Stardate 03:30:98
Tiny, Tired Mercury...
Mercury is not a good place for a vacation. Searing
hot in the day, and frigid cold at night, any future human outposts on
Mercury would likely be bathed in eternal twilight.
The good news there is that any Mercurians would
have a birthday every 88 Earth days. This tiny world was known as Hermes
to the Greeks, who assigned it the title of messenger to the Gods. Revolving
around the Sun so quickly, it must have seemed a swift messenger indeed.
Issac Asimov believed that Mercury, although known
to the ancients, was the last bright planet discovered. By an interesting
coincidence, he also stated that the metal mercury was the last of the
metals to be discovered by people in the preliterate age. But, this seems
to be nothing more than pure coincidence. The reason the planet Mercury
was the last of the planets visible to the naked eye to be discovered is
partly due to the fact that it is always seen near the Sun, and so is only
visible for a short while before sunrise, or after sunset.
Tiny, battered Mercury is only about 40 percent
of the size of the Earth, as it has a diameter of about 4900 km (about
3000 miles). While rocket ships leaving the Earth have to travel about
7 miles per second to avoid being drawn back to the surface, a rocket leaving
Mercury would only need to travel about 2.8 miles per second. This is also
coincidentally about 40% that of Earth, but the two are not directly related.
Incidentally, Mercury also orbits the Sun at a distance about 40% that
of the Earth. A person who weighed 150 pounds on the Earth, would weigh
just 60 pounds on the battered face of Mercury.
It was once believed that Mercury was locked gravitationally
with the Sun, thereby always facing the same side toward the Sun, as our
Moon always presents us with the same face night after night. Incidentally,
this is not due to the fact that the planet or moon does not rotate. It
is because such a satellite has a "day" exactly as long as it's
"year". We now know a day Mercury lasts as long as over 58 Earth
days. Here, we can easily see that there are 88/58, or only about one and
a half Mercury days in a Mercury year.
A single impact crater on Mercury, the Caloris
basin, is 1300 km (over 800 miles) in diameter. The impact which formed
the crater spread debris for 800 km (500 miles) around the impact site.
One fascinating aspect of the surface of Mercury are features known as
lobate scarps. They are fault like folds on the surface of the planet,
and often cross craters. This seems to indicate that Mercury cooled and
shrank after many of it's craters had formed.
Although Mercury is much like our moon, there
are some striking differences. Perhaps the most important of these is the
difference in the cores of Mercury and the Moon. Although the Moon is metal
poor, Mercury seems to have a significant metal core. Measurements by the
Mariner 10 spacecraft also found a weak magnetic field surrounding this
world.
You should be able to see Mercury this week, hovering
low over the western horizon, soon after sunset. If you view it through
a telescope or binoculars, you will see that it exhibits phases like the
Moon and Venus.