Based on computer simulations, Astrophysicists at the University of Bern conclude that the comet Chury did not obtain its duck-like form during the formation of our solar system 4.5 billion years ago. Although it does contain primordial material, they are able to show that the comet in its present form is hardly more than a billion years old. ...
How primordial is the structure of comet 67P/C-G? Combined collisional
and dynamical models suggest a late formation - M. Jutzi et al
[img3="This image showcases changes identified in high-resolution images of Comet 67P/Churyumov-Gerasimenko during more than two years of monitoring by ESA's Rosetta spacecraft. Credits: Top center images: ESA/Rosetta/NAVCAM, CC BY-SA 3.0 IGO; all others: ESA/Rosetta/MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA"]https://www.jpl.nasa.gov/spaceimages/im ... _hires.jpg[/img3][hr][/hr]
Images returned from the European Space Agency's Rosetta mission indicate that during its most recent trip through the inner solar system, the surface of comet 67P/Churyumov-Gerasimenko was a very active place - full of growing fractures, collapsing cliffs and massive rolling boulders. Moving material buried some features on the comet's surface while exhuming others. ...
"As comets approach the sun, they go into overdrive and exhibit spectacular changes on their surface," said Ramy El-Maarry ... "This is something we were not able to really appreciate before the Rosetta mission, which gave us the chance to look at a comet in ultra-high resolution for more than two years."
Most comets orbit our sun in highly elliptical orbits that cause them to spend most of their time in the extremely cold outer solar system. When a comet approaches the inner solar system, the sun begins to warm the ice on and near the comet's surface. When the ice warms enough it can rapidly sublimate (turn directly from the solid to the vapor state). This sublimation process can occur with variable degrees of intensity and time-scales and cause the surface to change rapidly. Between August 2014 and September 2016, Rosetta orbited comet 67P during the comet's swing through the inner-solar system. ...
<<Toy company Hasbro has replaced the boot, the thimble and the wheelbarrow with a Tyrannosaurus rex, a penguin and a rubber ducky in the latest version of its popular board game Monopoly.
More than 4.3 million voters from 146 countries weighed in on which tokens they wanted to see in future versions of the property-acquisition game, which is based on the real-life streets of Atlantic City. Hasbro announced the winners on Friday morning.
The existing scottish terrier, battleship, racing car, top hat and cat tokens will carry on.>>
[img3="A plume of dust from comet 67P/Churyumov-Gerasimenko, seen by the OSIRIS wide-angle camera on ESA’s Rosetta spacecraft on 3 July 2016. The plume originates from the Imhotep region. Credit: ESA/Rosetta/MPS for OSIRIS Team
MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA"]http://www.mps.mpg.de/5120076/standard_ ... 014113.jpg[/img3][hr][/hr]
When comet 67P emitted a jet of dust into space in July 2016, five instruments from the Rosetta spacecraft were able to record the event. The scientific evaluation is now available.
The impressive jets of dust that comets emit into space during their journey around the Sun are not driven solely by the sublimation of frozen water. In some cases further processes augment the outbreaks. Possible scenarios include the release of pressurized gas stored below the surface or the conversion of one kind of frozen water into an energetically more favorable one. This is the result of a study published by a team of scientists headed by the Max Planck Institute for Solar System Research (MPS) in Germany analyzing a dust jet from Rosetta’s comet 67P/Chruyumov-Gerasimenko that occurred last year. The analysis, which has now been published in the journal Monthly Notices of the Royal Astronomical Society, compiles measurements of five instruments from ESA’s spacecraft Rosetta and was for the first time able to combine observations of the released dust as well as of the surface changes.
When the Sun rose over the Imhotep region of Rosetta’s comet on July 3, 2016, everything was just right: As the surface warmed and began to emit dust into space, Rosetta's trajectory led the probe right through the cloud. At the same time, the view of the scientific camera system OSIRIS coincidentally focused precisely on the surface region of the comet from which the fountain originated. A total of five instruments on board the probe were able to document the outburst in the following hours. ...
Evidence of sub-surface energy storage in comet 67P from the outburst of 2016 July 03 - J. Agarwal et al
Monthly Notices of the RAS: Supplement 469(S2):s606 (July 2017) DOI: 10.1093/mnras/stx2386
RAS: Comet Mission Reveals "Missing Link" in our Understanding of Planet Formation
The missing link in our understanding of planet formation has been revealed by the first ever spacecraft to orbit and land on a comet, say German scientists. The study is published in a recent edition of the journal Monthly Notices of the Royal Astronmical Society.
Based on the results of the Rosetta mission, Blum and colleagues conclude that comet 67P is composed of millimetre-sized dust pebbles. It is assumed that the pebbles inside the comet consist of a mixture of dust and ice (light blue spheres in the image) and only the uppermost layers, which are exposed to direct sunlight, do not contain ice (dark grey spheres).
A research team led by Jürgen Blum (Technische Universität Braunschweig, Germany) have analysed data from the historicRosetta mission to uncover how comet 67P/Churyumov-Gerasimenko, or "Chury" for short, came into existence more than four and a half billion years ago.
Understanding the evolution of our solar system and its planets was one of the main objectives of the Rosetta mission to comet 67P/Churyumov-Gerasimenko. For Jürgen Blum and his international team it was worth it, because results from the various Rosetta and Philae instruments have revealed that only one out of many proposed models can explain their observations. Comet 67P consists of 'dust pebbles' ranging between millimetres and centimetres in size.
Professor Blum explains the implications of the team's observations "Our results show that only a single model for the formation of larger solid bodies in the young solar system may be considered for Chury. According to this formation model, 'dust pebbles' are concentrated so strongly by an instability in the solar nebula that their joint gravitational force ultimately leads to a collapse."
This process forms the missing link between the well-established formation of 'dust pebbles' ('planetary building blocks' formed in the solar nebula by sticking collisions between dust and ice particles) and the gravitational accretion of planetesimals into planets, which scientists have pondered over for years.
"Although it sounds very dramatic" Blum continues, "it's actually a gentle process in which the dust agglomerates are not destroyed, but are combined into a larger body with an even greater gravitational attraction - the accumulation of the dust agglomerates into a coherent body is virtually the birth of the comet." Due to the relatively small mass of comet 67P, the pebbles survived intact until today, allowing scientists to confirm the hypothesis for the first time.
In fact, the pebble-collapse formation model can explain many observed properties of comet 67P, for instance its high porosity and how much gas is escaping from inside. "Now all phases in the planet-formation model have been established", concludes Blum.
Evidence for the formation of comet 67P/Churyumov-Gerasimenko through gravitational collapse of a bound clump of pebbles
Jürgen Blum et al
For the first time, researchers from the COSIMA team present a quantitative analysis of which chemical elements make up comet 67P/Churyumov-Gerasimenko.
The dust that comet 67P/Churyumov-Gerasimenko emits into space consists to about one half of organic molecules. The dust belongs to the most pristine and carbon-rich material known in our solar system and has hardly changed since its birth. These results of the COSIMA team are published today in the journal Monthly Notices of the Royal Astronomical Society. COSIMA is an instrument onboard the Rosetta spacecraft, which investigated comet 67P/Churyumov-Gerasimenko from August 2014 to September 2016. In their current study, the involved researchers including scientists from the Max Planck Institute for Solar System Research (MPS) analyze as comprehensively as ever before, what chemical elements constitute cometary dust.
Carbon-Rich Dust in Comet 67P/Churyumov-Gerasimenko Measured by COSIMA/Rosetta - Anaïs Bardyn et al
All high-resolution images and the underpinning data from Rosetta's pioneering mission at Comet 67P/Churyumov-Gerasimenko are now available in ESA's archives, with the last release including the iconic images of finding lander Philae, and Rosetta's final descent to the comet's surface.
A new study reveals that, contrary to first impressions, Rosetta did detect signs of an infant bow shock at the comet it explored for two years – the first ever seen forming anywhere in the Solar System.
From 2014 to 2016, ESA's Rosetta spacecraft studied Comet 67P/Churyumov-Gerasimenko and its surroundings from near and far. It flew directly through the 'bow shock' several times both before and after the comet reached its closest point to the Sun along its orbit, providing a unique opportunity to gather in situ measurements of this intriguing patch of space. ...
Rosetta looked for signs of such a feature over its two-year mission, and ventured over 1500 km away from 67P’s centre on the hunt for large-scale boundaries around the comet – but apparently found nothing. ...
“However, it seems that the spacecraft actually did find a bow shock, but that it was in its infancy. In a new analysis of the data, we eventually spotted it around 50 times closer to the comet’s nucleus than anticipated in the case of 67P. It also moved in ways we didn’t expect, which is why we initially missed it.”
On 7 March 2015, when the comet was over twice as far from the Sun as the Earth and heading inwards towards our star, Rosetta data showed signs of a bow shock beginning to form. The same indicators were present on its way back out from the Sun, on 24 February 2016. ...
The Infant Bow Shock: A New Frontier at a Weak Activity Comet ~ Herbert Gunell et al
Feeling stressed? You’re not alone. ESA’s Rosetta mission has revealed that geological stress arising from the shape of Comet 67P/Churyumov–Gerasimenko has been a key process in sculpting the comet's surface and interior following its formation.
Small, icy comets with two distinct lobes seem to be commonplace in the Solar System, with one possible mode of formation a slow collision of two primordial objects in the early stages of formation some 4.5 billion years ago. A new study using data collected by Rosetta during its two years at Comet 67P/C-G has illuminated the mechanisms that contributed to shaping the comet over the following billions of years.
The researchers used stress modelling and three-dimensional analyses of images taken by Rosetta’s high resolution OSIRIS camera to probe the comet’s surface and interior.
“We found networks of faults and fractures penetrating 500 metres underground, and stretching out for hundreds of metres,” says lead author Christophe Matonti of Aix-Marseille University, France. “These geological features were created by shear stress, a mechanical force often seen at play in earthquakes or glaciers on Earth and other terrestrial planets, when two bodies or blocks push and move along one another in different directions. This is hugely exciting: it reveals much about the comet’s shape, internal structure, and how it has changed and evolved over time.” ...
Bilobate Comet Morphology and Internal Structure Controlled by Shear Deformation ~ C. Matonti et al
http://www.esa.int/Our_Activities/Space_Science/Rosetta/Rosetta_s_comet_sculpted_by_stress wrote:
“We think this effect originally came about because of the comet’s rotation combined with its initial asymmetric shape. A torque formed where the neck and ‘head’ meet as these protruding elements twist around the comet’s centre of gravity.” The observations suggest that the shear stress acted globally over the comet and, crucially, around its neck. The fact that fractures could propagate so deeply into 67P/C-G also confirms that the material making up the interior of the comet is brittle, something that was previously unclear.
"None of our observations can be explained by thermal processes,” adds co-author Nick Attree of the University of Stirling, UK. “They only make sense when we consider a shear stress acting over the entire comet and especially around its neck, deforming and damaging and fracturing it over billions of years.” The new study indicates that, even at large distances from the Sun, shear stress would then act over a timescale of billions of years following formation, while sublimation erosion takes over on shorter million-year timescales to continue shaping the comet’s structure – especially in the neck region that was already weakened by shear stress.
Excitingly, NASA’s New Horizons probe recently returned images from its flyby of Ultima Thule, a trans-Neptunian object located in the Kuiper belt, a reservoir of comets and other minor bodies at the outskirts of the Solar System. The data revealed that this object also has a dual-lobed shape, even though somewhat flattened with respect to Rosetta’s comet. “The similarities in shape are promising, but the same stress structures don’t seem to be apparent in Ultima Thule,” comments Christophe. As more detailed images are returned and analysed, time will tell if it has experienced a similar history to 67P/C-G or not.
“Comets are crucial tools for learning more about the formation and evolution of the Solar System,” says Matt Taylor, ESA’s Rosetta Project Scientist. “We’ve only explored a handful of comets with spacecraft, and 67P is by far the one we’ve seen in most detail. Rosetta is revealing so much about these mysterious icy visitors and with the latest result we can study the outer edges and earliest days of the Solar System in a way we’ve never been able to do before.”>>
The OSIRIS Image Viewer makes all images of Rosetta’s comet 67P taken by the scientific camera system OSIRIS easily accessible on the internet.
Between 2014 and 2016, the scientific camera system OSIRIS onboard ESA’s Rosetta spacecraft captured almost 70000 images of comet 67P/Churyumov-Gerasimenko. They not only document the most extensive and demanding comet mission to date, but also show the duck-shaped body in all its facets. In a joint project with the Department of Information and Communication at Flensburg University of Applied Sciences, the Max Planck Institute for Solar System Research (MPS), head of the OSIRIS team, has now published all of these images. The OSIRIS Image Viewer is suited to the needs of both laymen and expert and offers quick and easy access to one of the greatest scientific treasures of recent years. ...
Under the leadership of astrophysicist Kathrin Altwegg, Bernese researchers have found an explanation for why very little nitrogen could previously be accounted for in the nebulous covering of comets: the building block for life predominantly occurs in the form of ammonium salts, the occurrence of which could not previously be measured. The salts may be a further indication that comet impacts may have made life on Earth possible in the first place.
More than 30 years ago, the European comet mission Giotto flew past Halley’s comet. The Bernese ion mass spectrometer IMS, led by Prof. em. Hans Balsiger, was on board. A key finding from the measurements taken by this instrument was that there appeared to be a lack of nitrogen in Halley’s coma – the nebulous covering of comets which forms when a comet passes close to the sun. Although nitrogen (N) was discovered in the form of ammonia (NH3) and hydrocyanic acid (HCN), the incidence was far removed from the expected cosmic incidence.
More than 30 years later, researchers have solved this mystery thanks to a happy accident. This is a result of the analysis of data from the Bernese mass spectrometer ROSINA, which collected data on the comet 67P/Churyumov-Gerasimenko, called Chury for short, on board the ESA space probe Rosetta ...
Evidence of Ammonium Salts in Comet 67P as Explanation
for the Nitrogen Depletion in Cometary Comae ~ K. Altwegg et al
<<In animals, the main excretory products are carbon dioxide, ammonia (in ammoniotelics), urea (in ureotelics), uric acid (in uricotelics), guanine (in Arachnida) and creatine.
Birds excrete their nitrogenous wastes as uric acid in the form of a paste. Although this process is metabolically more expensive, it allows more efficient water retention and it can be stored more easily in the egg. Many avian species, especially seabirds, can also excrete salt via specialized nasal salt glands, the saline solution leaving through nostrils in the beak.
Aquatic animals usually excrete ammonia directly into the external environment, as this compound has high solubility and there is ample water available for dilution. In terrestrial animals ammonia-like compounds are converted into other nitrogenous materials as there is less water in the environment and ammonia itself is toxic.In insects, a system involving Malpighian tubules is utilized to excrete metabolic waste. Metabolic waste diffuses or is actively transported into the tubule, which transports the wastes to the intestines. The metabolic waste is then released from the body along with fecal matter.>>
Bern: Puzzle About Nitrogen Solved Thanks to Cometary Analogues
One of the basic building blocks of life is nitrogen. An international consortium was able to detect ammonium salt containing nitrogen on the cometary surface of Chury thanks to a method using analogues for comet material. The method on which the study on the detection of ammonium salt is based was developed at the University of Bern.
Comets and asteroids are objects in our solar system that have not developed much since the planets were formed. As a result, they are in a sense the archives of the solar system, and determining their composition could also contribute to a better understanding of the formation of the planets.
One way to determine the composition of asteroids and comets is to study the sunlight reflected by them, since the materials on their surface absorb sunlight at certain wavelengths. We talk about a comet's spectrum, which has certain absorption features. VIRTIS (Visible, InfraRed and Thermal Imaging Spectrometer) on board the European Space Agency's (ESA) Rosetta space probe mapped the surface of comet 67P/Churyumov-Gerasimenko, known as Chury for short, from August 2014 to May 2015. The data gathered by VIRTIS showed that the cometary surface is uniform almost everywhere in terms of composition: The surface is very dark and slightly red in color, because of a mixture of complex, carbonaceous compounds and opaque minerals. However, the exact nature of the compounds responsible for the measured absorption features on Chury has been difficult to establish until now. ...
Ammonium Salts Are a Reservoir of Nitrogen on a Cometary
Nucleus and Possibly on Some Asteroids ~ Olivier Poch et al
Data from Southwest Research Institute-led instruments aboard ESA’s Rosetta spacecraft have helped reveal auroral emissions in the far ultraviolet around a comet for the first time.
At Earth, auroras are formed when charged particles from the Sun follow our planet’s magnetic field lines to the north and south poles. There, solar particles strike atoms and molecules in Earth’s atmosphere, creating shimmering curtains of colorful light in high-latitude skies. Similar phenomena have been seen at various planets and moons in our solar system and even around a distant star. SwRI’s instruments, the Alice far-ultraviolet (FUV) spectrograph and the Ion and Electron Sensor (IES), aided in detecting these novel phenomena at comet 67P/Churyumov-Gerasimenko (67P/C-G).
“Charged particles from the Sun streaming towards the comet in the solar wind interact with the gas surrounding the comet’s icy, dusty nucleus and create the auroras,” said SwRI Vice President Dr. Jim Burch who leads IES. “The IES instrument detected the electrons that caused the aurora.”
The envelope of gas around 67P/C-G, called the “coma,” becomes excited by the solar particles and glows in ultraviolet light, an interaction detected by the Alice FUV instrument.
“Initially, we thought the ultraviolet emissions at comet 67P were phenomena known as ‘dayglow,’ a process caused by solar photons interacting with cometary gas,” said SwRI’s Dr. Joel Parker who leads the Alice spectrograph. “We were amazed to discover that the UV emissions are aurora, driven not by photons, but by electrons in the solar wind that break apart water and other molecules in the coma and have been accelerated in the comet’s nearby environment. The resulting excited atoms make this distinctive light.” ...
