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AUTHOR COMMENTARIES - From Special Topics

Astrochemistry - April 2008

Ehrenfreund

"One of the greatest challenges is to reconstruct the processes which actually formed our solar system."

Professor Pascale Ehrenfreund
From the Special Topic of Astrochemistry

According to our April 2008 Special Topic on Astrochemistry, the work of Professor Pascale Ehrenfreund ranks at #5 by total cites, #6 by papers, and #5 by cites per paper. Her record in this analysis includes 20 papers cited a total of 445 times. Three of these papers are on the list of the 20 most-cited papers over the past decade, and one is on the list of the 20 most-cited papers over the past two years.

In Essential Science IndicatorsSM from Thomson Reuters, Prof. Ehrenfreund's record includes two Highly Cited Papers in the fields of Chemistry and Space Science. Her most-cited paper is "Organic molecules in the interstellar medium, comets, and meteorites: a voyage from dark clouds to the early Earth," (Ehrenfreund P and Charnley SB, Annu. Rev. Astron. Astrophys. 38: 427-+, 2000), with 211 cites at the time of this feature's publication.


Prof. Ehrenfreund is currently a Research Professor at the Space Policy Institute at George Washington University's Elliot School of International Affairs. Over the past decade, she has been Professor at Nijmegen, Leiden, and Amsterdam Universities in the Netherlands. Since 2001, she led the Astrobiology Laboratory at the Leiden Institute of Chemistry, and investigated organic matter in the interstellar medium and in solar system bodies, including planetary surfaces, comets, and meteorites. She served as Principal Investigator and Co-Investigator on many different NASA/ESA space missions, including satellites, planetary probes, and experiments on the International Space Station.

In the interview below, she talks with ScienceWatch.com correspondent Gary Taubes about her highly cited work.

  How did you first get involved with research on organic molecules in the interstellar medium?

I studied molecular biology and astronomy at the University of Vienna and completed my Master's thesis in the field of protein chemistry at the Austrian Academy of Sciences in Salzburg. I decided to continue with an interdisciplinary Ph.D. thesis combining biology, chemistry, and astronomy. In 1985, my advisors in graduate school at the University of Paris VII, Dr. Alain Leger and Dr. Louis d'Hendecourt, published the discovery of aromatic polycyclic hydrocarbons (PAHs) in the interstellar medium. When I arrived in Paris for my thesis in 1988, I decided to work on this exciting new topic, looking at the largest organic molecules identified in interstellar space—that's how I entered the field of astrochemistry.

After my Ph.D., I moved to the University of Leiden and worked predominantly on ice chemistry in molecular clouds with the late Prof. Mayo Greenberg and Prof. Ewine van Dishoeck. I was privileged to contribute to the solid state database for the Infrared Space Observatory (ISO) and to be involved in the ISO satellite data interpretation for many years. Another topic I have pursued since the early '90s is the identification of the carriers of the diffuse interstellar bands (DIBs) and the chemistry of diffuse interstellar clouds. We reported in 1994 evidence for C60+ in the interstellar medium. Over the last 15 years, I have been observing DIBs in many galactic and extragalactic environments with Dr. Bernard Foing, my students, and collaborators all over the world. Those observations provided important constraints on the organic nature of the DIB carriers that are ubiquitously observed in the universe.

"...stable isotope measurements that probe the early solar nebula will help us to better understand the fundamental questions about forming planets, solar system chemistry, and the emergence of life on Earth."

After my habilitation in 1999, I started my own Astrobiology group and moved more into solar system research, still working with the same molecules. We investigated the carbon pathways between interstellar and circumstellar regions and the forming solar system by targeting the following topics:

  • Astronomical observations of interstellar clouds

  • Laboratory studies on the photostability of organics in space environment

  • Mars simulations (survival of organics and microorganisms, oxidation)

  • Analyses of the organic composition of carbonaceous meteorites

  • Space hardware development and ground validation

  • Microgravity research

Extraterrestrial delivery via comets and meteorites has deposited organic molecules originally formed in the interstellar medium and solar nebula to the early Earth. The assumption is that some of these molecules may have been used to build up life here on Earth and maybe on Mars.

Due to our participation in the European ExoMars mission, we also focused our research in recent years on aspects relevant for life detection on Mars.

  What prompted you to write your highly cited 2000 review paper in the Annual Review of Astronomy and Astrophysics? What was your goal in writing that review?

I was invited by the editors. The final document benefited from the theoretical expertise of my co-author, Steven Charnley, and my experimental knowledge in astrochemistry. We wanted to collect all the material available and decide what is truly important concerning organic chemicals in space, in the interstellar medium, and on comets and meteorites. We tried to make the connection between these different regimes.

  How has the state of the science changed in the eight years since publication? In other words, what would you write today that you couldn’t say then?

What has become evident since then is that during solar system formation, the material that enters the inner region of the forming solar system is strongly modified. We can see remnant material from the original interstellar cloud but it is obvious that the solar nebula had its own active chemistry. And that gives a strong signature to the material, which is then forming planets.

At the time we wrote our original paper, we did not have enough evidence for this scenario. Our research field really benefited strongly from recent cometary missions—in particular, Deep Impact and Stardust. More meteorites have been analyzed in recent years with advanced laboratory instrumentation and consequently our knowledge on the early solar nebula has significantly improved. Recent observations of proto-planetary disks, using new instruments, can probe deeper and deeper into the interior of disks; astronomers can look closer to the star, and really begin to understand what happened in the early stages of planetary development. Every year, it seems, we get a closer and closer look at this process.

  What’s the most challenging aspect of your research?

One of the greatest challenges is to reconstruct the processes which actually formed our solar system. The number of well-studied meteorites and comets is still scarce.

This is why some of the ultimate questions—the questions relevant to the origin of life on Earth—are still wide open. What material came to the young planets via comets and meteorites? Where did the water come from on planet Earth? What were the conditions on the early Earth that allowed life to form and proliferate? These are major questions, and difficult ones to answer.

  Are you satisfied with the pace of research in the field? What you’ve learned since you entered it in the mid-1980s?

I’m happy for every piece of the puzzle we find, but the progress has been rather predictable. The Stardust mission confirmed ideas that some scientists had already, namely that the solar nebula was very active. It was a natural development in my career to move into solar system research and astrobiology. In 1999 I learned to analyze extraterrestrial samples in Prof. Jeff Bada's group at the University of California, San Diego, on my sabbatical leave, and I also got involved in life-detection strategies and instrumentation. That was a great experience that paved the way for my future research. I am convinced that astrochemistry will greatly benefit from a strong exchange between astronomers and meteoriticists.

  How do you see the current state of affairs in your field and its prospects for the future?

I have to say that I think the future looks bright. In the next decade, we will have a European space mission, Rosetta, that will land on Comet 67P/Churyumov-Gerasimenko (in 2014). This will allow us, for the first time, to study the composition of a cometary nucleus in situ. This space mission promises exciting results about the formation of our solar system and the material that has been deposited on the young Earth through extraterrestrial delivery. The US Mars mission Phoenix touched down on May 25, 2008 in polar latitudes and look for ice and organics. And there are two additional robotic mars missions in preparation that will investigate organic material and life: the US Mars Science Laboratory in 2009 and the European ExoMars mission in 2013. We may even have an asteroid sample-return mission in the not-too-distant future.

"Extraterrestrial delivery via comets and meteorites has deposited organic molecules originally formed in the interstellar medium and solar nebula to the early Earth. The assumption is that some of these molecules may have been used to build up life here on Earth and maybe on Mars."

In astronomy, the instrumentation keeps getting better and better. Herschel, a European mission, will be launched at the end of this year to do sub-millimeter astronomy. There are large-scale telescopes, such as ALMA—the Atacama Large Millimeter/submillimeter Array—that will be coming online soon. Then the James Webb Telescope, the replacement for the Hubble Space Telescope, will be going up in the next decade. So there are a lot of opportunities in astronomy to continue to look at the structure of interstellar clouds, proto-stellar disks, proto-planetary nebulae, etc.

The improvement of laboratory instrumentation will lead to more accurate data of meteorites. In particular, stable isotope measurements that probe the early solar nebula will help us to better understand the fundamental questions about forming planets, solar system chemistry, and the emergence of life on Earth.

  Do you have any new research projects you would like to discuss?

I am currently strongly involved in the preparation of the future European Mars mission ExoMars, scheduled for launch in 2013. ExoMars will be the first robotic mission to Mars that is dedicated to the search for life. I work on instrumentation development of the key instruments UREY and MOMA, and I also try to understand where organic molecules could actually survive on Mars. Organic material and life are believed to be destroyed by the combination of radiation and oxidizing agents and the absence of liquid water on the surface.

I am part of the Wisconsin Astrobiology Research Consortium funded by the NASA Astrobiology Institute and perform research to study the stability of organic material in Martian soil analogs with particular emphasis on the interplay between the mineral matrix and organics. We also monitor the effect of a simulated Martian environment on microorganisms and organics in order to understand how and where biomolecules may survive in the subsurface of Mars. These ground-based data are used to calibrate our instruments that will search for life on Mars in 2013.

  What unexpected or serendipitous events arose in the course of your research?

In this kind of research, progress can sometimes be achieved by just grasping chances. Last month, we had a press release from my former student Dr. Zita Martins about her thesis work. She was analyzing carbonaceous meteorites from the Antarctic and found unprecedented amino acid levels that were 20-30 times higher than in any meteorite ever measured before. So we looked at the data and said, "Okay, that can't be right, so let's do it again." But we measured it again and it turned out to be true.

There are lucky surprises. I remember once we had a week scheduled on a telescope, and we had terrible, dreadful weather throughout the run. One night, Dr. Emmanuel Dartois and I opened the dome for two hours and observed at the zenith—we had no choice, because this was the only position without clouds. The observed distant star BD+63 1964 showed the strongest diffuse interstellar bands ever measured and we submitted a letter to Astronomy & Astrophysics after the observing run. Surprises happen and make science so very exciting.

Pascale Ehrenfreund
Leiden Institute of Chemistry
Leiden University
Leiden, The Netherlands
and
Space Policy Institute
Elliot School of Inter
national Affairs
Washington, DC, USA

Professor Pascale Ehrenfreund's most-cited paper with 211 cites to date:
Ehrenfreund P, Charnley SB, "Organic molecules in the interstellar medium, comets, and meteorites: a voyage from dark clouds to the early Earth," Annu. Rev. Astron. Astrophys. 38: 427+, 2007. 211 cites. Source: Essential Science Indicators from Clarivate Analytics.

Keywords: pascale ehrenfreund, interstellar medium, comets, meteorites, astrochemistry, astrobiology, ice chemistry, molecular clouds, diffuse interstellar bands, proto-planetary discs, planet formation, alma, herschel mission, james webb telescope, rosetta cometary mission, exomars.

  



Special Topics : Astrochemistry : Pascale Ehrenfreund - Special Topic of Astrochemistry