From Simple English Wikipedia, the free encyclopedia
On April 28, 1905, the American
astronomer
William H. Pickering
said that he had found a tenth
moon
of the planet
Saturn
. Pickering named the moon
Themis
. No other astronomer has ever seen the moon that Pickering said he saw. Because of this, astronomers do not count Themis as an official moon of Saturn.
Pickering tried to figure out an
orbit
for Themis. He thought that Themis had an
inclination
of 39.1° to the
ecliptic
, with 0.23
eccentricity
(0.23) and a
semi-major axis
distance of 1,457,000 km. This meant that Themis had an orbit like the moons
Titan
and
Hyperion
. Pickering believed that it took Themis 20.85 days to orbit Saturn, in a
prograde
motion.
Pickering thought that the
diameter
of Themis was about 38 miles (61 km). Pickering had also discovered the moon
Phoebe
, but modern astronomers know that Pickering made a mistake when he gave 42 miles (68 km) as the diameter of Phoebe. Because astronomers know how Pickering made his mistake, they can say that if Themis existed, it would have a diameter of 200 km.
In April 1861,
Hermann Goldschmidt
also thought he discovered a new satellite of Saturn between Titan and Hyperion. Goldschmidt called this moon
Chiron
. The moon Chiron also does not exist, but the name was used much later for the
comet
/
asteroid
2060 Chiron
.
In 1906, the
French Academy of Sciences
gave Pickering the
Lalande Prize
of the
French Academy of Sciences
for his "discovery of the ninth and tenth satellites of Saturn".
The actual tenth satellite of Saturn (in order of discovery) was
Janus
, which was discovered in 1966 and confirmed in 1980. Its orbit is far from the supposed orbit of Themis.
There is also an asteroid named
24 Themis
.
- John Varley
's
science fiction
novel
Titan
takes place on an expedition to Saturn. As they approach the planet and prepare to enter orbit, the astronomer onboard discovers a new moon. At first she believes she has recovered Pickering's lost moon, so she names it Themis.
- Robert Anton Wilson's
novel
Schrodinger's Cat trilogy
makes frequent reference to Pickering's Moon as a satellite that revolves the "wrong way" around its primary.