phone (281) 486-2113
fax (281) 486-2162
Research Interests
My research interests include: the dynamics of the solar system,
the formation and evolution of planetary systems, and analyzing
astronomical observations of planetary objects and circumstellar
disks.
1. Planet Formation. A major portion of my research concentrates
on theoretical investigations of the origins of planetary
systems, with an emphasis on the gravitational interactions that
are exerted between protoplanets and the planet-forming
circumstellar disk. Of special interest to me is the excitation
and propagation of spiral waves in such disks. Spiral waves are
common in galactic disks and in planetary rings, and these waves
are very effective at communicating angular momentum between a
disk and an embedded perturber. Consequently, the propagation of
spiral waves can be of considerable importance in a
planet-forming environment as they can, for example, drive
planet migration and also open gaps in a disk.
2. The Kuiper Belt, which is a vast swarm of distant comets
orbiting beyond Neptune, is also of great interest to me since
it preserves a dynamical record of formative events that
occurred during the early history of the outer solar system.
Kuiper Belt Objects have a rather peculiar distribution of
orbits that strongly suggests that Neptune's early orbit
had expanded outwards some 8 AU. To examine this in detail I
used a symplectic N-body integrator to follow the orbital
migration that occurs when the recently-formed giant planets
gravitationally scatter the residual planetesimal debris
from which they formed. I am currently using this model to
investigate the dynamical sculpting that occurs in the Kuiper
Belt as Neptune migrates outwards. Detailed comparisons between
the modeled and the observed Kuiper Belt endstates are being
performed in order to rigorously test the planet-migration
hypothesis. Neptune may also have launched spiral waves in the
early Kuiper Belt, and studies of their dynamical as well as
observational consequences are continuing.
3. Comets and Interplanetary Dust. I have also analyzed the
Hubble Space Telescope observations of Comet Shoemaker-Levy 9
that were acquired prior to that comet's impact with Jupiter. In
order to better understand the dusty cometary comae associated
with the 20-odd comet fragments, I developed a cometary dust-tail
model that, when fitted to the observations, allowed me to
characterize the properties of the comet dust as well as place
tight bounds on the sizes of the nuclei that were embedded within
each comae. And more recently I have analyzed images of the inner
zodiacal light (which is sunlight that is reflected by
interplanetary dust) that were acquired by the Clementine
spacecraft while in lunar orbit. By fitting a model of the
interplanetary dust complex to these observations, I have been
able to infer the spatial distribution of the interplanetary dust
and also answer an age-old question: what fraction of
this dust is contributed by asteroids and what fraction comes
from comets?
4. Circumstellar Disks. I also have a longstanding
interest in observations of circumstellar disks since such
objects may be sites of ongoing planet formation. In 1999 I
used the ESO 3.6m telescope telescope to acquire adaptive
optics-corrected images of circumstellar disks, and this
project will continue in the summer of 2002 at the Palomar 200
inch telescope.
The following selections are a poorly organized sample of some of my
research interests. Follow these links to find some of my LPSC abstracts,
slide from some of my talks, preprints, and conference posters.
My 2002 LPSC abstract on
Secular Resonance Sweeping in a Self-Gravitating Planetesimal Disk,
with Application to the Kuiper Belt.
This PDF slideshow is from the seminar
I recently gave at the LPI on the
Clementine
observations of the inner zodiacal light.
This PDF file contains the slides I showed at the
2001 Gordon Conference on the Origins of Planetary Systems;
the subject is planet-migration.
Yours truly is the local host for the 2001 AAS Division on Dynamical Astronomy annual meeting.
1999 AAS poster displayed in Austin, TX.
"Orbital Evolution of Planets Embedded in a Planetesimal Disk"
Transparencies from my 2000 DDA talk given in Yosemite CA, entitled "Planet Migration Via Numerous Stochastic Scattering Events". This is a 3.5 Mb Postscript file.
Simulations of spiral bending waves launched at a vertical
secular resonance:
(1.) Waves launched by a planet precessing
at a fixed rate.
(2.) Waves launched by a freely precessing planet
that is driven by the disk-gravity.
A Postscript version of a talk given at the
1999 meeting of the AAS Division for Dynamical Astronomy, which
describes this phenomenon.
This directory contains my 2002 DPS poster on spiral waves in the primordial Kuiper Belt, plus some animations of this phenomenon.
My abstract entitled "The Outer Edge of
the Kuiper Belt" from the XXXI Lunar and Planetary Science
Conference in March 2000.
The Icarus paper is also
available.
Some research results on planet-migration:
by Hahn and Malhotra, accepted for publication in the Astronomical Journal.
Download the 0.2 Mbyte gzipped postscript preprint
or the 17 Mbyte postscript preprint.
planet formation graphics.
other_files