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. 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.
Deep Impact project (since 2005)
During January 2005 – August 2006, I was a member of
the Deep Impact team at the University of Maryland. I analyzed images
made by the Deep Impact spacecraft (e.g., I wrote IDL codes). I studied
automatic recognition of cosmic ray signatures on Deep Impact CCDs (e.g., S.I. Ipatov
et al., Adv. Space Res., 2007, v. 40,
160-172; http://www.astro.umd.edu/~ipatov/CRcodes.htm).
I was also a co-author of papers by M.F. A’Hearn et al. (Science, 2005, v. 310,
258-264) and K.P. Klaasen et al. (Rev. Sci. Instruments J., 2008, v. 79, 091301-77).
Since April 2008 I have
worked at the Catholic University of America as a PI of the NASA DDAP grant “Velocities and amount of material ejected at
different times after the Deep Impact collision” (e.g., S.I. Ipatov and M.F. A'Hearn, Proc. IAU Symp. 263, in press; http://arxiv.org/abs/0810.1294). The obtained
results were presented at several conferences (e.g., DDA 2009, IAU GA 2009, DPS
2009).
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; http://www.dtm.ciw.edu/users/ipatov/lpsc2008atm.ppt).
Dynamics of mixing and
transport processes in the presolar cloud and in the solar nebular (since
2006). 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 and in the solar nebular (A.P. Boss et al., ApJL, 2008, v.
686, L119-123; A.P. Boss et al., ApJ, 2010, v. 708, 1268-1280; S.I. Ipatov et
al., LPSC 2007). Several tens of movies showing the dynamics were made.
Formation of small body binaries (2009)
Formation of small body binaries at
the stage of rarefied preplanetesimals was studied (S.I. Ipatov, MNRAS, in
press, http://arxiv.org/abs/0904.3529). 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.
Migration of dust particles and small bodies (since
2001)
We (e.g., S.I. Ipatov and J.C. Mather, Advances in
Space Research, 2004, v. 33, N 9, 1524-1533; Earth, Moon, and
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 JFCs and 1500 asteroids at the
resonances 3:1 and 5:2 with Jupiter under the gravitational influence of the
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 different error limits (for an
integration step of the symplectic method not greater than 10 days). 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 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 objects 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 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 the 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 numerically studied the migration of 20,000 dust particles
with the same initial velocities and positions 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, 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 obtained orbital elements with a step of 20 yr, we
calculated probabilities of collisions of dust particles with planets (S.I.
Ipatov, IAU
We compared (e.g., Ipatov et al., Icarus, 2008, v. 194, 797-788) our
computer simulation results of dust migration and distribution with the results
of observations of dust (e.g.,
with 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 TNOs). The results of modeling are relatively insensitive to
the scattering function considered. We estimated the
fractions of zodiacal dust produced by asteroids, comets, and TNOs (based, e.g.,
on that spectra are different for different parent bodies) and 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 (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.
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.
Ipatov (Solar
Syst. Res., 1995, v. 29, 9-20; Celest. Mech. & Dyn. Astron., 1999, v. 73,
107-116) also demonstrated that, due to the gravitational influence of the
largest TNOs, the semimajor axes of several percent of the 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).
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 based on computer simulations of the evolution of disks 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
considered. 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 evolution 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 the channel routing
for two-layer chips (1985-1990) and for the generation of acoustic waves under
the influence of fluids on walls of pores (2001). 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