This older page lists research project topics, last updated in 2014.
My main research focus is on atmospheric gas and cloud composition, especially as
tracers of atmospheric chemistry, climate, evolution, and origins.
I study planetary atmospheres using a wide range of techniques and facilities: the mass spectrometers
on the Galileo Probe and Curiosity Mars Rover, sensors on spacecraft missions like Cassini,
and remote sensing with ground-based
and space telescopes like Keck and Hubble.
MARS ATMOSPHERIC COMPOSITION
SAM on Curiosity measured accurate ratios of isotopes and molecules
in Mars' atmosphere, producing some interesting surprises. A higher than expected argon/nitrogen
ratio presents an intriguing puzzle when compared with Mars meteorite data: how could this gas ratio
have changed so much over only a few million years? Oxygen has been observed by MSL (ChemCam and SAM) to
vary over the martian year, but this too is completely unexpected. The atmosphere of Mars is more compositionally
dynamic than we thought!
Collaborator Chris Go was the first to notice in early
2006 that White Oval BA had become Red Oval BA, and some
people nicknamed the storm "Red Spot Jr." Our team used
Hubble's finest-resolution camera (the ACS/HRC; upper left picture) to image
the Red Oval, and we retrieved very precise velocity fields
with the data. We also studied the variation of haze above
the Oval, which did not change much between 1995 and
While studying Oval BA with Hubble and the Keck
telescope, and comparing it with the Great Red Spot (GRS)
and smaller ovals, we made several key discoveries. We
described the circulation within these vortices that
preserves them from decaying away. We found that large
vortices like the GRS and Oval BA may have thin arcs around
them in infrared images at 5 μm (lower left image), while smaller
anticyclones are completely surrounded by complete rings in
images at this wavelength. Finally, we found that dynamical
models of the Oval BA and the GRS require that the vortices
must extend down to the water cloud layer---and that the
abundance of water in this layer is supersolar.
Most recently, we imaged the GRS with Hubble to help figure out whether its rate of shrinking
really is accelerating,
as suggested by amateur observations.
We made the first detection of
the ammonia ice spectral feature at 10 μm in the thermal
One possible explanation for the general lack of ammonia
ice spectral signatures in Jupiter's atmosphere is that
"soot" produced by stratospheric photochemistry drifts down
and contaminates fresh ammonia ice particles, masking their
spectral signatures. With Kostas Kalogerakis, we studied this effect in the lab and with models.
We submitted a "fresh clouds" model that estimates cloud densities based on the
strength of updrafts delivering cloud-forming gases from below.
We have been collecting high-spectral resolution measurements of Jupiter's
radiation at 5 μm wavelengths, where methane features can
serve as "spectral dipsticks," a technique pioneered by Gordy Bjoraker
to determine the depths of the otherwise hidden water cloud.
Advances in technology used by amateur astronomers led to
the discovery three impacts on Jupiter in 2009 and
2010. The first of these, discovered by Anthony Wesley and
confirmed by Chris Go, was large enough to leave a "scar"
of high-altitude aerosols that appear bright in the
methane-band images shown here.
The first observations in
the sequence serendipitously became very the first science data
taken by Hubble's Wide Field Camera 3, because the impact
happened while Hubble was being checked out after its final
servicing mission. At that time, I was a Visiting
Scientist at STScI (Hubble headquarters).
Jupiter's clouds are ever changing: belts and zones
shift colors, intriguing new features appear and disappear,
the powerful east-west jets shift slightly in latitude and speed,
and spectacularly large convective plumes erupt from the
deep water cloud layer and reach all the way up to the
These events are interesting in their own right, and we
work hard to describe the physics behind the
events. But the rich history of time-domain Jupiter
data is also of great value because it provides a whole new
angle of attack (distinct from spatial-domain imaging data
or from spectral-domain data) to understand processes such
as heat transport, atmospheric structure and evolution, and
the formation of clouds and hazes.
The images to the left show one of the changes in 2007:
a drop in the cloud density close to the equator, darkening
the equatorial zone. I proposed a technique (2007 AGU
poster, below) for using this cloud change to measure the
source of Jupiter's equatorial tropospheric haze.
With Máté Ádámkovics I
researched a "morning drizzle" in Titan's atmosphere. This
important part of the methane cycle on Titan---analogous to
the hydrologic cycle on Earth---involved ground-based
hyperspectral adaptive-optics imaging on some of the
world's largest infrared telescopes.
Binary asteroids are the holy grail of the study of
asteroid interiors, because measuring their orbits yields
the mass of the system, which leads to a determination of
the asteroids' density. Trojan asteroids, which orbit two
jovian "months" ahead and behind Jupiter, are thought to be
remnants of the same population of planetesimals that
formed the outer planets. 617 Patroclus and 624 Hektor are
the only known binary Trojans. Franck Marchis and I
discovered Hektor's companion during an adaptive optics
observing run at Keck. We have also been accumulating
lightcurve data on many Trojan asteroids and other small
solar system bodies.
One of my first projects upon arriving at Berkeley to work
as a postdoc
with Imke de Pater was to analyze near-infrared
spectroscopic observations of Jupiter's ring and moons taken with
NIRSPEC at Keck. We also attempted to measure thermal radiation
emitted from elusive larger bodies in Jupiter's ring using
the ultra-sensitive Spitzer Space Telescope, but
unfortunately those data were awash with stray light
from the much brighter Jupiter.
I spent my graduate years in Michigan working with a tiny
but priceless stream of
some 7000 integers. These numbers from the Galileo
Probe Mass Spectrometer were the only direct in
situ record of Jupiter's atmospheric composition,
between the levels of about 0.5 and 22 bar. From this data
we measured nitrogren and noble gas isotopic ratios,
cosmochemical constraints that are difficult or impossible to collect
We measured strange profiles of the cloud forming gases,
and struggled to explain the "jovian desert" the probe had
descended into. Unfortunately, the deep water abundance was
not measured due to the meteorology of the probe entry
site. Indirect measurements, now including vortex models,
generally agree that the probe would have measured a
supersolar water abundance, had it descended into a
"normal" area of the planet.
We also measured surprisingly high levels of complex
hydrocarbons... at levels as deep as 10 bar! These
chemicals are thought to form in the rarified stratosphere
and diffuse down into the troposphere, but
it seems impossible that the high concentrations measured
could have been stratospherically generated. The probe did
not carry an imaging camera, so even if a hydrocarbon spray
from a jellyblimp---savagely slain by a razorwing---had
splattered the GPMS inlets, we would have had no sign that
anything was amiss, other than elevated hydrocarbon levels.
Jellyblimps and swordtails taken from