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

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