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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Disintegration of Long-period Comet C/2019 Y4 (ATLAS). I. Hubble Space Telescope Observations

The near-Sun comet C/2019 Y4 (ATLAS) is the first member of a long-period comet group observed to disintegrate well before perihelion. Here we present our investigation into this disintegration event using images obtained in a three-day Hubble Space Telescope campaign. We identify two fragment clusters produced by the initial disintegration event, corresponding to fragments C/2019 Y4-A and C/2019 Y4-B identified in ground-based data. These two clusters started with similar integrated brightness but exhibit different evolutionary behavior. C/2019 Y4-A was much shorter-lived compared to C/2019 Y4-B and showed signs of significant mass loss and changes in size distribution throughout the three-day campaign. The cause of the initial fragmentation is undetermined by the limited evidence but crudely compatible with either the spin-up disruption of the nucleus or runaway sublimation of subsurface supervolatile ices, either of which would lead to the release of a large amount of gas as inferred from the significant bluing of the comet observed shortly before its disintegration. Gas can only be produced by the sublimation of volatile ices, which must have survived at least one perihelion passage at a perihelion distance of q = 0.25 au. We speculate that Comet ATLAS is derived from the ice-rich interior of a nonuniform, kilometer-wide progenitor that split during its previous perihelion. This suggests that comets down to a few kilometers in diameter can still possess complex, nonuniform interiors that can protect ices against intense solar heating.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Cometary Activity Begins at Kuiper Belt Distances: Evidence from C/2017 K2

We study the development of activity in the incoming long-period comet C/2017 K2 over the heliocentric distance range 9 ≲ r {sub H} ≲ 16 au. The comet continues to be characterized by a coma of submillimeter-sized and larger particles ejected at low velocity. In a fixed co-moving volume around the nucleus we find that the scattering cross section of the coma, C, is related to the heliocentric distance by a power law, C∝r{sub H}{sup -s}, with heliocentric index s = 1.14 ± 0.05. This dependence is significantly weaker than the r {sub H} {sup -2} variation of the insolation as a result of two effects. These are, first, the heliocentric dependence of the dust velocity and, second, a lag effect due to very slow-moving particles ejected long before the observations were taken. A Monte Carlo model of the photometry shows that dust production beginning at r {sub H} ~ 35 au is needed to match the measured heliocentric index, with only a slight dependence on the particle size distribution. Mass-loss rates in dust at 10 au are of order 10{sup 3} kg s{sup -1}, while loss rates in gas may be much smaller, depending on the unknown dust to gas ratio. Consequently, the ratio of the nongravitational acceleration to the local solar gravity, α', may, depending on the nucleus size, attain values of ~10{sup -7} ≲ α' ≲ 10{sup -5}, comparable to values found in short-period comets at much smaller distances. Nongravitational acceleration in C/2017 K2 and similarly distant comets, while presently unmeasured, may limit the accuracy with which we can infer the properties of the Oort cloud from the orbits of long-period comets.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Meteoroid Stream of Comet C/1961 T1 (Seki) and Its Relation to the December ρ-Virginids and γ-Sagittariids

We answer the question of whether long-period comet C/1961 T1 (Seki) is the parent body of a meteor shower observed in Earth’s atmosphere. We model discrete parts of a meteoroid stream associated with this comet and follow the orbital evolution of its particles via a numerical integration of their orbits. The gravitational perturbations of major planets and the Poynting–Robertson effect, which influences the motion of the particles, are taken into account. We predict two showers which are related to C/1961 T1. One of these showers was identified with the December ρ-Virginids, #502. This identification confirms an earlier suggested relationship between the shower and the comet. The second predicted shower was identified with the γ-Sagittariids, #657. The radiant areas of both showers are symmetrical in respect to the apex of Earth’s heliocentric motion.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Chemical Composition of Outbursting Comet C/2015 ER61 (PanSTARRS)

Comet C/2015 ER61 (PanSTARRS) is a long-period Oort cloud comet whose favorable approach to the inner parts of the solar system in 2017 April–May enabled us to characterize its primary volatile composition using the iSHELL spectrograph mounted on the 3 m NASA Infrared Telescope Facility (IRTF) on Maunakea, Hawaii. We used three iSHELL settings (covering ~2.8–5.2 μm) to sample fluorescent emissions from H{sub 2}O, OH, CH{sub 3}OH, HCN, C{sub 2} H{sub 2}, NH{sub 3}, CO, CH{sub 4}, C{sub 2}H{sub 6}, H{sub 2}CO, and OCS on multiple dates ranging from UT 2017 April 15 (shortly after its April 4 outburst) to May 13, nearly 30 days before the detection of its double nucleus. Our observations also offered the opportunity to obtain sensitive 3σ upper limits for cyanoacetylene (HC{sub 3}N). We report rotational temperatures (T{sub rot}), production rates (Qs), abundance (mixing) ratios (relative to H{sub 2}O and C{sub 2}H{sub 6}), and spatial distributions in the coma. ER61 exhibits variability in production rates of many species on short (day-to-day) and long (pre- versus post-perihelion) timescales. The relative abundances of these volatile species remained consistent within uncertainties during our pre-perihelion observations but tended to decrease during our post-perihelion observations (with the exception of CH{sub 3}OH and HCN). The short-timescale variability in the production rates of these volatiles could be due to diurnal effects (over the course of the rotation of the nucleus) and/or the effect of its outburst. The decrease in the production rates and hence the mixing ratios in some volatiles in post-perihelion dates could be due to the presence of seasonal effects in ER61.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗