Dr. William Ward, an Institute Scientist in the Department, has been announced as the recipient of the 2004 Dirk Brouwer Prize from the American Astronomical Society's Division on Dynamical Astronomy. The Brouwer Prize was established by the DDA to recognize outstanding contributions to the field of dynamical astronomy, including celestial mechanics, astrometry, geophysics, stellar systems, galactic and extra galactic dynamics.
The text of his award reads:
William R. Ward has made a truly remarkable number of fundamental,
creative, and seminal contributions to a wide range of topics
concerning the origin and evolution of planets and satellites.
Ward was the first to recognize that the obliquity of Mars undergoes
large oscillations that are driven by secular variations in the orbit
of Mars. These oscillations have profound implications for past
variations of Martian climate. Over the years he has made a number of
other insightful contributions concerning the evolution of the Martian
obliquity. After the chaotic motion of the planets was discovered, he
realized (with Rudy) that this might allow a secular spin-orbit
resonance to be crossed and that even larger variations in obliquity
might then occur. This work inspired later demonstrations that the
obliquity of Mars undergoes large chaotic variations. Ward has made
many other contributions to the obliquity dynamics of the planets and
their satellites. He show
ed that the Moon has undergone large
obliquity variations, he was the first to realize that the Earth's
obliquity variations are small because of the large lunar contribution
to the precession, and he showed that as the Moon continues to recede
from the Earth, the Earth will encounter a secular spin-orbit
resonance and undergo large obliquity variations.
Ward is particularly well-known for his many works modeling the
dynamical interaction between planetary embryos, gaseous, and particle
disks. In 1984 (with Hourigan), he derived the minimum mass that a
planet must have in order to open a gap in an inviscid disk, and
observed that once such a gap was opened, rapid tidal drift would
terminate. To describe these two drift regimes, he later coined the
terms Type I and Type II migration now adopted in the literature,
where the former is relatively rapid when the planet has not opened a
gap in the nebula, and the latter occurs on the viscous time scale of
the disk after the plane
t becomes large enough to open a gap. In a
1986 paper, Ward examined the sources of asymmetry in disk-planet
interaction in the pre-gap phase and concluded that in a Keplerian
disk, exterior torques would dominate and the planet would migrate
inward. Here the idea that there would be a systematic inward decay
of satellites and/or planets due to their interaction with an
accompanying disk was first established, and thus Ward predicted, well
before the discovery of extrasolar planets in close orbits, that
planets would spiral inward. These works are central to our
understanding the ubiquity of "hot Jupiters" and the consequences for
the survival of terrestrial type planets.
For his many contributions to the field of dynamics, including his
fundamental contributions to our understanding of planetesimal
formation, planetary obliquity variation, secular resonance sweeping,
the origin of the Moon, lunar evolution and dynamics, planet-disk
interactions, planet migration, and pla
netary formation dynamics, Bill
Ward is truly deserving of the Division of Dynamical Astronomy's
Brouwer Award.
See the official SwRI press release