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.
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.
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.