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 Kirkwood gaps, the asteroid and comet hazard to the Earth, recognition of cosmic ray signatures on CCD images, 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

During January 2005 – August 2006 I was a member of the Deep Impact team at the University of Maryland. Since April 2008 I have worked at 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”. I analyzed (e.g., wrote IDL codes) images made by the Deep Impact spacecraft. 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) and velocities and relative amount of material ejected from the comet at different times after the collision (e.g., S.I. Ipatov and M.F. A’Hearn, http://arxiv.org/abs/0810.1294). The obtained results were presented at several conferences (LPSC 2006, 2008; ACM 2005, 2008; 207th AAS meeting, COSPAR 2006, 2008, 26th IAU GA, DPS 2008). 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).

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 Belgium for 5 months via the grant of the Belgian office for scientific, technical and cultural affairs (DWTC). In the observatory together with Dr. Eric Elst and Dr. T. Pauwels, I took part in observations of asteroids and comets with the use of a 0.85 m Schmidt telescope with a CCD-camera (3072x2048 pixels). In autumn 1999 I have made about 700 sky images. We were the first to observe several new asteroids, six of them have already got numbers. Based on the codes in BASIC written by Eric Elst, I wrote a FORTRAN code for determination of orbits. Laplace's approach (the modification by Danjon) was used.

 

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 Moscow team of the INTAS grant (“Migration of celestial bodies from different regions of the solar system to near-Earth space”, project 240 of INTAS Call 2000).

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 Moscow State University (these lectures were published as a book in 2000). I taught mathematics at Russian high schools as a volunteer in mid-70s. In 2002-2003 I supervised the work of P. Taylor, who was a summer student in NASA/GSFC in 2002 and 2003, and worked part time between these summers.