The Mysterious Moons of
(left), and Phobos (right), above Mars in this composite picture.
They [the Laputians] have likewise discovered
two lesser stars, or satellites, which revolve about Mars, whereof
the innermost is distant from the center of the primary planet
exactly three of its diameters, and the outermost five; the former
revolves in the space of ten hours, and the latter in twenty-one
and a half; so that the squares of their periodical times are
very near the same proportion with the cubes of their distance
from the center of Mars, which evidently shows them to be governed
by the same law of gravitation that influences the other heavenly
bodies. - Gulliver's Travels - Jonathan Swift - 1726
The fourth planet out from the Sun, Mars, has two
moons. The are named Phobos (meaning "fear") and Deimos (meaning
"panic"); appropriate companions for Mars, the God of War.
Swift: Was his prediction about the existance of the two
Martian moons just a lucky guess?
Over a hundred years before the moons' discovery,
in 1877, British writer and satirist Jonathan Swift "predicted"
their existence in the book we now know as "Gulliver's Travels."
There is no way Swift could have known the moons were real yet
he described Phobos' orbital period as 10 hours (very close to
the real figure of 7.6) and Deimos' as 21.5 (close to the real
30.2). Both seem to be very lucky guesses.
How was Swift able to predict the existence of the
moons and their attributes so well? Some have seriously suggested
he had psychic powers. More likely, though, Swift may have employed
the same logic as the French writer Voltaire did a quarter century
later when he also predicted two Martian moons. Voltaire knew
that the inner planets, Mercury and Venus had no moons and the
outer planets, Jupiter and Saturn each had many. Earth had one.
It seemed likely to Voltaire that Mars, that next out from Earth,
probably had at least two.
Even if Swift had employed the same logic to figure
the number of moons his estimate on the duration of their orbits
was still startlingly accurate.
Swift's prediction isn't the only mystery about
the Martian moons. In 1862 scientists were looking for them carefully
because conditions for finding Martian satellites were extremely
favorable. The scientists found nothing. Fifteen years later Asaph
Hall, an American astronomer working at the US Naval Observatory
in Washington D.C., discovered them at time when conditions for
observation weren't nearly as good.
U.S. Naval Observatory in the 19th century: No probelm seeing
Why did Hall find Phobos and Deimos when better
equipped scientists failed to find them earlier? One American
scientist, Frank Salisbury, suggested, in the journal Science,
the moons were actually artificial satellites and the failure
to detect them was due to them only being launched, by the Martians,
sometime after 1862.
We now know from space probe observations that both
Phobos and Deimos are natural objects. Phobos is a chunk of blackish
carbonaceous chondrite rock some 17 miles long by 12 miles wide.
Its most striking feature is a giant depression, Stickney Crater,
which is about a half a mile across.
Demios, 10 miles long and 7.5 miles wide, is like
Phobos in composition, but with a smoother surface. Both are very
similar to the many asteroids found between the orbit of Mars
and Jupiter. This leads some scientists to speculate that they
actually originated in the asteroid belt and only later were captured
by Mars' gravity.
Copyright Lee Krystek 1997-2012.
All Rights Reserved.