The Red
Planet had a fiery and watery past. New research reveals that beginning about 3.5
billion years ago, five episodes of violent volcanic activity spewed lava and
hot water onto the Martian surface, sculpting the landscape into the dimpled
world we see today.
Unlike on
Earth, researchers say, the fashioning of the Martian surface has proceeded in
spurts and stops. The rocky slabs that form Earth's outer surface steadily inch
along to mold the mountains and valleys that shape our planet.
The
results, presented last week at the Lunar and Planetary Science Conference at
League City, Texas, depicted periods of volcanic activity alternating with
relatively quiescent stints on Mars.
"We
now have good evidence that volcanism on Mars and the release of water was not
at the same level at all times, but it was episodic," said Gerhard Neukum of
Freie University of Berlin and principal investigator for Mars Express, the
spacecraft which returned the data behind this study.
Dating
rocks
Neukum and his
colleagues analyzed images from the High Resolution Stereo Camera (HRSC) on Mars Express.
In order to estimate the ages of volcanic material on Mars, Neukum's team
counted the number of small craters carved into the surface. The older the
surface, the more craters it would have accumulated as meteorites of all sizes
bombarded its surface.
"We
can now determine the ages of large regions and resurfacing events on the
planet," Neukum said. Resurfacing occurs when volcanic eruptions spread
lava across the planet's surface.
From this
technique, the team estimated five volcanic periods: 3.5 billion years ago,
1.5 billion years ago, between 400 million and 800 million years ago, 200
million years ago and 100 million years ago. The dates of the earlier episodes,
Neukum estimates, are correct to within 100 million to 200 million years and
the later dates are correct to within 20 million to 30 million years.
The most
recent activity on Olympus Mons,
Mars's largest volcano, occurred at the summit around 150 million years ago with minor flows in some areas as recent as 2 million years ago. Neukum added that peaks in eruptions of the volcano match the dates his team found
for global volcanic activity.
The team also
investigated two large channels, Kasei Valles and Mangala Valles, revealing
episodes of water flow that roughly match the times of high volcanic activity.
"So
water flowed over the surface of Mars not just at the beginning but again and
again throughout its history," Neukum told SPACE.com.
Martian
plates
The bursts
of volcanic activity could be explained by plate tectonics, or lack thereof.
Whereas Earth is covered with a puzzle of rocky slabs called plates, Mars
is a one-plate planet.
Over time,
heat from Mars's interior builds up and can cause the crust to crack in some
areas, releasing fiery magma (called lava when it reaches the surface). The
internal heat generated by the volcanic activity also may have caused water to
erupt from the interior, leading to wide-scale flash flooding.
These
episodes might not be over.
"The
interior of the planet is not cold yet, so this could happen again," Neukum
said. But the chances of Mars Express or another orbiter spying such events are
slim, because the eruptions happen much less frequently on Mars than on Earth,
he added.
"So Mars
is not dead," Neukum said.
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