We recently interviewed Dr. Kevin Grazier, on of the scientist who has worked extensively on the Cassini mission. Here’s what he had to tell us about that mission’s discoveries.
“My name is Kevin Grazier. I am a planetary scientist, and for my research I do long-term integrations or simulations of early solar system evolution. I’m a former scientist on the Cassini mission and a consultant to several TV series such as Defiance, Falling Skies, the movie Gravity, and formerly, Battlestar Galactica.”
What are Cassini’s most amazing discoveries?
“Cassini has essentially rewritten the book on the Saturn system. I was on the spacecraft team for 15 years. I worked as a science planner and as the Investigation Scientist on the ISS instrument. (That’s Imaging Science Subsystem, not International Space Station.) And of the discoveries we found, I’m trying to think of what I’d call or classify as the most exciting.”
“One was predicted – the fact that it was believed that there could be ice volcanoes on Enceladus. And as a matter of fact, there are volcanoes on Enceladus, or active venting, however you want to look at that. Those vents create the “E” ring, so we have a ring created by material vented off Enceladus. That’s pretty exciting, because we see an active object venting material, and there aren’t a lot of active objects in the solar system.”
This mosaic of Titan was created from the first flyby of the moon by Cassini in 2004. Credit: NASA/JPL/SS
“The surface of Titan is really fantastic. We have open oceans or seas of hydrcarbons on Titan. We have the possibility of an open ocean underneath the crust, just like we believe is under the surface of Europa. We have one image which seems to capture what might be a volcanic eruption. That’s important, because in the outer solar system, planetary science considers ice a rock. What a rock is defined as depends on where you are in the solar system. So in the outer solar system, ice is a rock. All of the moons in the outer solar system except Io have icy crusts. Now, if you have a volcanic eruption on Titan, we have an eruption of magma, and if ice is a rock, that eruption is water. So we have evidence of magma chambers which could be cauldrons of life-giving water.”
“How cool is that? How counter-intuitive is that? How science-fiction-y is that? That one of the most interesting places to look for is a lava chamber or magma chamber that could be suitable for sustaining life. I think that’s really exciting.”
The theory of Lithopanspermia states that life can be shared between planets within a planetary system. Credit: NASA
With the recent discovery that Europa has geysers, and therefore definitive proof of a liquid ocean, there’s a lot of talk about the possibility of life in the outer solar system.
According to a new study, there is a high probably that life spread from Earth to other planets and moons during the period of the late heavy bombardment — an era about 4.1 billion to 3.8 billion years ago — when untold numbers of asteroids and comets pummeled the Earth. Rock fragments from the Earth would have been ejected after a large meteoroid impact, and may have carried the basic ingredients for life to other solar system bodies.
These findings, from Pennsylvania State University, strongly support lithopanspermia: the idea that basic life forms can be distributed throughout the solar system via rock fragments cast forth by meteoroid impacts.
Strong evidence for lithopanspermia is found within the rocks themselves. Of the over 53,000 meteorites found on Earth, 105 have been identified as Martian in origin. In other words an impact on Mars ejected rock fragments that then hit the Earth.
The researchers simulated a large number of rock fragments ejected from the Earth and Mars with random velocities. They then tracked each rock fragment in n-body simulations — models of how objects gravitationally interact with one another over time — in order to determine how the rock fragments move among the planets.
“We ran the simulations for 10 million years after the ejection, and then counted up how many rocks hit each planet,” said doctoral student Rachel Worth, lead author on the study.
Their simulations mainly showed a large number of rock fragments falling into the Sun or exiting the solar system entirely, but a small fraction hit planets. These estimations allowed them to calculate the likelihood that a rock fragment might hit a planet or a moon. They then projected this probability to 3.5 billion years, instead of 10 million years.
In general the number of impacts decreased with the distance away from the planet of origin. Over the course of 3.5 billion years, tens of thousands of rock fragments from the Earth and Mars could have been transferred to Jupiter and several thousand rock fragments could have reached Saturn.
“Fragments from the Earth can reach the moons of Jupiter and Saturn, and thus could potentially carry life there,” Worth told Universe Today.
The researchers looked at Jupiter’s Galilean satellites: Io, Europa, Ganymede and Callisto and Saturn’s largest moons: Titan and Enceladus. Over the course of 3.5 billion years, each of these moons received between one and 10 meteoroid impacts from the Earth and Mars.
It’s statistically possible that life was carried from the Earth or Mars to one of the moons of Jupiter or Saturn. During the period of late bombardment the solar system was much warmer and the now icy moons of Saturn and Jupiter didn’t have those protective shells to prevent meteorites from reaching their liquid interiors. Even if they did have a thin layer of ice, there’s a large chance that a meteorite would fall though, depositing life in the ocean beneath.
In the case of Europa, six rock fragments from the Earth would have hit it over the last 3.5 billion years.
It has previously been thought that finding life in Europa’s oceans would be proof of an independent origin of life. “But our results suggest we can’t assume that,” Worth said. “We would need to test any life found and try to figure out whether it descended from Earth life, or is something really new.”
The paper has been accepted for publication in the journal Astrobiology and is available for download here.
UV observations from Hubble show the size of water vapor plumes coming from Europa's south pole (NASA, ESA, and M. Kornmesser)
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.
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.
“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)
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
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.
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)
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.
Researchers work in the Antarctic polar night during a storm (Credit: Stefan Hendricks, Alfred Wegner Institute)
Some day, human explorers will land a spacecraft on the surface of Europa, Enceladus, Titan, or some other icy world and investigate first-hand the secrets hidden beneath its frozen surface. When that day comes — and it can’t come too soon for me! — it may look a lot like this.
One of a series of amazing photos by Stefan Hendricks taken during the Antarctic Winter Ecosystem & Climate Study (AWECS), a study of Antarctica’s sea ice conducted by the Alfred Wegener Institute in Germany, the image above shows researchers working on the Antarctic ice during a winter snowstorm. It’s easy to imagine them on the night-side surface of Europa, with the research vessel Polarstern standing in for a distant illuminated lander (albeit rather oversized).
Hey, one can dream!
One of the goals of the campaign, called CryoVex, was to look at how ESA’s CryoSat mission can be used to understand the thickness of sea ice in Antarctica. The extent of the Antarctic sea ice in winter is currently more than normal, which could be linked to changing atmospheric patterns.
Antarctica’s massive shelves of sea ice in winter are quite dramatic landscapes, and remind us that there are very alien places right here on our own planet.
See this and more photos from the mission on the ESA website (really, go check them out!)
Jupiter with polka dot shadows cast by Io, Europa and Callisto as depicted around 1 a.m. EDT Oct. 12. Watch for the Great Red Spot to come into view during the transit. Created with Claude Duplessis' Meridian software
Talk about a great fall lineup. Three of Jupiter’s four brightest moons plan a rare show for telescopic observers on Friday night – Saturday morning Oct. 11-12. For a span of just over an hour, Io, Europa and Callisto will simultaneously cast shadows on the planet’s cloud tops, an event that hasn’t happened since March 28, 2004.
Who doesn’t remember their first time looking at Jupiter and his entourage of dancing moons in a telescope? Because each moves at a different rate depending on its distance from the planet, they’re constantly on the move like kids in a game of musical chairs. Every night offers a different arrangement.
Jupiter and its four brightest moons seen in a small telescope. Credit: Bob King
Some nights all four of the brightest are strung out on one side of the planet, other nights only two or three are visible, the others hidden behind Jupiter’s “plus-sized” globe. Occasionally you’ll be lucky enough to catch the shadow of one of moons as it transits or crosses in front of the planet. We call the event a shadow transit, but to someone watching from Jupiter, the moon glides in front of the sun to create a total solar eclipse.
Since the sun is only 1/5 as large from Jupiter as seen from Earth, all four moons are large enough to completely cover the sun and cast inky shadows. To the eye they look like tiny black dots of varying sizes. Europa, the smallest, mimics a pinprick. The shadows of Io and Callisto are more substantial. Ganymede, the solar system’s largest moon at 3,269 miles (5,262 km), looks positively plump compared to the others. Even a small telescope magnifying around 50x will show it.
Jupiter on Sept. 24 with its moon Europa (at left) casting a pinhead black shadow on Jupiter’s clouds. Credit: John Chumack
The three inner satellites – Io, Europa and Ganymede – have shadow transits every orbit. Distant Callisto only transits when Jupiter’s tilt relative to Earth is very small, i.e. the plane of the planet’s moons is nearly edge-on from our perspective. Callisto transits occur in alternating “seasons” lasting about 3 years apiece. Three years of shadow play are followed by three years of shadowless misses. Single transits are fairly common; you can find tables of them online like this one from Project Pluto or plug in time and date into a free program like Meridian for a picture and list of times.
Because Io, Europa and Ganymede orbit in a 4:2:1 resonance (Io revolves four times around Jupiter in the time it takes Ganymede to orbit once; Europa completes two orbits for Ganymede’s one) it’s impossible for all three to line up – along with Callsto – for a “quadruple transit”. Credit: Matma Rex / Wikipedia
Seeing two shadows inch across Jupiter’s face is very uncommon, and three are as rare as a good hair day for Donald Trump. Averaged out, triple transits occur once or twice a decade. Friday night Oct. 11 each moon enters like actors in a play. Callisto appears first at 11:12 p.m. EDT followed by Europa and then Io. By 12:32 a.m. all three are in place.
Catch them while you can. Groups like these don’t last long. A little more than an hour later Callisto departs, leaving just two shadows. You’ll find the details below. All times are Eastern Daylight or EDT. Subtract one hour for Central time and add four hours for BST (British Summer Time):
* Callisto’s shadow enters the disk – 11:12 p.m. Oct. 11
* Europa – 11:24 p.m.
* Io – 12:32 a.m. ** TRIPLE TRANSIT from 12:32 – 1:37 a.m.
* Callisto departs – 1:37 a.m.
* Europa departs – 2:01 a.m.
* Io departs – 2:44 a.m.
Looking at Jupiter from high above the plane of the solar system in this diagram from more than a century ago, we can better picture how shadow transits and eclipses happen. The tiny disk of Io and the shadow of Ganymede are seen in transit; Callisto is about to be eclipsed by Jupiter’s shadow. Credit: Garrett Serviss from “Pleasures of the Telescope” (annotations: Bob King)
The triple transit will be seen across the eastern half of the U.S., Europe and western Africa. Those living on the East Coast have the best view in the U.S. with Jupiter some 20-25 degrees high in the northeastern sky around 1 a.m. local time. Things get dicier in the Midwest where Jupiter climbs to only 5-10 degrees. From the mountain states the planet won’t rise until Callisto’s shadow has left the disk, leaving a two-shadow consolation prize. If you live in the Pacific time zone and points farther west, you’ll unfortunately miss the event altogether.
From the Eastern Time Zone Jupiter will be well-placed in the eastern sky during the transit. Created with Stellarium
Key to seeing all three shadows clearly, especially if Jupiter is low in the sky, is steady air or what skywatchers call “good seeing”. The sky can be so clear you’d swear there’s a million stars up there, but a look through the telescope will sometimes show dancing, blurry images due to invisible air turbulence. That’s “bad seeing”. Unfortunately, bad seeing is more common near the horizon where we peer through a greater thickness of atmosphere. But don’t let that keep you inside Friday night. With a spell of steady air, all you need is a 4-inch or larger telescope magnifying around 100x to spot all three.
The March 28, 2004 triple transit. Shadows from left: Ganymede, Io and Callisto. You can also see the disks of Io (white dot) and Ganymede (blue dot) in this photo taken in infrared light by the Hubble Space Telescope. Credit: NASA/ESA
If bad weather blocks the view, there are two more triple transits coming up soon – a 95-minute-long event on June 3, 2014 starring Europa, Ganymede and Callisto (not visible in the Americas) and a 25-minute show on Jan. 24, 2015 featuring Io, Europa and Callisto and visible across Western Europe and the Americas. That’s it until dual triple transits in 2032.
Reprocessed Galileo image of Europa's frozen surface by Ted Stryk (NASA/JPL/Ted Stryk)
According to research by NASA astronomers using the next-generation optics of the 10-meter Keck II telescope, Jupiter’s ice-encrusted moon Europa has hydrogen peroxide across much of the surface of its leading hemisphere, a compound that could potentially provide energy for life if it has found its way into the moon’s subsurface ocean.
“Europa has the liquid water and elements, and we think that compounds like peroxide might be an important part of the energy requirement,” said JPL scientist Kevin Hand, the paper’s lead author. “The availability of oxidants like peroxide on Earth was a critical part of the rise of complex, multicellular life.”
The paper, co-authored by Mike Brown of the California Institute of Technology in Pasadena, analyzed data in the near-infrared range of light from Europa using the Keck II Telescope on Mauna Kea, Hawaii, over four nights in September 2011. The highest concentration of peroxide found was on the side of Europa that always leads in its orbit around Jupiter, with a peroxide abundance of 0.12 percent relative to water. (For perspective, this is roughly 20 times more diluted than the hydrogen peroxide mixture available at drug stores.) The concentration of peroxide in Europa’s ice then drops off to nearly zero on the hemisphere of Europa that faces backward in its orbit.
Hydrogen peroxide was first detected on Europa by NASA’s Galileo mission, which explored the Jupiter system from 1995 to 2003, but Galileo observations were of a limited region. The new Keck data show that peroxide is widespread across much of the surface of Europa, and the highest concentrations are reached in regions where Europa’s ice is nearly pure water with very little sulfur contamination.
This color composite view combines violet, green, and infrared images of Europa acquired by Galileo in 1997 for a view of the moon in natural color (left) and in enhanced color (right). Credit: NASA/JPL/University of Arizona
The peroxide is created by the intense radiation processing of Europa’s surface ice that comes from the moon’s location within Jupiter’s strong magnetic field.
“The Galileo measurements gave us tantalizing hints of what might be happening all over the surface of Europa, and we’ve now been able to quantify that with our Keck telescope observations,” Brown said. “What we still don’t know is how the surface and the ocean mix, which would provide a mechanism for any life to use the peroxide.”
The scientists think hydrogen peroxide is an important factor for the habitability of the global liquid water ocean under Europa’s icy crust because hydrogen peroxide decays to oxygen when mixed into liquid water. “At Europa, abundant compounds like peroxide could help to satisfy the chemical energy requirement needed for life within the ocean, if the peroxide is mixed into the ocean,” said Hand.
What’s notable to add, on March 26, 2013, the U.S. President signed a bill that would increase the budget for NASA’s planetary science program as well as provide $75 million for the exploration of Europa. Exactly how the funds will be used isn’t clear — perhaps for components on the proposed Europa Clipper mission? — but it’s a step in the right direction for learning more about this increasingly intriguing world. Read more on SETI’s Destination: Europa blog.
Astronomers hypothesize that chloride salts bubble up from the icy moon's global liquid ocean and reach the frozen surface where they are bombarded with sulfur from volcanoes on Jupiter's largest moon, Io. This illustration of Europa (foreground), Jupiter (right) and Io (middle) is an artist's concept. Credit: Keck Observatory.
Astronomer Mike Brown and his colleague Kevin Hand might be suffering from “Pump Handle Phobia,” as radio personality Garrison Keillor calls it, where those afflicted just can’t resist putting their tongues on something frozen to see if it will stick. But Brown and Hand are doing it all in the name of science, and they may have found the best evidence yet that Europa has a liquid water ocean beneath its icy surface. Better yet, that vast subsurface ocean may actually shoot up to Europa’s surface, on occasion.
In a recent blog post, Brown pondered what it would taste like if he could lick the icy surface of Jupiter’s moon Europa. “The answer may be that it would taste a lot like that last mouthful of water that you accidentally drank when you were swimming at the beach on your last vacation. Just don’t take too long of a taste. At nearly 300 degrees (F) below zero your tongue will stick fast.”
His ponderings were based on a new paper by Brown and Hand which combined data from the Galileo mission (1989 to 2003) to study Jupiter and its moons, along with new spectroscopy data from the 10-meter Keck II telescope in Hawaii.
The study suggests there is a chemical exchange between the ocean and surface, making the ocean a richer chemical environment.
“We now have evidence that Europa’s ocean is not isolated—that the ocean and the surface talk to each other and exchange chemicals,” said Brown, who is an astronomer and professor of planetary astronomy at Caltech. “That means that energy might be going into the ocean, which is important in terms of the possibilities for life there. It also means that if you’d like to know what’s in the ocean, you can just go to the surface and scrape some off.”
“The surface ice is providing us a window into that potentially habitable ocean below,” said Hand, deputy chief scientist for solar system exploration at JPL.
Europa’s ocean is thought to cover the moon’s whole globe and is about 100 kilometers (60 miles) thick under a thin ice shell. Since the days of NASA’s Voyager and Galileo missions, scientists have debated the composition of Europa’s surface.
Salts were detected in the Galileo data – “Not ‘salt’ as in the sodium chloride of your table salt,” Brown wrote in his blog, “Mike Brown’s Planets,” “but more generically ‘salts’ as in ‘things that dissolve in water and stick around when the water evaporates.’”
That idea was enticing, Brown said, because if the surface is covered by things that dissolve in water, that strongly implies that Europa’s ocean water has flowed on the surface, evaporated, and left behind salts.
But there were other explanations for the Galileo data, as Europa is constantly bombarded by sulfur from the volcanoes on Io, and the spectrograph that was on the Galileo spacecraft wasn’t able to tell the difference between salts and sulfuric acid.
But now, with data from the Keck Observatory, Brown and Hand have identified a spectroscopic feature on Europa’s surface that indicates the presence of a magnesium sulfate salt, a mineral called epsomite, that could have formed by oxidation of a mineral likely originating from the ocean below. This view of Jupiter’s moon Europa features several regional-resolution mosaics overlaid on a lower resolution global view for context. The regional views were obtained during several different flybys of the moon by NASA’s Galileo mission. Image credit: NASA/JPL-Caltech/University of Arizona.
Brown and Hand started by mapping the distribution of pure water ice versus anything else. The spectra showed that even Europa’s leading hemisphere contains significant amounts of non-water ice. Then, at low latitudes on the trailing hemisphere — the area with the greatest concentration of the non-water ice material — they found a tiny, never-before-detected dip in the spectrum.
The two researchers tested everything from sodium chloride to Drano in Hand’s lab at JPL, where he tries to simulate the environments found on various icy worlds. At the end of the day, the signature of magnesium sulfate persisted.
The magnesium sulfate appears to be generated by the irradiation of sulfur ejected from the Jovian moon Io and, the authors deduce, magnesium chloride salt originating from Europa’s ocean. Chlorides such as sodium and potassium chlorides, which are expected to be on the Europa surface, are in general not detectable because they have no clear infrared spectral features. But magnesium sulfate is detectable. The authors believe the composition of Europa’s ocean may closely resemble the salty ocean of Earth.
While no one is going to be traveling to Europa to lick its surface, for now, astronomers will continue to use the modern giant telescopes on Earth to continue to “take spectral fingerprints of increasing detail to finally understand the mysterious details of the salty ocean beneath the ice shell of Europa,” Brown said.
Also, NASA is looking into options to explore Europa further. (Universe Today likes the idea of a big drill or submarine!)
But in the meantime what happens next? “We look for chlorine, I think,” Brown wrote. “The existence of chlorine as one of the main components of the non-water-ice surface of Europa is the strongest prediction that this hypothesis makes. We have some ideas on how we might look; we’re working on them now. Stay tuned.”
