WHAT’S THE BIGGEST MOUNTAIN IN THE SOLAR SYSTEM?

Mars’s Olympus Mons is often described as the highest mountain in the Solar System. One of many volcanoes on the Red Planet, it towers over its neighbours at 21.2km above the Martian equivalent of ‘sea level’, making it about two and a half times as tall as Earth’s Mount Everest (8.8km). However, an unnamed mountain peak comes a strong second. Situated at the centre of a huge crater on the asteroid Vesta, it has a height of at least 20km. Its size is even more impressive when you consider that Vesta’s diameter is only 530km. Determining a clear winner is challenging, partly because of the difficulties in establishing a reference height equivalent to sea level on Earth. For example, ‘zero altitude’, the equivalent of sea level on Mars, is often measured as the height in which temperature and atmospheric pressure would allow water to exist simultaneously in all three states: solid, liquid and gas.

Over 300 people are known to have died scaling Everest since 1922. Injuries and bad weather can be deadly in this remote environment, and our bodies have not evolved to cope with low oxygen levels at high altitude. Altitude sickness can lead to fatal pulmonary or cerebral oedemas, which occur when the lack of oxygen results in leakage of fluid into the lungs or brain. To avoid this, mountaineers acclimatise in stages, allowing their bodies to adjust gradually. Above 8,000 metres, climbers enter ‘the death zone’ where the air pressure is so low that humans cannot survive for long periods without supplementary oxygen.

In 2019, high winds left just a few suitable days for climbers to attempt Everest’s summit. Many were forced to wait their turn at punishingly high altitudes, amplifying the effects of exhaustion and altitude sickness. This led to one of the mountain’s deadliest years ever, with 11 reported fatalities.