Water Floods the Cosmos, But Where's the Reservoir?
Water, water everywhere, and not a drop to be used by alien life, yet.
This molecule which is ever so important for life as we know it can be found in so many places in the cosmos that it is no wonder that some scientists think the chance of finding a life-friendly planet is good — although we have yet to detect water-drinking ET. Before it gets to a planet, however, it starts in a place like this, the Orion Nebula.
Oh sure, this is not the Orion Nebula as you are used to seeing it. The “invisible light” that our eyes cannot see often highlights new features and processes that we would have otherwise missed. If you go to longer wavelengths than what our eyes can see, you eventually get to the sub-millimeter wave regime, in this fuzzy region between the radio and the infrared.
This is where water can absorb and emit light, so it helps to get out of our own water-laden atmosphere. That is what astronomers did with the Submillimeter Wave Astronomy Satellite, or SWAS. The image above zooms in on the Orion Molecular Ridge, a “warm*” piece of cloud that has ultraviolet light shining on it from the nearby nascent stars. With the UV light, gas, and dust, this is a hotbed of astrochemistry action. Okay, “warmbed”…
Astronomers can model how much water a cloud will have based on how much hydrogen and oxygen are around, how dusty it is, how much UV light there is, the temperature, the density, and a whole host of other factors. Yet SWAS discovered that the models over-predicted the amount of water by 100 to 1000 times! However, it was SWAS data that came to the rescue in this recent work by Gary Melnick and collaborators.
This study helps solidify the hypothesis that we see less water because it only exists on the surface of the cloud as water vapor. The water emission only seems to be coming from a thin layer. Further into the clouds, the water is freezing onto dust grains as ice where it can no longer be seen by SWAS. So the water is still there, it is just trapped up as a solid.
They say that to find life one must “follow the water.” I’m glad to see that some astronomers take that literally to mean following the water from the very clouds from which stars and planets may one day form!
* “Warm” in the interstellar medium is 20-40 Kelvin, around -240 degrees Celsius. Brrr!
Image: Pretty picture this is not, but it is scientifically important. Brightness of the emission from water vapor in the Orion Molecular Ridge by SWAS. Credit: Melnick, et al. 2011
The research has been published in Astrophysical Journal, and a preprint is available at arxiv.org.