April 22, 2017

Megalodon and Platybelodon

Megalodon and Platybelodon

Megalodon is an extinct species of shark that lived approximately 23 to 2.6 million years ago, during the Cenozoic Era (early Miocene to end of Pliocene).

The taxonomic assignment of C. megalodon has been debated for nearly a century, and is still under dispute. The two major interpretations are Carcharodon megalodon (under family Lamnidae) or Carcharocles megalodon (under the family Otodontidae). Consequently, the scientific name of this species is commonly abbreviated C. megalodon in the literature.

Regarded as one of the largest and most powerful predators in vertebrate history, C. megalodon probably had a profound impact on the structure of marine communities. Fossil remains suggest that this giant shark reached a length of 18 metres (59 ft), and also indicate that it had a cosmopolitan distribution. Scientists suggest that C. megalodon looked like a stockier version of the great white shark, Carcharodon carcharias.

Platybelodon was a genus of large herbivorous mammal related to the elephant (order Proboscidea). It lived during the late Miocene Epoch in Asia and the Caucasus.

Platybelodon was very similar to Amebelodon, another, closely related gomphothere genus. Due to the shape of the two lower teeth, in common with many gomphothere genera (such as Platybelodon, Archaeobelodon, Konobelodon, and Amebelodon), they are popularly known as "shovel tuskers."

Platybelodon was previously believed to have fed in the swampy areas of grassy savannas, using its teeth to shovel up aquatic and semi-aquatic vegetation. However, wear patterns on the teeth suggest that it used its lower tusks to strip bark from trees, and may have used the sharp incisors that formed the edge of the "shovel" more like a modern-day scythe, grasping branches with its trunk and rubbing them against the lower teeth to cut it from a tree. Adult animals in particular might have eaten coarser vegetation more frequently than juveniles.

Image Credit & Copyright: Julius Csotonyi
Explanation from: https://en.wikipedia.org/wiki/Megalodon and https://en.wikipedia.org/wiki/Platybelodon

Earth at Night: the Americas

Earth at Night: the Americas

Suomi NPP satellite

Image Credit: NASA

Earth and the Moon seen between the Rings of Saturn by Cassini spacecraft

Earth and the Moon seen between the Rings of Saturn by Cassini spacecraftEarth and the Moon seen between the Rings of Saturn by Cassini spacecraft

This view from NASA's Cassini spacecraft shows planet Earth as a point of light between the icy rings of Saturn.

The spacecraft captured the view on April 12, 2017 at 10:41 p.m. PDT (1:41 a.m. EDT). Cassini was 870 million miles (1.4 billion kilometers) away from Earth when the image was taken. Although far too small to be visible in the image, the part of Earth facing toward Cassini at the time was the southern Atlantic Ocean.

Earth's moon is also visible to the left of our planet in a cropped, zoomed-in version of the image.

The rings visible here are the A ring (at top) with the Keeler and Encke gaps visible, and the F ring (at bottom). During this observation Cassini was looking toward the backlit rings, making a mosaic of multiple images, with the sun blocked by the disk of Saturn.

Seen from Saturn, Earth and the other inner Solar System planets are all close to the Sun, and are easily captured in such images, although these opportunities have been somewhat rare during the mission. The F ring appears especially bright in this viewing geometry.

Image Credit: NASA/JPL-Caltech/Space Science Institute
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA21445

April 21, 2017

Earth Day 2017



Mosasaurs are an extinct group of large marine reptiles. Their first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. Mosasaurs probably evolved from an extinct group of aquatic lizards known as aigialosaurs in the Early Cretaceous. During the last 20 million years of the Cretaceous period (Turonian-Maastrichtian ages), with the extinction of the ichthyosaurs and pliosaurs, mosasaurs became the dominant marine predators. They became extinct as a result of the K-T event at the end of the Cretaceous period, about 66 million years ago.

Mosasaurs breathed air, were powerful swimmers, and were well-adapted to living in the warm, shallow inland seas prevalent during the Late Cretaceous period. Mosasaurs were so well adapted to this environment that they gave birth to live young, rather than returning to the shore to lay eggs as sea turtles do.

The smallest-known mosasaur was Dallasaurus turneri, which was less than 1 m (3.3 ft) long. Larger mosasaurs were more typical, with many species growing longer than 4 m (13 ft). Mosasaurus hoffmannii, the largest known species may have reached up to 17 m (56 ft) in length. Currently, the largest publicly exhibited mosasaur skeleton in the world is on display at the Canadian Fossil Discovery Centre in Morden, Manitoba. The specimen, nicknamed "Bruce", is just over 13 m (43 ft) long.

Mosasaurs had a body shape similar to those of modern-day monitor lizards (varanids), but were more elongated and streamlined for swimming. Their limb bones were reduced in length and their paddles were formed by webbing between their long finger and toe bones. Their tails were broad, and supplied their locomotive power. Until recently, mosasaurs were assumed to have swum in a method similar to the one used today by conger eels and sea snakes, undulating their entire bodies from side to side. However, new evidence suggests that many advanced mosasaurs had large, crescent-shaped flukes on the ends of their tails, similar to those of sharks and some ichthyosaurs. Rather than use snake-like undulations, their bodies probably remained stiff to reduce drag through the water, while their tails provided strong propulsion. These animals may have lurked and pounced rapidly and powerfully on passing prey, rather than chasing after it.

Early reconstructions showed mosasaurs with dorsal crests running the length of their bodies, which were based on misidentified remains of tracheal cartilage. By the time this error was discovered, depicting mosasaurs with such crests in artwork had already become a trend.

Mosasaurs had double-hinged jaws and flexible skulls (much like those of snakes), which enabled them to gulp down their prey almost whole. A skeleton of Tylosaurus proriger from South Dakota included remains of the diving seabird Hesperornis, a marine bony fish, a possible shark, and another, smaller mosasaur (Clidastes). Mosasaur bones have also been found with shark teeth embedded in them.

One of the food items of mosasaurs were ammonites, molluscs with shells similar to those of Nautilus, which were abundant in the Cretaceous seas. Holes have been found in fossil shells of some ammonites, mainly Pachydiscus and Placenticeras. These were once interpreted as a result of limpets attaching themselves to the ammonites, but the triangular shape of the holes, their size, and their presence on both sides of the shells, corresponding to upper and lower jaws, is evidence of the bite of medium-sized mosasaurs. Whether this behaviour was common across all size classes of mosasaurs is not clear.

Virtually all forms were active predators of fish and ammonites; a few, such as Globidens, had blunt, spherical teeth, specialized for crushing mollusk shells. The smaller genera, such as Platecarpus and Dallasaurus, which were about 1–6 m (3.3–19.7 ft) long, probably fed on fish and other small prey. The smaller mosasaurs may have spent some time in fresh water, hunting for food. The larger mosasaurs, such as Tylosaurus, and Mosasaurus, reached sizes of 10–15 m (33–49 ft) long and were the apex predators of the Late Cretaceous oceans, attacking other marine reptiles, as well as preying on large fish and ammonites.

Based on features such as the double row of pterygoid ("flanged") teeth on the palate, the loosely hinged jaw, modified/reduced limbs and probable methods of locomotion, many researchers believe that snakes share a common marine ancestry with mosasaurs, a suggestion advanced in 1869 by Edward Drinker Cope, who coined the term Pythonomorpha to unite them. The idea lay dormant for more than a century, to be revived in the 1990s. Recently, the discovery of Najash rionegrina, a fossorial snake from South America, cast doubt on the marine origin hypothesis.

The skeleton of Dallasaurus turneri, described by Bell and Polcyn (2005), has a mixture of features present in the skeletons of derived mosasaurs and in the skeletons of mosasaurid ancestors, such as aigialosaurids. Dallasaurus retains facultatively terrestrial limbs similar in their structure to the limbs of aigialosaurids and terrestrial squamates (plesiopedal limb condition), unlike derived mosasaurids, which evolved paddle-like limbs (hydropedal limb condition). However, the skeleton of Dallasaurus simultaneously had several characters that linked it with derived members of the subfamily Mosasaurinae; the authors of its description listed "invasion of the parietal by medial tongues from the frontal, teeth with smooth medial enamel surface, high coronoid buttress on surangular, interdigitate anterior scapulo-coracoid suture, humeral postglenoid process, elongate atlas synapophysis, sharp anterodorsal ridge on synapophyses, vertically oriented vertebral condyles, elongate posterior thoracic vertebrae, and fused haemal arches" as the characters uniting Dallasaurus with Mosasaurinae. The phylogenetic analysis conducted by Bell and Polcyn indicated that hydropedal mosasaurids did not form a clade that wouldn't also include plesiopedal taxa, such as Dallasaurus, Yaguarasaurus, Russellosaurus, Tethysaurus, Haasiasaurus and Komensaurus (in 2005 only informally known as "Trieste aigialosaur"); the analysis indicated that hydropedal limb condition evolved independently in three different groups of mosasaurs (Halisaurinae, Mosasaurinae and the group containing the subfamilies Tylosaurinae and Plioplatecarpinae). The result of this phylogenetic study was subsequently mostly confirmed by the analyses conducted by Caldwell and Palci (2007) and Leblanc, Caldwell and Bardet (2012); the analysis conducted by Makádi, Caldwell and Ősi (2012) indicated that hydropedal limb condition evolved independently in two groups of mosasaurs (in Mosasaurinae and in the clade containing Halisaurinae, Tylosaurinae and Plioplatecarpinae). Conrad et al. (2011), on the other hand, recovered hydropedal mosasaurs forming a clade that excluded their plesiopedal relatives. If the hypothesis of Bell and Polcyn (2005) is correct, then mosasaurs in the traditional sense of the word, i.e. "lizards that evolved paddle-like limbs and radiated into aquatic environments in the late Mesozoic, going extinct at the end of that era", are actually polyphyletic; Bell and Polcyn (2005) maintained monophyletic Mosasauridae by including Dallasaurus and other aforementioned plesiopedal taxa in the family as well, while Caldwell (2012) suggested (though explicitly stated that it was not "a formal proposal of new nomenclature") to restrict Mosasauridae only to the genus Mosasaurus and its closest hydropedal relatives.

The exact phylogenetic position of the clade containing mosasaurids and their closest relatives (aigialosaurids and dolichosaurs) within Squamata remains uncertain. Some cladistic analyses recovered them as the closest relatives of snakes, taking into account similarities in jaw and skull anatomies; however, this has been disputed and the morphological analysis conducted by Conrad (2008) recovered them as varanoids closely related to terrestrial monitor lizards instead. Subsequent analysis of anguimorph relationships conducted by Conrad et al. (2011) based on morphology alone recovered mosasaurids, aigialosaurids and dolichosaurs as anguimorphs lying outside the least inclusive clade containing monitor lizards and helodermatids; the analysis based on combined datasets of morphological and molecular data, on the other hand, found them more closely related to monitor lizards and the earless monitor lizard than to helodermatids and the Chinese crocodile lizard. The large morphological analysis conducted by Gauthier et al. (2012) recovered mosasaurids, aigialosaurids and dolichosaurids in an unexpected position as basal members of the clade Scincogekkonomorpha (containing all taxa sharing a more recent common ancestor with Gekko gecko and Scincus scincus than with Iguana iguana) that didn't belong to the clade Scleroglossa. The phylogenetic position of these taxa turned out to be highly dependent on which taxa were included in or excluded from the analysis. When mosasaurids were excluded from the analysis, dolichosaurs and aigialosaurids were recovered within Scleroglossa, forming a sister group to the clade containing snakes, amphisbaenians, dibamids and the American legless lizard. When mosasaurids were included in the analysis, and various taxa with reduced or absent limbs other than snakes (such as dibamids or amphisbaenians) were excluded, mosasaurids, aigialosaurids and dolichosaurs were recovered inside Scleroglossa forming the sister group to snakes. Longrich, Bhullar and Gauthier (2012) conducted a morphological analysis of squamate relationships using a modified version of the matrix from the analysis of Gauthier et al. (2012); they found the phylogenetic position of the clade containing mosasaurs and their closest relatives within Squamata to be highly unstable, with the clade "variously being recovered outside Scleroglossa (as in Gauthier et al., 2012) or alongside the limbless forms".

Image Credit & Copyright: Matte FX
Explanation from: https://en.wikipedia.org/wiki/Mosasaur

Europe and Africa at Night

Europe at Night

Suomi NPP satellite

Image Credit: NASA

April 20, 2017

Valley of the Dinosaurs

Valley of the Dinosaurs

The Valley of the Dinosaurs is an area in the state of Paraíba, Brazil, that contains many fossilized dinosaur tracks. It contains the Valley of the Dinosaurs Area of Relevant Ecological Interest, a sustainable use area of relevant ecological interest. This in turn contains the smaller and fully protected Valley of the Dinosaurs Natural Monument. In 2015–16 there was concern that renovations to the tourist attraction, which had been delayed through lack of funding, might not be respecting the integrity of the site.

The Valley of the Dinosaurs is an area in the sedimentary basin of the Peixe River that holds over 50 types of ancient animal tracks, including those of stegosaurus, allosaurus and iguanodons. The valley covers an area of about 700 square kilometres (270 sq mi) that includes the city of Sousa, Paraíba, and ten other municipalities. It is in a Caatinga biome. Tracks have been found in about 30 locations in the valley, with fossilized footprints of over 80 species at about 20 different stratographic levels. Most of the tracks are of carnivorous dinosaurs.

The tracks the dinosaurs made in the damp earth beside ponds and rivers in rainy periods hardened over long periods of drought, gained new layers of sand and clay from floods, and fossilized. Footprints are as small as 5 centimetres (2.0 in), perhaps from dinosaurs the size of modern chickens, up to 40 centimetres (16 in) long, such as that of a four-ton iguanodon. The most visited site is the island called the Passagem das Pedras (Crossing of Stones) in the bed of the Peixe River. This is about 7 kilometres (4.3 mi) from the urban centre of Sousa.

Explanation from: https://en.wikipedia.org/wiki/Valley_of_the_Dinosaurs,_Para%C3%ADba

Europe at Night

Europe at Night

Suomi NPP satellite

Image Credit: NASA

Supermassive Black Hole in Elliptical Galaxy NGC 4696

Supermassive Black Hole in Elliptical Galaxy NGC 4696

  • A black hole has been "beating" about every 5 to 10 million years, pumping material and energy into its environment.
  • This black hole is at the center of a large elliptical galaxy located within the core of the Centaurus Cluster of galaxies.
  • Data from Chandra and other telescopes show evidence for repeated bursts, or eruptions, from the black hole.
  • These bursts created cavities within the hot, X-ray emitting gas that pervades the cluster.

At the center of the Centaurus galaxy cluster, there is a large elliptical galaxy called NGC 4696. Deeper still, there is a supermassive black hole buried within the core of this galaxy.

New data from NASA's Chandra X-ray Observatory and other telescopes has revealed details about this giant black hole, located some 145 million light years from Earth. Although the black hole itself is undetected, astronomers are learning about the impact it has on the galaxy it inhabits and the larger cluster around it.

In some ways, this black hole resembles a beating heart that pumps blood outward into the body via the arteries. Likewise, a black hole can inject material and energy into its host galaxy and beyond.

Supermassive Black Hole in Elliptical Galaxy NGC 4696Supermassive Black Hole in Elliptical Galaxy NGC 4696Supermassive Black Hole in Elliptical Galaxy NGC 4696
Data from Chandra and other telescopes have provided evidence for repeated bursts of energetic particles generated by the supermassive black hole at the center of the Centaurus Cluster. These images show X-ray data from Chandra that reveals the hot gas in the cluster, and radio data from the VLA that shows high-energy particles produced by jets powered by the black hole. Visible light data from Hubble show galaxies in the cluster as well as galaxies and stars outside the cluster.
By examining the details of the X-ray data from Chandra, scientists have found evidence for repeated bursts of energetic particles in jets generated by the supermassive black hole at the center of NGC 4696. These bursts create vast cavities in the hot gas that fills the space between the galaxies in the cluster. The bursts also create shock waves, akin to sonic booms produced by high-speed airplanes, which travel tens of thousands of light years across the cluster.

This composite image contains X-ray data from Chandra (red) that reveals the hot gas in the cluster, and radio data from the NSF's Karl G. Jansky Very Large Array (blue) that shows high-energy particles produced by the black hole-powered jets. Visible light data from the Hubble Space Telescope (green) show galaxies in the cluster as well as galaxies and stars outside the cluster.

Supermassive Black Hole in Elliptical Galaxy NGC 4696
Astronomers employed special processing to the Chandra X-ray data of NGC 4696 to emphasize nine cavities visible in the hot gas. These cavities are labeled A through I in an additional image, and the location of the black hole is labeled with a cross. The cavities that formed most recently are located nearest to the black hole, in particular the ones labeled A and B.

Astronomers employed special processing to the X-ray data (shown above) to emphasize nine cavities visible in the hot gas. These cavities are labeled A through I in an additional image, and the location of the black hole is labeled with a cross. The cavities that formed most recently are located nearest to the black hole, in particular the ones labeled A and B.

Supermassive Black Hole in Elliptical Galaxy NGC 4696
A different type of processing of the Chandra X-ray data of NGC 4696 reveals a sequence of curved and approximately equally spaced features in the hot gas. These may be caused by sound waves generated by the black hole's repeated bursts. In a galaxy cluster, the hot gas that fills the cluster enables sound waves — albeit at frequencies far too low for the human hear to detect — to propagate.

The researchers estimate that these black hole bursts, or "beats", have occurred every five to ten million years. Besides the vastly differing time scales, these beats also differ from typical human heartbeats in not occurring at particularly regular intervals.

A different type of processing of the X-ray data (shown above) reveals a sequence of curved and approximately equally spaced features in the hot gas. These may be caused by sound waves generated by the black hole's repeated bursts. In a galaxy cluster, the hot gas that fills the cluster enables sound waves — albeit at frequencies far too low for the human hear to detect — to propagate. (Note that both images showing the labeled cavities and this image are rotated slightly clockwise to the main composite.)

The features in the Centaurus Cluster are similar to the ripples seen in the Perseus cluster of galaxies. The pitch of the sound in Centaurus is extremely deep, corresponding to a discordant sound about 56 octaves below the notes near middle C. This corresponds to a slightly higher (by about one octave) pitch than the sound in Perseus. Alternative explanations for these curved features include the effects of turbulence or magnetic fields.

Supermassive Black Hole in Elliptical Galaxy NGC 4696
By examining the details of the X-ray data from Chandra, scientists found evidence for repeated bursts of energetic particles in jets generated by the supermassive black hole at the center of NGC 4696. These bursts create vast cavities in the hot gas that fills the space between the galaxies in the cluster. The bursts also create shock waves, akin to sonic booms produced by high-speed airplanes, which travel tens of thousands of light years across the cluster.

The black hole bursts also appear to have lifted up gas that has been enriched in elements generated in supernova explosions. The authors of the study of the Centaurus cluster created a map showing the density of elements heavier than hydrogen and helium. The brighter colors in the map show regions with the highest density of heavy elements and the darker colors show regions with a lower density of heavy elements. Therefore, regions with the highest density of heavy elements are located to the right of the black hole. A lower density of heavy elements near the black hole is consistent with the idea that enriched gas has been lifted out of the cluster's center by bursting activity associated with the black hole. The energy produced by the black hole is also able to prevent the huge reservoir of hot gas from cooling. This has prevented large numbers of stars from forming in the gas.

Image Credit: X-ray: NASA/CXC/MPE/J.Sanders et al.; Optical: NASA/STScI; Radio: NSF/NRAO/VLA
Explanation from: http://chandra.harvard.edu/photo/2017/ngc4696/

Exoplanet LHS 1140b

Exoplanet LHS 1140b

This planet is located in the liquid water habitable zone surrounding its host star, a small, faint red star named LHS 1140. The planet weighs about 6.6 times the mass of Earth and is shown passing in front of LHS 1140. Depicted in blue is the atmosphere the planet may have retained.

Image Credit: M. Weiss/CfA

Newly Discovered Exoplanet May be Best Candidate in Search for Signs of Life

Newly Discovered Exoplanet May be Best Candidate in Search for Signs of Life

An exoplanet orbiting a red dwarf star 40 light-years from Earth may be the new holder of the title “best place to look for signs of life beyond the Solar System”. Using ESO’s HARPS instrument at La Silla, and other telescopes around the world, an international team of astronomers discovered a “super-Earth” orbiting in the habitable zone around the faint star LHS 1140. This world is a little larger and much more massive than the Earth and has likely retained most of its atmosphere. This, along with the fact that it passes in front of its parent star as it orbits, makes it one of the most exciting future targets for atmospheric studies. The results will appear in the 20 April 2017 issue of the journal Nature.

The newly discovered super-Earth LHS 1140b orbits in the habitable zone around a faint red dwarf star, named LHS 1140, in the constellation of Cetus (The Sea Monster). Red dwarfs are much smaller and cooler than the Sun and, although LHS 1140b is ten times closer to its star than the Earth is to the Sun, it only receives about half as much sunlight from its star as the Earth and lies in the middle of the habitable zone. The orbit is seen almost edge-on from Earth and as the exoplanet passes in front of the star once per orbit it blocks a little of its light every 25 days.

“This is the most exciting exoplanet I’ve seen in the past decade,” said lead author Jason Dittmann of the Harvard-Smithsonian Center for Astrophysics (Cambridge, USA). “We could hardly hope for a better target to perform one of the biggest quests in science — searching for evidence of life beyond Earth.”

"The present conditions of the red dwarf are particularly favourable — LHS 1140 spins more slowly and emits less high-energy radiation than other similar low-mass stars," explains team member Nicola Astudillo-Defru from Geneva Observatory, Switzerland.

For life as we know it to exist, a planet must have liquid surface water and retain an atmosphere. When red dwarf stars are young, they are known to emit radiation that can be damaging for the atmospheres of the planets that orbit them. In this case, the planet's large size means that a magma ocean could have existed on its surface for millions of years. This seething ocean of lava could feed steam into the atmosphere long after the star has calmed to its current, steady glow, replenishing the planet with water.

The discovery was initially made with the MEarth facility, which detected the first telltale, characteristic dips in light as the exoplanet passed in front of the star. ESO’s HARPS instrument, the High Accuracy Radial velocity Planet Searcher, then made crucial follow-up observations which confirmed the presence of the super-Earth. HARPS also helped pin down the orbital period and allowed the exoplanet’s mass and density to be deduced.

The astronomers estimate the age of the planet to be at least five billion years. They also deduced that it has a diameter 1.4 times larger than the Earth — almost 18 000 kilometres. But with a mass around seven times greater than the Earth, and hence a much higher density, it implies that the exoplanet is probably made of rock with a dense iron core.

This super-Earth may be the best candidate yet for future observations to study and characterise its atmosphere, if one exists. Two of the European members of the team, Xavier Delfosse and Xavier Bonfils both at the CNRS and IPAG in Grenoble, France, conclude: “The LHS 1140 system might prove to be an even more important target for the future characterisation of planets in the habitable zone than Proxima b or TRAPPIST-1. This has been a remarkable year for exoplanet discoveries!”.

In particular, observations coming up soon with the NASA/ESA Hubble Space Telescope will be able to assess exactly how much high-energy radiation is showered upon LHS 1140b, so that its capacity to support life can be further constrained.

Further into the future — when new telescopes like ESO’s Extremely Large Telescope are operating — it is likely that we will be able to make detailed observations of the atmospheres of exoplanets, and LHS 1140b is an exceptional candidate for such studies.

Image Credit: ESO
Explanation from: https://www.eso.org/public/news/eso1712/

Great Cold Spot discovered on Jupiter

Great Cold Spot discovered on JupiterGreat Cold Spot discovered on JupiterGreat Cold Spot discovered on JupiterGreat Cold Spot discovered on Jupiter

So big it could engulf several Earths, Jupiter’s Great Red Spot is a gigantic storm that has been raging for centuries with winds blasting at over 600 kilometres per hour. But it has a rival: astronomers have discovered that Jupiter has a second Great Spot, this time a cold one.

In the polar regions of the planet, astronomers using the CRIRES instrument on ESO's Very Large Telescope, along with other facilities, have found a dark spot in the upper atmosphere (below the aurora to the left) about 200 °C cooler than its surroundings. Aptly nicknamed the “Great Cold Spot”, this intriguing feature is comparable in size to the Great Red Spot — 24 000 km across and 12 000 km tall. But data taken over 15 years show that the Great Cold Spot is much more volatile than its slowly-changing cousin. It changes dramatically in shape and size over days and weeks — but never disappears, and always stays roughly in the same location.

The Great Cold Spot is thought to be caused by the planet’s powerful aurorae, which drive energy into the atmosphere in the form of heat that flows around the planet. This creates a cooler region in the upper atmosphere, making the Great Cold Spot the first weather system ever observed to be generated by aurorae.

Image Credit: ESO/T. Stallard
Explanation from: https://www.eso.org/public/images/potw1716a/

April 19, 2017

Dinosaur Extinction

Dinosaur ExtinctionDinosaur ExtinctionDinosaur ExtinctionDinosaur ExtinctionDinosaur ExtinctionDinosaur ExtinctionDinosaur ExtinctionDinosaur ExtinctionDinosaur Extinction

The impact of a large body with the Earth may have been the punctuation mark at the end of a progressive decline in biodiversity during the Maastrichtian Age of the Cretaceous Period. The result was the extinction of three-quarters of Earth's plant and animal species. The impact created the sharp break known as K–Pg boundary (formerly known as the K–T boundary). Earth's biodiversity required substantial time to recover from this event, despite the probable existence of an abundance of vacant ecological niches.

Despite the severity of K-Pg extinction event, there was significant variability in the rate of extinction between and within different clades. Species which depended on photosynthesis declined or became extinct as atmospheric particles blocked solar energy. As is the case today, photosynthesizing organisms, such as phytoplankton and land plants, formed the primary part of the food chain in the late Cretaceous, and all else that depended on them suffered as well. Herbivorous animals, which depended on plants and plankton as their food, died out as their food sources became scarce; consequently, the top predators such as Tyrannosaurus rex also perished. Yet only three major groups of tetrapods disappeared completely; the non-avian dinosaurs, the plesiosaurs and the pterosaurs. The other Cretaceous groups that did not survive into the Cenozoic era, the ichthyosaurs and last remaining temnospondyls and non-mammalian cynodonts were already extinct millions of years before the event occurred.

Coccolithophorids and molluscs, including ammonites, rudists, freshwater snails and mussels, as well as organisms whose food chain included these shell builders, became extinct or suffered heavy losses. For example, it is thought that ammonites were the principal food of mosasaurs, a group of giant marine reptiles that became extinct at the boundary.

Omnivores, insectivores and carrion-eaters survived the extinction event, perhaps because of the increased availability of their food sources. At the end of the Cretaceous there seem to have been no purely herbivorous or carnivorous mammals. Mammals and birds which survived the extinction fed on insects, larvae, worms and snails, which in turn fed on dead plant and animal matter. Scientists theorise that these organisms survived the collapse of plant-based food chains because they fed on detritus.

In stream communities, few groups of animals became extinct. Stream communities rely less on food from living plants and more on detritus that washes in from land. This particular ecological niche buffered them from extinction. Similar, but more complex patterns have been found in the oceans. Extinction was more severe among animals living in the water column, than among animals living on or in the sea floor. Animals in the water column are almost entirely dependent on primary production from living phytoplankton, while animals living on or in the ocean floor feed on detritus or can switch to detritus feeding.

The largest air-breathing survivors of the event, crocodilians and champsosaurs, were semi-aquatic and had access to detritus. Modern crocodilians can live as scavengers and can survive for months without food and go into hibernation when conditions are unfavourable, and their young are small, grow slowly, and feed largely on invertebrates and dead organisms or fragments of organisms for their first few years. These characteristics have been linked to crocodilian survival at the end of the Cretaceous.

Explanation from: https://en.wikipedia.org/wiki/Dinosaur#Extinction_of_major_groups

Nile River at Night

Nile River at Night

Suomi NPP satellite

Image Credit: NASA

Wolf-Rayet Star EZ Canis Majoris

Wolf-Rayet Star EZ Canis Majoris

This entrancing image shows a few of the tenuous threads that comprise Sh2-308, a faint and wispy shell of gas located 5200 light-years away in the constellation of Canis Major (The Great Dog).

Sh2-308 is a large bubble-like structure wrapped around an extremely large, bright type of star known as a Wolf-Rayet Star — this particular star is called EZ Canis Majoris. These type of stars are among the brightest and most massive stars in the Universe, tens of times more massive than our own Sun, and they represent the extremes of stellar evolution. Thick winds continually poured off the progenitors of such stars, flooding their surroundings and draining the outer layers of the Wolf-Rayet stars. The fast wind of a Wolf-Rayet star therefore sweeps up the surrounding material to form bubbles of gas.

EZ Canis Majoris is responsible for creating the bubble of Sh2-308 — the star threw off its outer layers to create the strands visible here. The intense and ongoing radiation from the star pushes the bubble out further and further, blowing it bigger and bigger. Currently the edges of Sh2-308 are some 60 light-years apart!

Beautiful as these cosmic bubbles are, they are fleeting. The same stars that form them will also cause their death, eclipsing and subsuming them in violent supernova explosions.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1716a/

April 18, 2017



Dinosaurs are a diverse group of reptiles of the clade Dinosauria that first appeared during the Triassic. Although the exact origin and timing of the evolution of dinosaurs is the subject of active research, the current scientific consensus places their origin between 231 and 243 million years ago. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201 million years ago. Their dominance continued through the Jurassic and Cretaceous periods and ended when the Cretaceous–Paleogene extinction event led to the extinction of most dinosaur groups 66 million years ago.

Until the late 20th century, all groups of dinosaurs were believed to be extinct. The fossil record, however, indicates that birds, which are now termed "avian dinosaurs," are the modern descendants of feathered dinosaurs, having evolved from theropod ancestors during the Jurassic Period. As such, birds were the only dinosaur lineage to survive the mass extinction event. Throughout the remainder of this article, the term "dinosaur" is sometimes used generically to refer to the combined group of avian dinosaurs (birds) and non-avian dinosaurs; at other times it is used to refer to the non-avian dinosaurs specifically, while the avian dinosaurs are sometimes simply referred to as "birds". This article deals primarily with non-avian dinosaurs.

Dinosaurs are a varied group of animals from taxonomic, morphological and ecological standpoints. Birds, at over 10,000 living species, are the most diverse group of vertebrates besides perciform fish. Using fossil evidence, paleontologists have identified over 500 distinct genera and more than 1,000 different species of non-avian dinosaurs. Dinosaurs are represented on every continent by both extant species (birds) and fossil remains. Through the first half of the 20th century, before birds were recognized to be dinosaurs, most of the scientific community believed dinosaurs to have been sluggish and cold-blooded. Most research conducted since the 1970s, however, has indicated that all dinosaurs were active animals with elevated metabolisms and numerous adaptations for social interaction. Some are herbivorous, others carnivorous. Evidence suggests that egg laying and nest building are additional traits shared by all dinosaurs.

While dinosaurs were ancestrally bipedal, many extinct groups included quadrupedal species, and some were able to shift between these stances. Elaborate display structures such as horns or crests are common to all dinosaur groups, and some extinct groups developed skeletal modifications such as bony armor and spines. While the dinosaurs' modern-day surviving avian lineage (birds) are generally small due to the constraints of flight, many prehistoric dinosaurs (non-avian and avian) were large-bodied—the largest sauropod dinosaurs are estimated to have reached lengths of 39.7 meters (130 feet) and heights of 18 meters (59 feet) and were the largest land animals of all time. Still, the idea that non-avian dinosaurs were uniformly gigantic is a misconception based in part on preservation bias, as large, sturdy bones are more likely to last until they are fossilized. Many dinosaurs were quite small: Xixianykus, for example, was only about 50 cm (20 in) long.

Since the first dinosaur fossils were recognized in the early 19th century, mounted fossil dinosaur skeletons have been major attractions at museums around the world, and dinosaurs have become an enduring part of world culture. The large sizes of some dinosaur groups, as well as their seemingly monstrous and fantastic nature, have ensured dinosaurs' regular appearance in best-selling books and films, such as Jurassic Park. Persistent public enthusiasm for the animals has resulted in significant funding for dinosaur science, and new discoveries are regularly covered by the media.

Explanation from: https://en.wikipedia.org/wiki/Dinosaur

The United States at Night

The United States at Night

Suomi NPP satellite

Image Credit: NASA

Galaxy Cluster XDCP J0044.0-2033

Galaxy Cluster XDCP J0044.0-2033

  • The most distant massive galaxy cluster, located about 9.6 billion light years from Earth, has been found and studied.
  • Astronomers nicknamed this object the "Gioello" (Italian for "Jewel") Cluster.
  • Using Chandra data, researchers were able to accurately determine the mass and other properties of this cluster.
  • Results like this help astronomers understand how galaxy clusters have evolved over time.

A newly discovered galaxy cluster is the most massive one ever detected with an age of 800 million years or younger. Using data from NASA's Chandra X-ray Observatory, astronomers have accurately determined the mass and other properties of this cluster. This is an important step in understanding how galaxy clusters, the largest structures in the Universe held together by gravity, have evolved over time.

A composite image shows the distant and massive galaxy cluster that is officially known as XDCP J0044.0-2033. Researchers, however, have nicknamed it "Gioiello", which is Italian for "jewel". They chose this name because an image of the cluster contains many sparkling colors from the hot, X-ray emitting gas and various star-forming galaxies within the cluster. Also, the research team met to discuss the Chandra data for the first time at Villa il Gioiello, a 15th century villa near the Observatory of Arcetri, which was the last residence of prominent Italian astronomer Galileo Galilei. In this new image of the Gioiello Cluster, X-rays from Chandra are purple, infrared data from ESA's Hershel Space Telescope appear as large red halos around some galaxies, and optical data from the Subaru telescope on Mauna Kea in Hawaii are red, green, and blue.

Astronomers first detected the Gioiello Cluster, located about 9.6 billion light years away, using ESA's XMM-Newton observatory. They were then approved to study the cluster with Chandra in observations that were equivalent to over four days of time. This is the deepest X-ray observation yet made on a cluster beyond a distance of about 8 billion light years.

The long observing time allowed the researchers to gather enough X-ray data from Chandra that, when combined with scientific models, provides an accurate weight of the cluster. They determined that the Gioiello Cluster contains a whopping 400 trillion times the mass of the Sun.

Previously, astronomers had found an enormous galaxy cluster, known as "El Gordo," at a distance of 7 billion light years away and a few other large, distant clusters. According to the best current model for how the Universe evolved, there is a low chance of finding clusters as massive as the Gioiello Cluster and El Gordo. The new findings suggest that there might be problems with the theory, and are enticing astronomers to look for other distant and massive clusters.

Image Credit: X-ray: NASA/CXC/INAF/P.Tozzi, et al; Optical: NAOJ/Subaru and ESO/VLT; Infrared: ESA/Herschel
Explanation from: http://chandra.harvard.edu/photo/2014/xdcp004/

April 17, 2017

Global map of Earth at Night

Global map of Earth at Night

NASA scientists are releasing new global maps of Earth at night, providing the clearest yet composite view of the patterns of human settlement across our planet.

Satellite images of Earth at night — often referred to as "night lights" — have been a gee-whiz curiosity for the public and a tool for fundamental research for nearly 25 years. They have provided a broad, beautiful picture, showing how humans have shaped the planet and lit up the darkness. Produced every decade or so, such maps have spawned hundreds of pop-culture uses and dozens of economic, social science and environmental research projects.

But what would happen if night lights imagery could be updated yearly, monthly or even daily? A research team led by Earth scientist Miguel Román of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, plans to find out this year.

In the years since the 2011 launch of the NASA-NOAA Suomi National Polar-orbiting Partnership (NPP) satellite, Román and colleagues have been analyzing night lights data and developing new software and algorithms to make night lights imagery clearer, more accurate and readily available. They are now on the verge of providing daily, high-definition views of Earth at night, and are targeting the release of such data to the science community later this year.

Since colleagues from the National Oceanic and Atmospheric Administration and NASA released a new Earth at night map in 2012, Román and teammates at NASA's Earth Observing Satellite Data and Information System (EOSDIS) have been working to integrate nighttime data into NASA's Global Imagery Browse Services (GIBS) and Worldview mapping tools. Freely available to the science community and the public via the Web, GIBS and Worldview allow users to see natural- and false-color images of Earth within hours of satellite acquisition.

Today they are releasing a new global composite map of night lights as observed in 2016, as well as a revised version of the 2012 map. The NASA group has examined the different ways that light is radiated, scattered and reflected by land, atmospheric and ocean surfaces. The principal challenge in nighttime satellite imaging is accounting for the phases of the moon, which constantly varies the amount of light shining on Earth, though in predictable ways. Likewise, seasonal vegetation, clouds, aerosols, snow and ice cover, and even faint atmospheric emissions (such as airglow and auroras) change the way light is observed in different parts of the world. The new maps were produced with data from all months of each year. The team wrote code that picked the clearest night views each month, ultimately combining moonlight-free and moonlight-corrected data.

​Román and colleagues have been building remote sensing techniques to filter out these sources of extraneous light, gathering a better and more consistent signal of how human-driven patterns and processes are changing. The improved processing moves Suomi NPP closer to its full potential of observing dim light down to the scale of an isolated highway lamp or a fishing boat. The satellite's workhorse instrument is the Visible Infrared Imaging Radiometer Suite (VIIRS), which detects photons of light reflected from Earth's surface and atmosphere in 22 different wavelengths. VIIRS is the first satellite instrument to make quantitative measurements of light emissions and reflections, which allows researchers to distinguish the intensity, types and the sources of night lights over several years.

Suomi NPP observes nearly every location on Earth at roughly 1:30 p.m. and 1:30 a.m. (local time) each day, observing the planet in vertical 3000-kilometer strips from pole to pole. VIIRS includes a special “day-night band,” a low-light sensor that can distinguish night lights with six times better spatial resolution and 250 times better resolution of lighting levels (dynamic range) than previous night-observing satellites. And because Suomi NPP is a civilian science satellite, the data are freely available to scientists within minutes to hours of acquisition.

Armed with more accurate nighttime environmental products, the NASA team is now automating the processing so that users will be able to view nighttime imagery within hours of acquisition. This has the potential to aid short-term weather forecasting and disaster response.

"Thanks to VIIRS, we can now monitor short-term changes caused by disturbances in power delivery, such as conflict, storms, earthquakes and brownouts," said Román. "We can monitor cyclical changes driven by reoccurring human activities such as holiday lighting and seasonal migrations. We can also monitor gradual changes driven by urbanization, out-migration, economic changes, and electrification. The fact that we can track all these different aspects at the heart of what defines a city is simply mind-boggling."

For instance, VIIRS detected power outages in the wake of Hurricane Matthew, a major storm that struck the northeastern Caribbean and the southeastern United States in late September 2016. NASA’s Disasters Response team provided the data to colleagues at the Federal Emergency Management Agency; in the future, NASA, FEMA and the Department of Energy hope to develop power outage maps and integrate the information into recovery efforts by first responders.

The NASA team envisions many other potential uses by research, meteorological and civic groups. For instance, daily nighttime imagery could be used to help monitor unregulated or unreported fishing. It could also contribute to efforts to track sea ice movements and concentrations. Researchers in Puerto Rico intend to use the dataset to reduce light pollution and help protect tropical forests and coastal areas that support fragile ecosystems. And a team at the United Nations has already used night lights data to monitor the effects of war on electric power and the movement of displaced populations in war-torn Syria.

In a separate, long-term project, Román is working with colleagues from around the world to improve global and regional estimates of carbon dioxide emissions. The team at NASA’s Global Modeling and Assimilation Office (GMAO) is combining night lights, urban land use data, and statistical and model projections of anthropogenic emissions in ways that should make estimates of sources much more precise.

Image Credit: NASA Earth Observatory images by Joshua Stevens, using Suomi NPP VIIRS data from Miguel Román, NASA's Goddard Space Flight Center
Explanation from: https://www.nasa.gov/feature/goddard/2017/new-night-lights-maps-open-up-possible-real-time-applications

California's Wildflower Super Bloom

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California, USA