Tag Archives: #asteroid

Asteroid 16 Psyche Might Not Be What Scientists Expected (Planetary Science)

New UArizona research finds that the target asteroid of NASA’s Psyche mission may not be as metallic or dense as previously predicted

The widely studied metallic asteroid known as 16 Psyche was long thought to be the exposed iron core of a small planet that failed to form during the earliest days of the solar system. But new University of Arizona-led research suggests that the asteroid might not be as metallic or dense as once thought, and hints at a much different origin story.

Scientists are interested in 16 Psyche because if its presumed origins are true, it would provide an opportunity to study an exposed planetary core up close. NASA is scheduled to launch its Psyche mission in 2022 and arrive at the asteroid in 2026.

UArizona undergraduate student David Cantillo is lead author of a new paper published in The Planetary Science Journal that proposes 16 Psyche is 82.5% metal, 7% low-iron pyroxene and 10.5% carbonaceous chondrite that was likely delivered by impacts from other asteroids. Cantillo and his collaborators estimate that 16 Psyche’s bulk density – also known as porosity, which refers to how much empty space is found within its body – is around 35%.

These estimates differ from past analyses of 16 Psyche’s composition that led researchers to estimate it could contain as much as 95% metal and be much denser.

“That drop in metallic content and bulk density is interesting because it shows that 16 Psyche is more modified than previously thought,” Cantillo said.

Rather than being an intact exposed core of an early planet, it might actually be closer to a rubble pile, similar to another thoroughly studied asteroid — Bennu. UArizona leads the science mission team for NASA’s OSIRIS-REx mission, which retrieved a sample from Bennu’s surface that is now making its way back to Earth.

“Psyche as a rubble pile would be very unexpected, but our data continues to show low-density estimates despite its high metallic content,” Cantillo said.

Asteroid 16 Psyche is about the size of Massachusetts, and scientists estimate it contains about 1% of all asteroid belt material. First spotted by an Italian astronomer in 1852, it was the 16th asteroid ever discovered.

“Having a lower metallic content than once thought means that the asteroid could have been exposed to collisions with asteroids containing the more common carbonaceous chondrites, which deposited a surface layer that we are observing,” Cantillo said. This was also observed on asteroid Vesta by the NASA Dawn spacecraft.

Asteroid 16 Psyche has been estimated to been worth $10,000 quadrillion (that’s $10,000 followed by 15 more zeroes), but the new findings could slightly devalue the iron-rich asteroid.

“This is the first paper to set some specific constraints on its surface content. Earlier estimates were a good start, but this refines those numbers a bit more,” Cantillo said.

The other well-studied asteroid, Bennu, contains a lot of carbonaceous chondrite material and has porosity of over 50%, which is a classic characteristic of a rubble pile.

Such high porosity is common for relatively small and low-mass objects such as Bennu – which is only as large as the Empire State Building – because a weak gravitational field prevents the object’s rocks and boulders from being packed together too tightly. But for an object the size of 16 Psyche to be so porous is unexpected.

“The opportunity to study an exposed core of a planetesimal is extremely rare, which is why they’re sending the spacecraft mission there,” Cantillo said, “but our work shows that 16 Psyche is a lot more interesting than expected.”

Past estimates of 16 Psyche’s composition were done by analyzing the sunlight reflected off its surface. The pattern of light matched that of other metallic objects. Cantillo and his collaborators instead recreated 16 Psyche’s regolith – or loose rocky surface material – by mixing different materials in a lab and analyzing light patterns until they matched telescope observations of the asteroid. There are only a few labs in the world practicing this technique, including the UArizona Lunar and Planetary Laboratory and the Johns Hopkins Applied Physics Laboratory in Maryland, where Cantillo worked while in high school.

“I’ve always been interested in space,” said Cantillo, who is also president of the UArizona Astronomy Club. “I knew that astronomy studies would be heavy on computers and observation, but I like to do more hands-on kind of work, so I wanted to connect my studies to geology somehow. I’m majoring geology and minoring in planetary science and math.”

“David’s paper is an example of the cutting-edge research work done by our undergraduate students,” said study co-author Vishnu Reddy, an associate professor of planetary sciences who heads up the lab in which Cantillo works. “It is also a fine example of the collaborative effort between undergraduates, graduate students, postdoctoral fellows and staff in my lab.”

The researchers also believe the carbonaceous material on 16 Psyche’s surface is rich in water, so they will next work to merge data from ground-based telescopes and spacecraft missions to other asteroids to help determine the amount of water present.


Reference: David C. Cantillo, Vishnu Reddy et al., “Constraining the Regolith Composition of Asteroid (16) Psyche via Laboratory Visible Near-infrared Spectroscopy”, The Planetary Science Journal, 2(3), 2021. Link to paper


Provided by University of Arizona

Did Heat From Impacts on Asteroids Provide the Ingredients For Life On Earth? (Planetary Science)

A research group from Kobe University has demonstrated that the heat generated by the impact of a small astronomical body could enable aqueous alteration (*1) and organic solid formation to occur on the surface of an asteroid. They achieved this by first conducting high-velocity impact cratering experiments using an asteroid-like target material and measuring the post-impact heat distribution around the resulting crater. From these results, they then established a rule-of-thumb for maximum temperature and the duration of the heating, and developed a heat conduction model from this.

The research group consisted of the following members from Kobe University’s Graduate School of Science; Lecturer YASUI Minami, TAZAWA Taku (a 2nd year masters student at the time of research), HASHIMOTO Ryohei (then a 4th year undergraduate in the Faculty of Science) and Professor ARAKAWA Masahiko, in addition to JAXA Space Exploration Center’s Associate Senior Researcher OGAWA Kazunori (who was a technical specialist at Kobe University at the time of the study). 

These results have expanded the spatial and temporal range over which the necessary conditions for aqueous alteration and organic solid formation could occur. This is expected to significantly increase the number of prospective astronomical bodies that could have brought water and the origins of life to Earth.

These research results were published in the British scientific journal Communications Earth and Environment (Nature Publishing Group) on May 18, 2021.

Main points

  • The researchers used porous gypsum as an imitation asteroid and inserted multiple thermocouples (*2) inside it. They conducted high-velocity impact experiments on this target at impact speeds of 1km/s and over, and succeeded in measuring changes in temperature duration around the resulting crater soon after impact.
  • This revealed that, regardless of the impact speed and projectile’s size and density, the maximum temperature and its duration were dependent upon dimensionless distance (the distance from the impact point scaled by the crater radius).
  • Using the above results, the researchers calculated the temporal changes in thermal heat distribution after the crater’s formation on the asteroid’s surface. These calculations suggested that, at distances within 2 astronomical units (*3), aqueous alteration can occur if the crater has a radius of over 20km, and organic solid formation can be supported by craters of over 1km.
  • These findings will enable an increased number of astronomical bodies to be considered as candidates for the source of the water and organic substances necessary for the beginning of life on Earth.

Research Background

It is believed that the water and organic substances necessary for life to begin on Earth were the result of a comet or asteroid impacting the planet. Minerals and organic substances that have experienced aqueous alteration have been discovered in meteorites (from which asteroids originate), providing proof that they once contained water. However, a heat source is necessary for the chemical reactions that cause aqueous alteration and organic solid formation inside asteroids.

One sufficiently strong heat source is the radioactive decay heating of 26Al (aluminum, *5), a short-lived radioactive nuclide found inside rocks. However, it is said that the radioactive heating that caused aqueous alteration and solid formation on asteroid parent bodies (*4) could have only occurred at the beginning of the solar system’s history due to the short half-life of 26Al (720,000 years).

In recent years, the theory that the impact heat generated when a small astronomical body hits an asteroid could also be a viable heat source has started to gain attention. However, it is not known how much heat is generated depending on the astronomical body’s characteristics (size, density, impact speed) and how far within the asteroid this generated heat is transmitted. Up until now, there have been no studies that have experimentally investigated this heat generation and propagation process to determine whether aqueous alteration and organic substance formation would be possible.

Research Methodology

This research group conducted laboratory experiments to investigate the relationship between the impact heat generated on an asteroid (as a result of a small astronomical body’s impact) and the impact’s characteristics. For the target, they used gypsum (a porous mineral composed of calcium sulfate dihydrate) to imitate an asteroid. They accelerated projectiles at the target at high impact velocities of between 1km/s to 5km/s using Kobe University’s two-stage horizontal gas gun (Figure 1). Multiple thermocouples were set in the gypsum target in order to measure the temperature changes post-impact. In this series of experiments, the researchers changed the size, density, impact speed of the projectiles and the thermocouples’ positions in order to investigate the differences in heat duration depending on the characteristics of the impact (Figure 2).

Figure 1. The two-stage horizontal gas gun located at Kobe University.
Figure 2. Example of thermal changesThe x-axis indicates the elapsed time, with 0 being the time of impact. The y axis shows the differences in temperature from pre-impact onwards. This impact was made by an aluminum projectile with an impact velocity of 4.3km/s. The different colored lines indicate the distance between the point of impact and the thermocouples. The duration is the time that it takes for the maximum temperature to drop by half. The photo shows the impact crater. Thermocouples were embedded in the target. © Kobe University
Figure 3. A. Relationship between maximum temperature and dimensionless distance. B. Relationship between duration and dimensionless distance.Duration is scaled by thermal diffusion (*6) time. The colors indicate different projectiles and impact speeds: PC is a polycarbonate sphere with a diameter of 4.7mm and Al is an aluminum sphere with a diameter of 2mm. © Kobe University
Figure 4. Heat distribution around the crater floor of asteroid parent bodies calculated using the Heat conduction modelThe dotted lines are isotherm contour lines. The numbers that meet the isotherm contour lines indicate the value obtained when normalizing the distance from the impact point by the crater radius. © Kobe University

From the heat duration graph, the research group investigated the maximum temperature and its duration, and looked at how this related to the impact characteristics (Figure 3). By using the dimensionless distance obtained by normalizing the distance from the impact point (where the projectile hit the target) by the crater radius, they successfully determined how maximum temperature and its duration are altered by impact characteristics and came up with a rule-of-thumb for this.

Subsequently constructing a heat conduction model incorporating this rule of thumb, enabled them to calculate the heat distribution around the crater formed on the asteroid surface (Figure 4). The research group checked the numerical results from the heat conduction model against data on the required heat and duration for aqueous alteration and organic solid formation obtained from past analyses of meteorites.

These results showed that aqueous alteration could occur if a crater with a radius of over 20km was formed within 2au from the Sun. In addition, they estimated that even a small crater with a 100m radius on an asteroid within 4au could heat up to 100°C, meaning that it could support organic solid formation. Most asteroids are located within 4au. The researchers also found that if a crater with a radius of over 1km is formed within 2au, the circumference of the crater can heat up to 0°C (the temperature at which ice becomes water), thus enabling organic solids to be formed.

Further Developments

It is thought that radioactive decay heating of 26Al triggers the chemical reactions for aqueous alteration and organic solid formation on asteroids. However, this heating can only occur near the core of comparatively large asteroids that are tens of kilometers in diameter. Furthermore, it is said that this could have only occurred within a million years after the Sun’s formation due to the short half-life of 26Al. On the other hand, collisions between asteroids still occur today, and it is possible that such collisions heat up the surface of even small asteroids, providing that the impact does not destroy the asteroid itself. In other words, these research results show that the potential for asteroids to support aqueous alteration and organic solid formation is temporarily and spatially far greater than previously thought. This will contribute towards an increased number of astrological bodies being considered as candidates that brought the water and organic substances for the beginning of life on Earth.

Next the research group hopes to examine samples returned from asteroid exploration missions conducted not only by Japan but other countries as well. If aqueously altered minerals or organic substances were to be discovered in the collected samples, this could provide evidence of impact heating’s effects.

Glossary

  • Aqueous alteration: This refers to when the minerals inside a rock change as the result of a chemical reaction between the rock and water.
  • Thermocouple: A heat sensor consisting of two rods, each made from different metals.
  • Astronomical units (au): The distance from the center of the Sun. One astronomical unit is the distance from the center of the Sun to Earth (approx. 150 million kilometers).
  • Asteroid parent bodies: Astronomical bodies from which current asteroids originate. It is thought that asteroids are fragments that remain after the parent body was destroyed by an impact, or are an aggregation of fragments re-accumulated by gravity.
  • Radioactive decay heating of 26AI (a short-lived radioactive nuclide): A nuclide is a distinct kind of nucleus characterized by a specific number of protons or neutrons. Among these, nuclides that are energetically unstable emit radiation which causes them to become a different kind of nuclide called a radionuclide. The process whereby these nuclides emit radiation and eventually change type is called radioactive decay. During this process, energy is also emitted, generating heat. When 26Al decays it becomes 26Mg (magnesium) but the time that it takes for one half of the atomic nuclei in 26Al to decay (i.e. the half-life) is a relatively short 720,000 years.
  • Thermal diffusion time: The estimated amount of time that it takes heat to be dispersed from the heat source. In this study this was calculated as (crater radius)2 / (thermal diffusion coefficient). The thermal diffusion coefficient is the matter’s characteristic value.

Acknowledgements

A portion of these experiments was performed in collaboration with the Hypervelocity Impact Facility at JAXA’s Institute of Space and Astronautical Science (ISAS). In addition, this research received funding from the following: a basic scientific research grant from the Sumitomo Foundation (research theme: ‘Measurements of post shock temperature after impact crater formation: Implications for thermal evolution of asteroids’, Principle Investigator: Yasui Minami), and JSPS KAKENHI grants JP16K17794 (Principle Investigator: Yasui Minami), JP16H04041 and JP19H00719 (Principle Investigator: Arakawa Masahiko).

Journal Information

Minami Yasui, Taku Tazawa, Ryohei Hashimoto, Masahiko Arakawa, Kazunori Ogawa, “Impacts may provide heat for aqueous alteration and organic solid formation on asteroid parent bodiesCommunications Earth and Environment(Nature Publishing Group), 2021.


Provided by Kobe University

Three Years Ago, A Breach From the Heart of Vesta (Planetary Science)

Twenty-three fragments of the meteorite that impacted the earth’s surface on 2 June 2018 have been recovered and studied by an international group of researchers. Among them also the Italian Davide Farnocchia of NASA, to whom we asked how it went and what are the results obtained

On June 2, 2018, a fragment of the 2018 asteroid LA entered Earth’s atmosphere and a handful of meteorite fragments crashed to the ground, in the Central Kalahari Wildlife Reserve , in Botswana, Africa. In those same days scientists and researchers from all over the world gathered in Munich, Germany, to discuss the bodies of the Solar System whose orbit has a non-zero probability of crossing that of the Earth: the Near Earth Objects (or Neo) . Among them were Davide Farnocchia , of the Center for Near-Earth Object Studies of NASA ‘s JPL , and Eric Christensen, the manager of the Catalina Sky Survey, the observational program conducted by the University of Arizona Lunar and Planetary Laboratory that first identified the asteroid 2018 LA.

«June 2, 2018 was a Saturday, and we had a day off after a busy week of work. We had organized a trip to the Nördlinger Ries crater », says Farnocchia, a mathematician by training and now a navigation engineer at NASA. «Despite the bad internet signal in the area, around lunchtime I received the notification of our automatic program that warned of the possible impact in the following hours. As soon as we got back to the hotel, Eric and I started analyzing Catalina’s astrometric images to improve the calculation of the orbit and the possibility of impact ».

The 2018 LA asteroid viewed by Skymapper. Credits: Christian Wolf et al./Anu

It was in fact the second time ever in which an object was monitored in space before its impact on the ground. The researchers retrieved the archive data from the program SkyMapper Southern Survey of ‘ Australian National University(Anu) which showed the asteroid rotating around its axis once every four minutes, alternately presenting a wide and a narrow side. Farnocchia combined astronomical observations of the asteroid with satellite data from the United States government to calculate the fall area on the Earth’s surface. With other astrometric data, scientists were able to accurately calculate the approach orbit, rotation period and shape of the asteroid. In order to triangulate the position of the approaching “fireball”, it was necessary to trace numerous recordings made by people who witnessed the scene, such as this video by Barend Swanepoel and Vicus van Zyl. Since then, an international team of researchers led by Peter Jenniskens, meteorite expert astronomer at the Seti Institute , has found twenty-three fragments of the Motopi Pan meteorite , a study published last April in the journal Meteoritics and Planetary Science reports  .

Davide Farnocchia. Credits: Jpl / Nasa

“My contribution involved identifying the impact following the discovery. I also calculated the trajectory of 2018 LA and its projection on the ground to identify the place where the meteorites could have been found. The area where we looked for them is located within the Central Kalahari Wildlife Reserve, where potentially dangerous animals such as leopards and lions are found. The scientists were kept safe by Botswana rangers in charge of wildlife protection “, remembers Farnocchia, who at Jpl is a member of the Solar System dynamics group (part of the section that deals with the navigation of space modules for the various missions ), with the role of navigation engineer and among other tasks he also has that of calculating the trajectory of asteroids and comets.

Before the impact, LA 2018 was a solid rock about 156 centimeters in diameter with a high bulk density (over 2.80 grams per cubic centimeter), capable of reflecting about 25 percent of the sunlight. The dynamic study of its orbit supported the hypothesis that LA 2018 was a vestoid coming from the inner part of the asteroid belt where Vesta is located , the second largest body of the main asteroid belt and the brightest among those visible from Earth.

Group photo on the occasion of the second discovery of a piece of asteroid 2018 LA recovered in the Central Kalahari Game Reserve in central Botswana. Credits: Seti Institute

According to scientists, the material that composes Motopi Pan was formed following a strong warming following a huge impact on Vesta about 4.23 billion years ago. This impact led to the formation of the Veneneia crater while a subsequent second major impact occurred about twenty-two million years ago produced another crater, Rheasilvia, which sent LA 2018 out of its original orbit catapulting it into an orbit towards Earth.

“There are at least two reasons for studying these objects,” Farnocchia explains. “The first reason is that asteroidal impacts pose a risk to the Earth. 2018 LA was too small to cause harm but it was still good exercise. Despite the small size, it was discovered by our telescopes, we were able to recognize the next impact and accurately calculate its trajectory. Each of these steps is an essential ingredient if there is an actually dangerous asteroid. The second reason concerns the fact that the composition and orbital dynamics of asteroids give us valuable information on the formation process of the Solar System ».

«The importance of this study», Farnocchia concludes, «lies in the fact that we can link the properties of these meteorites with the area of ​​origin of the asteroid 2018 LA. In fact, we know the pre-impact orbit of 2018 LA around the Sun and this allows us to track its motion in the past and connect it with all probability to the asteroid Vesta. The fact that the meteorites found are of the Hed type (howardite – eucrite – diogenite) confirms this interpretation. In short, we had the opportunity to study an asteroid coming from the main belt between Mars and Jupiter without needing a space mission, it was the asteroid that came to us ».

Featured image: A fragment of the 2018 LA asteroid recovered in the Central Kalahari Wildlife Reserve in Botswana, Africa. Credits: Seti Institute


To know more: 

  • Read on Meteoritics & Planetary Science the article “ The impact and recovery of asteroid 2018 LA“By P. Jenniskens, M. Gabadirwe, Q. Yin, A. Proyer, O. Moses, T. Kohout, F. Franchi, RL Gibson, R. Kowalski, EJ Christensen, AR Gibbs, A. Heinze, L. Denneau , D. Farnocchia, PW Chodas, W. Gray, M. Micheli, N. Moskovitz, CA Onken, C. Wolf, Hadrien AR Devillepoix, Q. Ye, DK Robertson, P. Brown, E. Lyytinen, J. Moilanen, J. Albers, T. Cooper, J. Assink, Evers, P. Lahtinen, L. Seitshiro, M. Laubenstein, N. Wantlo, P. Moleje, J. Maritinkole, H. Suhonen, ME Zolensky, L. Ashwal, T . Hiroi, DW Sears, Alexander Sehlke, A. Maturilli, ME Sanborn, MH Huyskens, S. Dey, K. Ziegler, H. Busemann, MEI Riebe, MM Meier, KC Welten, MW Caffee, Q. Zhou, Q. Li , X. Li, Yu Liu, G. Tang, HL Mclain, JP Dworkin, DP Glavin, P. Schmitt-kopplin, H. Sabbah, C. Joblin, M. Granvik, B. Mosarwa and K. Botepe

Provided by INAF

OSIRIS-REx Bids Farewell to Asteroid Bennu (Planetary Science)

On April 9, 2021, NASA’s Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) spacecraft took one last look at Bennu, the asteroid from which it scooped up a sample last October. Slated for return to Earth in 2023, the mission is on track to deliver a sample of pristine material left over from the formation of our solar system into the hands of researchers on Earth.

This image, the last one taken by the spacecraft, shows crescent Bennu with its night side merging with the complete black of space as the spacecraft pushed away from Bennu. 

For two years, OSIRIS-REx studied the asteroid, revealing the many secrets of this ancient body and delivering clues about its rubble-pile-like consistency and surface terrain, which turned out to be much rockier and more rugged than initially expected from the observations of ground-based telescope.

On May 10, 2021, the spacecraft embarked on its return voyage to Earth. On Sept. 24, 2023, the spacecraft will jettison the sealed capsule containing the sample and send it onto a trajectory to touch down in the Utah desert.

Image Credits: NASA/Goddard/University of Arizona; Writer Daniel Stolte, University of Arizona


Provided by NASA

Asteroid That Hit Botswana in 2018 Likely Came From Vesta (Planetary Science)

An international team of researchers searched for pieces of a small asteroid tracked in space and then observed to impact Botswana on June 2, 2018. Guided by SETI Institute meteor astronomer Peter Jenniskens,  they found 23 meteorites deep inside the Central Kalahari Game Reserve and now have published their findings online in the journal Meteoritics and Planetary Science.

“Combining the observations of the small asteroid in space with information gleaned from the meteorites shows it likely came from Vesta, second largest asteroid in our Solar System and target of NASA’s DAWN mission,” said Jenniskens. “Billions of years ago, two giant impacts on Vesta created a family of larger, more dangerous asteroids. The newly recovered meteorites gave us a clue on when those impacts might have happened.”

The asteroid

The small asteroid that impacted Botswana, called 2018 LA, was first spotted by the University of Arizona’s Catalina Sky Survey as a faint point of light moving among the stars. The Catalina Sky Survey searches for Earth-crossing asteroids as part of NASA’s Planetary Defense program.

“Small meter-sized asteroids are no danger to us, but they hone our skills in detecting approaching asteroids,” said Eric Christensen, director of the Catalina Sky Survey program.

The team recovered archival data from the SkyMapper Southern Survey program in Australia that showed the asteroid spinning in space, rotating once every 4 minutes, alternatingly presenting a broad and a narrow side to us while reflecting the sunlight.

On its journey to Earth, cosmic rays bombarded the asteroid and created radioactive isotopes. By analyzing those isotopes, the researchers determined that 2018 LA was a solid rock about 1.5 m in size, which reflected about 25% of sunlight.

The recovery

“This is only the second time we have spotted an asteroid in space before it hit Earth over land,” said Jenniskens. “The first was asteroid 2008 TC3 in Sudan ten years earlier.” Jenniskens also guided the search for fragments of 2008 TC3.

This time, fewer observations led to more uncertainty in the asteroid’s position in its orbit. Davide Farnocchia of NASA JPL’s Center for Near-Earth Object Studies combined astronomical observations of the asteroid with US Government Satellite data of the fireball to calculate the fall area. Esko Lyytinen of the Ursa Finnish Fireball Network made a parallel effort.

“When Jenniskens first arrived in Maun, he needed our help narrowing down the fall area,” says Oliver Moses of the Okavango Research Institute. “We subsequently tracked down more video records in Rakops and Maun and were able to triangulate the position of the fireball.”

After confirming the fall area, Moses and Jenniskens joined geologist Alexander Proyer of the Botswana International University of Science and Technology (BIUST) in Palapye and geoscientist Mohutsiwa Gabadirwe of the Botswana Geoscience Institute (BGI) in Lobatse and their colleagues to search for the meteorites.

“On the fifth day, our last day of searching, Lesedi Seitshiro of BIUST found the first meteorite only 30 meters from camp,” said Jenniskens. “It was 18 grams and about 3 cm in size.”

The search area was in the Central Kalahari Game Reserve, home to diverse wildlife, including leopards and lions. Researchers were kept safe by the staff of the Botswana Department of Wildlife and National Parks. BGI coordinated the search with the Department of National Museum and Monuments in Botswana.

“The meteorite is named ‘Motopi Pan’ after a local watering hole,” said Gabadirwe, now the curator of this rare sample of an asteroid observed in space before impacting Earth. “This meteorite is a national treasure of Botswana.”

The meteorite type

Non-destructive analysis at the University of Helsinki, Finland, showed that Motopi Pan belongs to the group of Howardite-Eucrite-Diogenite (HED) meteorites, known to have likely originated from the giant asteroid Vesta, which was recently studied in detail by NASA’s DAWN mission.

“We managed to measure metal content as well as secure a reflectance spectrum and X-ray elemental analysis from a thinly crusted part of the exposed meteorite interior,” said Tomas Kohout of the University of Helsinki. “All the measurements added well together and pointed to values typical for HED type meteorites.”

Dynamical studies show that the orbit of 2018 LA is consistent with an origin from the inner part of the asteroid belt where Vesta is located. The asteroid was delivered into an Earth-impacting orbit via the resonance situated in the asteroid belt’s inner side.

“Another HED meteorite fall we investigated in Turkey in 2015, called Sariçiçek, impacted on a similarly short orbit and produced mostly smallish 2 to 5-gram meteorites,” said Jenniskens.

When Jenniskens returned to Botswana in October of 2018, the team found 22 more small meteorites. Gabadirwe was the first to spot another out-of-this-world rock. Surprisingly, subsequent meteorite finds showed a lot of diversity in their outward appearance.

“We studied the petrography and mineral chemistry of five of these meteorites and confirmed that they belong to the HED group,” said Roger Gibson of Witts University in Johannesburg, South Africa. “Overall, we classified the material that asteroid 2018 LA contained as being Howardite, but some individual fragments had more affinity to Diogenites and Eucrites.”

Other studies also confirmed the surprising diversity of the team’s finds, such as reflection spectroscopy and the content of polyaromatic hydrocarbons in the sample. The asteroid was a breccia, a mixture of cemented rock pieces from different parts on Vesta.

Fragment of asteroid 2018 LA recovered in Central Kalahari Game Reserve in central Botswana. © SETI

Origin of the meteorites

A previous hypothesis proposed that Sariçiçek originated from Vesta in the collision that created the Antonia impact crater imaged by DAWN. Still showing a visible ejecta blanket, that young crater was formed about 22 million years ago. One-third of all HED meteorites that fall on Earth were ejected 22 million years ago. Did Motopi Pan originate from the same crater?

“Noble gas isotopes measurements at ETH in Zürich, Switzerland, and radioactive isotopes measured at Purdue University showed that this meteorite too had been in space as a small object for about 23 million years,” said Kees Welten of UC Berkeley, “but give or take 4 million years, so it could be from the same source crater on Vesta.”

Researchers found Motopi Pan and Sariçiçek to be similar in some ways but different in others. Like Motopi Pan, Sariçiçek exploded at 27.8 km altitude, but produced less light in that breakup.

“The infrasound shockwave measured in South Africa was not as strong as expected from US Government sensor detections of the bright light,” said Peter Brown of the University of Western Ontario, Canada.

From lead isotopes in zircon minerals, researchers found that both Sariçiçek and Motopi Pan solidified at Vesta’s surface about 4563 million years ago. But phosphate grains in Motopi Pan experienced another melting event more recently. Sariçiçek did not.

“About 4234 million years ago, the material in Motopi Pan was close to the center of a large impact event,” said Qing-zhu Yin of UC Davis, “Sariçiçek was not.”

Vesta experienced two significant impact events that created the Rheasilvia impact basin and the underlying, and therefore older, Veneneia impact basin.

“We now suspect that Motopi Pan was heated by the Veneneia impact, while the subsequent Rheasilvia impact scattered this material around,” said Jenniskens. ” If so, that would date the Veneneia impact to about 4234 million years ago. On top of Rheasilvia impact ejecta is the 10.3-km diameter Rubria impact crater, slightly smaller than the 16.7-km Antonia crater, and slightly younger at 19 +/- 3 million years, but a good candidate for the origin crater of Motopi Pan.”

In November 2020, an expedition led by Fulvio Franchi from BIUST discovered one more Motopi Pan meteorite. This 92-gram meteorite is now the largest fragment of asteroid 2018 LA recovered to date and another small piece of the giant asteroid Vesta.

Featured image: Mohutsiwa Gabadirwe (center of photo) and Peter Jenniskens (left, kneeling) at the site of the second find of a piece of asteroid 2018 LA recovered in the Central Kalahari Game Reserve in central Botswana. © SETI


Links:

The manuscript is available at: https://onlinelibrary.wiley.com/doi/full/10.1111/maps.13653


Provided by SETI Institute


About the SETI Institute

Founded in 1984, the SETI Institute is a non-profit, multi-disciplinary research and education organization whose mission is to explore, understand, and explain the origin and nature of life in the universe and the evolution of intelligence. Our research encompasses the physical and biological sciences and leverages expertise in data analytics, machine learning and advanced signal detection technologies. The SETI Institute is a distinguished research partner for industry, academia and government agencies, including NASA and NSF.

Different Neutron Energies Enhance Asteroid Deflection (Planetary Science)

A research collaboration between Lawrence Livermore National Laboratory (LLNL) and the Air Force Institute of Technology (AFIT) investigates how the neutron energy output from a nuclear device detonation can affect the deflection of an asteroid.

Scientists compared the resulting asteroid deflection from two different neutron energy sources, representative of fission and fusion neutrons, allowing for side-by-side comparisons. The goal was to understand which neutron energies released from a nuclear explosion are better for deflecting an asteroid and why, potentially paving the way for optimized deflection performance.  

The work is featured in Acta Astronautica and was led by Lansing Horan IV, as part of a collaboration with LLNL’s Planetary Defense and Weapon Output groups during his nuclear engineering master’s program at AFIT. Co-authors from LLNL include Megan Bruck Syal and Joseph Wasem from LLNL’s Weapons and Complex Integration Principal Directorate, and the co-authors from AFIT include Darren Holland and Maj. James Bevins.

Horan said the research team focused on the neutron radiation from a nuclear detonation since neutrons can be more penetrative than X-rays.

“This means that a neutron yield can potentially heat greater amounts of asteroid surface material, and therefore be more effective for deflecting asteroids than an X-ray yield,” he said.

Neutrons of different energies can interact with the same material through different interaction mechanisms. By changing the distribution and intensity of the deposited energy, the resulting asteroid deflection also can be affected.

The research shows that the energy deposition profiles — which map the spatial locations at and beneath the asteroid’s curved surface, where energy is deposited in varying distributions — can be quite different between the two neutron energies that were compared in this work. When the deposited energy is distributed differently in the asteroid, this means that the melted/vaporized blow-off debris can change in amount and speed, which is what ultimately determines the asteroid’s resulting velocity change.

Defeating an asteroid

Horan said there are two basic options in defeating an asteroid: disruption or deflection.

Disruption is the approach of imparting so much energy to the asteroid that it is robustly shattered into many fragments moving at extreme speeds.

“Past work found that more than 99.5 percent of the original asteroid’s mass would miss the Earth,” he said. “This disruption path would likely be considered if the warning time before an asteroid impact is short and/or the asteroid is relatively small.”

Deflection is the gentler approach, which involves imparting a smaller amount of energy to the asteroid, keeping the object intact and pushing it onto a slightly different orbit with a slightly changed speed.

“Over time, with many years prior to impact, even a miniscule velocity change could add up to an Earth-missing distance,” Horan said. “Deflection might generally be preferred as the safer and more ‘elegant’ option, if we have sufficient warning time to enact this sort of response. This is why our work focused on deflection.”

Connecting energy deposition to asteroid response

The work was conducted in two primary phases that included neutron energy deposition and asteroid deflective response.

For the energy deposition phase, Los Alamos National Laboratory’s Monte Carlo N-Particle (MCNP) radiation-transport code was used to simulate all of the different case studies that were compared in this research. MCNP simulated a standoff detonation of neutrons that radiated toward a 300 m SiO2 (silicon oxide) spherical asteroid. The asteroid was divided by hundreds of concentric spheres and encapsulated cones to form hundreds of thousands of cells, and energy deposition was tallied and tracked for each individual cell in order to generate the energy deposition profiles or spatial distributions of energy throughout the asteroid.

For the asteroid deflection phase, LLNL’s 2D and 3D Arbitrary Lagrangian-Eulerian (ALE3D) hydrodynamics code was used to simulate the asteroid material’s response to the considered energy depositions. The MCNP-generated energy deposition profiles were imported and mapped into the ALE3D asteroid in order to initialize the simulations. The resulting deflection velocity change was obtained for various configurations of neutron yields and neutron energies, allowing for the effect of the neutron energy on the resulting deflection to be quantified.

One small step for deflection

Horan said the work is one small step forward for nuclear deflection simulations.

“One ultimate goal would be to determine the optimal neutron energy spectrum, the spread of neutron energy outputs that deposit their energies in the most ideal way to maximize the resulting velocity change or deflection,” he said. “This paper reveals that the specific neutron energy output can impact the asteroid deflection performance, and why this occurs, serving as a stepping stone toward the larger goal.”

Horan said the research showed that precision and accuracy in the energy deposition data is important. “If the energy deposition input is incorrect, we should not have much confidence in the asteroid deflection output,” he said. “We now know that the energy deposition profile is most important for large yields that would be used to deflect large asteroids.”

He said if there were to be a plan to mitigate a large incoming asteroid, the energy deposition spatial profile should be accounted for to correctly model the expected asteroid velocity change.

“On the other hand, the energy coupling efficiency is always important to consider, even for low yields against small asteroids,” he said. “We found that the energy deposition magnitude is the factor that most strongly predicts the overall asteroid deflection, influencing the final velocity change more than the spatial distribution does.”

For planning an asteroid mitigation mission, it will be necessary to account for these energy parameters to have correct simulations and expectations.

“It is important that we further research and understand all asteroid mitigation technologies in order to maximize the tools in our toolkit,” Horan said. “In certain scenarios, using a nuclear device to deflect an asteroid would come with several advantages over non-nuclear alternatives. In fact, if the warning time is short and/or the incident asteroid is large, a nuclear explosive might be our only practical option for deflection and/or disruption.”

Featured image: A standoff detonation of a nuclear device irradiates an asteroid and deposits energy at and beneath the surface. In this work, two neutron yields (50 kt and 1 Mt) and two neutron energies (14.1 MeV and 1 MeV) were the primary case studies compared side-by-side. The black dots represent the location of the standoff nuclear device. The colors in the asteroids show the intensities and distributions of differing neutron energy depositions. The dark blue color indicates where the asteroid remains solid. All other colors are where material is melted and/or vaporized, which allows for blow-off debris to be ejected, changing the asteroid’s velocity and deflecting it. Note that the asteroid considered in this research was 300 meters in diameter, but the visuals above show much smaller asteroids with 0.8m and 5m diameters — this is solely for the purpose of visualization, to enlarge the area of the energy deposition © LLNL


Reference: Lansing S. Horan, Darren E. Holland, Megan Bruck Syal, James E. Bevins, Joseph V. Wasem, Impact of neutron energy on asteroid deflection performance, Acta Astronautica, Volume 183, 2021, Pages 29-42, ISSN 0094-5765, https://doi.org/10.1016/j.actaastro.2021.02.028. (https://www.sciencedirect.com/science/article/pii/S0094576521001028)


Provided by LLNL

NASA OSIRIS-REx’s Final Asteroid Observation Run (Planetary Science)

NASA’s OSIRIS-REx mission is on the brink of discovering the extent of the mess it made on asteroid Bennu’s surface during last fall’s sample collection event. On Apr. 7, the OSIRIS-REx spacecraft will get one last close encounter with Bennu as it performs a final flyover to capture images of the asteroid’s surface. While performing the flyover, the spacecraft will observe Bennu from a distance of about 2.3 miles (3.7 km) – the closest it’s been since the Touch-and-Go Sample Collection event on Oct. 20, 2020.

The OSIRIS-REx team decided to add this last flyover after Bennu’s surface was significantly disturbed by the sample collection event. During touchdown, the spacecraft’s sampling head sunk 1.6 feet (48.8 centimeters) into the asteroid’s surface and simultaneously fired a pressurized charge of nitrogen gas. The spacecraft’s thrusters also mobilized a substantial amount of surface material during the back-away burn. Because Bennu’s gravity is so weak, these various forces from the spacecraft had a dramatic effect on the sample site – launching many of the region’s rocks and a lot of dust in the process. This final flyby of Bennu will provide the mission team an opportunity to learn how the spacecraft’s contact with Bennu’s surface altered the sample site and the region surrounding it.

The single flyby will mimic one of the observation sequences conducted during the mission’s Detailed Survey phase in 2019. OSIRIS-REx will image Bennu for 5.9 hours, which is just over a full rotation period of the asteroid. Within this timeframe, the spacecraft’s PolyCam imager will obtain high-resolution images of Bennu’s northern and southern hemispheres and its equatorial region. The team will then compare these new images with the previous high-resolution imagery of the asteroid obtained during 2019.

Most of the spacecraft’s other science instruments will also collect data during the flyover, including the MapCam imager, the OSIRIS-REx Thermal Emission Spectrometer (OTES), the OSIRIS-REx Visible and Infrared Spectrometer (OVIRS), and the OSIRIS-REx Laser Altimeter (OLA). Exercising these instruments will give the team a chance to assess the current state of each science instrument onboard the spacecraft, as dust coated the instruments during the sample collection event. Understanding the health of the instruments is also part of NASA’s evaluation of possible extended mission opportunities after the sample is delivered to Earth.

After the Bennu flyby, it will take several days for the data from the flyover to be downlinked to Earth. Once the data are downlinked, the team will inspect the images to understand how OSIRIS-REx disturbed the asteroid’s surface material. At this point, the team will also be able to evaluate the performance of the science instruments.

The spacecraft will remain in asteroid Bennu’s vicinity until May 10, when the mission will enter its Return Cruise phase and begin its two-year journey back to Earth. As it approaches Earth, the spacecraft will jettison the Sample Return Capsule (SRC) that contains the rocks and dust collected from Bennu. The SRC will then travel through the Earth’s atmosphere and land under parachutes at the Utah Test and Training Range on Sep. 24, 2023.

Once recovered, the capsule will be transported to the curation facility at the agency’s Johnson Space Center in Houston, where the sample will be removed for distribution to laboratories worldwide, enabling scientists to study the formation of our solar system and Earth as a habitable planet.

NASA’s Goddard Space Flight Center in Greenbelt, Maryland, provides overall mission management, systems engineering, and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator, and the University of Arizona also leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Denver built the spacecraft and provides 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, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.

Featured image: This artist’s concept shows the planned flight path of NASA’s OSIRIS-REx spacecraft during its final flyby of asteroid Bennu, which is scheduled for April 7. Credits: NASA/Goddard/University of Arizona


Provided by NASA

Scientists Determine the Origin of Extra-solar Object ‘Oumuamua’ (Planetary Science)

In 2017, the first interstellar object from beyond our solar system was discovered via the Pan-STARRS astronomical observatory in Hawaii. It was named ‘Oumuamua, meaning “scout” or “messenger” in Hawaiian. The object was like a comet, but with features that were just odd enough to defy classification.

Two Arizona State University astrophysicists, Steven Desch and Alan Jackson of the School of Earth and Space Exploration, set out to explain the odd features of ‘Oumuamua and have determined that it is likely a piece of a Pluto-like planet from another solar system. Their findings have been recently published in a pair of papers in the AGU Journal of Geophysical Research: Planets.

“In many ways ‘Oumuamua resembled a comet, but it was peculiar enough in several ways that mystery surrounded its nature, and speculation ran rampant about what it was,” said Desch, who is a professor in the School of Earth and Space Exploration.

From observations of the object, Desch and Jackson determined several characteristics of the object that differed from what would be expected from a comet.

In terms of speed, the object entered the solar system at a velocity a bit lower than would be expected, indicating that it had not been traveling in interstellar space for more than a billion years or so. In terms of size, its pancake shape was also more flattened than any other known solar system object.

They also observed that while the object acquired a slight push away from the sun (a “rocket effect” common in comets as sunlight vaporizes the ices they are made of), the push was stronger than could be accounted for. Finally, the object lacked a detectable escaping gas, which is usually depicted visibly by a comet’s tail. In all, the object was very much like a comet, but unlike any comet that had ever been observed in the solar system.

Desch and Jackson then hypothesized that the object was made of different ices and they calculated how quickly these ices would sublimate (passing from a solid to a gas) as ‘Oumuamua passed by the sun. From there, they calculated the rocket effect, the object’s mass and shape, and the reflectivity of the ices.

Credit: Arizona State University

“That was an exciting moment for us,” Desch said. “We realized that a chunk of ice would be much more reflective than people were assuming, which meant it could be smaller. The same rocket effect would then give ‘Oumuamua a bigger push, bigger than comets usually experience.”

Desch and Jackson found one ice in particular—solid nitrogen—that provided an exact match to all the object’s features simultaneously. And since solid nitrogen ice can be seen on the surface of Pluto, it is possible that a cometlike object could be made of the same material.

“We knew we had hit on the right idea when we completed the calculation for what albedo (how reflective the body is) would make the motion of ‘Oumuamua match the observations,” said Jackson, who is a research scientist and an Exploration Fellow at ASU. “That value came out as being the same as we observe on the surface of Pluto or Triton, bodies covered in nitrogen ice.”

They then calculated the rate at which chunks of solid nitrogen ice would have been knocked off the surfaces of Pluto and similar bodies early in our solar system’s history. And they calculated the probability that chunks of solid nitrogen ice from other solar systems would reach ours.

“It was likely knocked off the surface by an impact about half a billion years ago and thrown out of its parent system,” Jackson said. “Being made of frozen nitrogen also explains the unusual shape of ‘Oumuamua. As the outer layers of nitrogen ice evaporated, the shape of the body would have become progressively more flattened, just like a bar of soap does as the outer layers get rubbed off through use.”

Could ‘Oumuamua have been alien technology?

Although ‘Oumuamua’s cometlike nature was quickly recognized, the inability to immediately explain it in detail led to speculation that it is a piece of alien technology, as in the recently published book “Extraterrestrial: The First Signs of Intelligent Life Beyond Earth” by Avi Loeb of Harvard University.

Illustration of a plausible history for ‘Oumuamua: Origin in its parent system around 0.4 billion years ago; erosion by cosmic rays during its journey to the solar system; and passage through the solar system, including its closest approach to the Sun on Sept. 9, 2017, and its discovery on October 2017. At each point along its history, this illustration shows the predicted size of ‘Oumuamua, and the ratio between its longest and shortest dimensions. Credit: S. Selkirk/ASU

This has sparked a public debate about the scientific method and the responsibility of scientists not to jump to unwarranted conclusions.

“Everybody is interested in aliens, and it was inevitable that this first object outside the solar system would make people think of aliens,” Desch said. “But it’s important in science not to jump to conclusions. It took two or three years to figure out a natural explanation—a chunk of nitrogen ice—that matches everything we know about ‘Oumuamua. That’s not that long in science, and far too soon to say we had exhausted all natural explanations.”

Although there is no evidence that it is alien technology, as a fragment of a Pluto-like planet, ‘Oumuamua has provided scientists with a special opportunity to look at extrasolar systems in a way that they have not been able to before. As more objects like ‘Oumuamua are found and studied, scientists can continue to expand our understanding of what other planetary systems are like and the ways in which they are similar to, or different from, our own solar system.

“This research is exciting in that we’ve probably resolved the mystery of what ‘Oumuamua is and we can reasonably identify it as a chunk of an ‘exo-Pluto,’ a Pluto-like planet in another solar system,” Desch said. “Until now, we’ve had no way to know if other solar systems have Pluto-like planets, but now we have seen a chunk of one pass by Earth.”

Desch and Jackson hope that future telescopes, like those at the Vera Rubin Observatory/Large Synoptic Survey Telescope in Chile, which will be able to survey the entire southern sky on a regular basis, will be able to start finding even more interstellar objects that they and other scientists can use to further test their ideas.

“It’s hoped that in a decade or so we can acquire statistics on what sorts of objects pass through the solar system, and if nitrogen ice chunks are rare or as common as we’ve calculated,” Jackson said. “Either way, we should be able to learn a lot about other solar systems, and whether they underwent the same sorts of collisional histories that ours did.”

Featured image: This painting by William K. Hartmann, who is a senior scientist emeritus at the Planetary Science Institute in Tucson, Arizona, is based on a commission from Michael Belton and shows a concept of the ‘Oumuamua object as a pancake-shaped disk. Credit: William Hartmann


References: (1) Alan P. Jackson et al. 1I/’Oumuamua as an N 2 ice fragment of an exo‐Pluto surface: I. Size and Compositional Constraints, Journal of Geophysical Research: Planets (2021). DOI: 10.1029/2020JE006706 https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JE006706 (2) S. J Desch et al. 1I/’Oumuamua as an N 2 ice fragment of an exo‐pluto surface II: Generation of N 2 ice fragments and the origin of ‘Oumuamua, Journal of Geophysical Research: Planets (2021). DOI: 10.1029/2020JE006807 https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JE006807


Provided by University of Arizona

What Is The Mass and Density of Asteroid (16) Psyche? Astronomers Provide New Insights (Planetary Science)

Asteroid (16) Psyche is currently of great interest to the planetary science community as it is the target of NASA’s eponymous Psyche mission currently scheduled to be launched in 2022. This interest stems from the fact that the asteroid is currently believed to be a metallic asteroid and potentially the exposed core of a protoplanet due to both its relatively high bulk density as well as surface properties based on spectroscopic and radar observations. There have, however, been concerns that Psyche’s relatively high bulk density of approximately 4 g/cm3 is still too low to be consistent with iron meteorites and that the asteroid may instead have a stony-iron composition and could thus be a parent body for mesosiderites. Ferrovolcanic activity has recently been suggested as an alternative mechanism that would explain the observational data on Psyche. Ferrovolcanism would cause Psyche’s surface to consist of stony mantle surrounded by a metallic surface layer resulting from past eruptions of molten iron. This theory is consistent with both a relatively low bulk density and a metalrich surface composition.

Figure 1. Probability distribution for the mass of Psyche. The upper x-axis shows the bulk density that corresponds to the mass on the lower x axis assuming a volume-equivalent diameter of 222 km. They note that the bulk density does not take the diameter’s uncertainty into account. The dashed vertical lines represent our 1σ limits whereas the black curve represents a kernel density estimate fitted to the normalized histogram. © Siltala & Granvik

Now, Siltala and Granvik by applying their novel Markov-chain Monte Carlo (MCMC)-based algorithm computed asteroid (16) Psyche mass. They estimated the mass of (1.117 ± 0.039)×10¯11 M for asteroid (16) Psyche which corresponds to a bulk density of (3.88 ± 0.25) g/cm3. This is lower than reported by most other studies. The estimated bulk density rules out the possibility of Psyche being an exposed, solid iron core of a protoplanet, but is fully consistent with the recent hypothesis that ferrovolcanism would have occurred on Psyche.

“We expect that astrometry from, e.g., the Gaia mission will provide further constraints on the mass and bulk density in the future.”

— said Siltala, lead author of the study

In addition, they have successfully tested their algorithm by obtaining masses of (4.73±0.02) × 10¯10 M and (1.27±0.02)×10¯10 M for Ceres and Vesta, respectively, that are in agreement with the accurate estimates produced by the Dawn mission.

Featured image: An artist’s concept of asteroid 16 Psyche. Credit: Maxar/ASU/P.Rubin/NASA/JPL-Caltech


Reference: Lauri Siltala, Mikael Granvik, “Mass and Density of Asteroid (16) Psyche”, ArXiv, 2021. https://arxiv.org/abs/2103.01707


Copyright of this article totally belongs to our author S. Aman. One is allowed to reuse it only by giving proper credit either to him or to us.