You never know what might drift across your field of view while observing. Recently, the exoplanet-hunting space telescope Kepler nabbed an amazing view of something relatively close to home—the planet Neptune and its moons. Launched on March 6, 2009, in a dramatic night shot out of Cape Canaveral, Kepler wrapped up its primary mission hunting for transiting exoplanets in 2013. Kepler has since been repurposed to conduct an expanded exoplanet-hunting campaign, known as K2. Hobbled by failed reaction wheels, the idea behind K2 is to search along the plane of the Solar System using the solar wind pressure as an “extra stabilizer”. This unique orientation pointing along the ecliptic plane means that outer Solar System objects—such as the planet Neptune—can also pop into view.
Neptune can be seen entering stage right, and is bright enough to oversaturate Kepler’s detectors. The video covers a 70-day span of observations and 101,580 images taken from November 2014 to January 2015 compressed into just 34 seconds. Note that about midway through the video, Neptune begins to move backwards. This is known as retrograde motion, and is the apparent motion due to the movement of Kepler itself around the Sun. Kepler follows the Earth in a heliocentric orbit. In the video, several asteroids seem to photobomb the shot, streaking by at random intervals. Also keep an eye out for Neptune’s large moon Triton and its smaller moon Nereid. Neptune has 14 known moons in all. But beyond just the cool factor, astronomers also hope to use Kepler’s unique vantage point to study outer Solar System objects, such as Neptune, long term. To date, only Voyager 2 has explored Neptune up close. And we’re only three years from the launch of Kepler’s exoplanet hunting successor, the Transiting Exoplanet Survey Satellite (TESS). Keep an eye on the sky, both on Earth and in space . . . you never know what might pop by.