Julie Bellerose

Bio: Julie Bellerose is an academic researcher from California Institute of Technology. The author has contributed to research in topics: Asteroid & Near-Earth object. The author has an hindex of 12, co-authored 34 publications receiving 805 citations. Previous affiliations of Julie Bellerose include University of Michigan & Jet Propulsion Laboratory.

Radar Imaging of Binary Near-Earth Asteroid (66391) 1999 KW4

Abstract: High-resolution radar images reveal near-Earth asteroid (66391) 1999 KW4 to be a binary system. The ∼1.5-kilometer-diameter primary (Alpha) is an unconsolidated gravitational aggregate with a spin period ∼2.8 hours, bulk density ∼2 grams per cubic centimeter, porosity ∼50%, and an oblate shape dominated by an equatorial ridge at the object9s potential-energy minimum. The ∼0.5-kilometer secondary (Beta) is elongated and probably is denser than Alpha. Its average orbit about Alpha is circular with a radius ∼2.5 kilometers and period ∼17.4 hours, and its average rotation is synchronous with the long axis pointed toward Alpha, but librational departures from that orientation are evident. Exotic physical and dynamical properties may be common among near-Earth binaries.

Dynamical configuration of binary near-Earth asteroid (66391) 1999 KW4.

Abstract: Dynamical simulations of the coupled rotational and orbital dynamics of binary near-Earth asteroid 66391 (1999 KW4) suggest that it is excited as a result of perturbations from the Sun during perihelion passages. Excitation of the mutual orbit will stimulate complex fluctuations in the orbit and rotation of both components, inducing the attitude of the smaller component to have large variation within some orbits and to hardly vary within others. The primary's proximity to its rotational stability limit suggests an origin from spin-up and disruption of a loosely bound precursor within the past million years.

Shape of (101955) Bennu indicative of a rubble pile with internal stiffness

Abstract: The shapes of asteroids reflect interplay between their interior properties and the processes responsible for their formation and evolution as they journey through the Solar System. Prior to the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) mission, Earth-based radar imaging gave an overview of (101955) Bennu’s shape. Here we construct a high-resolution shape model from OSIRIS-REx images. We find that Bennu’s top-like shape, considerable macroporosity and prominent surface boulders suggest that it is a rubble pile. High-standing, north–south ridges that extend from pole to pole, many long grooves and surface mass wasting indicate some low levels of internal friction and/or cohesion. Our shape model indicates that, similar to other top-shaped asteroids, Bennu formed by reaccumulation and underwent past periods of fast spin, which led to its current shape. Today, Bennu might follow a different evolutionary pathway, with an interior stiffness that permits surface cracking and mass wasting.Near-Earth asteroid Bennu has a top-like shape with longitudinal ridges, macroporosity, prominent boulders and surface mass wasting, suggesting that it is a stiff rubble pile, according to early observations by the OSIRIS-REx mission.

The Restricted Hill Full 4-Body Problem: application to spacecraft motion about binary asteroids

Abstract: The Restricted Hill Full 4-Body Problem (RHF4BP) models the motion of a spacecraft or particle about two mutually orbiting distributed bodies in the tidal gravity field of a larger body. The practical application of this problem is to the motion of a spacecraft or particle about a binary asteroid system. Current estimates are that up to 16% of near-Earth asteroids (NEAs) may be binary asteroids, thus this is an extremely relevant topic for future missions to NEAs. It is also an interesting topic from an academic point of view, as this problem integrates four classical problems of astrodynamics: the Hill problem, the restricted 3-body problem, the non-spherical orbiter problem, and the full 2-body problem. In this paper, we define the RHF4BP in terms of these classical models and present results that the RHF4BP inherits from these classical problems. Some initial steps towards the analysis of this problem are also given, relating to the stability of motion about the Lagrange points in the Restricted Full 3...

Hayabusa2 arrives at the carbonaceous asteroid 162173 Ryugu—A spinning top–shaped rubble pile

Abstract: The Hayabusa2 spacecraft arrived at the near-Earth carbonaceous asteroid 162173 Ryugu in 2018. We present Hayabusa2 observations of Ryugu’s shape, mass, and geomorphology. Ryugu has an oblate “spinning top” shape, with a prominent circular equatorial ridge. Its bulk density, 1.19 ± 0.02 grams per cubic centimeter, indicates a high-porosity (>50%) interior. Large surface boulders suggest a rubble-pile structure. Surface slope analysis shows Ryugu’s shape may have been produced from having once spun at twice the current rate. Coupled with the observed global material homogeneity, this suggests that Ryugu was reshaped by centrifugally induced deformation during a period of rapid rotation. From these remote-sensing investigations, we identified a suitable sample collection site on the equatorial ridge.

Rotational breakup as the origin of small binary asteroids

Abstract: Many asteroids and trans-neptunian objects have satellites: the tally stands at over 150 on http://tinyurlcom/dweqf The smallest of these binary systems are main-belt and near-Earth asteroids, but the environments of these two types of object are very different, making it difficult to work out a common mechanism to explain their formation Now Walsh et al present a model that fits the bill Properties of the observed main-belt and near-Earth asteroids with satellites are matched by simulations involving the slow spinup of a 'rubble pile' asteroid via the thermal YORP effect (where radiation from an irregular body exerts a net force on that body) The mass shed from the equator of a spinning body accretes into a satellite if the material consists of particles undergoing energy-dissipating collisions Binary asteroids are created by the slow spin up of a 'rubble pile' asteroid via the thermal YORP effect (where radiation from an irregularly shaped body exerts a net force on the body) The mass shed from the equator of a critically spinning body accretes into a satellite if the material is collisionally dissipative Asteroids with satellites are observed throughout the Solar System, from subkilometre near-Earth asteroid pairs to systems of large and distant bodies in the Kuiper belt The smallest and closest systems are found among the near-Earth and small inner main-belt asteroids, which typically have rapidly rotating primaries and close secondaries on circular orbits About 15 per cent of near-Earth and main-belt asteroids with diameters under 10 km have satellites1,2 The mechanism that forms such similar binaries in these two dynamically different populations was hitherto unclear Here we show that these binaries are created by the slow spinup of a ‘rubble pile’ asteroid by means of the thermal YORP (Yarkovsky–O’Keefe–Radzievskii–Paddack) effect We find that mass shed from the equator of a critically spinning body accretes into a satellite if the material is collisionally dissipative and the primary maintains a low equatorial elongation The satellite forms mostly from material originating near the primary’s surface and enters into a close, low-eccentricity orbit The properties of binaries produced by our model match those currently observed in the small near-Earth and main-belt asteroid populations, including 1999 KW4 (refs 3, 4)

The significance of meteorite density and porosity

Abstract: Non-destructive, non-contaminating, and relatively simple procedures can be used to measure the bulk density, grain density, and porosity of meteorites. Most stony meteorites show a relatively narrow range of densities, but differences within this range can be useful indicators of the abundance and oxidation state of iron and the presence or absence of volatiles. Typically, ordinary chondrites have a porosity of just under 10%, while most carbonaceous chondrites (with notable exceptions) are more than 20% porous. Such measurements provide important clues to the nature of the physical processes that formed and evolved both the meteorites themselves and their parent bodies. When compared with the densities of small solar system bodies, one can deduce the nature of asteroid and comet interiors, which in turn reflect the accretional and collisional environment of the early solar system.

Radar Imaging of Binary Near-Earth Asteroid (66391) 1999 KW4

Abstract: High-resolution radar images reveal near-Earth asteroid (66391) 1999 KW4 to be a binary system. The ∼1.5-kilometer-diameter primary (Alpha) is an unconsolidated gravitational aggregate with a spin period ∼2.8 hours, bulk density ∼2 grams per cubic centimeter, porosity ∼50%, and an oblate shape dominated by an equatorial ridge at the object9s potential-energy minimum. The ∼0.5-kilometer secondary (Beta) is elongated and probably is denser than Alpha. Its average orbit about Alpha is circular with a radius ∼2.5 kilometers and period ∼17.4 hours, and its average rotation is synchronous with the long axis pointed toward Alpha, but librational departures from that orientation are evident. Exotic physical and dynamical properties may be common among near-Earth binaries.