Dynamical spreading of asteroid families by the Yarkovsky effect

The Tharsis mantle source of depleted shergottites revealed by 90 million impact craters

The only martian rock samples on Earth are meteorites ejected from the surface of Mars by asteroid impacts. The locations and geological contexts of the launch sites are currently unknown. Determining the impact locations is essential to unravel the relations between the evolution of the martian interior and its surface. Here we adapt a Crater Detection Algorithm that compile a database of 90 million impact craters, allowing to determine the potential launch position of these meteorites through the observation of secondary crater fields. We show that Tooting and 09-000015 craters, both located in the Tharsis volcanic province, are the most likely source of the depleted shergottites ejected 1.1 million year ago. This implies that a major thermal anomaly deeply rooted in the mantle under Tharsis was active over most of the geological history of the planet, and has sampled a depleted mantle, that has retained until recently geochemical signatures of Mars' early history.

Generalized synchronization in a conservative and nearly conservative systems of star network

We report the coexistence of synchronized and unsynchronized states in a mutually coupled star network of nearly conservative non-identical oscillators. Generalized synchronization is observed between the central oscillator with the peripherals, and phase synchronization is found among the peripherals in weakly dissipative systems. However, the basin size of the synchronization region decreases as dissipation strength is increased. We have demonstrated these phenomena with the help of Duffing and Lorenz84 oscillators with conservative, nearly conservative, and dissipative properties. The observed results are robust against the network size.

Organic matter in extraterrestrial water-bearing salt crystals

Direct evidence of complex prebiotic chemistry from a water-rich world in the outer solar system is provided by the 4.5-billion-year-old halite crystals hosted in the Zag and Monahans (1998) meteorites. This study offers the first comprehensive organic analysis of the soluble and insoluble organic compounds found in the millimeter-sized halite crystals containing brine inclusions and sheds light on the nature and activity of aqueous fluids on a primitive parent body. Associated with these trapped brines are organic compounds exhibiting wide chemical variations representing organic precursors, intermediates, and reaction products that make up life's precursor molecules such as amino acids. The organic compounds also contain a mixture of C-, O-, and N-bearing macromolecular carbon materials exhibiting a wide range of structural order, as well as aromatic, ketone, imine, and/or imidazole compounds. The enrichment in ¹⁵N is comparable to the organic matter in pristine Renazzo-type carbonaceous chondrites, which reflects the sources of interstellar ¹⁵N, such as ammonia and amino acids. The amino acid content of the Zag halite deviates from the meteorite matrix, supporting an exogenic origin of the halite, and therefore, the Zag meteorite contains organics synthesized on two distinct parent bodies. Our study suggests that the asteroidal parent body where the halite precipitated, potentially asteroid 1 Ceres, shows evidence for a complex combination of biologically and prebiologically relevant molecules.

Solar System evolution from compositional mapping of the asteroid belt

Advances in the discovery and characterization of asteroids over the past decade have revealed an unanticipated underlying structure that points to a dramatic early history of the inner Solar System. The asteroids in the main asteroid belt have been discovered to be more compositionally diverse with size and distance from the Sun than had previously been known. This implies substantial mixing through processes such as planetary migration and the subsequent dynamical processes.

Acceleration of the rotation of asteroid 1862 Apollo by radiation torques

The anisotropic reflection and thermal re-emission of sunlight from an asteroid's surface acts as a propulsion engine. The net propulsion force (Yarkovsky effect) changes the orbital dynamics of the body at a rate that depends on its physical properties; for irregularly shaped bodies, the propulsion causes a net torque (the Yarkovsky-O'Keefe-Radzievskii-Paddack or YORP effect) that can change the object's rotation period and the direction of its rotation axis. The Yarkovsky effect has been observed directly, and there is also indirect evidence of its role in the orbital evolution of asteroids over long time intervals. So far, however, only indirect evidence exists for the YORP effect through the clustering of the directions of rotation axes in asteroid families. Here we report a change in the rotation rate of the asteroid 1862 Apollo, which is best explained by the YORP mechanism. The change is fairly large and clearly visible in photometric lightcurves, amounting to one extra rotation cycle in just 40 years even though Apollo's size is well over one kilometre. This confirms the prediction that the YORP effect plays a significant part in the dynamical evolution of asteroids.

Geometric mechanics and the dynamics of asteroid pairs

The purpose of this paper is to describe the general setting for the application of techniques from geometric mechanics and dynamical systems to the problem of asteroid pairs. The paper also gives some preliminary results on transport calculations and the associated problem of calculating binary asteroid escape rates. The dynamics of an asteroid pair, consisting of two irregularly shaped asteroids interacting through their gravitational potential is an example of a full-body problem or FBP in which two or more extended bodies interact. One of the interesting features of the binary asteroid problem is that there is coupling between their translational and rotational degrees of freedom. General FBPs have a wide range of other interesting aspects as well, including the 6-DOF guidance, control, and dynamics of vehicles, the dynamics of interacting or ionizing molecules, the evolution of small body, planetary, or stellar systems, and almost any other problem in which distributed bodies interact with each other or with an external field. This paper focuses on the specific case of asteroid pairs using techniques that are generally applicable to many other FBPs. This particular full two-body problem (F2BP) concerns the dynamical evolution of two rigid bodies mutually interacting via a gravitational field. Motivation comes from planetary science, where these interactions play a key role in the evolution of asteroid rotation states and binary asteroid systems. The techniques that are applied to this problem fall into two main categories. The first is the use of geometric mechanics to obtain a description of the reduced phase space, which opens the door to a number of powerful techniques, such as the energy-momentum method for determining the stability of equilibria and the use of variational integrators for greater accuracy in simulation. Second, techniques from computational dynamic systems are used to determine phase space structures that are important for transport phenomena and dynamic evolution.

Direct Detection of the Yarkovsky Effect by Radar Ranging to Asteroid 6489 Golevka

Radar ranging from Arecibo, Puerto Rico, to the 0.5-kilometer near-Earth asteroid 6489 Golevka unambiguously reveals a small nongravitational acceleration caused by the anisotropic thermal emission of absorbed sunlight. The magnitude of this perturbation, known as the Yarkovsky effect, is a function of the asteroid's mass and surface thermal characteristics. Direct detection of the Yarkovsky effect on asteroids will help constrain their physical properties, such as bulk density, and refine their orbital paths. Based on the strength of the detected perturbation, we estimate the bulk density of Golevka to be 2.7(+0.4)(-0.6) grams per cubic centimeter.

The vector alignments of asteroid spins by thermal torques

Collisions have been thought to be the dominant process altering asteroid rotations, but recent observations of the Koronis family of asteroids suggest that this may be incorrect. This group of asteroids was formed in a catastrophic collision several billion years ago; in the intervening period their rotational axes should have become nearly random because of subsequent collisions, with spin rates that follow a maxwellian distribution. What is seen, however, is that the observed family members with prograde spins have nearly identical periods (7.5-9.5 h) and obliquities between 42 and 50 degrees, while those with retrograde spins have obliquities between 154 and 169 degrees with periods either <5 h or >13 h. Here we show that these non-random orientations and spin rates can be explained by 'thermal torques' (arising from differential solar heating), which modify the spin states over time. In some cases, the asteroids become trapped in spin-orbit resonances. Our results suggest that thermal torques may be more important than collisions in changing the spin states (and possibly shapes) of asteroids with diameters <40 km.

Disruption of fragmented parent bodies as the origin of asteroid families

Asteroid families are groups of small bodies that share certain orbit and spectral properties. More than 20 families have now been identified, each believed to have resulted from the collisional break-up of a large parent body in a regime where gravity controls the outcome of the collision more than the material strength of the rock. The size and velocity distributions of the family members provide important constraints for testing our understanding of the break-up process, but erosion and dynamical diffusion of the orbits over time can erase the original signature of the collision. The recently identified young Karin family provides a unique opportunity to study a collisional outcome almost unaffected by orbit evolution. Here we report numerical simulations modelling classes of collisions that reproduce the main characteristics of the Karin family. The sensitivity of the outcome of the collision to the internal structure of the parent body allows us to show that the family must have originated from the break-up of a pre-fragmented parent body, and that all large family members formed by the gravitational reaccumulation of smaller bodies. We argue that most of the identified asteroid families are likely to have had a similar history.

The recent breakup of an asteroid in the main-belt region

The present population of asteroids in the main belt is largely the result of many past collisions. Ideally, the asteroid fragments resulting from each impact event could help us understand the large-scale collisions that shaped the planets during early epochs. Most known asteroid fragment families, however, are very old and have therefore undergone significant collisional and dynamical evolution since their formation. This evolution has masked the properties of the original collisions. Here we report the discovery of a family of asteroids that formed in a disruption event only 5.8 +/- 0.2 million years ago, and which has subsequently undergone little dynamical and collisional evolution. We identified 39 fragments, two of which are large and comparable in size (diameters of approximately 19 and approximately 14 km), with the remainder exhibiting a continuum of sizes in the range 2-7 km. The low measured ejection velocities suggest that gravitational re-accumulation after a collision may be a common feature of asteroid evolution. Moreover, these data can be used to check numerical models of larger-scale collisions.