Monday, 18 September 2017

Asteroid 2017 RV2 passes the Earth.

Asteroid 2017 RV2 passed by the Earth at a distance of about 832 100 km (2.17 times the average distance between the Earth and the Moon, or 0.56% of the distance between the Earth and the Sun), slightly before 2.25 am GMT on Tuesday 12 September 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 RV2 has an estimated equivalent diameter of 11-34 m (i.e. it is estimated that a spherical object with the same volume would be 11-34 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 15 km above the ground, with only fragmentary material reaching the Earth's surface.

The calculated orbit of 2017 RV2  Minor Planet Center.

2017 RV2 was discovered on 14 September 2017 (two days after its closest approach to the Earth) by the Atlas MLO Telescope at Mauna Loa Observatory in Hawaii. The designation 2017 RV2 implies that the asteroid was the 71st object (object V2) discovered in the first half of September 2017 (period 2017 R). 

2017 RV2 has a 691 day orbital period and an eccentric orbit tilted at an angle of 0.21° to the plane of the Solar System, which takes it from 0.98 AU from the Sun (i.e. 98% of he average distance at which the Earth orbits the Sun, slightly inside the orbit of Venus) to 2.08 AU from the Sun (i.e. 208% of the average distance at which the Earth orbits the Sun, considerably more than the distance at which the planet Mars orbits). It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). This means that close encounters between the asteroid and Earth are fairly common, with the last thought to have happened in June 2002 and the next predicted in June 2019. 

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Cholera kills 44 in Borno State, Nigeria.

Forty four people are known to have died, and another 2300 possible cases have been reported, in an outbreak of Cholera in Borno State, Nigeria, since the first cases were reported on 16 August 2017. The UN Office for the Coordination of Humanitarian Affairs in Nigeria estimates that 3.7 million people are at immediate threat, particularly the large number of internally displaced people living in temporary camps in the state, due to the ongoing conflict between Nigerian Government troops and Boko Haram Islamic Militants, and is working to improve sanitation in these camps, in addition to setting up four specialist treatment centres for severe cases and seven rehydration centres for less severe cases.

A Cholera treatment centre in Borno State. Medecins Sans Frontieres.

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 5.8 Earthquake off the coast of Choapa Province, Chile.

The United States Geological Survey recorded a Magnitude 5.8 Earthquake at a depth of 10 km, 95 km offshore of the city of Illapel in the Chilean province of Choapa, slightly after 10.45 am local time (slightly after 1.45 pm GMT) on Monday 18 September 2017. There are no reports of any damage or injuries associated with this event, but people have reported feeling the event in the Santiago and Valparaiso areas.

The approximate location of the 18 September 2017 Antofagasta Earthquake. USGS.

Chile is located on the west coast of South America, which is also the convergent margin between the Nazca and South American Plates. The Nazca Plate is being subducted beneath the South American Plate and is sinking beneath the South American Plate. This is not a smooth process, the rocks of the two plates continuously stick together then, as the pressure builds up, break apart again, causing Earthquakes. As the Nazca Plate sinks deeper it is partially melted by the heat of the Earth's interior. Some of the melted material then rises up through the overlying South American Plate as magma, fuelling the volcanoes of the Chilean Andes.
 The subduction of the Nazca Plate beneath the South American Plate, and how it causes Earthquakes and volcanoes. Pacific Earthquake Engineering Research Center.
Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organisation Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.
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Sunday, 17 September 2017

Maevia eureka: A new species of Jumping Spider from Miocene Chipas Amber.

Jumping Spiders, Salticidae, are the largest family of Spiders, with about 5800 described species in 600 genera, roughly 13% of all described species. They are noted for their exceptional vision, possibly the best of any Arthropods, which is used in hunting, with these Spiders being active hunters that stalk their prey before catching it with a final leap, as well as in mating, with many species having evolved elaborate courtship rituals. 

In a paper published in the journal Peer J on 25 July 2017, Francisco Riquelme of the Laboratorio de Sistemática Molecular at the Universidad Autónoma del Estado de Morelos, and Miguel Menéndez-Acuña of the Centro de Investigación en Biodiversidad y Conservación, also at the Universidad Autónoma del Estado de Morelos, describe a new species of Jumping Spider from a peace of Miocene amber from Chiapas State in Mexico.

The ambers of Chiapas State, Mexico, were laid down in the Miocene (and possibly Oligocene) in shallow marine environments. The amber is thought to be derived from resin secreted from a Leguminous tree of the genus Hymenaea, which lived in mangrove forests along the Caribbean shoreline. This amber is almost identical to amber produced in similar mangrove forests during the Miocene in the Dominican Republic and to a lesser extent other parts of the Caribbean, and a thriving, and sometimes illegal, trade in these fossils, combined with poor recording by commercial fossil collectors (particularly those acting illegally) means that fossils in Caribbean amber derived from private collections can be hard to connect to their point of origin.

The new species is placed in the extant genus Maevia, which contains a number of extant species from North America, and possibly South America and Australasia, but no previously described fossil species, and given the specific name eureka, refering to the 'eureka moment' that occured when the specimen was found, it having been dug out by habd during the excavation of a latrine for use during fieldwork. The species is described from a single female specimen, 3.6 mm in length and pale brown in colour, with white markings, preserved in a piece of almost clear amber.

Maevia eureka. Amber inclusion as seen in raw condition using regular light. (A) Dorsal view. (B) Ventral. Scale bar 2 mm. Riquelme & Menéndez-Acuña (2017).

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Calculating the mass of Cressida.

Cressida is one of ten small inner moons of the planer Uranus discovered by the Voyager 2 space probe during its January 1986 flyby of the planet. The moon orbits Uranus every eleven hours at an altitude of 61 800 km, and has an average radius of about 41 km, though it is poorly understood, as it is almost impossible to directly observe from Earth.

Voyager 2 image of the Uraniun moons Portia, Cressida and Ophelia. NASA/Wikimedia Commons.

In a paper published on the arXiv database at Cornell University Library on 24 August 2017, Robert Chancia and Matthew Hedman of the Department of Physics at the University of Idaho, and Richard French of the Astronomy Department at Wellesley College, present an estimation of the mass and density of Cressida based upon its interations with Uranus' η Ring.

The η Ring is one os a system of nine narrow rings around Uranus discovered in 1977 as the occulated (came in front of) the star SAO158687 (the others being the 6, 5, 4, α, β, ε, γ and δ rings). Like the inner moons of Uranus, these rings are extremely hard to observe directly, the η Ring having only been directly imaged twice since it was discovered, both times by the Voyager 2 probe. The ring is estimated to have a core 1-2 km thick surrounded by a more diffuse outer zone about 40 km in radius, and is orbiting the planet at 47 175 km.

However, while these rings are very hard to observe directly, they can be detected when they occulate stars, and while this in itself is a rare event, it is a predictable one. The η Ring has been observed to occulate stars 49 times since its discovery; forty seven times from Earth-based observatories, and twice from Voyager 2. Chancia et al. were able to use these observations to calculate the orbit of the particles within the ring, thereby demonstrating that they were in a 3:2 resonance with the moon Cressida.

An exaggerated cartoon model of ring particle streamlines around a planet and near a 3:2 ILR with an exterior moon, in the co-rotating frame of the moon. The resonant radius is marked with a dashed line and included three ring particle streamlines on either side of the resonance. This shows the stable con guration on either side of the resonance, where a periapse (apoapse) is aligned with the moon interior (exterior) to the resonance. Chancia et al. (2017).

Using this disturbance Chancia et al. calculate the mass of Cressida to be 250 000 000 000 000 000 kilograms. Since the radius of the moon is known and its volume can be calculated from this, then the density can also be calculated, which Chancia et al. calculate at 0.86 grams per square centimetre.(slightly lower than the density of water ice).

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Eruption on Mount Zhupanovsky, Kamchatka Peninsula.

The Kamtchatka Volcanic Eruption Response Team reported an eruption on Mount Zhupanovsky, a 2923 m volcano on the southern Kamchatka Peninsula in the Russian Far East. The eruption produced an gas column that rose 4 km above the volcano, and prompted the Response Team to raise the alert level around the volcano, and the Tokyo Volcanic Ash Advisory Center to issue a warning to aviation.

The approximate location of Mount Zhupanovsky. Google Maps.

Zhupanovsky is an elongated volcanic complex on the southeast of the Kamchatka Peninsula in the Russian Far East, comprising four overlapping stratovolcanoes (cone shaped volcanoes) in a line running roughly east to west. Three of these volcanoes date from the Pleistocene, with the easternmost being a Holocene structure upon which all recorded historical eruptions have occurred. This volcano probably began erupting between 7000 and 5000 years ago. The current phase of eruptive activity began in October 2013, prior to which it had been inactive since the 1950s.

The Kamchatka Peninsula lies on the eastern edge of the Okhotsk Plate, close to its margin with the Pacific and North American Plates. The Pacific Plate is being subducted along the Kuril Kamchatka Trench, to the east and south of the peninsula, and as it does so it passes under the southern part of the Kamchatka Peninsula, and as it does so is partially melted by the friction and the heat of the Earth's interior. Some of the melted material then rises through the overlying Okhotsk Plate as magma and fuelling the volcanoes of southern Kamchatka.

 Simple diagram showing the subduction of the Pacific Plate beneath the Okhotsk Plate along the Kuril Kamchatka Trench. The Kamchatka Peninsula is at the top of the diagram. Auburn University.

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Magnitude 5.0 Earthquake in South Kivu Province, Dempcratic Republic of Congo.

The United States Geological Survey Recorded a Magnitude 5.0 Earthquake at a depth of 13 km about 25 km to the southwest of the city of Bukavu in South Kivu Province, Democratic Republic of Congo, at about 7.45 pm local time (about 5.45 pm GMT) on Friday 15 September 2017. There are no reports of any damage or casualties associated with this event at this time, but it was felt  across much of the Lake Kivu Basin and Rwanda.

The approximate location of the 15 September 2017 South Kivu Earthquake. USGS.

Lake Kivu lies within the the of the Great Rift Valley, which is slowly splitting the African Plate in two along a line from the Red Sea through Ethiopia, and which includes the great lakes and volcanoes of east-central Africa. This has the potential to open into a new ocean over the next few tens of millions of years, splitting Africa into two new, smaller, continents; Nubia to the west and Somalia to the east.

 Movement on the African Rift Valley, with associated volcanoes. Rob Gamesby/Cool Geography.

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organisation Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.

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