Previous
and current research. Sergei Ipatov
Short information about my research interests
I studied different problems of the migration of celestial bodies
(planetesimals, asteroids, trans-Neptunian objects, planets) and dust in the
forming and present Solar System, the accumulation of planets, the asteroid and
comet hazard to the Earth, the ejection of material from Comet Tempel 1, the recognition
of cosmic ray signatures on CCD images, the formation of satellites of small
bodies, the origin of the Kirkwood gaps, the collapse of the presolar cloud,
the radiative transfer in atmospheres, etc. These studies were based on
computer models and mathematical methods of image
processing. Various FORTRAN and IDL codes were written. Several
codes (e.g., FLASH, SBDART, SWIFT) written by other scientists were also used. I
have also a few months’ experience in observations of minor bodies and in
lecturing. Besides astronomy, I also made computer models of other physical
processes. There was no problem for me to successfully solve the problems for
which I had no previous experience and skills.
Analysis of images made by the Deep
Impact spacecraft (since 2005)
During January 2005 – August 2006, I was a member of the Deep Impact
team at the
Formation
of small body binaries (2009)
Formation of small body binaries at
the stage of rarefied preplanetesimals was studied (e.g., S.I. Ipatov, MNRAS,
2010, v. 403, 405-414, http://arxiv.org/abs/0904.3529).
In particular, it was shown that the momentum of two collided rarefied
homogeneous Hill spheres moved in circular orbits exceeds the momentum of a
corresponding present binary of the same total mass.
Radiative transfer in
astmospheres (2007-2008). Together with James
Cho, I studied (e.g., using SBDART) the radiative transfer in atmospheres of
test extrasolar planets (e.g., S.I. Ipatov and J. Cho, LPSC, 2008, #2554; http://www.dtm.ciw.edu/users/ipatov/lpsc2008atm.ppt). The outputs from the general circulation model (GCM) simulations were
used to compute model spectra for atmospheres of Earth and exo-Earth rotating
with period equal to 1 and 100 days, respectively.
Triggered collapse of
the presolar cloud (2006-2007). Together with
Alan Boss, I applied the FLASH adaptive mesh refinement code to study the
dynamics of mixing and transport processes in the presolar cloud (A.P. Boss et
al., ApJL, 2008, v. 686, L119-123; A.P. Boss et al., ApJ, 2010, v. 708, 1268-1280;
Ipatov et al., LPSC, 2007, #1018). Several tens of movies showing the dynamics were
made.
Migration of dust particles and small bodies (since
2001)
S.I. Ipatov and J.C. Mather (e.g., Advances in Space
Research, 2004, v. 33, N 9, 1524-1533; Earth, Moon &
Planets, 2003, v. 92, 89-98; Annals of the New York Acad. of Sci., 2004, v. 1017,
46-65; Proc. IAU 236, 2007, 55-64) studied the migration
of Jupiter-family comets (JFCs) to near-Earth object (NEO) orbits.
We integrated the orbital evolution of 30,000 test JFCs and 1500 test asteroids
at the resonances 3:1 and 5:2 with Jupiter under the gravitational influence of
all planets. For integration we used the Bulirsh-Stoer method (BULSTO) and a
symplectic method. We found that the main results of the orbital evolution of
JFCs and asteroids are the same for different methods and for an integration
step of the symplectic method not greater than 10 days or the integration step
error not greater than 10-8. A few migrating JFCs reached orbits
with semimajor axes a<2 AU and had
aphelion distances Q<4.2 AU for more than 0.5 Myr. Several former JFCs
moved in such orbits for tens or even hundreds of Myrs, and some of them even
reached Aten orbits, inner-Earth orbits, and typical main-belt asteroidal
orbits.
Based on orbital elements
sampled with a 500 yr step, we calculated the mean probabilities of
collisions of JFCs with planets. These collision probabilities can differ
by two orders of magnitudes for different series of calculations, in each of
which we consider initial orbits of bodies close to those of just one comet. If
we use initial orbits close to those of various JFCs and even exclude a few
bodies with the largest probabilities, the mean probability of a collision of a
former JFC with the Earth during its dynamical lifetime of the object exceeds
4·10-6, enough for delivering an amount of water equal to the mass
of Earth oceans during the formation of the giant planets.
We studied numerically the migration of 20,000 dust particles
with the initial velocities and positions to be the same as those of the
numbered asteroids, trans-Neptunian objects, and several comets. We used the Bulirsh-Stoer method of
integration and took into account the gravitational influence of all planets,
radiation pressure, Poynting-Robertson drag and solar wind drag. The
integrations were made for values of the ratio between the radiation pressure
force and the gravitational force β from 0.0001 to 0.4. For silicate
particles such values of β correspond to diameters between 4000 and 1 microns,
respectively. Based on the orbital
elements obtained with a step of 20 yr, we calculated the probabilities of
collisions of dust particles with all planets (e.g., S.I. Ipatov, Proc. IAU Symp. 263, 2010,
41-44, http://arxiv.org/abs/0910.3017). Our results on the migration of
interplanetary dust are presented in (S.I. Ipatov
et al., Annals of the New York Acad. of Sci., 2004, v. 1017, 66-80; S.I.
Ipatov and J.C. Mather, Advances in Space Research, 2006, v. 37, 126-137). The
problem of delivery of volatiles to the terrestrial planets was discussed in
several papers by M. Ya. Marov and S.I. Ipatov (e.g., Solar System Research, 2005, v. 39, 374-380).
We compared (e.g., Ipatov et al., Icarus, 2008, v. 194, 769-788) our
computer simulation results of dust migration and distribution with the results
of observations of dust (e.g.,
with the spectral observations of the zodiacal light presented by Reynolds et al., 2004, Astrophys.
J., v. 612, 1206-1213). Considering the
distributions of coordinates and velocities of dust particles obtained in our calculations,
the solar spectrum, and a model of scattering of light by dust, we calculated the
spectrum of a dust cloud produced by different small bodies (asteroids, comets,
and trans-Neptunian objects). The results of modeling are relatively insensitive to the scattering
function considered. Based on the comparison of our model with the observations
(e.g., based on that dust spectra are different for
different parent bodies), we estimated the fractions
of zodiacal dust produced by asteroids, comets, and trans-Neptunian objects and
the typical eccentricities of zodiacal dust particles. For example, we concluded that cometary
dust particles can play a considerable role in the zodiacal light.
Migration
of small bodies (before 2001)
The evolution of orbits of
asteroids, Jupiter-crossing objects, and trans-Neptunian objects (TNOs)
under the gravitational influence of planets was studied on the basis of
numerical integrations of the equations of motion. For example, Ipatov (e.g., Sov.
Astron. Lett., 1989, v. 15, 324-328; Icarus, 1992, v. 95, 100-114) showed for
the first time that for the 5:2 resonance with Jupiter, the range of semimajor
axes, eccentricities, and inclinations in which fictitious asteroids became
Mars-crossers in 105 yrs is close to the zone that is avoided by
real asteroids. Ipatov (Solar Syst. Res., 1995, v.
29, 9-20; Celest. Mech. & Dyn. Astron., 1999, v. 73, 107-116) demonstrated
that due to the gravitational influence of the largest TNOs, the
semimajor axes of several percent of TNOs could have changed by more than 1 AU
during the last 4 Gyr. Moreover, small variations in the orbital elements of
TNOs caused by their mutual gravitational interactions can lead to large
variations of these elements under the gravitational influence of the planets
(S.I. Ipatov & J. Henrard, Solar Syst. Res., 2000, v. 34, 61-74).
The studies of the evolution
of orbits of two gravitationally interacting bodies moving around the
Sun were based mainly on the results of numerical integration of the equations
of motion of the plane three-body problem. Some analytical investigations were
also made. The following types of evolution were studied (S.I. Ipatov, Solar Syst. Res., 1994, v. 28, 494-512): the motion
around triangular points of libration in tadpole and horseshoe synodical
orbits, the case of close encounters of bodies, and the chaotic variations in
orbital elements when close encounters can't take place.
Observations of asteroids (1999). In 1999 I visited
the Royal observatory of
Migration of
bodies and planets in the forming solar system (1975-1993)
In 1975-1993 I studied mainly the process
of planet formation. The studies were based on computer simulations of the
evolution of disks consisted initially of several hundred gravitating bodies
coagulating under collisions. The mutual gravitational influence of bodies was
taken into account with the use of the method of spheres (i.e., outside a given
sphere, the bodies were assumed to move around the Sun in unperturbed Keplerian
orbits, whereas inside that sphere the relative motion was considered as a
two-body problem). An effective method for choosing the pairs of encountering
bodies was worked out. Our
results on the evolution of disks of gravitating bodies coagulating under
collisions in the feeding zone of the terrestrial planets, which were obtained
by the method of spheres (e.g., S.I. Ipatov, Sov. Astron. 1981, v. 25(58),
617-623; S.I. Ipatov, Solar Syst. Res., 1993, v. 27, 65-79), are close to the
results obtained later by numerical integration. The evolution of the disks
corresponding to the feeding zones of the giant planets was also studied. It was
shown for the first time that if embryos of Uranus and Neptune had been
initially located near Saturn's orbit, then they could increase their semimajor
axes to the present values during the migration caused by the interactions of
planets with migrating planetesimals even for masses of these embryos greater
than ten Earth's masses. In favor of the method of spheres of action, we can
mention that the same results of migration of the embryos of Uranus and Neptune
that were obtained by us with this method with the use of a slow computer (S.I.
Ipatov, Soviet Astron. Letters, 1991, v. 17, 113-119; S.I. Ipatov, Solar System
Research, 1993, v. 27, 65-79) were obtained about ten years later by numerical
integrations using computers that are at least three orders of magnitude
faster, and using much more computer time.
Mathematical modeling for
non-astronomical problems
Besides astronomy,
I have an experience in mathematical modeling for encountering of two
spacecrafts with a minimum expenditure of fuel (1973-1974) and for the channel
routing for two-layer microchips (1985-1990).
In 2001 I took part in the grant “Studies of
generation of acoustic waves under the influence of fluids on walls of pores
and their spreading in porous medium with fluids and gas” of the Schlumberger
oil company. In this grant I was responsible for mathematical modeling.
Teaching
experience
In 1998 I delivered lectures on migration of celestial
bodies in the Solar System at the astronomical department of