Where Should We Look for Life in the Solar System?
Emily Lakdawalla is the senior editor and planetary evangelist for the Planetary Society. She’s also one of the most knowledgeable people I know about everything that’s going on in the Solar System. From Curiosity’s exploration of Mars to the search for life in the icy outer reaches of the Solar System, Emily can give you the inside scoop.
In this short interview, Emily describes where she thinks we should be looking for life in the Solar System.
This view of Saturn's moon Enceladus and its prominent plumes was taken by the Cassini spacecraft on April 2, 2013. Credit: NASA/JPL-Caltech/Space Science Institute.
We can never get enough of seeing those intriguing jets and plumes from Saturn’s moon Enceladus, especially this great view from the Cassini spacecraft where the plumes are back-it from the Sun while the moon’s surface is lit with reflected light from Saturn. And as you can see, those jets are still firing. There are close to 100 geyser jets of varying sizes near Enceladus’s south pole spraying water vapor, icy particles, and organic compounds out into space. If you look closely, you’ll see the entire plume is as large as the moon itself.
Can we please send another spacecraft just to study this fascinating moon?
The image was taken in blue light with the Cassini spacecraft narrow-angle camera on April 2, 2013, when Cassini was about 517,000 miles (832,000 kilometers) from Enceladus.
We all know that Saturn’s moon Enceladus has a whole arsenal of geysers jetting a constant spray of ice out into orbit (and if you didn’t know, learn about it here) but Enceladus isn’t the only place in the Saturnian system where jets can be found — there are some miniature versions hiding out in the thin F ring as well!
Watch the 50-mile-wide Prometheus dip into the F ring (CLICK TO PLAY) NASA/JPL/SSI. Animation by J. Major.
The image above, captured by the Cassini spacecraft on June 20, 2013, shows a segment of the thin, ropy F ring that encircles Saturn just beyond the A ring (visible at upper right). The bright barb near the center is what scientists call a mini jet, thought to be caused by small objects getting dragged through the ring material as a result of repeated passings by the shepherd moon Prometheus.
Coincidentally, it’s gravitational perturbations by Prometheus that help form the objects — half-mile-wide snowball-like clusters of icy ring particles — in the first place.
Unlike the dramatic jets on Enceladus, which are powered by tidal stresses that flex the moon’s crust, these mini jets are much more subtle and occur at the casual rate of 4 mph (2 meters/second)… about the speed of a brisk walk.
The reflective jets themselves can be anywhere from 25 to 112 miles (40 to 180 kilometers) long.
See more images of mini jets — also called “classic trails” — below:
Various images of mini jets captured by Cassini from 2005 to 2008.
Dramatic plumes, both large and small, spray water ice out from many locations along the famed "tiger stripes" near the south pole of Saturn's moon Enceladus. Credit: NASA/JPL/SSI.
The geyser jets of Enceladus don’t shoot out in a continuous stream, but are more like an adjustable garden hose nozzle, says Cassini scientist Matt Hedman, author of a new paper about the inner workings of this fascinating tiger-striped moon. Observations from Cassini has found that the bright plume emanating from Enceladus’ south pole varies predictably. The fluctuating factor appears to be how far or close Enceladus is to its home planet, Saturn.
Scientists have hypothesized that the intensity of the jets likely varied over time, but until now had not been able to show they changed in a recognizable pattern. Hedman and colleagues were able to see the changes by examining infrared data of the plume as a whole, obtained by Cassini’s visual and infrared mapping spectrometer (VIMS), and looking at data gathered since 2004 when Cassini entered Saturn’s orbit. In 2005, the jets that form the plumes were discovered.
“The way the jets react so responsively to changing stresses on Enceladus suggests they have their origins in a large body of liquid water,” said Christophe Sotin, a co-author and Cassini team member. “Liquid water was key to the development of life on Earth, so these discoveries whet the appetite to know whether life exists everywhere water is present.”
This set of images from NASA’s Cassini mission shows how the gravitational pull of Saturn affects the amount of spray coming from jets at the active moon Enceladus. Enceladus has the most spray when it is farthest away from Saturn in its orbit (inset image on the left) and the least spray when it is closest to Saturn (inset image on the right). Credit: NASA/JPL-Caltech/University of Arizona/Cornell/SSI.
The scientists say this new finding adds to evidence that a liquid water reservoir or ocean lurks under the icy surface of the moon. This is the first clear observation the bright plume emanating from Enceladus’ south pole varies predictably. The findings were published in a scientific paper in this week’s edition of Nature.
The VIMS instrument, which enables the analysis of a wide range of data including the hydrocarbon composition of the surface of another Saturnian moon, Titan, and the seismological signs of Saturn’s vibrations in its rings, collected more than 200 images of the Enceladus plume from 2005 to 2012.
These data show the plume was dimmest when the moon was at the closest point in its orbit to Saturn. The plume gradually brightened until Enceladus was at the most distant point, where it was three to four times brighter than the dimmest detection. This is comparable to moving from a dim hallway into a brightly lit office.
Adding the brightness data to previous models of how Saturn squeezes Enceladus, the scientists deduced the stronger gravitational squeeze near the planet reduces the opening of the tiger stripes and the amount of material spraying out. They think the relaxing of Saturn’s gravity farther away from planet allows the tiger stripes to be more open and for the spray to escape in larger quantities.
“Cassini’s time at Saturn has shown us how active and kaleidoscopic this planet, its rings and its moons are,” said Linda Spilker, Cassini project scientist at JPL. “We’ve come a long way from the placid-looking Saturn that Galileo first spied through his telescope. We hope to learn more about the forces at work here as a microcosm for how our Solar System formed.”
Enceladus has likely been subject to other gravitational forces over time as well. Previous studies have shown that over hundreds of millions of years, an existing gravitational interaction between Enceladus and another moon, Dione, has caused the orbit of Enceladus to grow increasingly more elongated, or eccentric.
In turn, this produced much more tidal stress in the past and scientists think that contributed to the wide-scale fracturing and friction within Enceladus’ icy crust. The friction leads to melting of internal ice and produces an ocean and eruptions of water and organics on the surface.
Plumes from Enceladus' geysers are illuminated by reflected light from Saturn. Credit: NASA/JPL-Caltech, Space Science Institute.
According to planetary scientist and Cassini imaging team leader Carolyn Porco, about 98 geyser jets of all sizes near Enceladus’s south pole are spraying water vapor, icy particles, and organic compounds out into space. The spray from those geysers are evident in this new image from Cassini, showing a big, beautiful plume, illuminated by light reflected off of Saturn. Look closely to see that the plume is as large as the moon itself.
Cassini first discovered the jets of water ice particles in 2005, and since then scientists have been trying to learn more about how they behave, what they are made of and – most importantly – where they are coming from. The working theory is that Enceladus has a liquid subsurface ocean, and pressure from the rock and ice layers above combined with heat from within force the water up through surface cracks near the moon’s south pole. When this water reaches the surface it instantly freezes, sending plumes of ice particles hundreds of miles into space.
A patchwork network of frozen ridges and troughs cover the face of Enceladus. Credit: NASA/ESA, image processed by amateur astronomer Gordan Ugarkovic.
Cassini has flown through the spray several times now, and instruments have detected 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.
Enceladus is just 504 kilometers (313 miles) across, but it potentially could be one of the best spots in the solar system for finding life.
The top image was taken on January 18, 2013. This view looks toward the Saturn-facing side of Enceladus, and was taken when Cassini was approximately 483,000 miles (777,000 kilometers) from Enceladus. Image scale is 3 miles (5 kilometers) per pixel.
The second, face-on, color view of Enceladus was taken by the Cassini spacecraft on January 31 2011, from a distance of 81,000 km, and processed by amateur astronomer Gordan Ugarkovic.
Saturn's moon Enceladus sprays its salty sea out into space. Those plumes are rich in phosphates. (NASA/JPL/SSI/J. Major)
Thanks to the Cassini mission we’ve known about the jets of icy brine spraying from the south pole of Saturn’s moon Enceladus for about 8 years now, but this week it was revealed at the 44th Lunar and Planetary Science Conference outside Houston, Texas that Enceladus’ jets very likely reach all the way down to the sea — a salty subsurface sea of liquid water that’s thought to lie beneath nearly 10 kilometers of ice.
Enceladus’ jets were first observed by the Cassini spacecraft in 2005. The jets constantly spray fine particles of ice into space which enter orbit around Saturn, creating the hazy, diffuse E ring in which Enceladus resides.
Emanating from deep fissures nicknamed “tiger stripes” that gouge the 512-km (318-mile) -wide moon’s south pole the icy jets — and the stripes — have been repeatedly investigated by Cassini, which has discovered that not only do the ice particles contain salts and organic compounds but also that the stripes are surprisingly warm, measuring at 180 Kelvin (minus 135 degrees Fahrenheit) — over twice as warm as most other regions of the moon.
Where the jets are getting their supply of liquid water has been a question scientists have puzzled over for years. Is friction caused by tidal stresses heating the insides of the stripes, which melts the ice and shoots it upwards? Or do the fissures actually extend all the way down through Enceladus’ crust to a subsurface ocean of liquid water, and through tidal pressure pull vapor and ice up to the surface?
“Baghdad Sulcus,” one of many tiger stripe fissures on Enceladus (NASA/JPL/SSI)
Researchers are now confident that the latter is the case.
In a presentation at the Lunar and Planetary Science Conference titled “How the Jets, Heat and Tidal Stresses across the South Polar Terrain of Enceladus Are Related” (see the PDF here) Cassini scientists note that the amount of heating due to tidal stress seen along Enceladus’ tiger stripes isn’t nearly enough to cause the full spectrum of heating observed, and the “hot spots” that have been seen don’t correlate with the type of heating caused by shear friction.
Instead, the researchers believe that heat energy is being carried upwards along with the pressurized water vapor from the subsurface sea, warming the areas around individual vents as well as serving to keep their channels open.
With 98 individual jets observed so far on Enceladus’ south polar terrain and surface heating corresponding to each one, this scenario, for lack of a better term… seems legit.
What this means is that not only does a moon of Saturn have a considerable subsurface ocean of liquid water with a heat source and Earthlike salinity (and also a bit of fizz) but also that it’s spraying that ocean, that potentially habitable environment, out into local space where it can be studied relatively easily — making Enceladus a very intriguing target for future exploration.
“To touch the jets of Enceladus is to touch the most accessible salty, organic-rich, extraterrestrial body of water and, hence, habitable zone, in our solar system.”
– Cassini imaging team leader Carolyn Porco et al.
Enceladus is actively spraying its habitable zone out into space (NASA/JPL/SSI)
Research notes via C. Porco, D. DiNino, F. Nimmo, CICLOPS, Space Science Institute at Boulder, CO, and Earth and Planetary Sciences at UC Santa Cruz, CA.
Top image: color-composite of Enceladus made from raw Cassini images acquired in 2010. The moon is lit by reflected light from Saturn while the jets are backlit by the Sun.
It’s just one extreme to another in this image from the Cassini spacecraft. Of course, you can’t miss the ginormous Saturn. But do you see three of what appear to be eentsy, tiny moons of the ringed planet?
Tethys (660 miles, or 1,062 kilometers across) is on the right of the image, below the rings. Smaller Enceladus (313 miles, or 504 kilometers across) is on the left of the view, below the rings. Pandora (50 miles, or 81 kilometers across) is also present in this view but is barely visible. It appears as a small grey speck above the rings on the extreme left edge of the image. Pandora has been slightly brightened by the imaging team by a factor 1.2 relative to the rest of the image.
The image was taken with the Cassini spacecraft wide-angle camera on Dec. 7, 2011 using a spectral filter sensitive to wavelengths of near-infrared light centered at 752 nanometers. The view was obtained at a distance of approximately 1.3 million miles (2.1 million kilometers) from Saturn. Image scale is about 77 miles (124 kilometers) per pixel.
Image caption: Saturn and three small moons. Credit: NASA/JPL-Caltech/Space Science Institute
Here’s the May 3, 2012 edition of the Weekly Space Hangout, where we were joined by our usual cast of space journalists, including Alan Boyle, Nicole Gugliucci, Ian O’Neill, Jason Major, Emily Lakdawalla and Fraser Cain. We were then joined by two new people, Amy Shira Teitel from Vintage Space and Sawyer Rosenstein from the Talking Space Podcast.
Want to watch an episode live? We record the Weekly Space Hangout every Thursday at 10:00am PDT, 1:00pm EDT. The live show will appear in Fraser’s Google+ stream, or on our YouTube Channel. You can also watch it live over on Cosmoquest.org.
Enceladus' southern ice geysers are brilliant in backlit sunlight (NASA/JPL/SSI/J. Major)
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The latest images are in from Saturn’s very own personal paparazzi, NASA’s Cassini spacecraft, fresh from its early morning flyby of the ice-spewing moon Enceladus. And, being its last closeup for the next three years, the little moon didn’t disappoint!
The image above is a composite I made from two raw images (this one and this one) assembled to show Enceladus in its crescent-lit entirety with jets in full force. The images were rotated to orient the moon’s southern pole — where the jets originate — toward the bottom.
Cassini was between 72,090 miles (116,000 km) and 90,000 miles (140,000 km) from Enceladus when these images were acquired.
This morning’s E-19 flyby completed a trio of recent close passes by Cassini of the 318-mile (511-km) -wide moon, bringing the spacecraft as low as 46 miles (74 km) above its frozen surface. The goal of the maneuver was to gather data about Enceladus’ internal mass — particularly in the region around its southern pole, where a reservoir of liquid water is thought to reside — and also to look for “hot spots” on its surface that would give more information about its overall energy distribution.
Cassini had previously discovered that Enceladus radiates a surprising amount of heat from its surface, mostly along the “tiger stripe” features — long, deep furrows (sulcae) that gouge its southern hemisphere, they are the source of the water-ice geysers.
Cassini also used the flyby opportunity to study Enceladus’ gravitational field.
By imaging the moon with backlit lighting from the Sun the highly-reflective ice particles in the jets become visible. More direct lighting reduces the jets’ visibility in images, which must be exposed for the natural light of the scene or risk “blowing out” due to Enceladus’ natural high reflectivity.
The images below are raw spacecraft downloads right from the Cassini’s imaging headquarters in Boulder, CO.
Enceladus' geysers in action on May 2, 2012. (NASA/JPL/SSI)Enceladus sprays ice into the hazy E ring, which orbits Saturn (NASA/JPL/SSI)
Cassini also swung closely by Dione during this morning’s flyby but the images from that encounter aren’t available yet. Stay tuned to Universe Today for more postcards from Saturn!
As always, you can follow along with the ongoing Cassini mission on JPL’s dedicated site here, as well as on the Cassini Imaging Central Laboratory for Operations (CICLOPS) site.
Below a darkened Enceladus, a plume of water ice is backlit in this view. Credit: NASA/JPL-Caltech/Space Science Institute
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On May 2, the Cassini spacecraft will be swooping past the moon we all love to love — Enceladus — and coming within 74 kilometers (46 miles) of its fractured, jet-spewing surface. The images should be spectacular, and the science should be just as enticing. With Cassini’s radio science experiment, scientists hope to learn more about how mass is distributed under Enceladus’ south polar region, the very interesting place which features jets of water ice, water vapor and organic compounds spraying out of long fractures.
This is the last close flyby of Enceladus until 2015, so we have to take advantage of the views!
Cassini scientists will be looking specifically for a concentration of mass in that region could indicate subsurface liquid water or an intrusion of warmer-than-average ice that might explain the unusual plume activity. They’ll also be observing the plumes and looking for hot spots to try and understand the global energy balance of Enceladus.
They also hope to learn more about the moon’s internal structure by measuring variations in the gravitational pull of Enceladus against the steady radio link to NASA’s Deep Space Network on Earth.
Additionally, Cassini’s composite infrared spectrometer instrument will be observing the side of Enceladus that always faces away from Saturn to monitor for hot spots. The imaging camera team also plans to take images of the plume to look for variability in the jets.
Cassini will also be flying by Dione at a distance of about 8,000 kilometers (5,000 miles), enabling the imaging cameras to create several mosaic images of the icy moon, and the composite infrared spectrometer to monitor heat emission.
We’ll try to post images and info as they become available!
