Search

Highlights • Yarkovsky effect important for asteroid long-term evolution and impact risk warning. • Las Cumbres Observatory (LCOGT) measures the Yarkovsky effect on 36 asteroids. • Target asteroids predicted to yield a Yarkovsky detection with LCOGT astrometry. • 18 out of 36 (50%) target asteroids yield > 3σ Yarkovsky detections. • 78% of confirmed (> 3σ) Yarkovsky drifters are retrograde rotaters. Abstract The Las Cumbres Observatory (LCOGT) provides an ideal platform for follow-up and characterization of Solar System objects (e.g. asteroids, Kuiper belt objects (KBOs), comets, and near-Earth objects (NEOs)) as well as for the discovery of new objects. The LCOGT network allows for regular monitoring of a sample of targets, such as that of NEOs for which we can attempt to measure the Yarkovsky effect. We have used LCOGT's global network of nine 1.0-m telescopes to measure the Yarkovsky effect on 36 asteroids through precise astrometric measurements using the Gaia-DR1 catalog; 18 (50%) of the 36 asteroids yielded > 3 σ Yarkovsky detections. The target asteroids were selected through simulated observations each month to determine the objects for which new astrometry would yield the highest likelihood of a Yarkovsky detection. The Gaia-DR1 release has greatly improved the quality of the astrometry obtained, making the detection of the Yarkovsky effect more likely and secure by greatly reducing systematic catalog zonal errors. LCOGT is ideally suited to perform these observations due to its ability to monitor many targets over several days by employing dynamic scheduling, weather avoidance, and use of multiple sites around the globe. [ABSTRACT FROM AUTHOR]

Vatira-class near-Earth objects (NEOs) have orbits entirely interior to the orbit of Venus with aphelia 0.307 < Q < 0.718 au. Recently discovered asteroid 2020 AV2 by the Zwicky Transient Facility on 2020 January 4 is the first known object on a Vatira orbit. Numerical integrations of 2020 AV2's nominal orbit show it remaining in the Vatira region for the next few hundred kyr before coupling to Venus and evolving onto an Atira orbit (NEOs entirely interior to Earth's orbit with 0.718 < Q < 0.983 au) and eventually scattering out to Earth-crossing. The numerical integrations of 9900 clones within 2020 AV2's orbital uncertainty region show examples of Vatira orbits trapped in the 3:2 mean-motion resonance with Venus at semimajor axis a ≈ 0.552 au that can survive on the order of a few Myr. Possible 2020 AV2 orbits also include those on Vatira orbits between Mercury and Venus that only rarely cross that of a planet. Together, the 3:2 resonance and these rarely-planet-crossing orbits provide a meta-stable region of phase space that is stable on time-scales of several Myr. If 2020 AV2 is currently in this meta-stable region (or was in the past), that may explain its discovery as the first Vatira and may be where more are discovered. [ABSTRACT FROM AUTHOR]

The New Horizons spacecraft fly-through of the Pluto system in July 2015 will provide humanity’s first data for the crater populations on Pluto and its binary companion, Charon. In principle, these surfaces could be dated in an absolute sense, using the observed surface crater density (# craters/km 2 larger than some threshold crater diameter D ). Success, however, requires an understanding of both the cratering physics and absolute impactor flux. The Canada-France Ecliptic Plane Survey (CFEPS) L7 synthetic model of classical and resonant Kuiper belt populations (Petit, J.M. et al. [2011]. Astron. J. 142, 131–155; Gladman, B. et al. [2012]. Astron. J. 144, 23–47) and the scattering object model of Kaib et al. (Kaib, N., Roškar, R., Quinn, T. [2011]. Icarus 215, 491–507) calibrated by Shankman et al. (Shankman, C. et al. [2013]. Astrophys. J. 764, L2–L5) provide such impact fluxes and thus current primary cratering rates for each dynamical sub-population. We find that four sub-populations (the q < 42 AU hot and stirred main classicals, the classical outers, and the plutinos) dominate Pluto’s impact flux, each providing ≈ 15 – 25 % of the total rate. Due to the uncertainty in how the well-characterized size distribution for Kuiper belt objects (with impactor diameter d > 100 km ) connects to smaller projectiles, we compute cratering rates using five model impactor size distributions: a single power-law, a power-law with a knee, a power-law with a divot, as well as the “wavy” size distributions described in Minton et al. (Minton, D.A. et al. [2012]. Asteroids Comets Meteors Conf. 1667, 6348) and Schlichting et al. (Schlichting, H.E., Fuentes, C.I., Trilling, D.E. [2013]. Astron. J. 146, 36–42). We find that there is only a small chance that Pluto has been hit in the past 4 Gyr by even one impactor with a diameter larger than the known break in the projectile size distribution ( d ≈ 100 km ) which would create a basin on Pluto ( D ⩾ 400 km in diameter). We show that due to present uncertainties in the impactor size distribution between d = 1 – 100 km , computing absolute ages for the surface of Pluto is entirely dependent on the extrapolation to small sizes and thus fraught with uncertainty. We show, however, what the ages would be for several cases and illustrate the relative importance of each Kuiper belt sub-population to the cratering rate, both now and integrated into the past. In addition, we compute the largest “fresh” crater expected to have formed in 1 Gyr on the surface of Pluto and in 3 Gyr on Charon (to 95% confidence) and use the “wavy” size distribution models to predict whether these largest “fresh” craters will provide surfaces for which portions of the crater production function can be measured should most of the target’s surface appear saturated. The fly-through results coupled with telescopic surveys that bridge current uncertainties in the d = 10 – 100 km regime should eventually result in the population estimate uncertainties for the Kuiper belt sub-populations, and thus the impact fluxes onto Pluto and Charon, dipping to < 30 % . We also compute “disruption timescales” (to a factor of three accuracy) for Pluto’s smaller satellites: Styx, Nix, Kerberos, and Hydra. We find that none of the four satellites have likely undergone a catastrophic disruption and reassembly event in the past ≈ 4 Gyr . In addition, we find that for a knee size distribution with α faint ⩽ 0.4 (down to sub-km diameters), satellites of all sizes are able to survive catastrophic disruption over the past 4 Gyr. [ABSTRACT FROM AUTHOR]

Abstract: Canada’s Near-Earth Object Surveillance Satellite (NEOSSat), set to launch in early 2012, will search for and track Near-Earth Objects (NEOs), tuning its search to best detect objects with a <1.0AU. In order to construct an optimal pointing strategy for NEOSSat, we needed more detailed information in the a <1.0AU region than the best current model (Bottke, W.F., Morbidelli, A., Jedicke, R., Petit, J.M., Levison, H.F., Michel, P., Metcalfe, T.S. [2002]. Icarus 156, 399–433) provides. We present here the NEOSSat-1.0 NEO orbital distribution model with larger statistics that permit finer resolution and less uncertainty, especially in the a <1.0AU region. We find that Amors=30.1±0.8%, Apollos=63.3±0.4%, Atens=5.0±0.3%, Atiras (0.718< Q <0.983AU)=1.38±0.04%, and Vatiras (0.307< Q <0.718AU)=0.22±0.03% of the steady-state NEO population. Vatiras are a previously undiscussed NEO population clearly defined in our integrations, whose orbits lie completely interior to that of Venus. Our integrations also uncovered the unexpected production of retrograde orbits from main-belt asteroid sources; this retrograde NEA population makes up ≃0.1% of the steady-state NEO population. The relative NEO impact rate onto Mercury, Venus, and Earth, as well as the normalized distribution of impact speeds, was calculated from the NEOSSat-1.0 orbital model under the assumption of a steady-state. The new model predicts a slightly higher Mercury impact flux. [Copyright &y& Elsevier]

For any asteroid on an impact trajectory, the amount of time prior to impact a deflection can be implemented can drastically change the amount of deflection impulse required. In this study we use the precision cloud-based asteroid orbit propagation and targeting capabilities of the Asteroid Institute's Asteroid Decision Analysis and Mapping (ADAM) platform to investigate the distribution of deflection Δ v required to divert asteroids on Earth-impacting trajectories (Chesley and Spahr, 2004) as a function of time prior to impact for 10,000 synthetic impacting asteroids. We target a miss distance of one Earth radius above the surface of the Earth and calculate the distribution of deflection Δ v required if applied 10, 20, 30, 40, and 50 years prior to impact. We find that the median required deflection impulse decreases as approximately t − 1 for increasing time before impact (Ahrens and Harris, 1992), where the median required Δ v is 1.4 cm/s, 0.76 cm/s, 0.55 cm/s, 0.46 cm/s, and 0.38 cm/s for 10, 20, 30, 40, & 50 years before impact, respectively. We find a considerable spread in the distribution of required deflection Δ v including a small fraction of asteroids that require an order of magnitude smaller or larger deflection Δ v than the median for each decade of time before impact studied. • Asteroid Decision Analysis and Mapping (ADAM) platform built for orbit propagation. • Deflection delta-v computed for 10,000 synthetic impactors 10–50 yrs pre-impact. • Median delta-v decreases as 1/t with time before impact. • Large spread found in required deflection impulse distributions for any epoch. • Small fraction of impactors have ¿10x larger or smaller delta-v than median value. [ABSTRACT FROM AUTHOR]