Sky and Telescope - July 2018 - 33
t PHOTOGRAPHIC INTERPRETATION Although great
strides occurred in the improvement of astronomical
photography in the 20th century, film emulsion never
surpassed the resolving capacity of the human eye. Earl
C. Slipher, who worked at Lowell Observatory from 1909
until his death in 1964, compiled the most comprehensive photographic record of Mars, spanning 50 years. He
never gave up his belief in the canals, going so far as to
publish drawn interpretations of his photographs.
From the start, however, even scientists who
accepted Schiaparelli's reports of channels on
Mars favored natural explanations. A sobering
review by Dublin astronomer J. R. Holt in the
September 1894 issue of L'Astronomie summarizes it eloquently:
The overall opinion is that the Martian canals
are ﬁssures on the planet's surface created when
Mars transitioned from a liquid to solid phase and
consequently are older than the seas. On the other
hand, some astronomers believe them to be artiﬁcial,
or rivers and canals redirected by the inhabitants for
He concludes that the canals were probably
caused by ﬂuvial erosion, in part due to shrinkage
of the ancient seas:
It is likely that the oldest "continents" are mostly
deserts, and that life, if it does exist, is relegated
to terrains only recently laid bare by retreat of the
waters and the canals. It must also be said that the
ﬂuvial erosions must have been massive, if these
rivers have indeed [ﬂowed] for millions of years
along these same basins.
This seems remarkably prescient given the poor
state of knowledge about Mars at the time.
Finally, what was known of the physical and
geological conditions on Mars in the late 1800s?
Spectroscopy and photography were just coming of age as powerful new astronomical tools,
as were increasingly larger telescopes. The ﬁrst
spectroscopic studies of the Martian atmosphere
compared it to that of the airless Moon and
incorrectly concluded it contained water vapor.
That ﬁnding no doubt fueled the debate about
canals and life on Mars. By 1894, however, Lick
astronomer William Campbell showed that the
water-vapor signature in the Martian spectrum
was actually due to the Earth's atmosphere.
Likewise, astronomical photography, which
had vastly improved by the turn of the 20th
century (S&T: March 2014, p. 68), did not convincingly record the network of canals. Despite
Lowell astronomers Carl Otto Lampland and later Earl C.
Slipher's determined efforts to do so, their very best images
only revealed broad, diffuse linear features, very similar to
those drawn by Eugène Antoniadi using the 32.6-inch refractor
at Meudon Observatory in Paris. Antoniadi's sketches, in fact,
correspond quite closely to modern charts of the major geologic features on the planet as revealed by orbiting spacecraft.
So, in the end, were all of the Red Planet's presumptive
canals imaginary? Not quite, but they were decidedly not
artiﬁcial. As Mars expert William Hartmann points out in his
engaging book A Traveler's Guide to Mars, while many consider
that Lowell and his followers let their imaginations get the
best of them, were they really so crazy? The answer seems to be
no. As Hartmann says, "Proof that some of Schiaparelli's and
Lowell's much-criticized canals were based on real features can
be found in a Martian region known as Xanthe Terra."
As we now know, this extensive desert region contains
two large craters with dark, windblown dust streaks and the
gigantic canyon Valles Marineris. All three features were
portrayed as canals by many 19th-century astronomers and
given various names. For example, Lowell's canal Coprates
corresponds to Valles Marineris. Other canals that correspond to actual Martian features include Cerberus, named by
Schiaparelli, a prominent fracture zone now called Cerberus
Fossae. Similarly, many other canals
are dark linear streaks caused by
windswept dust on the Martian surface, which gradually changed from
one opposition to the next, especially
as seen with Earth-based telescopes.
The Lingering Romance
As Sheehan and others have pointed
out, Lowell, Schiaparelli, and Flamp CLOSING THE BOOK
Today, Mars has been
marion, as well as many of their
explored by numerous
contemporaries, set the stage for
a hopeful if not overly romantic
and rovers, which have
notion of Mars as an abode of life,
conclusively shown that
especially in the public mind. Talk of
no artificial canals exist
on the Red Planet.
"intelligent beings" disappeared in
the early 20th century as new data
emerged on the tenuous nature of the Martian atmosphere,
its desiccated, frigid surface conditions, and its lack of liquid
water. Even after NASA's historic Mariner 4 spacecraft ﬂyby
in the mid-1960s, such luminaries as Carl Sagan and Gerard
Kuiper argued that the shrinking polar caps and darkening of
adjacent landscape on Mars might be evidence of lichen-like
organisms consuming water vapor released by melting frost.
While we now know this isn't the case, the quest for past or
even present life on Mars remains a major scientiﬁc goal of
current space exploration. And so the romance continues.
¢ KLAUS BRASCH is professor emeritus of biology at California State University, San Bernardino, and docent in the public
program at Lowell Observatory.
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