is a Martian volcano
, notable for results from the European Space Agency
's Mars Express
mission which indicate a major eruption took place 350 million years ago. The eruption created a caldera
10km in diameter. It has been suggested that glacial deposits later partly filled the caldera and an adjacent depression. Crater counts indicate this happened as recently as 5 to 20 million years ago. However climate models show that ice is not stable at Hecates Tholus today, pointing to climate change since the glaciers were active. It has been shown that the age of the glaciers correspond to a period of increased obliquity
of Mars' rotational axis.
The volcano is at location 32.1°N 150.2°E, in Elysium Planitia, and has a diameter of 183.0 km. It is the northernmost of the Elysium volcanoes; the others are Elysium Mons and Albor Tholus.
In planetary nomenclature, a "tholus" is a "small domical mountain or hill".