Cool engineering for cold science
Has there ever been life on Mars? We’re not sure, and current investigations focus around what happened to the water on Mars, which has long since disappeared from the planet’s surface. In 2007, the Opportunity rover detected the presence of meridianiite at its landing site in Meridiani Planum. Meridianiite (also known as MS11) is MgSO4∙11H2O, a hydrated sulfate mineral that is only stable at temperatures below 2°C. Satellite observations tell us that there are outcrops of hydrated sulfate minerals, several kilometres thick, in the walls of Valles Marineris, and meridianiite is thought to be widespread on Mars. Could hydrated minerals such as these be locking away all the water that once flowed on Mars?
Putting satellites into orbit around Mars, or sending rovers to surface, are both great ways to explore the planet, but they’re expensive. An alternative is to use experiments here on Earth to investigate what’s going on, but, until now, the slow formation of meridianiite meant it wasn’t possible to study its development here at Diamond.
That’s all changed now that we have the Long Duration Experiment (LDE) facility on the I11 beamline. The LDE is a unique facility, specially designed for experiments that need to be monitored over long periods of time – months, or even years. The LDE hosts several experiments at once. Every Monday the automated systems bring the experiments out into the beam, one by one, collects the necessary X-ray diffraction measurements, and then puts them back to quietly do their thing in the background.
It’s the ideal place to run a long-term experiment on the formation of meridianiite, but that experiment needs a temperature-controlled environment, allowing for very slow cooling rates of around 0.3°C per day. This presented an engineering challenge. We’ve got a lot of temperature-controlled environments at Diamond, but they normally use a cryostat where the detector and the samples can be sealed in together. That won’t work on the LDE, where the detector needs to be free to move into position for each experiment.
Video 1: The different components f the Cold Cell in the Long Duration Experiment hutch.
Diamond engineers Jon Kelly and Andy Male solved this problem by designing a new cold cell for the LDE, which provides the necessary thermal insulation while remaining transparent to the X-ray beam. They went through a couple of design iterations for the cold cell, which needed to be small and light enough to move easily, with flexible connections.
The finished design is made from Palight® insulating foam, which is durable and easy to engineer, with triple glazing of Kapton™ for the beam windows. Within the cold cell is a copper block, through which cooled anti-freeze is circulated by a commercial chiller. The small sample chambers have diamond windows that allow transmission of the X-ray beam.
The cold cell has been in use on the LDE for a year, and is still going strong. The first results from the meridianiite study show that it’s an effective design for this type of subzero temperature formation studies. Meridianiite formed by the fourth week of the experiment, between -7 and -8°C. The relatively quick speed at which it formed and locked away water could well explain why we don’t see long-standing bodies of water on Mars. The full results of the long-term study will be published in due course.
Video 2: A Look inside the hutch while all the samples on th eLong Duration Experiement are being investigated.
Murray CA et al. New synchrotron powder diffraction facility for long-duration experiments. Journal of Applied Crystallography 50(1), 172-183 (2017). DOI:doi.org/10.1107/S1600576716019750.