Explanation:
Jupiter's moons
circle Jupiter.
The featured video depicts Europa and Io, two of
Jupiter's largest moons, crossing in front of
the grand planet's
Great Red Spot,
the largest known storm system in our
Solar System.
The video was composed from images taken by the
robotic Cassini spacecraft as it passed Jupiter in 2000, on its way to Saturn.
The two moons visible are
volcanic Io, in the distance, and
icy Europa.
In the time-lapse video, Europa appears to overtake Io, which is
odd because Io is closer to
Jupiter and moves faster.
The explanation is that the motion of the fast
Cassini spacecraft changes the camera location significantly during imaging.
Jupiter is currently being visited by
NASA's robotic
Juno spacecraft,
while ESA's
Jupiter Icy Moons Explorer (JUICE),
launched in April, is enroute.
