On 26 September 2022, the Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos. This demonstrated the efficacy of a ...kinetic impactor for planetary defense by changing the orbital period of Dimorphos by 33 minutes (Thomas et al. 2023). Measuring the period change relied heavily on a coordinated campaign of lightcurve photometry designed to detect mutual events (occultations and eclipses) as a direct probe of the satellite's orbital period. A total of 28 telescopes contributed 224 individual lightcurves during the impact apparition from July 2022 to February 2023. We focus here on decomposable lightcurves, i.e. those from which mutual events could be extracted. We describe our process of lightcurve decomposition and use that to release the full data set for future analysis. We leverage these data to place constraints on the post-impact evolution of ejecta. The measured depths of mutual events relative to models showed that the ejecta became optically thin within the first ~1 day after impact, and then faded with a decay time of about 25 days. The bulk magnitude of the system showed that ejecta no longer contributed measurable brightness enhancement after about 20 days post-impact. This bulk photometric behavior was not well represented by an HG photometric model. An HG1G2 model did fit the data well across a wide range of phase angles. Lastly, we note the presence of an ejecta tail through at least March 2023. Its persistence implied ongoing escape of ejecta from the system many months after DART impact.
The Double Asteroid Redirection Test (DART) spacecraft successfully performed the first test of a kinetic impactor for asteroid deflection by impacting Dimorphos, the secondary of near-Earth binary ...asteroid (65803) Didymos, and changing the orbital period of Dimorphos. A change in orbital period of approximately 7 minutes was expected if the incident momentum from the DART spacecraft was directly transferred to the asteroid target in a perfectly inelastic collision, but studies of the probable impact conditions and asteroid properties indicated that a considerable momentum enhancement (\(\beta\)) was possible. In the years prior to impact, we used lightcurve observations to accurately determine the pre-impact orbit parameters of Dimorphos with respect to Didymos. Here we report the change in the orbital period of Dimorphos as a result of the DART kinetic impact to be -33.0 +/- 1.0 (3\(\sigma\)) minutes. Using new Earth-based lightcurve and radar observations, two independent approaches determined identical values for the change in the orbital period. This large orbit period change suggests that ejecta contributed a significant amount of momentum to the asteroid beyond what the DART spacecraft carried.
A detailed description of the Halley-type Comet C/2001 OG
108 (LONEOS) has been derived from visible, near-infrared, and mid-infrared observations obtained in October and November 2001. These data ...represent the first high-quality ground-based observations of a bare Halley-type comet nucleus and provide the best characterization of a Halley-type comet other than 1P/Halley itself. Analysis of time series photometry suggests that the nucleus has a rotation period of
57.2
±
0.5
h
with a minimum nuclear axial ratio of 1.3, a phase-darkening slope parameter
G of
−
0.01
±
0.10
, and an estimated
H
=
13.05
±
0.10
. The rotation period of C/2001 OG
108 is one of the longest observed among comet nuclei. The
V-
R color index for this object is measured to be
0.46
±
0.02
, which is virtually identical to that of other cometary nuclei and other possible extinct comet candidates. Measurements of the comet's thermal emission constrain the projected elliptical nuclear radii to be
9.6
±
1.0
km
and
7.4
±
1.0
km
, which makes C/2001 OG
108 one of the larger cometary nuclei known. The derived geometric albedo in
V-band of
0.040
±
0.010
is typical for comet nuclei. Visible-wavelength spectrophotometry and near-infrared spectroscopy were combined to derive the nucleus's reflectance spectrum over a 0.4 to 2.5 μm wavelength range. These measurements represent one of the few nuclear spectra ever observed and the only known spectrum of a Halley-type comet. The spectrum of this comet nucleus is very nearly linear and shows no discernable absorption features at a 5% detection limit. The lack of any features, especially in the 0.8 to 1.0 μm range such as are seen in the spectra of carbonaceous chondrite meteorites and many low-albedo asteroids, is consistent with the presence of anhydrous rather than hydrous silicates on the surface of this comet. None of the currently recognized meteorites in the terrestrial collections have reflectance spectra that match C/2001 OG
108. The near-infrared spectrum, the geometric albedo, and the visible spectrophotometry all indicate that C/2001 OG
108 has spectral properties analogous to the D-type, and possibly P-type asteroids. Comparison of the measured albedo and diameter of C/2001 OG
108 with those of Damocloid asteroids reveals similarities between these asteroids and this comet nucleus, a finding which supports previous dynamical arguments that Damocloid asteroids could be composed of cometary-like materials. These observations are also consistent with findings that two Jupiter-family comets may have spectral signatures indicative of D-type asteroids. C/2001 OG
108 probably represents the transition from a typical active comet to an extinct cometary nucleus, and, as a Halley-type comet, suggests that some comets originating in the Oort cloud can become extinct without disintegrating. As a near-Earth object, C/2001 OG
108 supports the suggestion that some fraction of the near-Earth asteroid population consists of extinct cometary nuclei.
Near-Earth Asteroid (29075) 1950 DA may closely encounter Earth in 2880. The probability of Earth impact may be as high as 1/300, but the outcome of the encounter depends critically on the physical ...properties of the asteroid Giorgini et al., 2002. Science 196, 132–136. We have used Arecibo and Goldstone radar data and optical lightcurves to estimate the shape, spin state, and surface structure of 1950 DA. The data allow two distinct models. One rotates prograde and is roughly spheroidal with mean diameter
1.16
±
0.12
km
. The other rotates retrograde and is oblate and about 30% larger. Both models suggest a nickel–iron or enstatite chondritic composition. Ground-based observations should be able to determine which model is correct within the next several decades.
An analysis of our photometric observations of near-Earth asteroids 1999 TY
2, 1999 SF
10, and 1998 WB
2 has revealed their rotation periods to be 7.2807±0.0003, 2.4663±0.0005, and 18.8±0.3 min, ...respectively. Their rotations are so fast that the bodies cannot be held together by self-gravitation alone, and must therefore be monoliths. Their absolute magnitudes, 23.1±0.3, 24.0±0.5, and 22.1±0.2, respectively, indicate that they are small bodies with mean diameters in the range 60–120 m. The current statistics of asteroid spin rates vs size suggest that the range where monoliths start to dominate among asteroids is below a diameter of about 200 m, corresponding to
H≈22, as suggested by P. Pravec and A. W. Harris (2000, Icarus, in press).
We explored the statistical and compositional link between Chelyabinsk meteoroid and potentially hazardous asteroid (86039) 1999 NC43 to investigate their proposed relation proposed by Borovička et ...al. (2013). Using detailed computation we confirm that the orbit of the Chelyabinsk impactor is anomalously close to 1999 NC43. We find about (1-3) x 10-4 likelihood of that to happen by chance. Taking the standpoint that the Chelyabinsk impactor indeed separated from 1999 NC43 by a cratering or rotational fission event, we run a forward probability calculation, which is an independent statistical test. However, we find this scenario is unlikely at the about (10-3 -10-2) level. We also verified compositional link between Chelyabinska and 1999NC43. Mineralogical analysis of Chelyabinsk (LL chondrite) and (8) Flora (the largest member of the presumed LL chondrite parent family) shows that their olivine and pyroxene chemistries are similar to LL chondrites. Similar analysis of 1999 NC43 shows that its olivine and pyroxene chemistries are more similar to L chondrites than LL chondrites (like Chelyabinsk). We also took photometric observations of 1999 NC43 over 54 nights during two apparitions (2000, 2014). The lightcurve of 1999 NC43 resembles simulated lightcurves of tumblers in Short-Axis Mode with the mean wobbling angle 20-30 deg. While, a mechanism of the non-principal axis rotation excitation is unclear, we can rule out the formation of asteroid in disruption of its parent body as a plausible cause, as it is unlikely that the rotation of an asteroid fragment from catastrophic disruption would be nearly completely halted. Considering all these facts, we find the proposed link between the Chelyabinsk meteoroid and the asteroid 1999 NC43 to be unlikely.
A detailed description of the Halley-type Comet C/2001 OG sub(108) (LONEOS) has been derived from visible, near-infrared, and mid-infrared observations obtained in October and November 2001. These ...data represent the first high- quality ground-based observations of a bare Halley-type comet nucleus and provide the best characterization of a Halley-type comet other than 1P/Halley itself. Analysis of time series photometry suggests that the nucleus has a rotation period of 57.2+/-0.5 h with a minimum nuclear axial ratio of 1.3, a phase-darkening slope parameter G of -0.01+/-0.10, and an estimated H=13.05+/-0.10. The rotation period of C/2001 OG sub(108) is one of the longest observed among comet nuclei. The V-R color index for this object is measured to be 0.46+/-0.02, which is virtually identical to that of other cometary nuclei and other possible extinct comet candidates. Measurements of the comet's thermal emission constrain the projected elliptical nuclear radii to be 9.6+/-1.0 km and 7.4+/-1.0 km, which makes C/2001 OG sub(108) one of the larger cometary nuclei known. The derived geometric albedo in V-band of 0.040+/- 0.010 is typical for comet nuclei. Visible-wavelength spectrophotometry and near-infrared spectroscopy were combined to derive the nucleus's reflectance spectrum over a 0.4 to 2.5 mu m wavelength range. These measurements represent one of the few nuclear spectra ever observed and the only known spectrum of a Halley-type comet. The spectrum of this comet nucleus is very nearly linear and shows no discernable absorption features at a 5% detection limit. The lack of any features, especially in the 0.8 to 1.0 mu m range such as are seen in the spectra of carbonaceous chondrite meteorites and many low-albedo asteroids, is consistent with the presence of anhydrous rather than hydrous silicates on the surface of this comet. None of the currently recognized meteorites in the terrestrial collections have reflectance spectra that match C/2001 OG sub(108). The near-infrared spectrum, the geometric albedo, and the visible spectrophotometry all indicate that C/2001 OG sub(108) has spectral properties analogous to the D-type, and possibly P-type asteroids. Comparison of the measured albedo and diameter of C/2001 OG sub(108) with those of Damocloid asteroids reveals similarities between these asteroids and this comet nucleus, a finding which supports previous dynamical arguments that Damocloid asteroids could be composed of cometary-like materials. These observations are also consistent with findings that two Jupiter-family comets may have spectral signatures indicative of D-type asteroids. C/2001 OG sub(108) probably represents the transition from a typical active comet to an extinct cometary nucleus, and, as a Halley-type comet, suggests that some comets originating in the Oort cloud can become extinct without disintegrating. As a near-Earth object, C/2001 OG sub(108) supports the suggestion that some fraction of the near-Earth asteroid population consists of extinct cometary nuclei.
The recent close approach of the NEA (3200) Phaethon offered a rare opportunity to obtain high-quality observational data. We used the newly obtained optical light curves to improve the spin and ...shape model of Phaethon and to determine its surface physical properties derived by thermophysical modeling. We also used the available astrometric observations of Phaethon, including those obtained by the Arecibo radar and the Gaia spacecraft, to constrain the secular drift of the orbital semimajor axis. This constraint allowed us to estimate the bulk density by assuming that the drift is dominated by the Yarkovsky effect. We used the convex inversion model to derive the 3D shape model of Phaethon, and a detailed numerical approach for an accurate analysis of the Yarkovsky effect. We obtained a unique solution for Phaethon's pole orientation at \((318,-47)^{\circ}\) ecliptic longitude and latitude (uncertainty of \(5^{\circ}\)), and confirm the previously reported thermophysical properties (\(D=5.1\pm0.2\) km, \(\Gamma=600\pm200\) SI). Phaethon has a top-like shape with possible north-south asymmetry. The characteristic size of the regolith grains is 1-2 cm. The orbit analysis reveals a secular drift of the semimajor axis of \(-(6.9\pm1.9)\times 10^{-4}\) au Myr\(^{-1}\). With the derived volume-equivalent size of 5.1~km, the bulk density \(\rho\) is \(1.67\pm0.47\) g cm\(^{-3}\). If the size is slightly larger \(\sim5.7\) km, as suggested by radar data, \(\rho\) would decrease to \(1.48\pm0.42\) g cm\(^{-3}\). We further investigated the suggestion that Phaethon may be in a cluster with asteroids (155140) 2005 UD and (225416) 1999 YC that was formed by rotational fission of a critically spinning parent body. Phaethon's \(\rho\) is consistent with typical values for large (\(>100\) km) C-complex asteroids and supports its association with asteroid (2) Pallas. These findings render a cometary origin unlikely for Phaethon.
