2024 Occultations by Near-Earth Asteroids - New 2024 January 3
In early January, there are important good occultations by the Hayabusa-2 extended mission target (98943) 2001 CC21
In 2022 October, a large expedition in Japan observed a significant shift during an occultation by (3200) Phaethon, so 4 occultations in North America this year are now of great interest, to better understand the evolution of the orbit of this important object
The Asteroids, Comets, Meteors Conference (ACM 2023) in Flagstaff, Arizona brought major asteroid scientists and occultation workers from around the world together in June 2023.
One paper there, about the 20 most dangerous km-sized asteroids during the next 1000 years, gives us important new targets for occultations
These occultations are described and illustrated (with maps and tables) in this .pdf document. There are hot links to external Web pages, but links to internal files, especially the .xml input files used by the Occult program, are given at the bottom of this page. At the bottom is a link to another Web page that has links to papers and presentations about NEA occultations that gives useful background information. Especially for those less familiar with occultations, some good links are in the short "Basic Information" section below. Important is a description of the Google Earth files set up to follow terrain with parallel "fence" lines to coordinate site selection to optimize coverage for NEA occultations (since this currently can not be done with Occult Watcher), and the links for Occult input data for generating your own local predictions, are all given after the sections below _ _ _ Early January occultations by (98943) 2001 CC21 Here are the OW cloud links for the events on Jan. 4, 6, and 7: Jan. 4 Jan. 6 Jan. 7 Occult maps are in the .pdf document, but also given below: Jan. 4 Jan. 6 Jan. 7 The Google Earth files with parallel fence lines that correct for elevation above sea level are linked to below: Jan. 4 Jan. 6 Jan. 7 See the section below: GOOGLE EARTH FILES FOR NEA OCCULTATIONS for an explanation of using the Google Earth files. If you might be able to try one of these events (or later ones), please send me (David) an email at dunham@starpower.net so we can coordinate coverage with unique line assignments. _ _ _ THE GOAL FOR (98943) 2001 CC21 This estimated 600m NEA is a flyby target of the Hayabusa2 extended mission (the flyby will occur in July 2026). The Japanese space agency JAXA is interested in characterizing 2001 CC21 that is currently occulting many stars. The goal now is to obtain a FIRST GOOD detection of the asteroid via an occultation, in a situation like we were with Didymos before radar and DART tracking refined its orbit in 2022 September. The current 1-sigma uncertainty is over 6 path-widths, with typical event rank of 8 on Occult Watcher. We are trying to cover the sky plane around the current best orbit in a semi-organized fashion, but the changing direction of the object's motion complicates this. Six large expeditions were mounted in Japan in early 2023; 2 were clouded out and the others had 10 and 12 stations that had no occultation, except for an event on 2023 Mar. 5 that had one positive that was used to update the orbit. Unfortunately, that star had a high Gaia RUWE, and a larger-than- expected error, which caused the new orbit to be wrong, with all observers having no occultation for the subsequent events that were attempted. Now in early 2024, we have more opportunities, although the durations are quite short; those will improve later this year. Once anyone records an occultation of a Gaia star with a good astrometric solution (RUWE <1.4) by the object, the orbit can be determined well enough that subsequent efforts will be successful with only a few observers. For now, we need to cover the predicted paths as best we can out to 12 or more path-widths (to 2-sigma or better) when possible. _ _ _ OTHER NEA OCCULTATIONS - FUTURE EMPHASIS ON MOST THREATENING PHAs Besides Didymos and Phaethon, other events considered were from a new list of asteroids that are potentially hazardous during the next 1000 years, according to a presentation from the Asteroids, Comets, Meteors (ACM) meeting; the abstract for the talk lists 20 objects 1km across or larger whose mean orbit intersection distance (MOID) with Earth will pass through zero during the next 1000 years, and whose current orbit is indeterminant (error in the mean anomaly becomes greater than 180 deg.) within the next few hundred years due to accumulation of the current uncertainty in the mean motion of the object's orbit. So these objects are most important to observe with high-precision observations (occultations and radar) to reduce the current errors in their orbital elements, to enable more accurate propagation of their orbits to see if there might be any possible collisions when the MOID for them becomes very small. Early efforts concentrated on 9 objects, including (4179) Toutatis, (4183) Cuno, (5011) Ptah, (7092) Cadmus, (7482) 1994 PC1, (66391) Moshup, (143404) 2003 BD44, (143651) 2003 QO104, and (314082) Dryope. But in our 2024 NEA prediction files, we consider all 20 objects in the list. _ _ _ BASIC INFORMATION ON HOW TO RECORD OCCULTATIONS For those less familiar with recording occultations, you can learn about the main techniques, equipment, and software currently used in a good primer by George Viscome. Some more detailed information can be found in the observing tab of IOTA's main Web site. WEATHER FORECASTS Usually, we will provide little, if any, cloud cover forecast information on the event Web pages, like we did for some previous events. Mobile observers are encouraged to get their own cloud cover forecasts for their target areas, using Web sites and advice that I give on this cloud-cover forecast Web page. _ _ _ GOOGLE EARTH FILES FOR NEA OCCULTATIONS Since the paths for these events are all very narrow, one must travel to the paths with mobile equipment to observe them, rather like grazing occultations of stars by the Moon. And like lunar grazes, it is necessary to adjust the location for elevation above sea level. John Irwin in the UK has helped IOTA with this by supplying special Google Earth files that take elevation into account. Consequently, we can not use Occult Watcher (OW) for these events, since OW does not take elevation into account. Instead, we use the Google Earth (GE) files by J. Irwin that he describes in this .pdf document. In Dec. 2022, Dave Herald updated his Occult4 program to generate GE files similar to John Irwins, but Dave uses the same color scheme used in other parts of the program, so unlike Irwin, Heralds central line is green, the limits are dark blue, and the 1-sigma limits are red. The parallel fence lines for observers are light yellow and can be set up with a specified spacing on the sky plane and a specified number from either side of center. But unlike Irwins GE file, the Occult one does not include lines for the occultation by Dimorphos, so Irwins file is preferred for Didymos events. However, they are fine for NEAs with no known moons, such as for (98943) 2001 CC21. _ _ _ _ _ _ OCCULT INPUT .XML FILES FOR 2024 IOTAs Occult4 program is a free comprehensive occultation prediction program for Windows systems. You can use it with the input files below to generate your own predictions for your observatory or region, as described in this .pdf document. It describes a prediction input file for planetary and asteroidal files called All2023.xml. You can use that file to generate local predictions for many mainly main-belt occultations, but you can replace it with the other files listed below to generate predictions for more occultations, mainly of fainter stars than shown on the maps, or for other parts of the world: When you open these files with your Web browser, you should get a display that looks like this. The larger files may take a couple of minutes to show this appearance, showing a messed-up display before then. Once the proper view appears, right-click anywhere on the display, then "Save as" to a directory on your computer; the best directory is the \Asteroid\ subdirectory in your Occult\ directory. Always, to get the latest orbit update, you should view the event with Occult Watcher (OW) , or its OW cloud page. For the 23 NEA events mapped and tabulated in the main .pdf document But these all use orbits from August 2023; better orbits are now available for most of them via Occult Watcher. About 137 NEA events for N. America of stars brighter than mag. 13. 4242 Worldwide selected NEA occultations to mag. 14, including occultations by the NEA's listed in the .pdf document and 2005 UD (a Phaethon-like small extended mission target of DESTINY+) but NOT any of the 20 most threatening NEAs described above. Worldwide main belt (and many NEA) events from Steve Preston - for them, prediction maps and data are available at https://www.asteroidoccultation.com/. Worldwide NEA events from Steve Preston - when unzipped, there are 12 files with monthly NEA occultation events worldwide. They include most NEA events, including by the 20 "most hazardous" ones. OTHER IOTA ASTEROIDAL OCCULTATION PREDICTION WEB SITES for 2024 Bright Main-Belt Asteroids, has links to the others and see it for corrections to the printed RASC Observers Handbook for 2024; several pages about occultations are affected. Trojan Asteroids (Lucy targets are emphasized) Selected Special Main-Belt Asteroids IOTA main asteroidal occultations predictions ______ MORE INFORMATION ON NEA OCCULTATIONS is given with many links and discussion on this Web page. ______ David and Joan Dunham, 2024 January 3 e-mail: dunham@starpower.net cell phone: 301-526-5590