27 research outputs found
Origin of the Moon and Lunar Water
Three principal concepts regarding lunar formation have been examined: the
accretion hypothesis, the mega-impact theory, and the multi-impact model. The
multi-impact model amalgamates the salient facets of the mega-impact theory and
the accretion hypothesis. As per this model, fragments of the terrestrial crust
are ejected into space during collisions with numerous planetesimals
(proto-asteroids) with diameters around 10-100 kilometers. This ejecta
interacts with the accretion disk, augmenting its mass. Different models of
lunar formation yield varied conclusions regarding the quantity of lunar water,
its subsurface distribution, and isotopic composition. Geomorphological
structures in the lunar polar regions (smoothed craters, landslides, regular
patterns) suggest the presence of a substantial permafrost layer with an
approximate thickness of a kilometer.Comment: Review article, published in "Earth and Planetary Science", 2023,
2(2
The NGST and the zodiacal light in the Solar system
We develop a physical model of the zodiacal cloud incorporating the real dust
sources of asteroidal, cometary, and kuiperoidal origin. Using the inferred
distribution of the zodiacal dust, we compute its thermal emission and
scattering at several wavelengths (1.25, 5, and 20 m) as a function of
NGST location assumed to be at 1 AU or 3 AU. Areas on the sky with a minimum of
zodiacal light are determined.Comment: 6 pages, incl. 2 colored figures, uses paspconf.sty. To be published
in "The NGST Science and Technology Exposition" (eds. Eric P. Smith and Knox
Long). Publications of the Astronomical Society of the Pacific, 200
Signatures of exosolar planets in dust debris disks
We apply our recently elaborated, powerful numerical approach to the
high-resolution modeling of the structure and emission of circumstellar dust
disks, incorporating all relevant physical processes. Specifically, we examine
the resonant structure of a dusty disk induced by the presence of one planet.
It is shown that the planet, via resonances and gravitational scattering,
produces (1) an asymmetric resonant dust belt with one or more clumps
intermittent with one or a few off-center cavities; and (2) a central cavity
void of dust. These features can serve as indicators of a planet embedded in
the circumstellar dust disk and, moreover, can be used to determine its major
orbital parameters and even the mass of the planet. The results of our study
reveal a remarkable similarity with various types of highly asymmetric
circumstellar disks observed with the James Clerk Maxwell Telescope around
Epsilon Eridani and Vega. The proposed interpretation of the clumps in those
disks as being resonant patterns is testable -- it predicts the asymmetric
design around the star to revolve, viz., by 1.2--1.6 deg/yr about Vega and
0.6--0.8 deg/yr about Epsilon Eri.Comment: to be published in ApJ Letters (v. 537, July 10, 2000), 5 pages,
incl. 2 figures. Position of (color) Fig. 2 corrected to make the Figure
caption fully readabl
Four Cometary Belts Associated with the Orbits of Giant Planets: A New View of the Outer Solar System's Structure Emerges from Numerical Simulations
Using numerical simulations, we examine the structure of a cometary
population near a massive planet, such as a giant planet of the Solar system,
starting with one-planet approximation (the Sun plus one planet). By studying
the distributions of comets in semimajor axis, eccentricity, pericenter, and
apocenter distances, we have revealed several interesting features in these
distributions. The most remarkable ones include (i) spatial accumulation of
comets near the planetary orbit (which we call the `cometary belt') and (ii)
avoidance of resonant orbits by comets. Then we abandon one-planet
approximation and examine as to how a cometary belt is modified when the
influence of all four giant planets is taken into consideration. To this end,
we simulate a stationary distribution of comets, which results from the
gravitational scattering of the Kuiper belt objects on the four giant planets
and accounts for the effects of mean motion resonances. Accounting for the
influence of four giant planets makes the cometary belts overlapping, but
nevertheless keeping almost all their basic features found in one-planet
approximation. In particular, the belts maintain the gaps in the (a,e)- and
(a,i)-space similar to the Kirkwood gaps in the main asteroid belt. We conclude
that the large-scale structure of the Solar system is featured by the four
cometary belts expected to contain 20-30 millions of scattered comets, and only
a tiny fraction of them is currently visible as Jupiter-, Saturn-, etc. family
comets.Comment: 16 pages, 1 table, 13 figures in the .ps.gz format, LaTEX uses
aasms4. Accepted for publication in Planetary and Space Scienc