NASA's Kepler catches Neptune dancing with its moons

NASA's Kepler spacecraft has caught images of Neptune together with two of its moons, in one of the longest continuous studies of an outer solar system object.

Featured in a grainy, 34-second video, Neptune appears as a bright light with the moons Triton and Nereid quickly rotating around it at different times. The movie comprises 70 days of uninterrupted observation.

Neptune appears on day 15 of the movie but does not travel alone. The small faint object closely orbiting it is its large moon Triton, which circles Neptune every 5.8 days. Appearing from the left at day 24 is the tiny moon Nereid in its slow 360-day orbit around the planet. A few, speeding asteroids make cameo appearances in the movie, showing up as streaks across the K2 field of view.

The red dots in the movie are a few of the stars K2 examines in its search for transiting planets outside of our solar system.

Launched in 2009, the famous space telescope tasked with finding Earth-like planets has identified more than 1,000 exoplanets among 4,175 candidates it's discovered. After completing its primary mission in 2012, NASA extended its life by four years hoping to build on its early success.

The movie - which is part of its second act - was based on 101,580 images taken from November 2014 through January 2015 during K2's Campaign 3.

Neptune's atmosphere reflects sunlight, creating the burst of light that cuts across the screen. The reflected light floods a number of pixels of the spacecraft's onboard 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 should appear white from a distance.

The interesting motion of Neptune and its moons beginning at day 42 can be explained by their relative orbit speeds. 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.

NASA researchers hope to use the latest 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.

  • Michael Casey

    Michael Casey covers the environment, science and technology for