Jarosite: A Natural Geological Clock on Mars

Jarosite, a yellow-brown mineral comprising potassium, iron, and sulphate, has potential as a natural geological clock on Mars. This capability arises from its luminescence properties due to stored energy from natural radiation.

Research Findings

• Sample Collection
  A team of researchers from India collected six jarosite veins from Kachchh in Gujarat, an area resembling Mars due to its arid and salty terrain.
• Laboratory Analysis
  • The grains were washed in weak acid, doubling their brightness.
  • They were subjected to radiation, heating, and cooling cycles, revealing four distinct emissions at approximately 100° C, 150° C, 300° C, and 350° C, even after exposure to 450 °C.
• Significance of Luminescence
  • Jarosite's ability to luminesce indicates it can withstand heating by a rover’s drill without losing luminescence.
  • The glow increased with added radiation, with saturation occurring between 590 and 2,600 gray (an SI unit for absorbed radiation dose).

Implications for Mars Exploration

• On Mars, natural radiation is about 65 milligray/year, allowing jarosite to record events from up to 25,000 years ago.
• Given jarosite’s prevalence on Mars, durability, and ease of reading with small heaters and LEDs, it is suggested as a tool for dating events like dust storms, ancient floods, and volcanic ash on the planet.