The study also points out that convection – an incredibly efficient way of cooling that relies on a fluid – doesn’t operate normally either. Taking place everywhere, from Earth’s slowly mobile-but-solid mantle to the air around you, the lack of gravity interferes with it.
The astronauts' space fevers could be partly explained by these mechanisms. Curiously, the higher CBTs also seem to correlate with inflammation in the body linked to microgravity – perhaps your body mistaking near-weightlessness for an infection of sorts – higher-than-average radiation rates, psychological stress, or a combination of all of the above.
At present, it’s not entirely clear what causes persistently higher CBTs in space, but it does put astronauts in a bit of a bind. If they don’t exercise regularly, the microgravity environment will weaken and degrade their muscles and bones.
This difficulty in cooling themselves down, though, may mean that they are more prone to suffering from potentially dangerous exhaustion after a particularly straining session on the low-grav bikes on the International Space Station, for example.
Some astronauts during exercise had CBTs reaching around or even exceeding 40°C (104°F). If this is sustained for too long, it can induce a medical emergency.
The international research team, which was led by Charité – the Berlin University of Medicine, conclude in their paper that “since even minor increases in CBT can impair physical and cognitive performance, both findings have a considerable impact on astronauts’ health and well-being during future long-term spaceflights.”