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Sonntag, 22. Februar 2015 - 17:32 Uhr

Mars-Chroniken - MARS HÜGEL VERBERGEN EISIGE VERGANGENHEIT

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Phlegra Montes southern tip

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A complex network of isolated hills, ridges and small basins spanning 1400 km on Mars is thought to hide large quantities of water-ice.
Phlegra Montes stretches from the Elysium volcanic region at about 30ºN and deep into the northern lowlands at about 50°N, and is a product of ancient tectonic forces. Its age is estimated to be 3.65–3.91 billion years.
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Phlegra Montes in context
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ESA’s Mars Express imaged the portion of Phlegra Montes seen here on 8 October 2014. It captures the southernmost tip of the range centred on 31ºN / 160ºE.
Based on radar data from NASA’s Mars Reconnaissance Orbiter combined with studies of the region’s geology from other orbiters, scientists believe that extensive glaciers covered this region several hundred million years ago.
And it is thought that ice is still there today, perhaps only 20 m below the surface.
The tilt of the planet’s polar axis is believed to have varied considerably over time, leading to significantly changing climatic conditions. This allowed the development of glaciers at what are today the mid-latitudes of Mars.
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Phlegra Montes southern tip topography
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Features visible in the Phlegra Montes mountain range providing strong evidence for glacial activity include aprons of rocky debris surrounding many of the hills. Similar features are seen in glacial regions on Earth, where material has gradually slumped downhill through the presence of subsurface ice.
Additional features in the region include small valleys cutting through the hills and appearing to flow into regions of lower elevation, in particular towards the centre of the image.
The hummocky terrain provides a distinct contrast to the smooth plains that dominate the upper portion of this image. The material here is thought to be volcanic in origin, perhaps originating from the Hecates Tholus volcano in Elysium some 450 km to the west, some time after the formation of Phlegra Montes.
Upon closer inspection, ‘wrinkle ridges’ can be seen in the lava plain. These features arise from the cooling and contraction of lava owing to compressive tectonic forces following its eruption onto the surface.
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Perspective view of Phlegra Montes
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Phlegra Montes southern tip in 3D
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This region of Phlegra Montes and its local surrounds illustrate some of the key geological processes that have worked to shape the Red Planet over time, from ancient tectonic forces, to glaciation and volcanic activity.
Quelle: ESA

Tags: Mars-Chroniken 

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Sonntag, 22. Februar 2015 - 17:23 Uhr

Astronomie - Zum ersten Mal verzeichnen Raumfahrzeuge Sonnen-Schockwellen nach Ausbruch: "ultrarelativistische, Killer Elektronen innerhalb 60 Sekunden

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Earth's magnetosphere is depicted with the high-energy particles of the Van Allen radiation belts (shown in red) and various processes responsible for accelerating these particles to relativistic energies indicated. The effects of an interplanetary shock penetrate deep into this system, energizing electrons to ultra-relativistic energies in a matter of seconds.

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On Oct. 8, 2013, an explosion on the sun's surface sent a supersonic blast wave of solar wind out into space. This shockwave tore past Mercury and Venus, blitzing by the moon before streaming toward Earth. The shockwave struck a massive blow to the Earth's magnetic field, setting off a magnetized sound pulse around the planet.

NASA's Van Allen Probes, twin spacecraft orbiting within the radiation belts deep inside the Earth's magnetic field, captured the effects of the solar shockwave just before and after it struck.
Now scientists at MIT's Haystack Observatory, the University of Colorado, and elsewhere have analyzed the probes' data, and observed a sudden and dramatic effect in the shockwave's aftermath: The resulting magnetosonic pulse, lasting just 60 seconds, reverberated through the Earth's radiation belts, accelerating certain particles to ultrahigh energies.
"These are very lightweight particles, but they are ultrarelativistic, killer electrons -- electrons that can go right through a satellite," says John Foster, associate director of MIT's Haystack Observatory. "These particles are accelerated, and their number goes up by a factor of 10, in just one minute. We were able to see this entire process taking place, and it's exciting: We see something that, in terms of the radiation belt, is really quick."
The findings represent the first time the effects of a solar shockwave on Earth's radiation belts have been observed in detail from beginning to end. Foster and his colleagues have published their results in the Journal of Geophysical Research.
Catching a shockwave in the act
Since August 2012, the Van Allen Probes have been orbiting within the Van Allen radiation belts. The probes' mission is to help characterize the extreme environment within the radiation belts, so as to design more resilient spacecraft and satellites.
One question the mission seeks to answer is how the radiation belts give rise to ultrarelativistic electrons -- particles that streak around the Earth at 1,000 kilometers per second, circling the planet in just five minutes. These high-speed particles can bombard satellites and spacecraft, causing irreparable damage to onboard electronics.
The two Van Allen probes maintain the same orbit around the Earth, with one probe following an hour behind the other. On Oct. 8, 2013, the first probe was in just the right position, facing the sun, to observe the radiation belts just before the shockwave struck the Earth's magnetic field. The second probe, catching up to the same position an hour later, recorded the shockwave's aftermath.
Dealing a "sledgehammer blow"
Foster and his colleagues analyzed the probes' data, and laid out the following sequence of events: As the solar shockwave made impact, according to Foster, it struck "a sledgehammer blow" to the protective barrier of the Earth's magnetic field. But instead of breaking through this barrier, the shockwave effectively bounced away, generating a wave in the opposite direction, in the form of a magnetosonic pulse -- a powerful, magnetized sound wave that propagated to the far side of the Earth within a matter of minutes.
In that time, the researchers observed that the magnetosonic pulse swept up certain lower-energy particles. The electric field within the pulse accelerated these particles to energies of 3 to 4 million electronvolts, creating 10 times the number of ultrarelativistic electrons that previously existed.
Taking a closer look at the data, the researchers were able to identify the mechanism by which certain particles in the radiation belts were accelerated. As it turns out, if particles' velocities as they circle the Earth match that of the magnetosonic pulse, they are deemed "drift resonant," and are more likely to gain energy from the pulse as it speeds through the radiation belts. The longer a particle interacts with the pulse, the more it is accelerated, giving rise to an extremely high-energy particle.
Foster says solar shockwaves can impact Earth's radiation belts a couple of times each month. The event in 2013 was a relatively minor one.
"This was a relatively small shock. We know they can be much, much bigger," Foster says. "Interactions between solar activity and Earth's magnetosphere can create the radiation belt in a number of ways, some of which can take months, others days. The shock process takes seconds to minutes. This could be the tip of the iceberg in how we understand radiation-belt physics."
Quelle: SD

Tags: Astronomie 

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Sonntag, 22. Februar 2015 - 10:14 Uhr

Raumfahrt - Zeremonie für Baubeginn von Crew Access Tower Construction

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Boeing and United Launch Alliance teams held a ceremonial groundbreaking Feb. 20 to begin construction on the first new crew access structure at Cape Canaveral Air Force Station in decades. The preparations will enable Space Launch Complex 41 to host astronauts and their support personnel for flight tests and missions to the International Space Station.
The tower will be used for launches of Boeing's CST-100 spacecraft atop an Atlas V rocket. Boeing was selected to finalize the design of its integrated crew transportation system and work with NASA’s Commercial Crew Program to certify it for crew launches to the station by 2017.
"Fifty-three years ago today, John Glenn became the first American to orbit the Earth, launching on an Atlas just a few miles from here,” said Jim Sponnick, vice president of ULA’s Atlas and Delta programs. “The ULA team is very proud to be collaborating with Boeing and NASA on the Commercial Crew Program to continue that legacy and to return America to launching astronauts to the station.”
Boeing and ULA finished the design for the 200-foot-tall, metal latticework crew access structure in the summer of 2013. The design was made modular so crews could build large sections of the structure away from the pad then truck them in and stack them up to complete the work in between Atlas V launches. It will take about 18 months to build the tower.
“This is truly an integrated effort by a lot of partners and that’s really represented here today by the guests celebrating this groundbreaking with us,” said John Mulholland, Boeing Vice President of Commercial Programs. “This is the first construction of its type on the Cape since the 1960s, so building this crew tower, returning of the human launch capability to the United States, is very significant.”
Construction crews will face all the usual challenges of building a 20-story-high tower beside the ocean, plus the fact that one of the busiest launchers in the American catalog is not going to take time off during the construction phase.
The crew access structure will visually stand out at SLC-41, largely because the launch complex is a "clean pad" design with only the reinforced concrete hard stand and four lightning towers in place. About 1,800 feet to the south is a building called the Vertical Integration Facility, which houses the cranes and work platforms to assemble an Atlas V.
"Besides the VIF and the lightning towers, the crew access tower will be the tallest structure at the launch site," said Howard Biegler, Launch Operations lead of Human Launch Services for ULA.
The Atlas V launch pad has been used only for non-crewed spacecraft to this point, hosting Titan rockets beginning in 1965 and then the Atlas V since 2002. NASA missions launched from SLC-41 include the Viking robots that landed on Mars, the Voyager spacecraft that toured the outer planets, the New Horizons probe now headed to Pluto, and the Curiosity rover currently traversing Mars.
Although the pad has proved adept at servicing those extremely complex spacecraft and probes, the demands for handling a capsule that will carry humans are far greater. For instance, the rocket cannot be rolled to the pad and fueled while astronauts are aboard. Safety considerations also require a way to get away from the rocket quickly in case of an emergency before the rocket lifts off.
"I can’t wait to see this tower erected and an Atlas V up there with a CST-100 headed off to the International Space Station," said Bob Cabana, director of NASA’s Kennedy Space Center. "This historic pad has launched a number of NASA scientific missions and will now launch an even more valuable, precious piece of cargo, and that’s NASA astronauts to the station."
Missions flown on commercial crew spacecraft are vital to the national goal of restoring to America the ability to launch astronauts to the station so the unique orbiting laboratory can continue to fulfill its promise of achieving cutting-edge research for the benefit of all on Earth. With the new spacecraft, the station's crew can expand by one, which will enable research time on the station to double from its current 40 hours a week to 80 hours a week.
“This is a shining example of the progress we’ll see along the Space Coast as industry works toward safely flying our astronauts to and from the station,” said Kathy Lueders, manager of NASA’s Commercial Crew Program. “Once this crew access tower is complete, this historical launch complex will be an integral part of a new era in human spaceflight.”
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Officials take part in the formal groundbreaking at Space Launch Complex 41 where the Commercial Crew Access Tower will be built. The 200-foot-tall structure is designed to provide safe access for flight and ground crews to the Boeing CST-100 spacecraft at the pad.
Quelle: NASA

Tags: Raumfahrt 

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Samstag, 21. Februar 2015 - 20:40 Uhr

Raumfahrt - EVA-Vorbereitungen auf ISS für Freitag, Feb. 20; Dienstag, Feb. 24; und Sonntag, März 1.

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13.02.2015

The mirror like visor of NASA astronaut Reid Wiseman reflects NASA astronaut Barry Wilmore during their Oct. 15, 2014 spacewalk outside the International Space Station. Both Flight Engineers are in the process of making repairs which include removing and replacing a power regulator known as a sequential shunt unit, which failed back in mid-May. The two spacewalkers also moved TV and camera equipment in preparation for the relocation of the Leonardo Permanent Multipurpose Module to accommodate the installation of new docking adapters for future commercial crew vehicles.

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NASA TV Previews and Broadcasts Space Station U.S. Spacewalks

Two NASA astronauts from the International Space Station’s Expedition 42 crew will venture outside the orbital complex on Friday, Feb. 20; Tuesday, Feb. 24; and Sunday, March 1. They will prepare cables and communications gear for new docking ports that will allow future crews launched from Florida on U.S. commercial spacecraft to dock to the space station.

NASA TV will provide comprehensive coverage, beginning with a preview news briefing Wednesday, Feb. 18.
The preview briefing will be broadcast at 2 p.m. EST from NASA’s Johnson Space Center in Houston. Media may take part in person or by telephone. Reporters who want to ask questions by phone must call Johnson’s newsroom at 281-483-5111 no later than 1:45 p.m. Wednesday. Cell phones are discouraged.
The panelists for the briefing are:
Kenneth Todd, International Space Station Operations and Integration manager
Tomas Gonzalez-Torres, Expedition 42 lead flight director
Karina Eversley, Extravehicular Activity (EVA) # 29 officer
Sarah Korona, EVA # 30 officer
Arthur Thomason, EVA # 31 officer
Expedition 42 Commander Barry Wilmore and Flight Engineer Terry Virts will exit the station from the Quest airlock for each of the three spacewalks around 7:10 a.m. NASA TV coverage of the approximately six-and-a-half hour spacewalks will begin at 6 a.m.
Built by Boeing under contract to NASA, the International Docking Adapters are a critical component of the station's reconfiguration to ensure long-term docking ports for future commercial crew and other visiting spacecraft. They will permit the standard station crew size to grow from six to seven, potentially doubling the amount of time devoted to research aboard the orbiting laboratory.
The two new docking adapters will be launched to the station on a pair of SpaceX Dragon cargo spacecraft this year. Astronauts will install the first of two adapters on Pressurized Mating Adapter-2 on the forward end of the station’s Harmony module during a future spacewalk. The second adapter will be installed on Pressurized Mating Adapter-3 after it is relocated robotically to the space-facing port of Harmony later this year.
The spacewalks will be the 185th, 186th and 187th in support of space station assembly and maintenance. Wilmore has conducted one spacewalk in his career last October. The spacewalks will be the first of Virts' career.
Quelle: NASA
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Update: 19.02.2015
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Expedition 42 spacewalkers Barry Wilmore and Terry Virts are scheduled to conduct three spacewalks with the first to begin Friday. Credit: NASA
NASA astronauts Barry Wilmore and Terry Virts are counting down to the first of three assembly spacewalks set to begin Friday at 7:10 a.m. EST. The duo checked out their rescue jet packs they would use in the unlikely event they became untethered from the International Space Station. The spacewalks will prepare the station for new commercial crew vehicle docking ports.
Quelle: NASA
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Update: 20.02.2015
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First of Three Spacewalks Now Set for Saturday
(From left) Expedition 42 cosmonauts Elena Serova, Anton Shkaplerov and Alexander Samokutyaev work inside Japan’s Kibo laboratory module. Credit: NASA TV
NASA astronauts Barry Wilmore and Terry Virts are preparing to ready the International Space Station for a pair of international docking adapters (IDAs) that will allow future commercial crew vehicles to dock. The duo is almost set to start a series of three spacewalks routing cables and preparing the Canadarm2 for the installation of the IDAs to be delivered later this year.
The first spacewalk is now set to begin Saturday at 7:10 a.m. EST with NASA TV live coverage starting at 6 a.m. The second and third spacewalks are planned for Feb. 25 and March 1, both beginning at 7:10 a.m.
Amidst the spacewalk preparations, the Expedition 42 crew members continued ongoing advanced microgravity science benefiting life on Earth and current and future crew members. The crew looked at stem growth for the Aniso Tubule botany experiment, cell cultures grown on orbit and a crew member’s cardiac activity during long-duration missions.
Quelle: NASA
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Update: 21.02.2015 
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Upcoming Spacewalks to Prepare Space Station for U.S. Commercial Crew Arrivals
Change is on the horizon for the International Space Station as three upcoming spacewalks prepare the orbiting laboratory for future arrivals by U.S. commercial crew spacecraft.
The spacewalks are designed to lay cables along the forward end of the U.S. segment to bring power and communication to two International Docking Adapters slated to arrive later this year. The new docking ports will welcome U.S. commercial spacecraft launching from Florida beginning in 2017, permitting the standard station crew size to grow from six to seven and potentially double the amount of crew time devoted to research.
The third of the three space walks will see the installation of two new communication antennas on opposite ends of the station’s truss to assist in the commercial crew vehicles approach for docking. The spacewalks are planned for Saturday, Feb. 21; Wednesday, Feb. 25; and Sunday, March 1, with Expedition 42 Commander Barry Wilmore and Flight Engineer Terry Virts participating in all three.
“The challenge for the ISS is going to be continuing maturity over multiple decades of the station and what it will do for crew on the path to commercialization,” said Kenny Todd, International Space Station Operations Integration manager. “It’s fun, it’s exciting and we’re looking forward to transforming the station.”
The goal of these spacewalks is to prepare two berthing ports on the U.S. for the docking for commercial crew transport ships. The station has eight ports for cargo and crew total, including the U.S. and international segments.
All three EVAs will be performed in U.S. spacesuits, and will last around six and a half hours each.
Boeing and SpaceX were recently awarded Commercial Crew Transportation Capability contracts with NASA to develop solutions for U.S. astronaut transportation to and from the space station. After NASA crews begin fly with these contractors, it is expected to double the amount of time devoted to science in space from 40 hours to 80 hours per week. U.S. commercial crew capabilities also could provide a faster turnaround to bring completed experiments from the orbiting laboratory back to Earth.
SpaceX’s sixth commercial resupply mission is scheduled to launch to the station no earlier than April and will bring with supplies and equipment to support more than 200 research investigations. The two new docking adapters will be launched to the station on a pair of SpaceX Dragon cargo spacecraft later this year. SpaceX is targeting its new Crew Dragon spacecraft to make an uncrewed flight test in late 2016 and a crewed flight test in early 2017.
Boeing is working with NASA on its CST-100 spacecraft, which will launch on a United Launch Alliance Atlas V rocket. Boeing recently announced future projects including a pad abort test in February 2017, an orbital flight test in April 2017, and a crewed flight test with one Boeing test pilot and one NASA astronaut in July 2017.
The International Space Station is a convergence of science, technology and human innovation that demonstrates new technologies and makes research breakthroughs not possible on Earth. The space station has been occupied continuously since November 2000. In that time, more than 200 people and a variety of international and commercial spacecraft have visited the orbiting laboratory. The space station remains the springboard to NASA's next great leap in exploration, including future missions to an asteroid and Mars.
Quelle: NASA
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SS042E277380 (02/16/2015) — U.S. Astronaut Terry Virts, Flight Engineer for Expedition 42 on the International Space Station Feb. 16, 2015 checks out his spacesuit in preparation for the upcoming Extracurricular Activity (EVA) or Spacewalk for installation of a new port. This port will be for the commercial spacecraft as well as other craft in the future.
NASA Television will provide live coverage of tomorrow’s U.S. spacewalk conducted from the International Space Station beginning at 6 a.m. EST. The spacewalk is scheduled to begin at 7:10 a.m. and run about 6 1/2 hours.
Expedition 42 Commander Barry Wilmore and Flight Engineer Terry Virts will venture outside the orbital complex in the first of three spacewalks in the coming days to prepare cables and communications gear for new docking ports that will allow future crews launching from Florida on U.S. commercial spacecraft to dock to the space station.
Quelle: NASA
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Update: 16.30 MEZ
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Change is on the horizon for the International Space Station as three upcoming spacewalks prepare the orbiting laboratory for future arrivals by U.S. commercial crew spacecraft. NASA astronauts Barry Wilmore and Terry Virts will route cables and prepare the Canadarm2 for the installation of the International Docking Adaptors to be delivered later this year. The first 6.5-hour spacewalk began this morning at 7:45 a.m. EST.
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Quelle: NASA-TV

Tags: Raumfahrt März 1. Feb. 20; Dienstag Feb. 24; und Sonntag 

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Samstag, 21. Februar 2015 - 18:27 Uhr

Raumfahrt - Mit Firefly Raumschiff auf den Weg zu Alpha Centauri ?

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The Icarus Interstellar 'Firefly' starship concept could use novel nuclear fusion techniques to power its way to Alpha Centauri within 100 years.
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As part of Icarus Interstellar's continuing series of guest articles on Discovery News, Michel Lamontagne, Project Icarus Core Designer, discusses a conceptual starship that could use novel fusion techniques to travel to the nearby star system Alpha Centauri.
The Icarus Interstellar Firefly
Robert Freeland wants to launch an interstellar probe -- not 100 years from now, but within his lifetime.
As Icarus Board Member and Deputy Project Leader, Freeland presented at the Tennessee Valley Interstellar Workshop (TVIW) in November, to propose a design for an starship that has all the things he likes: speed, elegance, and a short lead time.
"Firefly" (named so for its bright tail) is almost too pretty. It doesn't seem right, after decades of tin can projects by NASA, to envision elegance in a practical design.
But let the hard science fans be reassured: the entire morphology of the vessel follows directly from physical constraints. Even the pretty curve of the radiators was chosen to follow the actual heat load from the drive, while minimizing pumping distance and pipe/coolant mass. The design is backed by as much hard science as is available today.
Firefly's main drive is fueled by deuterium-deuterium (DD) fusion in a Z-pinch reactor. Z-pinch fusion was first explored in the late 1960s, but plasma instabilities relegated it to the dustbin. The idea languished for decades until recent research by Uri Shumlak at the University of Washington brought it back.
Shumlak's design resolves the plasma instabilities by introducing a strong shear flow of plasma through the pinch area. Simulations and laboratory experiments have shown that this strong shear flow "smooths out" the plasma instabilities that would otherwise occur, resulting in a stable pinch. Lab tests have thus far only been performed with non-fusing plasmas for safety reasons, but the theory and tests strongly indicate that a properly-designed Z-pinch could maintain a stable fusion core.
This is not fringe science -- Sandia National Laboratories is doing tests on Z-pinch fusion, and NASA's Huntsville-based "Charger One" facility is preparing to undertake its own lab tests this year.
Pure deuterium fusion was selected for Firefly because it is available in sea water at about 150 ppm as "heavy water", and is already commonly extracted in facilities all over the world for service in CANDU type fission reactors. If hydrogen becomes a common fuel source here on Earth, deuterium could readily be extracted even more cheaply as a byproduct of bulk hydrogen production plants.
This contrasts with more exotic fuel choices commonly proposed for fusion starships, particularly deuterium-helium3 (DHe3). The DHe3 reaction is fundamentally more desirable because its first-level reactions are all aneutronic; meaning that they produce only charged particles, with no damaging neutrons. The problem is that He3 is unavailable on Earth except in microscopic quantities, so it would have to be mined from the moon or the gas giant planets. This would require an extensive space program that then pushes an interstellar launch far into the future.
The unfortunate reality of DD fusion, though, is the tremendous flux of damaging high-energy neutron radiation. Even considering beneficial secondary reactions, neutrons account for almost half of the energy released by the reaction.
The Z-pinch drive compounds this problem with a very high flux of x-ray Bremsstrahlung radiation as well, produced as the super-heated electrons in the plasma bang into each other. Owing to its long, thin core, essentially all of the neutrons and x-ray radiation produced in the Z-pinch drive immediately escape the core.
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The scale of the 'Firefly' concept aside an Apollo era Saturn V rocket.
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Freeland recognized early on that shielding all of this radiation would result in an unworkably massive vessel, so he took the opposite approach, designing Firefly to dump as much of the damaging radiation as possible directly into space. The vessel is long and pointy to minimize its radiation exposure, and most of the tail end of the ship is basically a giant radiator to handle the waste heat that can't otherwise be avoided.
The fuel tanks follow the principle of the Saturn 5 rocket, shown beside the ship for scale in the graphic above). Why add extra structure if the tanks themselves can be the structure? Michel Lamontagne's tank design does away with the structural spine common to most other designs and reduces structure to the barest minimum. Like Saturn 5, the forward part of the ship is mostly tank. The payload resides in the middle area, just before a large radiation shield that protects it from the drive's radiation.
Firefly is a big ship, although small by interstellar ship design standards. Like all the current Project Icarus designs, it would accelerate out into space, coast for a number of years, then decelerate at the Alpha Centauri system and release a swarm of sub-probes, all within a travel time of 100 years. This is faster than needed, really; increasing the travel time to several hundred years would reduce the technical challenges tremendously.
But from a practical standpoint, a 100-year mission lies at the very limit of organizational support. The Daedalus team, for instance, designed their 1978 probe for a 50-year flyby mission, because this was deemed the upper limit for a NASA engineer's professional career. Practicality in design extends not just to the technology, but to the social support necessary to make the mission possible.
There are still some important unresolved issues with the Firefly design:
The viability of Z-pinch fusion has yet to be confirmed, though Sandia National Labs and now NASA's Marshall Space Flight Center are undertaking lab tests.
The electrodes needed to supply power to the pinch must be constructed of advanced composite materials that have seen very little laboratory testing.
The direct energy conversion system needed to recapture energy from the exhaust stream to sustain the pinch is purely theoretical, with few published papers.
The high-temperature beryllium phase-change radiators that Michel Lamontagne designed for Firefly haven't yet been studied due to the expense and toxicity of beryllium. Similar systems using lithium have been used in fission reactors, but 2000K beryllium necessitates advanced piping materials (like zirconium carbide) to resist corrosion. Such systems need to be studied in a lab.
The system for communications between the vessel and Earth is rather vaguely specified at present.
Modeling the real behavior of a fusion drive exhaust in magnetic nozzles is another area where research lags considerably behind the needs of starship designers. Real world experiments -- necessarily in the large vacuum of space -- are needed to obtain data. The use of VASIMR on the ISS -- as a booster to keep the station at the proper orbit -- is a step in the right direction. (VASIMR will include the first magnetic nozzle "flown", or actually used in space.)
Design is an iterative process, and next year's Icarus Firefly may have changed considerably from this year's. Some of the prettiness may disappear if the numbers require it. But if Robert Freeland gets his way, two things are certain: it will be faster, and it will be easier to build.
Quelle: D-News

Tags: Raumfahrt 

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Samstag, 21. Februar 2015 - 11:13 Uhr

Astronomie - Hubble sieht gigantische Gas- und Staubscheibe rings um den 20-Millionen-jahre alten Stern Beta Pictoris

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The photo at the bottom is the most detailed picture to date of a large, edge-on, gas-and-dust disk encircling the 20-million-year-old star Beta Pictoris. The new visible-light Hubble image traces the disk in closer to the star to within about 650 million miles of the star (which is inside the radius of Saturn's orbit about the sun).

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Owed to its long-duration mission, Hubble can spot short-duration changes in celestial objects, revealing unprecedented detail in an otherwise ‘unchanging’ sky. Take Beta Pictoris for example. This 20 million year-old star sports an extensive edge-on protoplanetary disk and Hubble has been watching motion in this dust, stirred up by the presence of a massive exoplanet.
This is yet another cosmic first for the veteran space telescope; astronomers have been able to compare Hubble observations of Beta Pictoris 1997 and 2012 and would therefore be able to track any morphological changes in its protoplanetary disk.
As the exoplanet’s orbit is predicted to have an orbital period of between 18-20 years, over the 15 years between observations, the exoplanet would have shifted considerably, but Hubble has noticed little change in the distribution of dust in the protoplanetary disk, confirming some models about how protoplanetary disks mingling with exoplanets work.
“Some computer simulations predicted a complicated structure for the inner disk due to the gravitational pull by the short-period giant planet,” said Daniel Apai of the University of Arizona. “The new images reveal the inner disk and confirm the predicted structures. This finding validates models, which will help us to deduce the presence of other exoplanets in other disks.”
From these observations, astronomers can see that the circumstellar dust is orbiting in unison with the exoplanet “like a carousel,” according to a Hubble news release. This suggests that the inner dusty disk is “smooth and continuous” as it orbits the star.
Beta Pictoris, however, isn’t believed to be a ‘typical’ young star with a protoplanetary disk.
“The Beta Pictoris disk is the prototype for circumstellar debris systems, but it may not be a good archetype,” said co-author Glenn Schneider of the University of Arizona.
Beta Pictoris was the first star to be discovered to have a bright circumstellar disk. It’s believed that asteroids and comets in the system are continuously colliding, populating the disk with copious quantities of dust. Also, a lobe-like feature in the disk is thought to be the dusty remains of a pulverized Mars-sized body.

Located only 63 light-years from Earth, Beta Pictoris is the closest circumstellar disk system, so it is a protoplanetary Petri-dish of sorts, providing astronomers with a smorgasbord of planetary phenomena.

Interestingly, the researchers suggest that by studying star systems with circumstellar disks known also to contain exoplanets, we may begin to fathom the ‘fingerprint’ in these disks so previously hidden exoplanets may be revealed around other stars.

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Quelle: D-News


Tags: Astronomie 

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Freitag, 20. Februar 2015 - 19:00 Uhr

UFO-Forschung - Venus und Mars dicht bei Mondsichel in der Abenddämmerung von 20./21. Februar

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14.02.2015

Nach dem wir aktuell schon verstärkt UFO-Meldungen bei unserer UFO-Meldestelle in Mannheim bei klarer Abenddämmerung durch die Planeten Venus und Jupiter haben, erwartet uns demnächst eine weitere astronomische Herausforderung am frühen Abendhimmel vom 20. Februar 2015. Mars und Venus stehen dicht nebeneinander bei der schmalen Mondsichel  und werden sicherlich für manchen Zufallsbeobachter "UFO-Alarm" auslösen, daher hier schon einmal die astronomische Erklärung:


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When it comes to "eyeball astronomy," nothing is more satisfying than to see a pair of celestial objects appear close together in the sky, what astronomers call a conjunction. And 2015, notes S&T's longtime contributing editor Fred Schaaf, truly deserves to be called the "Year of the Conjunctions." In January we watched Venus and Mercury come together in the evening twilight, and this month features a similarly close and prolonged pairing of Venus and Mars.
The two worlds have been edging closer together all month. Venus has become obvious in the southwest after sunset, and it's been climbing a little higher week by week. Mars, meanwhile, has lingered in roughly the same part of the post-sunset sky for several months, refusing to depart. Last week Mars was about 8° above Venus, but for a 9-day run beginning February 17th, the two remain within 2° of each other. That separation shrinks to less than 1° from the 20th through the 23rd.
The climax comes on February 21st, when the two planets are just 0.4° apart at dusk, as seen from the Americas. Since the pairing is so close, Schaaf cautions, "little Mars might be hard to see in Venus's glare without optical aid."
Both worlds will fit together in a medium-power telescopic view, with Venus clearly dominant — nearly 100 times brighter. Its dazzling yellow-white disk, shining at magnitude –3.9, is 12 arcseconds wide and 88% illuminated, whereas peach-colored Mars is much dimmer, magnitude +1.2 or +1.3, and just 4 arcseconds across.
As an added bonus, a thin crescent Moon is passing through this celestial scene. It clusters dramatically with the two planets in the deepening dusk on February 21st, one day before Venus and Mars are closest. Get those cameras ready!
The dance continues through the end of February, when Mars is still within 4° of Venus. But by then the ordering has switched, with Mars lower down. Yet the Red Planet refuses to exit the evening stage. Watch carefully these coming weeks, and you'll see it seemingly slide to the right (northward) relative to the sunset point — yet not really get any lower!
Quelle. Sky&Telescope
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Update: 18.02.2015
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Mars und Venus üben schon und man kann es sehen wenn kein Hochnebel die Sicht behindert...
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VENUS AND MARS: When the sun goes down tonight, step outside and face west. Venus is beaming through the twilight, so bright that it is often mistaken for a landing plane. Wait a while as the sky grows darker. Fainter Mars pops out right beside Venus. Didier Van Hellemont photographed the pair at sunset on Feb. 17th over Sint-Laureins, Belgium:
In only a few days, the two planets will be dramatically closer together. At closest approach on Feb. 21st, they will be only 0.4o apart, less than the width of a full Moon. The night before closest approach might be best of all: On Feb. 20th, the crescent Moon will pass right by the converging planets. Mark both dates on your calendar, Feb. 20th and 21st, and watch the western sky at sunset. It's a great way to end the day.
Quelle: Spaceweather
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Update: 20.02.2015 / 19.00 MEZ
Am Westhimmel über Mannheim
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Fotos: ©-hjkc
 

Tags: UFO-Forschung 

1994 Views

Freitag, 20. Februar 2015 - 11:18 Uhr

Mars-Chroniken - Wissenschaftler identifizieren Mineral, das organische Verbindungen zerstört, welche Auswirkungen auf die Mars-Mission Curiosity hat

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Scientists have discovered that the mineral jarosite breaks down organic compounds when it is flash-heated, with implications for Mars research.
Jarosite is an iron sulphate and it is one of several minerals that NASA's Curiosity Mission is searching for, as its presence could indicate ancient habitable environments, which may have once hosted life on the red planet.
In a new study published today in the journal Astrobiology, researchers from Imperial College London and the Natural History Museum replicated a technique that one of the Curiosity Rover's on-board instruments is using to analyse soil samples, in its quest to find organic compounds. They tested a combination of jarosite and organic compounds. They discovered that the instrument's technique -which uses intense bursts of heat called flash-heating - broke down jarosite into sulphur dioxide and oxygen, with the oxygen then destroying the organic compounds, leaving no trace of it behind.
The concern is that if jarosite is present in soil samples that Curiosity analyses, researchers may not be able to detect it because both the jarosite and any organic compounds could be destroyed by the flash-heating process.
In 2014, Professor Mark Sephton, co-author of today's study, investigated the mineral perchlorate. This mineral also causes problems for flash-heating experiments as it breaks down to give off oxygen and chlorine gas, which in turn react with any organic compounds, breaking them down into carbon dioxide and water. Professor Sephton showed that though perchlorate was problematic, scientists could potentially use the carbon dioxide resulting from the experiment to detect the presence of organic compounds in the sample being analysed.
Professor Sephton, from the Department of Earth Science and Engineering at Imperial College London, said: "The destructive properties of some iron sulphates and perchlorate to organic matter may explain why current and previous missions have so far offered no conclusive evidence of organic matter preserved on Mars' surface. This is despite the fact that scientists have known from previous studies that organic compounds have been delivered to Mars via comets, meteorites and interplanetary dust throughout its history."
To make Curiosity's search for signs of life more effective, the team are now exploring how Curiosity might be able to compensate for the impact of these minerals on the search for organic compounds. Their work could have important implications for both the Curiosity mission and also the upcoming European-led ExoMars 2018 Rover mission, which will be drilling for subsurface samples of the red planet and using the same flash-heating method to look for evidence of past or present alien life.
James Lewis, co-author of the study from the Department of Earth Science and Engineering at Imperial College London, added: "Our study is helping us to see that if jarosite is detected then it is clear that flash-heating experiments looking for organic compounds may not be completely successful. However, the problem is that jarosite is evidence of systems that might have supported life, so it is not a mineral that scientists can completely avoid in their analysis of soils on Mars. We hope our study will help scientists with interpreting Mars data and assist them to sift through the huge amount of excellent data that Curiosity is currently generating to find signs that Mars was once able to sustain life."
On Earth, iron sulphate minerals like jarosite form in the harsh acidic waters flowing out of sulphur rich rocks. Despite the adverse conditions, these waters are a habitat for bacteria that use these dissolved sulphate ions. This makes these minerals of great interest to scientists studying Mars, as their presence on the red planet provide evidence that acidic liquid water was present at the same time the minerals formed, which could have provided an environment favourable for harbouring ancient microbial Martian life.
On board Curiosity, the Sample Analysis at Mars (SAM) instrument analyses soil samples for evidence of organic compounds by progressively heating samples up to around 1000 C, which releases gases. These gases can then be analysed by techniques called gas chromatography and mass spectrometry, which can identify molecules in the gas and see if any organic compounds are present. It is these SAM instrument experiments that the researchers behind today's study replicated with jarosite and organic compounds.
The researchers stress that not all sulphates break down to react with organic compounds. For example, those containing calcium and magnesium would not break down until extremely high temperatures were reached during the analysis, and therefore would not affect any organic compounds present.
The team suggest that if jarosite is found in samples on Mars, then it may be possible for Curiosity's SAM instrument to distinguish a spike in carbon dioxide level, which, as Professor Sephton has shown previously with perchlorate, would act as an indicator that organic material is present and being broken down by the heating process.
The next step will see the researchers using synthetic jarosite in their experiments, which will enable a cleaner decomposition process to occur when the mineral is flash-heated. This will allow for more precise quantitative measurements to be taken when the oxygen is being released. Ultimately, they hope this will enable more precise calculations to be carried out on Mars mineral samples to find ways in which Curiosity can identify the presence of these mineral to mitigate their impact on organic matter.
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The jarosite samples used in the experiments in the study were collected from Brownsea Island in Dorset, with the permission and assistance from the National Trust.
Quelle: AAAS

Tags: Mars-Chroniken das organische Verbindungen zerstört 

1934 Views

Freitag, 20. Februar 2015 - 11:00 Uhr

Raumfahrt - Mars-Orbiter MAVEN erreicht Mars-Orbit - Update-2

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25.09.2014

MAVEN Spacecraft Returns First Mars Observations
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NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft has obtained its first observations of the extended upper atmosphere surrounding Mars.
The Imaging Ultraviolet Spectrograph (IUVS) instrument obtained these false-color images eight hours after the successful completion of Mars orbit insertion by the spacecraft at 10:24 p.m. EDT Sunday, Sept. 21, after a 10-month journey.  
The image shows the planet from an altitude of 36,500 km in three ultraviolet wavelength bands.  Blue shows the ultraviolet light from the sun scattered from atomic hydrogen gas in an extended cloud that goes to thousands of kilometers above the planet’s surface.  Green shows a different wavelength of ultraviolet light that is primarily sunlight reflected off of atomic oxygen, showing the smaller oxygen cloud. Red shows ultraviolet sunlight reflected from the planet’s surface; the bright spot in the lower right is light reflected either from polar ice or clouds.
The oxygen gas is held close to the planet by Mars’ gravity, while lighter hydrogen gas is present to higher altitudes and extends past the edges of the image. These gases derive from the breakdown of water and carbon dioxide in Mars’ atmosphere. Over the course of its one-Earth-year primary science mission, MAVEN observations like these will be used to determine the loss rate of hydrogen and oxygen from the Martian atmosphere.  These observations will allow us to determine the amount of water that has escaped from the planet over time. 
MAVEN is the first spacecraft dedicated to exploring the tenuous upper atmosphere of Mars.
Quelle: NASA
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Update: 14.10.2014
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NASA Mission Provides Its First Look at Martian Upper Atmosphere
Three views of an escaping atmosphere, obtained by MAVEN’s Imaging Ultraviolet Spectrograph. By observing all of the products of water and carbon dioxide breakdown, MAVEN's remote sensing team can characterize the processes that drive atmospheric loss on Mars.
Image Credit: University of Colorado/NASA
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NASA's Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft has provided scientists their first look at a storm of energetic solar particles at Mars, produced unprecedented ultraviolet images of the tenuous oxygen, hydrogen, and carbon coronas surrounding the Red Planet, and yielded a comprehensive map of highly-variable ozone in the atmosphere underlying the coronas.
The spacecraft, which entered Mars' orbit Sept. 21, now is lowering its orbit and testing its instruments. MAVEN was launched to Mars in November 2013, to help solve the mystery of how the Red Planet lost most of its atmosphere.
"All the instruments are showing data quality that is better than anticipated at this early stage of the mission," said Bruce Jakosky, MAVEN Principal Investigator at the University of Colorado, Boulder. "All instruments have now been turned on -- although not yet fully checked out -- and are functioning nominally. It's turning out to be an easy and straightforward spacecraft to fly, at least so far. It really looks as if we're headed for an exciting science mission."
Solar energetic particles (SEPs) are streams of high-speed particles blasted from the sun during explosive solar activity like flares or coronal mass ejections (CMEs). Around Earth, SEP storms can damage the sensitive electronics on satellites. At Mars, they are thought to be one possible mechanism for driving atmospheric loss.
A solar flare on Sept. 26 produced a CME that was observed by NASA satellites on both sides of the sun. Computer models of the CME propagation predicted the disturbance and the accompanying SEPs would reach Mars on Sept. 29. MAVEN's Solar Energetic Particle instrument was able to observe the onset of the event that day.
"After traveling through interplanetary space, these energetic particles of mostly protons deposit their energy in the upper atmosphere of Mars," said SEP instrument lead Davin Larson of the Space Sciences Laboratory at the University of California, Berkeley. "A SEP event like this typically occurs every couple weeks. Once all the instruments are turned on, we expect to also be able to track the response of the upper atmosphere to them."
The hydrogen and oxygen coronas of Mars are the tenuous outer fringe of the planet's upper atmosphere, where the edge of the atmosphere meets space. In this region, atoms that were once a part of carbon dioxide or water molecules near the surface can escape to space. These molecules control the climate, so following them allows us to understand the history of Mars over the last four billion years and to track the change from a warm and wet climate to the cold, dry climate we see today. MAVEN observed the edges of the Martian atmosphere using the Imaging Ultraviolet Spectrograph (IUVS), which is sensitive to the sunlight reflected by these atoms.
"With these observations, MAVEN's IUVS has obtained the most complete picture of the extended Martian upper atmosphere ever made," said MAVEN Remote Sensing Team member Mike Chaffin of the University of Colorado, Boulder. "By measuring the extended upper atmosphere of the planet, MAVEN directly probes how these atoms escape to space. The observations support our current understanding that the upper atmosphere of Mars, when compared to Venus and Earth, is only tenuously bound by the Red Planet's weak gravity."
IUVS also created a map of the atmospheric ozone on Mars by detecting the absorption of ultraviolet sunlight by the molecule.
"With these maps we have the kind of complete and simultaneous coverage of Mars that is usually only possible for Earth," said MAVEN Remote Sensing Team member Justin Deighan of the University of Colorado, Boulder. "On Earth, ozone destruction by refrigerator CFCs is the cause of the polar ozone hole. On Mars, ozone is just as easily destroyed by the byproducts of water vapor breakdown by ultraviolet sunlight. Tracking the ozone lets us track the photochemical processes taking place in the Martian atmosphere. We'll be exploring this in more complete detail during MAVEN's primary science mission."
There will be about two weeks of additional instrument calibration and testing before MAVEN starts its primary science mission. This includes an end-to-end test to transmit data between NASA's Curiosity rover on the surface of Mars and Earth using the MAVEN mission's Electra telecommunications relay. The mission aims to start full science gathering in early to mid-November.
MAVEN's principal investigator is based at the University of Colorado's Laboratory for Atmospheric and Space Physics. The university provided two science instruments and leads science operations, as well as education and public outreach, for the mission. The University of California at Berkeley's Space Sciences Laboratory also provided four science instruments for the mission. NASA's Goddard Space Flight Center in Greenbelt, Maryland manages the MAVEN project and provided two science instruments for the mission. Lockheed Martin built the spacecraft and is responsible for mission operations. NASA's Jet Propulsion Laboratory in Pasadena, California provides navigation and Deep Space Network support, as well as the Electra telecommunications relay hardware and operations.
Quelle: NASA
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Update: 16.12.2014
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Early discoveries by NASA’s newest Mars orbiter are starting to reveal key features about the loss of the planet’s atmosphere to space over time.
The findings are among the first returns from NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) mission, which entered its science phase on Nov. 16. The observations reveal a new process by which the solar wind can penetrate deep into a planetary atmosphere. They include the first comprehensive measurements of the composition of Mars’ upper atmosphere and electrically charged ionosphere. The results also offer an unprecedented view of ions as they gain the energy that will lead to their to escape from the atmosphere.
“We are beginning to see the links in a chain that begins with solar-driven processes acting on gas in the upper atmosphere and leads to atmospheric loss,” said Bruce Jakosky, MAVEN principal investigator with the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder. “Over the course of the full mission, we’ll be able to fill in this picture and really understand the processes by which the atmosphere changed over time.”
On each orbit around Mars, MAVEN dips into the ionosphere – the layer of ions and electrons extending from about 75 to 300 miles above the surface. This layer serves as a kind of shield around the planet, deflecting the solar wind, an intense stream of hot, high-energy particles from the sun.
Scientists have long thought that measurements of the solar wind could be made only before these particles hit the invisible boundary of the ionosphere. MAVEN’s Solar Wind Ion Analyzer, however, has discovered a stream of solar-wind particles that are not deflected but penetrate deep into Mars’ upper atmosphere and ionosphere.
Interactions in the upper atmosphere appear to transform this stream of ions into a neutral form that can penetrate to surprisingly low altitudes. Deep in the ionosphere, the stream emerges, almost Houdini-like, in ion form again. The reappearance of these ions, which retain characteristics of the pristine solar wind, provides a new way to track the properties of the solar wind and may make it easier to link drivers of atmospheric loss directly to activity in the upper atmosphere and ionosphere.
MAVEN’s Neutral Gas and Ion Mass Spectrometer is exploring the nature of the reservoir from which gases are escaping by conducting the first comprehensive analysis of the composition of the upper atmosphere and ionosphere. These studies will help researchers make connections between the lower atmosphere, which controls climate, and the upper atmosphere, where the loss is occurring.
The instrument has measured the abundances of many gases in ion and neutral forms, revealing well-defined structure in the upper atmosphere and ionosphere, in contrast to the lower atmosphere, where gases are well-mixed. The variations in these abundances over time will provide new insights into the physics and chemistry of this region and have already provided evidence of significant upper-atmospheric “weather” that has not been measured in detail before.
New insight into how gases leave the atmosphere is being provided by the spacecraft’s Suprathermal and Thermal Ion Composition (STATIC) instrument. Within hours after being turned on at Mars, STATIC detected the “polar plume” of ions escaping from Mars. This measurement is important in determining the rate of atmospheric loss.
As the satellite dips down into the atmosphere, STATIC identifies the cold ionosphere at closest approach and subsequently measures the heating of this charged gas to escape velocities as MAVEN rises in altitude. The energized ions ultimately break free of the planet’s gravity as they move along a plume that extends behind Mars.
The MAVEN spacecraft and its instruments have the full technical capability proposed in 2007 and are on track to carry out the primary science mission. The MAVEN team delivered the spacecraft to Mars on schedule, launching on the very day in 2013 projected by the team 5 years earlier. MAVEN was also delivered well under the confirmed budget established by NASA in 2010.
The team’s success can be attributed to a focused science mission that matched the available funding and diligent management of resources. There were also minimal changes in requirements on the hardware or science capabilities that could have driven costs. It also reflects good coordination between the principal investigator; the project management at NASA’s Goddard Space Flight Center; the Mars Program Office at NASA’s Jet Propulsion Laboratory in Pasadena, California; and the Mars Exploration Program at NASA Headquarters.
The entire project team contributed to MAVEN’s success to date, including the management team, the spacecraft and science-instrument institutions, and the launch-services provider.
“The MAVEN spacecraft and its instruments are fully operational and well on their way to carrying out the primary science mission,” said Jim Green, director of NASA’s Planetary Science Division at NASA Headquarters in Washington. “The management team’s outstanding work enabled the project to be delivered on schedule and under budget.”
MAVEN’s principal investigator is based at the University of Colorado’s Laboratory for Atmospheric and Space Physics in Boulder, and NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the mission.
Quelle: NASA
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Update: 20.02.2015 
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NASA’s MAVEN Spacecraft Completes First Deep Dip Campaign
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NASA’S Mars Atmosphere and Volatile Evolution has completed the first of five deep-dip maneuvers designed to gather measurements closer to the lower end of the Martian upper atmosphere.
“During normal science mapping, we make measurements between an altitude of about 150 km and 6,200 km (93 miles and 3,853 miles) above the surface,” said Bruce Jakosky, MAVEN principal investigator at the University of Colorado's Laboratory for Atmospheric and Space Physics in Boulder. “During the deep-dip campaigns, we lower the lowest altitude in the orbit, known as periapsis, to about 125 km (78 miles) which allows us to take measurements throughout the entire upper atmosphere.”
The 25 km (16 miles) altitude difference may not seem like much, but it allows scientists to make measurements down to the top of the lower atmosphere. At these lower altitudes, the atmospheric densities are more than ten times what they are at 150 km (93 miles).
“We are interested in the connections that run from the lower atmosphere to the upper atmosphere and then to escape to space,” said Jakosky. “We are measuring all of the relevant regions and the connections between them.”
The first deep dip campaign ran from Feb. 10 to 18. The first three days of this campaign were used to lower the periapsis. Each of the five campaigns lasts for five days allowing the spacecraft to observe for roughly 20 orbits.  Since the planet rotates under the spacecraft, the 20 orbits allow sampling of different longitudes spaced around the planet, providing close to global coverage.
This month’s deep dip maneuvers began when team engineers fired the rocket motors in three separate burns to lower the periapsis. The engineers did not want to do one big burn, to ensure that they didn’t end up too deep in the atmosphere.  So, they “walked” the spacecraft down gently in several smaller steps.
“Although we changed the altitude of the spacecraft, we actually aimed at a certain atmospheric density,” said Jakosky. “We wanted to go as deep as we can without putting the spacecraft or instruments at risk.” 
Even though the atmosphere at these altitudes is very tenuous, it is thick enough to cause a noticeable drag on the spacecraft.  Going to too high an atmospheric density could cause too much drag and heating due to friction that could damage spacecraft and instruments.
At the end of the campaign, two maneuvers were conducted to return MAVEN to normal science operation altitudes. Science data returned from the deep dip will be analyzed over the coming weeks. The science team will combine the results with what the spacecraft has seen during its regular mapping to get a better picture of the entire atmosphere and of the processes affecting it.
One of the major goals of the MAVEN mission is to understand how gas from the atmosphere escapes to space, and how this has affected the planet's climate history through time. In being lost to space, gas is removed from the top of the upper atmosphere. But it is the thicker lower atmosphere that controls the climate.  MAVEN is studying the entire region from the top of the upper atmosphere all the way down to the lower atmosphere so that the connections between these regions can be understood. 
MAVEN is the first mission dedicated to studying the upper atmosphere of Mars. The spacecraft launched Nov. 18, 2013, from Cape Canaveral Air Force Station in Florida. MAVEN successfully entered Mars’ orbit on Sept. 21, 2014.
MAVEN's principal investigator is based at the University of Colorado's Laboratory for Atmospheric and Space Physics. The university provided two science instruments and leads science operations, as well as education and public outreach, for the mission. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the MAVEN project and provided two science instruments for the mission. Lockheed Martin built the spacecraft and is responsible for mission operations. The University of California at Berkeley's Space Sciences Laboratory also provided four science instruments for the mission. NASA's Jet Propulsion Laboratory in Pasadena, California, provides navigation and Deep Space Network support, as well as the Electra telecommunications relay hardware and operations.


Tags: Raumfahrt 

2334 Views

Donnerstag, 19. Februar 2015 - 09:47 Uhr

Astronomie - Der seltsame Fall des verschollenen Zwerges / Das neue Instrument SPHERE zeigt sein Können

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Das SPHERE-Instrument ist hier kurz nach seiner Anbringung am VLT-Hauptteleskop 3 der ESO zu sehen. Das Instrument selbst ist der schwarze Kasten, der sich auf der Plattform an der Seite des Teleskops befindet.

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Bislang gingen Astronomen davon aus, dass ein Brauner Zwerg den ungewöhnlichen Doppelstern V471 Tauri begleitet. Das neue Instrument SPHERE am Very Large Telescope der ESO hat ihnen den nun bisher besten Blick auf die Umgebung dieses faszinierenden Objekts geliefert und sie fanden — nichts. Das überraschende Fehlen dieses mit großer Sicherheit vorhergesagten Braunen Zwerges bedeutet, dass die herkömmliche Erklärung für das merkwürdige Verhalten von V471 Tauri falsch sein muss. Das unerwartete Ergebnis wird in der ersten Veröffentlichung überhaupt beschrieben, die auf Beobachtungen von SPHERE beruht.
Manche Sternpaare bestehen aus zwei normalen Sternen mit nur geringfügig unterschiedlichen Massen. Wenn der Stern mit der etwas höheren Masse altert und sich ausdehnt, um zu einem Roten Riesen zu werden, geht Materie von diesem Stern zum anderen über und umgibt schließlich beide Sterne mit einer riesigen gasförmigen Hülle. Sobald sich diese Wolke auflöst, nähern sich beide Sterne einander an und es entsteht ein sehr kompaktes Paar aus einem Weißen Zwerg und einem zusätzlichen gewöhnlichen Stern [1].
Ein solches Sternpaar trägt den Namen V471 Tauri [2]. Es ist Teil des Sternhaufens der Hyaden im Sternbild Stier und schätzungsweise um die 600 Millionen Jahre alt und etwa 163 Lichtjahre von der Erde entfernt. Beide Sterne liegen sehr dicht beieinander und umkreisen sich gegenseitig alle 12 Stunden. Zweimal pro Umrundung zieht ein Stern von der Erde aus gesehen vor dem anderen vorbei — was zu regelmäßigen Änderungen in der Helligkeit des Sternpaares führt, da sie sich gegenseitig verdunkeln.
Das Team um den Astronomen Adam Hardy von der Universidad Valparaíso in Chile verwendete zunächst das ULTRACAM-System am New Technology Telescope der ESO, um diese Helligkeitsänderungen sehr präzise zu vermessen. Die Zeiten der Verfinsterungen wurden dabei mit einer Genauigkeit von unter zwei Sekunden bestimmt.
Die Verdunklungszeiten waren zwar nicht gleichmäßig, konnten aber mit der Annahme, dass es einen Braunen Zwerg gibt, der beide Sterne umkreist und dessen Anziehungskraft die Umlaufbahn der Sterne stört, gut erklärt werden. Sie fanden ebenso Hinweise auf ein zweites kleineres Begleitobjekt.
Bis heute ist es allerdings unmöglich gewesen, einen lichtschwachen Brauen Zwerg mit so geringem Abstand zu viel helleren Sternen tatsächlich abzubilden. Das neu installierte SPHERE-Instrument am Very Large Telescope der ESO erlaubte den Astronomen zum ersten Mal genauer an die Stelle zu schauen, an der sie Begleiter in Form einen Braunen Zwerges erwarteten. Gesehen haben sie allerdings nichts, obwohl die hochauflösenden Bilder von SPHERE ihn leicht hätten enttarnen sollen [3].
„Es gibt viele Veröffentlichungen, in denen die Existenz solcher zirkumbinären Objekte angenommen wird, aber die Ergebnisse hier liefern einen vernichtenden Beweis gegen diese Hypothese“, merkt Adam Hardy an.
Wenn es kein umlaufendes Objekt gibt, was verursacht dann die merkwürdigen Änderungen in der Umlaufbahn des Doppelsterns? Mehrere Ansätze wurden vorgeschlagen und während einige bereits ausgeschlossen werden konnten, wäre es möglich, dass dieser Effekt durch Veränderungen im Magnetfeld des größeren der beiden Sterne verursacht wird [4], ähnlich kleineren Veränderungen, die bei der Sonne beobachtet werden können.
„Eine Untersuchung wie diese war seit Jahren notwendig, aber konnte erst mit dem Aufkommen solch leistungsstarker neuer Instrumente wie SPHERE möglich gemacht werden. So funktioniert Wissenschaft: Beobachtungen mit neuer Technologie können frühere Ideen entweder bestätigen oder widerlegen, wie es hier der Fall war. Für dieses tolle Instrument ist dies ein großartiger Start ins Beobachtungsleben“, fasst Hardy zusammen.
Endnoten
[1] Solche Doppelsternsysteme bezeichnet man auch als Post-Common-Envelope-Doppelsterne bekannt.
[2] Der Name bedeutet, dass das Objekt der 471. in seiner Helligkeit veränderliche Stern ist, der im Sternbild Stier bestimmt wurde. Wie genauere Untersuchungen zeigen, kommen die Helligkeitsänderungen in diesem Fall durch die Doppelnatur des Systems zustande.
[3] Die Bilder von SPHERE sind so hochauflösend, dass sie in der Lage wären, einen Begleiter wie einen Braunen Zwerg zu finden, der 70.000 mal lichtschwächer als der Hauptstern und nur 0.26 Bogensekunden von ihm entfernt ist. Der in diesem Fall erwartete Begleiter in Form eines Braunen Zwerges wurde als viel heller vorhergesagt.
[4] Dieser Effekt wird als Applegate-Mechanismus bezeichnet und führt zu regelmäßigen Änderungen in der Form des Sterns, welche wiederum zu Veränderungen in der scheinbaren Helligkeit des Doppelsterns führt, wie sie von der Erde aus erscheint.
Weitere Informationen
Die hier vorgestellten Ergebnisse von A. Hardy et al. erscheinen am 18. Februar 2015 unter dem Titel "The First Science Results from SPHERE: Disproving the Predicted Brown Dwarf around V471 Tau" in den Astrophysical Journal Letters .
Die beteiligten wissenshcaftler sind A. Hardy (Universidad Valparaíso, Valparaíso, Chile; Millennium Nucleus "Protoplanetary Disks in ALMA Early Science", Teil des Millennium Science Initiative Program, Universidad Valparaíso), M.R. Schreiber (Universidad Valparaíso), S.G. Parsons (Universidad Valparaíso), C. Caceres (Universidad Valparaíso), G. Retamales (Universidad Valparaíso), Z. Wahhaj (ESO, Santiago de Chile), D. Mawet (ESO, Santiago de Chile), H. Canovas (Universidad Valparaíso), L. Cieza (Universidad Diego Portales, Santiago, Chile; Universidad Valparaíso), T.R. Marsh (University of Warwick, Coventry, Großbritannien), M.C.P. Bours (University of Warwick), V.S. Dhillon (University of Sheffield, Sheffield, Großbritannien) und A. Bayo (Universidad Valparaíso).
Die Europäische Südsternwarte (engl. European Southern Observatory, kurz ESO) ist die führende europäische Organisation für astronomische Forschung und das wissenschaftlich produktivste Observatorium der Welt. Getragen wird die Organisation durch 16 Länder: Belgien, Brasilien, Dänemark, Deutschland, Finnland, Frankreich, Großbritannien, Italien, die Niederlande, Österreich, Polen, Portugal, Spanien, Schweden, die Schweiz und die Tschechische Republik. Die ESO ermöglicht astronomische Spitzenforschung, indem sie leistungsfähige bodengebundene Teleskope entwirft, konstruiert und betreibt. Auch bei der Förderung internationaler Zusammenarbeit auf dem Gebiet der Astronomie spielt die Organisation eine maßgebliche Rolle. Die ESO verfügt über drei weltweit einzigartige Beobachtungsstandorte in Chile: La Silla, Paranal und Chajnantor. Auf dem Paranal betreibt die ESO mit dem Very Large Telescope (VLT) das weltweit leistungsfähigste Observatorium für Beobachtungen im Bereich des sichtbaren Lichts und zwei Teleskope für Himmelsdurchmusterungen: VISTA, das größte Durchmusterungsteleskop der Welt, arbeitet im Infraroten, während das VLT Survey Telescope (VST) für Himmelsdurchmusterungen ausschließlich im sichtbaren Licht konzipiert ist. Die ESO ist einer der Hauptpartner bei ALMA, dem größten astronomischen Projekt überhaupt. Auf dem Cerro Armazones unweit des Paranal errichtet die ESO zur Zeit das European Extremely Large Telescope (E-ELT) mit 39 Metern Durchmesser, das einmal das größte optische Teleskop der Welt werden wird.
Die Übersetzungen von englischsprachigen ESO-Pressemitteilungen sind ein Service des ESO Science Outreach Network (ESON), eines internationalen Netzwerks für astronomische Öffentlichkeitsarbeit, in dem Wissenschaftler und Wissenschaftskommunikatoren aus allen ESO-Mitgliedsländern (und einigen weiteren Staaten) vertreten sind. Deutscher Knoten des Netzwerks ist das Haus der Astronomie in Heidelberg.
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Der ungewöhnliche Doppelstern V471 Tauri im Sternbild Stier
Diese Karte zeigt die Lage des ungewöhnlichen Doppelsterns V471 (roter Kreis). Alle Sterne, die mit bloßem Auge in einer dunklen Nacht sichtbar sind, sind eingezeichnet. Das Objekt selbst kann leicht mithilfe eines kleinen Teleskops beobachtet werden, erscheint allerdings nur wie ein unauffälliger, leuchtschwacher Stern. V471 Tauri ist ein abseits gelegendes Mitglied des hellen Sternhaufens der Hyaden.
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Großfeldansicht der Himmelsregion um den ungewöhnlichen Doppelstern V471 Tauri
Dieses Bild zeigt die Himmelsregion um den unwöhnlichen Doppelstern V471 Tauri. Das Objekt selbst ist als unauffällig scheinender Stern mittlerer Helligkeit in der Mitte des Bildes zu sehen. Dieses Bild wurde aus Aufnahmen des Digitized Sky Survey 2 zusammengesetzt.
Quelle: ESO

Tags: Astronomie 

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