Across the Universe: Taking the Heat

This column from The Tablet first ran in September 2011


Meteorites in thin section look much cooler than the equipment used in our lab to measure their physical properties...

In 2011 we started with a stack of styrofoam cups...

... like this stack of styrofoam cups...

Science is a marriage of theory and experiment. Sometimes the marriage is literal. The colleagues I visited this month [2011] at Louisiana State University, Brad and Martha Schaefer, have been married 30 years; she’s a whiz in the lab, he’s a math guru.

The three of us have been looking for a quick and non-destructive way to measure the heat absorbed in a meteorite when it is raised from the cold temperatures of space to the temperature where water melts. Meteoritic material is typical of the rocky stuff mixed with ice in the moons of Jupiter and Saturn; if those moons melt, the molten regions could be oceans of life beneath their icy crusts. Indeed, Jupiter’s moons deflect its magnetic field in just the way you’d expect from deep internal oceans; and, more dramatically, we actually see geysers spurting out the surface of the Saturn moon, Enceladus.

If you want to know how much heat it takes to melt those moons, you have to keep track of all the different places where that heat can go. Measuring heat capacity can be done with great precision using (expensive) modern equipment. But it requires carving your meteorite into a little disk; and it takes two days to run each measurement.

So instead we’ve come up with a fast-and-dirty way to determine the heat content of our meteorites. We drop a sample into a container of liquid nitrogen, and watch the liquid boil away until the rock is as cold as the nitrogen… a cool 200 degrees below zero (Celsius), about the same as Saturn’s moons. We know how much heat it takes to boil away a gram of liquid nitrogen; count the number of grams gone, and (in theory) you know how much heat came out of the rock.

The details, of course, are devilish. For the past month, Martha has been designing the best way to set up the experiment. For example, after trying many different kinds of liquid nitrogen containers, she finally concluded that a stack of styrofoam coffee cups works better than far more elaborate dewars. (Well, we wanted a simple, cheap solution.) Brad, meanwhile, has worked out the surprisingly complicated equations to correct for how much heat is absorbed from the bottom and sides of the cup instead of the meteorite.

We’ve also been perplexed by any number of inexplicable fluctuations from run to run. Why the variations? Alas, the results of any experiment may tell you something that is completely true, but the question it answers isn’t necessarily the one you though you were asking. If we’re actually only seeing how static electricity on the styrofoam affects the electronics of the scale, when we thought we were measuring fluctuations in the heat content, we will draw seriously erroneous conclusions.

Error in experiment comes in two varieties. Some error is random; you hope that by running the experiment many times, this sort of error will eventually average itself out. But other error is built into the system, and always misleads you in the same direction.

When teasing truth from nature, it’s useful to have some ground truth (in our case, the well known heat capacity of a standard mineral, like quartz) against which you can test your procedure, to look for systematic errors. Knowing what the answer ought to look like – theory – is a good test for an experiment’s accuracy.

But, of course, some error is just... well... a mistake; as we discovered when Brad (or was it Martha?) discovered that an essential term in Brad’s equations had mysteriously disappeared from the computer code Martha was using to process her data. When theory and experiment don’t agree, each side is liable to blame the other. But then, a strong marriage isn’t afraid of a little bickering.

Br. Guy Consolmagno

About Br. Guy Consolmagno

Brother Guy Consolmagno SJ is Director of the the Vatican Observatory and President of the Vatican Observatory Foundation. A native of Detroit, Michigan, he earned undergraduate and masters' degrees from MIT, and a Ph. D. in Planetary Science from the University of Arizona; he was a postdoctoral research fellow at Harvard and MIT, served in the US Peace Corps (Kenya), and taught university physics at Lafayette College before entering the Jesuits in 1989.

At the Vatican Observatory since 1993, his research explores connections between meteorites, asteroids, and the evolution of small solar system bodies, observing Kuiper Belt comets with the Vatican's 1.8 meter telescope in Arizona, and applying his measure of meteorite physical properties to understanding asteroid origins and structure. Along with more than 200 scientific publications, he is the author of a number of popular books including Turn Left at Orion (with Dan Davis), and most recently Would You Baptize an Extraterrestial? (with Father Paul Mueller, SJ). He also has hosted science programs for BBC Radio 4, been interviewed in numerous documentary films, appeared on The Colbert Report, and for more than ten years he has written a monthly science column for the British Catholic magazine, The Tablet.

Dr. Consolmagno's work has taken him to every continent on Earth; for example, in 1996 he spent six weeks collecting meteorites with a NASA team on the blue ice regions of East Antarctica. He has served on the governing boards of the Meteoritical Society; the American Astronomical Society Division for Planetary Sciences (of which he was chair in 2006-2007); and IAU Commission 16 (Planets and Satellites). In 2000, the small bodies nomenclature committee of the IAU named an asteroid, 4597 Consolmagno, in recognition of his work. In 2014 he received the Carl Sagan Medal from the American Astronomical Society Division for Planetary Sciences for excellence in public communication in planetary sciences.

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Across the Universe: Taking the Heat — 2 Comments

  1. That is a great post! So, since this was originally written in 2011, did you all get the kinks worked out? Did you get it to work? And, as regards “actually only seeing how static electricity on the styrofoam affects the electronics of the scale” — you need a high-precision *mechanical* scale against which to compare results.

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