(6478) Gault::Physical characterization of an active main-belt asteroid

In December 2018, the main-belt asteroid (6478) Gault was reported to display activity. Gault is an asteroid belonging to the Phocaea dynamical family and was not previously known to be active, nor was any other member of the Phocaea family. In this work we present the results of photometric and spectroscopic observations that commenced soon after the discovery of activity. We obtained observations over two apparitions to monitor its activity, rotation period, composition, and possible non-gravitational orbital evolution. We find that Gault has a rotation period of P = 2.4929 ± 0.0003 hours with a lightcurve amplitude of 0.06 magnitude. This short rotation period close to the spin barrier limit is consistent with Gault having a density no smaller than ρ = 1.85 g cm−3 and its activity being triggered by the YORP spin-up mechanism. Analysis of the Gault phase curve over phase angles ranging from 0.4○ to 23.6○ provides an absolute magnitude of H = 14.81 ± 0.04, G1 = 0.25 ± 0.07, and G2 = 0.38 ± 0.04. Model fits to the phase curve find the surface regolith grain size constrained between 100-500 μm. Using relations between the phase curve and albedo we determine that the geometrical albedo of Gault is pv = 0.26 ± 0.05 corresponding to an equivalent diameter of D=2.8+0.4−0.2 km. Our spectroscopic observations are all consistent with an ordinary chondrite-like composition (S, or Q-type in the Bus-DeMeo taxonomic classification). A search through archival photographic plate surveys found previously unidentified detections of Gault dating back to 1957 and 1958. Only the latter had been digitized, which we measured to nearly double the observation arc of Gault. Finally, we did not find any signal of activity during the 2020 apparition or non-gravitational effects on its orbit

Exogenous Material on Asteroids

The Almahata Sitta meteorites produced from the breakup of 2008 TC3 were highly unusual, as the stones contained various meteorite types, with stones spanning almost every meteorite petrologic type. This was considered a remarkable event at the time since meteorites of different types had never been found among the same fall before. However, new discoveries of exogenous material on (4) Vesta, (101955) Bennu, and (162173) Ryugu in subsequent years imply that this event may be more common than initially thought. This is unexpected due to the high average collisional velocity in the asteroid belt of ~5 km/s. High velocity impacts are more likely to have low impact retention efficiencies, which lowers the likelihood of xenoliths surviving the collision. Our understanding of this material and the mechanisms by which it is delivered can give insights into the dynamic histories of these asteroids and even the greater dynamic history of the asteroid belt

ASSESSMENT OF THE DEEP SEA WRECK USS INDEPENDENCE

As part of ongoing efforts to better understand the nature of shipwrecks in National Marine Sanctuaries which may pose some level of pollution risk, and in this case, to definitively locate what is likely the only shipwreck in a sanctuary involved in both nuclear testing and nuclear waste disposal, NOAA’s Office of National Marine Sanctuaries collaborated with NOAA’s Office of Ocean Exploration and The Boeing Company, which provided their autonomous underwater vehicle, Echo Ranger, to conduct the first deep-water archaeological survey of the scuttled aircraft carrier USS Independence in the waters of Monterey Bay National Marine Sanctuary (MBNMS) in March 2015. The presence of the deep-sea scuttled radioactive aircraft carrier USS Independence off the California coast has been the source of consistent media speculation and public concern for decades. The survey confirmed that a sonar target charted at the location was Independence, and provided details on the condition of the wreck, and revealed no detectable levels of radioactivity. At the same time, new information from declassified government reports provided more detail on Independence’s use as a naval test craft for radiological decontamination as well as its use as a repository for radioactive materials at the time of its scuttling in 1951. While further surveys may reveal more, physical assessment and focused archival work has demonstrated that the level of concern and speculation of danger from either a radioactive or oil pollution threat posed may be exaggerated

NIUST AUV\u27s Study Shipwrecks In the Northern Gulf of Mexico

In October 2009 two autonomous underwater vehicles (AUV\u27s), the explorer class Eagle Ray and the seabed class Mola Mola, were launched from the NOAA ship Nancy Foster to locate and retrieve information about sunken ships of historic interest, some of which had disappeared below the water surface of the northern Gulf of Mexico, almost 200 years ago. In a collaboration between the National Institute for Undersea Science and Technology (NIUST,) the US Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE) and the US NOAA Office of Ocean Exploration and Research (OER), targets identified in side scan sonar images, were selected and investigated by the AUVs. Eagle Ray, due to its large size and design features, performed initial multibeam surveys of the target areas, producing high-resolution maps of the seafloor. These maps were used to determine safe working areas for the Mola Mola, which was subsequently launched to take a continuous series of photographs in close proximity to the seafloor, producing a photo-mosaic map of the target area. Operational procedures and results from these dives will be presented, showing the complementing features of these two very different AUVs in operation. © 2010 IEEE

NIUST AUVs - Expanding Possibilities

The National Institute of Undersea Science and Technology (NIUST)\u27s Underwater Vehicle Technology Center (UVTC) expanded their operational capabilities by acquiring a SeaBED class AUV in early 2009. This vehicle dubbed, Mola Mola after the Ocean Sunfish, is a superb addition to the UVTC, as it adds photographic capabilities at very slow moving speeds to the centers repertoire. The vehicle is designed to fly at speeds of 0.2 ms-1 about 3m above the seafloor, snapping high resolution digital images of the seafloor at preset intervals of 4 to 5 seconds. Normal mission behavior, programmed prior to launch of the vehicle, is to cover a certain area on the seafloor in a lawn mowing track, with parallel lines covering the entire area. At the end of the mission, geo-referenced photo mosaic maps of the target of interest on the sea floor are computed. The vehicle was deployed for several missions on the NASA vessel Liberty Star in the Bahamas. High resolution imagery of the bottom fauna and flora from depths too deep for deep divers to reach, provided insight into the distribution of Lion Fish in the coral reefs of the Bahamas. At the end of the field season engineering efforts were started to reorganize and replace certain hardware components to allow for improved navigation and data handling within the vehicles software architecture. They vehicle itself has since been modified from its original design, adding guided inertial navigation and improvements in its image acquisition process. Changes further include obstacle avoidance, GPS positioning and addition of a VHF radio beacon. In October 2009 combined efforts of both AUVs, the Mola Mola and the Explorer class Eagle Ray [1] were needed in the Gulf of Mexico aboard the NOAA ship Nancy Foster, to locate and retrieve information about sunken ships of historic interest, some of which may have disappeared below the water surface of the northern Gulf of Mexico, almost 200 years ago. In a collaboration between NIUST, MMS and NOAA Office of Ocean Exploration and Research, targets identified in side scan sonar images, were selected and investigated by the AUVs. Eagle Ray, due to its large size and design features, performed initial multibeam surveys of the target areas, producing high-resolution maps of the seafloor. These maps were used to determine safe working areas for the Mola Mola, which was subsequently launched to take a continuous series of photographs in close proximity to the seafloor, producing a photo-mosaic map of the target area. Eagle Ray served as a platform for a mass spectrometer mapping of the Mississippi Canyon Block 118 Hydrate Mount as a part of the Gas Hydrate Observatory efforts. Results o this dive produced a high resolution spatial map of methane gas distribution 6m above the seafloor, discovering three new methane seeps in the area Continued mapping efforts in the Hudson Canyon together with the National Marine Fisheries Service and Rutgers University. High resolution multibeam data from the canyon revealed interesting never before seen detail and bottom features in this area. Enough data to spark new and diverse interest about sub bottom composition and marine live within the canyon. ©2010 IEEE