Sunday 31 December 2017

Asteroid 2017 YS1 passes the Earth.

Asteroid 2017 YS1 passed by the Earth at a distance of about 743 100 km (1.93 times the average distance between the Earth and the Moon, or 0.50% of the distance between the Earth and the Sun), at about 4.45 pm GMT on Sunday 24 December 2017. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2017 YS1 has an estimated equivalent diameter of 3-9 m (i.e. it is estimated that a spherical object with the same volume would be 3-9 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 more than 30 km above the ground, with only fragmentary material reaching the Earth's surface.

The calculated orbit of 2017 YS1. Minor Planet Center.

2017 YS1 was discovered on 22 December 2017 (two 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 2017 YS1 implies that the asteroid was the 43rd object (object S1) discovered in the second half of December 2017 (period 2017 Y).  

2017 YS1 has a 354 day orbital period, with an elliptical orbit tilted at an angle of 5.67° to the plain of the Solar System which takes in to 0.93 AU from the Sun (93% of the distance at which the Earth orbits the Sun) and out to 1.02 AU (2% 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 June this year and the next predicted in December 2018. Although it does cross the Earth's orbit and is briefly further from the Sun on each cycle, 2017 YS1 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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Cholera outbreak kills forty one in Lusaka, Zambia.

Forty one people have been confirmed dead and over 1500 people have been infected in an epidemic in the Zambian capital Lusaka this year. The first cases occurred in September 2017, and are though to have been related to unsafe water from shallow wells in poorer parts of the city, with tests showing that 42% of such water sources were infected with the Bacterium. The spread of the disease appeared to abate in October, then returned sharply in November, with about 60 new cases being reported every day by the end of December. This renewed outbreak has been linked to poor hygiene in the cities food markets and street food stalls, with samples of fresh fruits and vegetables, as well as cooked meats and other ready-to-eat foods found to be infected.

Cholera victims being treated in an emergency field hospital in Lusaka. Lusaka Times.

Cholera is caused by the Bacterium Vibrio cholerae, a Gram-negative, comma-shaped Gammaproteobacteria, related to other pathogenic Bacteria such as Yersinia pestis (Bubonic Plague), and Esherchia coli (food poisoning). The Bacteria produce proteins which can cause watery diarrhoea, which helps spread the disease, and can prove fatal in severe cases, as patients are killed by extreme dehydration.

 SEM image of Vibrio cholerae Bacteria. Kim et al. (2000).

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Magnitude 1.9 Earthquake off the coast of Devon.

The British Geological Survey recorded a Magnitude 1.9 Earthquakes off the south coast of Devon (about 40 km to the southeast of Dartmouth), slightly before 9.00 am GMT on Sunday 31 December 2017. Quakes of this size do not present any threat to human life or property, and there are no reports of this one having been felt by anybody.

The approximate location of the 31 December 2017 English Channel Earthquake. Google Maps.

Earthquakes become more common as you travel north and west in Great Britain, with the west coast of Scotland being the most quake-prone part of the island and the northwest of Wales being more prone  to quakes than the rest of Wales or most of England. However, while quakes in southern England are less frequent, they are often larger than events in the north, as tectonic pressures tend to build up for longer periods of time between events, so that when they occur more pressure is released.

The precise cause of Earthquakes in the UK can be hard to determine; the country is not close to any obvious single cause of such activity such as a plate margin, but is subject to tectonic pressures from several different sources, with most quakes probably being the result of the interplay between these forces.

Britain is being pushed to the east by the expansion of the Atlantic Ocean and to the north by the impact of Africa into Europe from the south. It is also affected by lesser areas of tectonic spreading beneath the North Sea, Rhine Valley and Bay of Biscay. Finally the country is subject to glacial rebound; until about 10 000 years ago much of the north of the country was covered by a thick layer of glacial ice (this is believed to have been thickest on the west coast of Scotland), pushing the rocks of the British lithosphere down into the underlying mantle. This ice is now gone, and the rocks are springing (slowly) back into their original position, causing the occasional Earthquake in the process.

 (Top) Simplified diagram showing principle of glacial rebound. Wikipedia. (Bottom) Map showing the rate of glacial rebound in various parts of the UK. Note that some parts of England and Wales show negative values, these areas are being pushed down slightly by uplift in Scotland, as the entire landmass is quite rigid and acts a bit like a see-saw. Climate North East.

Glacial rebound seems an unlikely cause of Earthquakes beneath the English Channel to the south of Cornwall, an area that was never glaciated, but this is not entirely the case. The northwest of Scotland is rising up faster than any other part of the UK, but the Earth's crust on land in the UK is fairly thick, and does not bend particularly freely, whereas the crust beneath the Channel is comparatively thin and more inclined to bend under stress. Thus uplift in Scotland can cause the entire landmass of Great Britain to pivot, causing movement in the rocks beneath the Channel.

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. If you felt this quake, or were in the area but did not (which is also useful information) then you can report it to the British Geological Survey here.

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Millitant group claims to have blown up oil pipeline in Khuzestan Province, Iran.

The Ahwaz Martyrs Brigade of Ansar al-Furqan, a militant Sunni Muslim group thought to have connections to the Syrian branch of Al-Qaeda (also known as Ha’yat Tahrir al-Sham, Jabhat al-Nusra, and Jahbat Fateh al-Sham) has claimed responsibility for a pipeline explosion close to the city of Ahwaz in Khuzestan Province, Iran. The incident happened overnight between Friday 29 and Saturday 30 December 2017. Authorities in Iran are yet to comment on the incident.

Image of an alleged pipeline explosion in Khuzestan Province, Iran. AMN News.

Khuzestan Province is an oil-rich region in the south of Iran, with a large Sunni population often at odds with the nation's theocratic Shia government. The Ahwaz Martyrs Brigade of Ansar al-Furqan, a group that first appeared in 2013, is one of a number of organisations in the area campaigning against the government, which accuses Saudi Arabia of funding them (a claim denied by Saudi authorities). The group has been linked to a number of previous incidents, including suicide bombings, but has not previously been known to attack the country's oil infrastructure.

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Landslide kills three in Chittagong District, Bangladesh.

Three people including a child, have died in a landslide in the Chittagong District of Chittagong Division, Bangladesh, on Saturday 30 December 2017. The three, named as Mohamed Didar, 38, Amir Ali, 37, and Mohamed Sakib, 10, were engaged in hill-cutting (removing soil from the side of a hill, usually for sale), when a section of the hillside collapsed onto them, crushing them to death, at about 2.30 pm local time. Several other individuals are reported to have been involved in the hill-cutting operation, but fled the scene without offering assistance.

The approximate location of the 30 December 2017 Chittagong landslide. Google Maps.

Hill cutting without a specific permit is illegal in Bangladesh, but has become a major industry in the Chittagong Hills, where the law is widely flouted. The unregulated nature of this industry means that few, if any, safety measures tend to be implemented, and accidents are frequent. The industry also has major environmental impacts, destroying farmland and making the area mote prone to landslips and flash floods that destroy homes and infrastructure. The majority of those involved in the actual hill cutting are poor farmers and day labourers, with limited access to other means of income, but the profits from the industry go to wealthier individuals involved in the sale of the soil, and there is speculation that the weak law-enforcement in the are is due to the involvement of senior political figures in the industry.

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Earth approaches perihelion.

On Wednesday 3 January 2018 at 5.34 am, GMT, the Earth will reach its perihelion; the closest point on its orbit to the Sun, when it will be 147 097 233 km from the Sun. This is because the Earth's orbit is not a perfect circle, but varies by 3.3% over the course of a year. The Earth will reach its furthest point from the Sun, at a distance of 152 095 566 km, at 5.46 pm GMT on 6 July 2016. This perihelion distance varies each year; in 2017 the Earth reached 147 100 988 from the Sun and in 2019 it will reach 147 099 760. 

The Earth's Aphelion and Perihelion. My Dark Sky.

This means that the Earth is at its closest to the Sun in the middle of the Northern Hemisphere's winter, counter-intuitive to most of the planet's population. This is, however, purely coincidental; the Earth's season's are not caused by its distance from the Sun, which only varies by 3.3%, but rather by the tilt of the planet. The Earth is currently tilted at an angle of 25.5° to its plane of orbit (this varies on a timescale of tens of thousands of years, but remains fixed from the point of view of any human observer), causing the Sun to appear to rise higher and lower in the skies of each hemisphere as the year goes by. In the northern winter the Southern Hemisphere is tilted towards the Sun, so that the days are longer there (and in around the Southern Solstice in December, permanently above the horizon at the South Pole). In addition the Sun being directly overhead means that the energy from the Sun has to pass through less of the atmosphere before it reaches the surface of the Earth, so that less energy is lost to the atmosphere, causing the surface to warm.

 How the tilt of the Earth relative to its plane of orbit causes the seasons. ESA.

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Saturday 30 December 2017

Ostromia crassipes: A second species of Bird from the Solnhofen Limestone.

The first known fossil Bird, Archaeopteryx lithographica, was described from the Late Jurassic Solnhofen Limestone of Bavaria in 1861, only two years after the publication of Darwin's On the origin of species by means of natural selection, and, showing a clear connection between modern Birds and the Theropod Dinosaurs, provided the first strong evidence in support of Darwin's theories after the publication of the book. Since that time many fossil Bird species have been described, but until the 2012, when Birds were described from the Tiaojishan Formation of eastern China, Archaeopteryx lithographica was the only Bird species known from the Jurassic, and remains to this day the only described Jurassic Bird species from outside of China.

In a paper published in the journal BMC Evolutionary Biology on 2 December 2017, Christian Foth of the Department of Geosciences at the Université de Fribourg, and the Staatliches Museum für Naturkunde Stuttgart, and Oliver Rauhut of the Bayerische Staatssammlung für Paläontologie und Geologie at Ludwig-Maximilians-University Munich, describe a second species of Bird from the Solnhofen Limestone.

The new species is described from a specimen first described as a Pterodactyl in 1857 under the name Pterodactylus crassipes. This specimen was identified as a Bird in 1970, and assigned to the species Archaeopteryx lithographica, and has since then been known as the 'Haarlem specimen', as it is kept in Teylers Museum in Haarlem, the Netherlands.

Overview of the 'Haarlem specimen'. Foth & Rauhut (2017).

The Haarlen specimen is not a complete Bird, like the more famous Berlin and London specimens, but rather a partial specimen comprising portions of a wing and hindlimb, which has prevented direct comparison to other specimens assigned to the species. Foth and Rauhut carried out a morphometric analysis of the bones that were preserved intact in order to compare the Haarlem specimen to better preserved examples of the species.

Morphometric analysis is a tool used by palaeontologists, archaeologists, anthropologists and forensic pathologists to analyse and compare specimens. It relies on taking numerous measurements of an object such as a bone or shell, and comparing both these measurements and ratios between measurements to those obtained from other specimens in order to establish relationships between them.

Using this methodology Foth and Rauhut found that almost all of the proportions of the Haarlem specimen fell outside those of other Archaeopteryx lithographica, specimens, strongly suggesting that it is a member of a new species. In order to test this further, they carried out a cladistic analysis (computerised analysis of relationships within the group based entirely upon shared common features rather than assumed relationships) including the Haarlem specimen, Archaeopteryx lithographica, and a selection of other early Birds and Maniraptoran Dinosaurs (the group of Therapods that includes Birds). This strongly suggested that the Haarlem specimen is more closely related to the Tiaojishan Birds Pedopenna, Eosinopteryx, and Anchiornis, than it is to Archaeopteryx

On this basis Foth and Rauhut conclude that the Haarlem specimen represents a second species of Bird from the Solnhofen Limestone, and formally describe that species as Ostromia crassipes, where 'Ostromia' honours John Ostrom, who first recognised the specimen was a Bird rather than a Pterodactyl, and 'crassipes' is the original species name assigned to the specimen in 1857.

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