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Melissa McClure

Leiden astronomers launch biggest space-ice database ever: ‘A kind of phone book, but for ice’

It is the largest database for space ice yet: The Leiden Ice Database for Astrochemistry: LIDA. Created by astrophysicists at the Leiden Observatory, LIDA includes not only hundreds of measurement data, but also software to examine astronomical observations and prepare new measurements with the James Webb Space Telescope (JWST). The corresponding paper has been selected as a highlight in the scientific journal Astronomy & Astrophysics.

‘The space-ice we study is found in very thin layers around small dust particles floating through space,’ explains Will Rocha of the Leiden Laboratory for Astrophysics and first author of the LIDA paper. ‘The molecules formed in this space ice form the basis of chemicals that will ultimately become the building blocks for life (see info box). Think of organic molecules such as sugars and amino acids. It is therefore important to have a good idea of where in space this ice  can be found and in what quantities, and what  its composition is. In the end, this will for a large part determine the chemical composition of planets and everything on them.’

Space ice is more than just frozen water

Ice in space consists not only of water, but also of other frozen substances, such as carbon dioxide, methane, methanol and ammonia. These substances form at extremely low temperatures (around -260°C) on micrometer sized dust particles. Here, they create microscopically thin layers of ice. You can find space ice wherever it is cold enough in between and around stars.

The ice on the dust particles is constantly bombarded by incoming atoms, electrons, ultraviolet photons and cosmic particles. This creates highly reactive molecules in the ice: free radicals. These then react with other particles, creating larger and larger molecules and eventually complex organic molecules: the building blocks for life.

The barcode, also known as the absorption spectrum of the organic molecule ethanol: an alcohol also found in most alcoholic beverage

Making space ice in a Leiden lab

‘When you want to know what ice is present in space, you must first be able to recognise that ice,’ says Rocha. ‘In our lab, we therefore make our own space ice and study how different ices absorb different wavelengths of (infrared) light. Some colours are absorbed, others remain. The missing colours together form a special pattern we call a spectrum. Each type of molecule absorbs light differently and thus has a unique absorption spectrum, almost like a barcode.’

But that’s not all. Rocha: ‘An absorption spectrum is determined not only by the molecules present in the ice, but also by their temperature= or interactions with other molecules. By systematically measuring all these spectra in the lab, we have been able to steadily build up a database with precise data. These are needed to interpret the signals we see with JWST in space.’

‘Think of it as a phone book, but for space ice.’

Looking at the bigger picture with the James Webb Telescope

‘The purpose of LIDA is mainly to provide data to the astronomical community, think of it as a kind of phone book, but for ice,’ says Professor Harold Linnartz, head of the Laboratory for Astrophysics. But collecting data is not the only goal. ‘At the same time, we are trying to get to the bigger picture, to understand how frozen molecules can react with each other, how quickly and how this depends, for instance, on temperature or the intensity of radiation in space. Which molecules are present in gas clouds and which of them were formed in ice? And how does this ultimately determine the chemical composition of a planet-forming disc? To address these questions, you need very precise astronomical observations. That is why we are very happy with the new James Webb Space Telescope (JWST).’

‘There are even researchers using our database who “accidentally” find ice, it really is everywhere in space.’

Stay tuned for a space ice scoop

Co-author Melissa McClure is the principal investigator  of Ice Age, one of the first projects with data from the JWST. She investigates the evolution of ice from dark dust clouds to planet-forming disks. ‘One of the conditions we had to fulfill in order to be among the first to measure with the JWST was that we would make all relevant ice data publically available to the community.. LIDA is the direct result of this condition. Many of our colleagues are already using it. There are even research groups that now “accidentally” spot ice, because ice really is everywhere in space. Soon we will publish our first Ice Age results. One of the highlights is the discovery of ice in dark clouds in space, possibly even with complex organic molecules. Stay tuned!’

Professor Ewine van Dishoeck uses LIDA to conduct research with data from MIRI: one of the measuring instruments on board JWST, and largely of Dutch manufacture. ‘It is becoming increasingly clear that complex organic molecules must have their origin on icy dust particles. Only in this way can you explain why many star-forming regions have roughly the same relative densities of different molecules: they share a common chemical history.’

Quite a challenge, but the start is there

According to Rocha, getting the database online was quite a challenge. ‘Not only scientifically, but also in terms of programming. It all had to be safe. In the near future, we want to expand further. More laboratory ice spectra, also in collaboration with other research groups, and detailed information about the behaviour of light in ices. For instance, the way light is refracted in ice tells us something about its structure. We will also continue to update the software to interpret new JWST spectra or simulate upcoming measurements. The start is there, time to build further. We are happy that our colleagues already know how to find LIDA.’

Database en publication

The LIDA-database is freely accessible. Take a look at https://icedb.strw.leidenuniv.nl.

Read the scientific publication in Astronomy & Astrophysics: LIDA: The Leiden Ice Database for Astrochemistry, 2022. W. R. M. Rocha, M. G. Rachid, B. Olsthoorn, E. F. van Dishoeck, M. K. McClure and H. Linnartz. A&A, 668 (2022) A63

Help from dozens of students and a new setup

Many dozens of students, PhD students, postdocs and other scientists have been measuring data in the lab for three decades. ‘Especially a large number of bachelor students, but also graduate students from HBO institutions,’ Linnartz says. ‘In this, the support from NOVA, the Dutch Research School for Astronomy, and NWO has also been essential.’ In the immediate run-up to the JWST measurements, PhD student Marina Rachid built a new setup in the lab. Rachid: ‘Over the past few years, I have been measuring all kinds of frozen complex molecules. It is wonderful that now, in the last year of my PhD work, we are able to compare these data directly with the spectra from the James Webb telescope.’ Meanwhile, a new PhD student, Katie Slavicinska, has started. She will spend the next few years looking for new types of ice.

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