Rolling Ironstones from Earth and Mars: Terrestrial Hydrothermal Ooids as a Potential Analogue of Martian Spherules

High-resolution images of Mars from National Aeronautics and Space Administration
(NASA) rovers revealed mm-size loose haematite spherulitic deposits (nicknamed “blueberries”)
similar to terrestrial iron-ooids, for which both abiotic and biotic genetic hypotheses have been
proposed. Understanding the formation mechanism of these haematite spherules can thus improve
our knowledge on the possible geologic evolution and links to life development on Mars. Here, we
show that shape, size, fabric and mineralogical composition of the Martian spherules share similarities
with corresponding iron spherules currently forming on the Earth over an active submarine
hydrothermal system located off Panarea Island (Aeolian Islands, Mediterranean Sea). Hydrothermal
fluids associated with volcanic activity enable these terrestrial spheroidal grains to form and grow.
The recent exceptional discovery of a still working iron-ooid source on the Earth provides indications
that past hydrothermal activity on the Red Planet is a possible scenario to be considered as the cause
of formation of these enigmatic iron grains.