Prof. Dr. Ewine van
From the Special Topic of
In our recent analysis of astrochemistry research over
the past decade, the work of Prof. Dr. Ewine van Dishoeck
ranks at #1, with 43 papers cited a total of 687 times.
Three of these papers are included in the list of the 20
most-cited papers in this field for the past 10 years, and
another three are on the two-year paper list.
Prof. Dr. van Dishoeck's record includes 179 papers, the majority of which
are classified in the field of Space Science, cited a total of 3,663 times
between January 1, 1997 and December 31, 2007. She is also a Highly Cited
Researcher in Space Sciences.
Prof. Dr. van Dishoeck is on the Faculty of the Leiden Observatory in
the Netherlands, where she holds the title of Professor of Molecular
In the interview below, she talks with
ScienceWatch.com about her highly cited research.
Please tell us a little about your research
and educational background.
I studied chemistry at Leiden University and was originally determined to
continue with my Ph.D. in theoretical quantum chemistry. However, the
professor had died a few years earlier and it became clear that there was
not going to be a successor, so I was forced to look elsewhere. My
then-boyfriend (now husband), Tim de Zeeuw, was studying astronomy and had
just had a lecture about interstellar molecules. "Isn't that something for
you?" he asked. And indeed it was!
Supervised by the world's expert at Harvard, Prof. Dalgarno, and Prof.
Habing in Leiden, I made the switch to astrochemistry and did my thesis on
this interdisciplinary topic. I then moved to the US for six years,
spending time at Harvard, Princeton, and Caltech, where I continued to
broaden my astronomy background with observations at a variety of
In front of the Very
Large Telescope at Cerro Paranal
I returned to Holland in 1990 to set up an interdisciplinary group within
the astronomy department, but with close collaboration with chemistry. At
any given time, my group consists of a mix of astronomers and chemists. The
Raymond & Beverly Sackler Laboratory for Astrophysics, which simulates
chemical processes in interstellar space, is also closely connected with my
research. While most of our publications are in astronomy journals, we do
also regularly publish in chemical physics journals.
What drew your interest to this particular area of
My interests are both in basic molecular processes (e.g., how does a
molecule fall apart under the influence of UV radiation?) and the use of
these molecules as diagnostics of the regions in which they are found
(e.g., can they tell us how hot or cold it is?). Astrochemistry is the
perfect combination of these two interests.
Lately, I have also become fascinated in the question of how new stars like
our Sun and planets like Earth formed, and especially which chemical
building blocks are available that could potentially lead to life on new
planets. But, as discussed above, my career happened at least partly by
I understand that your research group focuses on
basic chemistry in space as well as the formation of stars and
planets. Would you talk a little about each aspect of your research
and the methods you use?
Our research can be divided into several related parts:
1. Basic chemistry:
Our aim is to provide insight into basic chemical processes under the
unusual conditions in space (extremely low densities and temperatures,
harsh UV) and provide actual numbers (rates) for astronomers to use in
their models (e.g., how rapidly does a molecule fall apart in a typical
interstellar cloud?). Thus, it has a basic chemistry aspect (mechanisms)
and an application (rate) aspect.
We use ab initio quantum chemistry and molecular dynamics
techniques, in collaboration with the chemistry department. Also, together
with Harold Linnartz, we simulate interstellar ices and gases in the
Sackler Laboratory for Astrophysics.
2. Formation of stars and planets
Our aim is to use molecules to understand the physics of how new stars and
planets are formed from the tenuous clouds, as well as to probe the
chemistry during star and planet formation. The different aspects are:
Molecules as chemical diagnostics: as a new star is formed and
heats up its surrounding envelope, the chemistry changes. Thus,
some molecules are very good tracers of the coldest collapsing
clouds, others of the hotter gas when the star is forming.
Your most-cited paper in our astrochemical Special
Topic is the 1998 Annual Review of Astronomy and Astrophysics
article, "Chemical evolution of star-forming regions," (36: 317-68,
1998). Would you sum up the main points of this review for our
In this review, Geoff Blake and I made a synthesis of the available
literature up to 1997 on observations and models of regions in which stars
have only just been born and are still deeply embedded in their natal
clouds. It was very timely, because systematic studies of these very young
stars, ranging from those as massive as the stars in Orion to low-mass
stars comparable to our "baby" Sun, had only just become possible due to
the increased sensitivity of ground-based and space-based telescopes.
In particular, the launch of the Infrared Space Observatory (ISO) had
opened up the infrared window from space (from the ground, much of it is
not accessible due to H2O and CO2 in our own
atmosphere). ISO was particularly powerful for studying the dust grains in
space, i.e., the tiny (submicron-sized) solid particles present in every
cloud, often surrounded by ice mantles. These dust grains play an important
role in the chemistry. Thus, complete chemical inventories—both of
the gas and of the ice—were now possible for star-forming regions.
We outlined a general scenario applicable to both high- and low-mass stars
in which gases freeze out onto the cold dust grains during the collapse
phase, but then start to evaporate back into the gas when the young star
heats up its surroundings, where they drive a so-called hot core chemistry
leading to complex organic molecules. A key point was that we were able to
identify clear chemical and physical diagnostics for each evolutionary
One of your most-cited original papers in our
database is the 2000 Astrophysical Journal paper, "An inventory of
interstellar ices toward the embedded protostar W33A," (Gibb EL,
et al., 536: 347-56, 10 June 2000). Please tell us a
little bit about the goals and findings of this paper.
This paper reported one of the first complete mid-infrared spectra of a
high-mass protostar, obtained with the ISO. The dust grains are so cold (10
K) that they act as a deep-freeze: molecules from the gas collide with the
grains perhaps once every 10,000 years and then have a 100% chance to stick
(except for H2 and He). This is just as what happens on a cold
night with your car window: the H2O molecules from the
atmosphere freeze-out and form an icy layer. Once on the grains, a
different chemistry can occur than in the gas.
Although ices had been detected in the early 1970s from the ground, much
was still unknown because of obscuration by our own atmosphere. ISO allowed
the first complete inventory of interstellar ices and the source W 33A
happens to be one of the most ice-rich sources. Thus, it rapidly became
the standard reference to compare with for all other ice studies.
The detected ices nicely confirmed a theory, postulated in the early 1980s
by Xander Tielens, that hydrogenation is the primary grain surface process.
Thus, C, N, and O are turned into CH4, NH3, and
H2O ice, and CO into methanol ice (CH3OH).
As a side note, stimulated by these observations, we are now actually
studying this hydrogenation directly in the Leiden laboratory.
Another paper that is one of my own favorites is our 2006 letter, "Hot
organic molecules toward a young low-mass star: a look at inner disk
chemistry," by Lahuis et al. (Astrophysical Journal
636: L145-8, 10 January 2006), where we detected abundant acetylene and
hydrogen cyanide in the planet-forming zones of disks around young stars.
View NASA press release.
Where do you see this research going in five to
First, we will focus on water in star- and planet-forming regions, a key
ingredient in the chemistry and for the origin of life. As noted before,
water needs to be studied from space. ISO observed water and other ices;
the Herschel Space Observatory, which will be launched within a year, will
study water gas. Our group is leading an international team to study water
from the earliest to the later phases of star formation and from low- to
high-mass stars. Visit for more detail.
Second, the Atacama Large Millimeter Array (ALMA) will become operational
in the next five years and will be particularly powerful to zoom in on the
planet-forming disks around young stars and image the chemistry directly in
zones where new planets are forming.
Also, the successor of the Hubble Space Telescope, the James Webb
Telescope, will be launched around 2014 and will have a new powerful
What should the "take-away lesson" about your work
be for the general public?
Take-away lesson 1: Complex organic molecules, which could form the
building blocks for the origin of life, are widespread in regions where new
stars and planets are formed.
Take-away lesson 2: One always finds something new and unexpected with a
new observational facility (opening up a new wavelength range or jump in
sensitivity, spectral and/or spatial resolution). Sometimes one has to dig
deep, but if one digs deep enough, there is always something exciting to
Take-away lesson 3: Interdisciplinary science is fun and
Prof. Dr. Ewine F. van Dishoeck
Leiden, the Netherlands
Keywords: Prof. Dr. Ewine van Dishoeck, astrochemistry, planet
formation, star formation, interstellar cloud, inner disk chemistry,
interstellar ices, origin of life.