The marvel of meridianiite

20th June 2018

Image shows the Long Duration Experiment Facility
Examining the slow in situ precipitation of meridianite

Putting satellites into orbit around Mars, or sending rovers to the surface, are great ways to see if there has ever been life on Mars, but they’re expensive. An alternative to sending more rovers is to use experiments here on earth to investigate what’s going on, but, until recently, the slow formation of meridianiite meant it wasn’t possible to study its development at Diamond Light Source, the UK’s national synchrotron science facility,

Meridianite is important because in 2007, the Opportunity rover detected its presence. It is a hydrated sulphate mineral that is only stable at temperatures below 2°C and satellite observations tell us that there are outcrops of hydrated sulphate 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?

Now that Diamond has the unique Long Duration Experiment (LDE) facility on the I11 beamline (the only one in the world that has been specially designed for experiments that need to be monitored over long periods of time – months, or even years) the facility can run a long-term experiment on the formation of meridianiite. However, it needed a temperature-controlled environment, allowing for very slow cooling rates of around 0.3°C per day. This presented an engineering challenge. Although Diamond has a lot of temperature-controlled environments, 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.

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 sub-zero 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.





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