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Pin-pointing water in space
For the first time, scientists succeeded in localising large amounts of water in a disk around a young star
Water is regarded as a key ingredient for life - and water exists plenty in the universe.
Now scientists have found the precious element in a disk around a young star, similar to our Sun.
This disk, supposedly the birth place for future planets, contains a hundred times more than all oceans
on Earth. The astronomical observations obtained with the IRAM interferometer appear very promising to
solve the mystery around the origin of water in our solar system.
Most of the water in the Earth's oceans likely originated in a tenuous cloud between the stars, which
collapsed to form our solar system. Exactly where the water was produced and how the molecules made their
way from this giant cloud to a tiny planet like Earth some 4.5 billion years ago is one of the main questions
in the study of our origins.
Fig. 1: Artists impression of the young Star NGC 1333 IRAS4B. Scientists assume
that planets form in the surrounding disk. For the first time they were now able to detect large
amounts of water in this disk.
Copyright: NASA/JPL-Caltech/R. Hurt (SSC)
While astronomers cannot turn back the clock to observe our own young solar system, they can study planetary
systems in formation around other nearby young stars. The IRAM Interferometer on the Plateau de Bure in the
French alps has pinpointed for the first time the location of the bulk of the hot water vapour in the
rotating disk around a very young star, analogue to our Sun.
Because of obscuration by the large amounts of water in our own atmosphere, astronomical observations
of normal water (H216O) require satellites such as the recently launched Herschel Space Observatory.
However, about 1 in 500 water molecules in space contain the heavier 18O isotope. Some signatures from
this heavier water (H218O) are able to penetrate the Earth's atmosphere and reach the IRAM telescopes.
Since telescopes on Earth are much bigger and see a hundred times sharper than any existing satellites,
this allows astronomers to zoom in on the forming stars and determine the location of water.
The astronomers Ewine van Dishoeck at the Max-Planck Institute for Extraterrestrial Physics in Garching
and Leiden Observatory and Jes Jørgensen at University of Bonn and Centre for Star and Planet Formation
in Copenhagen used the IRAM Plateau de Bure interferometer to look for heavy water (H218O) around a young
star, NGC 1333 IRAS4B that formed only 10,000-50,000 years ago. The astronomers found that most of the
steam around the young star is located within the inner 25 Astronomical Units of the rotating disk. This
distance corresponds approximately to the orbit of Neptune in our own solar system (1 AU is the distance
Earth-Sun, about 150 million kilometres).
Previous observations of this protostar had suggested that water vapour is pouring down from the cloud
and accretes onto the disk. The IRAM data show that the amount of water actually in the disk is a factor
of hundred larger than in any such shocks - about 100 times more than the content of Earth's oceans.
Fig. 2: Radio image obtained with the IRAM interferometer: Top left the spectral
"fingerprint" of water can be clearly discerned. Bottom left, the distribution of water in the disk
around the young star NGC 1333 IRAS4B is shown.
Copyright: Ewine van Dishoeck/Jes Jørgensen
'The water is likely located in a hot layer just above the disk midplane, where most of the available
oxygen is driven into water by chemical reactions,' says Ewine van Dishoeck. 'We now know that most water
enters the disk in the form of ice around dust grains from the cold collapsing cloud, and that these
"icy mantles" evaporate in the higher temperatures close to the young star.'
'These observations of water vapour have opened up a whole new avenue to study water in young solar
systems, complementary to that possible with satellites,' says Jes Jørgensen, lead author on the paper.
'Only the IRAM Plateau de Bure Interferometer is currently able to catch and image these very weak signals
of the water isotopologue. Moreover, the long wavelengths at which the Plateau operates allow us to see
much deeper into the disk and we can thereby study the physical and chemical processes that control the
early evolution of these disks that may set the stages for the eventual formation of planets.'
Over the next 3 years, the Herschel Space Observatory will survey normal water in many star-forming clouds
in our own and other galaxies. Combined with similar ground-based observations, astronomers will be able to
determine exactly how much water is located where and at which stage of the evolution of a young star. "The
combined access to the powerful IRAM telescopes and the Herschel-PACS instrument makes the Max Planck
Institute for extraterrestrial Physics a unique environment to carry out such comprehensive studies of
water in young solar systems", says Ewine van Dishoeck.
Jes K. Jørgensen, Ewine F. van Dishoeck
Water Vapor in the Inner 25 AU of a Young Disk around a Low-Mass Protostar
The Astrophysical Journal Letters, Volume 710, Issue 1, pp. L72-L76 (2010)
MPG Press Release February 25, 2010
IRAM and the Interferometer at the Plateau de Bure
The Herschel Satellite
"Taking a peek into the hidden universe",
MPG Press release regarding the launch of Herschel.
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Prof. Dr. Ewine F. van Dishoeck
Infrared/Submillimeter Astronomy Group
Max Planck Institute for extraterrestrial Physics
Phone: +49 89 30000-3592
Dr. Hannelore Hämmerle
Max Planck Institute for Astrophysics
and Max Planck Institute for extraterrestrial Physics
Phone: +49 89 30000-3980