Back in 2015, as Rosetta’s comet, 67P, was approaching perihelion, scientists noticed the surface changing before their eyes. These “very significant alterations,” according to the European Space Agency, were located in Imhotep, the smooth region on the comet’s large lobe.

One exciting aspect of the Rosetta mission was that on a comet, there was a high expectation that visible changes would occur during perihelion, which is the point in the orbit where the comet makes its closest approach to the Sun. How these changes relate to the processes theorised to happen on comets is still a work in progress. Many new papers are proposing various mechanisms, and data from the mission will be informing scientific results for years to come.

Thousands of Rosetta images are available from the European Space Agency. In March 2016, ESA put out a call for citizen scientists to help spot changes on the comet’s surface.

I like looking through comet images for changes, so I decided to contribute. It’s a wonderful way for non-scientists to get involved. The process has been very rewarding—as one becomes more and more familiar with features, changes start to jump out, and there are usually multiple images of the same area to help validate differences.

Here’s a change I discovered last year. Take a look at these two raw images. Can you spot the difference?