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From August through early December, the OSIRIS-REx spacecraft aimed three of its science instruments toward Bennu and began making the mission's first observations of the asteroid. During this period, the spacecraft traveled the last 1.4 million miles (2.2 million km) of its outbound journey to arrive at a spot 12 miles (19 km) from Bennu on Dec. 3. The science obtained from these initial observations confirmed many of the mission team's ground-based observations of Bennu and revealed several new surprises.

This mosaic image of asteroid Bennu is composed of 12 PolyCam images collected on Dec. 2 by the OSIRIS-REx spacecraft from a range of 15 miles (24 km) [Credit: NASA/Goddard/University of Arizona]

Team members of the mission, which is led by the University of Arizona, presented the results at the Annual Fall Meeting of the American Geophysical Union, or AGU, in Washington, D.C. on Dec. 10.

In a key finding for the mission's science investigation, data obtained from the spacecraft's two spectrometers, the OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) and the OSIRIS-REx Thermal Emissions Spectrometer (OTES), reveal the presence of molecules that contain oxygen and hydrogen atoms bonded together, known as "hydroxyls." The team suspects that these hydroxyl groups exist globally across the asteroid in water-bearing clay minerals, meaning that at some point, the rocky material interacted with water. While Bennu itself is too small to have ever hosted liquid water, the finding does indicate that liquid water was present at some time on Bennu's parent body, a much larger asteroid.

"This finding may provide an important link between what we think happened in space with asteroids like Bennu and what we see in the meteorites that scientists study in the lab," said Ellen Howell, senior research scientist at the UA's Lunar and Planetary Laboratory (LPL) and a member of the mission's spectral analysis group. "It is very exciting to see these hydrated minerals distributed across Bennu's surface, because it suggests they are an intrinsic part of Bennu's composition, not just sprinkled on its surface by an impactor."

"The presence of hydrated minerals across the asteroid confirms that Bennu, a remnant from early in the formation of the solar system, is an excellent specimen for the OSIRIS-REx mission to study the composition of primitive volatiles and organics," said Amy Simon, OVIRS Deputy Instrument Scientist at NASA Goddard Space Flight Center.

Additionally, data obtained from the OSIRIS-REx Camera Suite (OCAMS) corroborate ground-based radar observations of Bennu and confirm that the original model -- developed in 2013 by OSIRIS-REx Science Team Chief Michael Nolan, now based at LPL, and collaborators -- closely predicted the asteroid's actual shape. Bennu's diameter, rotation rate, inclination and overall shape presented almost exactly as projected.

Soon after the asteroid later named Bennu was discovered in 1999, Nolan's group used the Arecibo Observatory in Puerto Rico to gather clues about its size, shape and rotation by bouncing radar waves off of it during one of its close approaches to Earth, about five times the distance between Earth and the moon.

"Radar observations don't give us any information about colors or brightness of the object, so it is really interesting to see the asteroid up close through the eyes of OSIRIS-REx," Nolan said. "As we are getting more details, we are figuring out where the craters and boulders are, and we were very pleasantly surprised that virtually every little bump we saw in our radar image back then is actually really there."

The mission team used this ground-based Bennu model when designing the OSIRIS-REx mission. The accuracy of the model means that the mission, spacecraft, and planned observations were appropriately designed for the tasks ahead at Bennu.

One outlier from the predicted shape model is the size of the large boulder near Bennu's south pole. The ground-based shape model calculated this boulder to be at least 33 feet (10 meters) in height. Preliminary calculations from OCAMS observations show that the boulder is closer to 164 feet (50 meters) in height, with a width of approximately 180 feet (55 meters).

As expected, the initial assessment of Bennu's regolith indicates that the surface of Bennu is a mix of very rocky, boulder-filled regions and a few relatively smooth regions that lack boulders. However, the quantity of boulders on the surface is higher than was expected. The team will make further observations at closer ranges to more accurately assess where a sample can be taken on Bennu for later return to Earth.

"Our initial data show that the team picked the right asteroid as the target of the OSIRIS-REx mission. We have not discovered any insurmountable issues at Bennu so far," said Dante Lauretta, OSIRIS-REx principal investigator and professor of planetary science and cosmochemistry at LPL. "The spacecraft is healthy and the science instruments are working better than required. It is time now for our adventure to begin."

"What used to be science fiction is now a reality," said UA President Robert C. Robbins. "Our work at Bennu brings us a step closer to the possibility of asteroids providing astronauts on future missions into the solar system with resources like fuel and water."

The mission is currently performing a preliminary survey of the asteroid, flying the spacecraft in passes over Bennu's north pole, equator and south pole at ranges as close as 4.4 miles (7 km) to better determine the asteroid's mass. This survey also provides the first opportunity for the OSIRIS-REx Laser Altimeter (OLA), an instrument contributed by the Canadian Space Agency, to make observations now that the spacecraft is in proximity to Bennu. The spacecraft's first orbital insertion is scheduled for Dec. 31, and OSIRIS-REx will remain in orbit until mid-February 2019, when the mission transitions into the next survey phase. During this first orbital phase, the spacecraft will orbit the asteroid at a range of 0.9 miles (1.4 km) to 1.24 miles (2 km) from the center of Bennu -- setting two new records for the smallest body ever orbited by a spacecraft and the closest orbit of a planetary body by any spacecraft.

Author: Erin Morton and Daniel Stolte | Source: University of Arizona [December 10, 2018]

A team led by Southwest Research Institute has concluded that the surface of dwarf planet Ceres is rich in organic matter. Data from NASA's Dawn spacecraft indicate that Ceres's surface may contain several times the concentration of carbon than is present in the most carbon-rich, primitive meteorites found on Earth.

NASA's Dawn spacecraft captured this 12.5-mile-across close-up of the central peak of the 99-mile-wide Urvara impact crater on Ceres. The remarkable 6,500-foot central ridge is made from materials uplifted from depth,  arising from terrains enriched with products of rock-water interactions, such as carbonates [Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA]

"Ceres is like a chemical factory," said SwRI's Dr. Simone Marchi, a principal scientist who was the lead author of research published in Nature Astronomy. "Among inner solar system bodies, Ceres' has a unique mineralogy, which appears to contain up to 20 percent carbon by mass in its near surface. Our analysis shows that carbon-rich compounds are intimately mixed with products of rock-water interactions, such as clays."

Ceres is believed to have originated about 4.6 billion years ago at the dawn of our solar system. Dawn data previously revealed the presence of water and other volatiles, such as ammonium derived from ammonia, and now a high concentration of carbon. This chemistry suggests Ceres formed in a cold environment, perhaps outside the orbit of Jupiter. An ensuing shakeup in the orbits of the large planets would have pushed Ceres to its current location in the main asteroid belt, between the orbits of Mars and Jupiter.

"With these findings, Ceres has gained a pivotal role in assessing the origin, evolution and distribution of organic species across the inner solar system," Marchi said. "One has to wonder about how this world may have driven organic chemistry pathways, and how these processes may have affected the make-up of larger planets like the Earth."

SwRI scientists constructed a possible schematic path for the evolution of Ceres' upper crust. The figure shows  the presence of carbonaceous chondrite-like materials (black) mixed with products of aqueous alteration such as phyllosilicates, carbonates and magnetite (green) and organics (orange). Shaded blue regions indicate water, and blue lines represent conduits for water migration. Organics may have formed in place during aqueous alteration or could have been concentrated by fluids ascending to the upper crust, resulting in the inferred higher-than-chondritic carbon concentration on Ceres' surface. Over time, the surface gets homogenized by mixing due to collisions and other processes [Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA]

Geophysical, compositional and collisional models based on Dawn data revealed that Ceres' partially differentiated interior has been altered by fluid processes. Dawn's Visible and Infrared Mapping Spectrometer has shown that the overall low albedo of Ceres'' surface is a combination of rock-water interaction products such as phyllosilicates and carbonates and a significant amount of spectrally neutral darkening agents, such as an iron oxide called magnetite.

Because Dawn's Gamma Ray and Neutron Detector limits magnetite to only a few percent by mass, the data point to the presence of an additional darkening agent, probably amorphous carbon, a carbon-rich organic material. Interestingly, specific organic compounds have also been detected near a 31-mile-wide impact crater named Ernutet, giving further support to the widespread presence of organics in Ceres' shallow subsurface.

The new study also finds that 50-60 percent of Ceres' upper crust may have a composition similar to primitive carbonaceous chondrite meteorites. This material is compatible with contamination from infalling carbonaceous asteroids, a possibility supported by Ceres' battered surface.

"Our results imply that either Ceres' accreted ultra-carbon-rich materials or that carbon was concentrated in its crust," said said Marchi. "Both potential scenarios are important, because Ceres' mineralogical composition indicates a global-scale event of rock-water alteration, which could provide conditions favorable to organic chemistry."

Source: Southwest Research Institute [December 10, 2018]

For the second time in history, a human-made object has reached the space between the stars. NASA's Voyager 2 probe now has exited the heliosphere -- the protective bubble of particles and magnetic fields created by the Sun.

This illustration shows the position of NASA’s Voyager 1 and Voyager 2 probes, outside of the heliosphere, a protective bubble created by the Sun that extends well past the orbit of Pluto [Credit: NASA/JPL-Caltech]

Members of NASA's Voyager team will discuss the findings at a news conference at 11 a.m. EST (8 a.m. PST) today at the meeting of the American Geophysical Union (AGU) in Washington. The news conference will stream live on the agency's website.

Comparing data from different instruments aboard the trailblazing spacecraft, mission scientists determined the probe crossed the outer edge of the heliosphere on Nov. 5. This boundary, called the heliopause, is where the tenuous, hot solar wind meets the cold, dense interstellar medium. Its twin, Voyager 1, crossed this boundary in 2012, but Voyager 2 carries a working instrument that will provide first-of-its-kind observations of the nature of this gateway into interstellar space.

Voyager 2 now is slightly more than 11 billion miles (18 billion kilometers) from Earth. Mission operators still can communicate with Voyager 2 as it enters this new phase of its journey, but information -- moving at the speed of light -- takes about 16.5 hours to travel from the spacecraft to Earth. By comparison, light traveling from the Sun takes about eight minutes to reach Earth.

The most compelling evidence of Voyager 2's exit from the heliosphere came from its onboard Plasma Science Experiment (PLS), an instrument that stopped working on Voyager 1 in 1980, long before that probe crossed the heliopause. Until recently, the space surrounding Voyager 2 was filled predominantly with plasma flowing out from our Sun. This outflow, called the solar wind, creates a bubble -- the heliosphere -- that envelopes the planets in our solar system. The PLS uses the electrical current of the plasma to detect the speed, density, temperature, pressure and flux of the solar wind. The PLS aboard Voyager 2 observed a steep decline in the speed of the solar wind particles on Nov. 5. Since that date, the plasma instrument has observed no solar wind flow in the environment around Voyager 2, which makes mission scientists confident the probe has left the heliosphere.


"Working on Voyager makes me feel like an explorer, because everything we're seeing is new," said John Richardson, principal investigator for the PLS instrument and a principal research scientist at the Massachusetts Institute of Technology in Cambridge. "Even though Voyager 1 crossed the heliopause in 2012, it did so at a different place and a different time, and without the PLS data. So we're still seeing things that no one has seen before."

In addition to the plasma data, Voyager's science team members have seen evidence from three other onboard instruments -- the cosmic ray subsystem, the low energy charged particle instrument and the magnetometer -- that is consistent with the conclusion that Voyager 2 has crossed the heliopause. Voyager's team members are eager to continue to study the data from these other onboard instruments to get a clearer picture of the environment through which Voyager 2 is traveling.

"There is still a lot to learn about the region of interstellar space immediately beyond the heliopause," said Ed Stone, Voyager project scientist based at Caltech in Pasadena, California.

Together, the two Voyagers provide a detailed glimpse of how our heliosphere interacts with the constant interstellar wind flowing from beyond. Their observations complement data from NASA's Interstellar Boundary Explorer (IBEX), a mission that is remotely sensing that boundary. NASA also is preparing an additional mission -- the upcoming Interstellar Mapping and Acceleration Probe (IMAP), due to launch in 2024 -- to capitalize on the Voyagers' observations.

At the end of 2018, the cosmic ray subsystem aboard NASA's Voyager 2 spacecraft provided evidence that Voyager 2 had left the heliosphere. There were steep drops in the rate of heliospheric particles that hit the instrument's radiation detector, and significant increases in the rate of cosmic rays [Credit: NASA/JPL-Caltech/GSFC]

"Voyager has a very special place for us in our heliophysics fleet," said Nicola Fox, director of the Heliophysics Division at NASA Headquarters. "Our studies start at the Sun and extend out to everything the solar wind touches. To have the Voyagers sending back information about the edge of the Sun's influence gives us an unprecedented glimpse of truly uncharted territory."

While the probes have left the heliosphere, Voyager 1 and Voyager 2 have not yet left the solar system, and won't be leaving anytime soon. The boundary of the solar system is considered to be beyond the outer edge of the Oort Cloud, a collection of small objects that are still under the influence of the Sun's gravity. The width of the Oort Cloud is not known precisely, but it is estimated to begin at about 1,000 astronomical units (AU) from the Sun and to extend to about 100,000 AU. One AU is the distance from the Sun to Earth. It will take about 300 years for Voyager 2 to reach the inner edge of the Oort Cloud and possibly 30,000 years to fly beyond it.

The Voyager probes are powered using heat from the decay of radioactive material, contained in a device called a radioisotope thermal generator (RTG). The power output of the RTGs diminishes by about four watts per year, which means that various parts of the Voyagers, including the cameras on both spacecraft, have been turned off over time to manage power.

"I think we're all happy and relieved that the Voyager probes have both operated long enough to make it past this milestone," said Suzanne Dodd, Voyager project manager at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. "This is what we've all been waiting for. Now we're looking forward to what we'll be able to learn from having both probes outside the heliopause."

The set of graphs on the left illustrates the drop in electrical current detected in three directions by Voyager 2's plasma science experiment (PLS) to background levels. They are among the key pieces of data that show that Voyager 2 entered interstellar space in November 2018 [Credit: NASA/JPL-Caltech/MIT]

Voyager 2 launched in 1977, 16 days before Voyager 1, and both have traveled well beyond their original destinations. The spacecraft were built to last five years and conduct close-up studies of Jupiter and Saturn. However, as the mission continued, additional flybys of the two outermost giant planets, Uranus and Neptune, proved possible. As the spacecraft flew across the solar system, remote-control reprogramming was used to endow the Voyagers with greater capabilities than they possessed when they left Earth. Their two-planet mission became a four-planet mission. Their five-year lifespans have stretched to 41 years, making Voyager 2 NASA's longest running mission.

The Voyager story has impacted not only generations of current and future scientists and engineers, but also Earth's culture, including film, art and music. Each spacecraft carries a Golden Record of Earth sounds, pictures and messages. Since the spacecraft could last billions of years, these circular time capsules could one day be the only traces of human civilization.

Voyager's mission controllers communicate with the probes using NASA's Deep Space Network (DSN), a global system for communicating with interplanetary spacecraft. The DSN consists of three clusters of antennas inGoldstone, California; Madrid, Spain; and Canberra, Australia.

Author: Dwayne Brown / Karen Fox | Source: NASA/Jet Propulsion Laboratory [December 10, 2018]