Map of Mercury
ATLAS OF THE UNIVERSE
T
he first serious attempts at mapping Mercury
were made between 1881 and 1889 by the
Italian astronomer G. V. Schiaparelli, who used
22-centimetre (8^1 ⁄ 2 -inch) and 49-centimetre (19-
inch) refractors. Schiaparelli observed in broad
daylight, when both Mercury and the Sun were
high in the sky. He believed the rotation period to
be synchronous, so that the same regions were
always in sunlight, and he recorded various bright
and dark features.
A more detailed map was published in 1934
by E. M. Antoniadi, who used the 83-centimetre
(33-inch) refractor at the Meudon Observatory,
near Paris. He too believed in a synchronous
rotation, and also thought (wrongly) that the
Mercurian atmosphere was dense enough to sup-
port clouds. He drew various features, and named
them; thus a large dark patch was called the
Solitudo Hermae Trismegisti (the Wilderness of
Hermes the Thrice Greatest). However, when the
Mariner 10 results were received, it was found
that the earlier maps were so inaccurate that their
nomenclature had to be abandoned.
Mariner mapped less than half the total sur-
face; at each active pass the same regions were
sunlit, but there is no reason to believe that
the remaining areas are basically different.
Superficially the surface looks very like the Moon;
it is coated with a layer of porous silicate ‘dust’
forming a regolith which probably extends down-
wards for a few metres or a few tens of metres
(10 to 100 feet). There are craters, which have
been named after people; plains (planitia) named
from the names of Mercury in different languages;
mountains (montes); valleys (valles) named after
radar installations; scarps (dorsa) named after
famous ships of exploration and discovery; and
ridges (rupes) named after astronomers who have
paid particular attention to Mercury. Some craters
have ray systems, notably Kuiper, which is named
after the Dutch astronomer who played such a
major role in the early days of planetary explor-
ation by spacecraft.
The south pole of Mercury lies in the crater
Chao Meng Fu. It has been agreed that the
20th meridian passes through the centre of the
1.5-kilometre (1-mile) crater Hun Kal, 0.58
degrees south of the Mercurian equator. The name
Hun Kal is taken from the word for the numeral
20 in the language of the Maya, who used a base-
20 number system.
It has been suggested that there may be ice
inside some of the polar craters, whose floors
are always in shadow. However, this is now
regarded as most unlikely, if only because the
same effects have been recorded in areas which
do receive sunlight, and where ice could not
possibly exist. Maps of Mercury,
prepared by Paul Doherty
using data from Mariner 10.N
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