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Life in the Lab
06.09.2009 10:03 AM
Julie Castillo

By Julie Castillo
Planetary Ices

Hi Everyone,

Welcome to my blog. I am a planetary scientist focusing mostly on the geophysical evolution of small icy objects, asteroids and outer planet satellites. A couple of years ago I participated in the development of a new laboratory at JPL to measure the physical properties of ices and especially to simulate tidal stress in planetary material analogs. After spending all these years comfortably sitting in front of a computer, it was a shock, at first, to be working in a cold room at -20 deg. C for several hours. However, this has turned to be a very cool experience, and I will document a lot of it on this blog. I’ll talk a bit on numerical modeling too, and a lot on Solar system icy objects in general.

This week was much devoted to laboratory work. On Tuesday we started testing a new sample of monocrystalline ice from the ice magician Hermann Engelhardt from the Caltech Ice and Mars Simulation Laboratory.

This new sample will be subject to a long cyclic loading run in our Planetary Tides Simulation Facility.

Compression system used for the measurements

We have been studying monocrystalline ice for about one year now. First we have been working at relatively high stress and short cyclic periods (barely reaching Enceladus’ tidal period of about 39 hours). Then we realized that a significant improvement of the system capability was within reach and we could achieve simulations at the period of Jupiter’s satellite Europa (about 92 hrs). Imagine that you have to draw a circle with a 20 micron radius in 92 hours and with a constant pace (and without shaking!) This is close to what we ask our system to perform.

The cryo-genius in our ice physics lab, Joe Young, made it happen and even more, as he connected the system to permanent liquid nitrogen feeding (no more LN2 tanks to carry, youhou!) We were back in business in December and since then we have been focusing on a series of measurements at frequencies between Europa’s and seismic frequencies (up to 1 Hz). We need to acquire many cycles in order to obtain a good signal to noise ratio, and since we are working with periods as long as 3.5 days, it can take up to several weeks to obtain a single datapoint we can be happy with.
Between December and March we have been working at temperatures colder than -20 deg. C. The last test will focus on the deformation of the sample in the premelting regime, a domain of great interest to modelers trying to understand the role of tidal heating in the endogenic activity of outer planet satellites. I am looking forward to this test, and I will let you know how it goes as we progress with it over the next three months.
Other news, on Tuesday we made our first batch of polycrystalline ice using seeds made up from water sprayed in liquid nitrogen. It’s “cooking” right now, under high pressure (1000 atmospheres) in order to remove all porosity. We will have the solid sample in a couple of days and will characterize its structure with JPL cryo-ESEM (Environmental Scanning Electron Microscope) and our cryo-microscope. This will be the topic of a future post with cool pictures obtained with that facility.


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