Doug Hamilton's Research Interests

In my research, I attempt to use classical physics to understand basic features of the solar system. Depending on the specific requirements of a given project, I develop theory, do computer modeling, make telescopic observations, and/or analyze spacecraft data. Below is list of the general areas in which my research is focussed as well as some specific projects. More details can be found in my Scientific Publications and in my Recent Talks. See also my Cover Images. There is always more to say, and so I will be adding more to this page as time permits!

Shoemaker Levy 9 Data from Calar Alto

SL9 Movies!!

Gallery of SL9 Images

There is lots of good SL9 stuff at JPL's SL9 Home Page. Here, for example, are the Top 20 SL9 Images requested over the internet during impact week. Our first A image from the Calar Alto Observatory is number 1! These images are brought to you by the Calar Alto SL9 Team.

Ulysses and Galileo Dust Detectors

What Do They Do?

The Discovery of Interstellar Dust

The Discovery of Jovian Dust Streams

Want to know more? Check out the
DDS Home Page. The Galileo/Ulysses/Cassini DDS Team Meeting was held here at the University of Maryland May 27-29, 1998.

Non-Gravitational Forces

Non-Gravitational forces strongly influence the orbital motions of dust both in planetary rings and in interplanetary space. These forces typically become important for dust grains a few microns in size, and dominant for grains a few tenths of a micron in size. Electromagnetic effects are important in shaping the jovian ring and Saturn's E and G rings, cause the jovian system to emit high-speed dust streams, eject tiny dust grains out of the solar system, and deflect small incoming interstellar grains. Radiation Pressure helps to shape Saturn's E ring and the putative martian rings, causes dust to form elegant comet tails, and sweeps the environs of asteroids free of millimeter and smaller objects. Various Drag Forces broaden the jovian ring, cause interplanetary grains to spiral into the Sun, and bring dark dust from Phoebe inward to icy Iapetus to create the striking black/white asymmetry seen on that satellite (see below).

Orbital Dynamics of Planetary Rings

Dusty rings and small satellites are intimately related since impacts of interplanetary micrometeoroids into small moons eject significant amounts of debris into circumplanetary orbit. These become ring particles which usually end their lives by striking the embedded moonlet, sometimes energetically enough to release still more debris. Steady state is established with losses balancing production while perturbation forces govern the shape and structure of the rings. This interplay is particularly interesting at Mars, where the moons Phobos and Deimos are predicted create a faint ring of debris whose evolution is dominated by radiation pressure and planetary oblateness. On May 28, 2001, we used the Hubble Space Telescope to look for these rings. Unfortunately, we found no new rings or moons in our search, which was 3000 times more sensitive than the one done with the Viking cameras. The new upper limit on the Mars rings makes them fainter than the faintest ring material that we have seen anywhere in the Solar System. Do Mars rings exist? Almost certainly, they are just exceedingly faint!

This image (click for higher resolution) shows the distribution of 40 (blue), 100 (green), and 250 (red) micron grains in the martian rings as seen from above Mars' north pole. The rings are displayed in a rotating frame with the Sun off to the right side of the plot. Note that:

This image (click for higher resolution) shows the distribution of 40 micron grains (blue) and larger grains (green & red) in the martian rings as seen from above Mars' equator. The rings are displayed in a non-rotating frame. Note that:

What Happened to Iapetus?

What happened here? We suspect that black dust from a more distance satellite, Phoebe, (which is a very dark object orbiting Saturn in the opposite sense as Iapetus) drifts inwards and preferentially strikes the leading hemisphere of icy Iapetus. Keith Watt, a graduate student at UMD, and I have worked out some of the details. The effort constituted Keith's second year project, one of UMD's requirements for admission to Ph.D. candidacy.

Planetary Formation
(under construction)

Heather Fleming , a U. Maryland Physics graduate student, worked on her thesis research with me on the topic of planetary formation. As the giant planets accreted gas and icy planetesimals from the primitive solar nebula, they ejected many kilometer-sized icy objects to the outer solar system. These planetesimals now reside in the Oort cloud surrounding our solar system, which is where long period comets come from. The ejection of planetesimals also caused the orbits of the giant planets to evolve, and Heather is currently studying what happens to debris caught in resonances with the giant planets during this orbital evolution.

The 1995-96 Saturn Ring Plane Crossings
(under construction)


The rings of Saturn were exactly edge-on as seen from Earth on 22 May 1995, 10 August 1995, and 12 February 1996; on 19 November 1995, the rings were edge-on as seen from the Sun. During these periods of unique geometry, which reoccurs only every 15 years, the brightness of Saturn's rings fades to nearly nothing and faint features in the saturnian system - small satellite and dusty rings - become visible to ground-based telescopes. Lori Lanier, a U Maryland Senior, and I are currently reducing data that I obtained from Calar Alto during May, August, and November 1995. More information can be found on the Saturn Ring Plane Crossing Homepage.

Dynamical Evolution of the Solar System

The solar system was formed in a state which differs from that observed today by 4.5 billion years of dynamical evolution. By studying the details of dynamical evolution, we can learn more about the condition of the solar system shortly after its formation. We can also understand our solar system better by studying the evolution of others like it. The following striking example shows that solar perturbations acting on planetary satellites on polar orbits rapidly destabilize the orbits. If the moon's orbit were inclined by 90 degrees out of the ecliptic, it would crash into the Earth in about 6.5 years! It is perhaps not coincidental that no satellites in the solar system have such highly-inclined orbits! Similar dynamics causes some comets to become Sun-grazing and allows Oort cloud objects to enter the inner solar system. [RPX LOGO]

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