We’re all still reeling from the Met Office’s warning that we may be facing a decade of miserable summers
. Perhaps it will help to recall that we don’t know everything about the sun. That burning ball of gas in the sky remains something of a mystery, and not just for its refusal to shine with any consistency over the UK.
The centre of the sun is fairly straightforward. Atoms of hydrogen fuse, forming atoms of helium and releasing energy that powers more fusion. That ongoing chain reaction, burning several million tonnes of hydrogen per second, heats the core of the sun to temperatures of roughly 15m°.
The laws of thermodynamics tell us that energy moves from hot to cold, and so heat starts moving towards the surface of the sun, where the temperature is a balmy 6,000°. It’s not an easy journey, though. It’s only about 700,000 kilometres, or a trip from the earth to the moon and back, but it takes the packets of energy released in nuclear fusion something like 40,000 years to reach the sun’s surface.
It’s hard to fathom that the warmth you feel (or don’t feel) today was created at a time when Neanderthals were still around. Yet that is not the real mystery. The problem that has scientists scratching their heads is the temperature of the outer layer of the sun’s atmosphere, the corona. The temperature of this blanket of ionised gas is roughly 1m° to 2m°. Bafflingly, the further away you move from the furnace at the centre of the sun, the hotter it gets.
The solution to this puzzle lies in the region of the sun known as the chromosphere. This is the layer that lies between the surface and the corona. That is why Nasa has just launched a telescope to take a closer look. For the next two years, the Interface Region Imaging Spectrograph (Iris)
will watch the chromosphere from its position in orbit 400 miles above Planet Earth.
It’s ironic that Iris’s launch on 27 June was delayed by a power outage that took Vandenberg Air Force Base’s systems offline: that is exactly what Iris may help prevent. The huge quantity of energy trapped in the chromosphere powers the solar wind, a stream of particles that emanates from the sun, as well as events such as the coronal mass ejections that occasionally catapult hundred-billionkilogram gobs of plasma out into space at speeds of up to seven million miles per hour.
When those hot plasma balls (they start off at 10m°) head our way, things can get pretty tricky here on earth. Interactions between the plasma balls and the earth’s magnetic field can cause havoc with our power grids and threaten vital infrastructure.
The US National Academy of Sciences has estimated that, in a worst-case scenario, a freak space storm could cause a catastrophe that would leave the US government with a repair bill of up to $2trn
. Improving our understanding of the chromosphere is one way to tell how badly the sun could hurt us, so the $100m to build Iris and look into the possibilities seems a bargain.
The main working part of the spacecraft is a telescope that inspects the ultraviolet radiation coming from the 2,000-mile gap between the surface and the corona. It will take an image every ten seconds or so and analyse the spectrum of radiation for clues to how the heat is moving around to produce such odd changes in temperature. In a couple of years, we may have solved the biggest mystery in our solar system. Then we can sit, shivering under steel-grey skies, marvelling at human scientific ingenuity and wondering why someone can’t do something about the weather.