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Posted: 05 Mar 2015 05:16 AM PST
NASA’s next mission to Mars, scheduled to launch one year from today to examine the Red Planet’s deep interior and investigate how rocky planets like Earth evolved, now has one specific site under evaluation as the best place to land and deploy its science instruments. The mission called InSight -- an acronym for "Interior Exploration using Seismic Investigations, Geodesy and Heat Transport" -- is scheduled to launch from Vandenberg Air Force Base, California. The launch period runs from March 4 to March 30, 2016, and will mark the first California launch of an interplanetary mission. Installation of science-instrument hardware onto the spacecraft has begun and a key review has given thumbs up to integration and testing of the mission's component systems from several nations participating in the international project.
The landing-site selection process evaluated four candidate locations selected in 2014. The quartet is within the flat-lying "Elysium Planitia," less than five degrees north of the equator, and all four appear safe for InSight's landing. The single site will continue to be analyzed in coming months for final selection later this year. If unexpected problems with this site are found, one of the others would be imaged and could be selected. The favored site is centered at about four degrees north latitude and 136 degrees east longitude. "This is wondrous terrain, exactly what we want to land on because it is smooth, flat, with very few rocks in the highest-resolution images," said InSight's site-selection leader, Matt Golombek of NASA's Jet Propulsion Laboratory, Pasadena, California. Mars orbiters have provided detailed information about the candidate sites, which are mapped as landing ellipses about 81 miles (130 kilometers) west-to-east by about 17 miles (27 kilometers) north-to-south. An ellipse covers the area within which InSight has odds of about 99 percent of landing, if targeted for the ellipse center. Several types of terrain, such as "cratered," "etched" and "smooth" were mapped in each ellipse. The one chosen for final evaluations has highest proportion in the smooth category. After InSight reaches Mars on Sept. 28, 2016, the mission will assess properties of the planet's crust, mantle and core. The interior of Mars has not been churned as much as Earth's because Mars lacks the tectonic activity that recycles Earth's crustal plates back into the mantle. Thus, Mars offers an opportunity to find clues no longer present on Earth about how rocky planets such as Earth, Mars, Venus and Mercury formed and evolved. InSight's primary science will study the planet's interior, not surface features. Besides safety for the landing, the main site-selection criterion is for the ground within reach of the lander's robotic arm to be penetrable for a heat-flow probe designed to hammer itself into the soil to a depth three to five yards, or meters. Evidence that the ground will be suitable for the probe, rather than rock solid, comes from assessment by the Thermal Imaging System on NASA's Mars Odyssey orbiter of how quickly the ground cools at night or warms in sunlight, and evaluation of images from the High Resolution Imaging Science Experiment on NASA's Mars Reconnaissance Orbiter. The heat-flow probe is a key part of InSight's Heat Flow and Physical Properties Package (HP3) provided by the German Aerospace Center (DLR). Electronics for that instrument were the first hardware from the science payload put onto the InSight spacecraft being assembled and tested at Lockheed Martin Space Systems, Denver. "As flight components such as the HP3 electronics become available, our team continues to integrate them on the spacecraft and test their functionality," said Stu Spath, InSight spacecraft program manager at Lockheed Martin. "We're steadily marching toward the start of spacecraft environmental testing this spring." InSight's robotic arm will also place another science instrument onto the ground. This is the Seismic Experiment for Interior Structure, or SEIS, from the French Space Agency (CNES), with components from Germany, Switzerland, the United Kingdom and the United States. A third experiment will use the radio link between InSight and NASA's Deep Space Network antennas on Earth to measure precisely a wobble in Mars' rotation that could reveal whether the planet has a molten or solid core. Wind and temperature sensors from Spain's Center for Astrobiology and a pressure sensor will monitor weather, and a magnetometer will measure magnetic disturbances. The project passed its System Integration Review in February. "A panel of experts from outside the project reviewed the system-level integration and test program," said InSight Project Manager Tom Hoffman, of JPL. "For Insight, there are multiple systems being brought together from several countries for final integration and testing in Denver." InSight and other NASA current and future projects will help inform the journey to Mars, an agency priority to send humans to the Red Planet in the 2030s. JPL manages InSight for NASA's Science Mission Directorate in Washington. InSight is part of NASA's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. Credit: NASA  | ||||
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Posted: 04 Mar 2015 02:33 PM PST
Using NASA's Chandra X-ray Observatory, astronomers have found that the growth of galaxies containing supermassive black holes can be slowed down by a phenomenon referred to as cosmic precipitation. Cosmic precipitation is not a weather event, as we commonly associate the word -- rain, sleet, or snow. Rather, it is a mechanism that allows hot gas to produce showers of cool gas clouds that fall into a galaxy. Researchers have analyzed X-rays from more than 200 galaxy clusters, and believe that this gaseous precipitation is key to understanding how giant black holes affect the growth of galaxies. "We know that precipitation can slow us down on our way to work," said Mark Voit of Michigan State University (MSU) in East Lansing, lead author of the paper that appears in the latest issue of Nature. "Now we have evidence that it can also slow down star formation in galaxies with huge black holes."
Astronomers have long pursued the quest to understand how supermassive black holes, which can be millions or even billions of times the mass of the sun, affect their host galaxies.
"We've known for quite some time that supermassive black holes influence the growth of their host galaxies, but we haven't yet figured out all of the details," said co-author Megan Donahue, also of MSU. "These results get us a step closer."
The study looked at some of the largest known galaxies lying in the middle of galaxy clusters. These galaxies are embedded in enormous atmospheres of hot gas. This hot gas should cool and many stars should then form. However, observations show that something is hindering the star birth.
The answer appears to lie with the supermassive black holes at the centers of the large galaxies. Under specific conditions, clumps of gas can radiate away their energy and form cool clouds that mix with surrounding hot gas. Some of these clouds form stars, but others rain onto the supermassive black hole, triggering jets of energetic particles that push against the falling gas and reheat it, preventing more stars from forming. This cycle of cooling and heating creates a feedback loop that regulates the growth of the galaxies.
"We can say that a typical weather forecast for the center of a massive galaxy is this: cloudy with a chance of heat from a huge black hole," said co-author Greg Bryan of Columbia University in New York.
Voit and his colleagues used Chandra data to estimate how long it should take for the gas to cool at different distances from the black holes in the study. Using that information, they were able to accurately predict the "weather" around each of the black holes.
They found that the precipitation feedback loop driven by energy produced by the black hole jets prevents the showers of cold clouds from getting too strong. The Chandra data indicate the regulation of this precipitation has been going on for the last 7 billion years or more.
"Without these black holes and their jets, the central galaxies of galaxy clusters would have many more stars than they do today," said co-author Michael McDonald of the Massachusetts Institute of Technology in Cambridge.
While a rain of cool clouds appears to play a key role in regulating the growth of some galaxies, the researchers have found other galaxies where the cosmic precipitation had shut off. The intense heat in these central galaxies, possibly from colliding with another galaxy cluster, likely "dried up" the precipitation around the black hole.
Future studies will test whether this precipitation-black hole feedback process also regulates star formation in smaller galaxies, including our own Milky Way galaxy.
A pre-print of the Nature study by Mark Voit (Michigan State University), Megan Donahue (Michigan State), Greg Bryan (Columbia University), and Michael McDonald (Massachusetts Institute of Technology) is available online; the study builds on work by Voit and Donahue that was published in the January 20th, 2015 issue of The Astrophysical Journal Letters and is available online.
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for the agency's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.
Credit: chandra.si.edu
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Posted: 04 Mar 2015 02:12 PM PST
China has been researching the technical feasibility of exploring Mars and asteroids, a top space scientist and national political advisor revealed on Tuesday. Ye Peijian, from the China Academy of Space Technology and chief scientist with the country's lunar probe mission, said Chinese space researchers had tackled some of the technical difficulties associated with the exploration of Mars and asteroids. However, he added, the projects are only at the technical preparation stage, which suggests that it will be some time before an official project is announced.
Ye is an vocal advocate for a China Mars mission. If the project was given the green light, he said, the probe should orbit, land, and explore the surface of Mars all in one mission.
Ye said that as a developing country, China should narrow its space exploration focus to certain planets.
The country should also explore asteroids as many preserve information dating back to the Big Bang, not to mention that some pose a risk to the human race, he said.
"I hope [these plans] win the support of the people of China, and things kick off as soon as possible," said the scientist, who is in Beijing for the annual session of China's top political advisory body.
An earlier report showed that a feasibility study on China's first Mars mission had been completed. In November last year, a model of a Mars rover prototype was displayed at the Airshow China 2014.
Credit: xinhuanet.com
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Posted: 04 Mar 2015 01:52 PM PST
Images from the OSIRIS scientific imaging camera taken during the close flyby on 14 February have now been downlinked to Earth, revealing the surface of Comet 67P/C-G in unprecedented detail, and including the shadow of the spacecraft encircled in a wreath of light. The image released Wednesday shows an area near the edge of the comet’s “belly” close to the Imhotep-Ash regional boundary, where a mesh of steep slopes separates smooth-looking terrains from a craggier area. The image was taken from a distance of 6 km from the comet’s surface and has a resolution of 11 cm/pixel. It covers an area of 228 x 228 m.
To better identify the exact region on the comet, in the graphic below we compare the new OSIRIS narrow-angle camera image with a wider view of the comet, along with the NAVCAM image taken at 14:15 UT, noting that there are uncertainties in the distance to the surface and change in perspective between the images. Indeed, while the match on the smooth-looking region at the bottom of the NAC image in the displayed orientation is good, it is harder to match the upper half because of the lack of shadows in the NAC image, and because the geometry/viewing perspective has changed between the images. This means that the NAC image would have to be distorted and "draped" over the surface to fit the NAVCAM properly.
During the flyby, Rosetta not only passed closer by the comet than ever before, but also passed through a unique observational geometry: for a short time the Sun, spacecraft, and comet were exactly aligned. In this geometry, surface structures cast almost no shadows, and therefore the reflection properties of the surface material can be discerned.
“Images taken from this viewpoint are of high scientific value,” says OSIRIS Principal Investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany. “This kind of view is key for the study of grain sizes.”
As a side effect of this exceptional observational geometry, Rosetta’s shadow can be seen cast on the surface of Comet 67P/C-G as a fuzzy rectangular-shaped dark spot surrounded by a bright halo-like region.
The shadow is fuzzy and somewhat larger than Rosetta itself, measuring approximately 20 x 50 metres. If the Sun were a point source, the shadow would be sharp and almost exactly the same size as Rosetta (approximately 2 x 32 m). However, even at 347 million km from 67P/C-G on 14 February, the Sun appeared as a disc about 0.2 degrees across (about 2.3 times smaller than on Earth), resulting in a fuzzy “penumbra” around the spacecraft’s shadow on the surface. In this scenario and with Rosetta 6 km above the surface, the penumbra effect adds roughly 20 metres to the spacecraft’s dimensions, and which is cast onto the tilted surface of the comet.
If you were standing on the surface with Rosetta high above you, there would be no place in the shadow where the entire Sun would be blocked from view, which explains why there is no fully dark core to the shadow.
Rosetta is not the first spacecraft to capture its own shadow in this way. In 2005, JAXA’s Hayabusa spacecraft captured its shadow on asteroid Itokawa. However, because Hayabusa was only a few tens of metres above the surface, the penumbral effect was much less, resulting in a sharper and darker shadow of the spacecraft.
Also, the comet surface surrounding Rosetta’s shadow on Comet 67P/C-G appears significantly brighter than the rest of the surface seen in the image. Scientists refer to this effect as the ‘opposition surge’ and it is commonly observed when highly-structured regolith surfaces on planets and moons are illuminated directly behind the observer. For example, astronauts on the lunar surface saw the effect surrounding their own shadows. The primary cause of opposition surge is ‘shadow hiding’. When the Sun is directly behind the observer, the shadows cast by small grains disappear from the perspective of the observer, hidden behind the grains themselves, leading to a pronounced increase in brightness. There may also be a contribution from coherent backscatter due to the retro-reflective properties of small dust grains.
Credit: ESA
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Posted: 04 Mar 2015 12:34 PM PST
NASA's Curiosity Mars rover is expected to remain stationary for several days of engineering analysis following an onboard fault-protection action on Feb. 27 that halted a process of transferring sample material between devices on the rover's robotic arm. Telemetry received from the rover indicated that a transient short circuit occurred and the vehicle followed its programmed response, stopping the arm activity underway at the time of the irregularity in the electric current.
"We are running tests on the vehicle in its present configuration before we move the arm or drive," said Curiosity Project Manager Jim Erickson, of NASA's Jet Propulsion Laboratory in Pasadena, California. "This gives us the best opportunity to determine where the short is."
A transient short in some systems on the rover would have little effect on rover operations. In others, it could prompt the rover team to restrict use of a mechanism.
When the fault occurred, the rover was conducting an early step in the transfer of rock powder collected by the drill on the arm to laboratory instruments inside the rover. With the drill bit pointed up and the drill's percussion mechanism turned on, the rock powder was descending from collection grooves in the bit assembly into a chamber in the mechanism that sieves and portions the sample powder. The sample powder is from a rock target called "Telegraph Peak." The same transfer process was completed smoothly with samples from five previous drilling targets in 2013 and 2014.
NASA's Mars Science Laboratory Project is using Curiosity to assess ancient habitable environments and major changes in Martian environmental conditions. JPL, a division of the California Institute of Technology in Pasadena, built the rover and manages the project for NASA's Science Mission Directorate in Washington.
Credit: NASA
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2015년 3월 5일 목요일
Astro Watch
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