|Movie Shows Ceres at Opposition from SunNASA's Dawn spacecraft successfully observed Ceres at opposition on April 29, taking images from a position exactly between the sun and Ceres' surface. Mission specialists had carefully maneuvered Dawn into a special orbit so that the spacecraft could view Occator Crater, which contains the brightest area of Ceres, from this new perspective.|
A new movie shows these opposition images, with contrast enhanced to highlight brightness differences. The bright spots of Occator stand out particularly well on an otherwise relatively bland surface. Dawn took these images from an altitude of about 12,000 miles (20,000 kilometers).
Based on data from ground-based telescopes and spacecraft that previously viewed planetary bodies at opposition, scientists correctly predicted that Ceres would appear brighter from this opposition configuration. This increase in brightness, or "surge," relates the size of the grains of material on the surface, as well as the porosity of those materials. The science motivation for performing these observations is further explained in the March issue of the Dawn Journal blog.
Dawn's observations of Ceres during its more than two years there cover a broader range of illumination angles than almost any body in the solar system. This provides scientists with an opportunity to gain new insights into the surface properties. They are currently analyzing the new data.
The new observations and images were largely unaffected by the loss of function of Dawn's third reaction wheel. The spacecraft is healthy and orients itself using its hydrazine thrusters.
Dawn's mission is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. UCLA is responsible for overall Dawn mission science. Orbital ATK Inc., in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, Max Planck Institute for Solar System Research, Italian Space Agency and Italian National Astrophysical Institute are international partners on the mission team.
For a complete list of Dawn mission participants, visit:
quinta-feira, 18 de maio de 2017
|Scientists Look to Skies to Improve Tsunami DetectionA team of scientists from Sapienza University in Rome, Italy, and NASA's Jet Propulsion Laboratory in Pasadena, California, has developed a new approach to assist in the ongoing development of timely tsunami detection systems, based upon measurements of how tsunamis disturb a part of Earth's atmosphere.|
The new approach, called Variometric Approach for Real-time Ionosphere Observation, or VARION, uses observations from GPS and other global navigation satellite systems (GNSS) to detect, in real time, disturbances in Earth's ionosphere associated with a tsunami. The ionosphere is the layer of Earth's atmosphere located from about 50 to 621 miles (80 to 1,000 kilometers) above Earth's surface. It is ionized by solar and cosmic radiation and is best known for the aurora borealis (northern lights) and aurora australis (southern lights).
When a tsunami forms and moves across the ocean, the crests and troughs of its waves compress and extend the air above them, creating motions in the atmosphere known as internal gravity waves. The undulations of internal gravity waves are amplified as they travel upward into an atmosphere that becomes thinner with altitude. When the waves reach an altitude of between 186 to 217 miles (300 to 350 kilometers), they cause detectable changes to the density of electrons in the ionosphere. These changes can be measured when GNSS signals, such as those of GPS, travel through these tsunami-induced disturbances.
VARION was designed under the leadership of Sapienza's Mattia Crespi. The main author of the algorithm is Giorgio Savastano, a doctoral student in geodesy and geomatics at Sapienza and an affiliate employee at JPL, which conducted further development and validation of the algorithm. The work was outlined recently in a Sapienza- and NASA-funded study published in Nature's Scientific Reports journal.
In 2015, Savastano was awarded a fellowship by Consiglio Nazionale degli Ingegneri (CNI) and Italian Scientists and Scholars in North America Foundation (ISSNAP) for a two-month internship at JPL, where he joined the Ionospheric and Atmospheric Remote Sensing Group under the supervision of Attila Komjathy and Anthony Mannucci.
"VARION is a novel contribution to future integrated operational tsunami early warning systems," said Savastano. "We are currently incorporating the algorithm into JPL's Global Differential GPS System, which will provide real-time access to data from about 230 GNSS stations around the world that collect data from multiple satellite constellations, including GPS, Galileo, GLONASS and BeiDou." Since significant tsunamis are infrequent, exercising VARION using a variety of real-time data will help validate the algorithm and advance research on this tsunami detection approach.
Savastano says VARION can be included in design studies for timely tsunami detection systems that use data from a variety of sources, including seismometers, buoys, GNSS receivers and ocean-bottom pressure sensors.
Once an earthquake is detected in a specific location, a system could begin processing real-time measurements of the distribution of electrons in the ionosphere from multiple ground stations located near the quake's epicenter, searching for changes that may be correlated with the expected formation of a tsunami. The measurements would be collected and processed by a central processing facility to provide risk assessments and maps for individual earthquake events. The use of multiple independent data types is expected to contribute to the system's robustness.
"We expect to show it is feasible to use ionospheric measurements to detect tsunamis before they impact populated areas," said Komjathy. "This approach will add additional information to existing systems, complementing other approaches. Other hazards may also be targeted using real-time ionospheric observations, including volcanic eruptions or meteorites."
Observing the ionosphere, and how terrestrial weather below it interfaces with space above, continues to be an important focus for NASA. Two new missions -- the Ionospheric Connection Explorer and the Global-scale Observations of the Limb and Disk -- are planned to launch by early 2018 to observe the ionosphere, which should ultimately improve a wide array of models used to protect humans on the ground and satellites in space.
|NASA's CPEX Tackles a Weather FundamentalA NASA-funded field campaign getting underway in Florida on May 25 has a real shot at improving meteorologists' ability to answer some of the most fundamental questions about weather: Where will it rain? When? How much?|
Called the Convective Processes Experiment (CPEX), the campaign is using NASA's DC-8 airborne laboratory outfitted with five complementary research instruments designed and developed at NASA. The plane also will carry small sensors called dropsondes that are dropped from the plane and make measurements as they fall. Working together, the instruments will collect detailed data on wind, temperature and humidity in the air below the plane during the birth, growth and decay of convective clouds -- clouds formed by warm, moist air rising off the subtropical waters around Florida.
"Convection is simply a column or bubble of warm air rising," said CPEX Principal Investigator Ed Zipser of the University of Utah in Salt Lake City. That rising air may become the seed of a rainstorm; in the tropics and subtropics, including the U.S. South, convection is the most common way for precipitation to form. Convective clouds can join together to form a major rainstorm or can even become a hurricane.
Even though convection is such a fundamental atmospheric process, the start of convection has proven difficult to predict. Bjorn Lambrigtsen of NASA's Jet Propulsion Laboratory in Pasadena, California, a member of the CPEX science team, explained why: "Tropical convection flares up quickly. A thunderstorm pops up, does its thing, and goes away in an hour or so. And they're not very large." They're typically less than six miles (10 kilometers) across. Satellites can't observe much detail about a feature that small even if they happen to be looking at the right place at the right time. "To understand what makes a thunderstorm form and grow, we need field campaigns. We need to fly to where the storms are, look at them and their environment in detail, and measure all the important features at the same time," said Lambrigtsen.
Zipser is particularly interested in areas of deep convection, with cloud tops higher than jets fly. "If you look at a vacation poster of Hawaii, you see a sky full of little cotton balls," he says. "Those clouds are only a few kilometers deep, and you might get a light shower out of them. The troposphere over the tropics is 14 or 15 kilometers [9 miles] deep, and the top half of deep convective clouds is full of ice particles instead of liquid drops. If these deep clouds become better organized, grow into a large system and move over land, you can have widespread, heavy rainfall for the better part of a day. We need to find out when deep convection is going to form and why."
One Month, One Plane, Five Instruments
The CPEX team plans to log 10 to 16 flights in June for a total of about 100 flight hours, weather permitting. They hope to record the entire evolution of convective storms, from birth to decay. They'll fly in whichever direction the weather seems most promising, whether it's the Gulf of Mexico, the Caribbean or the western Atlantic Ocean. The most interesting data should come when the plane is able to penetrate deep but moderate convection without the threat of lightning, collecting data from inside a storm or storm system.
The five NASA instruments are flying together as a group for the first time:
Better Understanding, Improved Models
With a career stretching back to the 1960s, Ed Zipser knows as well as anyone how a good data set from field research can advance understanding of the atmosphere and improve the accuracy of weather and climate models. "We've known since the 1970s that the key to a successful forecast is being able to understand and treat the role of convection," he said. "We've made a lot of progress, but none of the model treatments of convection is anything you could call perfect. We need to observe better and understand more. CPEX is a pretty exciting opportunity to learn more about convection and its evolution."
quarta-feira, 3 de maio de 2017
|Cassini Finds 'The Big Empty' Close to SaturnAs NASA's Cassini spacecraft prepares to shoot the narrow gap between Saturn and its rings for the second time in its Grand Finale, Cassini engineers are delighted, while ring scientists are puzzled, that the region appears to be relatively dust-free. This assessment is based on data Cassini collected during its first dive through the region on April 26.|
With this information in hand, the Cassini team will now move forward with its preferred plan of science observations.
"The region between the rings and Saturn is 'the big empty,' apparently," said Cassini Project Manager Earl Maize of NASA's Jet Propulsion Laboratory in Pasadena, California. "Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected."
A dustier environment in the gap might have meant the spacecraft's saucer-shaped main antenna would be needed as a shield during most future dives through the ring plane. This would have forced changes to how and when Cassini's instruments would be able to make observations. Fortunately, it appears that the "plan B" option is no longer needed. (There are 21 dives remaining. Four of them pass through the innermost fringes of Saturn's rings, necessitating that the antenna be used as a shield on those orbits.)
Based on images from Cassini, models of the ring particle environment in the approximately 1,200-mile-wide (2,000-kilometer-wide) region between Saturn and its rings suggested the area would not have large particles that would pose a danger to the spacecraft.
But because no spacecraft had ever passed through the region before, Cassini engineers oriented the spacecraft so that its 13-foot-wide (4-meter-wide) antenna pointed in the direction of oncoming ring particles, shielding its delicate instruments as a protective measure during its April 26 dive.
Cassini's Radio and Plasma Wave Science (RPWS) instrument was one of two science instruments with sensors that poke out from the protective shield of the antenna (the other being Cassini'smagnetometer). RPWS detected the hits of hundreds of ring particles per second when it crossed the ring plane just outside of Saturn's main rings, but only detected a few pings on April 26.
When RPWS data are converted to an audio format, dust particles hitting the instrument's antennas sound like pops and cracks, covering up the usual whistles and squeaks of waves in the charged particle environment that the instrument is designed to detect. The RPWS team expected to hear a lot of pops and cracks on crossing the ring plane inside the gap, but instead, the whistles and squeaks came through surprisingly clearly on April 26.
"It was a bit disorienting -- we weren't hearing what we expected to hear," said William Kurth, RPWS team lead at the University of Iowa, Iowa City. "I've listened to our data from the first dive several times and I can probably count on my hands the number of dust particle impacts I hear."
The team's analysis suggests Cassini only encountered a few particles as it crossed the gap -- none larger than those in smoke (about 1 micron across).
Cassini will next cross through the ring plane Tuesday, May 2, at 12:38 p.m. PDT (3:38 p.m. EDT) in a region very close to where it passed on the previous dive. During this orbit, in advance of the crossing, Cassini's cameras have been looking closely at the rings; in addition, the spacecraft has rotated (or "rolled") faster than engineers have ever allowed it to before, in order to calibrate the magnetometer. As with the first finale dive, Cassini will be out of contact during closest approach to Saturn, and is scheduled to transmit data from this dive on May 3.
More information about Cassini's Grand Finale, including images and video, is available at:
The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. JPL designed, developed and assembled the Cassini orbiter.
More information about Cassini: