Subscribe to our free daily newsletters
  Space Travel News  




Subscribe to our free daily newsletters



JOVIAN DREAMS
A Second Look at Plumes and the Search for life on Europa
by Sheyna Gifford for Astrobiology Magazine
Moffett Field CA (SPX) Oct 05, 2016


This composite image shows suspected plumes of water vapor erupting at the 7 o'clock position off the limb of Jupiter's moon Europa. Image courtesy NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center.

Once can be a coincidence. Twice can be luck. Seeing a hundred-mile-high column of water spew out of Jupiter's icy moon Europa three times in a row has been cited as a good reason to get excited.

Plumes - great jets of subsurface water forced through the moon's thick ice sheet - were first spotted spraying out of Europa's southern pole in December 2012. At least, that's what the scientific community hoped was going on when Hubble first captured images of something bright in the ultraviolet spectrum "shooting" out of an area known to have fissures, or cracks that arise as Europa is deformed by Jupiter's gravity.

In the hopes of finding more evidence that this image was, indeed, a plume, not some other phenomenon, a separate team of scientists started watching Europa as it passed between Earth and Jupiter. The idea was this: if a liquid is being squeezed out of a solid body into space, it should spray cross Jupiter's face, leaving a shadow.

The plan panned out beautifully. Ten times over fifteen months, scientists from the Space Telescope Science Institute watched Europa cut across the gas giant. Thirty percent of the time, Jupiter's glow dimmed slightly: in the same place as the potential plume from 2012.

The importance of plumes and the role they might play in finding life beyond Earth was described in this 2014 article. To sum it up: if these images reflect the presence of plumes, it means that we can explore the subsurface of Europa without having to dig, drill, or even land. Europa's water, and whatever may be living in it, will come to us: we simply have to fly to it and through it.

Sampling run to Jupiter, anyone?

The Importance of Plumes
The Hubble Space Telescope is famous for finding black holes. It can pick out thousands of galaxies in a patch of sky the size of a thumbprint. The most powerful space telescope ever built, the Hubble provided evidence that the Universe isn't slowing down in its infinite rush into whatever lies beyond.

But the Hubble's cosmic firepower was recently put to a new purpose: searching for a billowing cloud of water vapor on Jupiter's moon Europa. The plumes are a sign that extraterrestrial life could be lurking within our own Solar System. Before we head way out there, we need to know a little about the eruptions happening at home.

Plumes: Warm and Nearby
On Earth, the plumes are a hallmark of energy in motion. Here, active geology often takes the form of pyroclastic eruptions. Pyro is Greek for "fire," while "clastic" derives from "broken." Pyroclastic eruptions feature solid rock, semi-solid fragments and hot gases expelled from the mantle through areas of weakness in the crust.

They create the plumes of ash and smoke we typically associate with volcanos. Even when volcanos are underwater, as many are, they send up steaming columns of lava fragments, bits of rock and heated gas. These underwater plumes of hot material rise hundreds of meters. The heated underwater plumes that make it to the surface of the ocean can be seen from space.

While these displays are impressive, not all that explodes from the Earth's crust is pyroclastic. Geysers are long columns of water. Their bases lie close enough to the mantle to be heated by its 1,000 C (1,832 F) temperatures. The heated water expands and rises, forcing its way to the surface. Once the water and steam reach the surface, the pressure falls, as does the plume of vapor, after inertia shoots it briefly into space.

In all of these formations, heated gases escape from the interior and reach the surface. There, they rapidly expand and cool, dissipating the fierce energies that drove them to erupt. In this way, volcanism reflects the build-up of pressure within a planet or other large body on which it is known to occur.

In March of 2006, geysers were discovered spewing water from the surface of Enceladus, one of Saturn's icy moons. Thus began a race to explain how a moon with surface temperatures of -330 Fahrenheit (-201 Celsius) could have active geology, and to discover if those geysers could signal a warm core for Enceladus and other icy moons.

Plumes: Cold and Far Away
Cold cryoclastic plumes may play a key role in finding superhabitable zones in areas around gas giants where tidal forces create enough heat to sustain life. Nonetheless, they differ from traditional volcanism in many respects. One respect is temperature.

"Much of what we see taking place or see evidence of having taken place looks like lava and sort of normal volcanism on Earth except it involves warm water," said Bruce Marsh, a geophysicist at the Department of Earth and Planetary Sciences, Johns Hopkins University.

Warm, in this case, is relative. Cassini, a NASA satellite, noticed that the area around these vents is substantially warmer than the surrounding ice: as high as -120 Fahrenheit (190 Kelvin). Where pyroclastic explosions emit fragments of broken fire, cryoclastic eruptions are bursts of icy material hundreds of degrees warmer than the surrounding surface, but still well below freezing.

Another point of difference between Earth's plumes and icy world plumes is contents. Enceladus' plumes spew water vapor and dust, which rapidly disperse into surrounding space. Then, there's the point of origin. There are no volcanoes on Enceladus. Instead, these plumes originate from vents in the southern polar terrain, also known as "tiger stripes." Now, at least two of the ingredients necessary for life are present on Enceladus: water and warmth.

Unfortunately, the existence of relatively warm vents and escaping water are insufficient to prove that active heating is occurring deep within the moon, or that an ocean lies within its ice sheet. Local radioactivity and flexing forces from Saturn may be creating underground liquid reservoirs in the regions around the vents. That would raise temperature in just that region, melting ice that could then pool into the cracks. If this were true, water vapor plumes on Enceladus might originate relatively near the surface, instead of from a life-breeding ocean.

The discovery of the plume on Enceladus was sufficient to prove that icy moons undergoing tidal forces are geologically active. It was a good sign that we should look for others.

As it happens, there is another icy moon, namely Europa, circling a closer planet, that has all of ingredients for life as well. It also has an extremely thick ice sheet, a saltwater signature and possibly an enormous ocean with twice as much water as all of the oceans on Earth combined. Organic material has been found on the surface. The surface itself is known to undergo continual remodeling, bringing organics down and any subsurface life-signatures up. Many scientists believed that if plumes could be found on Europa, that would be a portent that we should head there to look for further signs of life.

Until recently, though, none had been seen. It turns out that finding a geyser 500,000 miles away is tricky business. How the Hubble happened to be looking right at Europa the moment a plume exploded is more than pure coincidence.

Pretty Elusive Eruptions
"Plumes on Europa could be tough to catch in the act," said Lynnae Quick, a planetary scientist and postdoctoral fellow at NASA's Goddard Space Flight Center. "If observing at visible wavelengths, there have to be enough particles (in the plume) in order for it to be seen. Icy satellites (like Europa and Enceladus) have very bright, reflective surfaces. The light reflected off of these surfaces can obscure plumes from being seen. For this reason, you want to look at the limb."

Looking at the limb of a planetary body requires a perpendicular point of view. It's not a natural viewpoint for humans. We tend to look straight at an object of interest, focusing on the center of it.

Imagine examining a tree. The natural thing to do is to look directly at the trunk. The limbs of a tree are everywhere, scattered in all directions at the periphery of your visual field. The tiniest tree limbs are nearly impossible to see without standing close to the tree and craning your neck. In the case of Europa, standing close isn't an option. That's one reason a really big telescope is needed.

Considering the tree analogy, another problem becomes obvious: tree limbs are only visible against a different-colored background, like a blue sky or white clouds. Europa's surface is made of water. The plumes are too.

"On Europa, plumes are very hard to see because you are putting ice crystals on top of an icy surface," said Louise Prockter, a superviser at Johns Hopkins University's Applied Physics Laboratory's planetary exploration group.

Looking at the limb of Europa, where the edge of the moon meets the dark space of space, is like dropping a black curtain in the background. That's a better contrast than the white ice. However, there's another problem.

"The problem with [water] plumes is that they are very tenuous," said Prockter, "We've seen plumes off the limb of Io (Jupiter's innermost Galilean moon) because they tend to be pretty fierce and pretty long lasting. They caused massive changes on the surface on the time scale that Galileo was there."

On smaller Enceladus, plumes remain suspended for a time. By contrast, the expulsion of water vapor into the near-vacuum surrounding Europa is short-lived. Europa's more substantial gravity yanks the frozen water spouts back toward the surface. Ice lands on ice, leaving barely a trace. So the only chance to catch a plume on Europa is to look at the disc and the limb, and keep looking until one happens right in front of us.

The Hubble Space Telescope is currently the only tool powerful enough to crane its neck at just the right angle to catch a transient puff of the water vapor 400 million miles away. Even so, Hubble hunted for a plume on Europa for years without success. It was aimed at Europa in October 1999, November 2012 and December 2012 before finally catching one using its spectrograph.

Caught on Camera in Invisible Light
A spectrograph is an instrument that separates light into color components by wavelength. Spectrographs are invaluable instruments in astronomy. Objects in space that can't be seen with visible light can still be detected by the radiation around them. Hubble's Space Telescope Imaging Spectrograph (STIS) allows it to detect black holes. In Europa's case, the STIS picked up the plume's vapor cloud by its ultraviolet light, which is just beyond what's visible to the eye.

In the ultraviolet spectrum, the plume of water vapor seen by Hubble Space Telescope in December 2012 extended more than 125 miles (200 kilometers) into space.

"I'm really excited about these observations because they seem to suggest that some areas of Europa's crust are being intensely heated to create the vapor," said Jason Goodman, assistant professor of physics at Wheaton college, who has published research on hydrothermal plumes on Europa. "We can't say for sure yet whether this is a cyclical process or a chance event, or whether the vapor is coming from warm but solid ice, partially-melted ice, or from the ocean, but it's definitely a sign that Europa has some exciting internal activity going on right now."

Putting On the Gloves
Even with the Hubble Space Telescope hard at work, we are uncertain how water gets just below the surface of Europa. We have many models about how, and quite a few notions about when. For example, at the farthest point, or apocenter, Europa experiences tensions that may cause plume production at weak spots in the ice.

"At apocenter, the surface fractures in the south polar region experience tension. This tension might open the cracks and allow the water vapor to escape from a subsurface liquid reservoir," said Lorenz Roth, first author on the Science paper that described the plume's discovery. "Confirmation of the initial detection and the proposed connection to Europa's orbital position is crucial now."

Using Hubble to look for further plumes during the entire orbit will bring us closer to some answers. However, we won't truly understand what's going on inside Europa's salty oceans, possibly warm for the last 4 billion years, until we take a much, much closer look.

"More Hubble data will help," said Goodman. "But this vapor plume is right at the limit of what telescopes near Earth can see. To really get to the bottom of this story, we need to send a spacecraft to Europa."

With plumes, water vapor bursts through the ice shell and arches away at amazing speed. The resulting ballistic arc of freezing droplets can be seen from half a million miles away. Better still, they can be sampled without having to land, drill, melt or dig.

"What this means is that we can now go and sample the subsurface by flying through a plume," said Prockter. "There's a very good chance that we can sample the material in five to 10 or 15 years."

Now that we know when and where Europa is active, a mission can be launched with plumes specifically in mind.

"A spacecraft in a low enough orbit could fly through the plume," said Quick.

A plume is a million pieces of Europa's interior. These pieces might be from the depths of the sea or from just below the surface. Either way, to reach into the ice of a faraway moon, all we have to do is catch a plume.

"That's really exciting. Europa comes to us," said Prockter. "I can't think of anywhere better for life than Europa."


Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Contributor
$5 Billed Once


credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly


paypal only

.


Related Links
Astrobiology Magazine
Jupiter and its Moons
Explore The Ring World of Saturn and her moons
The million outer planets of a star called Sol
News Flash at Mercury






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

Previous Report
JOVIAN DREAMS
Hubble spots possible water plumes erupting on Jupiter's Moon Europa
Baltimore MD (SPX) Sep 27, 2016
Astronomers using NASA's Hubble Space Telescope have imaged what may be water vapor plumes erupting off the surface of Jupiter's moon Europa. This finding bolsters other Hubble observations suggesting the icy moon erupts with high-altitude water vapor plumes. The observation increases the possibility that missions to Europa may be able to sample Europa's ocean without having to drill throu ... read more


JOVIAN DREAMS
ULA gets $860 million contract modification for expendable launch vehicle

Trusted Ariane 5 lays foundations for Ariane 6

Orbital ATK and Stratolaunch partner to offer competitive launch opportunities

Ariane 5 reaches the launch zone for Arianespace's October 4 liftoff

JOVIAN DREAMS
Schiaparelli readied for Mars landing

Opportunity at First Science Spot of its 10th Extended Mission

Study predicts next global dust storm on Mars

NASA flight program tests Mars Lander vision system

JOVIAN DREAMS
Exploration Team Shoots for the Moon with Water-Propelled Satellite

Space tourists eye $150mln Soyuz lunar flyby

Roscosmos to spend $7.5Mln studying issues of manned lunar missions

Lockheed Martin, NASA Ink Deal for SkyFire Infrared Lunar Discovery Satellite

JOVIAN DREAMS
Shedding light on Pluto's glaciers

Chandra detects low-energy X-rays from Pluto

Scientists discover what extraordinary compounds may be hidden inside Jupiter and Neptune

New Horizons Spies a Kuiper Belt Companion

JOVIAN DREAMS
TESS will provide exoplanet targets for years to come

The death of a planet nursery?

Protoplanetary Disk Around a Young Star Exhibits Spiral Structure

New Low-Mass Objects Could Help Refine Planetary Evolution

JOVIAN DREAMS
Successful escape, landing for Blue Origin's rocket

Welding on massive fuel tank for first flight of SLS completed

Work underway on hardware that will do double duty on first SLS flight

Ascent Trajectories and the Gravity Turn

JOVIAN DREAMS
Closing windows on Shenzhou 11

Beijing exhibition means plenty of "space" for everyone

From nothing to glory in six decades - China's space program

Space for Shenzhou 11

JOVIAN DREAMS
Origin of minor planets' rings revealed

Rosetta's comet adventure in numbers

Farewell Rosetta: ESA Mission to Conclude on Comet's Surface

Alice Ultraviolet Spectrograph Completes Rosetta Mission to Comet 67P




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News






The content herein, unless otherwise known to be public domain, are Copyright 1995-2017 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement