Monday, 5 December 2016

The Gemenid Meteors.

The Geminid Meteor Shower is expected to peak on Sunday 13-Monday 14 December this year (2016) with potentially up to 120 meteors per hour being visible in areas of the Northern Hemisphere with a clear sky. However this coincides with the Full Moon, which falls on the 14th, so the shower may be somewhat obscured. The meteors appear to radiate from a point in the constellation of Gemini, hence their name.

The relative positions of the radiant point of the Gemenid Meteors (i.e. the point from which the meteors radiate), the Moon and the constellations Gemini and Orion on 14 December 2016.

Oddly for a meteor shower, the Geminids do not appear to be related to a comet, but instead are associated with an object called 3200 Phaethon, which is classed as an Apollo Asteroid (an asteroid with an orbit that crosses that of the Earth). 3200 Phaethon has a highly elliptical orbit, which takes it in as close as 0.14 Au (14% of the distance between the Earth and the Sun, more than twice as close as Mercury) and out as far as 2.4 AU (2.4 times as far from the Sun as the Earth or 1.6 times as far as Mars). 3200 Phaethon does not appear to produce any sort of halo (a cloud of material produced by the evaporation of gas ice from the surface of a comet, thought to be the source of most meteor showers); rather it appears dark in colour an is classed as a B-type Carbonaceous Asteroid, thought to have a surface covering of  anhydrous silicates, hydrated clay minerals, organic polymers, magnetite, and sulphides.

Asteroid 3200 Phaethon is a 5 km body with a highly eccentric orbit similar to that of a comet, which takes it closer to the Sun than any other named Asteroid. It appears to be the parent body of the Geminid Meteors, which share essentially the same orbit as it, as well as a group of larger bodies known as the Phaethon-Geminid Complex. Such meteor showers typically form from the tail of a comet; as the comet approaches its perihelion (the closest point in its orbit to the Sun), ice at the surface sublimates away (turns directly from a solid to a gas - liquids do not form in a vacuum), releasing particles of silica trapped in the ice, which continue to follow essentially the same path as the comet, creating a meteor shower every time the Earth passes through this stream. However, 3200 Phaethon, which has a 1.43 year orbital period in which it reaches 0.14 AU from the Sun (14% of the distance between the Earth and the Sun, or less than half the distance at which Mercury orbits) is thought to regularly suffer surface temperatures in excess of 1000K, making it highly unlikely that it has ice on its surface, which calls its potential role as the parent body to the Geminid Meteors into question.

In a paper published on the arXiv online database at Cornell University Library on 17 June 2013, David Jewitt of the Department of Earth and Space Sciences and Department of Physics and Astronomy at the University of California Los AngelesJing Li of the Department of Earth and Space Sciences at the University of California Los Angeles, and Jessica Agarwal of the Max Planck Institute for Solar System Research, describe the results of a study of 3200 Phaeton using the NASA STEREO Spacecraft.

Jewitt et al. observed two successive perihelions of 3200 Phaeton, in June 2009 and May 2012. On both occasions they were able to observe a faint comet-like dust tail emerging from the body, even though it was apparently reaching temperatures that would rapidly destroy an icy comet. This tail grew rapidly, reaching a length of over 250 000 km within a day of first appearing, and appeared to represent material being lost from the parent body at a rate of about 3 kg per second.

 Composite images of 3200 Phaethon in 2009 (top row) and 2012 (bottom row) compared with the projected sun- comet line (white). The Sun is to the upper right in each panel. Insets are 49000 square and show eld stars near to Phaethon to demonstrate the point spread function of the data. Each panel has North to the top, East to the left and shows the median of 30 images taken over a 1 day period. Jewitt et al. (2013).

Jewitt et al. suggest that at it's perihelion 3200 Phaethon is being heated to such a degree that hydrated minerals at its surface could be thermally fractured and desiccated, leading to the ejection of dust particles.

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Fatality confirmed after sinkhole swallows cars in San Antonio, Texas.

One person has been confirmed dead after a sinkhole swallowed two cars in San Antonio, Texas on Sunday 4 December 2016. One of the vehicles drove into the hole, which was obscured by standing water, slightly before 5.30 pm, and the driver, described as a man of sixty was rescued by a passer by and treated in a nearby hospital. However a second car was found submerged upside down within the hole, and officials from the San Antonio Fire Department have now confirmed a body within this vehicle.

Officials from the San Antonio Fire Department assessing the sinkhole prior to attempting vehicle recovery. ABCKSAT12.

Sinkholes are generally caused by water eroding soft limestone or unconsolidated deposits from beneath, causing a hole that works its way upwards and eventually opening spectacularly at the surface. Where there are unconsolidated deposits at the surface they can infill from the sides, apparently swallowing objects at the surface, including people, without trace.

On this occasion the hole the hole is believed to have been caused by a ruptured sewer main, which leaked water that then washed away soft sediment beneath the road, undermining the road until it collapsed.

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Sunday, 4 December 2016

Oreonectes daqikongensis: A blind Stone Loach from a cave system in Guizhou Province, China.

Stone Loaches, Nemacheilinae, are freshwater Cypriniform Fish (the group that includes other Loaches as well as Carp and Minnows) found across Eurasia and Africa. They favour fast moving upland streams, with many species having colonised cave systems (an essentially similar environment), where they often lose their eyes and pigmentation.

In a paper published in the journal ZooKeys on 28 November 2016, Huaiqing Deng and Huamei Wen of the School of Life Sciences at Guizhou Normal University, Ning Xiao of the Guiyang Nursing Vocational College, and Jiang Zhou, also of the School of Life Sciences at Guizhou Normal University describe a new species of blind Stone Loach from a cave system in Guizhou Province, China.

The species is placed in the genus Oreonectes, which includes sixteen species, all from underground karst limestone caves in East Asia, and given the specific name daqikongensis, meaning 'from Daqikong', the species having been been described from specimens washed out of a limestone cave at the Daqikong Scenic Area following heavy rain in January 2011. This cave contains a pool connected to a subterranean river which forms part of the Dagou River System, but which has not previously produced any Fish or other aquatic cave animals. The Fish were blind and colourless, and ranged from 31.28 to 70.96 mm in length.

Oreonectes daqikongensis, live specimen. Deng et al. (2016).

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Asteroid 2016 WG7 passes the Earth.

Asteroid 2016 WG7 passed by the Earth at a distance of 1 002 000 km (2.61 times the average distance between the Earth and the Moon, 0.67% of the average distance between the Earth and the Sun), at about 3.55 pm GMT on Thursday 1 December 2016. There was no danger of the asteroid hitting us, though had it done so it would have presented no threat. 2016 WG7 has an estimated equivalent diameter of 12-38 m (i.e. it is estimated that a spherical object with the same volume would be 12-38 m in diameter), and an object of this size would be expected to explode in an airburst (an explosion caused by superheating from friction with the Earth's atmosphere, which is greater than that caused by simply falling, due to the orbital momentum of the asteroid) in the atmosphere between 30 and 10 km above the ground, with only fragmentary material reaching the Earth's surface. 

The calculated orbit of 2016 WG7. Minor Planet Center.

2016 WG7 was discovered on 25 November 2016 (six days before its closest approach to the Earth) by the University of Arizona's Mt. Lemmon Survey at the Steward Observatory on Mount Lemmon in the Catalina Mountains north of Tucson. The designation 2016 WG7 implies that the asteroid was the 182nd object (object G7) discovered in the second half of November 2016 (period 2016 W).
2016 WG7 has a 340 day orbital period, with an elliptical orbit tilted at an angle of 4.53° to the plain of the Solar System which takes in to 0.75 AU from the Sun (75% of the distance at which the Earth orbits the Sun; slightly outside the orbit of the planet Venus) and out to 1.16 AU (16% further away from the Sun than the Earth). This means that close encounters between the asteroid and Earth are fairly common, with the last thought to have happened in March this year and the next predicted in November 2017. 2016 WG7  also has frequent close encounters with the planet Venus, with the next predicted forJuly 2024. Although it does cross the Earth's orbit and is briefly further from the Sun on each cycle, 2016 WG7 spends most of its time closer to the Sun than we are, and is therefore classified as an Aten Group Asteroid.
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Heilongjiang mine explosion kills twenty one miners.

Twenty one miners have been confirmed dead following an explosion at a coal mine in the city of Qitaihi in Heilonghiang Province, China on Tuesday 29 November 2016. The incident happened at about 9.00 pm local time, and trapped a further 32 workers bellow ground, one of whom was still trapped on Saturday 3 December. Details of the incident have yet to be released, but photographs of the scene show extensive damage to surface facilities at the mine, implying the explosion was large and close to the surface, and four members of the mine's management team have been arrested, suggesting that local authorities believe there were serious breaches of health and safety regulations at the mine.

Rescue workers at the Qitaihi coal mine in Heilongjiang following the 29 November explosion. Reuters.

Coal is formed when buried organic material, principally wood, in heated and pressurised, forcing off hydrogen and oxygen (i.e. water) and leaving more-or-less pure carbon. Methane is formed by the decay of organic material within the coal. There is typically little pore-space within coal, but the methane can be trapped in a liquid form under pressure. Some countries have started to extract this gas as a fuel in its own right. When this pressure is released suddenly, as by mining activity, then the methane turns back to a gas, expanding rapidly causing, an explosion. This is a bit like the pressure being released on a carbonated drink; the term 'explosion' does not necessarily imply fire in this context, although as methane is flammable this is quite likely.

Visible damage to surface works at the Qitaihi coal mine in Heilongjiang following the 29 November explosion. Wang Song/Xinhua.

Coal is also comprised more or less of pure carbon, and therefore reacts freely with oxygen (particularly when in dust form), to create carbon dioxide and (more-deadly) carbon dioxide, while at the same time depleting the supply of oxygen. This means that subterranean coal mines need good ventilation systems, and that fatalities can occur if these break down.

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Saturday, 3 December 2016

Thalassina pratas: A new species of Mud Lobster from Dongsha Island.

Mud Lobsters, Thalassina pratas, are large, Shrimp-like Decapod Crustaceans found in Mangrove forests from Southern India east to the Ryukyu Islands and southeast to Australia, Fiji and Samoa. The largest species can reach 30 m in length, but most species have an adult size of 6-20 cm. Mud Lobsters often dig extensive burrow systems, and are considered to be a serious pest around Fish and Prawn farms, though this burrowing is considered to play an important role in the recycling of nutrients in Mangrove ecosystems and many other animals are associated with the burrow systems.

In a paper published in the Raffles Bulletin of Zoology on 20 May 2016, Feng-Jiau Lin of the Tainan Hydraulics Laboratory at the National Cheng Kung University, Tomoyuki Komai of the Natural History Museum and Institute in Chiba, and Tin-Yam Chan of the Institute of Marine Biology and Center of Excellence for the Oceans at the National Taiwan Ocean University describe a new species of Mud Lobster from Dongsha Island in the South China Sea.

The new species is named Thalassina pratas, 'Pratas' being an alternative name for Dongsha Island, and also meaning a Grass lawn or meadow in Latin; the species is unusual in that it was found in subtidal Seagrass beds, 1-2 m below the surface, rather than tidal Mangrove forests. The species is described from a single female specimen, 144.4 mm in length and orange-brown in colour with a whitish underside.

Thalassina pratas, live animal in habitat when collected. Lin et al. (2016).

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Sceloporus goldmani: New populations of Goldman's Bunchgrass Lizard discovered in Mexico.

Spiney Lizards, Sceloporus, are among the most numerous and commonly seen Iguanid Lizards in North and Central America. However while some species are extremely common and widespread, others have much more localized populations and lower mumbers, making them vulnerable to extinction. Goldman's Bunchgrass Lizard, Sceloporus goldmani, is known only from two areas in the arid grasslands of northwest Mexico, one straddling the border between Nuevo León and San Luis Potosi states and the second in southern Coahuila State. However no Lizards have been seen at the second site for some years and the grassland there has largely been converted to agricultural land. Due to the small area inhabited by the species and its decreasing range it is currently considered to be Endangered under the terms of the International Union for the Conservation of Nature’s Red List of Threatened Species.

In a paper published in the journal Revista Mexicana de Biodiversidad on 31 October 2016, Rubén Alonso Carbajal-Márquez of the Departamento de Conservación de la Biodiversidad at the Unidad Chetumal and Conservación de la Biodiversidad del Centro de México and Gustavo Ernesto Quintero-Díaz, also of Conservación de la Biodiversidad del Centro de México and of the Centro de Ciencias Básicas of the Universidad Autónoma de Aguascalientes, describe four new, previously undescribed, populations from Mexico.

Dorsal view of male (A) and female (B) specimens of Sceloporus goldmani. Carbajal-Márquez & Quintero-Díaz (2016).

Carbajal-Márquez and Quintero-Díaz were unable to locate the species at either of the previous known locations, however they did locate the Lizards at four locations where it had not previously been recorded, in San Luis Potosi, Aguascalientes, Jalisco and Zacatecas states.

Locations where Sceloporus goldmani was found; the most southerly points represent new records from San Luis Potosi, Aguascalientes, Jalisco and Zacatecas states. Points in the center and north represent the previously known locations in Coahuila, Nuevo León and San Luis Potosi states. The ploted area represents the range recorded on the International Union for the Conservation of Nature’s Red List of Threatened Species.

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