Space travel of water: from interstellar clouds to habitable planets

Chalmers University of Technology

An international team of astronomers, including Chalmers scientists, has published a comprehensive survey of the journey of water through space. Using data from the Herschel Space Observatory, they showed that the most important molecule of life can thrive in all newborn solar systems – not just ours.

Only ten years ago it was not known how and where water formed in space, and how it eventually ends up on a planet like Earth.

Now, an international research team has put together everything scientists know about water in interstellar clouds, and the origin of water on newborn, possibly habitable, planets. The article, published in the journal Astronomy & Astrophysics, is based on observations with the Herschel Space Observatory.

Space telescopes

Seeing water in space is a challenge for astronomers. Even the best terrestrial telescopes are hit by water vapor in our own atmosphere.

During his four-year mission, Herschel had as one of its main goals to explore water in space. Of particular importance was the HIFI instrument, which was built under Dutch leadership with important contributions from Sweden, and especially from Chalmers.

In the new study, Ewine van Dishoeck and her colleagues were able to study how water molecules follow every part of the process that leads to the birth of new stars and planets.

Starts with Ice

The new study shows that most of the water is formed like ice on tiny dust particles in cold and weak interstellar clouds.

When a cloud collapses to new stars and planets, this water is mostly conserved and quickly anchored in rock-sized dust. In the rotating disk around the young star, these pebbles then form the building blocks for new planets.

“Water is mostly transported as ice by large interstellar clouds to these disks. The ice does not appear to melt or disintegrate during entry. We still can’t say exactly how much water is in these disks, but it’s enough to form oceans on terrestrial planets, ”says Per Bjerkeli, an astronomer at Chalmers.

Groundwater also migrated here in this way, the researchers believe. In addition, they calculated that most new solar systems are born with enough water to fill several thousand oceans.

“It’s fascinating to note that when you drink a glass of water, most of those molecules were made more than 4.5 billion years ago in the cloud from which our sun and the planets formed,” says Ewine Van Dishoeck.

For water molecules, the path from interstellar clouds to the glass is complex, the scientists show. Previous studies with the Herschel Space Observatory have shown how hot water vapor seen and abundantly produced near forming stars is lost to space in powerful outflows. Now, the researchers were also able to track both cold water vapor and ice deposits in these star systems, including examining weak signals from heavy water (where the molecule H20 contains one or two atoms of heavy hydrogen, or deuterium).

Many mysteries remain about the path of water to the planets that new and future telescopes will have to deal with. The NASA / ESA James Webb telescope, which will be launched later this year, as well as the ALMA radio telescope in Chile and the future SKA radio telescope, all have roles. The MIRI instrument on the James Webb telescope will be able to detect hot water vapor in the innermost areas of dust disks.

– Herschel has already shown that planet-shaped disks are rich in water ice. With MIRI we can now follow that path to the regions where terrestrial planets are forming, says Michiel Hogerheijde, an astronomer at Leiden University and the University of Amsterdam.

More about the research and the Herschel Space Observatory

Herschel was a European Space Agency (ESA) space telescope built in collaboration with NASA. Its HIFI and PACS instruments were used for the water exploration. HIFI was designed and built by a consortium of institutes and university departments across Europe, Canada and the United States under the guidance of SRON Dutch Institute for Space Research, the Netherlands, with important contributions from Germany, France and the United States. The PACS instrument was developed by a consortium of institutes and universities across Europe led by the Max Planck Institute for Extraterrestrial Physics in Germany. Chalmers scientists played an active role in scientific planning for Herschel, and participated in several projects using data from the telescope.

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Ewine van Dishoeck led the water research program WISH (Water in Starform regions with Herschel). The team consists of 50 astronomers, including Chalmers scientists Per Bjerkeli, René Liseau and Magnus Persson, and Bengt Larsson (Stockholm University).

Pictures

A (top) – The path of water molecules from vast interstellar clouds to potentially habitable planets has been traced in the star region Rho Ophiuchi, 440 light-years away in the constellation Ophiuchus. This wide-angle image of Herschel, taken in light with a wavelength between 70 and 250 micrometers by the telescope’s PACS camera, is 4 degrees wide (equivalent to eight full moons). In the brightest part of the picture (top right) lies the young star VLA 1623, the subject of detailed observations of water using the HIFI instrument.

Image: ESA / Herschel / NASA / JPL-Caltech, CC BY-SA 3.0 IGO; Acknowledgment: R. Hurt (JPL-Caltech)

B – The star region Rho Ophiuchi, 440 light-years away in the constellation Ophiuchus. This wide-angle image of Herschel, taken in light with a wavelength between 70 and 250 micrometers by the telescope’s PACS camera, is 4 degrees wide (equivalent to eight full moons). In the brightest part of the picture (top right) lies the young star VLA 1623, the subject of detailed observations of water using the HIFI instrument.

Image: ESA / Herschel / NASA / JPL-Caltech, CC BY-SA 3.0 IGO; Acknowledgment: R. Hurt (JPL-Caltech)

C – This illustration shows the journey of water from interstellar clouds to habitable worlds. From top left to right: water in a cold interstellar cloud, close to a young, forming star with an outflow, in a protoplanetary disk, in a comet and in the oceans of an exoplanet. The first three stages show the spectrum of water vapor measured by the HIFI instrument on the Herschel space observatory. The signals from the cold interstellar cloud and the protoplanetary disk were exaggerated in this image by a factor of 100 compared to those of the young, forming star in the center.

Image: ESA / ALMA / NASA / LE Kristensen

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