Comets, asteroids and meteors may be considered as the debris of the solar system. They are members of the group of objects known as Small Solar System Bodies, which are any solar system body too small to meet the definition of either a planet or dwarf planet. The CAM Section is involved in the observation of these bodies, which are important to our understanding of the formation and evolution of our solar system.
Definition of terms
The following definitions are from those accepted by the IAU.
An asteroid, also known as a minor planet, is an irregularly shaped rocky body orbiting the Sun that does not meet the definition of either a planet or dwarf planet.
A comet is a small body orbiting the Sun, and comprising a substantial fraction of its composition as volatile matter, which can sublimate under the effect of solar radiation to form a coma.
A meteoroid is a solid natural object of a size roughly between 30 µm and 1m moving in, or coming from, interplanetary space.
A meteor is the light and associated physical phenomena (heat, shock, ionization), which result from the high speed entry of a solid object from space into a gaseous atmosphere. A meteor brighter than visual magnitude –4 is termed a bolide or a fireball.
A meteorite – is any natural solid object that survived the meteor phase in a gaseous atmosphere without being completely vaporized.
A meteor shower is a group of meteors produced by meteoroids of the same meteoroid stream, and may be formed by either a comet or asteroid.
What observations can be made?
The Section is involved with the following observations:
Comets – for observations to be of scientific value the observer should concentrate on:
- Estimates of the total visual magnitude of the comet, preferably made over the entire apparition to allow construction of a light curve
- Estimates of the diameter of the coma
- Estimates of the degree of condensation of the comet
- Estimates of the length and position angle of the tail
- Detailed visual descriptions, sketches and photographs of the comet
A guide to observing comets can be found here: Observing Comets
Asteroids – determination of size and shape by timing occultations of stars by asteroids, light curve studies to determine rotation rates.
Meteors – visual counts in order to determine time of maxima and generate activity profiles of showers, recording of shower meteor magnitudes to determine population index, and plotting of meteors to determine radiant position and structure. In addition the Section participates in global video monitoring networks, in order to detect new meteor streams and confirm showers listed by the IAU Meteor Data Centre (MDC).
A guide to observing meteors can be found here: Observing Meteors
Fireballs – any meteor of magnitude -4 or brighter should be reported
A form for reporting fireballs can be found here: Report a Sighting
A diary of events and observing details for specific events is published regularly in CAMnotes.
The latest issue can be found here:
Observers that would like to contribute to Section activities or requiring more information can contact the Director at CAMassa.saao.ac.za
The Botswana super-bolide and meteorites from asteroid 2018 LA
Meteorite MP-19, found by Tim Cooper in Central Kalahari Game Reserve on October 12, 2018. Image courtesy Dr Peter Jenniskens.
Almost three years since the entry of asteroid 2018 LA into the atmosphere over Botswana on June 2, 2018, the scientific results generated by sixty-six authors, collectively known as the ‘2018 LA Consortium’, and after an in-depth analysis of the recovered meteorites from 2018 LA, are now out in an article in Meteoritics and Planetary Science.
Discovered just a few hours earlier, asteroid 2018 LA entered earth’s atmosphere at 16h44 UT, and resulted in a bolide which reached magnitude -23 during its disruption at an altitude of 27.8 km. The resultant explosion deposited meteorites over a strewn field located in the northern part of the Central Kalahari Game Reserve (CKGR) in Botswana. Several videos were secured which captured the visible passage of the bolide, including the bright explosion, which enabled a precise determination of the location at which the disruption occurred. The screen grabs at right show the passage as seen from a commercial property in Gaborone just prior to the disruption of the meteor.
ASSA’s Tim Cooper calibrated videos of the bolide to help determine the location of the strewn field and also calibrated the footage which enabled photometry and subsequently the construction of the light curve of the meteor. An initial search during June 18-23, 2018 found one meteorite (MP-01), now referred to as Motopi Pan. Following revised astrometry, a new search was mounted with a team comprising members from the Botswana Geophysics Institute, Okavango Research Institute, Department of National Museum and Monuments (Botswana), the Department of Wildlife & National Parks, the Astronomical Society of Southern Africa (ASSA) and under the guidance of meteor astronomer Dr Peter Jenniskens from the SETI Institute. The search during October 9-12, 2018 found an additional 22 fragments of asteroid 2018 LA, all collectively known as Motopi Pan, and including fragment MP-19 (image top left) found by Tim Cooper on October 12, 2018. The discovery of these fragments now enabled a complete characterisation of the meteorites from asteroid 2018 LA, and determination of its origin in the solar system.
Following extensive analysis using multiple techniques, these show the Motopi Pan meteorite to be a HED polymict breccia derived from howardite, eucrite, and diogenite lithologies.
The findings and pre-atmospheric orbit are consistent with an origin for Motopi Pan at asteroid 4 Vesta, possibly from the 10 km crater Rubria (left image) during an impact ~22 Ma ago.
The full scientific results and findings can be found in the Meteoritics and Planetary Science article. The full story of the appearance of the bolide, eye-witness accounts, analysis of video footage to determine the strewn field location, measurement of the brightness of the meteor, and the October 2018 search for meteorites from asteroid 2018 LA will appear in the June issue of MNASSA.
Members of the October 2018 search team which found an additional 22 fragments of the Motopi Pan meteorite. Standing left to right Tim Cooper (ASSA), Oliver Moses (ORI), Mohutsiwe Gabadirwe (BGI), Thebe Kemosedile (ORI), Sarah Tsenene (DWNP), Kabelo Dikole (BGI), Mosarwa Babutsi (Botswana National Museum, Gaborone), kneeling Kagiso Kgetse (DWNP) and Peter Jenniskens (SETI Institute). ASSA = Astronomical Society of Southern Africa, BGI = Botswana Geoscience Institute, ORI = Okavango Research Institute of the University of Botswana at Maun, DWNP = Department of Wildlife and National Parks. Photo by team member Odirile Sempho.