members of the genus Homo) originating from a layer of dark, reddish clayey soil. This material includes two elongated hand axes, three ovate hand axes, one cordate hand axe, two leaf-shaped scrapers, one ‘Keilmesser’ backed bifacial knife, and a cleaver. The production method of these tools is consistent, which probably implies that they originate from a single temporary occupation of the site. Based upon the complexity of this technology the occupation is considered to date from the Middle-to-Late Acheulean, between 500 000 and 200 000 years ago, a period that brackets the emergence of the first Modern Humans in East Africa.

DEN12-A02 bifacial tools. (1) Flat cordate hand axe, (2) bifacial scraper, (3) ovate hand axe, (4) cleaver-like biface, (5) elongated hand axe, and (6) ‘Keilmesser’ bifacial knife. Vogelsang et al. (2018). 

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