Illustration of Jupiter and the Galilean satellites. Credit: NASA
It’s no accident that Jupiter shares its name with the king of the gods. In addition to being the largest planet in our Solar System – with two and a half times the mass of all the other planets combined – it is also home to some of the largest moons of any Solar planet. Jupiter’s largest moons are known as the Galileans, all of which were discovered by Galileo Galilei and named in his honor.
They include Io, Europa, Ganymede, and Callisto, and are the Solar System’s fourth, sixth, first and third largest satellites, respectively. Together, they contain almost 99.999% of the total mass in orbit around Jupiter, and range from being 400,000 and 2,000,000 km from the planet. Outside of the Sun and eight planets, they are also among the most massive objects in the Solar System, with radii larger than any of the dwarf planets.
We call it the Moon, but… what’s its real name? You know, the name that scientists call the Moon.
As of 2015, there are 146 official moons in the Solar System, and then another 27 provisional moons, who are still waiting on the status of their application. All official moons have names after gods or Shakespeare characters. Names like Callisto, Titan, or Prometheus. But there’s one moon in the Solar System with a super boring name… the one you’re most familiar with: Moon.
But come on, that’s such a boring name. Clearly that’s just its common name. So what’s the Moon’s real name? Its scientific name. The neato cool name. Like Krelon, Krona, Avron or Mua’Dib.
Are you ready for this? The answer is: The Moon. Here’s some hand-waving and excuse making. Really, this is our own damn fault. Until Galileo first turned his telescope to the skies in 1610, and realized that Jupiter had tiny spots of light orbiting around it, astronomers had no idea other planets had moons.
Humans have been around for a few hundred thousand years, and the Moon was a familiar object in the sky. We’ve only had evidence of other moons for a little over 400 years. We didn’t collectively understand the Earth was a planet until Copernicus developed the heliocentric model of the Solar System.
We still have a little trouble with that, even though we’re firing a probe directly at the Sun. We didn’t give into the idea that the Sun was a star until recently. Giordano Bruno proposed the idea in 1590 and we burned him at the stake for suggesting it. Seriously, I can’t stare at this any longer. Yes, we’re awful. I’m going to talk about “the Moon” again.
Scientists classify the Moon as a natural satellite. Somehow this helps distinguish it from the artificial satellites we’ve been launching for the last 60 years.
High resolution photo map of the moon’s far side imaged by NASA’s Lunar Reconnaissance Orbiter. Credit: NASA
What about terms like “Luna”? That’s Latin for Moon. It’s not an official title or scientific term, but ooh, fancy. Latin.
If you want to make sure people know you’re talking about “The Moon” and not “a moon”, it’s all about capitalization. Put a capital “M” in front of “oon” and you’re good to go.
The name of our solar system? It’s the Solar System (again, capitalized). Our galaxy? The Galaxy with a capital G. The universe? Capital U Universe.
What about the Sun? Isn’t it “sol”? That’s just the Latin word for “sun”. Helios? Greek God version of the Sun.
If we ever discover that we’re really living in a multiverse, we’ll need to give those other universes names. And people will wonder what the actual official title is for the Universe. I’ll make another video when that happens, I promise.
The official advice from the International Astronomical Union, who are the people you’re still mad at about Pluto, is that the capitalization is what makes the definition.
Supermoon through the clouds on September 9, 2014. Credit and copyright: scul-001 on Flickr.
Not everyone in the world adheres to the capitalization so carefully, which can tend to some confusion. Are we talking about the sun or the Sun? As someone who writes space articles, let me assure you, messing this up will light up the comments section with “Which is better Deep Space 9 vs. Voyager” level of shrill all caps screaming.
Calling it “the Moon” is kind of boring, but that’s only because scientific discovery has pushed our understanding of the Universe so far out. It’s amazing to think that we’ve discovered so many other moons in the Solar System, and soon, we’ll find them around other stars.
So, for now it’s The Universe. When we find others, this one will still be THE Capital-U Universe and the new ones will be Nimoy and Sagan and Clarke.
Why don’t we give the Moon a new name. Something with a little more razzle-dazzle. Make your suggestions in the comments below. Alternately, suggest a fancy Latin name of “Guide to Space”, I’ve got dibs on “Aether Libris”.
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The fifth and sixth Galileo navigation satellites launch Aug. 22, 2014 from French Guiana. Credit: European Space Agency
An independent investigation committee is looking at why two European navigation satellites are in the wrong orbits following their launch from French Guiana last week.
While the first part of the launch went well, officials said telemetry from the satellites showed that the satellites were not where they were supposed to be. The probe is ongoing, but officials believe it is related to a stage of the Soyuz rocket that hefted the satellites into space.
“According to the initial analyses, an anomaly is thought to have occurred during the flight phase involving the Fregat upper stage, causing the satellites to be injected into a noncompliant orbit,” wrote launch provider Arianespace in an update on Saturday (Aug. 23).
Artist’s conception of the completed Galileo navigation satellite system. Credit: ESA-P. Carril
The same day, the European Space Agency added that officials are looking into how the mission would be affected, if at all.
The Galileo satellites, the fifth and sixth of the constellation, are intended to serve as part of a cloud of navigation satellites that would be a European alternative to the United States GPS system. Officials are hoping to launch six to eight more satellites per year until 2017, when 24 satellites and six backups will be ready for full service.
The satellites were supposed to be in a circular orbit, inclined at 55 degrees to the Earth’s equator and have a maximum orbital radius (semi-major axis) of 29,900 km (18,579 miles). Telemetry now shows the satellites are in a non-circular orbit inclined at 49.8 degrees, with a semi-major axis of 26,200 km (16,280 miles).
Jupiter is like a jawbreaker. Dig down beneath the swirling clouds and you’ll pass through layer after layer of exotic forms of hydrogen. What’s down there, deep within Jupiter?
What’s inside Jupiter? Is it chameleons? Candy? Cake? Cheddar? Chemtrails? No one knows. No one can ever know.
Well, that’s not entirely true… or even remotely true. Jupiter is the largest planet in the Solar System and two and a half times the mass of the other planets combined. It’s a gas giant, like Saturn, Uranus, and Neptune. It’s almost 90% hydrogen and 10% helium, and then other trace materials, like methane, ammonia, water and some other stuff. What would be a gas on Earth behaves in very strange ways under Jupiter’s massive pressure and temperatures.
So what’s deep down inside Jupiter? What are the various layers and levels, and can I keep thinking of it like a jawbreaker? At the very center of Jupiter is its dense core. Astronomers aren’t sure if there’s a rocky region deep down inside. It’s actually possible that there’s twelve to forty five Earth masses of rocky material within the planet’s core. Now this could be rock, or hydrogen and helium under such enormous forces that it just acts that way. But you couldn’t stand on it. The temperatures are 35,000 degrees C. The pressures are incomprehensible.
Surrounding the core is a vast region made up of hydrogen. But it’s not a gas. The pressure and temperature transforms the hydrogen into an exotic form of liquid metallic hydrogen, similar to the liquid mercury you’d see in a thermometer. This metallic hydrogen region turns inside the planet, and acts like an electric dynamo. Similar to our planet’s own iron core, this gives the planet a powerful magnetic field.
The next level up is still liquid hydrogen, but the pressure’s lower, so it’s not metallic any more. And then above this is the planet’s atmosphere. The upper layers of Jupiter’s atmosphere is the only part we can see. Those bands on the planet are clouds of ammonia that rotate around the planet in alternating directions. The lighter color zones are colder ammonia ice upwelling from below. Here’s the exciting part. Astronomers aren’t sure what the darker regions are.
This animated gif shows Voyager 1’s approach to Jupiter during a period of over 60 Jupiter days in 1979. Credit: NASA.
Still think you want to descend into Jupiter, to try and walk on its rocky interior? NASA tried that. In order to protect Jupiter’s moons from contamination, NASA decided to crash the Galileo spacecraft into the planet at the end of its mission. It only got point two percent of the way down through Jupiter’s radius before it was completely destroyed.
Jupiter is a remarkably different world from our own. With all that gravity, normally lightweight hydrogen behaves in completely exotic ways. Hopefully in the future we’ll learn more about this amazing planet we share our Solar System with.
What do you think? Is there a rocky core deep down inside Jupiter?
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Europa's icy, cracked surface imaged by NASA's Galileo spacecraft Credit: NASA/JPL-Caltech/SETI Institute
Eureka – it’s Europa! And a brand-new image of it, too! (Well, kinda sorta.)
The picture above, showing the icy moon’s creased and cracked surface, was made from images acquired by NASA’s Galileo spacecraft during its exploration of Jupiter and its family of moons in 1997 and 1998. While the data itself isn’t new per se the view seen here has never been released by JPL, and so it’s new to you! (And to me too.)
Europa’s bizarre surface features suggest an actively churning ice shell above a salty liquid water ocean. Credit: JPL
The original high-resolution images were acquired on Nov. 6, 1997, in greyscale and colorized with data acquired during a later pass by Galileo in 1998. The whiter areas are regions of relatively pure water ice, while the rusty red bands are where ice has mixed with salts and organic compounds that have oozed up from deeper within Europa.
The entire image area measures about 101 by 103 miles across (163 km x 167 km).
Europa has long been one of the few places we know of outside our own planet where life could very well have evolved and potentially still exist. Getting a peek below the icy moon’s frozen crust — or even a taste of the recently-discovered water vapor spraying from its south pole — is all we’d need to further narrow down the chances that somewhere, something could be thriving in Europa’s subsurface seas. Get a planetary scientist’s perspective in a video interview with Dr. Mike Brown here.
Launched in October 1989, the Galileo spacecraft arrived at Jupiter in December 1995. Through primary and extended missions Galileo explored the giant planet and its family of moons until plunging into Jupiter’s atmosphere on September 21, 2003. Learn more about Galileo here, and check out some of the amazing images it acquired on the CICLOPS imaging diary page here.
NASA’s Galileo spacecraft arrived at Jupiter on December 7, 1995, and proceeded to study the giant planet for almost 8 years. It sent back a tremendous amount of scientific information that revolutionized our understanding of the Jovian system. By the end of its mission, Galileo was worn down. Instruments were failing and scientists were worried they wouldn’t be able to communicate with the spacecraft in the future. If they lost contact, Galileo would continue to orbit the Jupiter and potentially crash into one of its icy moons.
Galileo would certainly have Earth bacteria on board, which might contaminate the pristine environments of the Jovian moons, and so NASA decided it would be best to crash Galileo into Jupiter, removing the risk entirely. Although everyone in the scientific community were certain this was the safe and wise thing to do, there were a small group of people concerned that crashing Galileo into Jupiter, with its Plutonium thermal reactor, might cause a cascade reaction that would ignite Jupiter into a second star in the Solar System.
Hydrogen bombs are ignited by detonating plutonium, and Jupiter’s got a lot of hydrogen.Since we don’t have a second star, you’ll be glad to know this didn’t happen. Could it have happened? Could it ever happen? The answer, of course, is a series of nos. No, it couldn’t have happened. There’s no way it could ever happen… or is there?
Jupiter is mostly made of hydrogen, in order to turn it into a giant fireball you’d need oxygen to burn it. Water tells us what the recipe is. There are two atoms of hydrogen to one atom of oxygen. If you can get the two elements together in those quantities, you get water.
In other words, if you could surround Jupiter with half again more Jupiter’s worth of oxygen, you’d get a Jupiter plus a half sized fireball. It would turn into water and release energy. But that much oxygen isn’t handy, and even though it’s a giant ball of fire, that’s still not a star anyway. In fact, stars aren’t “burning” at all, at least, not in the combustion sense.
Jupiter as imaged by Michael Phillips on July 25th, 2009.
Our Sun produces its energy through fusion. The vast gravity compresses hydrogen down to the point that high pressure and temperatures cram hydrogen atoms into helium. This is a fusion reaction. It generates excess energy, and so the Sun is bright. And the only way you can get a reaction like this is when you bring together a massive amount of hydrogen. In fact… you’d need a star’s worth of hydrogen. Jupiter is a thousand times less massive than the Sun. One thousand times less massive. In other words, if you crashed 1000 Jupiters together, then we’d have a second actual Sun in our Solar System.
But the Sun isn’t the smallest possible star you can have. In fact, if you have about 7.5% the mass of the Sun’s worth of hydrogen collected together, you’ll get a red dwarf star. So the smallest red dwarf star is still about 80 times the mass of Jupiter. You know the drill, find 79 more Jupiters, crash them into Jupiter, and we’d have a second star in the Solar System.
There’s another object that’s less massive than a red dwarf, but it’s still sort of star like: a brown dwarf. This is an object which isn’t massive enough to ignite in true fusion, but it’s still massive enough that deuterium, a variant of hydrogen, will fuse. You can get a brown dwarf with only 13 times the mass of Jupiter. Now that’s not so hard, right? Find 13 more Jupiters, crash them into the planet?
As was demonstrated with Galileo, igniting Jupiter or its hydrogen is not a simple matter.
We won’t get a second star unless there’s a series of catastrophic collisions in the Solar System.
And if that happens… we’ll have other problems on our hands.
An artist's conception of the European Space Agency's ExoMars rover, scheduled to launch in 2018. Credit: ESA
When you have a Mars mission that is designed to search for life or life-friendly environments, it would be several shades of awkward if something biological was discovered — and it ended up being an Earth microbe that clung on for the ride. Beyond that, there’s the worry that an Earth microbe could contaminate the planet’s environment, altering or perhaps wiping out anything that was living there.
A recent European Space Agency post highlighted that agency’s efforts to keep Mars safe from its forthcoming ExoMars missions in 2016 or 2018. (And it also should be noted that NASA has its own planetary protection protocols, as well as other agencies.)
“We have a long-term programme at ESA – and also NASA – to regularly monitor and evaluate biological contamination in cleanrooms and on certain type of spacecraft,” stated Gerhard Kminek, ESA’s planetary protection officer. “The aim,” he added, “is to quantify the amount of biological contamination, to determine its diversity – finding out what is there using gene sequence analysis, and to provide long-term cold storage of selected samples.”
The process isn’t perfect, ESA admits, but the biological contamination that these scrutinized missions have is extraordinarily low compared to other Earthly manufacturing processes. There is, in fact, an obligation on the part of space-faring nations to keep planets safe if they signed on to the United Nations Outer Space Treaty. (That said, enforcement is a tricky legal issue as there is no international court for this sort of thing and that would make it hard to levy penalties.)
The NASA Curiosity rover in this undated photo inside the Jet Propulsion Laboratory’s spacecraft assembly facility. The team did around 4,500 samplings during assembly for contamination. Credit: NASA
Spacefaring nations have international standards for biological contamination limits, and they also must monitor the “impact probability” of an orbital spacecraft smacking into the planet or moon below when they do maneuvers. Sometimes this means that spacecraft are deliberately crashed in one spot to prevent contamination elsewhere. A famous example is the Galileo mission to Jupiter, which was thrown into the giant planet in 2003 so it wouldn’t accidentally hit the ice-covered Europa moon.
Moving forward to ExoMars — the Mars orbiting and landing missions of 2016 and 2018 — ESA plans to perform about 4,500 samplings of each spacecraft to monitor biological contamination. This estimate came from the number performed at NASA on the Curiosity rover, which is trundling around Mars right now. Changes in processing, though, mean the ESA checks will take less time (presumably making it less expensive.)
For the curious, yes, planetary protection protocols would also apply during a “sample return” mission where soil or other samples are sent back to Earth. While that’s a little ways off, ESA also elaborated on the procedures it takes to keep spacecraft it creates safe from contamination.
A technician does a check for contamination on the ExoMars 2016 descent camera in December 2013. The test took place at the European Space Agency’s European Space Research and Technology Centre in the Netherlands. Credit: ESA
“Samples are acquired in various ways: air samplers collect a certain amount of air on a filter, while wipes dampened with ultra-pure water are run across space hardware or cleanroom surfaces. Swabs are used to sample smaller items such as payloads or electronics,” ESA stated.
“To quantify the biological contamination, the samples are then filtered onto culture plates and incubated for between seven hours and three days depending on the specific method used, to see how much turns up. Statistical analysis is used to assess the overall cleanroom or flight hardware ‘bioburden’, and check whether it falls within the required standard or if further measures are needed to reduce it.”
Sometimes a hardy survivor is found, which is scientifically interesting because investigators want to know how it made it. ESA has a database of these microbes, and NASA has records as well. In November, the agencies announced a new bacterium, Tersicoccus phoenicis, that so far has only been found in “cleanrooms” for NASA’s Mars Phoenix lander (near Orlando, Florida) and ESA’s Herschel and Planck observatories (in Kourou, French Guiana).
Dr. Kevin Grazier was a planetary scientist with the Cassini mission for over 15 years, studying Saturn and its icy rings. He was also the science advisor for Battlestar Galactica, Eureka and the movie Gravity.
Mike Brown is a professor of planetary astronomy at Caltech. He’s best known as the man who killed Pluto, thanks to his team’s discovery of Eris and other Kuiper Belt Objects.
We recently asked them about many things – here’s what they shared with us about the rings of Saturn.
Saturn’s majestic, iconic rings define the planet, but where did they come from?
Kevin Grazier: “Saturn’s rings, good question. And the answer is different depending on which ring we’re discussing.”
That’s Dr. Kevin Grazier, a planetary scientist who worked on NASA’s Cassini mission or over 15 years, studying Saturn’s rings extensively.
Mike Brown: “Saturn’s rings – the strange things about Saturn’s rings is that they shouldn’t be there, really, in the sense that they don’t last for very long. So, if they are just left over from when Saturn was formed, they’d be gone by now. They would slowly work their way into Saturn and burn up and be gone. And yet they’re there. So they are either relatively new or somehow continuously regenerated. ‘Continuously regenerated’ seems strange and ‘relatively new’ seems also kind of strange. Something broke up – a large moon broke up, or a comet broke up – something had to have happened relatively recently. And by relatively recently, that means hundreds of millions of years ago for someone like me.”
And that’s Mike Brown, professor of planetary geology at Caltech, who studies many of the icy objects in the Solar System.
Saturn and its rings, as seen from above the planet by the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute. Assembled by Gordan Ugarkovic.
Saturn’s rings start just 7,000 km above the surface of the planet, and extend out to an altitude of 80,000 km. But they’re gossamer thin, just 10 km across at some points.
We’ve known about Saturn’s rings since 1610, when Galileo was the first person to turn a telescope on them. The resolution was primitive, and he thought he saw “handles” attached to Saturn, or perhaps what were big moons on either side.
In 1659, using a better telescope, the Dutch astronomer Christiaan Huygens figured out that these “handles” were actually rings. And finally in the 1670s, the Italian astronomer Giovanni Cassini was able to resolve the rings in more detail, even observed the biggest gap in the rings.
The Cassini mission, named after Giovanni, has been with Saturn for almost a decade, allowing us to view the rings in incredible detail. Determining the origin and evolution of Saturn’s rings has been one of its objectives.
Saturn’s rings. Credit: NASA/JPL/Space Science Institute.
So far, the argument continues:
Kevin Grazier: “There’s an age-old debate about whether the rings are old or new. And that goes back and forth – it’s been going back and forth for ages and it still goes back and forth. Are they old, or have they been there a long period of time? Are they new? I don’t know what to think, to be quite honest. I’m not being wishy-washy, I just don’t know what to think anymore.”
Evidence from NASA’s Voyager spacecraft indicated that the material in Saturn’s rings was young. Perhaps a comet shattered one of Saturn’s moons within the last few hundred million years, creating the rings we see today. If that was the case case, what incredible luck that we’re here to see the rings in their current form.
But when Cassini arrived, it showed evidence that Saturn’s rings are being refreshed, which could explain why they appear so young. Perhaps they are ancient after all.
Kevin Grazier: “If Saturn’s rings are old, a moon could have gotten too close to Saturn and been pulled apart by tidal stresses. There could have been a collision of moons. It could have been a pass by a nearby object, since in the early days of planetary formation, there were many objects zooming past Saturn. Saturn probably had a halo of material in it’s early days that was loosely bound to the moon.”
Enceladus, backdropped by Saturn’s rings. Credit: NASA/JPL/ Space Science Institute.
There is one ring that we know for certain is being refreshed…
Kevin Grazier: “The E-Ring, certainly a new ring, because the E-Ring consists of roughly micron-sized ice particles. And micron-sized ice particles don’t last in space. They sputter and sublimate – they go away in very short time periods, and we knew that. And so when we went to Saturn with Cassini, we knew to look for a source of materiel because we knew that the individual components of the E-Ring don’t last, so it has to be replenished. So the E-Ring stands alone from the established system, and the E-Ring is absolutely new.”
In 2005, scientist discovered that Saturn’s E-Ring is being constantly replenished by the moon Enceladus. Cryovolcanoes spew water ice into space from a series of fissures at its south pole.
So where did Saturn’s rings come from? We don’t know. Are the new or old? We don’t know. It just another great mystery of the Solar System.
Jupiter's moon, Europa, appears to have clay-like minerals on it (visible in blue in the false-color patch, amid red-colored water ice). The information came from new data analysis from NASA's Galileo mission, which concluded in 2003. The backdrop is a mosaic of visual-light images from Galileo's Near-Infrared Mapping Spectrometer. Credit: NASA/JPL-Caltech/SETI
The cool thing about space missions is long after they conclude, the data can yield the most interesting information. Here’s an example: Jupiter’s moon Europa may have a ripe spot for organic materials to take root.
Scouring the data from NASA’s past Galileo mission — which ended a decade ago — scientists unveiled an area with “clay-like minerals” on it that came to be after an asteroid or comet smashed into the surface. The connection? These celestial party-crashers often carry organics with them.
“Organic materials, which are important building blocks for life, are often found in comets and primitive asteroids,” stated Jim Shirley, a research scientist at NASA’s Jet Propulsion Laboratory. “Finding the rocky residues of this comet crash on Europa’s surface may open up a new chapter in the story of the search for life on Europa.”
Reprocessed Galileo image of Europa’s frozen surface by Ted Stryk (NASA/JPL/Ted Stryk)
Europa is considered one of the best spots in our solar system to look for life, due to the ocean lurking beneath its icy surface, surface salts that can provide energy, and a source of heat as the mighty Jupiter squeezes and releases the moon like a tennis ball.
The minerals (called phyllosilicates) emerged after Shirley’s team ran a new analysis on infrared pictures snapped by Galileo in 1998, basically working to refine the signal out of the images (which are much lower quality than what we are capable of today).
After the analysis, the phyllosilicates appeared in a “broken ring”, NASA stated, about 75 miles (120 kilometers) away from a crater site. The crater itself is about 20 miles (30 kilometers) in diameter. Scientists are betting that the ring of phyllosilicates is debris (“splash back of material”, NASA says), after a celestial body struck at or around a 45 degree angle from vertical. It’s unlikely the phyllosilicates came from Europa’s ocean given the crust, which can be as thick as 60 miles (100 kilometers).
Europa Report was a 2013 film that focused on a human mission to the Jovian moon. Poster by Start Motion Pictures.
“If the body was an asteroid, it was likely about 3,600 feet (1,100 meters) in diameter. If the body was a comet, it was likely about 5,600 feet (1,700 meters) in diameter. It would have been nearly the same size as the comet ISON before it passed around the sun a few weeks ago,” NASA stated.
To be clear, nobody has found organic materials on Europa directly, and even if they were detected it would then be another feat of science to determine if they related to life or not. This does, however, lend credence to theories that life came to Earth through comets and asteroids.
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.”
