From the Special Topic of
According to our April 2008 Special Topic on
astrochemistry, the scientist whose work ranks at #6 is Dr.
Katharina Lodders, with 4 papers cited 351 times. Dr.
Lodders also authored the paper at #1 on our 10-year list
with 323 citations: "Solar system abundances and
condensation temperatures of the elements,"
(Astrophys. J. 591: 1220-47, part 1, 10 July
2003). This paper is also a Highly Cited Paper in the field
of Space Science in
Science IndicatorsSM from
Reuters. Dr. Lodders is an Associate Research Professor
in the Department of Earth & Planetary Sciences at
Washington University in St. Louis, Missouri.
In the interview below, she talks
with ScienceWatch.com about her highly cited
Please tell us a little about your research
and educational background.
I am a chemist by education. I received my Doctorate in 1991 from the
Johannes-Gutenberg University in Mainz, Germany, and did my thesis work at
the Department for Cosmochemistry at the Max-Planck Institute for Chemistry
in Mainz. This work was about chemistry during core formation in the Earth
and in other planets and also related to meteorites.
"...it is interesting to follow
how the elements produced in different stars eventually
end up in new stars and planets."
I wanted to continue to work on cosmochemistry, which is closely related to
planetary science and astronomy. In 1992, I started working at Washington
University in St. Louis as a postdoctoral researcher, and currently I have
a position as Research Associate Professor here.
What do you consider the main focus of your
research, and what drew your interest to this particular
My research focuses on gas and dust chemistry in stellar environments and
planetary atmospheres. I got interested in dust formation in stellar
environments because dust grains that condensed in the ejecta of evolved
stars, such as supernovae, are found in some meteorites. Obviously, star
dust was one ingredient when our solar system formed. Other than hydrogen
and helium, all other chemical elements that we have in our solar system
were made in previous generations of stars.
The stardust grains in meteorites formed from the ejected matter of dying
stars. Therefore, grains can contain larger proportions of the elements
that the star produced during its lifetime, but grains may not capture all
elements completely, and some elements stay in the gas. We model these
chemical fractionations of the elements during the grain formation
processes with chemical thermodynamics and kinetics. Overall, it is
interesting to follow how the elements produced in different stars
eventually end up in new stars and planets.
The second major theme of my work is the atmospheric chemistry of gas giant
planets, both inside and outside of the solar system, and of brown dwarfs,
which are cool objects with insufficient mass to become real stars. The
exoplanets and brown dwarfs were only first discovered in 1995. The
different compositions of our gas giant planets—Jupiter, Saturn,
Uranus, and Neptune—tell us something about the chemistry during the
formation of our solar system. It is a natural extension to apply the
methods developed for the planets in our solar system to study the newly
discovered planets. Differences and similarities in the chemistry of our
gas giant planets and gas giant exoplanets can help us understand how
planetary systems form.
Your most-cited paper in our astrochemical Special
Topic is the 2003 Astrophysical Journal article, "Solar
system abundances and condensation temperatures of the elements."
Would you sum up the major points of this review for our
The composition of the Sun is commonly used as the baseline composition for
comparing and modeling elemental abundance variations in stars as well as
planets and meteorites. The solar elemental composition is derived from
spectroscopy of the Sun's photosphere and from geochemical analyses of
certain meteorites that contain the elements in similar proportions as the
Sun. In principle, the solar, or solar-system, composition can be well
determined from the analysis of the Sun's photospheric spectrum and
meteorite analysis, but refinements of the data are still necessary.
The last major evaluation of solar and meteoritic abundances of all stable
elements was done in 1989. Since then, re-analyses led to significant
revisions for important elements like C and O in the Sun. There were also
updates for several other elements and their isotopes that had been
re-measured in the Sun or in meteorites.
The composition of our Sun is not only important for comparison to
astronomical observations of other stars or for input to models of stellar
evolution. It is also important because it is representative of the
material from which everything in the solar system—the Sun, the
planets, their moons, asteroids, and comets—formed through chemical
and physical processes.
When the solar system formed, the elements were chemically fractionated
through condensation and evaporation processes. At a given temperature,
some elements prefer to be in a condensed phase whereas other elements
prefer to be in the gas. The condensation temperatures of the elements are
a quantitative measure of the temperatures that are needed to vaporize an
element out of solids or condense it out of the gas.
The changes in solar abundances, especially in C and O, influence what gas
molecules and solids are present at a given temperature and total pressure.
I found it therefore practical to summarize the best available abundance
determinations for the Sun and meteorites, derive the solar system
elemental composition, and then to use these data and chemical
thermodynamics to calculate a self-consistent set of condensation
Many of your original papers deal with the
chemical composition of stellar atmospheres. Would you talk a little
about this aspect of your work?
I am interested in the chemical speciation of the elements in planetary and
cool stellar atmospheres. The temperatures of the outer atmospheres of cool
stars, brown dwarfs, and giant planets are low enough that gas molecules
become abundant. Several molecular gases give characteristic absorption
features—molecular fingerprints so to speak—in the spectra of
cool stars and brown dwarfs, and the investigation of the underlying
chemistry is part of my work.
"Differences and similarities in
the chemistry of our gas giant planets and gas giant
exoplanets can help us understand how planetary systems
What makes these atmospheres quite interesting is that clouds can form out
of different materials. On Earth we have water clouds, but chemical
modeling predicts that brown dwarfs and gas giant planets have cloud layers
of refractory ceramics, iron metal, salts, water, and ammonia ice,
depending on how cool the atmosphere is on the outside. Jupiter has all
these materials as clouds with increasing depth, but only the ammonia
clouds on the top can be seen. There are already hints of silicate clouds
in brown dwarfs and very hot exoplanets, and it is probably just a matter
of time until the spectral signatures of different cloud materials become
clearly detectable for exoplanets.
Where do you see your research going in five to
I expect that other types of star dust minerals will be discovered in
meteorites, and that we will learn more about the compounds that are
present when stars and planetary systems form. We have made several
predictions as to which star dust minerals should be there; some have been
found, but others that we expect are elusive so far. The minerals may
indeed form at the stars, but a lot can happen to dust after leaving its
birthplace near a star, and the chemical modifications need to be better
I also expect that exoplanets will remain an exciting research area.
Currently, new exoplanet detections and more physical and chemical
information about them are almost regular items in the weekly news. It will
be interesting to see how different or similar planetary systems with
Earth-size planets will be from our own, and how unique the chemical
pathways are for making planets like our Earth.
What should the "take-away lesson" about your work
be for the general public?
A lot of gas and dust chemistry happens when stars and planetary systems
are born, and when stars die. On an astronomical scale, our Earth is a
"dust ball". Chemistry tells us what the dust is made of, and how it can be
Dr. Katharina Lodders
Department of Earth & Planetary Sciences
St. Louis, MO, USA
Katharina Lodders's most-cited paper with 323
cites to date:
Lodders K, "Solar system abundances and condensation
temperatures of the elements," Astrophys. J.
591(2): 1220-47, part 1, 10 July 2003. Source:
Essential Science Indicators
Keywords: astrochemistry, solar nebula, stellar
environments, planetary atmospheres, dust formation, gas giant
planets, brown dwarfs.