111 research outputs found
Formation of plasma around a small meteoroid: simulation and theory
Highâpower largeâaperture radars detect meteors by reflecting radio waves off dense plasma that surrounds a hypersonic meteoroid as it ablates in the Earth's atmosphere. If the plasma density profile around the meteoroid is known, the plasma's radar cross section can be used to estimate meteoroid properties such as mass, density, and composition. This paper presents head echo plasma density distributions obtained via two numerical simulations of a small ablating meteoroid and compares the results to an analytical solution found in Dimant and Oppenheim (2017a, https://doi.org/10.1002/2017JA023960, 2017b, https://doi.org/10.1002/2017JA023963). The first simulation allows ablated meteoroid particles to experience only a single collision to match an assumption in the analytical solution, while the second is a more realistic simulation by allowing multiple collisions. The simulation and analytical results exhibit similar plasma density distributions. At distances much less than λT, the average distance an ablated particle travels from the meteoroid before a collision with an atmospheric particle, the plasma density falls off as 1/R, where R is the distance from the meteoroid center. At distances substantially greater than λT, the plasma density profile has an angular dependence, falling off as 1/R^2 directly behind the meteoroid, 1/R^3 in a plane perpendicular to the meteoroid's path that contains the meteoroid center, and exp - 1.5(/λ)2/3/ in front of the meteoroid. When used for calculating meteoroid masses, this new plasma density model can give masses that are orders of magnitude different than masses calculated from a spherically symmetric Gaussian distribution, which has been used to calculate masses in the past.This work was supported by NSF grants AGS-1244842 and AGS-1056042. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant ACI-1548562. The authors acknowledge the Texas Advanced Computing Center (TACC) at The University of Texas at Austin for providing HPC resources that have contributed to the research results reported within this paper; URL: http://www.tacc.utexas.edu. Simulation-produced data are archived at TACC and available upon request. (AGS-1244842 - NSF; AGS-1056042 - NSF; ACI-1548562 - National Science Foundation)First author draf
On the atmospheric fragmentation of small asteroids
It is known, from observational data recorded from airbursts, that small
asteroids breakup at dynamical pressures lower than their mechanical strength.
This means that actual theoretical models are inconsistent with observations.
In this paper, we present a detailed discussion about data recorded from
airbursts and about several theoretical models. We extend and improve a theory
previously outlined for the fragmentation of small asteroids in the Earth
atmosphere. The new condition for fragmentation is given by the shock
wave-turbulence interaction, which results in sudden outburst of the dynamical
pressure.Comment: 10 pages, 3 figures. Accepted for the publication on Astronomy and
Astrophysics. Added new aa.cls macro fil
Mass Loss Due to Sputtering and Thermal Processes in Meteoroid Ablation
Conventional meteoroid theory assumes that the dominant mode of ablation is
by evaporation following intense heating during atmospheric flight. In this
paper we consider the question of whether sputtering may provide an alternative
disintegration process of some importance.For meteoroids in the mass range from
10^-3 to 10^-13 kg and covering a meteor velocity range from 11 to 71 km/s, we
numerically modeled both thermal ablation and sputtering ablation during
atmospheric flight. We considered three meteoroid models believed to be
representative of asteroidal (3300 kg m^-3 mass density), cometary (1000 kg
m^-3) and porous cometary (300 kg m^-3) meteoroid structures. Atmospheric
profiles which considered the molecular compositions at different heights were
used in the sputtering calculations. We find that while in many cases
(particularly at low velocities and for relatively large meteoroid masses)
sputtering contributes only a small amount of mass loss during atmospheric
flight, in some cases sputtering is very important. For example, a 10^-10 kg
porous meteoroid at 40 km/s will lose nearly 51% of its mass by sputtering,
while a 10^-13 kg asteroidal meteoroid at 60 km/s will lose nearly 83% of its
mass by sputtering. We argue that sputtering may explain the light production
observed at very great heights in some Leonid meteors. The impact of this work
will be most dramatic for very small meteoroids such as those observed with
large aperture radars.Comment: in pdf form, 48 pgs incl figures and table
Detection of an intergalactic meteor particle with the 6-m telescope
On July 28, 2006 the 6-m telescope of the Special Astrophysical Observatory
of the Russian Academy of Sciences recorded the spectrum of a faint meteor. We
confidently identify the lines of FeI and MgI, OI, NI and molecular-nitrogen
N_2 bands. The entry velocity of the meteor body into the Earth's atmosphere
estimated from radial velocity is equal to 300 km/s. The body was several tens
of a millimeter in size, like chondrules in carbon chondrites. The radiant of
the meteor trajectory coincides with the sky position of the apex of the motion
of the Solar system toward the centroid of the Local Group of galaxies.
Observations of faint sporadic meteors with FAVOR TV CCD camera confirmed the
radiant at a higher than 96% confidence level. We conclude that this meteor
particle is likely to be of extragalactic origin. The following important
questions remain open: (1) How metal-rich dust particles came to be in the
extragalactic space? (2) Why are the sizes of extragalactic particles larger by
two orders of magnitude (and their masses greater by six orders of magnitude)
than common interstellar dust grains in our Galaxy? (3) If extragalactic dust
surrounds galaxies in the form of dust (or gas-and-dust) aureoles, can such
formations now be observed using other observational techniques (IR
observations aboard Spitzer satellite, etc.)? (4) If inhomogeneous
extragalactic dust medium with the parameters mentioned above actually exists,
does it show up in the form of irregularities on the cosmic microwave
background (WMAP etc.)?Comment: 9 pages, 6 EPS figure
A novel approach to fireball modeling: The observable and the calculated
Estimating the mass of a meteoroid passing through the Earth's atmosphere is essential to determining potential meteorite fall positions. High-resolution fireball images from dedicated camera networks provide the position and timing for fireball bright flight trajectories. There are two established mass determination methods: the photometric and the dynamic. A new approach is proposed, based on the dynamic method. A dynamic optimization initially constrains unknown meteoroid characteristics which are then used in a parametric model for an extended Kalman filter. The extended Kalman filter estimates the position, velocity, and mass of the meteoroid body throughout its flight, and quantitatively models uncertainties. Uncertainties have not previously been modeled so explicitly and are essential for determining fall distributions for potential meteorites. This two-step method aims to automate the process of mass determination for application to any trajectory data set and has been applied to observations of the Bunburra Rockhole fireball. The new method naturally handles noisy raw data. Initial and terminal bright flight mass results are consistent with other works based on the established photometric method and cosmic ray analysis. A full analysis of fragmentation and the variability in the heat-transfer coefficient will be explored in future versions of the model
Deciphering the Origin of the Regular Satellites of Gaseous Giants - Iapetus: the Rosetta Ice-Moon
Here we show that Iapetus can serve to discriminate between satellite
formation models. Its accretion history can be understood in terms of a
two-component gaseous subnebula, with a relatively dense inner region, and an
extended tail out to the location of the irregular satellites, as in the SEMM
model of Mosqueira and Estrada (2003a,b). Following giant planet formation,
planetesimals in the feeding zone of Jupiter and Saturn become dynamically
excited, and undergo a collisional cascade. Ablation and capture of
planetesimal fragments crossing the gaseous circumplanetary disks delivers
enough collisional rubble to account for the mass budgets of the regular
satellites of Jupiter and Saturn. This process can result in rock/ice
fractionation provided the make up of the population of disk crossers is
non-homogeneous, thus offering a natural explanation for the marked
compositional differences between outer solar nebula objects and those that
accreted in the subnebulae of the giant planets. Consequently, our model leads
to an enhancement of the ice content of Iapetus, and to a lesser degree those
of Ganymede, Titan and Callisto, and accounts for the (non-stochastic)
compositions of these large, low-porosity outer regular satellites of Jupiter
and Saturn. (abridged)Comment: 33 pages, 7 figures, 2 tables, Accepted for publication to Icaru
- âŠ