The origin of water in the universe

[Palinurus]

Source (Dutch only): Sterrenkundige Ewine van Dishoeck over het raadsel van water in de ruimte: ‘Het water in uw koffie is ouder dan de aarde’

Interview - Astrochemist
Astronomer Ewine van Dishoeck on the enigma of water in space: 'The water in your coffee is older than the Earth'

Water is Ewine van Dishoeck's favorite molecule. She has been studying it all her scientific life. The creation of water in space, that is.

Joep Engels - 21 June 2021, 14:27

Her study is full of photos of the night sky. The Milky Way, comets, planets, galaxies. This is what everyone pays attention to who looks at the sky, she says. "You see stars and planets, maybe something as beautiful as the Andromeda Nebula. Very few people wonder what's in between. That area seems empty, but it's not. It is filled with a very, very thin gas. It is still much thinner there than in the very best vacuum we can make on Earth. But this is where we come from. In such an interstellar cloud we were born. The sun and the planets were formed in it, and we too are made of this gas and dust."

What is occurring there is her field of expertise: astrochemistry. Chemistry between the stars, she calls it herself. Ewine van Dishoeck is good at it. The professor at Leiden University is one of the most cited scientists in her field and has been garnering awards in recent years. She is also president of the International Astronomical Union, most recently published a review article on water in space, and received a major European grant a month ago for research on planet formation.

"I can't complain," she responds. "It's a fruitful time. It's also to the credit of the young people here. They are doing the work. I get to inspire them."

The profession, astrochemistry, did not exist in the middle of the last century. "Stars were an integral part of the cosmos until the 1950s. The idea that they are born and also die again didn't occur until those years. In those cold, tenuous conditions outside the stars, nothing at all seemed to be able to happen. The little that was there was mostly hydrogen. Other elements were barely there. A hydrogen atom might encounter something like an oxygen atom once every hundred thousand years. It wasn't until people pointed their telescopes at those interstellar clouds that they saw one molecule after another. It turned out to be a bountiful chemistry."

Ewine van Dishoeck - Image: Elodie Burillon

But for the practitioner, it remains strange chemistry. The astrochemist has no fume hood or flask. "That's the nice thing about this profession, you're forced to think twice about how you want to do research. You can't just go up and down to the Orion Nebula to do a little experiment. You have to rely on observations and models. You have an idea of what is happening. You test that in the computer or in the lab, and you compare the outcome with the observation."

One such idea concerned the question: how do substances react with each other? The fact that space is cold and ultra-thin is not the only barrier to some chemical action. "If you have hydrogen and oxygen molecules here on Earth, you bring hydrogen and oxygen molecules together, you get a huge bang. And then you have water. But if they come together in space, they can't get rid of the energy released in the reaction. There's no third molecule that can absorb the energy. Or a reactor wall that could get hot. And so the reaction would hardly be able to come to fruition."

Landing strips for atoms

The answer to that riddle was in the dust of interstellar clouds. Such a cloud contains tiny grains of sand, a factor of a thousand smaller than Earth's sand. But however small, they are perfect landing strips for atoms in space. "Very occasionally, maybe only once a day, a hydrogen atom lands on such a dust particle. A day later another one. And then one day an oxygen atom, which is the most common after hydrogen and helium. Now they can react because the particle absorbs the energy."

She opens her laptop and starts a video she once made based on her models. White spheres (hydrogen) and red ones (oxygen) descend on the sand grain and sometimes clump together. "See, the dust particle is a meet and greet for atoms. They run into each other and you see water molecules forming all over the place. I put it in the fast forward now: after ten thousand years, the dust particle is covered with a thin layer of water ice."

Water, it's a common thread in her career. The story of water was a journey of discovery for her, she tells herself. A journey closely tied to the Herschel. This European space telescope was launched in 2009 and had a Dutch measuring instrument on board. Because of that contribution, Dutch astronomers were given guaranteed observing time.

"That allowed us to develop a coordinated program. And that was entirely focused on water. We knew that the telescope was particularly well suited for observing water in space. Because of the amount of water in the atmosphere, telescopes on Earth can't do that. Our goal was to follow the entire trail of water. Where does it come from, how is it made, and how does it end up on a planet like Earth?"

The mission itself took four years, but the preparation took much longer. "I remember having my first meeting on the Herschel as a young PhD student in the early 1980s. But the real preparation also took ten years. And when the first measurement results arrived, it was like Santa Claus. As if we were allowed to unwrap presents. Whatever the results, it's always a surprise. But you also have to change gear quickly. You have to make use of the lead that you have gained through that guaranteed observation time."

It resulted in a stream of just under a hundred articles. And now there is also a large review article. "It took some effort to find the time for it, but I managed to do it during the Christmas vacations. I feel it is a duty to the next generation. It may be another thirty years before the next space telescope is launched. By then it will be handy to have all the Herschel information in one place."

Asked about the main lesson Herschel taught her, she starts about what she already knew. About the water that forms when a new star is formed. "We knew that in that phase there is a lot of water involved. In that phase it is also warm enough for the chemical reaction. But that water gets squirted out in a jet stream." She shows a photo of Iguaçu Falls, on the border of Argentina and Brazil, one of the largest waterfalls in the world. "At an ordinary young star, it's about 100 million Iguaçu waterfalls. Enough to fill all the oceans on Earth in a year."

But that water is thus disappearing into space. The water that remains in a planetary system comes from elsewhere. "That water comes from those little dust particles. When an interstellar cloud like that collapses and a new star forms, the dust particles end up in a disk that rotates around it. And they grow together by gravity. Dust particles become pebbles, grow into boulders, and eventually into planets. Half of the dust is water. That is the water of our solar system. Try to realize what that means. The water in your coffee - it has evaporated countless times, precipitated again as rain, flowed back to the sea - but the atoms are linked together on those specks of dust. The molecules in your coffee are older than the earth or the sun itself."

Half grit, half ice

She hadn't put this puzzle together right away, she says. The values Herschel relayed did not fit the calculations she had made on Earth. "The models predicted quite a bit of water. In a solar system like ours, there had to be enough water to fill 6,000 oceans. But we didn't see it. It took a lot of headaches before we figured it out. The water was trapped in those rocks!"

She walks over to her desk where there is a small replica of comet 67P, made famous by the landing the Rosetta probe tried to make on it in 2014. She takes it lovingly in her arms. "Look, this is such a boulder, half grit, half ice. In such chunks was the water that comes out of the tap. These chunks are still circling today in the outer regions of our solar system, in the so-called Oort cloud. The big question now is: how do you get the water to Earth? If you get too close to the sun, it evaporates immediately. It is likely that the large planets Jupiter and Saturn played a role in this. One theory is that they created chaos that directed those ice rocks to the inner part of the solar system."

These seem like questions for a new generation but, at 66 years old, she thinks otherwise. Soon to be launched is the James Webb Space Telescope, the successor to Hubble. This was already planned for 2014 but this fall it should really happen. The James Webb is no Herschel but it does have a Dutch instrument on board that searches for water. Hot water this time. "If all goes well, the first data will arrive in mid-2022. I'm already getting very excited about the idea of opening those presents again."

Once a scientist, always a scientist. "Not quite. In my younger years I played the violin. I was in a chamber orchestra, in a gypsy band. I might have made a living out of that, but in retrospect I'm glad I didn't go that way. I wouldn't have made it as far in music as I did in science. Music teacher is also not as exciting as science. Here I never have a dull moment."

"Science is in my blood. I'm of the hard science variety, but I can also enjoy a beautiful starry sky. My husband and I often go camping in the western United States, in one of the national parks. There it is completely dark at night and then the sight is overwhelming. Then you are forced to think about our place in the great universe. It was also the motto of the International Astronomical Union's centennial celebration two years ago: Under one sky. What are we worried about? We're companions in destiny."

Translated with www.DeepL.com/Translator (free version)

Sources:
Ewine van Dishoeck - Wikipedia
Ewine van Dishoeck - Wikipedia
Homepage of Ewine F. van Dishoeck

Long-awaited review reveals journey of water from interstellar clouds to habitable worlds - Astronomie.nl
https://www.aanda.org/articles/aa/full_html/2021/04/aa39084-20/aa39084-20.html
Ewine van Dishoeck

 

[mrtn]

Plants split water during photosynthesis, but I never thought of the fact that those atoms will never become water again on earth.
Broccoli is not a renewable source of energy!