Integral X-rays Earth's aurora

ESA’s Integral satellite has been scouring the skies around the Earth for signs of high-energy radiation since 2002, observing particles thrown off by extreme phenomena such as black holes, neutron stars, and supernova explosions. On 10 November 2015, the probe serendipitously spotted something especially interesting – and a little closer to home: intense auroras dancing around Earth’s north pole.

This image is a single frame from a longer sequence of images, and shows the auroras forming a rough semi-circle at Earth’s northern latitudes. The auroras were first spotted around east Siberia, north of Japan, at around 11:00 GMT, and later seen lingering over a wider area on the opposite side of the planet above Canada and Greenland.

Integral was initially preparing for astronomical research when it spied this aurora; the probe was planning to observe the skies at X-ray wavelengths to measure something known as the cosmic X-ray background, a diffuse level of radiation that pervades the cosmos and is linked to high-energy events such as black holes devouring nearby material in far away galaxies. This background is subtle and tricky to detect – and in this case, the unexpectedly strong auroras illuminating the Earth drowned it out.

However, the observations were far from wasted. They may be known for their breath-taking light shows, but auroras can reveal much about the space surrounding our planet. They are created as particles from the solar wind enter the upper layers of our atmosphere and interact with matter there, triggering bursts of light and filling the sky with their characteristic glimmering, rippling sheets of colour.

Auroras are transient and difficult to predict; capturing such an intense example with Integral helped scientists to understand more about the distribution and amount of charged particles surrounding our planet, and to characterise the interaction between the Sun and our magnetosphere – the region of space over which the Earth’s magnetic field dominates. Read more about the observations, which were reported on in 2016, here.

Integral took the X-ray images using the Imager on Board the INTEGRAL Satellite (IBIS) instrument at roughly eight minute intervals. The size, orientation and position of our planet within the frame changes from image to image with Integral’s position in orbit; the spacecraft travels on a highly eccentric 64-hour orbit, coming as close as 10 000 km and as distant as 140 000 km from Earth.