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By Emily Lakdawalla

Parallel planetary processes create semantic headaches

Jan. 26, 2012 | 14:55 PST | 22:55 UTC

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So here's a semantic problem I ran into today. Consider this photo, a radar image of the Congo river from Envisat.

Click to enlarge >

Synthetic aperture radar view of the Congo river
This wide-swath radar image is a mosaic of two images centred over the Congo River, one of the largest rivers in the world flowing 4,374 kilometres (2,718 miles) from Zambia to the Atlantic Ocean. It was taken on December 23, 2002 from Envisat and is a synthetic aperture radar image, in which brightness corresponds to roughness of the surface. Water appears black in these images. Credit: European Space Agency. All rights reserved.

And consider also this photo, a radar image of a river system on Titan.

Click to enlarge >

Titan's rivers and lakes
A Cassini RADAR swath across Titan's north polar regions passed over numerous methane-ethane lakes and river channels that feed them. There is not any evidence that any of the channels were actually running with flowing liquid when Cassini took the image; it's more likely that they are dry washes like those in Earth's deserts, and that they appear dark because a layer of fine sediment is deposited along their bottoms. The data are from flyby T28, April 10, 2007. Credit: NASA / JPL. Thanks to Jason Perry for posting and hosting Cassini's radar images.

Clearly, there are similar physical processes operating to create these landscapes. Rain falls out of the sky and flows downhill, collecting into streams that debouch into rivers and thence into lakes or oceans, whence it evaporates back into the sky. Scientists who study this process on one world have expertise valuable to understanding it on the other. On Earth, we call the study of this cycle (and related processes) hydrology, the study of water. On Titan, there's water present, but it's not running in the rivers; water, in its solid form, is the bedrock. It's methane and ethane that fall from Titan's sky, flow in its rivers, and collect in its oceans. On Pluto, it's theoretically possible that there's a liquid nitrogen cycle, at least during some parts of its year. What can you call a field of study that applies to similar processes of rainfall, runoff, erosion, sapping, and evaporation, in similar landforms of rivers, lakes, seas, and aquifers, when there are different fluids on different planets?

I posed this question on Twitter today and I got a lot of suggestions for neologisms, but that's not going to help me out; I need to call things by names that other people will understand when I use them. (Of these suggestions, my favorite was "humorology," referring not to the modern use as in "something funny" but instead to its original meaning of fluid or juice, as in the four humors of Hippocratic physiology, especially because it was followed by the suggestion of "cryology," not as in the thing we do when we're sad but as in cryo-, meaning icy or cold.) Several people suggested "fluid dynamics," but there's already a field of study called that, and it covers how things flow but now how they pool or evaporate or tumble rocks in streams to make them rounded or do all these other things.

Nearly every scientist who answered my question said that really it is "hydrology" that's in common use, even for these non-watery fluids. There are precedents of course. Although some people do talk about "selenology" and "areology" to refer to the physical histories and surface processes on the Moon and Mars, nearly everyone just uses the catch-all term of "geology" despite the fact that "geo" refers to "Earth." Using "hydrology" would make me feel less bad about also using "aquifer" when I'm talking about liquid methane flowing through Titanian sands or liquid nitrogen flowing under Pluto or Triton ices. But if we ever find a place where liquid rock occupies a similar role -- on an exoplanet, maybe, or on a slightly hotter Venus -- I wonder if we'd balk at calling the study of that "hydrology"?

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Comments

Hydrology

Well, we call the technology used in bulldozers and other earthmoving gear to raise and lower the blades and digging buckets "hydraulics," even though the system uses oil, not water.

#1 - phil - 01/26/2012 - 15:25

Crydrology

Crydrology isn't technically correct, but it rolls of the tongue nicely and the word doesn't already exist.

#2 - Dan Brennan - 01/26/2012 - 16:03

Off the Wall Idea

Suggest 'ekitaiolgy' just for the heck of it. "Ekitai" is the Japanese word for "fluid".

#3 - Nick Previsich - 01/26/2012 - 17:01

Similar issues arise when describing the movement of liquid hot magma.

#4 - stevesliva - 01/26/2012 - 17:10

Alkanology

The term "Alkanology" would be suitable for both methane and ethane as well as for other possible alkanes flowing on Titan.

#5 - Trurl - 01/26/2012 - 17:21

Play Ball

Loved the choice of photos. Issues of language are only important if confusion can arise from not making distinctions. There's an immense number of examples of wording created in one context migrating to mainstream speech or being adapted to other uses. Would a bat by another name... Play ball.

#6 - PL Monteiro - 01/27/2012 - 09:06

Manology

It seems that Latin (fluid) and Greek (rheology) for flow are taken already. There Is another Latin root for flow. Perhaps the term manology would be a suitable neologism. There is manometry but not manology in the science lexicon.

#7 - Mschneeg - 01/27/2012 - 11:52

Hydrodynamics and magnetohydrodynamics may once have been inspired by water and slat water behavior, but has long since been abstracted away. It would be confusing to name methane hydrology for something else.

Even worse, don't forget the recent inclusion of gases:

"In physics, fluid dynamics is a sub-discipline of fluid mechanics that deals with fluid flow—the natural science of fluids (liquids and gases) in motion. It has several subdisciplines itself, including aerodynamics (the study of air and other gases in motion) and hydrodynamics (the study of liquids in motion). [...]

Historically, hydrodynamics meant something different than it does today. Before the twentieth century, hydrodynamics was synonymous with fluid dynamics. This is still reflected in names of some fluid dynamics topics, like magnetohydrodynamics and hydrodynamic stability—both also applicable in, as well as being applied to, gases."

#8 - Torbjörn Larsson, OM - 01/27/2012 - 12:44

Oops, HTML link stripped

That was from Wikipedia.

#9 - Torbjörn Larsson, OM - 01/27/2012 - 12:48

Alkanology for Titan

Since the fluids that work on Titan are alkanes, it's probably best to call is alkanology. A theoretical nitrogen cycle could be studied by nitrology or azotology.

#10 - ayceman - 01/29/2012 - 03:13


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