Volcanoes in Space

Two sorts of geologic features are found on most solid planets and moons in our solar system. They are impact craters and volcanoes. We talk about volcanoes on worlds beyond Earth …

Spacecraft exploring our solar system have found volcanoes on other planets and moons.

The tallest volcano in the solar system — Olympus Mons — is on Mars. It’s about 25 kilometers — or 15 miles — tall. Some Martian lava flows seem relatively recent — less than a hundred million years old. Scientists are still hoping we might someday witness a “last gasp” volcanic eruption on Mars.

Meanwhile, Venus has more volcanoes than any other planet known so far. Venus is still hot — so scientists haven’t ruled out the possibility of on-going volcanic activity.

But the most powerful volcano in the solar system is a lava lake on Jupiter’s moon Io named Loki. It’s a cauldron of lava about 200 kilometers — or 120 miles — wide. This region on Io brightens and dims every few months. And that’s mysterious because volcanoes on Earth don’t follow a regular cycle in this way.

One explanation might be that lava on the surface of this volcanic lake on Jupiter’s moon cools and forms a crust. The crust is heavier than the hot lava churning below — so from time to time, blocks of crust sink — and hot lava wells up to take its place.

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Generally, bodies must be larger than Mars to still have enough heat to drive volcanism. Exceptions are moons (such as Io) that are subject to tidal forces due to the gravity of their parent planets.

Extinct volcanoes are seen on the surfaces of many of the other planets and moons in the solar system. Volcanic activity on Earth’s moon peaked three to four billion years ago. Even the youngest lunar volcano is probably over a billion years old. The moon is a relatively small world. It’s thought to have cooled off quickly — putting an end to its time of volcanic activity.

The age of volcanoes on Mars lasted longer. There are Martian lava flows less than a hundred million years old. Some may even continue to be active. Scientists hope we may someday witness a “last gasp” eruption on Mars.

Olympus Mons is the largest volcano on Mars and the tallest in the solar system. It rises nearly seventeen miles from the surrounding plateau. That’s three times as high as commercial airplanes fly. It’s base measures 372 miles from edge to edge — larger than the state of Arkansas — and its crater measures forty miles from rim to rim.

Many of Mars’s volcanoes erupted over a period of billions of years. Earth’s volcanoes grow to completion in a few million years before going extinct and eroding. There were volcanic eruptions for 98% of Mars’ history. Scientists hope we may someday witness a “last gasp” eruption on Mars.

Data from the Pioneer Venus probes showed a large quantity of sulfur dioxide in the Venusian atmosphere that declined over a period of a few decades. This could indicate that the sulfur dioxide was ejected by a volcano.

There’s still some debate about whether Venus is still volcanically active. The evidence is on the side of it having bursts of activity with quiescence in between. There hasn’t been much data about Venus in the last few years.

Volcanism on icy moons is called cryvolcanism. The magma is water slush. Water is a mineral just like silicates and metal oxides.

We do not see volcanoes on asteroids today — but we have volcanic rocks from meteorites that were probably derived from asteroids such as Vesta. Beth Ellen Clark-Joseph — a physicist at Ithaca College in New York — says it’s “absolutely impossible that anyone has spotted active volcanoes on asteroids in the last few years – asteroids are so small that their heat would have completely radiated away already. That is a physical impossibility. The volcanism we’re talking about occurred within 20 million years after the formation of the solar system and there hasn’t been any since. Old volcanoes!”

Shape of the Moon’s Volcanoes

The moon’s volcanoes don’t have the classic cone shape. Instead, they are flat and spread out, like lava fields. This is because the lava that came from them are basaltic. Basalt is low in silica, and silica is what makes lava stiff.

Volcanoes on Io

Perhaps the most interesting volcanoes have been found farther out in the solar system — on Jupiter’s moon Io.

Until 1979, scientists thought Jupiter’s moon Io would be like our moon — cold and covered with impact craters. Then the Voyager spacecraft captured images of Io’s active volcanoes.

The Voyager spacecraft took pictures of violent volcanic eruptions on Io. The volcanic plumes rose some 300 kilometers — or 200 miles — above its surface. Since then, scientists have observed new volcanoes and lava flows form on the surface. The plumes appear to be the result of hot lava contacting frost on the surface, which then explodes, creating jets of gas and dust. One volcanic plume moved 50 miles between being imaged by the Voyager and Galileo missions.

As Io orbits Jupiter, it’s tugged and stretched in different ways by Jupiter and two other moons — Europa and Ganymede. This flexing generates heat, which then leads to volcanic activity.

Loki — one of the biggest Io volcanoes — seems to erupt every 540 days — it did so through the 1990s. Loki appears to be a giant lava lake that’s over 100 miles across and has a crust that freezes. It seems to have an island floating in the middle. We see waves of material that sweep around the island — which could be a crust sinking. The lake is horseshoe shaped. Loki was discovered by Voyager in 1979. It was hard to follow it’s behavior on a regular basis because we didn’t have the ground based technology. But then telescopes in Hawaii and at Lowell Observatory and others were able to study it in the 1990s and reveal the repeating cycle of activity.

Io’s volcanoes are not like the classic cone-shaped volcanoes we see on Earth and several other bodies in the solar system. Io’s volcanoes tend to be large and relatively flat. The lava is very fluid — it seems to contain more iron and magnesium — and less silica — than Earth’s lava. In fact, it’s more like the lava that poured out onto Earth’s surface millions of years ago, during the Precambrian. Because it’s so fluid, it can’t pile up like a mountain. It flows too easily.

Volcanoes on Europa

Recently, another Galilean moon was scrutinized for possible volcanic activity. Scientists suspected that Europa — the moon next outward from Jupiter — got its look of a cracked cue ball from cold volcanoes spewing ice and slush.

Close-up images from NASA’s Galileo spacecraft haven’t revealed any currently active volcanoes on Europa. But they do show flows of icy masses, along with dark scarring on some of Europa’s cracks and ridges. These features fit scientists’ models of how volcanoes might shape the surface of this moon.

Scientists also speculate that there may be a liquid ocean beneath Europa’s frozen crust. The signs of past volcanic activity point to the presence of enough heat inside Europa to melt ice. Liquid water and heat would make Europa an exciting place to search for extraterrestrial life. So far no organic compounds have been found on this moon of Jupiter’s. But a future discovery might reveal them.

Just weeks before the Voyager I spacecraft made its closest approach to Io, a couple of scientists realized that Io might have a molten interior and active volcanism. They reasoned that the tidal forces created by competing gravitational tugs from Jupiter and the nearby moons could create a lot of heat. Io’s volcanoes are now believed to be driven by tidal friction caused by Jupiter’s gravity. There is speculation that much less intense heating may exist under the surface of Europa, which could account for the volcanic activity of the past.

Even farther out in the solar system, Neptune’s moon Triton is known to have geysers, which might be driven by solar heating. Triton’s surface is thought to act as a natural solar panel. A superficial layer of frozen, transparent nitrogen on this moon acts in much the same way as a glass. Infrared radiation gets trapped beneath the surface layer of this moon. When temperatures rise just a few degrees, ice begins to vaporize and erupt through vents.

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