Cuzzi J.N.,Ames Research Center |
Hogan R.C.,Bay Area Research Institute |
Bottke W.F.,Southwest Research Institute
Icarus | Year: 2010
Our goal is to understand primary accretion of the first planetesimals. Some examples are seen today in the asteroid belt, providing the parent bodies for the primitive meteorites. The primitive meteorite record suggests that sizeable planetesimals formed over a period longer than a million years, each of which being composed entirely of an unusual, but homogeneous, mixture of millimeter-size particles. We sketch a scenario that might help explain how this occurred, in which primary accretion of 10-100. km size planetesimals proceeds directly, if sporadically, from aerodynamically-sorted millimeter-size particles (generically "chondrules" ). These planetesimal sizes are in general agreement with the currently observed asteroid mass peak near 100. km diameter, which has been identified as a "fossil" property of the pre-erosion, pre-depletion population. We extend our primary accretion theory to make predictions for outer Solar System planetesimals, which may also have a preferred size in the 100. km diameter range. We estimate formation rates of planetesimals and explore parameter space to assess the conditions needed to match estimates of both asteroid and Kuiper Belt Object (KBO) formation rates. For parameters that satisfy observed mass accretion rates of Myr-old protoplanetary nebulae, the scenario is roughly consistent with not only the "fossil" sizes of the asteroids, and their estimated production rates, but also with the observed spread in formation ages of chondrules in a given chondrite, and with a tolerably small radial diffusive mixing during this time between formation and accretion. As previously noted, the model naturally helps explain the peculiar size distribution of chondrules within such objects. The optimum range of parameters, however, represents a higher gas density and fractional abundance of solids, and a smaller difference between Keplerian and pressure-supported orbital velocities, than "canonical" models of the solar nebula. We discuss several potential explanations for these differences. The scenario also produces 10-100. km diameter primary KBOs, and also requires an enhanced abundance of solids to match the mass production rate estimates for KBOs (and presumably the planetesimal precursors of the ice giants themselves). We discuss the advantages and plausibility of the scenario, outstanding issues, and future directions of research. © 2010. Source
News Article | April 9, 2016
Kepler spacecraft is in emergency mode, National Aeronautics and Space Administration (NASA) said in a statement. Charlie Sobeck, Kepler and K2 mission manager at NASA's Ames Research Center announced that after a scheduled contact with mission operations engineers last April 7, it was discovered that Kepler is presently in emergency mode (EM), the spacecraft's lowest operational mode. The team is working on recovering from EM, as it consumes significant amount of fuel. Since the spacecraft is 75 million miles away from Earth, even with the speed of light, communication takes about 13 minutes for the message to travel from the spacecraft and back. For this, the spacecraft now has priority access to ground-based communication on NASA's Deep Space Network. The spacecraft was fully operational and in good condition last April 4. According to the mission engineers, the spacecraft entered into EM about 36 hours prior to maneuvering towards the center of the Milky Way. The extended mission's purpose is to continue planet hunting and provide study material for supernovae, young stars, and other astronomical objects using gravitational microlensing. The agency said that they will provide further information about the spacecraft once it has more updates. Launched in 2009, Kepler's primary mission was to look for planets outside the Solar System. The mission, which was completed in 2012, detected about 5,000 exoplanets, more than 1,000 of which were confirmed. The team hopes to restore Kepler's operations back to normal as it did before. In July 2012, one of the gyroscopic reaction wheels that help aim the spacecraft failed. The second wheel failed in May 2013. The K2 mission began in 2014 and proceeded by using the sun's radiation pressure to orient the spacecraft. "The chance for the K2 mission to use gravity to help us explore exoplanets is one of the most fantastic astronomical experiments of the decade," said Steve Howell, project scientist for NASA's Kepler and K2 mission. © 2016 Tech Times, All rights reserved. Do not reproduce without permission.
« DOE seeking input on H2@scale: hydrogen as centerpiece of future energy system; 50% reduction in energy GHGs by 2050 | Main | Audi deepening partnerships with Alibaba, Baidu and Tencent on connected cars in China » Boeing and NASA researchers are testing a 13-foot-wingspan, 6% scale Blended Wing Body (BWB) model at a subsonic wind tunnel at the NASA Langley Research Center in Virginia. Boeing is readying the BWB for the next step in maturing the concept—a manned demonstrator. The BWB concept is unique in that it forgoes the conventional tube and wing shape of today’s airplanes, in favor of a triangular tailless aircraft that effectively merges the vehicle’s wing and body. (Earlier post.) Testing will validate testing methodology, as well as map airflow over the airplane using lasers and smoke with a technique known as particle imagery velocimetry (PIV). Time permitting, testing will be conducted to measure the effectiveness of various control surfaces. That data will be compared with and supplement the set of data collected over the last two years on the same model at NASA Langley and the much larger 40- by 80-foot subsonic tunnel at NASA Ames Research Center in California. Our tests are a continuation of more than two decades of successful research and development of this concept, which is unparalleled in industry. What we learn from this round of testing will be used to complete the definition of our aerodynamic, stability and control low-speed databases – a major milestone in the technology development of the concept. Boeing sees potential for a BWB-type aircraft to be developed in the next 10 years as a subsonic transport, possibly beginning with military transport variants for airlift and aerial refueling, said John Dorris III, Mobility senior manager, Phantom Works Fixed Wing Assembly for Boeing. Backed by decades of successful structural, wind tunnel and flight testing of two different X-48 aircraft configurations, Boeing is readying the BWB for the next step in maturing this technology: a manned demonstrator. NASA’s Aeronautics budget proposes the return of X-planes. Boeing has completed an extensive study of BWB X-plane options for NASA and is supportive of NASA’s desire to create a series of manned demonstrators as part of its mission to advance the science of aviation for public benefit, said Naveed Hussain, vice president, Aeromechanics Technology, at Boeing. Much of the current testing is a collaboration with NASA Aeronautics and is a follow-on to tests that NASA and Boeing completed in 2014 and 2015 under NASA’s Environmentally Responsible Aviation program. The goal of that program was to develop technologies that improve fuel efficiencies, lower noise levels and reduce emissions. With the exception of Boeing proprietary technology, NASA knowledge gained from this NASA/Boeing collaborative research will be documented and publicly available to benefit the aviation industry. The BWB remains one of many promising concepts for a future NASA X-plane. NASA’s funding for the BWB project was provided as part of programs that are available for others to apply and compete for. In addition, Boeing has provided an approximate equal share of the costs for these efforts.
News Article | January 9, 2016
The Kepler spacecraft is back in action and NASA has confirmed that it has found over 100 planets orbiting stars. Ian Crossfield from the University of Arizona announced the mission's discoveries at an American Astronomical Society conference Tuesday, noting that the revamped Kepler mission, now known as K2, found some planets different from what the original mission observed. Many of these were orbit stars and multi-planet systems hotter and brighter than those from the original Kepler field. For instance, K2 spotted a system with three planets bigger than Earth, found a planet within the Hyades star cluster and discovered a planet in the process of being ripped apart while orbiting a white dwarf star. "It's probing different types of planets [than the original Kepler mission]. ... The idea here is to find the best systems, the most interesting systems," said Tom Barclay from NASA's Ames Research Center. According to Crossfield, the first five of the K2 campaigns each observed a different part of the sky and found 7,000 transit-like signals. These signals went through a validation process to narrow down the planet candidates, which were then validated. A $600-million mission, Kepler was launched in 2009 with the task of determining how Earth-like planets commonly occur in the Milky Way galaxy. Over the course of four years, the mission discovered more than 1,000 planets, a number more than half of all the exoplanets that had been discovered. The Kepler spacecraft had been looking at the same patch of sky since it was launched, but it lost the ability to stare at the same spot in 2013. It underwent a few tweaks to get it back in order, resulting in the K2, but it can no longer observe the same spot indefinitely. With K2, the same patch of sky can only be observed for about 80 days at a time. Aside from observing planets as they orbit other stars, K2 is also on the lookout for supernovas and studying planets in the solar system. The mission logged a 70-day observation of Neptune in 2014 to study the planet's windy weather and is currently staring at Uranus. Afterwards, K2 is set to observe an asteroid population sharing Jupiter's orbit. The revamped Kepler mission is also looking at trying to spot planets wandering the galaxy without their own stars.
The Lawrence Livermore Microbial Detection Array (LLMDA) is a versatile tool that has been employed for all kinds of studies, from analyzing the purity of infant vaccines to detecting plague in a 14th century tooth, to learning more about combat wounds from soldiers injured in Iraq and Afghanistan. Now a team of scientists from LLNL and three NASA research centers will use the LLMDA to study microbes that are associated with astronauts and found inside the closed environment aboard the International Space Station. Researchers from NASA's Jet Propulsion Laboratory in Pasadena; NASA's Ames Research Center in Moffett Field, California; NASA's Johnson Space Center in Houston, and LLNL have received a three-year, $1.5 million NASA grant for characterizing microbes using state-of-the-art molecular techniques. "The aim of the project is to provide a survey of the microbial profiles inside the International Space Station and to evaluate the possibility of the presence of pathogens that could be harmful to the astronauts' health," said LLNL biologist Crystal Jaing, the project's principal investigator. The project, called Microbial Tracking-2, is a follow-on to NASA's Microbial Tracking-1 (MT-1) that is currently sampling and studying airborne and surface-associated populations of microorganisms aboard the International Space Station. The third and final experiment in the MT-1 series was launched to the space station on April 8 on a SpaceX cargo resupply mission. The Livermore LLMDA technology is a DNA-based detection system that does not require the culturing of samples, compared to traditional techniques that may require days. Additionally, many bacteria have trouble growing in culture at all or require unique culture media. "The LLMDA can process samples in about a day. And while traditional culturing often only covers 1 to 10 percent of the microorganisms present, the LLNL array provides about 50- to 100-fold greater coverage of microbes," Jaing said. Kasthuri Venkateswaran, a senior research scientist at the Jet Propulsion Laboratory (JPL), sees the use of the LLMDA as a way to ensure that there aren't microbes in the space station that could be harmful to the crew's health. "We can have countermeasures once we know what astronauts are breathing in and breathing out," Venkateswaran said. "Beyond the microbes affecting the crew, we need to know what's in the environment and is riding on the cargo." The vast majority of microbes, upward of 80 percent, are innocuous to people, while only somewhere around 10 percent to 20 percent are harmful, according to Venkateswaran. Some bacteria look for the opportunity to cause disease, Venkateswaran said, adding that microbes that are innocuous on Earth may behave differently under the extreme environment of space. Space can affect the presence of bacteria Among the bacteria that have been detected via gene sequencing on the space station are Corynebacterium (bacteria that could cause respiratory infection) and Propionibacterium (bacteria that could cause acne). Since the genes of these opportunistic pathogens were only detected from the space station samples, their virulence characteristics need to be confirmed. Humans naturally play host to tens of billions of mainly innocuous bacteria. And one study has found that when a person enters a room, the individual adds 37 million bacteria to the air for each hour they remain there. The LLNL and NASA research scientists anticipate gathering preflight, inflight and post-flight samples, with the preflight crew samples expected to be taken this fall and the inflight samples planned for spring 2017. As envisioned, 18 air samples and 24 surface wipes will be taken for the space station environment and some 264 crew samples, including mouth, saliva and skin samples, will be gathered. Previous NASA microbe studies have focused on either the crews or the environment inside the space station; this will be the first study to merge the two areas. Previous investigations of viruses in crew and the environment also have been conducted. During the research effort, JPL researchers will receive all of the space station and crew samples for pre-processing to extract DNA and then distribute the biomolecules to LLNL and Johnson Space Center (JSC) for analysis. JPL scientists will perform the microbiological analysis of the samples, using traditional culturing techniques and DNA sequencing to determine which microbes are alive. LLNL's researchers will focus on the molecular detection of microbes in the DNA samples, as well as any virulent or antibiotic resistant genes, using the LLMDA and DNA sequencing. The latter technology analyzes the genetic makeup of the DNA and the order of the material's four bases—adenine, guanine, thymine and cytosine. In addition to Jaing, the Livermore scientists working on the research include biologists Nicholas Be and James Thissen, computer scientist Jonathan Allen and biostatistician Kevin McLoughlin. JSC researchers Satish Mehta and Duane Pierson will analyze the viruses in the samples and determine which viruses might be harmful to the crew. An Ames Research Center scientist, David J. Smith, will be responsible for developing the air sampler that will be utilized for capturing microbes. Already, LLNL scientists have been using the LLMDA and DNA sequencing to study previously collected air filter and dust samples from the International Space Station in preparation for the research. Developed in 2008, the LLMDA permits the detection of any virus, bacteria or other microbe that has been sequenced and included among the technology's 400,000 probes – on a one-inch wide, three-inch long glass slide – within 24 hours. The LLMDA version to be used for the space station analysis can detect 12,609 species, including 6,906 bacteria, 4,776 viruses, 414 fungi, 143 protozoa and 370 archaea. After the study is completed, NASA could potentially consider miniaturizing the LLMDA or a similar instrument to use on deep space missions with human habitation, Venkateswaran said. "The crew could use the system before consuming food, drinking water or working in a closed area. If a crew member becomes ill, they could also use the system to help determine whether they've become sick through bacteria, fungi or viruses. This would enable NASA flight surgeons to administer the right kind of medicine to treat the illness." Once the LLMDA-type system is miniaturized, the system could be deployed in remote parts of the world and in extreme environments to assist scientists, emergency first responders and public health, Venkateswaran suggested.