Meteorite expert and researcher Peter Jenniskens with a fragment of the bolide seen over California on April 22, 2012. Image via Franck Marchis' Cosmic Diary blog.
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Meteorite hunters have been successful in locating fragments from the huge meteor visible in the daytime skies over California last weekend. One of the successful hunters was Peter Jenniskens, an expert in meteors and meteorites, perhaps best known for retrieving the fragments of asteroid 2008 TC3 which fell in Sudan in 2008. Astronomer Franck Marchis wrote in his Cosmic Diary blog that Jenniskens realized the size of the California meteor was very similar to 2008 TC3, and so fragments should have reached the surface, just like they did in 2008.
Jenniskens went out searching and found a four-gram fragment of the meteor in a parking lot in Lotus, California.
Update: NASA and the SETI Institute are asking the public to submit any amateur photos or video footage of the meteor that illuminated the sky over the Sierra Nevada mountains and created sonic booms that were heard over a wide area at 7:51 a.m. PDT Sunday, April 22, 2012.
Marchis wrote that several scientists from the Bay Area met at NASA Ames Research Center on April 24 to discuss a strategy for a search campaign, examining a radar data map which showed that dozens of fragments from the 100g to 1 kg range may have reached the ground.
Jenniskens said the fragment he found was a Carbonaceous Chondrites from the CM group of meteorites, “a rare type of primitive meteorite rich in organic compounds,” he said.
“We are very interested in this rare find,” said Greg Schmidt, deputy director of the NASA Lunar Science Institute. “With the public’s help, this could lead to a better understanding of these fascinating objects.”
“Getting fresh fragments of meteoroids, called meteorites, is key for astronomers to understand the composition of those remnants of the formation of the solar system,” Marchis wrote. “Fresh fragments are unaltered by the Earth’s weather and erosion processes, so they are pristine samples which can be used to detect organic materials for instance.”
Photos and video footage would help the scientists to better analyze the trajectory of the meteor and learn about its orbit in space. This information will also help scientists to locate the places along the meteor path where fragments may have fallen to the ground.
People who have photos or video of the meteorite are asked to contact Jenniskens at [email protected].
Marchis noted that a storm is heading towards the region and rain could alter the remaining fragments. So if you live nearby, consider heading out to take a look. Here is the radar map:
Radar map by Marc Fries showing the possible location of fragments (green area) of the meteor between Auburn and Placerville.
Marchis also said that if anyone has access to security camera footage taken on April 22, 2012 in the area of the fireball sighting, it may be useful to check them to see if the fireball was visible. “Astronomers could use them to pin down the site of the fall, maximizing the hunt for fragments,” he said.
UPDATE: After hearing from several experts, this fireball was likely NOT a re-entering rocket body. Bob Christy from Zarya.info confirmed that the two videos were reportedly made around 20:00 – 21:00 UTC, and according to SpaceTrack, the Centaur re-entered about 19 hours earlier at 01:23 UTC. Additionally, the re-entry ground track did not cross Brazil at a correlating time. Dr. Marco Langbroek from SatTrackCam concurred there is no chance this was a Centaur rocket. “Looking at the videos, to me it looks like a very slow, grazing meteor.”
We recently posted a video of a huge meteor streaking over the skies of Brazil. It turns out this wasn’t your average, ordinary, everyday meteor. It was actually a Centaur rocket body re-entering Earth’s atmosphere, according to fellow NASA Solar System Ambassador Eddie Irizarry. “An amazing video that shows a fireball lasting more than 30 seconds captured the reentry of a Centaur rocket body that was launched on 1985,” said Irizarry in an email, reporting for the Sociedad de Astronomía del Caribe, the Puerto Rican Astronomy Society. “The object was seen from southeast Brazil by hundreds of people on April 20, 2012 and on the same date, Intelsat 5A12’s rocket body was about to reenter Earth’s atmosphere, passing exactly over the ground track from which some people were able to capture amazing images,” reported Irizarry.
There’s a second video below, as well as a map of the area the fireball was seen.
The 820-foot-wide crack in Antarctica's Pine Island Glacier, seen from DC-8 during Operation IceBridge (Credit: NASA/DMS)
Data collected from a NASA ice-watching satellite reveal that the vast ice shelves extending from the shores of western Antarctica are being eaten away from underneath by ocean currents, which have been growing warmer even faster than the air above.
The animation above shows the circulation of ocean currents around the western Antarctic ice shelves. The shelf thickness is indicated by the color; red is thicker (greater than 550 meters), while blue is thinner (less than 200 meters).
Launched in January 2003, NASA’s ICESat (Ice, Cloud and land Elevation Satellite) studied the changing mass and thickness of Antarctica’s ice from its location in polar orbit. An international research team used over 4.5 million surface height measurements collected by ICESat’s GLAS (Geoscience Laser Altimeter System) instrument from Oct. 2005 to 2008. They concluded that 20 of the 54 shelves studied — nearly half — were losing thickness from underneath.
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Most of the melting ice shelves are located in west Antarctica, where the flow of inland glaciers to the sea has also been accelerating — an effect that can be compounded by thinning ice shelves which, when grounded to the offshore seabed, serve as dams to hold glaciers back.
Melting of ice by ocean currents can occur even when air temperature remains cold, maintaining a steady process of ice loss — and eventually increased sea level rise.
“We can lose an awful lot of ice to the sea without ever having summers warm enough to make the snow on top of the glaciers melt,” said Hamish Pritchard of the British Antarctic Survey in Cambridge and the study’s lead author . “The oceans can do all the work from below.”
The study also found that Antarctica’s winds are shifting in response to climate change.
“This has affected the strength and direction of ocean currents,” Pritchard said. “As a result warm water is funnelled beneath the floating ice. These studies and our new results suggest Antarctica’s glaciers are responding rapidly to a changing climate.”
ICESat completed operations in 2010 and was decommissioned in August of that year. Its successor ICESat-2 is anticipated to launch in 2016.
These composite images from the framing camera aboard NASA's Dawn spacecraft show three views of a terrain with ridges and grooves near Aquilia crater in the southern hemisphere of the giant asteroid Vesta. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
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Vesta is finally giving up its secrets, thanks to the Dawn spacecraft! The latest images sent back from Dawn are revealing new details about the giant asteroid, including its varied surface composition, sharp temperature changes and clues to its internal structure. Scientists say all the information garnered by Dawn will help us to better understand the early solar system and processes that dominated its formation.
“Dawn now enables us to study the variety of rock mixtures making up Vesta’s surface in great detail,” said Harald Hiesinger, a Dawn participating scientist at Münster University in Germany. “The images suggest an amazing variety of processes that paint Vesta’s surface.”
Images from Dawn’s framing camera and visible and infrared mapping spectrometer, taken 420 miles (680 kilometers) and 130 miles (210 kilometers) above the surface of the asteroid, show a variety of surface mineral and rock patterns. Coded false-color images help scientists better understand Vesta’s composition and enable them to identify material that was once molten below the asteroid’s surface.
Researchers also see breccias, which are rocks fused during impacts from space debris. Many of the materials seen by Dawn are composed of iron- and magnesium-rich minerals, which often are found in Earth’s volcanic rocks. Images also reveal smooth pond-like deposits, which might have formed as fine dust created during impacts settled into low regions.
These images of Tarpeia crater, near the south pole of the giant asteroid Vesta, were obtained by the visible and infrared mapping spectrometer on NASA’s Dawn spacecraft. Image credit: NASA/JPL-Caltech/UCLA/INAF
At the Tarpeia crater near the south pole of the asteroid, Dawn imagery revealed bands of minerals that appear as brilliant layers on the crater’s steep slopes. The exposed layering allows scientists to see farther back into the geological history of the giant asteroid.
The layers closer to the asteroid’s surface bear evidence of contamination from space rocks bombarding Vesta. Layers below preserve more of their original characteristics. Frequent landslides on the slopes of the craters also have revealed other hidden mineral patterns.
This colorized image from NASA’s Dawn mission shows temperature variations at Tarpeia crater, near the south pole of the giant asteroid Vesta. Image credit: NASA/JPL-Caltech/UCLA/INAF
“These results from Dawn suggest Vesta’s ‘skin’ is constantly renewing,” said Maria Cristina De Sanctis, lead of the visible and infrared mapping spectrometer team based at Italy’s National Institute for Astrophysics in Rome.
This set of images from NASA's Dawn mission shows topography of the southern hemisphere of the giant asteroid Vesta and a map of Vesta’s gravity variations that have been adjusted to account for Vesta’s shape. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Dawn has given scientists a near 3-D view into Vesta’s internal structure. By making ultra-sensitive measurements of the asteroid’s gravitational tug on the spacecraft, Dawn can detect unusual densities within its outer layers. Data now show an anomalous area near Vesta’s south pole, suggesting denser material from a lower layer of Vesta has been exposed by the impact that created a feature called the Rheasilvia basin. The lighter, younger layers coating other parts of Vesta’s surface have been blasted away in the basin.
Dawn obtained the highest-resolution surface temperature maps of any asteroid visited by a spacecraft. Data reveal temperatures can vary from as warm as minus 10 degrees Fahrenheit (minus 23 degrees Celsius) in the sunniest spots to as cold as minus 150 degrees Fahrenheit (minus 100 degrees Celsius) in the shadows. This is the lowest temperature measurable by Dawn’s visible and infrared mapping spectrometer. These findings show the surface responds quickly to illumination with no mitigating effect of an atmosphere.
“After more than nine months at Vesta, Dawn’s suite of instruments has enabled us to peel back the layers of mystery that have surrounded this giant asteroid since humankind first saw it as just a bright spot in the night sky,” said Carol Raymond, Dawn deputy principal investigator at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “We are closing in on the giant asteroid’s secrets.”
The latest findings were presented today at the European Geosciences Union meeting in Vienna, Austria.
The side of the SOFIA aircraft shows it's joint roots, a collaboration between NASA and German Scientists. Credit: Nick Howes
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One of the most remarkable observatories in the world does its work not on a mountaintop, not in space, but 45,000 feet high on a Boeing 747. Nick Howes took a look around this unique airliner as it made its first landing in Europe.
SOFIA (Stratospheric Observatory for Infrared Astronomy) came from an idea first mooted in the mid-1980s. Imagine, said scientists, using a Boeing 747 to carry a large telescope into the stratosphere where absorption of infrared light by atmospheric water molecules is dramatically reduced, even in comparison with the highest ground-based observatories. By 1996 that idea had taken a step closer to reality when the SOFIA project was formally agreed between NASA (who fund 80 percent of the cost of the 330 million dollar mission, an amount comparable to a single modest space mission) and the German Aerospace Centre (DLR, who fund the other 20 percent). Research and development began in earnest using a highly modified Boeing 747SP named the ‘Clipper Lindburgh’ after the famous American pilot, and where the ‘SP’ stands for ‘Special Performance’.
Maiden test flights were flown in 2007, with SOFIA operating out of NASA’s Dryden Flight Research Center at Edwards Airforce Base in the Rogers Dry Lake in California – a nice, dry location that helps with the instrumentation and aircraft operationally.
This scale model shows the telescope position and how the aircraft design works around it. Credit: Nick Howes.
As the plane paid a visit to the European Space Agency’s astronaut training centre in Cologne, Germany, I was given a rare opportunity to look around this magnificent aircraft as part of a European Space ‘Tweetup’ (a Twitter meeting). What was immediately noticeable was the plane’s shorter length to the ones you usually fly on, which enables the aircraft to stay in the air for longer, a crucial aspect for its most important passenger, the 2.7-metre SOFIA telescope. Its Hubble Space Telescope-sized primary mirror is aluminium coated and bounces light to a 0.4-metre secondary, all in an open cage framework that literally pokes out of the side of the aircraft.
As we have seen, the rationale for placing a multi-tonne telescope on an aircraft is that by doing so it is possible to escape most of the absorption effects of our atmosphere. Observations in infrared are largely impossible for ground-based instruments at or near sea-level and only partially possibly even on high mountaintops. Water vapour in our troposphere (the lower layer of the atmosphere) absorbs so much of the infrared light that traditionally the only way to beat this was to send up a spacecraft. SOFIA can fill a niche by doing nearly the same job but at far less risk and with a far longer life-span. The aircraft has sophisticated infrared monitoring cameras to check its own output,and water vapour monitoring to measure what little absorption is occurring.
The Sofia Telescope resides behind the multi tonne frame and control mechanism. Credit: Nick Howes.
The 2.7-metre mirror (although actually only 2.5-metres is really used in practice,) uses a glass ceramic composite that is highly thermally tolerant, which is vital given the harsh conditions that the aircraft puts the isolated telescope through. If one imagines the difficulty amateur astronomers have some nights with telescope stability in blustery conditions, spare a thought for SOFIA, whose huge f/19.9 Cassegrain reflecting telescope has to deal with an open door to the
800 kilometres per hour (500 miles per hour) winds .Nominally some operations will occur at 39,000 feet (approximately 11,880 metres) rather than the possible ceiling of 45,000 feet (13,700 metres), because while the higher altitude provides slightly better conditions in terms of lack of absorption (still above 99 percent of the water vapour that causes most of the problems), the extra fuel needed means that observation times are reduced significantly, making the 39,000
feet altitude operationally better in some instances to collect more data. The aircraft uses a cleverly designed air intake system to funnel and channel the airflow and turbulence away from the open telescope window, and speaking to the pilots and scientists, they all agreed that there was no effect caused by any output from the aircraft engines as well.
Staying cool
The cameras and electronics on all infrared observatories have to be maintained at very low temperatures to avoid thermal noise from them spilling into the image, but SOFIA has an ace up its sleeve. Unlike a space mission (with the exception of the servicing missions to the Hubble Space Telescope that each cost $1.5 billion including the price of launching a space shuttle), SOFIA has the advantage of being able to replace or repair instruments or replenish its coolant, allowing an estimated life-span of at least 20 years, far longer than any space-based infrared mission that runs out of coolant after a few years.
Meanwhile the telescope and its cradle are a feat of engineering. The telescope is pretty much fixed in azimuth, with only a three-degree play to compensate for the aircraft, but it doesn’t need to move in that direction as the aircraft, piloted by some of NASA’s finest, performs that duty for it. It can work between a 20–60 degree altitude range during science operations. It’s all been engineered to tolerances that make the jaw drop. The bearing sphere, for example, is polished to an accuracy of less than ten microns, and the laser gyros provide angular increments of 0.0008 arcseconds. Isolated from the main aircraft by a series of pressurised rubber bumpers, which are altitude compensated, the telescope is almost completely free from the main bulk of the 747, which houses the computers and racks that not only operate the telescope but provide the base station for any observational scientists flying with the plane.
PI in the Sky
The science principle investigators get to sit in relative comfort close to the telescope. Credit: Nick Howes.
The Principle Investigator station is located around the mid-point of the aircraft, several metres from the telescope but enclosed within the plane (exposed to the air at 45,000 feet, the crew and scientists would otherwise be instantly killed). Here, for ten or more hours at a time, scientists can gather data once the door opens and the telescope is pointing at the target of choice, with the pilots following a precise flight path to maintain both the instrument pointing accuracy and also to best avoid the possibility of turbulence. Whilst ground-based telescopes can respond quickly to events such as a new supernova, SOFIA is more regimented in its science operations and, with proposal cycles over six months to a year, one has to plan quite accurately how best to observe an object.
Forecasting the future
Science operations started in 2010 with FORCAST (Faint Object Infrared Camera for Sofia Telescope) and continued into 2011 with the GREAT (German Receiver for Astronomy at Teraherz Frequencies) instrument. FORCAST is a mid/far infrared instrument working with two cameras between at five and forty microns (in tandem they can work between 10–25 microns) with a 3.2 arcminute field-of-view. It saw first light on Jupiter and the galaxy Messier 82, but will be working on imaging the galactic centre, star formation in spiral and active galaxies and also looking at molecular clouds, one of its primary science goals enabling scientists to accurately determine dust temperatures and more detail on the morphology of star forming regions down to less than three-arcsecond resolution (depending on the wavelength the instrument works at). Alongside this, FORCAST is also able to perform grism (i.e. a grating prism) spectroscopy, to get more detailed information on the composition of objects under view. There is no adaptive optics system, but it doesn’t need one for the types of operations it’s doing.
FORCAST and GREAT are just two of the ‘basic’ science operation instruments, which also include Echelle spectrographs, far infrared spectrometers and high resolution wideband cameras, but already the science team are working on new instruments for the next phase of operations. Instrumentation switch over, whilst complex, is relatively quick (comparable to the time it takes to switch instruments on larger ground observatories), and can be achieved in readiness for observations, which the plane aims to do up to 160 times per year. And whilst there were no firm plans to build a sister ship for SOFIA, there have been discussions among scientists to put a larger telescope on an Airbus A380.
A model of the telescope shows its unique control and movement mechanism as well as the optical tube assembly. Credit: Nick Howes.
Sky Outreach
With a planned science ambassador programme involving teachers flying on the aircraft to do research, SOFIA’s public profile is going to grow. The science output and possibilities from instruments that are constantly evolving, serviceable and improvable every time it lands is immeasurable in comparison to space missions. Journalists had only recently been afforded the opportunity to visit this remarkable aircraft, and it was a privilege and honour to be one of the first people to see it up close. To that end I wish to thank ESA and NASA for the invitation and chance to see something so unique.
This is an artist’s depiction of a 10-kilometer (6-mile) diameter asteroid striking the Earth. New evidence in Australia suggests an asteroid 2 to 3 times larger than this struck Earth early in its life. Credit: Don Davis/Southwest Research Institute.
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Even though the Late Heavy Bombardment is somewhat of a controversial idea, new research has revealed this period of impacts to the Earth-Moon system may have lasted much longer than originally estimated and well into the time when early life was forming on Earth. Additionally, this “late-late” period of impacts — 3.8 billion to 2.5 billion years ago — was not for the faint of heart. Various blasts may have rivaled those that produced some of the largest craters on the Moon, and could have been larger than the dinosaur-killing impact that created the Chicxulub crater 65 million years ago.
“Our work provides a rationale that the last big impacts hit over an extended time,” said William Bottke principal investigator of the impact study team at the NASA Lunar Science Institute’s Center of Lunar Origin and Evolution (CLOE), based at the Southwest Research Institute (SwRI) in Boulder, Colorado.
The evidence for these prodigious impacts comes from bead-like impact ‘spherules’ found in millimeter- to centimeter-thick rock layers on Earth and date from the Archean period of Earth’s history, more recent than the estimated LHB period of 4.1 to 3.8 billion years ago.
“The beds speak to an intense period of bombardment of Earth,” Bottke said. “Their source long has been a mystery.”
The millimeter-scale circles and more irregular gray particles are formerly molten droplets ejected into space when an asteroid hit the early Earth. The image at left is from the Monteville layer in South Africa. Courtesy Bruce Simonson, Oberlin College and Conservatory
The circles seen in the image above are all formerly molten droplets ejected into space when an asteroid struck the Earth about 2.56 billion years ago. The droplets returned to Earth and were concentrated at the base of the Reivilo layer in South Africa.
The spherules still contain substantial extraterrestrial material, such as iridium (176 parts per million), which rules out alternative sources for the spherules, such as volcanoes, according to Bruce Simonson, a geologist from the Oberlin College and Conservatory who has studied these ancient layers for decades.
The timing of these impacts also coincides with a record of large lunar craters being created more recently than 3.8-billion years ago.
At least 12 spherule beds deposited between 3.47 and 1.7 billion years ago have been found in protected areas on Earth, such as in shales deposited on the seafloor below the reach of waves.
From these beds, the team found evidence of approximately 70 impacts on Earth during this time period that were likely larger than the Chicxulub impact.
In their paper, which was published in Nature, the team created a computer model of the ancient main asteroid belt and tracked what would have happened when the orbits of the giant planets changed. They extended the work of the Nice Model, which supports the theory that Jupiter, Saturn, Uranus and Neptune formed in different orbits nearly 4.5 billion years ago and migrated to their current orbits about 4 billion years ago, triggering a solar system-wide bombardment of comets and asteroids called known as the LHB.
This image shows a representation of how the giant planets have migrated to the current orbits, destabilizing the extension of the primordial asteroid belt closest to Mars. This drove numerous big impactors onto orbits where they could hit the terrestrial planets, though over a long enough time span that this drawn-out barrage may have lasted more than a billion years. The frequency of these impacts on Earth was enough to reproduce the known impact spherule beds. Image Courtesy David Kring, Center for Lunar Science and Exploration, and the Lunar and Planetary Institute
The new computer model shows that the innermost portion of the asteroid belt could have become destabilized, delivering numerous big impacts to Earth and Moon over longer time periods.
Have there been any previous indications about this period of impacts?
“The problem is that we have almost no Archean rocks,” Bottke told Universe Today. “The oldest terrestrial craters, Sudbury and Vredefort, are 1.85 and 2.02 billion years old. The spherule beds are our only window into impacts prior to this time.”
Also, Bottke said, the number of people who look for impact spherules is almost equally scarce. “People such as Bruce Simonson, Don Lowe, Gary Byerly, and Frank Kyte, have been carrying on a long, lonely quest to try to get people to consider the implications of their work, which are deeply profound, in my opinion,” Bottke said.
As for finding evidence of this later period of impacts on the Moon, Bottke said the problem there is the lack of solid ages for most impact events.
“This means it is difficult say anything definitive about the timing of major impacts,” Bottke said. “We are working this problem now with Michelle Kirchoff, who is counting craters on top of large lunar craters. This can be done now that we have LRO data.” (Listen to a podcast interview of Kirchoff on the 365 Days of Astronomy.)
Still, Bottke said, without using “fancy dynamics,” they can address some issues.
“Studies in the post-Apollo era suggested that the Moon has four 160-300 km craters that formed after Orientale, whose age is 3.7-3.8 billion years ago and (i.e., K/T-sized events or larger),” he said. “Crater counts from the Galileo mission and Apollo-era geologic analyses suggest at least one of these events took place near 3.2-3.5 billion years ago. If we account for the gravitational cross section of the planets, we know that for every lunar event, we should get about 20 on the Earth. So, from this argument alone, one should get a lot of big impacts on the Earth after the formation of Orientale.”
The new study fits with the available constraints about impacts on the Moon as well as finding the right distribution of spherule beds on Earth.
The best way to confirm everything, however, Bottke said, would be if more lunar rocks from various locations were available for study.
Arp 302 consists of a pair of very gas-rich spiral galaxies in their early stages of interaction. Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)
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A group of astronomers have discovered a vast structure of satellite galaxies and clusters of stars surrounding our Milky Way galaxy, stretching out across a million light years. The team says their findings may signal a “catastrophic failure of the standard cosmological model,” challenging the existence of dark matter. This joins another study released last week, where scientists said they found no evidence for dark matter.
PhD student Marcel Pawlowski and astronomy professor Pavel Kroupa from the University of Bonn in Germany are no strangers to the study – and skepticism — of dark matter. Together the two have a blog called The Dark Matter Crisis, and in a 2009 paper that also studied satellite galaxies, Kroupa declared that perhaps Isaac Newton was wrong. “Although his theory does, in fact, describe the everyday effects of gravity on Earth, things we can see and measure, it is conceivable that we have completely failed to comprehend the actual physics underlying the force of gravity,” he said.
While conventional cosmology models for the origin and evolution of the universe are based on the presence of dark matter, invisible material thought to make up about 23% of the content of the cosmos, this model is backed up by recent observations of the Cosmic Microwave Background that estimate the Universe is made of 4% regular baryonic matter, 73% dark energy and the remaining is dark matter.
But dark matter has never been detected directly, and in the currently accepted model – the Lambda-Cold Dark Matter model – the Milky Way is predicted to have far more satellite galaxies than are actually seen.
Pawlowski, Kroupa and their team say they have found a huge structure of galaxies and star clusters that extends as close as 33,000 light years to as far away as one million light years from the center of the galaxy, existing in right angles to the Millky Way, or in a polar structure both ‘north’ and ‘south’ of the plane of our galaxy.
This could be the ‘lost’ matter everyone has been searching for.
They used a range of sources to try and compile this new view of exactly what surrounds our galaxy, employing twentieth century photographic plates and images from the robotic telescope of the Sloan Deep Sky Survey. Using all these data they assembled a picture that includes bright ‘classical’ satellite galaxies, more recently detected fainter satellites and the younger globular clusters.
Altogether, it forms a huge structure.
“Once we had completed our analysis, a new picture of our cosmic neighbourhood emerged,” said Pawlowski.
The team said that various dark matter models struggle to explain what they have discovered. “In the standard theories, the satellite galaxies would have formed as individual objects before being captured by the Milky Way,” said Kroupa. “As they would have come from many directions, it is next to impossible for them to end up distributed in such a thin plane structure.”
Many astronomers, including astrophysicist Ethan Siegel in his Starts With a Bang blog, say the big picture of dark matter does a good job of explaining the structure of the Universe.
Siegel asks if any studies refuting dark matter “allow us to get away with a Universe without dark matter in explaining large-scale structure, the Lyman-alpha forest, the fluctuations in the cosmic microwave background, or the matter power spectrum of the Universe? The answers, at this point, are no, no, no, and no. Definitively. Which doesn’t mean that dark matter is a definite yes, and that modifying gravity is a definite no. It just means that I know exactly what the relative successes and remaining challenges are for each of these options.”
However, via Twitter today Pawlowski said, “Unfortunately the big picture of dark matter being reportedly fine only helps if looking from far away or with broken glasses.”
One explanation for how this structure formed is that the Milky Way collided with another galaxy in the distant past.
“The other galaxy lost part of its material, material that then formed our Galaxy’s satellite galaxies and the younger globular clusters and the bulge at the galactic centre.” said Pawlowski. “The companions we see today are the debris of this 11 billion year old collision.”
The team wrote in their paper: “If all the satellite galaxies and young halo clusters have been formed in an encounter between the young Milky Way and another gas-rich galaxy about 10-11 Gyr ago, then the Milky Way does not have any luminous dark-matter substructures and the missing satellites problem becomes a catastrophic failure of the standard cosmological model.”
“We were baffled by how well the distributions of the different types of objects agreed with each other,” said Kroupa. “Our model appears to rule out the presence of dark matter in the universe, threatening a central pillar of current cosmological theory. We see this as the beginning of a paradigm shift, one that will ultimately lead us to a new understanding of the universe we inhabit.”
This breathtaking view of Space Shuttle Enterprise at the Smithsonian lies ahead for New York City visitors. Credit: Ken Kremer
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Unstable weather has temporarily grounded the last flight of Space Shuttle Enterprise for just a few more days.
Visitors to New York City – Prepare yourselves for a breathtaking view !
NASA is tentatively targeting Friday, April 27 as the date of the historic ferryflight of Enterprise from the Washington, DC area to the New York City metropolitan area, if the weather cooperates.
“Managers shifted the flight from Wednesday to Friday because of a large region of low pressure dominating the East Coast. The weather is predicted to be more favorable Friday,” NASA said in a statement today.
Enterprise is a full scale prototype space shuttle orbiter that carried out critical approach and landing tests in California in the late 1970’s, setting the stage for the first shuttle blast off in 1981.The orbiter is named after the famed “Starship” in the iconic TV series “Star Trek”.
Space Shuttle Enterprise is already piggybacked atop NASA’s modified Boeing 747 Jumbo Jet at Dulles International Airport outside Washington, DC and awaits the GO command to take off for New York City’s John F. Kennedy International Airport.
As I wrote earlier, visitors to Dulles Airport can get an exquisite view of Enterprise strapped aboard the Shuttle Carrier Aircraft (SCA) from the upper levels of the Daily Parking garage. Go see it in these few extra days before it departs forever.
Space Shuttle Enterprise mounted atop NASA 747 Carrier Jet at Dulles Airport - Commercial Jets Fly By. The public can easily see NASA’s 1st orbiter bolted on top of the Shuttle Carrier Aircraft (SCA) from the upper levels of a Daily Parking Garage at Dulles Airport. On April 19, 2012, Enterprise was towed out of the Smithsonian's Steven F. Udvar-Hazy Center, Thursday, April 19, 2012, in Chantilly, Va. and swapped for shuttle Discovery. Enterprise will be flown to New York City this week. Credit: Ken Kremer
Originally the ferry flight had been scheduled for Monday and then switched to Wednesday, April 25. But a powerful storm swept through the US East Coast over the weekend and continuing poor weather has further disrupted the flight plans.
NASA and the FAA are coordinating the flight which is expected to arrive and conduct a series of breathtaking low flyovers over and near various landmarks and historic sites in the New York City between 930 and 1130 a.m, including the Statue of Liberty and the Intrepid Sea, Air and Space Museum – her permanent final home and resting place. The exact route and timing depend on weather and operational constraints.
When the flyover is complete, the SCA will land at John F. Kennedy International Airport and more than 1500 dignitaries are expected to be on hand to welcome Enterprise to the Big Apple.
In the weeks following the arrival, Enterprise will be “demated” from the top of the 747 using a pair of heavy duty cranes and placed on a barge for a dramatic seagoing voyage and will be moved by tugboat up New York’s Hudson River to the Intrepid museum in June. The shuttle will be lifted and placed on the flight deck of the Intrepid, where it will be on exhibit to the public starting this summer in a temporary climate-controlled pavilion.
The Intrepid museum is constructing a permanent exhibit facility nearby to showcase Enterprise and the museum’s space-related exhibits and education curriculum.
Since 2003, Enterprise has been on public display at the Smithsonian’s National Air & Space Museum Annex in Virginia.
Last week, Enterprise was replaced at the Smithsonian’s Steven F. Udvar-Hazy Center by Space Shuttle Discovery in a prestigious welcome ceremony featuring Astronaut and Senator John Glenn, 1st American in Orbit.
Ken will be on hand for the history making Grand Arrival of a magnificent NASA Space Shuttle flying over the superlative Manhattan skyline. Feel free to send me your Enterprise photos to post at Universe Today.
Infrared imaging of the Sombrero Galaxy (M104) reveals both elliptical and disk structures.
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The Sombrero galaxy has a split personalty, according to recent observations by NASA’s Spitzer Space Telescope. Infrared imaging has revealed a hazy elliptical halo of stars enveloping a dual-structured inner disk; before this, the Sombrero galaxy was thought to be only disk-shaped.
Spitzer’s heat-seeking abilities reveal both stars and dust within the Sombrero galaxy, also known as Messier 104 and NGC 4594. The starlight detected at 3.5 and 4.6 microns is represented in blue-green while the dust imaged at 8.0 microns is shown in red.
In addition, Spitzer discerned that the flat disk within the galaxy is made up of two sections — an inner disk composed almost entirely of stars with no dust, and an outer ring containing both dust and stars.
The galaxy’s dual personality couldn’t be so clearly seen in previous visible-light images.
Hubble image of M104. (NASA/The Hubble Heritage Team STScl/AURA)
“The Sombrero is more complex than previously thought,” said Dimitri Gadotti of the European Southern Observatory in Chile and lead author of the report. “The only way to understand all we know about this galaxy is to think of it as two galaxies, one inside the other.”
Although it might seem that the Sombrero is the result of a collision between two separate galaxies, that’s actually not thought to be the case. Such an event would have destroyed the disk structure that’s seen today; instead, it’s thought that the Sombrero accumulated a lot of extra gas billions of years ago when the Universe was populated with large clouds of gas and dust. The extra gas fell into orbit around the galaxy, eventually spinning into a flattened disk and forming new stars.
This is one of the first galaxies to be seen with such a dual structure — even though M104 has been known about since the mid-1700s.
“Spitzer is helping to unravel secrets behind an object that has been imaged thousands of times,” said Sean Carey of NASA’s Spitzer Science Center at CalTech. “It is intriguing Spitzer can read the fossil record of events that occurred billions of years ago within this beautiful and archetypal galaxy.”
At a magnitude of +8, the Sombrero galaxy is just beyond the limit of naked-eye visibility but can be seen with small telescopes (4-inch/100 mm or larger). It is 28 million light-years away and can be found in the night sky located 11.5° west of Spica and 5.5° northeast of Eta Corvi.
Location of daylight (8 AM) fireball over California on April 22, 2012. Credit: NASA's Meteor Watch
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A daytime fireball over the skies of central/northern California on Sunday morning, April 22, 2012 caused a loud explosion and the event was also detected on several seismographs stations in the area. According to Bill Cooke, head of NASA’s Meteoroid Environments Office, the source of the blast was a meteoroid about the size of a minivan, weighing in at around 70 metric tons (154,300 pounds) and at the time of disintegration released energy equivalent to a 5-kiloton explosion.
For comparison, conventional bombs yield energy from less than 1 ton to 44 tons, and the approximate energy released when the Chicxulub impact caused the mass extinction 65 million years ago was estimated to be equal to 96 million megatons of TNT.
“This was a BIG event,” said Elizabeth Silber of the Meteor Group at the Western University in Ontario, Canada.
“Most meteors you see in the night’s sky are the size of tiny stones or even grains of sand and their trail lasts all of a second or two,” said Don Yeomans of NASA’s Near-Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena, Calif. “Fireballs you can see relatively easily in the daytime and are many times that size – anywhere from a baseball-sized object to something as big as a minivan.”
Silber estimates the location of its explosion in the upper atmosphere above California’s Central Valley. It is not known yet if any pieces of the space rock survived to land as meteorites, but the entire object was likely vaporized before hitting the ground. However, you can bet there are people out looking. (Silber said on the Meteorobs newsgroup that based on infrasonic data the approximate source coordinates are 37.6N, 120.5W).
Descriptions of the fireball range from a “silver flash” to like a “green glittering sparkler,” and one person said their sighting of the object was followed 4-5 minutes later by a loud sonic boom.
Unfortunately, since the huge fireball occurred during the day, all of NASA’s meteor-seeking cameras were turned off, so images of the event are sparse. You can see some at news station KTVN’s website.
This type of fireball is quite rare, and visual observations of them are even more rare. “An event of this size might happen about once a year,” said Yeomans. “But most of them occur over the ocean or an uninhabited area, so getting to see one is something special.”
That the fireball occurred during the Lyrid meteor shower is probably a coincidence, most experts are saying, as meteor shower meteors are generally small bits space dust that don’t produce large fireballs. However, another large fireball also occurred on April 20 in Brazil. See more information about that bolide here.
