Water world: IR astronomy reveals cloudy system

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  • Published: Nov 1, 2011
  • Author: David Bradley
  • Channels: Infrared Spectroscopy
thumbnail image: Water world: IR astronomy reveals cloudy system

Water, water everywhere

Astronomers have used far-infrared instrumentation to show for the first time a cloud of water vapour swirling around a burgeoning solar system. The vapour is cold enough to form comets, which could eventually deliver oceans to the distant system's parched newly forming planets. Such observations, of course, hint at how water might have been deposited on the Earth and our neighbouring planets and moons as well as suggesting where life-giving water might be found elsewhere in our galaxy and beyond.

Water life's essential solvent has been found in quantities enough to fill the Earth's oceans thousands of times over circulating within the planet-forming disk surrounding the star TW Hydrae. TW Hydrae lies some 176 light years from Earth, in the constellation Hydra and is the closest known fledgling wannabe solar system.

The researchers used the Heterodyne Instrument for the Far-Infrared (HIFI) on-board the orbiting Herschel Space Observatory to detect the chemical signature of water. Ted Bergin of the University of Michigan and astronomical colleagues published details of the discovery in the journal Science. HIFI records the far-infrared wavelengths where organic molecules and water emit their chemical signatures. The instrument detected emission lines from both spin isomers of cold water vapor from the disk, the researchers say. This water vapour presumably originates from ice-coated solids near the disk surface, the researchers add.

Key materials

"This tells us that the key materials that life needs are present in a system before planets are born," explains Bergin, one of the HIFI investigators. "We expected this to be the case, but now we know it is because have directly detected it. We can see it."

Previously, scientists had identified the presence of warm water vapour in planet-forming disks close to the central star around which the accretion disk circulates. However, what they had not seen before was large oceanic quantities of water extending beyond into the cooler, far reaches of such disks in the region where comets and giant planets form. The presence of water at such far reaches from the central star means more water to form icy comets that might eventually smash into rocky planets closer in to the star depositing their aqueous payload in the process.

"The detection of water sticking to dust grains throughout the planet-forming disk would be similar to events in our own solar system's evolution, where over millions of years, these dust grains would then coalesce to form comets," explains the study's principal investigator Michiel Hogerheijde of Leiden University in The Netherlands, "These would be a prime delivery mechanism for water on planetary bodies." Higerheijde also worked with colleagues at the California Institute of Technology, the University of Amsterdam, the Harvard-Smithsonian Center for Astrophysics, Johns Hopkins University, the European Southern Observatory, NASA Jet Propulsion Lab and the Max-Planck-Institut für Extraterrestrische Physik in Germany.

HIFI data

Data from HIFI also supports the theory that ancient comets delivered most of the water that formed the Earth's oceans. The chemical signature of the icy comet Hartley 2 is identical to that of Earth's oceans. HIFI is thus helping astronomers better understand how water reaches terrestrial planets. If the icy disk surrounding TW Hydrae is typical of other young star systems, then the researchers suggest that there might be many other similar systems scattered across the universe any one which might have warm, rocky planets with sloshing oceans.

The team adds that, "The water?s ortho-to-para ratio falls well below that of solar system comets, suggesting that comets contain heterogeneous ice mixtures collected across the entire solar nebula during the early stages of planetary birth."


The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

 Credit: NASA/JPL-Caltech/T. Pyle (SSC/Caltech)
Oceans in space

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