Statement of Research Interests
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 formation of
the
Deep Impact project
During January 2005 – August 2006 I was a member of the Deep Impact team
at the
Radiative transfer in
astmospheres. 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).
Dynamics of mixing and
transport processes in the presolar cloud and in the solar nebular
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., AJL, 2008, v. 686, L119-123; S.I.
Ipatov et al., LPSC 2007). Several tens of movies showing the dynamics have
been made.
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 runs, in each of
which we consider initial orbits close to those of just one comet. If we
consider 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 similar to the mass of Earth oceans
during the formation of the giant planets.
Results of our runs testify in favor of at
least one of these conclusions (the third conclusion may be more valuable): 1)
the portion of 1-km former trans-Neptunian objects (TNOs) among NEOs can exceed
several tens of percents, 2) the number of TNOs migrating inside solar system
could be smaller by a factor of several than it was earlier considered, 3) most
of 1-km former TNOs that had got NEO orbits disintegrated into mini-comets and
dust during a smaller part of their dynamical lifetimes if these lifetimes are
not small.
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 8 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. 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, N
5, 374-380).
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., 612, 1206). Considering the distributions of coordinates and
velocities of dust particles obtained in our runs, 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.
Formation of
binaries at the stage of rarefied
preplanetesimals was studied. 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 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. Maximum eccentricities
and regions of initial data corresponding to these types were studied more
accurately than earlier. The results of computer simulations showed that the
maximum eccentricities of three gravitating particles moving around the Sun may
be some tens-fold larger than the values for two particles of the same masses.
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). Ipatov (Celest. Mech. & Dyn. Astron., 1999, v. 73, 107-116) studied
the migration of former TNOs inwards to Jupiter's orbit, as was done, e.g., by
H.F. Levison & M.J. Duncan (Icarus, 1997, v. 127, 13-23), and then
continued tracking the particles in to Earth-crossing orbits.
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 by 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). Usually the Tisserand sphere (also
called the sphere of action) is used in this method. In contrast to Opik's
scheme, in our algorithm the probability of an encounter of two bodies depends
also on the synodic period of the bodies. 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 (e.g., J.E. Chambers and
G.W. Wetherill, Icarus, 1998, v. 136, 304-327; J.E. Chambers, Icarus, 2001, v.
152, 205-224; H.F. Levison and C. Agnor, Astron. J., 2003, v. 125, 2692-2713).
The evolution of the disks corresponding to the feeding zones of the giant
planets was also considered. The mass of solids entering in Jupiter was
obtained to be larger than that in any other planet. 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 evolution due to the interactions 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 E.W. Thommes, M.J. Duncan, and
H.F. Levison (Nature, 1999, v. 402, 635-638; Astron. J., 2002, v. 123, 2862-2883) by numerical integrations
using computers that are at least three orders of magnitude faster, and using
much more computer time. This comparison shows that the method of spheres can
provide statistically reliable results for many bodies moving in eccentric
orbits.
Grants and foreign visits
Since April 2008 I have been a PI of the NASA DDAP grant “Velocities and amount of material ejected at
different times after the Deep Impact collision”. I was a principal
investigator of grants of the
Russian Foundation for Basic Research (RFBR) from 1993 to 1998 and from 2001 to
2003. In 2001-2004 I was a leader of
For one or two months, I visited Institute for
Theoretical Physics of the University of California in Santa Barbara in 1992,
Notre-Dame University in Namur (Belgium) in 1995, Berlin Institute of Planetary
Exploration in 1996, Royal Observatory of Belgium (Brussels) in 1998, and
Dresden Technical University in 2001. I made shorter visits to several other
foreign institutions and delivered lectures at conferences in various
countries. Some of these visits were supported by different travel grants.
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 (Schlumberger Cambridge Research Limited). 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