понедельник, 8 октября 2018 г.

HiPOD (30 September 2018): Lovely Sleekness   – This…


HiPOD (30 September 2018): Lovely Sleekness


   – This crescent-shaped dune (called a “barchan dune”) is located within a crater that is to the east of Toro Crater. (280 km above the surface, less than 1 km across)


NASA/JPL/University of Arizona


Bedforms and BedrockIn this Context Camera image in Terra…


Bedforms and Bedrock


In this Context Camera image in Terra Cimmeria, we see a 30-kilometer diameter crater, filled-in with materials that created bedrock, and through subsequent erosion, wind-driven particles.  


There is a ring of exposed light-toned bedrock at the base of the crater wall. This distinctive ring suggests high winds climbing up the crater wall slope may be responsible for the erosion and the extent of bedrock exposure we see. A close-up on the southeastern part of these deposits shows a mound of bedrock with beautiful color contrasts. The variation in color represents diverse minerals in the rock.


There is also a small degraded crater (about 300-meter diameter) to the left of the exposed bedrock. Fine-grained materials trapped inside the crater appear as wind-driven ripples or small dune-forms.


NASA/JPL/University of Arizona


Summit Dunes and Their Sand SourcesThe ultimate origin of the…


Summit Dunes and Their Sand Sources


The ultimate origin of the sediment that forms Martian dunes has long been debated. While sand dunes on Earth are primarily sourced by quartz-bearing components of granitic continental crust, it’s often suggested that sand on Mars derives from eroded volcanic flows or sedimentary deposits, but exact sources are often vague.


This image reveals a unique situation where this small dune field occurs along the summit of the large 1-mile-tall mound near the center of Juventae Chasma. The layered mound slopes are far too steep for dunes to climb, and bedform sand is unlikely to come from purely airborne material. Instead, the mound’s summit displays several dark-toned, mantled deposits that are adjacent to the dunes and appear to be eroding into fans of sandy material.


NASA/JPL/University of Arizona


Tell-Tale Bedrock in Tyrrhena TerraLarge craters, like this…


Tell-Tale Bedrock in Tyrrhena Terra


Large craters, like this 50-kilometer diameter one, can uplift material from below and form a mountain-like central peak. Craters of this size on Mars become unstable as they form and collapse due to gravity. Craters with central peaks and terraced rims are referred to as “complex” craters.


Geologists study these central peaks because the uplifted bedrock was once deep within the Martian crust. A 3D perspective shows heavily-fractured bedrock exposed within the peak, and also dark-toned and fragmental rocks that formed during the impact process.


Sometimes, we observe similar rocks in the crater wall terraces. Some areas of the terrace show dark-toned materials coating and surrounding the white- and green-colored bedrock. This dark-toned rock was the once-molten material that was produced by the tremendous energy generated during the formation of the crater. Similarly, the impact melt material coats and surrounds the higher-standing bedrock of the peak. There are additional exposures of bedrock in the northern wall-terraces of the crater. 


NASA/JPL/University of Arizona


The Velvety Blue Dunes of Melas ChasmaThis color-infrared image…


The Velvety Blue Dunes of Melas Chasma


This color-infrared image shows sand dunes in Melas Chasma, located within the Valles Marineris canyon system. The dark-blue and purple colors indicate coarse-grained sands that are comprised of basalt, an iron and magnesium-rich volcanic rock that formed from cooled lava millions of years ago when volcanism was an active process on Mars.


Migrating sand dunes often lead to the erosion and excavation of underlying material; regions where there are active dune fields are ideal places to search for exposed bedrock. Repeated imaging of dunes may also show changes that provide evidence for active surface processes related to wind patterns and climate. 


NASA/JPL/University of Arizona


HiPOD (5 October 2018): Erosion within Cerberus Fossae   – A…




HiPOD (5 October 2018): Erosion within Cerberus Fossae


   – A Context Camera image shows a small bench in the middle of the Cerberus Fossae at the head of Athabasca Valles. Small cataracts appear on this bench. Do these reflect erosion as water drained back into the subsurface at the conclusion of the flood? (279 km above the surface. Black and white is less than 5 km across; enhanced color is less than 1 km).


NASA/JPL/University of Arizona


HiPOD (6 October 2018): A Mess of Craters   – You can also see a…


HiPOD (6 October 2018): A Mess of Craters


   – You can also see a crater exit breach in the lower-middle-right. Was a result of overflow from the crater? HiRISE was requested to measure depth of exit breach and depth/width of associated flood channels: was this a single catastrophic flood or seasonally repeating flow? (334 km above the surface, less than 5 km across)


NASA/JPL/University of Arizona


HiPOD (7 October 2018): Landforms in Cydonia Region   – This…


HiPOD (7 October 2018): Landforms in Cydonia Region


   – This image was a request for the now canceled-Red Dragon landing on Mars. (300 km above the surface, less than 5 km across.)


NASA/JPL/University of Arizona


HiPOD (8 October 2018): Meanwhile, on Another Planet…   –…



HiPOD (8 October 2018): Meanwhile, on Another Planet…


   – These dark fans are exposed on the lighter-toned surface due to sublimation, and are blown around by the wind. (322 km above the surface. Black and white is less than 5 km across; enhanced color is less than 1 km.)


NASA/JPL/University of Arizona


Clues from Koalas Alongside protein-coding genes, the human…


Clues from Koalas


Alongside protein-coding genes, the human genome contains many non-coding sequences, so-called ’junk DNA’, including an estimated 8% of our DNA derived from retroviruses. These viruses replicate by inserting their DNA into their hosts’ genomes; if inserted into the DNA of germ cells, giving rise to ovules and sperm, they can be passed on to future generations, eventually losing their viral function. Retroviral insertions in our genome are very ancient, but a more recent, ongoing invasion has been discovered in koalas (pictured), allowing us to study this process in action. Research shows that shuffling genetic material during DNA replication, between koala retrovirus (KoRV) and more ancient retroviral elements in the genome, can quickly disable KoRV. Known as recombination, this mechanism is likely to be a key early step towards retroviral integration. As researchers continue to monitor koala retroviruses, these beloved Australian icons may help us piece together our own genome’s history.


Written by Emmanuelle Briolat



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Fireball over Florida caught on dashboard camera

AMS Event #4011-2018 recorded on dashcam by A. Superczynski from Daytona Beach, FL

Over 70 fireball reports from 3 states


The AMS has received over 70 reports so far about of a fireball event seen above Florida on October 6th, 2018 around 10:20pm EDT (October 7th 02:20 Universal Time). The fireball was seen primarily from Florida but was also seen from South Carolina and Georgia.



If you witnessed this event and/or if you have a video or a photo of this event, please

Submit an Official Fireball Report


If you want to learn more about Fireballs: read our Fireball FAQ.



AMS Event #4011-2018 – Witness Location and First Estimated Ground Trajectory

The event has been caught on tape by at least two witnesses that were kind enough to share their videos with the AMS:










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APOD: 2018 October 7 – The Scale of the Universe Interactive

APOD: 2018 October 7 – The Scale of the Universe Interactive


2018 Draconids to closely monitor

It was the Summer comet: 21P/Giacobini-Zinner became visible with a simple pair of binoculars, as it passed perihelion, in September, and reached +7 magnitude. One month later, the comet is fading, but another astronomical may bring it back to the front scene: Draconid meteor shower, associated to meteoroids released from 21P/Giacobini-Zinner nucleus is going to peak on October 8-9. And even if nothing exceptionnal is predicted, perihelion years are sometimes associated to activity outbursts. Stay alerted for the whole activity period!


2011 Draconids meteor outburst photographed by Juan Carlos Casado from Spain. Credit: Juan Carlos Casado
2011 Draconids meteor outburst photographed by Juan Carlos Casado from Spain. Credit: Juan Carlos Casado

In 1998 & 1999, 2005, 2011 & 2012, near the last perihelion dates for 21P/Giacobini-Zinner, Draconid outburst were recorded and observed. During the last return of the comet, a meteor outburst with ZHR reaching 300 was predicted and observed (in 2011). But one year later, in 2012, nothing was expected but another outburst, with similar activity levels, was recorded with radio/radar methods. This is why meteor observers shoudl keep alerted this year, even if nothing is predicted.


Comet 21PGiacobini-Zinner photographed from the French Pyrenees, with the 1 m-diameter telescope of the Pic du Midi, 3 days before the expected Draconid maximum of activity. Credit: François Colas
Comet 21P/Giacobini-Zinner photographed from the French Pyrenees, with the 1 m-diameter telescope of the Pic du Midi, 3 days before the expected Draconid maximum of activity. Credit: François Colas

The “node crossing”, which corresponds to the “classical” maximum, should be reached between October 8, 23h UT and October 9, 01h UT, with a maximum probability at 00h 10min UT on Oct 9. Regarding the potential activity outbursts, dates and times spreads over a longer period. Considering past outbursts, they could happen this year between October 8, 15h 30min UT (considering 2011 outburst) and October 9, 08h 50min UT (considering 1999 outburst). This is why observers should try to observe and monitor the shower as much as they can, because no one can predict when the outburst is more likely to occur.


Except for a potential slight activity enhancement when the Earth will pass close to a dust trail released in 1953, but which has been disturbed in 1985, when our planet came close to it. Rates are difficult to estimate, but times are quite coherent with the different models. Mikiya Sato predicts a ZHR ranging from 20 to 50 on Oct 9, 00h 14min UT, whereas Jérémie Vaubaillon predicts a ZHR~15 on Oct 8, 23h 31min UT, very close from Mikhail Maslov model, which gives a ZHR ~ 10-15 on Oct 8, 23h 34min UT.


Position of Draconids radiant: located in the head of Draco, it's circumpolar for most of Northern hemisphere observing sites. Credit: IMO
Position of Draconids radiant: located in the head of Draco, it’s circumpolar for most of Northern hemisphere observing sites. Credit: IMO

Draconids radiant is located in the head of Draco, and is thus circumpolar for many observing sites in the Northern hemisphere, even if it’s best located during the beginning of the night. Draconids are slow meteors: the meteoroid reentry speed is only 20 km/s. They will appear slow moving, even if they are located far from the horizon and radiant. But this slow apparent speed is a good indicator to disregard all sporadic meteor that would accidentally align with the radiant and false activity rates deduced from observations, especially if they are low.


Good luck and clear skies to all!


 


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When Is a Nova Not a ‘Nova’? When a White Dwarf and a Brown Dwarf Collide



ALMA image of CK Vulpeculae. New research indicates that this hourglass-like object is the result of the collision of a brown dwarf and a white dwarf. Credit: ALMA (ESO/NAOJ/NRAO)/S. P. S. Eyres.  Hi-res image




Johannes Hevelius, Figure 1 of ‘An extract of a letter of M. Hevelius, written to the publisher from Dantzick, August 17/27 1670, published in the Philosophical Transactions of the Royal Society, 1670, vol. 5, number 65, pp. 2087-2091; doi:10.1098/rstl.1670.0062 2053-9207. Hi-res image

In July of 1670, observers on Earth witnessed a “new star,” or nova, in the constellation Cygnus. Where previously there was dark sky, a bright pinprick of light appeared, faded, reappeared, and then disappeared entirely from view. Modern astronomers studying the remains of this cosmic event initially thought it heralded the merging of two main sequence stars – stars on the same evolutionary path as our Sun.


New observations with the Atacama Large Millimeter/submillimeter Array (ALMA) point to a more intriguing explanation. By studying the debris from this explosion, which takes the form of dual rings of dust and gas resembling an hourglass with a compact central object, the researchers concluded that a brown dwarf (a so-called failed star without the mass to sustain nuclear fusion) merged with a white dwarf (the elderly, cooling remains of a Sun-like star).


“It now seems what was observed centuries ago was not what we would today describe as a classic ‘nova.’ Instead, it was the merger of two stellar objects, a white dwarf and a brown dwarf. When these two objects collided, they spilled out a cocktail of molecules and unusual isotopes, which gave us new insights into the nature of this object,” said Sumner Starrfield, an astronomer at Arizona State University and co-author on a paper appearing in the Monthly Notices of the Royal Astronomical Society.


According to the researchers, the white dwarf would have been about ten times more massive than the brown dwarf, though much smaller in size. As the brown dwarf spiraled inward, intense tidal forces exerted by the white dwarf would have ripped it apart. “This is the first time such an event has been conclusively identified,” remarked Starrfield.


Since most star systems in the Milky Way are binary, stellar collisions are not that rare, the astronomers note. The new ALMA observations reveal new details about the 1670 event. By studying the light from two, more-distant stars as it shines through the dusty remains of the merger, the researchers were able to detect the telltale signature of the element lithium, which is easily destroyed in the interior of a main sequence star, but not inside a brown dwarf.


“The presence of lithium, together with unusual isotopic ratios of the elements carbon, nitrogen, and oxygen point to material from a brown dwarf star being dumped on the surface of a white dwarf. The thermonuclear ‘burning’ and an eruption of this material resulted in the hourglass we see today,” said Stewart Eyres, Deputy Dean of the Faculty of Computing, Engineering and Science at the University of South Wales and lead author on the paper.


Intriguingly, the hourglass is also rich in organic molecules such as formaldehyde (H2CO) and formamide (NH2CHO), which is derived from formic acid. These molecules would not survive in an environment undergoing nuclear fusion and must have been produced in the debris from the explosion. This lends further support to the conclusion that a brown dwarf met its demise in a star-on-star collision with a white dwarf.


The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Contact:

Charles Blue, 
Public Information Officer
(434) 296-0314; 
cblue@nrao.edu



The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).



ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.


Reference:


“ALMA Reveals the Aftermath of a White Dwarf—Brown Dwarf Merger in CK Vulpeculae,” Steward Eyres, University of Central Lancashire; Aneurin Evans, Keele University; Albert Zijlstra, Adam Avison, University of Manchester; Robert Gehrz, Charles Woodward, University of Minnesota; Marcin Hajduk, University of Warmia and Mazury; Sumner Starrfield, Arizona State University; Shazrene Mohamed, South African Astronomical Observatory; and R. Mark Wagner, The Ohio State University; Monthly Notices of the Royal Astronomical Society [Preprint: https://arxiv.org/abs/1809.05849]




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2018 October 8 Comet 12P Between Rosette and Cone Nebulas Image…


2018 October 8


Comet 12P Between Rosette and Cone Nebulas
Image Credit & Copyright: Fritz Helmut Hemmerich


Explanation: Small bits of this greenish-gray comet are expected to streak across Earth’s atmosphere tonight. Specifically, debris from the eroding nucleus of Comet 21P / Giacobini-Zinner, pictured, causes the annual Draconids meteor shower, which peaks this evening. Draconid meteors are easy to enjoy this year because meteor rates will likely peak soon after sunset with the Moon’s glare nearly absent. Patience may be needed, though, as last month’s passing of 21P near the Earth’s orbit is not expected to increase the Draconids’ normal meteor rate this year of (only) a few meteors per hour. Then again, meteor rates are notoriously hard to predict, and the Draconids were quite impressive in 1933, 1946, and 2011. Featured, Comet 21P gracefully posed between the Rosette (upper left) and Cone (lower right) nebulas two weeks ago before heading back out to near the orbit of Jupiter, to return again in about six and a half years.


∞ Source: apod.nasa.gov/apod/ap181008.html


APOD: 2018 October 7 – The Scale of the Universe Interactive

APOD: 2018 October 7 – The Scale of the Universe Interactive


Thornborough Henge at Sunset, Thornborough, Yorkshire, 7.10.18.Potentially one of the...






Thornborough Henge at Sunset, Thornborough, Yorkshire, 7.10.18.


Potentially one of the largest prehistoric sites in the UK, this series of massive henges stretches beyond the naked eye. Photographed here is the middle henge ring in the series of three just as the sun made its slow descent.


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