A ridge that follows the equator of Saturn's moon Iapetus gives it the appearance of a giant walnut. This image was taken by the Cassini spacecraft. Credit: NASA/JPL/SSI
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There’s a new theory for why Saturn’s moon Iapetus looks like a walnut. The moon has a mysterious large ridge that covers more than 75 percent of the moon’s equator. Figuring out the reason for the ridge, say researchers from Washington University in St. Louis, has been a tough nut to crack. But they propose that at one time Iapetus itself had its very own moon, and the orbit of this mini-moon-around-another-moon would have decayed because of tidal interactions with Iapetus, and those forces would have torn the sub-satellite apart, forming a ring of debris around Iapetus that would eventually slam into the moon near its equator.
This is not the nuttiest proposal ever…
A closeup of Iapetus' ridge. In 2007, Cassini flew within a few thousand kilometers of Iapetus' surface to take this dramatic image. Credit: NASA/JPL/SSI
The ridge on Iapetus is 100 kilometers (62 miles) wide and at place, 20 kilometers (12 miles) high. (The peak of Mount Everest, by comparison, is 8.8 km (5.5 miles) above sea level.) Iapetus itself is 1,470 km across, and is the 11th largest moon in the Solar System.
Professor William McKinnon and his former doctoral student, Andrew Dombard — now from the University of Illinois Chicago — came up with this idea.
“Imagine all of these particles coming down horizontally across the equatorial surface at about 400 meters per second, the speed of a rifle bullet, one after the other, like frozen baseballs,” said McKinnon. “Particles would impact one by one, over and over again on the equatorial line. At first the debris would have made holes to form a groove that eventually filled up.”
“When you have a debris ring around a body, the collisional interactions steal energy out of the orbit,” Dombard said. “And the lowest energy state that a body can be in is right over the rotational bulge of a planetary body — the equator. That’s why the rings of Jupiter, Saturn, Uranus and Neptune are over the equator.”
“We have a lot of corroborating calculations that demonstrate that this is a plausible idea,” added Dombard, “but we don’t yet have any rigorous simulations to show the process in action. Hopefully, that’s next.”
Other ideas for how the ridge was created are volcanism or mountain-building forces.
“Some people have proposed that the ridge might have been caused by a string of volcanic eruptions, or maybe it’s a set of faults,” said McKinnon. “But to align it all perfectly like that — there is just no similar example in the solar system to point to such a thing.”
Dombard said there are three critical observations that any model for the formation of the ridge has to satisfy: Why the feature is sitting on the equator; why only on the equator, and why only on Iapetus.
Dombard says that Iapetus’s Hill sphere — the zone close to an astronomical body where the body’s gravity dominates satellites — is far bigger than that of any other major satellite in the outer solar system, accounting for why Iapetus is the only body known to have such a ridge.
“Only Iapetus could have had the orbital space for the sub-satellite to then evolve and come down toward its surface and break up and supply the ridge,” he says.
Dombard will make a presentation on the preliminary findings Wed., Dec. 15, 2010, at the fall meeting of the American Geophysical Union in San Francisco. The team also included Andrew F. Cheng of the Johns Hopkins Applied Physics Laboratory, and Jonathan P. Kay, a graduate student at UIC.
SNR 0509 is the visible remnant of a powerful stellar explosion in the Large Magellanic Cloud. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA). Acknowledgement: J. Hughes (Rutgers University)
A festive, delicate ring –photographed by the Hubble Space Telescope — appears to float serenely in the depths of space, but this apparent calm hides an inner turmoil. The gaseous envelope formed as the expanding blast wave and ejected material from a supernova tore through the nearby interstellar medium. Called SNR B0509-67.5 (or SNR 0509 for short), the bubble is the visible remnant of a powerful stellar explosion in the Large Magellanic Cloud (LMC), a small galaxy about 160,000 light-years from Earth.
Ripples seen in the shell’s surface may be caused either by subtle variations in the density of the ambient interstellar gas, or possibly be driven from the interior by fragments from the initial explosion. The bubble-shaped shroud of gas is 23 light-years across and is expanding at more than 18 million km/h.
Astronomers have concluded that the explosion was an example of an especially energetic and bright variety of supernova. Known as Type Ia, such supernova events are thought to result when a white dwarf star in a binary system robs its partner of material, taking on more mass than it is able to handle, so that it eventually explodes.
Hubble’s Advanced Camera for Surveys observed the supernova remnant on 28 October 2006 with a filter that isolates light from the glowing hydrogen seen in the expanding shell. These observations were then combined with visible-light images of the surrounding star field that were imaged with Hubble’s Wide Field Camera 3 on 4 November 2010.
With an age of about 400 years, the supernova might have been visible to southern hemisphere observers around the year 1600, although there are no known records of a “new star” in the direction of the LMC near that time. A much more recent supernova in the LMC, SN 1987A, did catch the eye of Earth viewers and continues to be studied with ground- and space-based telescopes, including Hubble.
Artist concept of an InterOrbital Tubesat in space. Credit: InterOrbital.
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For a space geek, the ultimate do-it-yourself project would be building a satellite in your basement. Astronomer and writer Sandy Antunes is doing just that, but there’s an artsy side to this project, as well. His satellite, called Project Calliope, will collect data from the ionosphere and send it back to Earth in sound-based MIDI files, allowing music to be created from space. “It’ll be an ionospheric detector transmitting sonifiable data back to Earth,” said Antunes. “Conceptually, it’s a musical instrument in space, played by space rather than just after-the-fact sonified.”
Antunes decided to embark on this project after the commercial space company InterOrbital began offering small DIY, soda-can-sized picosatellites for the reasonable price of $8,000 – which includes the launch.
One of the major reasons for doing the project is to prove that anyone can build a satellite in their basement – although Antunes admits it is also a fairly cheap midlife crisis expenditure, especially when his boss at the Science 2.0 blog, Hank Campbell, decided to pitch in half of the price.
The skeleton of the Antunes' satellite, assembled. Cat is for scale. Credit: Sandy Antunes.
“When people ask, ‘where did you get your idea?’ that misses the mark,” Antunes told Universe Today. “The question should be, ‘What idea do you have?’ We’re at the point now where a single hobbyist can send something into orbit to do something useful. I think this is a new space age way of thinking. I’d like to see if this inspires people to do something cooler than me. To me that is what science is all about.”
Antunes is documenting his experiences on his blog, The Sky By Day. “I’m making mistakes so that other people won’t have to make them,” he said. “Hopefully I can make the path will be easier for others.”
Plus, Antunes hopes to answer the big question of what space sounds like. The sun interacts with the Earth’s magnetic field in the ionosphere, creating all sorts of activity; there are also changes in temperature and light.
“People don’t know what space sounds like,” he said. “You walk to ocean and close your eyes and you can hear the roar of the waves, the rushing of water, the moments of quiet; and you can get a good idea of what activity is going on. But we don’t know have an idea of the activity of space, or the ionosphere, where this satellite is going. Sonifying the ionosphere will give people an idea of the ebb and flow of it – how there are constant events going on, sometimes catastrophic-type events but there is also a quiescent stage.”
When the data comes back to Earth, Antunes will give musicians free rein. “Musicians can take it and rework it, much like how musicians have ambient noise, nature sounds, or whale songs in a piece,” Antunes said, “but in this case they can take sounds from the ionosphere. We are making it royalty free so anyone can use it.”
The packaged components for InterOrbital's $8,000 DIY satellite. Credit: Sandy Antunes.
Antunes said working with the pre-packaged TubeSat Personal Satellite Kit is different than what he initially imagined. The Hubble Space Telescope, it is not.
“It has a power system that’s basically two lithium AA batteries hooked together, a little stick of gum computer chip, and some very fragile solar cells,” Antunes said. “I thought it would be hard science and tricky engineering and unsolved problems, but everything I’m getting is off the shelf. The sensors are plug-ins, so the primary work is integrating things. So there are very different problems from what I thought, but this tells me that you don’t have to have a PhD to put up a satellite.”
The current liftoff date for the first InterOrbital Tubesat launch is March or April of 2011. The company has built the rocket engines and they are now doing testing and test firings.
Antunes knows that testing a rocket has a lot of ambiguity, and he anticipates some delays, as even when he has been part of a NASA project, he has never had a launch go on time. This being the first launch of InterOrbital’s commercial satellite venture, if it blows up, Antunes will get a chance to refly his satellite.
Project Calliope will go into a short-term polar orbit, and last about 6-12 weeks, so it is a short term experience, Antunes said.
But he will be tweaking his satellite right up until delivery.
“I wanted to do something that NASA cannot, and that a University wouldn’t, combining art and science,” Antunes said. “I like the idea of flying something in space whose purpose is to make music until it dies– music from science.”
Noctis Vista: West of Valles Marineris lies a checkerboard named Noctis Labyrinthus, which formed when the Martian crust stretched and fractured. As faults opened, they released subsurface ice and water, causing the ground to collapse. This westward view combines images taken during the period from April 2003 to September 2005 by the Thermal Emission Imaging System instrument on NASA's Mars Odyssey orbiter. It is part of a special set of images marking the occasion of Odyssey becoming the longest-working Mars spacecraft in history. The pictured location on Mars is 13.3 degrees south latitude, 263.4 degrees east longitude. Image Credit: NASA/JPL-Caltech/ASU
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At 3,340 days and counting, NASA’s Mars Odyssey orbiter established a new record for longevity as of Dec. 15 and thereby worked longer at the red planet than any other spacecraft in human history.
The previous Martian record holder was the Mars Global Surveyor (MGS) orbiter which operated in orbit from Sept. 11, 1997 to Nov. 2, 2006 until contact was lost following a computer glitch.
Odyssey has made numerous high impact scientific discoveries along the way. The probe also relayed most of the science data from Spirit, Opportunity and Phoenix and will continue that task for NASA’s upcoming Mars Science Laboratory (MSL) rover named Curiosity.
The spacecrafts name – 2001 Mars Odyssey – was chosen as a tribute to the vision and spirit of space exploration as embodied in the works of renowned science fiction author Arthur C. Clarke – including the movie “2001: A Space Odyssey”.
It was way back on Oct. 24, 2001 that the Odyssey spacecraft fired its main engine to brake the crafts speed and allow it to be captured by Mars and enter a highly elliptical orbit. A technique known as aerobraking was used over the next three months to fly through the upper atmosphere and utilize drag to gradually lower the crafts altitude and eventually enter its mapping orbit.
Ares Vallis: In Ares Vallis, teardrop mesas extend like pennants behind impact craters, where the raised rocky rims diverted the floods and protected the ground from erosion. Scientists estimate the floods had peak volumes many times the flow of today's Mississippi River. The pictured location on Mars is 15.9 degrees north latitude, 330 degrees east longitude. Image Credit: NASA/JPL-Caltech/ASU
Science operations began in earnest in February 2002. Within a few months, Odyssey made the key discovery of the entire mission when it found that the polar regions harbored substantial caches of water ice within a meter of the dry surface of Mars.
The detection of water – in the form of hydrogen — from orbit using the crafts Gamma Ray Spectrometer led directly to the proposal for the Phoenix mission which confirmed the discovery in 2008. Phoenix landed directly on top of vast sheets of frozen water ice in the northern polar region of Mars and scooped up samples of ice for analysis by the landers science suite.
Another notable achievement by Odyssey during the primary mission phase was to complete a survey of the radiation environment to determine the radiation-related risk to any future human explorers who may one day go to Mars.
In another first, Odyssey’s instruments globally mapped the amount and distribution of many chemical elements and minerals that make up the martian surface. Such data helps explain how the planet’s landforms developed over time, provides clues to the geological and climatic history of Mars, informs about the potential for finding past or present life and where are the best locations to search for life and send future landers such as the Curiosity rover set to launch in November 2011.
Artist concept of Mars Odyssey probe in orbit since Oct. 24, 2001
Mars Odyssey is equipped with three primary science instruments to accomplish the goals set out in NASA Mars Exploration Program:
• THEMIS (Thermal Emission Imaging System), for determining the distribution of minerals, particularly those that can only form in the presence of water;
• GRS (Gamma Ray Spectrometer), for determining the presence of 20 chemical elements on the surface of Mars, including hydrogen in the shallow subsurface (which acts as a proxy for determining the amount and distribution of possible water ice on the planet); and,
• MARIE (Mars Radiation Environment Experiment), for studying the radiation environment.
The primary mission lasted until August 2004. Since then the mission lifetime has been extended several times and further extensions are in the works according to Guy Webster, the Public Affairs Officer at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif., which manages the Odyssey mission.
“We are currently in the fourth extended mission which is funded through the end of September 2012,” Webster told me. “Extended missions are funded for about a one-Mars-year period, which is approximately equal to two years. The next extended mission period will be during the MSL’s prime surface mission and Odyssey is an integral part of the effort to relay MSL’s data from the surface and back to Earth.”
MSL is slated for an August 2012 landing on Mars. “It is expected that Odyssey will be approved for a fifth extended mission,” said Webster.
“The total investment in this mission so far — including development, assembly & test, launch, and operations — is $508 million,” added Webster.
Udzha Crater: Although it is 45 kilometers (28 miles) wide, countless layers of ice and dust have all but buried Udzha Crater. Udzha lies near the edge of the northern polar cap, and only the topmost edges of its crater rim rise above the polar deposits to hint at its circular shape. The pictured location on Mars is 81.8 degrees north latitude, 77.2 degrees east longitude. Image Credit: NASA/JPL-Caltech/ASU
A huge bonus of scientific accomplishments has been enabled during the extended mission phase that otherwise would not have been possible.
“The extra years have allowed us to build up the highest-resolution maps covering virtually the entire planet,” said Odyssey Project Scientist Jeffrey Plaut of JPL.
The maps were constructed using nearly 21,000 images taken by the THEMIS camera which was built and is operated by Arizona State University, Tempe. Surface details as small as 100 meters (330 feet) wide are visible. Check out this slide show of some of Odyssey’s greatest hits as compiled by the camera team and NASA: http://www.nasa.gov/mission_pages/odyssey/images/all-stars.html
Chasma Boreale is a long, flat-floored valley that cuts deep into Mars' north polar icecap. Its walls rise about 1,400 meters (4,600 feet) above the floor. Where the edge of the ice cap has retreated, sheets of sand are emerging that accumulated during earlier ice-free climatic cycles. Winds blowing off the ice have pushed loose sand into dunes and driven them down-canyon in a westward direction, toward our viewpoint. This scene combines images taken during the period from December 2002 to February 2005 by the Thermal Emission Imaging System instrument on NASA's Mars Odyssey orbiter. The pictured location on Mars is 84.9 degrees north latitude, 359.1 degrees east longitude. Image Credit: NASA/JPL-Caltech/ASU
The ability to monitor seasonal changes on Mars from year-to-year, such as the cycle of carbon-dioxide freezing out of the atmosphere in polar regions during each hemisphere’s winter, is another example of bonus science from the extended mission.
“It is remarkable how consistent the patterns have been from year to year, and that’s a comparison that wouldn’t have been possible without our mission extensions,” Plaut said.
The science team comprises numerous additional partners including the Russian Aviation and Space Agency, the University of Arizona, and Los Alamos National Laboratory.
Odyssey has served as the primary means of communications for NASA’s Mars surface explorers in the past decade and will continue that role for the upcoming Curiosity rover.
“More than 95 percent of the data from Spirit and Opportunity and approximately 79 percent of the data from Phoenix was relayed by Odyssey,” Webster stated.
Given the propellant reserves on board, Odyssey could continue operating until at least about 2016 and perhaps even well beyond if the ships systems remain healthy.
“21.6 kg of propellant remains with an average consumption rate of about 1.4 kg per year,” according to Webster. “However, there are other elements of the spacecraft that might suggest that Odyssey’s life expectancy could be closer to six years. Lifetime issues are extremely difficult to estimate. The best policy is to reevaluate the spacecraft’s health at regular intervals, and prior to important events, and determine if we’re up to a given task. So far we have been.”
Odyssey remains in good shape overall and will continue to actively pursue many science investigations in the years ahead.
Among the top priorities are extended coverage of Mars with mid-afternoon imaging by THEMIS. The orbit was adjusted last year to enable surface observations in mid-afternoon instead of late afternoon. Another goal is to extend year-to-year comparisons of seasonal changes on Mars.
Concerning the status of the science instruments, Webster informed me, “THEMIS and two parts of the GRS suite — the neutron spectrometer and the high-energy neutron detector — are currently in use. The third sensor for that suite — the gamma ray detector — is no longer in use. The payload’s MARIE radiation experiment stopped taking measurements several years ago.”
Lockheed Martin Space Systems, Denver built the Odyssey spacecraft which is operated in partnership with JPL.
Mars Odyssey was launched on April 7, 2001. For more information visit the mission website: http://mars.jpl.nasa.gov/odyssey/
Noctis Canyon: A false-color mosaic focuses on one junction in Noctis Labyrinthus where canyons meet to form a depression 4,000 meters (13,000 feet) deep. Dust (blue tints) lies on the upper surfaces, while rockier material (warmer colors) lies below. The pictures used to create this mosaic image were taken from April 2003 to September 2005 by the Thermal Emission Imaging System instrument on NASA's Mars Odyssey orbiter. The pictured location on Mars is approximately 13 degrees south latitude, 260 degrees east longitude. Image Credit: NASA/JPL-Caltech/ASU Bunge Crater Dunes: Fans and ribbons of dark sand dunes creep across the floor of Bunge Crater in response to winds blowing from the direction at the top of the picture. The frame is about 14 kilometers (9 miles) wide.The pictured location on Mars is 33.8 degrees south latitude, 311.4 degrees east longitude. Image Credit: NASA/JPL-Caltech/ASDual Crater: If a meteorite breaks in two shortly before hitting the ground, the typical bowl shape of a single impact crater becomes doubled. The two circular blast regions intersect, creating a straight wall separating the two craters. At the same time, 'wings' of ejected debris shoot out to the side. The image covers an area 13 kilometers (8 miles) wide. Image Credit: NASA/JPL-Caltech/ASU
SpaceX has gathered a long string of successes since its founding in 2002. Photo Credit: Alan Walters/awaltersphoto.com
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With the success of the first and second launches of the Falcon 9 rocket as well as the successful recovery of the Dragon spacecraft, Space Exploration Technologies (SpaceX) has stated its intent to accelerate the pace of the Commercial Orbital Transportation Services (COTS) program that the private space firm has with NASA. The company has been inspecting various elements of the Dragon spacecraft that launched to orbit on Dec. 8, to make potential changes to the next Dragon – in preparation for its flight.
The company became the first private organization in history to launch a vehicle into orbit and then have it successfully return safely to Earth. The company has, for some time, been working to step up the pace of the COTS program. Under this program the first three flights of the Dragon would be demonstration flights with the third, and final demonstration flight docking with the International Space Station (ISS).
SpaceX encountered delays in both of its Falcon 9 launches - but forged ahead in a manner reminiscent of the early days of manned space flight. Photo credit: Jason Rhian
SpaceX is, if anything, a young and restless company, a company on the move and as such they want to combine the mission requirements of the second and third flights – into one. In short, SpaceX is hoping to send their next Dragon – to the space station itself, cutting out one demonstration flight in the process. However, while officials at SpaceX and the company’s CEO and CTO Elon Musk are attempting to relive the golden age of manned spaceflight (this effort is somewhat similar to the accelerated launch of the Apollo 8 mission) – NASA appears uncertain about speeding up the process. NASA has stated that if all went well with the first flight of the Dragon that it would consider speeding up the program.
The next flight of the Dragon spacecraft could take place as soon as the middle of next year. According to Musk, there are few differences between the maneuvers that Dragon conducted on Orbit this past Wednesday – and those that would be required if the craft were to rendezvous with the ISS. For a mission to the orbiting outpost, the Dragon would need to be equipped with solar arrays and certain equipment on board the craft would need to be upgraded.
To date, NASA has only stated that it is assessing the possibility of accelerating the program and that it recognizes the successes that SpaceX has enjoyed. Those within the space community note that NASA has a risk-averse philosophy and that the agency will likely want to see the company complete the requirements of the initial contract and fully demonstrate the Dragon’s capabilities.
SpaceX launched the second of its Falcon 9 rockets from Cape Canaveral Air Force Station's launch complex 40 on December 8 at 10:43 p.m. EDT/15:43 UDT. Photo Credit: Alan Walters/awaltersphoto.com
Discovery on the launchpad. Credit: Alan Walters (awaltersphoto.com) for Universe Today
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NASA managers made the decision on Monday afternoon that space shuttle Discovery will be rolled back from the launchpad for inspections and/or repairs. There’s no word from NASA yet on the reason for the decision, but presumably it has to do with the cracks on the “stringers,” or structural ribs of the shuttle’s external tank. A tanking test was scheduled for today (Monday), but cold weather has delayed the test to no earlier than Dec. 17. According to reports on Twitter, the rollback will be done about five days after the tanking test.
The reason for the tanking test delay is that the sensors used to test the external tank won’t bond to the sides of the tank if temperatures are too low, and the current frigid conditions aren’t even close to being warm enough.
Additional word is that the shuttle is hoped to be returned to the launchpad by the middle of January in order to be ready for an anticipated launch in February. But that all depends on the nature of the work NASA engineers determine needs to be done. Since production of external tanks is now finished at the assembly facility in Louisiana, it would take at least two years — and probably more — for a new tank to be built.
More details have now emerged on the reasons for sending Discovery back to the Vehicle Assembly Building:
There, the engineers have better tools and better access to put the external tank through additional image scans. Once in the VAB, technicians would collect X-ray data on stringers on the back side of the external tank midsection, called the intertank, which is not accessible at the launch pad.
Additionally, the test instrumentation and foam insulation on those areas of the intertank would be removed and the area would be prepped again for launch.
Artist impression of Voyager 1, the first probe to traverse the heliosheath (NASA)
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The venerable Voyager spacecraft are truly going where no one has gone before. Voyager 1 has now reached a distant point at the edge of our solar system where it is no longer detecting the solar wind. At a distance of about 17.3 billion km (10.8 billion miles) from the Sun, Voyager 1 has crossed into an area where the velocity of the hot ionized gas, or plasma, emanating directly outward from the sun has slowed to zero. Scientists suspect the solar wind has been turned sideways by the pressure from the interstellar wind in the region between stars.
“The solar wind has turned the corner,” said Ed Stone, Voyager project scientist based at the California Institute of Technology in Pasadena, Calif. “Voyager 1 is getting close to interstellar space.”
The event is a major milestone in Voyager 1’s passage through the heliosheath, the turbulent outer shell of the sun’s sphere of influence, and the spacecraft’s upcoming departure from our solar system.
Since its launch on Sept. 5, 1977, Voyager 1’s Low-Energy Charged Particle Instrument has been used to measure the solar wind’s velocity.
When the speed of the charged particles hitting the outward face of Voyager 1 matched the spacecraft’s speed, researchers knew that the net outward speed of the solar wind was zero. This occurred in June, when Voyager 1 was about 10.6 billion miles from the sun.
However, velocities can fluctuate, so the scientists watched four more monthly readings before they were convinced the solar wind’s outward speed actually had slowed to zero. Analysis of the data shows the velocity of the solar wind has steadily slowed at a rate of about 45,000 mph each year since August 2007, when the solar wind was speeding outward at about 130,000 mph. The outward speed has remained at zero since June.
“When I realized that we were getting solid zeroes, I was amazed,” said Rob Decker, a Voyager Low-Energy Charged Particle Instrument co-investigator and senior staff scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. “Here was Voyager, a spacecraft that has been a workhorse for 33 years, showing us something completely new again.”
Scientists believe Voyager 1 has not crossed the heliosheath into interstellar space. Crossing into interstellar space would mean a sudden drop in the density of hot particles and an increase in the density of cold particles. Scientists are putting the data into their models of the heliosphere’s structure and should be able to better estimate when Voyager 1 will reach interstellar space. Researchers currently estimate Voyager 1 will cross that frontier in about four years.
Our sun gives off a stream of charged particles that form a bubble known as the heliosphere around our solar system. The solar wind travels at supersonic speed until it crosses a shockwave called the termination shock. At this point, the solar wind dramatically slows down and heats up in the heliosheath.
A sister spacecraft, Voyager 2, was launched in Aug. 20, 1977 and has reached a position 8.8 billion miles from the sun. Both spacecraft have been traveling along different trajectories and at different speeds. Voyager 1 is traveling faster, at a speed of about 38,000 mph, compared to Voyager 2’s velocity of 35,000 mph. In the next few years, scientists expect Voyager 2 to encounter the same kind of phenomenon as Voyager 1.
The results were presented at the American Geophysical Union meeting in San Francisco.
I grew up playing with Legos, but never constructed anything like this! Andrew Carol built a replica of the The Antikythera Mechanism, the oldest known scientific computer, which was built in Greece probably around 100 BCE. No one in the current age knew about it until it was recovered from a shipwreck in 1901. Even then, it took a century until anyone could figure out what it was: an astronomical clock that determines the positions of celestial bodies with extraordinary precision. It is an analog computer with over 100 gears and 7 differential gearboxes, and is accurate to a day or two over its range. Continue reading “Ancient Eclipse-Predicting Computer Rebuilt in Lego”
(596) Scheila, the asteroid with a tail. Image credit: Peter Lake
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When is an asteroid not an asteroid? When it turns out to be a comet, of course. Has this ever happened before? Why, yes it has. In fact it was just announced December 12, 2010 that the asteroid (596) Scheila has sprouted a tail and coma! This is likely a comet that has been masquerading as an asteroid.
Taken from New Mexico Skies between 8h15m and 11h45m UT. The image is a stack of 10 x 600 sec exposures using a 20 inch RCOS and STL11K camera. Scale is 0.91 asec/px.. Image courtesy of Joseph Brimacombe
Steve Larson of the Lunar and Planetary Laboratory (LPL), University of Arizona first reported that images of the minor planet (596) Scheila taken on December 11th showed the object to be in outburst, with a comet-like appearance and an increase in brightness from magnitude 14.5 to 13.4. The cometary appearance of the object was confirmed by several other observers within hours.
A quick check of archived Catalina images of Scheila from October 18, November 2 and November 11 showed Scheila to look star-like, which is what asteroids look like from Earth. They just happen to be moving across the field of view in contrast to the fixed background stars. The image taken by Catalina on December 3rd shows some slight diffuseness and an increase in overall brightness. So, it appears this event began on or around December 3rd.
Upon hearing the news, there was some speculation that this might be evidence of an impact event. Had something crashed into asteroid Scheila? It seems unlikely, and this is a story we have heard before.
The asteroid discovered in 1979 and named 1979 OW7 was lost to astronomers for years and then recovered in 1996. It was subsequently renamed 1996 N2. That same year it was discovered to have a comet-like appearance, and many believed this was the signature of an impact between two asteroids. After years of inactivity 1996 N2 sprouted a tail again in 2002. One collision between two asteroids was unlikely enough. The odds of it happening again to the same object were essentially zero. What we had was a comet masquerading as an asteroid. This object is now known by its cometary name 133P/Elst-Pizarro, named after the two astronomers who discovered its initial cometary outburst.
The 2002 outburst and the discovery of more active asteroids showing mass-loss led to a paper (Hsieh and Jewitt 2006, Science, 312, 561-563) introducing an entirely new class of solar system objects, Main Belt Comets (MBC). MBCs look like comets because they show comae and have tails but they have orbits inside Jupiter’s orbit like main belt asteroids.
The most likely cause of the mass loss activity in MBCs is sublimation of water ice as the surface of the MBC is heated by the Sun. This is suggested most strongly by the behavior of the best-studied example, namely 133P/Elst-Pizarro. Its activity is recurrent, and it is strongest near and after perihelion, the point in its orbit nearest the Sun, like other comets.
MBCs are interesting to astronomers because they appear to be a third reservoir of comets in our solar system, distinct from the Oort cloud and Kuiper belt. Since we know of no way for these other reservoirs to have deposited comets in the inner solar system, the ice in MBCs probably has a different history than the ice in the outer comets. This allows researchers to study the differences in the Sun’s proto-planetary disk at three separate locations. This might lead to information on the Earth’s oceans, one of the continuing lines of investigation by solar system scientists.
Now it seems we have another MBC to add to the sample. And Scheila will probably be getting a new name soon. Asteroid (596) Scheila was discovered Feb. 21, 1906, by A. Kopff at Heidelberg. The 113Km in diameter ‘asteroid’ was named after an acquaintance, an English student at Heidelberg. In the future it will be called XXXP/Lawson or something similar, and Kopff’s Scheila will become just another footnote in the history of astronomical nomenclature.
One of the discovery images of the system obtained at the Keck II telescope using adaptive optics system and the NIRC2 Near-Infrared Imager. Image shows all four confirmed planets indicated as b, c, d and e in the labeled image. Planet "b" is a ~5 Jupiter-mass planet orbiting at about ~68 AU, while planets c, d, and e are ~7 Jupiter-mass companions orbiting the star at about 38, 24 and 14.5 AU. Credit: NRC-HIA, C. Marois & Keck Observatory
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Among one of the first exoplanet systems imaged was HR 8799. In 2008, a team led by Christian Marois at the Herzberg Institute of Astrophysics in Canada, took a picture of the system directly imaging three giant planets. The team revisited the system in 2009 – 2010 with the Keck II telescope and discovered a fourth planet in the system.
The new planet, designated HR 8799e, orbits at a distance of 14.5 AU, making it the innermost planet in the system. The other planets all orbit at distances of >25 AU. The images were taken in the near infrared where they are most noticeable because the system is relatively young (<100 Myr) and the planets are still radiating large amounts of heat from their formation.
The youth of these planets is part of what makes them an interesting target for astronomers. There exists a controversy in the community of planetary astronomers on the formation method of large planets. One theory states that planets form from a single, monolithic collapse that creates the entire planet’s mass at one time. Another possibility is that the initial collapse forms small cores early on, but then there is substantial growth later, as the planetesimal sweeps up additional material.
The discovery of the new planet challenges both theories. Marois states, “none of [the theories] can explain the in situ formation of all four planets.” Thus, a combination of both methods may be in use in the system. Several belts of dust are also known in the system which may help astronomers determine what modes of formation were present.
In particular HR 8799e is challenging to an in situ formation because the gravitational perturbations from the parent star should disrupt the formation of large gas planets within 20-40 AU from a single formation. Instead, the new planet would likely have had to been a core collapse with subsequent accretion, or alternatively, moved to its present location via migration.
Schematic representation of the HR 8799 planetary system compared to our solar system (viewed pole on and at the same distance as HR 8799). HR 8799 planet orbits are plotted assuming a pole-on view and circular orbits. A Kuiper Belt-like ring and an asteroid-like belt of dust, suggested by excess infrared light seen by the IRAS and ISO satellites, have been added. The HR 8799 dust disk is one of the heaviest detected by ISO and IRAS. It is thought that HR 8799e and HR 8799b dynamically interact with those dust disks in a way very similar to Jupiter with the asteroid belt and Neptune with the Kuiper Belt. Credit: NRC-HIA & C. Marois
Studying systems such as this may help astronomers better understand the formation of our own solar system. The paper notes that the HR 8799 “does show interesting similarities with the Solar system with all
giant planets located past the system’s estimated snow line (~2.7 AU for the Solar system and ~6 AU for HR 8799)”. Additionally, both have debris disks beyond the outer orbits with similar temperatures.
Different methods of detecting planetary formation necessarily turn up different types of systems. Radial velocity studies detect massive, close-in planets whereas direct imaging most easily finds more distant planets. These two apparent populations represent different modes of planetary formation and for a full understanding, astronomers will need a continuous sampling that merges the two. Marois notes that we are still far from this goal as “[w]e just do not have enough exoplanets detected by direct imaging (~6 so far)” to make any conclusions besides constraints from the non-detections occurring thus far. To truly merge these two populations, astronomers will likely need to wait until more systems are discovered.
Previously, some work has been done to estimate the composition of the atmospheres of the three planets already discovered in the system. These systems have been suggested to have cloudy atmospheres for CH4 and CO. According to Marois, his team is, “planning more observations on e, but it will be hard. We might have to wait for new instruments, like the Gemini Planet Imager to do it properly.” This new instrument “will put a ‘thumb’ on the star (or what we call a coronagraph) to physically block the star light and allow ‘easy’ detection of nearby faint planets.”
While this discovery is a first, it will certainly be one of a long line of exoplanet images. Marois is obviously excited about the ability to directly image planets. I asked him what the single most important thing he wanted readers to get from this research. His response was simple, “That we now have the telescopes and instruments to SEE planets orbiting other stars – that’s really cool! The exoplanet field is still very young and we have so much to learn.”
