Today, it is well understood that Mars is a cold, dry, and geologically
dead planet. However, billions of years ago when it was still young, the planet
boasted a denser atmosphere and had liquid water on its surface. Millions of
years ago, it also experienced a significant amount of volcanic activity, which
resulted in the formation of its massive features – like Olympus Mons, the
largest volcano in the Solar System.
Until recently, scientists have understood that Martian volcanic
activity has been driven by sources other than tectonic movement, which the
planet has been devoid of for billions of years. However, after conducting a
study of Martian rock samples, a team of researchers from the UK and United
States concluded that eons ago, Mars was more volcanically active than
previously thought.
Their study, titled “Taking the Pulse of Mars via Dating of a Plume-fed
Volcano“, recently appeared in the scientific journal Nature Communications.
Led by Benjamin Cohen, a researcher with the Scottish Universities
Environmental Research Center (SUERC) and the School of Geographical and Earth
Sciences at the University of Glasgow, the team conducted an analysis of Mars’
volcanic past using samples of Martian meteorites.
On Earth, the majority of
volcanism occurs as a result of plate tectonics, which are driven by convection
in the Earth’s mantle.
But on Mars, the majority of
volcanic activity is the result of mantle plumes, which are highly-localized
upwellings of magma that rise from deep within the mantle. This is due to the
fact that Mars’ surface has remained static and cool for the past few billion
years.
Because of this, Martian
volcanoes (though similar in morophology to shield volcanoes on Earth), grow to
much larger sizes than those on Earth.
Olympus Mons, for example,
is not only the largest shield volcano on Mars, but the largest in the Solar
System. Whereas the tallest mountain on Earth – Mt. Everest – is 8,848 m
(29,029 ft) in height, Olympus Mons stands some 22 km (13.6 mi or 72,000 ft)
tall.
For the sake of their study,
Dr. Cohen and his colleagues used radioscopic dating techniques, which are
commonly used to determine the age and eruption rate of volcanoes on Earth.
However, such techniques have not been previously used for shield volcanoes on
Mars. As a result, the team’s study of Martian meteorite samples was the first
detailed analysis of growth rates in Martian volcanoes.
The six samples they
examined are known as nakhlites, a class of Martian meteorite that formed from
basaltic magma roughly 1.3 billion years ago.
These came to Earth roughly
11 million years ago after being were blasted from the face of Mars by an
impact event. By conducting an analysis of Martian meteorites, the team was
able to uncover about 90 million years’ worth of new information about Mars’ volcanic
past.
As Dr. Cohen explained in a
University of Glasgow press release:
“We know from previous
studies that the nakhlite meteorites are volcanic rocks, and the development of
age-dating techniques in recent years made the nakhlites perfect candidates to
help us learn more about volcanoes on Mars.”
The first step was to
demonstrate that the rock samples were indeed Martian in origin, which the team
confirmed by measuring their exposure to cosmogenic radiation. From this, they
determined that the rocks were expelled from the Martian surface 11 million
years ago, most likely as a result of an impact event on the Martian surface.
They then applied a high-precision radioscopic technique known as 40Ar/39Ar
dating.
This consisted of using a
noble gas mass spectromomer to measure the amount of argon built up in the samples,
which is the result of the natural radioactive decay of potassium. From this,
they were able to obtain 90 million years’ worth of new information about the
Martian surface. The results of their analysis indicated that there are
significant differences in volcanic history between the Earth and Mars.
As Dr. Cohen explained:
“We found that the nakhlites
formed from at least four eruptions over the course of 90 million years. This
is a very long time for a volcano, and much longer than the duration of terrestrial
volcanoes, which are typically only active for a few million years. And this is
only scratching the surface of the volcano, as only a very small amount of rock
would have been ejected by the impact crater – so the volcano must have been
active for much longer.”
In addition, the team was
also able to narrow down which volcanoes their rock samples came from. Previous
studies conducted by NASA revealed several candidates for the possible nakhlite
source crater. However, only one of the locations matched their results in
terms of the age of the volcanic eruptions and the impact that would have
ejected the samples into space.
This particular crater
(which is currently unnamed) is located in the volcanic plains known as Elysium
Planitia, roughly 900 km (560 mi) away from summit of the Elysium Mons
volcano – which stands 12.6 km (7.8 mi)
tall. It is also located about 2000 km (1243 mi) north of where the NASA Curiosity
rover currently is. As Cohen explained, NASA has some wonderfully detailed
satellite images of this particular crater.
“It is 6.5 km wide, and has
preserved ejecta rays of debris,” he said. “And we were able to see multiple
horizontal bands on the crater walls – which indicating the rocks form layers,
with each layer interpreted as a separate lava flow. This study has been able
to provide a clearer picture into the history of the nakhlite meteorites, and
in turn the largest volcanoes in the solar system.”
In the future, sample return
and crewed missions to Mars are sure to clear up this picture even further.
Given that Mars, like Earth, is a terrestrial planet, knowing all we can about
its geological history will ultimately improve our understanding of how the
rocky planets of the Solar System formed. In short, the more we know about
Mars’ volcanic history, the most we will be able to learn about the Solar
System’s formation and evolution.
Via UniverseToday