hydrogen, and at the centre of an astonishing collective of orbiting natural bodies.
In fact Jupiter's satellites form a shrunken version of a full planetary system: from the tightly bound larger
Galilean moons (orbiting in their Laplacian mean-motion resonances, akin to places like TRAPPIST-1) to the
remarkable array of smaller moonlets that encircle this world out to more that 30 million
kilometers.
These bodies circle Jupiter in anywhere from about 7 hours to an astonishing 1,000 days.
Until recently the catologed satellites totaled 67 in number. But only the innermost 15
of these orbit Jupiter in a prograde sense (in the direction of planet's spin).
The rest are retrograde, and are likely captured objects - other pieces of the solar system's solid inventory that
strayed into Jupiter's gravitational grasp,
The population of outer moon is mostly small stuff, only a few are 20-60 kilometers in
diameter, most are barely 1-2 kilometers in size, and increasingly difficult to spot.
New Astromomers Scott Sheppard, David Tholen and Chadwick Trujillo have added two more; bringing Jupiter 's Moon count to 69.
These additions are also about 1-2 km in size, and were spotted in images that were part of a survey for much
more distant abject S out in the Kuiper Belt. Jupiter just happened to be conveniently close in the sky at the
same time.
By themselves these small satellites don't amount to much. But they are a vivid reminder of the sheer abundance
of material out there in our solar system, and of Jupiter's royal gravitational status.
Scientific American-June 12,2017
