NASA’s OSIRIS-REx Spacecraft Enters Close Orbit Around Bennu, Breaking Record
By Erin Morton
By Erin Morton, OSIRIS-REx Asteroid Sample Return Mission - December 31, 2018
At 2:43 p.m. EST on December 31, while many on Earth prepared to welcome the New Year, NASA’s OSIRIS-REx spacecraft, 70 million miles (110 million kilometers) away, carried out a single, eight-second burn of its thrusters – and broke a space exploration record. The spacecraft entered into orbit around the asteroid Bennu, and made Bennu the smallest object ever to be orbited by a spacecraft.
“The team continued our long string of successes by executing the orbit-insertion maneuver perfectly,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson. “With the navigation campaign coming to an end, we are looking forward to the scientific mapping and sample site selection phase of the mission.”
Lauretta, along with his team, spent the last day of 2018 with his feet planted on Earth, but his mind focused on space. “Entering orbit around Bennu is an amazing accomplishment that our team has been planning for years,” Lauretta said.
Inching around the asteroid at a snail’s pace, OSIRIS-REx’s first orbit marks a leap for humankind. Never before has a spacecraft from Earth circled so close to such a small space object – one with barely enough gravity to keep a vehicle in a stable orbit.
Now, the spacecraft will circle Bennu about a mile (1.75 kilometers) from its center, closer than any other spacecraft has come to its celestial object of study. (Previously the closest orbit of a planetary body was in May 2016, when the Rosetta spacecraft orbited about four miles (seven kilometers) from the center of the comet 67P/Churyumov-Gerasimenko.) The comfortable distance is necessary to keep the spacecraft locked to Bennu, which has a gravity force only 5-millionths as strong as Earth’s. The spacecraft is scheduled to orbit Bennu through mid-February at a leisurely 62 hours per orbit.
Now that the OSIRIS-REx spacecraft is closer to Bennu, physical details about the asteroid will leap into sharper focus, and the spacecraft’s tour of this rubble pile of primordial debris will become increasingly detailed and focused.
“Our orbit design is highly dependent on Bennu’s physical properties, such as its mass and gravity field, which we didn’t know before we arrived,” said OSIRIS-REx’s flight dynamics system manager Mike Moreau, who is based at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
“Up until now, we had to account for a wide variety of possible scenarios in our computer simulations to make sure we could safely navigate the spacecraft so close to Bennu. As the team learned more about the asteroid, we incorporated new information to hone in on the final orbit design,” he said.
The simulations have played a critical role. The OSIRIS-REx mission, after all, was designed based on complex computer programs that predicted — quite accurately, as it turns out — the properties of Bennu and how the spacecraft’s trajectory would behave. This diligent preparation allowed the team to navigate the vehicle safely to Bennu in December and put some questions to rest (there are, indeed, signs of ancient water preserved in Bennu’s rocks) and to fly over its poles and equator in a preliminary survey that led to some surprises (Bennu has many large boulders).
Having completed the preliminary survey of Bennu with a flyby of its south pole on December 16, the spacecraft moved to a safe 31 miles (50 kilometers) away from the asteroid to give the navigation team a chance to regroup and prepare for orbit insertion. Next, Lockheed Martin engineers programmed the spacecraft to begin moving back to a position about nine miles (15 kilometers) over Bennu’s north pole to prepare for three burns of its thrusters over the course of 10 days that would place the spacecraft into orbit.
Even though OSIRIS-REx is in the most stable orbit possible, Bennu’s gravitational pull is so tenuous that keeping the spacecraft safe will require occasional adjustments, said Dan Wibben, OSIRIS-REx maneuver and trajectory design lead at KinetX Aerospace in Simi Valley, California.
“The gravity of Bennu is so small, forces like solar radiation and thermal pressure from Bennu’s surface become much more relevant and can push the spacecraft around in its orbit much more than if it were orbiting around Earth or Mars, where gravity is by far the most dominant force,” he said.
The OSIRIS-REx navigation team will use “trim” maneuvers to slightly thrust the spacecraft in one direction or another to correct its orbit and counter these small forces. If the spacecraft drifts away from Bennu, or some other problem forces it into safe mode, it has been programmed to fly away from the asteroid to stay safe from impact.
“It’s simple logic: always burn toward the Sun if something goes wrong,” said Coralie Adam, OSIRIS-REx lead optical navigation engineer at KinetX. Engineers can navigate the spacecraft back into orbit if it drifts away, Adam said, though that’s unlikely to happen.
The navigation and spacecraft operations teams are focused on the first orbital phase. Their primary goal is to transition away from star-based navigation, which allowed the team to locate the spacecraft based on pictures of the star formations around it taken by the cameras onboard. Navigators use methods like this since there is no GPS in deep space and we can’t see the spacecraft from Earth-based telescopes. From this point forward, though, the OSIRIS-REx team will rely on landmarks on Bennu’s surface to track OSIRIS-REx, a more precise technique that will ultimately guide them to a sample-collection site clear of boulders and large rocks, said Adam.
“After conducting a global imaging and mapping campaign during our recent preliminary survey phase, the science team has created 3-D models of Bennu’s terrain that we’re going to begin using for navigation around the asteroid,” she said.
Another critical objective of this orbital phase, Adam said, is to get a better handle on Bennu’s mass and gravity, features that will influence the planning of the rest of the mission, notably the short touchdown on the surface for sample collection in 2020. In the case of Bennu, scientists can only measure these features by getting OSIRIS-REx very close to the surface to see how its trajectory bends from Bennu’s gravitational pull.
“The Orbital A phase will help improve our detailed models for Bennu’s gravity field, thermal properties, orientation, and spin rate,” said Wibben. “This, in turn, will allow us to refine our trajectory designs for the even more challenging flight activities we will perform in 2019.”
The December 31 maneuver to place the spacecraft into orbit about Bennu is the first of many exciting navigation activities planned for the mission. The OSIRIS-REx team will resume science operations in late February. At that point, the spacecraft will perform a series of close flybys of Bennu for several months to take high-resolution images of every square inch of the asteroid to help select a sampling site. During the summer of 2020, the spacecraft will briefly touch the surface of Bennu to retrieve a sample. The OSIRIS-REx mission is scheduled to deliver the sample to Earth in September 2023.
Stellar Corpse Reveals Clues to Missing Stardust
The origin of stardust, which makes up most of the matter in our solar system, including us, is more complicated than previously thought, according to new observations of a mysterious object 15,000 light-years from Earth.
By Daniel Stolte, University Communications - December 19, 2018
Everything around you – your desk, your laptop, your coffee cup – in fact, even you – is made of stardust, the stuff forged in the fiery furnaces of stars that died before our sun was born. Probing the space surrounding a mysterious stellar corpse, scientists at the University of Arizona have made a discovery that could help solve a long-standing mystery: Where does stardust come from?
When stars die, they seed the cosmos around them with the elements that go on to coalesce into new stars, planets, asteroids and comets. Most everything that makes up Earth, even life itself, consists of elements made by previous stars, including silicon, carbon, nitrogen and oxygen. But this is not the whole story. Meteorites commonly contain traces of a type of stardust that, until now, was believed to form only in exceptionally violent, explosive events of stellar death known as novae or supernovae – too rare to account for the abundance preserved in meteorites.
Researchers at the UA used radio telescopes in Arizona and Spain to observe gas clouds in the young planetary nebula K4-47, an enigmatic object approximately 15,000 light-years from Earth. Classified as a nebula, K4-47 is a stellar remnant, which astronomers believe was created when a star not unlike our sun shed some of its material in a shell of outflowing gas before ending its life as a white dwarf.
To their surprise, the researchers found that some of the elements that make up the nebula – carbon, nitrogen and oxygen – are highly enriched with certain variants that match the abundances seen in some meteorite particles but are otherwise rare in our solar system: so-called heavy isotopes of carbon, nitrogen and oxygen, or 13C, 15N and 17O, respectively. These isotopes differ from their more common forms by containing an extra neutron inside their nucleus.
Fusing an additional neutron onto an atomic nucleus requires extreme temperatures in excess of 200 million degrees Fahrenheit, leading scientists to conclude those isotopes could only be formed in novae – violent outbursts of energy in aging binary star systems – and supernovae, in which a star blows itself apart in one cataclysmic explosion.
"The models invoking only novae and supernovae could never account for the amounts of 15N and 17O we observe in meteorite samples," said Lucy Ziurys, senior author of the paper, which is published in the Dec. 20 issue of the journal Nature. "The fact that we're finding these isotopes in K4-47 tells us that we don't need strange exotic stars to explain their origin. It turns out your average garden variety stars are capable of producing them as well."
In lieu of cataclysmic explosive events forging heavy isotopes, the team suggests they could be produced when an average-size star such as our sun becomes unstable toward the end of its life and undergoes a so-called helium flash, in which super-hot helium from the star's core punches through the overlaying hydrogen envelope.
"This process, during which the material has to be spewed out and cooled quickly, produces 13C, 15N and 17O," explained Ziurys, a professor with dual appointments in the UA's Steward Observatory and Department of Chemistry and Biochemistry. "A helium flash doesn't rip the star apart like a supernova does. It's more like a stellar eruption."
The findings have implications for the identification of stardust and the understanding of how common stars create elements such as oxygen, nitrogen and carbon, the authors said.
The discovery was made possible through a collaboration between disciplines that traditionally have remained relatively separate: astronomy and cosmochemistry. The team used radio telescopes at the Arizona Radio Observatory and Institut de Radioastronomie Millimetrique (IRAM) to observe rotational spectra emitted by the molecules in the K4-47 nebula, which reveal clues about their mass distribution and their identity.
"When Lucy and I started collaborating on this project, we realized that we could reconcile what we found in meteorites and what we observe in space," said co-author Tom Zega, associate professor of cosmochemistry, planetary materials and astrobiology in the UA's Lunar and Planetary Laboratory.
The researchers are eagerly awaiting the discoveries that lie ahead for NASA's OSIRIS-REx asteroid sample return mission, which is led by the UA. Just two weeks ago, the spacecraft arrived at its target asteroid, Bennu, from which it will collect a sample of pristine material in 2020. One of the mission's major goals is to understand the evolution of Bennu and the origins of the solar system.
"You can think of the grains we find in meteorites as stellar ashes, left behind by stars that had long died when our solar system formed," Zega said. "We expect to find those pre-solar grains on Bennu – they are part of the puzzle of the history of this asteroid, and this research will help define where the material on Bennu came from."
"We can now trace where those ashes came from," Ziurys added. "It's like an archeology of stardust."
"The study of explosive helium burning inside stars will start a new chapter in the story of the origin of the chemical elements," said Neville "Nick" Woolf, Professor Emeritus at Steward Observatory and the fourth co-author.
The article’s first author is Deborah Schmidt, a doctoral student at the Steward Observatory.
This research was funded by the National Science Foundation (Grant No. AST- 1515568) and NASA (Agreement No. NNX15AD94G).
UA Researcher Captures Rare Radar Images of Comet 46P/Wirtanen
A LPL-led team took the best known opportunity for the next 30 years to image a comet with radar, resulting in some unique and surprising information about Comet 46P/Wirtanen.
By Erin Morton, UA Lunar and Planetary Laboratory - December 20, 2018
Although barely visible to the naked eye, Comet 46P/Wirtanen keeps some secrets so close that only radar can uncover them.
As the comet was making its close approach to Earth on Dec. 16, it was studied by a team of scientists led by Ellen Howell from the UA's Lunar and Planetary Laboratory. The team used Arecibo Observatory’s planetary radar, which is supported by NASA’s Near-Earth Object Observations program.
Studying the comet with radar provides a glimpse of its nucleus, the solid portion of the comet usually hidden inside a cloud of gas and dust that makes up the coma and tail. Radar images also allow for a precise determination of the comet’s orbit, allowing scientists to better predict how the gas and dust emission can alter the orbit.
Arecibo Observatory, a facility of the National Science Foundation operated by the University of Central Florida, is the only radar facility with the sensitivity to acquire images of Comet 46P/Wirtanen’s nucleus during its flyby. The Arecibo radar observations of Comet 46P/Wirtanen began Dec. 10 and continued through Dec. 18.
The radar images of the nucleus revealed an elongated, somewhat lumpy body that is much rougher than others that have been studied.
The new radar observations provided the first definitive measurements of Comet 46P/Wirtanen’s diameter, which is approximately 0.9 miles (1.4 km). Previous size estimates of the diameter were derived from the comet’s brightness, but radar provides a more direct measurement.
Howell’s team, which included scientists from the University of Central Florida and the Lunar and Planetary Institute, was also able to observe the comet’s large-grain coma, which is only detectable to radar. They discovered that it contains a significant population of particles, defined as those just under an inch (2 cm) and larger. This coma skirt, seen in some but not all comets observed with radar, is very extensive and asymmetric in this active comet.
“Radar observations give us images of the comet nucleus we can’t get any other way. This comet has a really rugged looking surface, which might be related to the large population of grains in its coma,” said Howell, a senior research scientist at the Lunar and Planetary Laboratory. “Every comet we study is unique. Radar images are important pieces of the puzzle.”
Howell’s team was also able to find some surprising differences between this and other comets of the same family.
Comet 46P/Wirtanen is one of a group of comets called Jupiter family comets, as their orbits are controlled by Jupiter’s gravity. Two other Jupiter family comets, 45P/Honda-Mrkos-Pajdusakova and 41P/Tuttle-Giacobini-Kresak, were also recently studied by radar in 2017.
Although the three comets have similar orbits and activity levels, the radar observations show that they are actually quite different, especially with regard to the large grains in the coma. Comet 46P/Wirtanen has a large population of large grains, 45P/Honda-Mrkos-Pajdusakova has a smaller population of these grains, but 41P/Tuttle-Giacobini-Kresak had none.
Comet 46P/Wirtanen made its closest approach of Earth at about 7.2 million miles (11.6 million km), or 30 Earth-Moon distances, at a speed of over 22 thousand miles per hour (10 km/sec) relative to Earth. Howell’s team collaborated with a larger UA research group, headed by Lunar and Planetary Laboratory professor Walter Harris, to observe the comet at many different wavelengths during the pass to characterize the gas and dust emanating from the nucleus that forms the coma.
Comets are remnants of the planet-forming process, and are part of a group of objects made of water, ice and rocky material that formed beyond Neptune. The study of these objects gives us an idea of how our solar system formed and evolved over time.
This comet is only the eighth imaged using radar in the last 30 years, as comets rarely come close enough to the Earth to get detailed images. In fact, although 46P/Wirtanen has an orbital period of about 5.44 years, it rarely passes this close to Earth. The next close approach by Comet 46P/Wirtanen will be in 2029, but during that approach the comet will be 10 times farther away from the Earth than it is now.
This flyby was the best known opportunity to image a comet with radar for the next 30 years.
UA-Led OSIRIS-REx Discovers Water on Asteroid Bennu
Observations made by the spacecraft during its approach of Bennu reveal that the asteroid interacted with water in its early history and is an excellent specimen for the mission, which is slated to return a sample of surface material to Earth in 2023.
By Erin Morton/OSIRIS-REx and Daniel Stolte/University Communications - December 10, 2018
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.
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, or OVIRS, and the OSIRIS-REx Thermal Emissions Spectrometer — 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, or 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, or 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, 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.
NASA's Goddard Space Flight Center in Greenbelt, Maryland, provides overall mission management, systems engineering and the safety and mission assurance for OSIRIS-REx. Lauretta is the principal investigator, and the UA also leads the science team and the mission's science observation planning and data processing. Lockheed Martin Space Systems in Denver built the spacecraft and is providing flight operations. Goddard and KinetX Aerospace are responsible for navigating the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA's New Frontiers Program. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the agency's New Frontiers Program for the Science Mission Directorate in Washington.
UA Undergrad Works to ID OSIRIS-REx Touchdown Site
Systems engineering and mathematics double major Keara Burke is helping NASA's OSIRIS-REx spacecraft find the perfect place to collect samples at its far-flung destination, the asteroid Bennu.
By Emily Dieckman, UA College of Engineering - December 10, 2018
University of Arizona senior Keara Burke spent her first summer as a college student studying abroad with the Honors College, visiting eight countries in two months.
"I've never felt more connected to what it means to be human," Burke said. "The entire trip was focused on human identity."
As an image processing intern on the UA-led OSIRIS-REx NASA mission, the systems engineering and mathematics double major has expanded her exploration of humanity well beyond Europe's borders – indeed beyond Earth's atmosphere.
The seven-year OSIRIS-REx project, which began with the launch of the spacecraft in September 2016, aims to collect about two ounces of regolith – dust, dirt and rock particles – from the surface of Bennu, a near-earth asteroid 150 million miles away. Scientists will use the sample to study the history of the solar system and of humankind, seeking answers to questions about our origins and what lies ahead.
Carbon-rich asteroids like Bennu may contain some of the earliest records of our solar system and are thought to have delivered to Earth building blocks of life – amino acids, organic molecules and water. Someday, the water, organic compounds and precious metals on these asteroids could fuel spacecraft to explore deep space.
OSIRIS-REx arrived at Bennu on Dec. 3 and begin orbiting the asteroid to map and survey its surface before the scheduled July 2020 regolith collection. A capsule containing the sample is expected to depart Bennu in March 2021 and return to Earth in September 2023.
Counting Rocks and Calculating Risks
As a child, Burke was more interested in the humanities and arts than science. But the Scottsdale-area native has always enjoyed looking at the stars in the clear Arizona sky and pointing out the planets to her friends. A high school chemistry teacher told her she had a bright future ahead if she applied herself.
"Maybe in engineering," he suggested. "You could even be an astronaut!"
Burke hasn't looked back. She homed in on systems engineering at the UA because of its solid foundation in optimization, statistics and planning – areas that come naturally to her – and picked up a second major in math along the way. She started interning with the OSIRIS-REx team during her sophomore year.
Burke's task is to help identify the safest place on Bennu, one that isn't too rocky, for the spacecraft to collect a sample with its Touch-And-Go Sample Acquisition Mechanism. The TAGSAM arm is only expected to touch Bennu's surface for five seconds, but doing so in an area with lots of rocks could compromise the mission.
The TAGSAM will collect rocks only up to about three-quarters of an inch (2 centimeters) in diameter. Rocks larger than 21 centimeters can block the entire collection head, Burke explained, and rocks taller than 5 centimeters can cause the TAGSAM to tilt, affecting how much the chamber can collect.
"We have to be able to track all these hazards," said Burke, whose job involves counting the number of rocks in the images of Bennu that OSIRIS-REx sends back to Earth every day.
Using a combination of software and statistical analysis to determine the quantity, relative size and distribution of rocks on the asteroid, the image processing team hopes to identify the best possible sample site for OSIRIS-REx.
"The first part of our imaging campaign once we arrive at the asteroid will involve establishing the global distribution of rocks on the asteroid," Burke said. "Then we'll zoom in on the areas that seem safe, image those and pick a site that seems the safest for the TAGSAM to make contact."
Exceeding Expectations
Burke started her internship counting rocks in images of a simulated asteroid surface with a particle distribution similar to what the team expects to see on Bennu, and she offered to analyze the data when she finished. It was a big task for an undergraduate, but the mission's lead image processing scientist, Daniella DellaGiustina, agreed to let her try. Within weeks, Burke had installed a matrix laboratory, or MATLAB, library onto the mission's computers, giving the team better data analysis capabilities than ever before. The American Geophysical Union selected Burke to present at its December meeting, which is the largest Earth and space science conference in the world.
"It is rare to work with an undergraduate who is brilliant enough to lead Ph.D.-level research," DellaGiustina said. "I am continually impressed with her adeptness in both technical and professional matters."
Burke, the vice president of the Engineering Student Council, an Engineering Ambassador and a member of several honors societies, likes going down what she calls different "rabbit holes" of information. In her work on OSIRIS-REx, she's learned about everything from photogrammetry to 3D modeling to presenting research. The information she's gathered will come in handy in the coming months as she helps lead the analysis of the distribution of rocks across Bennu's surface.
"It's really nice to work in such a good, smart group of people," Burke said. "Being included in the conversations is kind of unreal. It took a while for me to really be able to believe, 'Wow, I'm on a NASA mission.'"
Unknown Treasure Trove of Planets Found Hiding in Dust
The first unbiased survey of protoplanetary disks surrounding young stars in the Taurus star-forming region turned up a higher-than-expected number of disks with features suggesting nascent planets.
By Daniel Stolte, University Communications - December 6, 2018
"Super-Earths" and Neptune-sized planets could be forming around young stars in much greater numbers than scientists thought, new research by an international team of astronomers suggests.
Observing a sampling of young stars in a star-forming region in the constellation Taurus, researchers found many of them to be surrounded by structures that can best be explained as traces created by invisible, young planets in the making. The research, published in the Astrophysical Journal, helps scientists better understand how our own solar system came to be.
Some 4.6 billion years ago, our solar system was a roiling, billowing swirl of gas and dust surrounding our newborn sun. At the early stages, this so-called protoplanetary disk had no discernable features, but soon, parts of it began to coalesce into clumps of matter – the future planets. As they picked up new material along their trip around the sun, they grew and started to plow patterns of gaps and rings into the disk from which they formed. Over time, the dusty disk gave way to the relatively orderly arrangement we know today, consisting of planets, moons, asteroids and the occasional comet.
Scientists base this scenario of how our solar system came to be on observations of protoplanetary disks around other stars that are young enough to currently be in the process of birthing planets. Using the Atacama Large Millimeter Array, or ALMA, comprising 45 radio antennas in Chile's Atacama Desert, the team performed a survey of young stars in the Taurus star-forming region, a vast cloud of gas and dust located a modest 450 light-years from Earth. When the researchers imaged 32 stars surrounded by protoplanetary disks, they found that 12 of them – 40 percent – have rings and gaps, structures that according to the team's measurements and calculations can be best explained by the presence of nascent planets.
"This is fascinating because it is the first time that exoplanet statistics, which suggest that super-Earths and Neptunes are the most common type of planets, coincide with observations of protoplanetary disks," said the paper's lead author, Feng Long, a doctoral student at the Kavli Institute for Astronomy and Astrophysics at Peking University in Bejing, China.
While some protoplanetary disks appear as uniform, pancake-like objects lacking any features or patterns, concentric bright rings separated by gaps have been observed, but since previous surveys have focused on the brightest of these objects because they are easier to find, it was unclear how common disks with ring and gap structures really are in the universe. This study presents the results of the first unbiased survey in that the target disks were selected independently of their brightness – in other words, the researchers did not know whether any of their targets had ring structures when they selected them for the survey.
"Most previous observations had been targeted to detect the presence of very massive planets, which we know are rare, that had carved out large inner holes or gaps in bright disks," said the paper's second author Paola Pinilla, a NASA Hubble Fellow at the University of Arizona's Steward Observatory. "While massive planets had been inferred in some of these bright disks, little had been known about the fainter disks."
The team, which also includes Nathan Hendler and Ilaria Pascucci at the UA's Lunar and Planetary Laboratory, measured the properties of rings and gaps observed with ALMA and analyzed the data to evaluate possible mechanisms that could cause the observed rings and gaps. While these structures may be carved by planets, previous research has suggested that they may also be created by other effects. In one commonly suggested scenario, so-called ice lines caused by changes in the chemistry of the dust particles across the disc in response to the distance to the host star and its magnetic field create pressure variations across the disk. These effects can create variations in the disk, manifesting as rings and gaps.
The researchers performed analyses to test these alternative explanations and could not establish any correlations between stellar properties and the patterns of gaps and rings they observed.
"We can therefore rule out the commonly proposed idea of ice lines causing the rings and gaps," Pinilla said. "Our findings leave nascent planets as the most likely cause of the patterns we observed, although some other processes may also be at work."
Since detecting the individual planets directly is impossible because of the overwhelming brightness of the host star, the team performed calculations to get an idea of the kinds of planets that might be forming in the Taurus star-forming region. According to the findings, Neptune-sized gas planets or so-called super-Earths – terrestrial planets of up to 20 Earth masses – should be the most common. Only two of the observed disks could potentially harbor behemoths rivaling Jupiter, the largest planet in the solar system.
"Since most of the current exoplanet surveys can't penetrate the thick dust of protoplanetary disks, all exoplanets, with one exception, have been detected in more evolved systems where a disk is no longer present," Pinilla said.
Going forward, the research group plans to move ALMA's antennas farther apart, which should increase the array's resolution to around five astronomical units (one AU equals the average distance between the Earth and the sun), and to make the antennas sensitive to other frequencies that are sensitive to other types of dust.
"Our results are an exciting step in understanding this key phase of planet formation," Long said, "and by making these adjustments, we are hoping to better understand the origins of the rings and gaps.”
This work was made possible through an international collaboration, including astronomers at UA's Steward Observatory and LPL. For a complete list of authors and funding information, please see the paper, "Gaps and Rings in an ALMA Survey of Disks in the Taurus Star-forming Region." A preprint of the article is available at https://arxiv.org/abs/1810.06044. Funding for this project was provided by Peking University, National Science Foundation of China, the Hubble Fellowship Program, the National Science Foundation, and the Earths in Other Solar Systems Nexus for Exoplanetary System Science program.
OSIRIS-REx Arrives at Asteroid Bennu
Since its launch on Sept. 8, 2016, OSIRIS-REx has spent two years catching up with asteroid Bennu on its orbit around the sun. The spacecraft's arrival at Bennu on Dec. 3 marks a major milestone, with the mission transitioning from flying toward the asteroid to orbiting around it.
By Daniel Stolte, University Communications - December 4, 2018
NASA’s OSIRIS-REx spacecraft arrived at its destination, asteroid Bennu, on Dec. 3. Led by the University of Arizona, the OSIRIS-REx mission is the first NASA mission to visit a near-Earth asteroid, survey the surface, collect a sample and deliver it safely back to Earth. The composition of the asteroid, Bennu, could shed more light on the origins of the solar system.
"Initial data from the approach phase show this object to have exceptional scientific value. We can't wait to get to work studying and characterizing Bennu's rough and rugged surface to find out where the right spot is to collect the sample and bring it back to Earth," said Dante Lauretta, the mission's principal investigator. "Today has been very exciting, but the true nail-biting moment will be the sample collection. The best times are ahead of us, so stay tuned. The exploration of Bennu has just begun, and we have a lifetime of adventure ahead of us."
OSIRIS-REx will spend the next month performing flybys of Bennu's north pole, equator and south pole, at distances ranging between 11.8 and 4.4 miles from the asteroid. These maneuvers will allow for the first direct measurement of Bennu's mass, as well as close-up observations of the surface. These trajectories will also provide the mission's navigation team with experience navigating near the asteroid.
The spacecraft will then spend the next 18 months extensively surveying the asteroid before the mission team identifies two possible sample sites. The spacecraft will study the asteroid with various instruments, providing mission scientists with a wealth of data about the asteroid's exact shape, chemical composition and physical properties influencing how it is affected by the sun and the surrounding space.
Sample collection is scheduled for July 2020, when OSIRIS-REx will ultimately touch the surface for five seconds to gather a sample of the asteroid. The spacecraft will head back toward Earth before ejecting the Sample Return Capsule for landing in the Utah desert on September 24, 2023.
"Working on this mission has been probably the most life-changing event that has happened to me so far," said UA senior Keara Burke, a systems engineering and mathematics double major who is helping the mission team find the perfect place to collect samples. "It's incredible to be able go to work every day and know that what I'm contributing to the conversation matters. Being able to be part of this type of mission – I don't think I would have gotten this opportunity anywhere else."
The UA leads the OSIRIS-REx mission on behalf of NASA. All science operations of the mission are housed at and led by UA's Lunar and Planetary Laboratory, where all science data gathered by the spacecraft are received and analyzed. More than 150 students, both at undergraduate and graduate level, have been working on the mission so far.
"It is really exciting to arrive at the asteroid that our team has been tracking now for a couple of years, and to see one of our students being so intimately involved in this project," UA President Robert C. Robbins said of Burke. "I think this highlights the fact that we are the place that not only does this kind of research, but also educates the next generations of leaders in this field."
OSIRIS-REx stands for Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer. The economic impact to Arizona of the OSIRIS-REx mission is $230.5 million. Of that, $172.3 million comes to Tucson.
We're at Bennu! What's Next?
The LPL-led OSIRIS-REx mission kicks into high gear while the spacecraft is on its final approach, closing in on asteroid Bennu and scheduled for arrival on Dec. 3. UA mission experts explain what comes next.
By Daniel Stolte, University Communications - November 29, 2018
Since it launched on Sept. 8, 2016, the spacecraft of the University of Arizona-led OSIRIS-REx asteroid sample return mission has been catching up with its destination, asteroid Bennu, on its trip around the sun. On Dec. 3, the spacecraft is scheduled for arrival. UANews asked mission experts about what lies ahead for the robotic explorer and its human companions here on Earth.
Once OSIRIS-REx arrives at Bennu, why will have to stay in orbit for two years before going for the sampling?
Dante Lauretta, OSIRIS-REx Principal Investigator: The OSIRIS-REx spacecraft will enter orbit around Bennu by moving at a very slow velocity, relative to the asteroid, on the order of 4 inches (10 centimeters) per second. To accomplish this feat, we must characterize the mass, shape and rotation state of the asteroid. Fortunately, the equations for orbital stability hold even for a very low mass object like Bennu. The challenge lies in the fact that other forces acting on the spacecraft, such as solar radiation pressure, spacecraft outgassing and thermal radiation, are of the same order of magnitude as Bennu’s gravity. The team must perform regular optical navigation-based orbit determination. This process is not required to keep us in orbit. Instead, it is needed for us to understand where in the orbit we are. Although small, these forces can move the spacecraft by as much as 180 degrees along its track within a few short days. If we lost track of the spacecraft position in orbit, we would not know where to point the science instruments to collect our data.
Christian Drouet d'Aubigny, OSIRIS-REx Camera Suite Deputy Instrument Scientist: We need to know exactly where we are with respect to Bennu. To an astronaut, it would be obvious: "The asteroid is over there and all I have to do is point the camera." But with a robot, it's always a challenge. The spacecraft knows exactly where it is with respect to stars, because it knows the constellations it sees with great precision, but it doesn't know exactly where it is with respect to Bennu. When we plan our operations, weeks ahead of time, we have to take into account that when we execute the observation, the spacecraft position with respect to Bennu won’t be known exactly. The spacecraft’s own knowledge of where it is located is based on observations that are at least a day old. It knows where it should be based on where it was yesterday.
Bashar Rizk, OSIRIS-REx Camera Suite Instrument Scientist: We don't have all the information we need to successfully and safely take a sample from the asteroid at this time. We have given ourselves enough time and margin to gather all the information we need to be able to analyze and chew on that information so it can successfully inform the next step in the process.
How does the spacecraft stay in orbit around Bennu?
Rizk: Driving a spacecraft around an object like Bennu is a fine art, and we're learning it as we go along. Unlike a spacecraft that orbits a planet such as Mars, the relative velocities are not high – we are crawling along – but because the gravitational forces are so weak, other effects begin to matter. Our spacecraft is constantly exposed to solar pressure and thermal asymmetry: whichever side happens to be facing the sun gets warmer and emits its own thermal radiation. That radiation carries momentum – a very slight momentum, but given enough time, it is going to make itself felt. In addition, you have the effects of the micro-thrusting maneuvers that help us move around. So far, every aspect about this object has been very successfully predicted, so we have high hopes, but there is no denying that there are challenges.
What "eyes" does the spacecraft use to see and study the asteroid?
d'Aubigny: The spacecraft has three science cameras – all were built here at the University of Arizona – PolyCam, MapCam and SamCam, plus a suite of wide-angle cameras made by Malin Space Science Systems for Lockheed Martin that are used for navigation. When the asteroid still was far away, we used PolyCam to acquire the first images from 1.2 million miles (2 million kilometers) away because it is the most sensitive of all the OSIRIS-REx cameras. On Nov. 15, when the spacecraft was only 75 miles (120 km) from Bennu, we switched to MapCam. We are progressively switching from higher magnification and narrower field of view to lower magnification and a wider field of view. It's similar to what you would do with an optical zoom lens, but done with different cameras. MapCam and PolyCam will be used to study the asteroid from up close. MapCam is going to map Bennu's surface. As we go past the asteroid and see different parts, we will point the spacecraft in various directions, take mosaic images and stitch them together. We'll go through different phases, getting progressively closer to Bennu, starting from 12.4 miles (20 km) and getting into orbit as close as .9 mile (1.5 km) from the asteroid. The closest approach will be is when we do our reconnaissance passes at 656 feet (200 meters) above the surface. The images with the highest resolution will be taken by PolyCam, which will serve as our high-power telephoto lens. At closest approach, the field of view comes down to a 10-foot-by-10-foot (3 m) square, or approximately the size of a bedroom, and with enough resolving power we could see a pea on a table. Using MapCam, which has not quite the high resolution and magnification of PolyCam, we're going to map the whole surface down to a scale of one-quarter of a meter (.82 feet), about the size of a soccer ball.
How will you prepare for the sampling?
d'Aubigny: Based on the images and combined information from all the instruments, such as LIDAR and the spectrometers, we will narrow down the search for sites that are interesting from a science standpoint, have the surface with material of the size we need for sampling and are free of hazards. We have to focus on up to five sites, we will image those with really high resolution with PolyCam from orbit, but also as we narrow down that list, at some point we will have just two – a primary and a secondary samples site – and that is where we will do the close reconnaissance passes.
Dani DellaGiustina, Lead Image Processing Scientist: The first thing we need to do before we can start mapping the surface and finding anything that could pose a hazard to the sampling mechanism is to relate the images taken by our cameras to the shape model of the asteroid. To do this, we take the images and map them into something that is similar to Google Earth, a special framework on which we can co-locate the features. We take two approaches to mapping out hazards: one is old-fashioned counting. Keara Burke, a UA undergraduate student who has taken the initiative to develop software for this project, is leading that work. Her team will count boulders on Bennu's surface. The other is using a crowdsourcing effort: we want to triage the areas that look really smooth and map them out. For this, we are partnering with CosmoQuest, a citizen science program. Early next year, we're going to launch "Bennu Mappers," which will enable citizen scientists to help OSIRIS-REx map the locations and the sizes of all the boulders on Bennu. We define any boulder that is bigger than 8.3 inches (21 cm) as a hazard, because that is the width of the inner chamber of our sampling mechanism and it could become clogged. When we've gotten to the point where we've mapped the surface to where we have narrowed down two potential sampling sites, we will look at cobbles and pebbles while searching for anything as small as .8 inch (2 cm). Particles that size or smaller are easily ingested by our sampling mechanism.
UA Ranked in Top 25 for Research Funding
The UA's strengths in physical sciences and NASA funding make it one of the top research universities in the country, according to the Higher Education Research and Development survey recently released by the NSF.
By Lucio Guerrero, UA Research, Discovery & Innovation - November 21, 2018
With $622 million in research activity in fiscal year 2017, the University of Arizona ranked as one of the top 25 largest research universities among all public institutions, according to data released Tuesday by the National Science Foundation.
The NSF's Higher Education Research and Development survey ranks more than 900 colleges and universities based on their research and development expenditures. It is viewed as the primary source of information on R&D expenditures at U.S. colleges and universities.
In the latest survey, the UA ranks 23rd among all public universities – the highest among Arizona institutions – and 38th among all U.S. universities, both public and private.
The UA's $622 million in R&D expenditures in fiscal year 2017 surpassed the previous year's total by nearly $20 million and put the UA among the top 5 percent of all universities nationwide.
"University of Arizona researchers have had great success over the past year, both in their efforts to attract funding for their work and in the impact that they have in Arizona and globally," said UA President Robert C. Robbins. "UA research is the foundation of our transformational student experience, and I am proud of this result, particularly our standing among Hispanic-Serving Institutions. This ranking is great recognition for the quality and promise of UA research, and I am also eager for the continued strides we will make towards our goals."
The HERD survey also found that the UA is the second largest research university nationwide among schools with high Hispanic enrollment. The university earned the designation of Hispanic-Serving Institution from the U.S. Department of Education for its success in the enrollment of Hispanic students and in providing educational opportunities to them.
The survey also showed that the UA was No. 5 in NASA funding among all universities (up from No. 8 in 2016) and No. 6 in physical sciences R&D expenditures nationwide. UA remained No. 1 among all universities in astronomy and astrophysics R&D.
"UA research is always on the move. Our researchers continue to drive us forward through innovative solutions, meaningful collaborations and impactful discoveries," said Kimberly Ogden, interim vice president for research at the UA. "The quality of our research is recognized around the world and it's because of the dedication and quality of our staff and faculty."
Some of the UA research that made headlines and had significant impact in fiscal year 2017 included:
- The UA Cancer Center was recognized for its multidisciplinary cancer research and research-driven clinical care through a highly competitive grant award from the National Cancer Institute. The NCI renewed the center's status as a Comprehensive Cancer Center and awarded a five-year, $17.6 million Cancer Center Support Grant, based on the strength, depth and breadth of basic laboratory, clinical, prevention, control and population-based research.
- NASA selected to fund the UA-led GUSTO mission, a $40 million endeavor is to send a balloon to near-space carrying a telescope that will study the interstellar medium – the gas and dust between the stars, from which all stars and planets originate.
- The UA is part of a multicampus program awarded a five-year U.S. Department of Transportation grant expected to be worth up to $15.6 million to help transform research, education and outreach related to the nation's pressing transportation issues.
Ceres Takes Life an Ice Volcano at a Time
By Emily Walla, NASA
By Emily Walla, NASA Intern/University Communications - September 14, 2018
Every year throughout its 4.5-billion-year life, ice volcanoes on the dwarf planet Ceres generate enough material on average to fill a movie theater, according to a new study led by the University of Arizona.
The study, led by UA planetary scientist Michael Sori, marks the first time a rate of cryovolcanic activity has been calculated from observations, and its findings help solve a mystery about Ceres’s missing mountains.
Discovered 2015 by NASA’s Dawn spacecraft, the 3-mile-tall ice volcano Ahuna Mons rises in solitude over the surface of Ceres. Still geologically young, the mountain is at most 200 million years old, meaning that – though it is no longer erupting – it was active in the recent past.
Ahuna Mons' youth and loneliness presented a mystery. It seemed unlikely Ceres had lain dormant for eons and suddenly erupted in one place. But if other ice volcanoes had risen out of the Cerean surface in ages past, where are those volcanoes now? Why is Ahuna Mons so alone?
Sori and his co-authors, including fellow UA scientist Ali Bramson and professor of planetary science Shane Byrne, sought to answer these questions.
In a paper published last year, they theorized that evidence of older volcanoes on the dwarf planet had been erased over time by a natural process called "viscous relaxation." Viscous materials, like honey or putty, can begin as a thick blob, but the weight of the blob causes it to ooze into a flatter shape over time.
"Rocks don’t do that under normal temperatures and timescales, but ice does," Sori said.
Because Ceres is made of both rock and ice, Sori pursued the theory that formations on the dwarf planet flow and move under their own weight, similar to how glaciers move on Earth. The formations' composition and temperature would affect how quickly they relax into the surrounding landscape. The more ice in a formation, the faster it flows; the lower the temperature, the slower it flows.
Though Ceres never grows warmer than -30 degrees Fahrenheit, the temperature varies across its surface.
"Ceres’ poles are cold enough that if you start with a mountain of ice, it doesn’t relax," Sori said. "But the equator is warm enough that a mountain of ice might relax over geological timescales."
Computer simulations showed that Sori's theory was viable. Model cryovolcanoes at the poles of Ceres remained frozen in place for eternity. At other latitudes on the dwarf planet, model volcanoes began life tall and steep, but grew shorter, wider and more rounded as time passed.
To prove the computer simulations had played out in reality, Sori scoured topographic observations from the Dawn spacecraft, which has been orbiting Ceres since 2015, to find landforms that matched the models.
Across the 1 million square miles of Cerean surface, Sori and his team found 22 mountains including Ahuna Mons that looked exactly like the simulation’s predictions.
"The really exciting part that made us think this might be real is that we found only one mountain at the pole," Sori said.
Though it is old and battered by impacts, the polar mountain, dubbed Yamor Mons, has the same overall shape as Ahuna Mons. It is five times wider than it is tall, giving it an aspect ratio of 0.2. Mountains found elsewhere on Ceres have lower aspect ratios, just as the models predicted: they are much wider than they are tall.
By matching the real mountains to the model mountains, Sori was able to determine the age of many of them. The volume of the volcanoes was estimated by studying their topography, and by combining age and volume, Sori’s team was able to calculate the rate at which cryovolcanoes form on Ceres.
"We found that one volcano forms every 50 million years," Sori said.
This amounts to an average of more than 13,000 cubic yards of cryovolcanic material each year – enough to fill a movie theater or four Olympic-sized swimming pools. This is much less volcanic activity than what is seen on Earth, where rocky volcanoes generate more than 1 billion cubic yards of material in a year.
In addition to being less productive, volcanic eruptions on Ceres are tamer than those on Earth. Instead of explosive eruptions, cryovolcanoes create the icy equivalent of a lava dome: the cryomagma – a salty mix of rocks, ice and other volatiles such as ammonia – oozes out of the volcano and freezes on the surface. Most of the once-mighty cryovolcanoes on Ceres likely formed this way before they relaxed away.
The causes of cryovolcanic eruptions on Ceres are still a mystery, but future research might yield answers, as signs of ice volcanoes have been spotted on other bodies in the solar system as probes have flown by. Ceres is the first cryovolcanic body a mission has orbited, but Europa and Enceladus, moons of Jupiter and Saturn, are likely candidates for cryovolcanism, as are Pluto and its moon Charon. Europa is of special interest because it is believed to have liquid oceans trapped below a thick icy shell, which some scientists believe to be dotted with ice volcanoes.
"There might be similarities between Europa and Ceres, but we need to send the next mission there before we can say for sure," Sori said.
As scientists explore other potentially cryovolcanic bodies in the solar system, it will be fun, Sori said, to see how Ceres compares.
The paper, "Cryovolcanic rates on Ceres revealed by topography," was recently published in Nature Astronomy. Funding was provided by the National Aeronautics and Space Administration (NASA) Dawn Guest Investigator Program.