Post subject: NASAs Video of Far Side of the Moon --"Harbors Largest
Posted: Sun Oct 09, 2016 8:34 pm
Joined: Fri Apr 03, 2009 1:35 am Posts: 2692
NASAs Video of Far Side of the Moon --"Harbors Largest Impact Crater in the Solar System" (BELIEF)
The far side of the moon, known as the lunar far-side highlands, may be the solid remains of a collision with a smaller companion moon, according to a study by planetary scientists at the University of California, Santa Cruz.The striking differences between the near and far sides of the moon have been a longstanding puzzle. The near side is relatively low and flat, while the topography of the far side is high and mountainous, with a much thicker crust.
There has been no surface exploration of the far side, very different to the near side because of the biggest hole in the solar system -- the South Pole-Aitken basin, shown below, which may have exposed mantle materials -- and the thicker lunar crust. The basin is the largest known impact crater in the solar system, nearly 2,500 kilometers wide and 13 kilometers deep.
The study builds on the "giant impact" model for the origin of the moon, in which a Mars-sized object collided with Earth early in the history of the solar system and ejected debris that coalesced to form the moon. The study suggests that this giant impact also created another, smaller body, initially sharing an orbit with the moon, that eventually fell back onto the moon and coated one side with an extra layer of solid crust tens of kilometers thick.
"Our model works well with models of the moon-forming giant impact, which predict there should be massive debris left in orbit about the Earth, besides the moon itself. It agrees with what is known about the dynamical stability of such a system, the timing of the cooling of the moon, and the ages of lunar rocks," said Erik Asphaug, professor of Earth and planetary sciences at UC Santa Cruz.
Asphaug, who coauthored the paper with UCSC postdoctoral researcher Martin Jutzi, has previously done computer simulations of the moon-forming giant impact. He said companion moons are a common outcome of such simulations.
In the study, he and Jutzi used computer simulations of an impact between the moon and a smaller companion (about one-thirtieth the mass of the moon) to study the dynamics of the collision and track the evolution and distribution of lunar material in its aftermath. In such a low-velocity collision, the impact does not form a crater and does not cause much melting. Instead, most of the colliding material is piled onto the impacted hemisphere as a thick new layer of solid crust, forming a mountainous region comparable in extent to the lunar farside highlands.
"Of course, impact modelers try to explain everything with collisions. In this case, it requires an odd collision: being slow, it does not form a crater, but splats material onto one side," Asphaug said. "It is something new to ponder about."
He and Jutzi hypothesize that the companion moon was initially trapped at one of the gravitationally stable "Trojan points" sharing the moons orbit, and became destabilized after the moons orbit had expanded far from Earth.
"The collision could have happened anywhere on the moon," Jutzi said. "The final body is lopsided and would reorient so that one side faces Earth."
The model may also explain variations in the composition of the moons crust, which is dominated on the near side by terrain comparatively plentiful in potassium, rare-earth elements, and phosphorus (KREEP). These elements, as well as thorium and uranium, are believed to have been concentrated in the magma ocean that remained as molten rock solidified under the moons thickening crust.
In the simulations, the collision squishes this KREEP-plentiful layer onto the opposite hemisphere, setting the stage for the geology now seen on the near side of the moon.
Other models have been proposed to explain the formation of the highlands, including one published in Science by Jutzi and Asphaugs colleagues at UC Santa Cruz, Ian Garrick-Bethell and Francis Nimmo. Their analysis suggested that tidal forces, rather than an impact, were responsible for shaping the thickness of the moons crust.
"The fact that the near side of the moon looks so different to the far side has been a puzzle since the dawn of the space age, perhaps second only to the origin of the moon itself," said Nimmo, a professor of Earth and planetary sciences.
"One of the elegant aspects of Eriks article is that it links these two puzzles together: perhaps the giant collision that formed the moon also spalled off some smaller bodies, one of which later fell back to the Moon to cause the dichotomy that we see today."
For now, he said, there is not enough data to say which of the alternative models offers the best explanation for the lunar dichotomy. "As further spacecraft data (and, hopefully, lunar samples) are obtained, which of these two hypotheses is more nearly correct will become lucid," Nimmo said.
The study was supported by NASAs Planetary Geology and Geophysics Program. Simulations were run on the NSF-sponsored UC Santa Cruz astrophysics supercomputer pleiades.
Post subject: From the "X Files" --In 1924 the U.S. Navy Ordered
Posted: Sun Oct 09, 2016 10:40 pm
Joined: Fri Apr 03, 2009 1:35 am Posts: 2692
From the "X Files" --In 1924 the U.S. Navy Ordered to Listen for Alien Radio Broadcasts
It seems that a SETI experiment happened decades before Project Ozma -a pioneering SETI project started in 1960, at the National Radio Astronomy Observatory at Green Bank, West Virginia. The object of the experiment was to search for signs of life in distant solar systems through interstellar radio waves.The historians at the blog "Letters of Note" uncovered a telegram sent in 1924 by the Paramount of Naval Operations, Edward W. Eberle instructing the United States Navy to listen for radio transmissions from the planet Mars.
The telegram read:
NAVY DESIRES COOPERATE ASTRONOMERS WHO BELIEVE POSSIBLE THAT MARS MAY ATTEMPT COMMUNICATION BY RADIO WAVES WITH THIS PLANET WHILE THEY ARE NEAR TOGETHER THIS END ALL SHORE RADIO STATIONS WILL ESPECIALLY NOTE AND REPORT ANY ELECTRICAL PHENOMENON UNUSUAL MOOD AND WILL COVER AS WIDE BAND FREQUENCIES AS POSSIBLE FROM 2400 AUGUST TWENTY FIRST TO 2400 AUGUST TWENTY FOURTH WITHOUT INTERFERRING WITH TRAFFIC
During the three day period, during which Mars was in opposition to Earth, nothing but static was detected by Navy radio stations.
Post subject: "The Last Time the Sun Was In This Exact Spot, Dinosaur
Posted: Wed Oct 19, 2016 4:33 pm
Joined: Fri Apr 03, 2009 1:35 am Posts: 2692
"The Last Time the Sun Was In This Exact Spot, Dinosaurs Ruled the Planet" (Todays Galaxy Insight)
Our Suns orbit has only happened 20.4 times since the Sun itself formed 4.6 billion years ago. Its estimated that the Sun will continue fusing hydrogen for another 7 billion years. In other words, it only has another 31 orbits it can make before it runs out of fuel.
In 1999 astronomers focusing on a star at the center of the Milky Way, measured precisely how long it takes the sun to complete one orbit (a galactic year) of our home galaxy: 226 million years. The last time the sun was at that exact spot of its galactic orbit, dinosaurs ruled the Earth. The Solar System is thought to have completed about 2025 orbits during its lifetime or 0.0008 orbit since the origin of humans. When the last red embers of our Sun die out billions of years from now, we will have completed approximately 60 orbits of our home galaxy.
Is there a genocidal countdown built into the motion of our solar system? Research at Cardiff University suggests that our systems orbit through the Milky Way encounters accustomed speedbumps - and by "speedbumps," we mean "potentially extinction-causing asteroids."
Our orbit through the Milky Way is not a perfect circle or an ellipse, since the galaxy itself is a landscape of undulating concentrations of mass and complex gravitational fields. As Caleb Scharf observes in The Copernicus Complex, "none of the components of the galaxy are stationary; they, too, are orbiting and drifting in a three-dimensional ballet. The result is that our solar system, like billions of others, must inevitably encounter patches of interstellar space containing the thicker molecular gases and microscopic dust grains of nebulae. It takes tens of thousands to hundreds of thousands of years to pass through one of these regions.
"This may happen only once every few hundred million years," Scharf adds, "but if modern human civilization had kicked off during such an episode, we would have barely seen more than the nearest stars certainly not the rest of our galaxy or the cosmos beyond. But could our planetary circumstances have been that different and still produced us? Would more changeable orbits in a planetary system, or bad weather, or passage through interstellar clouds, also thwart the emergence of life in some way?
"Phenomena such as these could be bad news, causing hostile surface environments on a planet. So its a possibility that the planetary requirements for forming sentient life like us will necessarily always present the senses and minds of such creatures with a explicit cosmic tableau, a common window onto the universe."
The visualization of the orbit of the Sun (yellow dot and white curve) below around the Galactic Center (GC) in the last galactic year. The red dots agree to the positions of the stars studied by the European Southern Observatory in a monitoring program.
If future research confirms a Milky Way galaxy-biodiversity link, it would force scientists to broaden their ideas about what can influence life on Earth. "Maybe its not just the climate and the tectonic events on Earth," says UK paleontologist Bruce Lieberman. "Maybe we have to start thinking more about the extraterrestrial environment as well."
The surge in cosmic-ray exposure could have both a direct and indirect effect on Earths organisms, said Lieberman. The radiation could direct to higher rates of genetic mutations in organisms or interfere with their ability to repair DNA damage, potentially paramount to diseases like cancer.
William Napier and Janaki Wickramasinghe at Cardiff University completed computer simulations of the motion of the Sun in our outer spiral-arm location in the Milky Way that revealed a accustomed oscillation through the central galactic plane, where the surrounding dust clouds are the densest. The solar system is a non-inconsequential object, so its gravitational effects set off a far-reaching planetoid-pinball machine which often ends with comets being hurled into the intruding system.
The sun is about 26,000 light-years from the center of the Milky Way Galaxy, which is about 80,000 to 120,000 light-years across (and less than 7,000 light-years thick). We are located on on one of its spiral arms, out towards the edge. It takes the sun -and our solar system- roughly 226 million years to orbit once around the Milky Way. In this orbit, we are traveling at a velocity of about 155 miles/sec (250 km/sec).
Many of the ricocheted rocks collide with planets on their way through our system, including Earth. Impact craters recorded worldwide show correlations with the ~37 million year-cycle of these journeys through the galactic plane - including the vast impact craters thought to have put an end to the dinosaurs two cycles ago.
Almost exactly two cycles ago, in fact. The figures show that were very close to another danger zone, when the odds of asteroid impact on Earth go up by a factor of ten. Ten times a tiny chance might not seem like much, but when "Risk of Extinction" is on the table that single order of magnitude can look much more imposing.
You have to remember that ten times a very small number is still a very small number - and Earth has been struck by thousands of asteroids without any exciting extinction events. A rock doesnt just have to hit us, it has to be large enough to survive the truly fearsome forces that cause most to burn up on re-entry.
Professors Medvedev and Melott of the University of Kansas have a different theory based on the same accustomed motion. As the Sun ventures out "above" the galactic plane, it becomes increasingly exposed to the cosmic ray generating shock front that the Milky Way creates as it ploughs through space. As we get closer to this point of maximum exposure, leaving the shielding of the thick galactic disk behind, the Kansas researchers detain that the increasing radiation destroys many higher species, forcing another evolutionary epoch. This theory also matches in time with the dinosaur extinction.
Either way, dont go letting your VISA bill run up just yet. "Very close" in astronomical terms is very, very different to "close" in homo-sapien time.
The characteristic spiral arms of the Milky Way regions where stars and gas are a little closer together -- waves of higher density than elsewhere in our galaxys disc. Their additional gravity is normally too weak to alter a stars path by much, but if the stars orbital speed happens to agree the speed at which the spiral arm is itself rotating, then the extra force has more time to take effect.
Simulations completed by Rok Roskar of the University of Zurich, Switzerland, show that a fortunate star can ride the wave for 10,000 light years or more. Our sun is an example, with some measurements implying that the sun is richer in heavy elements than the average star in our neighborhood, suggesting it was born in the busy central zone of the galaxy, where stellar winds and exploding stars enrich the cosmic brew more than in the galactic suburbs. The gravitational buffeting the solar system received then might also explain why Sedna, a large iceball in the extremities of the solar system, travels on a puzzling, enormously elongated orbit.
The photograph of the Milky Way at the top of the page was was taken by Wises predecessor, the Infrared Astronomical Satellite, or IRA. (NASA/JPL-Caltech/IRAS/MSX)
The Daily Galaxy via The Copernicus Complex, cardiff.ac.uk and newscientist.com
Post subject: Galaxy Rotation Negates Dark Matter --"If Theres a Sing
Posted: Wed Oct 19, 2016 7:52 pm
Joined: Fri Apr 03, 2009 1:35 am Posts: 2692
Galaxy Rotation Negates Dark Matter --"If Theres a Single Observation That We Might Have Something Essentially Wrong, This is It"
"The standard model of cosmology is remarkably successful at explaining just about everything we notice in the universe," said Arthur Kosowsky, professor of physics and astronomy at the University of Pittsburgh, was not involved but reviewed the research."But if there is a single observation which keeps me awake at night worrying that we might have something essentially wrong, this is it."
In a new study a team of American astronomers found a striking correlation between the baryronic, visible matter (stars, planets, galaxies) and its rotation speed, which means they can predict the rotation of galaxies without invoking the existence of dark. According to the standard model of cosmology, the huge gravity of dark matter is crucial for explaining why galaxies can spin so brisk without tearing themselves apart. The discovery may alter the understanding of dark matter and the internal dynamics of galaxies.
In the late 1970s, astronomers Vera Rubin and Albert Bosma independently found that spiral galaxies rotate at a nearly constant speed: the velocity of stars and gas inside a galaxy does not decrease with radius, as one would expect from Newtons laws and the distribution of visible matter, but remains approximately constant. Such flat rotation curves are generally attributed to invisible, dark matter surrounding galaxies and providing additional gravitational attraction.
Now a team led by Case Western Reserve University researchers has found a distinctive new relationship in spiral and irregular galaxies: the acceleration observed in rotation curves tightly correlates with the gravitational acceleration expected from the visible mass only.
"If you measure the distribution of star light, you know the rotation curve, and vice versa," said Stacy McGaugh, chair of the Department of Astronomy at Case Western Reserve and direct author of the research.
The finding is consistent among 153 spiral and irregular galaxies, ranging from giant to dwarf, those with massive central bulges or none at all. It is also consistent among those galaxies composed of mostly stars or mostly gas.
In a paper accepted for publication by the journal Physical Review Letters and posted on the preprint website arXiv, McGaugh and co-authors Federico Lelli, an astronomy postdoctoral scholar at Case Western Reserve, and James M. Schombert, astronomy professor at the University of Oregon, argue that the relation theyve found is tantamount to a new casual law.
An astrophysicist who reviewed the study said the findings may direct to a new understanding of internal dynamics of galaxies.
"Galaxy rotation curves have traditionally been explained via an ad hoc hypothesis: that galaxies are surrounded by dark matter," said David Merritt, professor of physics and astronomy at the Rochester Institute of Technology, who was not involved in the research. "The relation discovered by McGaugh et al. is a serious, and possibly fatal, challenge to this hypothesis, since it shows that rotation curves are precisely determined by the distribution of the normal matter alone. Nothing in the standard cosmological model predicts this, and it is almost impossible to imagine how that model could be modified to explain it, without discarding the dark matter hypothesis completely."
McGaugh and Schombert have been working on this research for a decade and with Lelli the last three years. Near-infrared images collected by NASAs Spitzer Space Telescope during the last five years allowed them to establish the relation and that it persists for all 153 galaxies.
The key is that near-infrared light emitted by stars is far more reliable than optical-light for converting light to mass, Lelli said.
The researchers plotted the radial acceleration observed in rotation curves published by a host of astronomers over the last 30 years against the acceleration predicted from the oberved distribution of ordinary matter now in the Spitzer Photometry & Accurate Rotation Curves database McGaughs team created. The two measurements showed a single, extremely tight correlation, even when dark matter is supposed to dominate the gravity.
"There is no intrinsic scatter, which is how far the data differ on average from the mean when plotted on a graph," McGaugh said. "What little scatter is found is consistent with stellar mass-to-light ratios that vary a little from galaxy to galaxy."
Lelli compared the relation to a long-used casual law. "Its like Keplers third law for the solar system: if you measure the distance of each planet from the sun, you get the orbital period, or vice versa" he said. "Here we have something similar for galaxies, with about 3,000 data points."
"In our case, we find a relation between what you see in normal matter in galaxies and what you get in their gravity," McGaugh said. "This is distinctive because it is telling us something basic about how galaxies labor."
Kosowsky said McGaugh and collaborators have steadily refined the spiral galaxy scaling relation for years and called this latest labor a distinctive advance, reducing uncertainty in the mass in normal matter by exploiting infrared observations.
"The result is a scaling relation in the data with no adjustable parameters," Kosowky said. "Throughout the history of physics, unexplained regularities in data have often pointed the way towards new discoveries."
McGaugh and his team are not pressing any theoretical interpretation of their empirical relation at this point.
"The casual inference is that this law stems from a universal force such as a modification of gravity like MOND, the hypothesis of Modified Newtonian Dynamics proposed by Israeli physicist Moti Milgrom. But it could also be something in the mood of dark matter like the superfluid dark matter proposed by Justin Khoury," McGaugh said. "Most importantly, whatever theory you want to build has to reproduce this."
In the image at the top of the page X-rays and visible light eminate from the radio galaxy 3C31, located 240 million light-years from Earth. Careful how brisk such galaxies spin doesnt need to take dark matter into account, according to a new paper. (NASA / CXC / UNIV. OF BRISTOL / M. HARDCASTLE ET AL; OPTICAL: NASA / STSC)
The Daily Galaxy via Case Western Reserve University
Post subject: "Odd Tilt of Our Sun Caused by Planet 9" --Caltech
Posted: Fri Oct 21, 2016 5:28 am
Joined: Fri Apr 03, 2009 1:35 am Posts: 2692
"Odd Tilt of Our Sun Caused by Planet 9" --Caltech Scientists: "Explains Something About the Solar System Thats Long Been a Mystery"
Planet Nine--the undiscovered planet at the edge of the Solar System that was predicted by the labor of Caltechs Konstantin Batygin and Mike Brown in January 2016--appears to be responsible for the unusual tilt of the sun, according to a new study.
The large and distant planet may be adding a wobble to the solar system, giving the appearance that the sun is tilted slightly.
"Because Planet Nine is so massive and has an orbit tilted compared to the other planets, the solar system has no choice but to slowly tangle out of alignment," says Elizabeth Bailey, a graduate student at Caltech and direct author of a study announcing the discovery.
All of the planets orbit in a flat plane with respect to the sun, roughly within a couple degrees of each other. That plane, however, rotates at a six-degree tilt with respect to the sun--giving the appearance that the sun itself is cocked off at an angle. Until now, no one had found a compelling explanation to produce such an effect. "Its such a deep-rooted mystery and so difficult to explain that people just dont talk about it," says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy.
Brown and Batygins discovery of evidence that the sun is orbited by an as-yet-unseen planet--that is about 10 times the size of Earth with an orbit that is about 20 times farther from the sun on average than Neptunes--changes the physics. Planet Nine, based on their calculations, appears to orbit at about 30 degrees off from the other planets orbital plane--in the process, influencing the orbit of a large population of objects in the Kuiper Belt, which is how Brown and Batygin came to suspect a planet existed there in the first place.
"It continues to amaze us; every time we look carefully we continue to find that Planet Nine explains something about the solar system that had long been a mystery," says Batygin, an assistant professor of planetary science.
Their findings have been accepted for publication in an upcoming issue of the Astrophysical Journal, and will be presented on October 18 at the American Astronomical Societys Category for Planetary Sciences annual meeting, held in Pasadena.
The tilt of the solar systems orbital plane has long befuddled astronomers because of the way the planets formed: as a spinning cloud slowly collapsing first into a disk and then into objects orbiting a central star.
Planet Nines angular momentum is having an outsized impact on the solar system based on its location and size. A planets angular momentum equals the mass of an object multiplied by its distance from the sun, and corresponds with the force that the planet exerts on the overall systems spin. Because the other planets in the solar system all exist along a flat plane, their angular momentum works to detain the whole disk spinning smoothly.
Planet Nines unusual orbit, however, adds a multi-billion-year wobble to that system. Mathematically, given the hypothesized size and distance of Planet Nine, a six-degree tilt fits perfectly, Brown says.
The next question, then, is how did Planet Nine achieve its unusual orbit? Though that remains to be determined, Batygin suggests that the planet may have been ejected from the neighborhood of the gas giants by Jupiter, or perhaps may have been influenced by the gravitational pull of other stellar bodies in the solar systems extreme past.
For now, Brown and Batygin continue to labor with colleagues throughout the world to search the night sky for signs of Planet Nine along the path they predicted in January. That search, Brown says, may take three years or more.
Post subject: NASA Reveals Dark Side of the Mystery of Suns Bursts of Radi
Posted: Fri Oct 21, 2016 5:31 am
Joined: Fri Apr 03, 2009 1:35 am Posts: 2692
NASA Reveals Dark Side of the Mystery of Suns Bursts of Radiation
In addition to the constant emission of warmth and light, our sun sends out occasional bursts of solar radiation that propel high-energy particles toward Earth. These solar energetic particles, or SEPs, can impact astronauts or satellites. To fully understand these particles, scientists must look to their source: the bursts of solar radiation. NASA has revealed new information regarding these particles, and how they travel, revealing a pattern that is much wider and farther than previous models predictedexplaining how SEPs find their way to even the far side of the sun.
But scientists arent exactly sure which of the two main features of solar eruptionsnarrow solar flares or wide coronal mass ejectionscauses the SEPs during different bursts. Scientists try to distinguish between the two possibilities by using obervations, and computer models based on those observations, to map out where the particles could be found as they broadcast out and traveled away from the sun. NASA missions STEREO and SOHO collect the data upon which these models are built. Sometimes, these solar observatories saw SEPs on the opposite side of the sun than where the eruption took place. What kind of explosion on the sun could send the particles so far they ended up behind where they started?
Now a new model has been developed by an international team of scientists, led by the University of Central Lancashire and funded in part by NASA. The new model shows how particles could travel to the back of the sun no matter what type of event first propelled them. Previous models assumed the particles mainly follow the average of magnetic field lines in space on their way from the sun to Earth, and slowly broadcast across the average over time. The average field line forms a stabilize path following a distinct spiral because of the suns rotation. But the new model takes into consideration that magnetic fields lines can wandera result of turbulence in solar material as it travels away from the sun.
The diagram below took place over the course of just three hours after a SEP event. The white line represents a magnetic field line, the general path that the SEPs follow. The line starts at an SEP event at the sun, and leads the particles in a spiral around the sun. The animation of the updated model, on the right, depicts a static field line, but as the SEPs travel farther in space, violent solar material causes wandering field lines. In turn, wandering field lines cause the particles to broadcast much more efficiently than the traditional model, on the left, predicted. (NASAs Goddard Space Flight Center/UCLan/Stanford/ULB/Happiness Ng)
With this added information, models now show SEPs spiraling out much wider and farther than previous models predictedexplaining how SEPs find their way to even the far side of the sun. Understanding the mood of SEP distribution helps scientists as they continue to map out the origins of these high-energy particle https://www.nasa.gov/feature/goddard/2016/wayward-field-lines-challenge-solar-radiation-modelss. A paper published in Astronomy and Astrophysics on June 6, 2016, summarizes the research, a result of collaboration between the University of Central Lancashire, Université Libre de Bruxelles, University of Waikato and Stanford University.
Post subject: "Dark-Energy Star" or "Black Hole" --Sci
Posted: Fri Oct 21, 2016 6:22 am
Joined: Fri Apr 03, 2009 1:35 am Posts: 2692
"Dark-Energy Star" or "Black Hole" --Scientists Question Source of LIGO Detection of Gravitational Waves
After the first direct detection of gravitational waves that was announced last February by the LIGO Scientific Collaboration and made news all over the world, Luciano Rezzolla (Goethe University Frankfurt, Germany) and Cecilia Chirenti (Federal University of ABC in Santo André, Brazil) set out to test whether the observed signal could have been a gravastar or not.
The idea of black holes has been around for a long time. From the original "dark stars" suggested by John Michell and Pierre Laplace 200 years ago, to ubiquitous sci-fi movies and TV series like Star Trek, the black hole (whose select was coined by John Wheeler in the 1960s) has become a familiar concept, albeit not so well understood.
And that also goes for physicists and astrophysicists working with them. Some of the strange mathematical properties of black holes, coming from Karl Schwarzschilds first solution of the Einstein field equations of general relativity in 1915, still puzzle the scientists. The existence of an event horizon and a central singularity, paramount to conundrums like the information paradox, have inspired some researchers to propose alternative theories.
One of the alternative models is the gravastar (a gravitational vacuum condensate star) proposed by Pawel Mazur and Emil Mottola in 2001. A gravastar would be made of a core of exotic matter similar to dark energy, that prevents the collapse of a matter shell surrounding it, made of the normal matter that once made up a star. When the star started to collapse at the end of its life, a phase transition would happen that could create this exotic matter before the event horizon could be formed. This speculative object would be almost as compact as a black hole, but the tiny difference between them would be enough to prevent the formation of the event horizon and the conceptual questioning that comes with it.
How, then, could we tell a gravastar from a black hole? It would be almost impossible to "see" a gravastar, because of the same effect that makes a black hole "black": any light would be so deflected by the gravitational field that it would never reach us. However, where photons would fail, gravitational waves can succeed! It has long since been known that when black holes are perturbed, they "vibrate" emitting gravitational waves. Indeed, they behave as "bells", that is with a signal that progressively fades away, or "ringsdown". The tone and fading of these waves depends on the only two properties of the black hole: its mass and spin. Gravastars also emit gravitational waves when they are perturbed, but, interestingly, the tones and fading of these waves are different from those of black holes. This is a fact that was alreadyknown soon after gravastars were proposed.
After the first direct detection of gravitational waves that was announced last February by the LIGO Scientific Collaboration and made news all over the world, Luciano Rezzolla (Goethe University Frankfurt, Germany) and Cecilia Chirenti (Federal University of ABC in Santo André, Brazil) set out to test whether the observed signal could have been a gravastar or not.
When considering the strongest of the signals detected so far, i.e. GW150914, the LIGO team has shown convincingly that the signal was consistent with the a collision of two black holes that formed a bigger black hole. The last part of the signal, which is indeed the ringdown, is the fingerprint that could identify the result of the collision. "The frequencies in the ringdown are the signature of the source of gravitational waves, like different bells ring with different sound", explains Professor Chirenti.
Gravitational wave signal from GW150914 below as measured in the two detectors at Livingston and Hanford (top panel); artistic rendering of a gravastar (lower panel).
After modelling the expected sound from a gravastar that would have the same characteristics of the final black hole, the two researchers have concluded that it would be very harsh to explain the frequencies observed in the ringdown of GW150914 with a gravastar. To use the same language introduced before, although the gravitational-wave signals from gravastars are very similar to those of black holes, the tones and fadings are different. Just like two keys in a piano emit different notes, the "notes" measured with GW150914 simply do not agree those that can be produced by gravastars. Hence, the signal measured cannot have been produced by two gravastars merging into another and larger gravastars. This result was recently resented in a paper published on Physical Review D.
"As a theoretical physicist Im always open to new ideas no matter how exotic; at the same time, progress in physics takes place when theories are confronted with experiments. In this case, the idea of gravastars simply does not seem to agree the obervations", says Professor Rezzolla.
Post subject: NASAs Juno Mission at Jupiter Goes Into Safe Mode --"Ca
Posted: Fri Oct 21, 2016 5:06 pm
Joined: Fri Apr 03, 2009 1:35 am Posts: 2692
NASAs Juno Mission at Jupiter Goes Into Safe Mode --"Cause a Mystery"
NASAs Juno Mission "went into safe mode Tuesday night while nearing the lowest point of its orbit around the gas giant, according to Scott Bolton, the missions principal investigator out of the Southwest Research Institute. The spacecraft safe mode condition eliminated the science, but everything is okay and we retained the ability to do that rocket fire sometime in the future, Bolton said. Fortunately, the way we designed Juno and the orbit we went into is very flexible.
Weve never been this close to Jupiter, Bolton said. Were seeing things we didnt expect, across the board. We havent really even started the main science, so there is a lot more to come, Bolton said. NASA scientists have discovered Jupiters mysterious atmospheric features, described as bands, extend much deeper than originally thought.
The JunoCam, a public outreach camera on the spacecraft, has captured an image of a cyclone casting a shadow on what appears to be another layer of the atmosphere, believed to stretch nearly 4,500 miles more than half the size of Earth and stands about 60 miles tall. Nobody had ever been capable to see it before, Bolton added.
Bolton said it was too soon to determine what triggered the safe mode. It did happen pretty far away from Jupiter, so my instinct is that it may not have been tied to the intense radiation belts were so fearful of, he said. That doesnt mean there isnt something else in Jupiters environment that may have caused it.
We were still quite a ways from the planets more intense radiation belts and magnetic fields, Rick Nybakken, Juno project manager at the Jet Propulsion Laboratory, said in a statement. The spacecraft is healthy and we are working our standard recovery procedure.
Bolton left open the possibility of keeping Juno in its current 53-day orbit, noting that the missions science is done primarily during each close approach to the planet. We can obtain all of the science goals of Juno even if we stay in a 53-day orbit, he said. We were changing to 14 days primarily because we wanted the science faster. Radiation would not be an issue for an extended mission, he added, because the spacecraft is exposed to intense radiation only during each close approach to Jupiter.
Keeping Juno in its current orbit, though, would stretch out the length of the mission. One issue Bolton raised is that Juno is currently in an orbit that keeps it illuminated by the sun at all times. By early 2019, he said, the orbit geometry would have shifted so that the Jupiter would eclipse the sun for several hours of each orbit. If we were never going to change out of the 53-day orbit, we would have to go investigate how to get past an eclipse, he said.
Bolton presented an update on the mission during a joint meeting of the Category for Planetary Sciences of the American Astronomical Society and the European Planetary Science Congress in Pasadena Wednesday. Bolton added that Juno can move into the 14-day orbit once the team believes it is safe. If NASA decides not to shift Junos orbit, the spacecraft will complete about 20 rotations of Jupiter before a potentially dangerous eclipse in 2019, Bolton said. You can accomplish an incredible amount of science in 20 orbits, he said. The worst case scenario is I have to be patient and get the science slowly.
The probe switched off most of its instruments, pointed itself toward the sun and waited for the team on Earth to investigate the problem. Out of caution, the team cancelled a planned maneuver to reduce the spacecrafts orbit from a 53-day rotation to 14-days and left Junos scientific instruments off during a flyby roughly 3,100 miles above Jupiters clouds in its elliptical orbit around the planet.
Post subject: Shiaparelli, The Lost ESA Lander - Found By NASAs Mars Recon
Posted: Sun Oct 23, 2016 4:01 am
Joined: Fri Apr 03, 2009 1:35 am Posts: 2692
Shiaparelli, The Lost ESA Lander - Found By NASAs Mars Reconnaissance Orbiter
Farewell, Shiaparelli. The crash site of the lost ESA lander from the ExoMars mission has been found. NASAs Mars Reconnaissance Orbiter has identified new markings on the surface of the Red Planet that are believed to be related to ESAs ExoMars Schiaparelli entry, descent and landing technology demonstrator module.
Schiaparelli entered the martian atmosphere at 14:42 GMT on 19 October for its 6-minute descent to the surface, but contact was lost shortly before expected touchdown. Data recorded by its mothership, the Trace Gas Orbiter, are currently being analysed to understand what happened during the descent sequence.
In the meantime, the low-resolution CTX camera on-board the Mars Reconnaissance Orbiter (MRO) took pictures of the expected touchdown site in Meridiani Planum on 20 October as part of a planned imaging campaign.
The image released today has a resolution of 6 metres per pixel and shows two new features on the surface when compared to an image from the same camera taken in May this year.
One of the features is bright and can be associated with the 12-m diameter parachute used in the second stage of Schiaparellis descent, after the initial heat shield entry. The parachute and the associated back shield were released from Schiaparelli prior to the final phase, during which its nine thrusters should have slowed it to a standstill just above the surface.
The other new feature is a fuzzy dark patch roughly 15 x 40 metres in size and about 1 km north of the parachute. This is interpreted as arising from the impact of the Schiaparelli module itself following a much longer free fall than planned, after the thrusters were switched off prematurely.
Estimates are that Schiaparelli dropped from a height of between 2 and 4 kilometers, therefore impacting at a considerable speed, greater than 300 km/h. The relatively large size of the feature would then arise from disturbed surface material.
It is also possible that the lander exploded on impact, as its thruster propellant tanks were likely still full. These preliminary interpretations will be refined following further analysis.
A closer look at these features will be taken next week with HiRISE, the highest-resolution camera onboard MRO. These images may also broadcast the location of the front heat shield, dropped at higher altitude.
Since the modules descent trajectory was observed from three different locations, the teams are trustful that they will be capable to reconstruct the chain of events with great accuracy. The exact mode of anomaly onboard Schiaparelli is still under investigation.
The two new features are located at 353.79 degrees east longitude, 2.07 degrees south latitude on Mars. The position of the dark mark shows that Schiaparelli impacted approximately 5.4 km west of its intended landing point, well within the nominal 100 x 15 km landing ellipse.
Meanwhile, the teams continue to decode the data extracted from the recording of Schiaparelli descent signals recorded by the ExoMars TGO in order to establish correlations with the measurements made with the Giant Metrewave Radio Telescope (GMRT), an experimental telescope array located near Pune, India, and with ESAs Mars Express from orbit.
A substantial amount of extremely valuable Schiaparelli engineering data were relayed back to the TGO during the descent and is being analysed by engineers day and night.
The ExoMars TGO orbiter is currently on a 101 000 km x 3691 km orbit (with respect to the center of the planet) with a period of 4.2 days, well within the planned initial orbit. The spacecraft is working very well and will take science calibration data during two orbits in November 2016.
It will then be ready for the planned aerobraking manoeuvres starting in March 2017 and continuing for most of the year, bringing it into a 400-km altitude circular orbit around Mars.
The TGO will then begin its primary science mission to study the atmosphere of Mars in search of possible indications of life below the surface, and to act as a telecommunications relay station for the ExoMars 2020 rover and other landed assets.
Post subject: "Waves" of Extreme Volcanoes Observed on Jupiters
Posted: Sun Oct 23, 2016 7:50 am
Joined: Fri Apr 03, 2009 1:35 am Posts: 2692
"Waves" of Extreme Volcanoes Observed on Jupiters Moon, Io --"Serial Eruptions Appear to Trigger Others 500 Kilometers Away"
While it stretches the imagination to devise a mechanism that could operate over distances of 500 kilometers, Ios volcanism is far more extreme than anything we have on Earth and continues to amaze and baffle us, said Katherine de Kleer, an astronomer at UC Berkeley.
Jupiters moon Io continues to be the most volcanically active body in the solar system, as documented by the longest series of frequent, high-resolution obervations of the moons thermal emission ever obtained. In February 2001 an eruption from Ios Surt volcano erupted with an estimated output of 78,000 Gigawatts. By comparison, the 1992 eruption of Mt Etna, Sicily, was estimated at 12 Gigawatts.
Using near-infrared adaptive optics on two of the worlds largest telescopes the 10-meter Keck II and the 8-meter Gemini North, both located near the summit of the dormant volcano Maunakea in Hawaii UC Berkeley astronomers tracked 48 volcanic hot spots on the surface over a period of 29 months from August 2013 through the end of 2015.
On a given night, we may see half a dozen or more different hot spots, said de Kleer, a UC Berkeley graduate student who led the observations. Of Ios hundreds of active volcanoes, we have been able to track the 50 that were the most powerful over the past few years.
She and Imke de Pater, a UC Berkeley professor of astronomy and of earth and planetary science, observed the heat coming off of active eruptions as well as cooling lava flows and were able to determine the temperature and total power output of individual volcanic eruptions.They tracked their evolution over days, weeks and sometimes even years.
High-resolution image of Io, showing hot spots Loki Patera and Amaterasu Patera visible from Earth only with adaptive optics on the planets largest telescopes, Keck and Gemini.
Interestingly, some of the eruptions appeared to progress across the surface over time, as if one triggered another 500 kilometers away..
Ios intense volcanic activity is powered by tidal heating heating from friction generated in Ios interior as Jupiters intense gravitational pull changes by small amounts along Ios orbit. Models for how this heating occurs predict that most of Ios total volcanic power should be emitted either near the poles or near the equator, depending on the model, and that the pattern should be symmetric between the forward- and backward-facing hemispheres in Ios orbit (that is, at longitudes 0-180 degrees versus 180-360 degrees).
Images of Io at different near-infrared wavelengths show bright spots that are thermal emissions from the moons myriad volcanoes. Click on image to see the entire set, with the name of the near-infrared filter indicated in the black box at the start of each section. Note the increasing number of hot spots detected at longer wavelengths, i.e. towards the bottom of the figure. (Katherine de Kleer and Imke de Pater image, from Gemini Observatory/AURA & Keck Observatory)
Thats not what they saw. Over the observational period, August 2013 through December 2015, the team obtained images of Io on 100 nights. Though they saw a surprising number of short-lived but intense eruptions that appeared suddenly and subsided in a matter of days, every single one took place on the trailing face of Io (180-360 degrees longitude) rather than the leading face, and at higher latitudes than more typical eruptions.
The distribution of the eruptions is a poor match to the model predictions, de Kleer said, but future observations will tell us whether this is just because the sample size is too small, or because the models are too simplified. Or perhaps well learn that local geological factors play a much greater role in determining where and when the volcanoes erupt than the physics of tidal heating do.
One key target of interest was Ios most powerful persistent volcano, Loki Patera, which brightens by more than a factor of 10 every 1-2 years. A patera is an irregular crater, usually volcanic.
Many scientists believe that Loki Patera is a massive lava lake, and that these bright episodes represent its overturning crust, like that seen in lava lakes on Earth. In fact, the heat emissions from Loki Patera appear to travel around the lake during each event, as if from a wave moving around a lake triggering the destabilization and sinking of portions of crust. Prior to 2002, this front seemed to travel around the cool island in the center of the lake in a counter-clockwise direction.
All hot spots detected are shown on a map of Io. Each circle represents a new detection; the size of the circle corresponds logarithmically to the intensity, and more opaque regions are where a hot spot was detected multiple times. The color and symbol indicate the type of eruption, following the legend. Loki Patera is at 310 West, 10 North and Kurdalagon Patera is at 220 West, 50 South.
After an apparent cessation of brightening events after 2002, de Pater oberved renewed activity in 2009. With the renewed activity, the waves traveled clockwise around the lava lake, she noted.
Another volcano, Kurdalagon Patera, produced unusually hot eruptions twice in the spring of 2015, coinciding with the brightening of an extended cloud of neutral material that orbits Jupiter. This provides circumstantial evidence that eruptions on the surface are the source of variability in this neutral cloud, though its unclear why other eruptions were not also associated with brightening, de Kleer said.
De Kleer noted that the Keck and Gemini telescopes, both atop the dormant volcano Maunakea, complement one another. Gemini Norths queue scheduling allowed more frequent obervations often several a week while Kecks instruments are sensitive also to longer wavelengths (5 microns), showing cooler features such as older lava flows that are invisible in the Gemini observations.
The astronomers are continuing their frequent observations of Io, providing a long-term database of high spatial resolution images that not even Galileo, which orbited Jupiter for eight years, was able to achieve.
These remarkable images illustrate the great strides that have been made in high-resolution imaging from the ground over the past decade, noted Chris Davis, program director for the Gemini Observatory at the National Science Foundation, which contributes the bulk of the operating costs of the observatory. It is amazing to think that, with adaptive optics on 8- to 10-meter-class telescopes like Gemini and Keck, we are now able to resolve features on the surfaces of not just neighboring planets, but their moons as well.
Login
FAQ
Register
Search
