Astronomy Cast Ep. 422: Geysers

So if you’ve been to Yellowstone National Park, you’ve seen one of the most amazing features of the natural world – geysers. In today’s episode, we’re going to talk about geysers on Earth, and where they might be in the solar system.

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Hubble Discovers Water Plumes Erupting from Europa

It’s been known since 2005 that Saturn’s 300-mile-wide moon Enceladus has geysers spewing ice and dust out into orbit from deep troughs that rake across its south pole. Now, thanks to the Hubble Space Telescope (after 23 years still going strong) we know of another moon with similar jets: Europa, the ever-enigmatic ice-shelled moon of Jupiter. This makes two places in our Solar System where subsurface oceans could be getting sprayed directly into space — and within easy reach of any passing spacecraft.

(Psst, NASA… hint hint.)

The findings were announced today during the meeting of the American Geophysical Union in San Francisco.

“The discovery that water vapor is ejected near the south pole strengthens Europa’s position as the top candidate for potential habitability,” said lead author Lorenz Roth of the Southwest Research Institute (SwRI) in San Antonio, Texas. “However, we do not know yet if these plumes are connected to subsurface liquid water or not.”

The 125-mile (200-km) -high plumes were discovered with Hubble observations made in December 2012. Hubble’s Space Telescope Imaging Spectrograph (STIS) detected faint ultraviolet light from an aurora at the Europa’s south pole. Europa’s aurora is created as it plows through Jupiter’s intense magnetic field, which causes particles to reach such high speeds that they can split the water molecules in the plume when they hit them. The resulting oxygen and hydrogen ions revealed themselves to Hubble with their specific colors.

Unlike the jets on Enceladus, which contain ice and dust particles, only water has so far been identified in Europa’s plumes. (Source)

Rendering showing the location and size of water vapor plumes coming from Europa's south pole.
Rendering showing the location and size of water vapor plumes coming from Europa’s south pole.

The team suspects that the source of the water is Europa’s long-hypothesized subsurface ocean, which could contain even more water than is found across the entire surface of our planet.

Read more: Europa’s Hidden Great Lakes May Harbor Life

“If those plumes are connected with the subsurface water ocean we are confident exists under Europa’s crust, then this means that future investigations can directly investigate the chemical makeup of Europa’s potentially habitable environment without drilling through layers of ice,” Roth said. “And that is tremendously exciting.”

One other possible source of the water vapor could be surface ice, heated through friction.

Cassini image of ice geysers on Enceladus (NASA/JPL/SSI)
Cassini image of ice geysers on Enceladus (NASA/JPL/SSI)

In addition the Hubble team found that the intensity of Europa’s plumes, like those of Enceladus, varies with the moon’s orbital position around Jupiter. Active jets have been seen only when Europa is farthest from Jupiter. But the researchers could not detect any sign of venting when Europa is closer.

One explanation for the variability is Europa undergoes more tidal flexing as gravitational forces push and pull on the moon, opening vents at larger distances from Jupiter. The vents get narrowed or even seal off entirely when the moon is closest to Jupiter.

Still, the observation of these plumes — as well as their varying intensity — only serves to further support the existence of Europa’s ocean.

“The apparent plume variability supports a key prediction that Europa should tidally flex by a significant amount if it has a subsurface ocean,” said Kurt Retherford, also of SwRI.

(Science buzzkill alert: although exciting, further observations will be needed to confirm these findings. “This is a 4 sigma detection, so a small uncertainly that the signal is just noise in the instruments,” noted Roth.)

“If confirmed, this new observation once again shows the power of the Hubble Space Telescope to explore and opens a new chapter in our search for potentially habitable environments in our solar system.”

– John Grunsfeld, NASA’s Associate Administrator for Science

Read more: Hydrogen Peroxide Could Feed Life on Europa

So. Who’s up for a mission to Europa now? (And unfortunately in this case, Juno doesn’t count.)

“Juno is a spinning spacecraft that will fly close to Jupiter, and won’t be studying Europa,” Kurt Retherford told Universe Today. “The team is looking hard how we can optimize, maybe looking for gases coming off Europa and look at how the plasma interacts with environment, so we really need a dedicated Europa mission.”

We couldn’t agree more.

The findings were published in the Dec. 12 online issue of Science Express.

Sources: Hubble news releases (US and ESA)

Image credits:
Graphic Credit: NASA, ESA, and L. Roth (Southwest Research Institute and University of Cologne, Germany)
Science Credit: NASA, ESA, L. Roth (Southwest Research Institute and University of Cologne, Germany), J. Saur (University of Cologne, Germany), K. Retherford (Southwest Research Institute), D. Strobel and P. Feldman (Johns Hopkins University), M. McGrath (Marshall Space Flight Center), and F. Nimmo (University of California, Santa Cruz)

“Snowing Microbes” On Saturn’s Moon?

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Enceladus, Saturn’s 318-mile-wide moon that’s become famous for its ice-spraying southern jets, is on astronomers’ short list of places in our own solar system where extraterrestrial life could be hiding — and NASA’s Cassini spacecraft is in just the right place to try and sniff it out.

On March 27, Cassini came within 46 miles (74 km) of Enceladus’ south pole, the region where the moon’s many active water-ice jets originate from. This was Cassini’s closest pass yet over the southern pole, allowing the spacecraft to use its ion and neutral mass spectrometer — as well as its plasma spectrometer, recently returned to service — to taste the icy spray emanating from deep fissures called “tiger stripes” that scar Enceladus’ surface.

(Fly along with Cassini toward Enceladus’ jets here.)

“More than 90 jets of all sizes near Enceladus’s south pole are spraying water vapor, icy particles, and organic compounds all over the place,” said Carolyn Porco, planetary scientist and Cassini Imaging science team leader. “Cassini has flown several times now through this spray and has tasted it. And we have found that aside from water and organic material, there is salt in the icy particles. The salinity is the same as that of Earth’s oceans.”

In addition to water, salt and organics, there is also a surprising amount of heat — heat generated in part by tidal friction, helping keep Enceladus’ underground water reserves liquid.

“If you add up all the heat, 16 gigawatts of thermal energy are coming out of those cracks,” Porco said.

This creates, in effect, a so-called “Goldilocks zone” of potential habitability orbiting around Saturn… a zone that Cassini has easy access to.

“It’s erupting out into space where we can sample it. It sounds crazy but it could be snowing microbes on the surface of this little world,” Porco said. “In the end, it’s the most promising place I know of for an astrobiology search. We don’t even need to go scratching around on the surface. We can fly through the plume and sample it. Or we can land on the surface, look up and stick our tongues out. And voilà…we have what we came for.”

Cassini's view down into a jetting "tiger stripe" in August 2010

Cassini’s latest results — and images! — from the flyby should be landing on Earth any time now. Stay tuned to Universe Today for more updates on Cassini and Enceladus.

Read more on NASA Science News here.

Image credits: NASA/JPL/SSI.

UPDATE: For images from Cassini’s flyby, showing closeups of Enceladus as well as Dione and Janus, check out the CICLOPS team page here.

Yellowstone Eruption

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Millions of people visit Yellowstone National Park every year, but how many think about the fact that they’re standing on top of one of the largest volcano calderas on Earth? Within the last 17 million years, there have been more than 100 large eruptions within the Yellowstone caldera, and thousands of smaller lava flows and steam explosions. In fact, the last great Yellowstone eruption happened about 70,000 years ago, and it only seems like a matter of time before it all happens again. Don’t panic, though, geologists monitor Yellowstone carefully, and they don’t think any large eruptions will happen soon.

The Yellowstone calderas measures 55 km wide by 72 km long, and rises to an elevation of 3,142 meters at its tallest point – Mount Sheridan. The constant uprise of the region created a plateau where there used to be a mountain range. These eruptions and uplift helped create the eastern Snake River Plain.

In the last 17 million years, there have been 142 caldera-forming eruptions in Yellowstone. This is an eruption large enough that a significant amount of lava, ash or rock were released – usually as an explosive eruption. Three of these eruptions have been classified as “super eruptions”, where up to 2,500 cubic km of ash and rock exploded out of the volcano. Just for comparison, Mount St. Helens, which erupted in 1980, only released 1 cubic km of material… so 2,500 times that in a single eruption. One of these super eruptions would have devastated most of North America, and cooled the climate of planet Earth for decades. The oldest of these Yellowstone eruptions happened 2.1 million years ago, which created the Huckleberry Ridge Tuff. The next oldest happened 1.3 million years ago, and the most recent super eruption happened about 640,000 years ago.

And since that last super eruption, there have been numerous smaller (but still powerful eruptions) non-explosive eruptions. The most recent lava flow has been estimated to have occurred about 70,000 years ago, and a steam explosion created a 5-km crater 13,800 years ago. The only eruptions that happen at Yellowstone today are the numerous geothermal vents around the caldera. These mix with water to create the famous geysers, like Old Faithful. These geysers indicate that Yellowstone is still a very active region, and more eruptions are likely.

Geologists are continuing to monitor the Yellowstone caldera, including the speed at this the caldera floor is rising up. Like Hawaii, Yellowstone is created by a single volcanic hotspot located under the Earth. The North American Plate is slowly moving over top of the hotspot, creating a long chain of calderas. The current caldera in Wyoming is the current location of the hotspot. Geologists have measured that the caldera floor is rising upwards at almost 7 cm per year. Fortunately, they find no evidence that we’re due for another super Yellowstone eruption. Of course, these things are difficult to predict.

We have written many articles about volcanoes for Universe Today. Here’s an article about about a Yellowstone-like formation on Mars, and an article about how extreme life in Yellowstone might offer hope for the search for life on Mars.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

Source: Wikipedia