Facts about tallest mountain on Mars

 Olympus Mons is a very large shield volcano on the planet Mars. The volcano has a height of over 21km as measured by Mars Orbiter Laser Altimeter (MOLA). 

Olympus Mons is about two and a half times Mountain Everest's height above sea level. It is second tallest mountain discovered in the solar system. Only Mons is the youngest of the large volcanoes on Mars, having formed during Mars 's Hesperian period. 

It's mountainous nature was suspected well before space probes confirm it's identity as mountain. It located in the western hemisphere of Mars. Olympus Mons is partially surrounded by a region of distinctive grooved or corrugated terrain known as the Olympus Mons aureole. The aureole consists of several large lobes.

The composition of Olympus Mons is approximately 44% silicates, 17.5% iron oxides (which give the planet its red coloration) 7% aluminum, 6% magnesium, 6% calcium, and particularly high proportions of sulfur oxide with 7%. These results point to the surface being largely composed of basalts and other mafic rocks, which would have erupted as low viscosity lava flows and hence lead to the low gradients on the surface of the planet.