So You Want to Analyze Asteroid Dirt
By Emily Litvack -
By Emily Litvack - May 18, 2017
In the year 2023, priceless property of the American people will land somewhere in the Utah desert. And when it does, a team of engineers and scientists will be waiting on the ground. Thousands will watch with eyes glued to smart phones and televisions. Headlines around the world will tell of its journey.
The priceless property is 2 to 70 ounces of asteroid dirt.
This 4.5-billion-year-old dirt, formally known as “regolith,” will look like a small pile of dusty rubble, gleaned in the five-second moment during which NASA’s OSIRIS-REx spacecraft vacuumed the surface of a carbon-rich, near-Earth asteroid called Bennu.
Landing, encapsulated, at the Utah Test and Training Range on the planet Earth will begin a new phase in its existence in the universe: analysis. After being transported to the Johnson Space Center in Houston, the dirt will be removed from its capsule, and then allocated to scientists for study.
OSIRIS-REx is the United States’ first mission to return an asteroid sample to Earth, but for scientists like Tom Zega, return to Earth is just the beginning. Zega is a sample scientist at the University of Arizona. As a collaborator on the OSIRIS-REx mission, led by NASA and the UA, he will be one of the first scientists to analyze regolith from Bennu.
Why Return Samples?
One of the main goals of the OSIRIS-REx mission, he says, is understanding the earliest history of our solar system, and the origins of life. Regolith from an asteroid might be our best shot at this.
“Sample return is great because otherwise you’re at the mercy of what falls from the sky,” says Zega. Simply, you get what you get. The regolith from Bennu will be untouched. Uncontaminated by our atmosphere. Pristine. “Sample return is a treasure trove of information.”
“You’re getting samples that are older than Earth. I can literally hold in my hand a piece of the origins of our solar system that predated Earth, predated human beings, predated everything we know,” says Zega. “These are atoms that assembled four and a half billion years ago and became the building blocks of our planet.”
The only question left is what to do with such a scientifically valuable pile of dirt.
Building a Lab Fit for Analysis
“Analysis” can mean many things. In the case of using asteroid regolith to understand the origins of the solar system, analysis means two things, both of which require large equipment in a stable environment. The first: high-resolution imaging. The second: measuring chemistry. Respectively, answering the questions “What does it look like?” and “What is it made of?”
“We’re sort of like forensic scientists,” says Zega. “Nature grew these materials, and we’re analyzing it at a fundamental level to figure out under what conditions.”
Zega does this in the 5,000-square-foot basement of the Kuiper Space Sciences building, constructed at the UA in 1964 with funds from NASA. The basement was once a mirror lab for telescopes and a publications vault. Telescopes got bigger, and so did the mirror lab. It now lives under UA’s Arizona Stadium. Publications went online. Now, the UA’s collection of high-tech electron microscopes—to be used for studying the returned asteroid dirt—live here.
Sensitive to stimulus, electron microscopes need a place with minimal vibrations, minimal electromagnetic interference, and good acoustics. As it turns out, explains Zega as he stands outside the two frosted doors of the lab, basements make good spots for these kinds of microscopes. As of today, the lab is “ready to hit the ground running” when the asteroid sample from OSIRIS-REx shows up.
In fact, the lab is in the process of studying a sample from Hayabusa 1, an asteroid sample return mission by JAXA, the Japanese equivalent of NASA. Like OSIRIS-REx, Hayabusa 2 is now cruising towards its target, the asteroid Ryugu.
He opens the doors, revealing a long, clean, fluorescent-lit corridor.
Analyzing the Sample
At the end of the corridor, in a room on the left, is where the asteroid sample’s time in the lab will truly begin. After it’s mounted on a glass slide and polished smooth, Zega will place the sample in an electron microprobe.
“The microprobe gives us the most context, and a lay of the land,” says Zega. It allows him to photograph the entire sample in high-resolution, and map out its chemistry, element by element. Those elements, like iron and nickel and magnesium, show up as colors on a computer screen.
“You want to sit down and really process that data. You might want to play around with the maps and overlay them onto the high-res images that you also created before you decide what the next step is. That can take some time,” says Zega. “You really want to take your time here before going onto a more detailed level of analysis.”
Then, all the way at the other end of the corridor, near the doorway, there are two scanning electron microscopes. Like the microprobe, they too image and chemically map the sample, but at an even more detailed level. Here, Zega can look at the dirt in micrometers and nanometers—a billionth of a meter. A single sheet of paper is about 100,000 nanometers thick.
In the room next door, a focused-ion-beam scanning-electron microscope can look at the sample in even greater detail. It can also drill a hole in a piece of dust from the asteroid by shooting gallium ions at it, like teeny-tiny bullets.
“Every atom has something to tell us,” says Zega, walking toward the final destination for the asteroid sample: the transmission electron microscope, or TEM. It’s a towering box of off-white and blue, about 12-feet-tall. There’s an innate humor in its largeness, because a TEM is the only machine in the world that can see something as tiny as an individual atom. The TEM, purchased from Hitachi High Technologies in 2016, was shipped by boat from Japan months earlier. A team of engineers from the company’s headquarters outside of Tokyo have been here since November, installing and calibrating the microscope. They are expected to head home in June.
“Looking at microstructures is useful for figuring out origins,” explains Zega. Which atoms of an element are next to, or layered on top of, which other atoms is critically important when you want to figure out how something formed.
Looking to the Stars for Answers
In the best case scenario, analyzing the asteroid dirt means “we rewrite the textbooks on our understanding of the origins of our solar system,” says Zega. “I think that’s the neatest thing about a mission like this. It can be full of surprises.”
“Scientist or not, we all look to the stars and ask ‘How?’ and ‘Why?’ We wonder how it all came to be,” says Zega. “The work that we do here at the University of Arizona contributes to answering those questions.”
HiRISE Brings the Red Planet's Beauty to Your Coffee Table
By Daniel Stolte
By Daniel Stolte, University Communications - May 15, 2017
A gorgeous, sumptuous tome chock-full of stunning images taken by the most powerful camera ever sent to another planet now brings Mars to armchair explorers on Earth.
Weighing in at nearly eight pounds, "Mars: The Pristine Beauty of the Red Planet" features close to 200 carefully selected photographs taken by the University of Arizona-led HiRISE camera, which has been orbiting Mars on NASA's Mars Reconnaissance Orbiter since 2006.
Arranged into chapters that guide the reader/viewer from familiar features such as sand dunes to more alien landscapes one cannot glimpse on our own planet, the photos and accompanying captions amount to 425 pages compiled by UA HiRISE scientists. Published by UA Press, the book is available at bookstores and online.
In a sense, the volume represents a "best of" from the treasure trove of high-resolution images snapped by the HiRISE camera for more than a decade. Orbiting Mars anywhere from 125 to 186 miles above the surface, the HiRISE camera has revealed a Red Planet that is anything but dead — at least in geological and climatic terms.
"Throughout the lifetime of this mission, I had been saving favorite images that I thought were interesting," says Alfred McEwen, principal investigator of the HiRISE project and one of the book's authors. "We encouraged our roughly 50 team members who work with the images coming down from the spacecraft to submit their favorites to the project."
Ari Espinoza, outreach coordinator for HiRISE and a co-author of the book, recalls how the project started.
"Through our 'Beautiful Mars' project, volunteers around the world had already translated some of the image captions into 24 other languages," he says, "and with that in mind, I wrote the book proposal and pitched it to UA Press. Fortunately for us, the editorial board was excited about the project."
The result is a visual journey across the surface of Mars. With artistic glimpses at actively eroding slopes, impact craters, strange polar landscapes, avalanches and even spectacular pictures capturing the Phoenix Lander and the Curiosity Rover descending on their parachutes, the reader gets to see what researchers are seeing.
"The really difficult part was to cull the photo material down to a couple of hundred," McEwen says.
Co-author Candice Hansen-Koharcheck, senior scientist at the Planetary Science Institute and deputy principal investigator of HiRISE, adds: "In the end, there were many hard decisions to make when we saw how many images hadn't made the cut. There were so many we looked at and realized, 'No, this has to go back in.'"
In the spirit of "the people's camera at Mars," all images beamed back to Earth are published on the HiRISE website, but for the book, the authors optimized each image to bring out the best possible detail or highlight the most interesting features. Because the captions had been written by members of the entire team, McEwen and Hansen-Koharcheck rewrote each of them to ensure they read with one voice.
"Even though we had a big head start with a huge pool of pictures and their initial captions, putting this together for a dedicated book format still required a lot of work," Hansen-Koharcheck says, explaining that the material is presented in a way that resembles what geologists call stratigraphy: an assembly of rock layers deposited over time.
"Except that in the book, we go from top to bottom, or youngest to oldest, which is the opposite of how a geologist would normally do it," Hansen-Koharcheck says. "We realized that because our images have so much detail, you almost have to train people how to look at them."
And so, the visual journey of the Red Planet begins "with the features that are the most obvious and ubiquitous when you first look at the Martian surface — the sand dunes," Hansen-Koharcheck explains. "Then, we explore more recent features like fresh impact craters, all the way to the bedrock at the bottom of ancient craters. But you can't start there, it's just too foreign."
McEwen says the book covers just a sampling, a small selection of Mars' surface, by necessity.
"Mars has so many different landforms, so much diversity, that we can include just a sampling in this publication," he says. "Everything you see here is at HiRISE scale, so if you zoomed out, you could see large, iconic features like Olympus Mons, for example, but here all we see is a small detail of the volcano."
Since HiRISE began collecting data in 2006, the camera has acquired more than 50,000 images, each one a giant, gigapixel-size file. To date, HiRISE has covered just 2.83 percent of the Martian surface, and that is by design, according to McEwen.
"The goal of HiRISE was never to make an exhaustive survey of Mars," he says. "We are looking at such high resolution that this simply would not be possible. HiRISE was designed to focus on identifying the best landing sites and the most scientifically interesting locations."
Instead of systematically mapping Mars, the HiRISE scientists put time and effort on very specific targets.
"We study the Red Planet at a geologist's scale," McEwen says, "and we follow up with previously imaged sites, too. We are learning about the forces that shape Mars as we go, we are documenting what changes are happening today, and we try to gather clues as to what ancient Mars looked like by studying bedrock composition and structures."
Each day, the HiRISE camera makes 13 trips around Mars, and it is scheduled to continue to do so for the foreseeable future.
"Every day at the HiRISE operations center here at the UA, we send the commands to the spacecraft, and we process the data and interpret the images," McEwen says.
Alumni Achievement Award for Dante Lauretta
By UA Alumni
By UA Alumni Association - May 9, 2017
Dante Lauretta, leader of the University of Arizona's biggest space mission, will receive the institution's Alumni Achievement Award.
Lauretta, a UA professor of planetary science and cosmochemistry and principal investigator of the OSIRIS-REx asteroid sample return mission, has reached the pinnacle of his field, and through his work the UA will remain at the forefront of space exploration for years to come.
Lauretta will receive the award during the University's Commencement ceremony on May 12. He also will be honored as the College of Humanities Alumnus of the Year during an event to be held Oct. 27.
The Alumni Achievement Award is the highest honor the UA Alumni Association can bestow on graduates of the University. It is given to an alumnus or alumna who has attained prominence in his or her field of endeavor and demonstrated outstanding service to the UA.
"I am honored to receive the UA Alumni Achievement Award," Lauretta said. "The University of Arizona has been an essential part of my career from my undergraduate days through my faculty appointment. I am proud to have studied here and to now be contributing to the UA's important education mission."
Lauretta is an expert in the analysis of extraterrestrial materials such as lunar samples, meteorites and comet particles. His work contributes to our understanding of the chemistry of the early solar system and the origin of complex molecules that may have led to life on Earth.
Lauretta is credited with more than 70 peer-reviewed publications and led or participated in more than 20 NASA grants and missions — all while teaching undergraduate and graduate students, giving scholarly presentations, participating in conferences, and serving on departmental, University and extramural committees.
The list of awards and honors Lauretta has received is long and varied. He has an asteroid named in his honor; he was named a Kavli Fellow of the National Academy of Sciences in 2008 and Innovator of the Year by the Arizona governor in 2011; and Good Housekeeping magazine named his Xtronaut game the Best Family Board Game of 2016.
On Sept. 8, 2016, Lauretta earned a spot in history for himself and the UA when the OSIRIS-REx spacecraft successfully launched on a seven-year journey to rendezvous with the asteroid Bennu and return a sample of its material.
As important as the OSIRIS-REx mission is to furthering our understanding of the early solar system, under Lauretta's leadership it also aims to further public engagement in science. The mission's website, asteroidmission.org, features entertaining and engaging videos about planetary science, and mission staff appear as guest speakers at local conventions and in classrooms.
Lauretta also has hosted a regular OSIRIS-REx Science Club at the Tucson Boys and Girls Club.
In 1993, Lauretta earned a Bachelor of Arts from the UA College of Humanities Department of East Asian Studies with an emphasis in Japanese, and also a Bachelor of Science in mathematics and physics from the UA College of Science. He went on to earn a Ph.D. in earth and planetary sciences from Washington University in St. Louis in 1997. He returned to the UA in 2001 to join the faculty of the Lunar and Planetary Laboratory.
Surveying the Scenery 90 Million Miles From Earth
By Daniel Stolte/UA
By Daniel Stolte/UA News and Erin Morton/LPL - February 9, 2017
A NASA spacecraft has begun its search for an enigmatic class of near-Earth objects known as Earth-Trojan asteroids. OSIRIS-REx, currently on a two-year outbound journey to the asteroid Bennu, will spend almost two weeks searching for evidence of these small bodies.
Trojan asteroids are trapped in stable gravity wells, called Lagrange points, which precede or follow a planet. OSIRIS-REx is currently traveling through Earth's fourth Lagrange point, which is located 60 degrees ahead in Earth's orbit around the sun, about 90 million miles (150 million kilometers) from our planet. The mission team will use this opportunity to take multiple images of the area with the spacecraft's MapCam camera in the hope of identifying Earth-Trojan asteroids in the region.
MapCam is one of three cameras built at the University of Arizona's Lunar and Planetary Laboratory that will guide the OSIRIS-REx spacecraft to Bennu and document the sampling mission. The search for Earth-Trojans will mark the first time a spacecraft conducts a search for these elusive objects from the L4 point.
The idea for the search originated years ago, shortly after NASA had selected the mission for funding, with Renu Malhotra, a Regents' Professor of Planetary Science at LPL. During a presentation given by Dante Lauretta, now the principal investigator of OSIRIS-REx, Malhotra noticed the spacecraft's trajectory would take it right by Earth's fourth Lagrange point.
"I said to Dante, 'Hey, while you're in that neighborhood of the solar system, you should check out the scenery!'" she says. "I'm thrilled that he and his team were very persistent in making the case to NASA, obtaining approval and making a plan on how to go about the survey."
The search commenced on Feb. 9 and continues through Feb. 20. On each observation day, the spacecraft's MapCam will take 135 survey images that will be processed and examined by the mission's imaging scientists at the UA's Michael J. Drake Building, the mission's headquarters.
Although scientists have discovered thousands of Trojan asteroids accompanying other planets, only one Earth-Trojan has been identified to date, asteroid 2010 TK7. Scientists predict that there should be more Trojans sharing Earth's orbit, but detecting them is extremely difficult, as observers have to point their telescopes to a portion of the sky close to the rising or setting sun. Plus, asteroids are intrinsically faint because they are so small.
"Because the Earth's fourth Lagrange point is relatively stable, it is possible that remnants of the material that built Earth are trapped within it," Lauretta says. "So this search gives us a unique opportunity to explore the primordial building blocks of Earth."
Malhotra echoes Lauretta's excitement: "The search would give us a whole new window on a population of asteroids that we know very little about because we can't see them very well from Earth. We don't know what they might look like — if they are truly primordial material that we don't have in our meteorite collections yet, or whether we might have samples in our collections and simply haven't recognized them as such. If they're out there, it's quite likely they have sent some meteorites to Earth, but we wouldn't know, because we have not been able to connect the dots.
"This is truly an exploration, and there is of course the possibility that we come up empty-handed."
But if it doesn't go that way, scientists will be able to tell us much more about our planet's place in space with regard to what else is out there.
"If there is a sizable population of Trojan bodies where we suspect them to be, it means some might leak out from time to time and possibly hit the Earth or the Moon," Malhotra says. "If we found substantial numbers of these asteroids, it would tell us that Earth's orbit has changed very little over time. Otherwise, it would have been very difficult to retain ancient asteroids in those locations."
Confirming populations of Trojans also might help planetary scientists solve the long-standing "mystery of the missing craters" on the moon, a fascinating side story all by itself.
As the moon travels through space along its orbit around Earth, it gets struck by space rocks crossing its path. Naturally, the hemisphere that is facing forward is being pelted more frequently than the moon's trailing hemisphere, Malhotra explains.
"Just like when you run through the rain, you get more drops on your forehead than on the back side of your head," she says.
But when the researchers calculated what should be the difference in cratering rate on the moon's leading versus its trailing side, they found a discrepancy, showing that the moon gets hit more frequently than it should, based on known asteroid populations.
"One possible explanation is there might be hidden populations of asteroids," Malhotra says, "and the Earth's Trojans could be one of them."
Regardless of whether the OSIRIS-REx team discovers any new asteroids, the search provides a valuable opportunity for a "rehearsal" exercise. The operations involved in searching for Earth-Trojan asteroids closely resemble those required to search for natural satellites and other potential hazards around Bennu when the spacecraft approaches its target in 2018. Being able to practice these mission-critical operations in advance will help the OSIRIS-REx team reduce mission risk once the spacecraft arrives at Bennu.
The study plan also includes opportunities for MapCam to image Jupiter, several galaxies, and the main belt asteroids 55 Pandora, 47 Aglaja and 12 Victoria.
The Mystery of Ahuna Mons, the Lonely Ice Volcano
By American
By American Geophysical Union/University Communications - February 2, 2017
A recently discovered solitary ice volcano on the dwarf planet Ceres may have some hidden older siblings, say scientists who have tested a likely way such mountains of icy rock — called cryovolcanoes — might disappear over millions of years.
NASA's Dawn spacecraft discovered Ceres' 4-kilometer-tall (2.5-mile) Ahuna Mons cryovolcano in 2015. Other icy worlds in our solar system, such as Pluto, Europa, Triton, Charon and Titan, also may have cryovolcanoes, but Ahuna Mons is conspicuously alone on Ceres. The dwarf planet, with an orbit between Mars and Jupiter, also lies far closer to the sun than other planetary bodies where cryovolcanoes have been found.
Now scientists show there may have been cryovolcanoes other than Ahuna Mons on Ceres millions or billions of years ago, but these cryovolcanoes may have flattened out over time and become indistinguishable from the planet's surface. They report their findings in a new paper accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.
"We think we have a very good case that there have been lots of cryovolcanoes on Ceres but they have deformed," said Michael Sori of the Lunar and Planetary Laboratory at the University of Arizona, the lead author of the new paper. Co-authors on the study include LPL members Shane Byrne, Ali Bramson and Christopher Hamilton.
Ahuna Mons is a prominent feature on Ceres, rising to about half the height of Mount Everest. Its solitary existence has puzzled scientists since they spied it.
"Imagine if there was just one volcano on all of Earth," Sori said. "That would be puzzling."
Adding to the puzzle are the steep sides and well-defined features of Ahuna Mons — usually signs of geologic youth, Sori said. That leads to two possibilities: Ahuna Mons is just as it appears, inexplicably alone after forming relatively recently on an otherwise inactive world. Or, the cryovolcano is not alone or unusual, and there is some process on Ceres that has destroyed its predecessors and left the young Ahuna Mons as the solitary cryovolcano on the dwarf planet, according to Sori.
Ceres has no atmosphere, so the processes that wear down volcanoes on Earth — wind, rain and ice — aren't possible on the dwarf planet. Sori and his colleagues hypothesized that another process, called viscous relaxation, could be at work.
Viscous relaxation is the idea that just about any solid will flow, given enough time. For example, a cold block of honey appears to be solid. But if given enough time, the block will flatten until there is no sign left of the original block structure.
On Earth, viscous relaxation is what makes glaciers flow, Sori explained. The process doesn't affect volcanoes on Earth because they are made of rock, but Ceres' volcanoes contain ice, making viscous relaxation possible. On Ceres, viscous relaxation could be causing older cryovolcanoes to flatten over millions of years so they are hard to discern. Ceres' location close to the sun could make the process more pronounced, Sori said.
To test the idea that viscous relaxation had caused cryovolcanoes to flatten out on Ceres, Sori and his colleagues created a model using the actual dimensions of Ahuna Mons to predict how fast the mountain might be flowing. They ran the model assuming different water contents of the material that makes up the mountain — ranging from 100 percent water ice to 40 percent water ice, Sori explained.
Ahuna Mons would need to be composed of more than 40 percent water ice to be affected by viscous relaxation, they found. At this composition, Sori estimates that Ahuna Mons should be flattening at a rate of 10 to 50 meters (30 to 160 feet) per million years. That is enough to render cryovolcanoes unrecognizable in hundreds of millions to billions of years, suggesting there could have been other cryovolcanoes on Ceres, according to the new study.
"Ahuna Mons is at most 200 million years old. It just hasn't had time to deform," Sori said.
The next step for Sori and his team will be to try to identify the flattened remnants of older cryovolcanoes on Ceres. The findings could help scientists better decipher the history of how the dwarf planet formed, he added.
The new study helps scientists expand their knowledge of what might be possible on planetary bodies in our solar system, said Kelsi Singer, a postdoctoral researcher who studies icy worlds at Southwest Research Institute in Boulder, Colorado, and was not involved with the new research.
"It would be fun to check some of the other features that are potentially older domes on Ceres to see if they fit in with the theory of how the shapes should viscously evolve over time," she said. "Because all of the putative cryovolcanic features on other worlds are different, I think this helps to expand our inventory of what is possible."
It's a Bird … It's a Plane … It's the Tiniest Asteroid!
By Daniel Stolte
By Daniel Stolte, University Communications - November 30, 2016
Astronomers have obtained observations of the smallest asteroid ever characterized in detail. At 2 meters (6 feet) in diameter, the tiny space rock is small enough to be straddled by a person in a hypothetical space-themed sequel to the iconic bomb-riding scene in the movie "Dr. Strangelove."
Interestingly, the asteroid, named 2015 TC25, is also one of the brightest near-Earth asteroids ever discovered. Using data from four different telescopes, a team of astronomers led by Vishnu Reddy, an assistant professor at the University of Arizona's Lunar and Planetary Laboratory, reports that 2015 TC25 reflects about 60 percent of the sunlight that falls on it.
Discovered by the UA's Catalina Sky Survey last October, 2015 TC25 was studied extensively by Earth-based telescopes during a close flyby that saw the micro world sailing past Earth at 128,000 kilometers, a mere third of the distance to the moon.
In a paper published in The Astronomical Journal, Reddy argues that new observations from the NASA Infrared Telescope Facility and Arecibo Planetary Radar show that the surface of 2015 TC25 is similar to a rare type of highly reflective meteorite called an aubrite. Aubrites consist of very bright minerals, mostly silicates, that formed in an oxygen-free, basaltic environment at very high temperatures. Only one out of every 1,000 meteorites that fall on Earth belong to this class.
"This is the first time we have optical, infrared and radar data on such a small asteroid, which is essentially a meteoroid," Reddy said. "You can think of it as a meteorite floating in space that hasn't hit the atmosphere and made it to the ground — yet."
Small near-Earth asteroids such as 2015 TC25 are in the same size range as meteorites that fall on Earth. Astronomers discover them frequently, but not very much is known about them as they are difficult to characterize. By studying such objects in more detail, astronomers hope to better understand the parent bodies from which these meteorites originate.
Asteroids are remaining fragments from the formation of the solar system that mostly orbit the sun between the orbits of Mars and Jupiter today. Near-Earth asteroids are a subset that cross Earth's path. So far, more than 15,000 near-Earth asteroids have been discovered.
Scientists are interested in meteoroids because they are the precursors to meteorites impacting Earth, Reddy said.
"If we can discover and characterize asteroids and meteoroids this small, then we can understand the population of objects from which they originate: large asteroids, which have a much smaller likelihood of impacting Earth," he said. "In the case of 2015 TC25, the likelihood of impacting Earth is fairly small."
The discovery also is the first evidence for an asteroid lacking the typical dust blanket — called regolith — of most larger asteroids. Instead, 2015 TC25 consists essentially of bare rock. The team also discovered that it is one of the fastest-spinning near-Earth asteroids ever observed, completing a rotation every two minutes.
Probably, 2015 TC25 is what planetary scientists call monolithic, meaning it is more similar to a "solid rock" type of object than a "rubble pile" type of object like many large asteroids, which often consist of many types of rocks held together by gravity and friction. Bennu, the object of the UA-led OSIRIS-REx sample return mission, is believed to be the latter type.
As far as the little asteroid's origin is concerned, Reddy believes it probably was chipped off by another impacting rock from its parent, 44 Nysa, a main-belt asteroid large enough to cover most of Los Angeles.
"Being able to observe small asteroids like this one is like looking at samples in space before they hit the atmosphere and make it to the ground," Reddy say. "It also gives us a first look at their surfaces in pristine condition before they fall through the atmosphere."
The telescope consortium used in this project includes University of Hawaii/NASA IRTF, USRA/Arecibo Planetary Radar, New Mexico Institute of Mining and Technology/Magdalena Ridge Observatory, Northern Arizona University and Lowell Observatory/Discovery Channel Telescope. Reddy's research on 2015 TC25 is funded by NASA's Near-Earth Object Observations program.
Cracked, Frozen and Tipped Over: New Clues From Pluto's Past
By Daniel Stolte
By Daniel Stolte, University Communications - November 16, 2016
Sputnik Planitia, a 1,000-kilometer-wide basin within the iconic heart-shaped region observed on Pluto's surface, could be in its present location because accumulation of ice made the dwarf planet roll over, creating cracks and tensions in the crust that point toward the presence of a subsurface ocean.
Published in the Nov. 17 issue of Nature, these are the conclusions of research by James Keane, a doctoral student at the University of Arizona's Lunar and Planetary Laboratory, and his adviser, assistant professor Isamu Matsuyama. They propose evidence of frozen nitrogen pileup throwing the entire planet off kilter, much like a spinning top with a wad of gum stuck to it, in a process called true polar wander.
"There are two ways to change the spin of a planet," Keane said. "The first — and the one we're all most familiar with — is a change in the planet's obliquity, where the spin axis of the planet is reorienting with respect to the rest of the solar system. The second way is through true polar wander, where the spin axis remains fixed with respect to the rest of the solar system, but the planet reorients beneath it."
Planets like to spin in such a way that minimizes energy. In short, this means that planets like to reorient to place any extra mass closer to the equator — and any mass deficits closer to the pole. For example, if a giant volcano were to grow on Los Angeles, the Earth would reorient itself to place L.A. on the equator.
To understand polar wander on Pluto, one first has to realize that unlike Earth, whose spin axis is only slightly tilted so that the regions around the equator receive the most sunlight, Pluto is like a spinning top lying on its side. Therefore, the planet's poles get the most sunlight. Depending on the season, it's either one or the other, while Pluto's equatorial regions are extremely cold, all the time.
Because Pluto is almost 40 times farther from the sun than we are, it takes the little ball of rock and ice 248 Earth-years to complete one of its own years. At Pluto's lower latitudes near the equator, temperatures are almost as cold as minus 400 degrees Fahrenheit — cold enough to turn nitrogen into a frozen solid.
Over the course of a Pluto year, nitrogen and other exotic gases condense on the permanently shadowed regions, and eventually, as Pluto goes around the sun, those frozen gases heat up, become gaseous again and re-condense on the other side of the planet, resulting in seasonal "snowfall" on Sputnik Planitia.
"Each time Pluto goes around the sun, a bit of nitrogen accumulates in the heart," Keane said. "And once enough ice has piled up, maybe a hundred meters thick, it starts to overwhelm the planet's shape, which dictates the planet's orientation. And if you have an excess of mass in one spot on the planet, it wants to go to the equator. Eventually, over millions of years, it will drag the whole planet over."
In a sense, Pluto is a (dwarf) planet whose shape and position in space are controlled by its weather.
"I think this idea of a whole planet being dragged around by the cycling of volatiles is not something many people had really thought about before," Keane said.
The two researchers used observations made during New Horizons' flyby and combined them with computer models that allowed them to take a surface feature such as Sputnik Planitia, shift it around on the planet's surface and see what that does to the planet's spin axis. And sure enough, in the models, the geographic location of Sputnik Planitia ended up suspiciously close to where one would expect it to be.
If Sputnik Planitia were a large positive mass anomaly — perhaps due to loading of nitrogen ice — it would naturally migrate to Pluto's tidal axis with regard to Charon, Pluto's largest moon, as it approaches a minimum energy state, according to Keane and Matsuyama. In other words, the massive accumulation of ice would end up where it causes the least wobble in Pluto's spin axis.
This phenomenon of polar wander is something that was discovered with the Earth's moon and with Mars, as well, but in those cases it happened in the distant past, billions of years ago.
"On Pluto, those processes are currently active," Keane said. "Its entire geology — glaciers, mountains, valleys — seems to be linked to volatile processes. That's different from most other planets and moons in our solar system."
And not only that, the simulations and calculations also predicted that the accumulation of frozen volatiles in Pluto's heart would cause cracks and faults in the planet's surface in the exact same locations where New Horizons saw them.
The presence of tectonic faults on Pluto hint at the existence of a subsurface ocean at some point in Pluto's history, Keane explained.
"It's like freezing ice cubes," he said. "As the water turns to ice, it expands. On a planetary scale, this process breaks the surface around the planet and creates the faults we see today."
The paper is published alongside a report by Francis Nimmo of the University of California, Santa Cruz, and colleagues, who also consider the implications for Pluto's apparent reorientation. The authors of that paper agree with the idea that tidal forces could explain the current location of Sputnik Planitia, but in order for their model to work, a subsurface ocean would have to be present on Pluto today.
Both publications underscore the notion of a surprisingly active Pluto.
"Before New Horizons, people usually only thought of volatiles in terms of a thin frost veneer, a surface effect that might change the color, or affect local or regional geology," Keane said. "That the movement of volatiles and shifting ice around a planet could have a dramatic, planet-moving effect is not something anyone would have predicted."
Co-authors on the research paper (http://dx.doi.org/10.1038/nature20120) are Shunichi Kamata of the Creative Research Institution, Hokkaido University, Sapporo, Japan, and Jordan Steckloff of Purdue University in West Lafayette, Indiana, and the Planetary Science Institute in Tucson, Arizona.
Psyche: Unexpected Discoveries on a Metal World
By Daniel Stolte
By Daniel Stolte, University Communications - October 21, 2016
Astronomers have discovered possible evidence for water on the surface of the largest metallic asteroid in the solar system.
Named 16 Psyche, the bolide is one of the most massive in the Asteroid Belt, measuring 186 miles across and consisting of almost pure nickel-iron metal. It is thought to be the remnant core of a planetary embryo that was mostly destroyed by impacts billions of years ago.
Previous observations of Psyche had shown no evidence for water on its surface. But in a paper accepted in The Astronomical Journal, Vishnu Reddy, an assistant professor at the University of Arizona's Lunar and Planetary Laboratory, argues that new observations from the NASA Infrared Telescope Facility show evidence for volatiles such as water or hydroxyl, a free radical consisting of one hydrogen atom bound to one oxygen atom, on Psyche's surface. In Earth's atmosphere, hydroxyl is extremely reactive and helps remove many chemical compounds. Hence, it is also known as the "detergent of the atmosphere."
"We did not expect a metallic asteroid like Psyche to be covered by water and/or hydroxyl," said Reddy, second author on the paper led by Driss Takir at the U.S. Geological Survey in Flagstaff, Arizona. "Metal-rich asteroids like Psyche are thought to have formed under dry conditions without the presence of water or hydroxyl, so we were puzzled by our observations at first."
The findings are interesting in the context of a proposed $500 million mission to send a spacecraft to Psyche, currently under review by NASA. Images taken by a spacecraft orbiting Psyche would enable us to distinguish between water and hydroxyl on the surface.
Asteroids are remaining fragments from the formation of the solar system that today orbit the sun between the orbits of Mars and Jupiter. Most of them fall into two broad categories: those rich in silicates, and those rich in carbon and volatiles. Metallic asteroids such as Psyche are extremely rare, making it a laboratory to study how planets formed.
While the source of this water on Psyche remains a mystery, Reddy and his colleagues propose two possible mechanisms for its formation.
"We think the water we see on Psyche might have been delivered to its surface by carbonaceous asteroids that impacted Psyche in the distant past," Reddy says.
"Our discovery of carbon and water on an asteroid that isn't supposed to have those compounds supports the notion that these building blocks of life could have been delivered to our Earth early in the history of our solar system history," said Reddy, who discovered similar dark, carbonaceous impactors rich in volatiles on the surface of asteroid Vesta by studying the images from NASA's Dawn mission. Alternatively, the hydroxyl could be the product of solar wind interacting with silicate minerals on Psyche's surface.
To further explore the hypothesis of carbon and water delivered to protoplanetary bodies by asteroids in the early solar system, the UA is leading NASA's OSIRIS-REx mission to bring back a sample from carbonaceous asteroid (101955) Bennu in 2023.
Reddy presented the findings at the joint 48th meeting of the Division for Planetary Sciences and 11th European Planetary Science Congress in Pasadena, California. His research on Psyche is funded by NASA's Planetary Science Division's Planetary Geology and Geophysics program. The research paper is available online.
More Evidence for 9th Planet on Solar System's Fringes
By Daniel Stolte -
By Daniel Stolte - University Communications, October 21, 2016
As the search for a hypothetical, unseen planet far beyond Neptune's orbit continues, research by a University of Arizona team provides additional support for the possible existence of such a world and narrows the range of its parameters and location.
Led by Renu Malhotra, a Regents' Professor of Planetary Sciences in the UA's Lunar and Planetary Laboratory, the team found that the four Kuiper Belt Objects with the longest known orbital periods revolve around the sun in patterns most readily explained by the presence of a hypothetical "Planet Nine" approximately 10 times the mass of Earth. Malhotra presented the results at the 48th meeting of the Division for Planetary Sciences of the American Astronomical Society in Pasadena, California.
According to the researchers' calculations, such a hypothetical planet would complete one orbit around the sun about every 17,000 years and, at its farthest point from our central star, it would swing out more than 660 astronomical units, with one AU being the average distance between the Earth and the sun.
Scientists think that objects in the Kuiper Belt, a vast region of dwarf planets and icy rocks populating the fringes of our solar system beyond the orbit of Neptune, dance mostly to the tune of the giant planets — Saturn, Jupiter, Uranus and Neptune — and are influenced by their gravity either directly or indirectly.
However, there are a few known Kuiper Belt objects, or KBOs, that are unlikely to be significantly perturbed by the known giant planets in their current orbits. Referred to as "extreme KBOs," or eKBOs, by the authors, all of these have extremely large orbital eccentricities. In other words, they get very close to the sun at one point on their orbital journey, only to swing far out into space once they pass the sun, on long elliptical orbits that take these strange mini-worlds hundreds of AUs away from the sun.
"We analyzed the data of these most distant Kuiper Belt Objects," Malhotra said, "and noticed something peculiar, suggesting they were in some kind of resonances with an unseen planet."
In their paper, "Corralling a Distant Planet With Extreme Resonant Kuiper Belt Objects," Malhotra and her co-authors, Kathryn Volk and Xianyu Wang, point out peculiarities of the orbits of the extreme KBOs that went unnoticed until now: They found that the orbital period ratios of these objects are close to ratios of small whole numbers. An example of this would be one KBO traveling around the sun once while another takes twice as long, or three times as long, or four times as long, etc. — but not, say, 2.7 times as long.
According to the authors, such ratios could arise most naturally if the extreme KBOs' orbital periods are in small whole-number ratios with a massive planet, which would help to stabilize the highly elliptical orbits of eKBOs.
The findings bolster previous work by other scientists that showed that six of those bodies travel on highly eccentric orbits whose long axes all point in the same direction. This clustering of orbital parameters of the most distant KBOs suggested a large, planetary size body shepherding their orbits.
Another paper published earlier this year presented the results of numerical simulations providing a range of possibilities for the mass and orbit for such a hypothetical planet, which could account for the observed clustering of eKBO orbits.
"Our paper provides more specific estimates for the mass and orbit that this planet would have, and, more importantly, constraints on its current position within its orbit," Malhotra said.
The team's calculations also suggest two likely orbital planes for the planet: one moderately close to the mean plane of the solar system and near the mean plane of the four eKBOs at about 18 degrees, and one steeper plane, inclined at about 48 degrees.
While the results provide additional support for the idea of a potential "Planet Nine" and lay out possible scenarios, the authors stress that their paper should not be considered definitive proof of the planet's existence.
For one, the very far and faint KBOs haven't been observed for very long, and, given their minuscule apparent motion along their immensely long journeys around the sun, the estimates for their closeness to whole-number ratios of orbital periods come with uncertainties that can be narrowed down only through more observations.
The authors also note that the long orbital timescales in this region of the outer solar system may allow formally unstable orbits to persist for very long times, possibly even to the age of the solar system, without the help of orbital resonances. In this scenario, orbits whose orderly parameters appear as testimony to the stabilizing influence of an unseen planet may in fact be in the process of deterioration but haven't been observed long enough for it to show.
Future observations and studies into the dynamical lifetimes of non-resonant planet-crossing orbits in the far regions of the outer solar system could help to further test the case for the existence and whereabouts of a ninth planet, Malhotra and her co-authors write.
Boynton's Mission to Mars, 30 Years in the Making
By Emily Litvack
By Emily Litvack, October 17, 2016
Before his life's work got to Mars, Bill Boynton toiled, witnessed an explosion, and mourned a loss. It's been 15 years since Mars Odyssey arrived at the red planet, and now Boynton talks about how it all came to be.
Mars Observer
In the 1980s, "space science" was just 11.5 percent of NASA's budget, and planetary science was an even smaller slice of that. The saying was "Better, faster, cheaper." (Boynton says "Pick two.") Out of this climate of tightfistedness, the Planetary Observer line was born. Planetary Observers were to be built on the cheap, using common technology from old spacecraft. The first and onlyobserver, the Mars Observer, launched in 1992, a whole 17 years after the United States' last mission to Mars. The Mars Observer was the culmination of eight years of work and $813 million – the original budget allocated $212 million – and it exploded just two days before it was due to arrive at Mars in 1993.
Boynton, professor of planetary sciences at the University of Arizona, was the lead scientist for one of the spacecraft's seven instruments: the gamma ray spectrometer, or GRS. The explosion, caused by a leaky valve filled with pressurized helium and fuel, was tough on him.
"When the thing blew up, it was devastating," he says. "It was like there had been a death in the family." His colleagues didn't know the right words to say when they'd crossed paths in the elevator, and his department head told him, "'Bill, we'll probably need to call off the celebrations.'" They had planned a big party for when the Observer entered orbit. Boynton proposed, instead, a wake, which felt truly appropriate for the death of the spacecraft.
At the wake, he says, "I gave a talk about what the mission would've been like, what we did learn from it, and explained why it was not a waste of millions of dollars." It was cathartic. It was reassuring. It was time to go back to work.
At first, the Mars Observer team planned to rebuild the same observer using parts set aside for such an event, until the then head of NASA, Daniel Goldin, suggested something drastically different. Goldin proposed building three new spacecraft from scratch, each only carrying two or three instruments. The idea was met with skepticism. "I think most of us were thinking it was stupid," says Boynton. "But in the end, it turned out to be a really good idea."
The Mars Odyssey
And just like that, the Mars Observer mission turned into the Mars Odyssey. The unmanned Mars Odyssey launched in 2001, in search of evidence of water and ice, new information about the planet's geology, and about its potential ability to sustain life. Aboard the spacecraft were three new scientific instruments, including Boynton’s gamma ray spectrometer, designed and built at the University of Arizona.
Mars Odyssey is a roughly seven-foot-tall spacecraft bearing a small fleet of solar panels that fan out like wings, and a 20-foot-long scaffold with the gamma ray spectrometer hanging off the end of it. This way, the spectrometer can detect gamma rays on the Martian surface without muddying the signal with its own electromagnetic radiation. The GRS measures gamma rays emitted by the surface of Mars and, in turn, calculates the abundance of chemical elements across the planet's surface.
Fifteen Years of Scientific Discovery
Since arriving at Mars 15 years ago on Oct. 24, the Mars Odyssey has mapped the surface of Mars, detected its elemental composition – Mars is rich in elements like silicon, aluminum, calcium, uranium, and chlorine – communicated with rovers to relay information, and, perhaps most remarkably, discovered large amounts of ice on Mars, covering its polar regions.
"The ice is buried a few inches beneath the surface, but hydrogen gives off a gamma ray, so we found it," says Boynton.
The mission was originally planned to last for two to three years, but remains operational, orbiting Mars. Eventually – soon, guesses Boynton – the spacecraft will give out and Mars Odyssey will come to an end, but Boynton will keep busy.
As a mission instrument scientist for the recently launched OSIRIS-REx spacecraft, Boynton and colleagues will now uncover new information about the origins and formation of our solar system.
Realizing he's dedicated more than 30 years of his life to ten different NASA missions, Boynton says, "I'm sorry. It's hard not to tear up over some of these things," and wipes his cheek with a smile.