Meeting Despina

Despina is a small moon of Neptune with an average diameter of only 148 km. It was discovered in 1989 from images taken by Voyager 2 as it approached the planet.

There were no other images of this moon until 2009, when the amateur astronomer and philosophy professor Ted Stryk discovered something really unexpected.

 Stryk was in fact analyzing a series of images obtained at nine-minute intervals taken by the Voyager 2 probe twenty years earlier when he noticed that on Neptune’s atmosphere there was a small dark spot that changed position between one pose and another. Continuing the analysis of the data Stryk realized that this spot was actually the shadow of a moon projected on the atmosphere of the planet! The professor understood that that moon was Despina and finally he also managed to find it: in one of the images it appeared in front of the planet, while in the other three it blended with the black of space.

The reason why Despina was not recognized in this series of images in the twenty years preceding Stryk is very simple. The moon is in fact much less bright than Neptune and in the images it appeared practically invisible, getting lost in the light of the planet. In the image of the post, the brightness of the moon has been artificially increased by several orders of magnitude in order to make it visible.

Credit: NASA/JPL/Ted Stryk.