Among the thousands of visitors to Mt. Etna this year, one group came not
just to look at one of most famous volcanoes on Earth. Dozens of scientists
trekked up Etna together this fall to observe what Etna has in common with
Mars.
Researchers interested in what makes the red planet tick can’t study the
planet in person-at least not yet. To help them interpret what they see in
Mars images and other remote sensing data–and to test their instruments and
procedures–they turn to Earth.
Though the two planets are very different, Earth offers many similarities,
or analogs, to Mars. Some of these, such as Antarctica, are definitely off
the beaten track. Others, however, such as Mt. Etna, are places where
ordinary travelers might find themselves– although perhaps unaware that
what they’re seeing is anything like our neighboring planet.
“A site can be like Mars in a variety of ways,” says JPL geologist Dr. Tom
Farr, one of the participants in the “Exploring Mars’ Surface and its Earth
Analogues” workshop at Mt. Etna. “Since Mars is really cold, the first
places you think of are Antarctica and the Arctic. These places provide a
way to see some of the processes that probably take place on Mars- glaciers
and permafrost. But a place can also be like Mars by having similar
geological features, such as volcanoes, or processes like erosion and
weathering.”
Volcanoes in Common
The prominent volcanoes on Mars are large, old and apparently no longer
active. “Though small by Mars’ standards, Etna, like the majority of
volcanoes on Earth, is basaltic,” says Mars Odyssey Project Scientist Dr.
Jeffrey Plaut, who was also in the Etna workshop. “We believe that Mars’
volcanoes have the same composition.”
Etna also has an example of a volcanic process that scientists think may
occur on Venus, the Moon, and possibly Mars, but until recently hadn’t been
seen before on Earth. “We see some long narrow channels on those planets
that don’t look like they were eroded by water,” says Farr. “We inferred
that they were produced by lava, but until their discovery on Etna, we had
never actually seen that happen.”
Not all of Earth’s volcanoes match those on Mars. “Mt. St. Helens is not a
good analog,” says Plaut, “it’s silica-rich and is a result of plate
tectonics that do not seem to occur on Mars”. For good examples of large
shield volcanoes, the most common type on Mars, Plaut picks Mauna Loa and
Kilauea. “The big island of Hawaii, which is the largest volcano on Earth,
has been a tremendous Mars analog.”
On Mars, super-sized volcanoes sculpted the landscape by releasing huge
amounts of lava. It’s possible to see what that sort of event did on Earth
along the Columbia River in Washington. “Some of the largest lava flows on
Earth took place there,” says Plaut. The area was repeatedly flooded by
lava, which formed the great basaltic cliffs called the Columbia River
Basalts. And in Idaho’s Snake River Plain, “rift lava seeped over a large
flat surface creating a volcanic plain that serves as a good terrestrial
analog for extensive sheet lavas on Mars as well as Venus and the Moon,”
says Farr.
Mars in the Desert
Earth’s deserts have many examples of geological processes at play on Mars.
“Processes in arid environments tend to create dunes and landforms eroded
and etched by winds like those we see on Mars,” says Plaut. “We also like
the desert because there’s not much vegetation and the geology is exposed at
the surface as it is on Mars.”
Drier and cooler than most deserts, the Atacama in Chile is often considered
a Mars analog. In the warm deserts of Tunisia at the edge of the Sahara and
California’s Mojave, wind-blown sand creates Mars-like dunes and landforms.
Deserts in North Africa, China, Asia, and North America are home to
wind-sculpted ridges known as yardangs, also common in the Martian
landscape.
On both planets, some of today’s deserts were probably yesterday’s lakes.
The same process that created Utah’s Bonneville Salt Flats may have shaped
the dry lakebeds that dot the Martian landscape. “Mars seems to have had
catastrophic floods,” says Plaut. “not unlike those that took place in the
Bonneville area in the ice age. As the glaciers retreated, the rapid
draining of a large lake carved up the landscape creating distinctive
landforms. There was a lot of water and a lot of energy.”
One of the most famous planetary analogies and laboratories is Death Valley.
“It’s like Mars in its tectonic, erosional and sedimentation processes,”
says Plaut. “It looks like Mars, too. There’s a spot called Mars Hill that
reminds people very much of the Viking 2 Lander site.”
Impact Zone
Many a meteor made its last stop on Mars and on Earth. Mars’ surface is
pockmarked with impact craters. Here on Earth, most are buried or have
eroded away. The Haughton Crater on Devon Island in the Canadian Arctic is a
well-known site for Mars-related studies. More accessible is the meteor
crater in Winslow, Ariz. “It’s fairly recent,” says Plaut, “and
well-preserved, like many we see on Mars.”
Geology may not be all that Mars and Earth have in common. In the search for
life in extreme environments, like those which may exist on Mars,
researchers are looking in places like Yellowstone and Hot Springs, Ark.
“Because the Mars environment is so cold and dry, getting liquid water to
the surface today may require hot spring activity,” says Plaut. “But people
are studying all kind of ground water environments, hot or not, and caves as
possible Mars analogs.”
As Mars exploration continues, new common ground between that planet and
this one is likely to emerge. “Even as we learn more about Mars from the new
missions,” says Farr, “we’ll go out and try to find places on Earth that are
similar, continuing our search for better Mars analogs.”
