Showing papers on "Yarkovsky effect published in 2015"

The Yarkovsky and YORP Effects

Abstract: The Yarkovsky effect describes a small but significant force that affects the orbital motion of meteoroids and asteroids smaller than $30-40$ kilometers in diameter It is caused by sunlight; when these bodies heat up in the Sun, they eventually re-radiate the energy away in the thermal waveband, which in turn creates a tiny thrust This recoil acceleration is much weaker than solar and planetary gravitational forces, but it can produce measurable orbital changes over decades and substantial orbital effects over millions to billions of years The same physical phenomenon also creates a thermal torque that, complemented by a torque produced by scattered sunlight, can modify the rotation rates and obliquities of small bodies as well This rotational variant has been coined the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect During the past decade or so, the Yarkovsky and YORP effects have been used to explore and potentially resolve a number of unsolved mysteries in planetary science dealing with small bodies Here we review the main results to date, and preview the goals for future work

The Yarkovsky and YORP Effects

Abstract: Interesting problems in science usually have a long and complex history. It is rare, though, that they have a prehistory or perhaps even mythology. Yet, until recently this was the case for the Yarkovsky effect. Ivan O. Yarkovsky, a Russian civil engineer born in a family of Polish descent, noted in a privately published pamphlet (Yarkovsky, 1901; Beekman, 2006) that heating a prograde-rotating planet should produce a transverse acceleration in its motion and thus help to counterbalance the assumed drag from the then-popular ether hypothesis. While this context of Yarkovsky’s work was mistaken and he was only roughly able to estimate the magnitude of the effect, he succeeded in planting the seed of an idea that a century later blossomed into a full-fledged theory of how the orbits of small objects revolving about the Sun are modified by the absorption and reemission of solar energy. It is mainly Ernst J. Opik who is to be credited for keeping Yarkovsky’s work alive and introducing it to western literature, long after the original pamphlet had been lost (Opik, 1951). Curiously, at about the same time, similar ideas also started to appear in Russian regular scientific literature through the works of Vladimir V. Radzievskii and his collaborators (Radzievskii, 1952). While Radzievskii was also the first to consider the effects of systematic photon thrust on a body’s rotation, his concept was based on a variable albedo coefficient across the surface (Radzievskii, 1954). However, there is no strong evidence of large enough albedo variations over surfaces of asteroids or meteoroids. Stephen J. Paddack and John O’Keefe pushed the idea forward by realizing that irregular shape, and thermal radiation rather than just reflected sunlight, will more efficiently change the meteoroid’s spin rate. Thence, the Yarkovsky-O’KeefeRadzievskii-Paddack (YORP) effect was born as an alter ego of the Yarkovsky effect little more than half a century after Yarkovsky’s work (see Paddack (1969), Paddack and Rhee (1975), and Rubincam (2000) for a summation of the history and coining of the terminology). Radzievskii’s school also briefly touched upon a concept of a radiation-induced acceleration of synchronous planetary satellites (Vinogradova

Asteroid Models from Multiple Data Sources

Abstract: In the past decade, hundreds of asteroid shape models have been derived using the lightcurve inversion method. At the same time, a new framework of 3-D shape modeling based on the combined analysis of widely different data sources such as optical lightcurves, disk-resolved images, stellar occultation timings, mid-infrared thermal radiometry, optical interferometry, and radar delay-Doppler data, has been developed. This multi-data approach allows the determination of most of the physical and surface properties of asteroids in a single, coherent inversion, with spectacular results. We review the main results of asteroid lightcurve inversion and also recent advances in multi-data modeling. We show that models based on remote sensing data were confirmed by spacecraft encounters with asteroids, and we discuss how the multiplication of highly detailed 3-D models will help to refine our general knowledge of the asteroid population. The physical and surface properties of asteroids, i.e., their spin, 3-D shape, density, thermal inertia, surface roughness, are among the least known of all asteroid properties. Apart for the albedo and diameter, we have access to the whole picture for only a few hundreds of asteroids. These quantities are nevertheless very important to understand as they affect the non-gravitational Yarkovsky effect responsible for meteorite delivery to Earth, or the bulk composition and internal structure of asteroids.

The orbital evolution of asteroids, pebbles and planets from giant branch stellar radiation and winds

Abstract: The discovery of over 50 planets around evolved stars and more than 35 debris discs orbiting white dwarfs highlight the increasing need to understand small body evolution around both early and asymptotic giant branch (GB) stars. Pebbles and asteroids are susceptible to strong accelerations from the intense luminosity and winds of GB stars. Here, we establish equations that can model time-varying GB stellar radiation, wind drag and mass loss. We derive the complete three-dimensional equations of motion in orbital elements due to (1) the Epstein and Stokes regimes of stellar wind drag, (2) Poynting-Robertson drag, and (3) the Yarkovsky drift with seasonal and diurnal components. We prove through averaging that the potential secular eccentricity and inclination excitation due to Yarkovsky drift can exceed that from Poynting-Robertson drag and radiation pressure by at least three orders of magnitude, possibly flinging asteroids which survive YORP spin-up into a widely dispersed cloud around the resulting white dwarf. The GB Yarkovsky effect alone may change an asteroid's orbital eccentricity by ten per cent in just one Myr. Damping perturbations from stellar wind drag can be just as extreme, but are strongly dependent on the highly uncertain local gas density and mean free path length. We conclude that GB radiative and wind effects must be considered when modelling the post-main-sequence evolution of bodies smaller than about 1000 km.

OSIRIS-REx Asteroid Sample-Return Mission

Abstract: The primary objective of the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission is to return pristine samples of carbonaceous material from the surface of a primitive asteroid. The target asteroid, near-Earth object (101955) Bennu, is the most exciting, accessible, and volatileand organic-rich remnant from the early Solar System. OSIRIS-REx returns a minimum of 60 g of bulk regolith and a separate 26 cm of fine-grained surface material from this body. Analyses of these samples provide unprecedented knowledge about presolar history, from the initial stages of planet formation to the origin of life. Prior to sample acquisition, OSIRIS-REx performs comprehensive global mapping of the texture, mineralogy, and chemistry of Bennu, resolving geological features, revealing its geologic and dynamic history, and providing context for the returned samples. The instruments also document the regolith at the sampling site in situ at scales down to the sub-centimeter. In addition, OSIRIS-REx studies the Yarkovsky effect, a non-Keplerian force affecting the orbit of this potentially hazardous asteroid (PHA), and provides the first ground truth for telescopic observations of carbonaceous asteroids.

Asteroid Models from Multiple Data Sources

Abstract: In the past decade, hundreds of asteroid shape models have been derived using the lightcurve inversion method. At the same time, a new framework of 3-D shape modeling based on the combined analysis of widely different data sources such as optical lightcurves, disk-resolved images, stellar occultation timings, mid-infrared thermal radiometry, optical interferometry, and radar delay-Doppler data, has been developed. This multi-data approach allows the determination of most of the physical and surface properties of asteroids in a single, coherent inversion, with spectacular results. We review the main results of asteroid lightcurve inversion and also recent advances in multi-data modeling. We show that models based on remote sensing data were confirmed by spacecraft encounters with asteroids, and we discuss how the multiplication of highly detailed 3-D models will help to refine our general knowledge of the asteroid population. The physical and surface properties of asteroids, i.e., their spin, 3-D shape, density, thermal inertia, surface roughness, are among the least known of all asteroid properties. Apart for the albedo and diameter, we have access to the whole picture for only a few hundreds of asteroids. These quantities are nevertheless very important to understand as they affect the non-gravitational Yarkovsky effect responsible for meteorite delivery to Earth, or the bulk composition and internal structure of asteroids.

The origin of long-lived asteroids in the 2:1 mean-motion resonance with Jupiter

Abstract: The 2:1 mean-motion resonance with Jupiter harbours two distinct groups of asteroids. The short-lived population is known to be a transient group sustained in steady state by the Yarkovsky semimajor axis drift. The long-lived asteroids, however, can exhibit dynamical lifetimes comparable to $4\,\mathrm{Gyr}$. They reside near two isolated islands of the phase space denoted $\mathrm{A}$ and $\mathrm{B}$, with an uneven population ratio $\mathrm{B}/\mathrm{A} \simeq 10$. The orbits of $\mathrm{A}$-island asteroids are predominantly highly inclined, compared to island $\mathrm{B}$. The size-frequency distribution is steep but the orbital distribution lacks any evidence of a collisional cluster. These observational constraints are somewhat puzzling and therefore the origin of the long-lived asteroids has not been explained so far. With the aim to provide a viable explanation, we first update the resonant population and revisit its physical properties. Using an $N$-body model with seven planets and the Yarkovsky effect included, we demonstrate that the dynamical depletion of island $\mathrm{A}$ is faster, in comparison with island $\mathrm{B}$. Then we investigate (i) the survivability of primordial resonant asteroids and (ii) capture of the population during planetary migration, following a recently described scenario with an escaping fifth giant planet and a jumping-Jupiter instability. We also model the collisional evolution of the resonant population over past $4\,\mathrm{Gyr}$. Our conclusion is that the long-lived group was created by resonant capture from a narrow part of hypothetical outer main-belt family during planetary migration. Primordial asteroids surviving the migration were probably not numerous enough to substantially contribute to the observed population.

Direct Detections of the Yarkovsky Effect: Status and Outlook

Abstract: We report the current results on a comprehensive scan of the near-Earth asteroid catalog for evidence of the Yarkovsky effect in the orbital motion of these bodies. While most objects do not have sufficient observational data to reveal such slight acceleration, we do identify 42 asteroids with a “valid” detection of the Yarkovsky effect, i.e., those with a signal at least 3 times greater than the formal uncertainty and a value compatible with the Yarkovsky mechanism.We also identify a special category of non-detection, which we refer to as “weak signal,” where the objects are of a size that would permit a clear detection if the Yarkovsky effect is maximized, and yet the orbit is clearly incompatible with such accelerations. The implication is that the Yarkovsky effect is reduced in these cases, presumably due to mid-range obliquity, but possibly also due to size, bulk density, thermal inertia, albedo, or spin rate markedly different from assumptions.Finally, there are a number of asteroids showing a significant signal for nongravitational acceleration, and yet with a magnitude too great to be attributed to the Yarkovsky effect. We term these “spurious detections” because most are due to erroneous optical astrometry, often involving a single isolated night from precovery observations. Some cases may be due to other nongravitational accelerations, such as outgassing, mass loss, or micro-meteoroid flux.

Detection of Yarkovsky acceleration in the context of precovery observations and the future Gaia catalogue

Abstract: Context. The Yarkovsky effect is a weak non-gravitational force leading to a small variation of the semi-major axis of an asteroid. Using radar measurements and astrometric observations, it is possible to measure a drift in semi-major axis through orbit determination. Aims: This paper aims to detect a reliable drift in semi-major axis of near-Earth asteroids (NEAs) from ground-based observations and to investigate the impact of precovery observations and the future Gaia catalogue in the detection of a secular drift in semi-major axis. Methods: We have developed a precise dynamical model of an asteroid's motion taking the Yarkovsky acceleration into account and allowing the fitting of the drift in semi-major axis. Using statistical methods, we investigate the quality and the robustness of the detection. Results: By filtering spurious detections with an estimated maximum drift depending on the asteroid's size, we found 46 NEAs with a reliable drift in semi-major axis in good agreement with the previous studies. The measure of the drift leads to a better orbit determination and constrains some physical parameters of these objects. Our results are in good agreement with the 1 /D dependence of the drift and with the expected ratio of prograde and retrograde NEAs. We show that the uncertainty of the drift mainly depends on the length of orbital arc and in this way we highlight the importance of the precovery observations and data mining in the detection of consistent drift. Finally, we discuss the impact of Gaia catalogue in the determination of drift in semi-major axis.

The origin of long-lived asteroids in the 2:1 mean-motion resonance with Jupiter

Abstract: The 2:1 mean-motion resonance with Jupiter harbours two distinct groups of asteroids. The short-lived population is known to be a transient group sustained in steady state by the Yarkovsky semimajor axis drift. The long-lived asteroids, however, can exhibit dynamical lifetimes comparable to $4\,\mathrm{Gyr}$. They reside near two isolated islands of the phase space denoted $\mathrm{A}$ and $\mathrm{B}$, with an uneven population ratio $\mathrm{B}/\mathrm{A} \simeq 10$. The orbits of $\mathrm{A}$-island asteroids are predominantly highly inclined, compared to island $\mathrm{B}$. The size-frequency distribution is steep but the orbital distribution lacks any evidence of a collisional cluster. These observational constraints are somewhat puzzling and therefore the origin of the long-lived asteroids has not been explained so far. With the aim to provide a viable explanation, we first update the resonant population and revisit its physical properties. Using an $N$-body model with seven planets and the Yarkovsky effect included, we demonstrate that the dynamical depletion of island $\mathrm{A}$ is faster, in comparison with island $\mathrm{B}$. Then we investigate (i) the survivability of primordial resonant asteroids and (ii) capture of the population during planetary migration, following a recently described scenario with an escaping fifth giant planet and a jumping-Jupiter instability. We also model the collisional evolution of the resonant population over past $4\,\mathrm{Gyr}$. Our conclusion is that the long-lived group was created by resonant capture from a narrow part of hypothetical outer main-belt family during planetary migration. Primordial asteroids surviving the migration were probably not numerous enough to substantially contribute to the observed population.

Detection of Yarkovsky acceleration in the context of precovery observations and the future Gaia catalogue

Abstract: The Yarkovsky effect is a weak non-gravitational force leading to a small variation of the semi-major axis of an asteroid. Using radar measurements and astrometric observations, it is possible to measure a drift in semi-major axis through orbit determination. This paper aims to detect a reliable drift in semi-major axis of near-Earth asteroids (NEAs) from ground-based observations and to investigate the impact of precovery observations and the future Gaia catalogue in the detection of a secular drift in semi-major axis. We have developed a precise dynamical model of an asteroid's motion taking the Yarkovsky acceleration into account and allowing the fitting of the drift in semi-major axis. Using statistical methods, we investigate the quality and the robustness of the detection. By filtering spurious detections with an estimated maximum drift depending on the asteroid's size, we found 46 NEAs with a reliable drift in semi-major axis in good agreement with the previous studies. The measure of the drift leads to a better orbit determination and constrains some physical parameters of these objects. Our results are in good agreement with the 1/D dependence of the drift and with the expected ratio of prograde and retrograde NEAs. We show that the uncertainty of the drift mainly depends on the length of orbital arc and in this way we highlight the importance of the precovery observations and data mining in the detection of consistent drift. Finally, we discuss the impact of Gaia catalogue in the determination of drift in semi-major axis.

CanariCam/GTC observations of (99942) Apophis

Abstract: The potentially hazardous asteroid (PHA) (99942) Apophis is one of the most remarkable near-Earth asteroids (NEA) in terms of impact hazard. A good determination of its surface thermal inertia is very important in order to evaluate the Yarkovsky effect on its orbital evolution. We present thermal infrared observations obtained on January 29, 2013, with CanariCam mid-infrared camera/spectrograph attached to the Gran Telescopio CANARIAS (GTC, Roque de los Muchachos Observatory, La Palma, Spain) using the Si2-8.7, Si6-12.5, and Q1-17.65 filters with the aim of deriving Apophis' diameter ($D$), geometric albedo ($p_V$), and thermal inertia ($\Gamma$). We performed a detailed thermophysical model analysis of the GTC data combined with previously published thermal data obtained using Herschel Space Observatory PACS instrument at 70, 100, and 160 $\mu$m.The thermophysical model fit of the data favors low surface roughness solutions (within a range of roughness slope angles $rms$ between 0.1 and 0.5), and constrains the effective diameter, visible geometric albedo, and thermal inertia of Apophis to be $D_{eff} =$~380 -- 393 m, $p_V = $~0.24--0.33 (assuming absolute magnitude $H = 19.09 \pm 0.19$) and $\Gamma =$~50 -- 500 Jm$^{-2}$ s$^{-0.5}$ K$^{-1}$, respectively.

Impact Hazard Monitoring: Theory and Implementation

Abstract: We review the most standard impact monitoring techniques. Linear methods are the fastest approach but their applicability regime is limited because of the chaotic dynamics of near-Earth asteroids. Among nonlinear methods, Monte Carlo algorithms are the most reliable ones but also most computationally intensive and so unpractical for routine impact monitoring. In the last 15 years, the Line of Variations method has been the most successful technique thanks to its computational efficiency and capability of detecting low probability events deep in the nonlinear regime. We also present some more recent techniques developed to deal with the new challenges arising in the impact hazard assessment problem. In particular, we describe keyhole maps as a tool to go beyond strongly scattering encounters and how to account for nongravitational perturbations, especially the Yarkovsky effect, when their contribution is the main source of prediction uncertainty. Finally, we discuss systematic ranging to deal with the short-term hazard assessment problem for newly discovered asteroids, when only a short observed arc is available thus leading to severe degeneracies in the orbit estimation process.

Impact Risk Estimation and Assessment Scales

Abstract: This chapter addresses the current state of the art in assessing the impact risk from any of the known near-Earth objects over the next century or so. The assessment is made by determining the orbits of potentially hazardous asteroids and comets using the latest sets of tracking measurements and then projecting into the future the possible positions for these objects during close approaches to the Earth. The chapter discusses various computerized risk assessment systems that perform these assessments, along with the scales that are used to assess these risks. The second part of the chapter addresses two important issues in accurately predicting the risk of impact on Earth that have been identified and addressed in recent years. The first of these is the “Yarkovsky effect,” which is the small recoil acceleration acting on an asteroid due to thermal emissions from its surface and which can now be detected, modeled, and accounted for. The second topic to be discussed is the phenomenon of “keyholes,” which are gravitational gateways that can take an asteroid from a close approach on one passage by the S. Chesley (*) • P. Chodas Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA e-mail: steve.chesley@jpl.nasa.gov; paul.w.chodas@jpl.nasa.gov # Springer International Publishing Switzerland 2015 J.N. Pelton, F. Allahdadi (eds.), Handbook of Cosmic Hazards and Planetary Defense, DOI 10.1007/978-3-319-03952-7_87 651 Earth to a later impact with our planet. Mapping the keyholes for a potential impactor is an important step in assessing the asteroid’s impact hazard and in planning a possible deflection mission.

Forced Keplerian-Like Systems

Abstract: Throughout this chapter, we are concerned with the existence of periodic non-collision solutions of some systems that include the classical newtonian models for the motion of a point particle under the influence of a gravitational or electrostatic potential and an external periodic force.

Apophis: Complex rotation and hazard assessment

Abstract: We present an updated hazard assessment for near-Earth asteroid (99942) Apophis. The stiff dynamics and the high precision of the trajectory of Apophis call for the most accurate dynamical model. In particular, the dominant source of ephemeris prediction uncertainty is the Yarkovsky effect. We include the Yarkovsky perturbation in the force model by numerically computing the related thermal recoil accelerations. These acceleration are statistically computed according to the known physical properties of Apophis and their uncertainties. Special effort is required to account for the non-principal axis rotation state of Apophis. Finally, we generated Monte Carlo samples to capture the uncertainty in both the orbital elements and the Yarkovsky accelerations and compute the probability of future Earth impacts. Whereas collisions with Earth before 2060 are ruled out, impacts are still possible starting in 2060. The highest impact probability is seven in a million for the April 2068 Earth encounter.