May 15, 2015
NASA's Kepler spacecraft, known for its planet-hunting prowess of other stars, is also studying solar system objects. In its new K2 mission, Neptune and two of its moons, Triton and Nereid, have been imaged. The movie illustrates 70 days of uninterrupted observation making this one of the longer continuous studies of an outer solar system object.
The movie, based on 101,580 images taken from November 2014 through January 2015 during K2's Campaign 3, reveals the perpetual clockwork of our solar system. The 70-day timespan is compressed into 34 seconds with the number of days noted in the top right corner.
Neptune appears on day 15 but does not travel alone in the video. The small faint object closely orbiting is its large moon Triton, which circles Neptune every 5.8 days. Appearing from the left at day 24, keen-eyed observers can also spot the tiny moon Nereid in its slow 360-day orbit around the planet. A few fast-moving asteroids make cameo appearances in the movie, showing up as streaks across the K2 field of view. The red dots are a few of the stars K2 examines in its search for transiting planets outside of our solar system.
Neptune's atmosphere reflects sunlight creating a bright appearance. The reflected light floods a number of pixels of the spacecraft's on board camera, producing the bright spikes extending above and below the planet. The celestial bodies in the stitched-together images are colored red to represent the wavelength response of the spacecraft's camera. In reality, Neptune is deep blue in color and its moons and the speeding asteroids are light grey while the background stars appear white from a distance.
Relative orbit speeds explain the interesting motion of Neptune and its moons beginning at day 42. Inner planets like Earth orbit more quickly than outer planets like Neptune. In the movie, Neptune's apparent motion relative to the stationary stars is mostly due to the circular 372-day orbit of the Kepler spacecraft around the sun. If you look at distant objects and move your head back and forth, you will notice that objects close to you will also appear to move back and forth, relative to objects far away. The same concept is producing the apparent motion of Neptune.
While NASA's Kepler spacecraft is known for its discoveries of planets around other stars, an international team of astronomers plans to use these data to track Neptune's weather and probe the planet's internal structure by studying subtle brightness fluctuations that can only be observed with K2.