Where Is Europa?

Europa is a moon of the biggest planet in our solar system, Jupiter. Jupiter is the fifth planet from the sun, and depending on where it is in its orbit, can be between 390 million to 600 million miles away.

Jupiter had four larger moons, along with over 100 smaller ones. The four bog moons, also called the Galilean moons, are Io, Europa, Ganymede, and Callisto. Europa is the smallest of these moons, and is the second out from the planet. You can see Europa along with the other Galilean moons, through a good pair of binoculars or a small telescope.

A Bit of History

Europa was discovered on January 7, 1610 by Galileo Galilei, the same person who first used a telescope to look at space. He discovered all four of Jupiter’s Galilean moons that day with his homemade telescope, just a few days after he first looked at Jupiter. This changed the way we saw the solar system—even the universe. Until that point, people thought Earth was the only planet to have a moon. We thought we were special. Remember, at that point in time, we barely recognized that Earth wasn’t the center of the universe, and that we revolved around the sun and not the other way around. This was astounding news!

After this discovery, not much more was learned about Europa. We could track its orbit around Jupiter, and that was about it for hundreds of years. In the very early 1970s, however, a couple of astronomers at Kitt Peak National Observatory looked at Europa through their huge telescope and measured the light they observed with a device called a spectrograph to see what Europa might be made of on the surface. They were surprised to find that the spectra from Europa looked very familiar. It was water ice!

A few years later when the Voyager spacecrafts flew by Europa, we saw the moon like never before. Voyager 1 flew by at about a million miles away and sent back images of a bright reflective moon. But Voyager 2 got much closer, and showed a surface criss-crossed with dark orange-brown lines. Scientists saw very few craters, which they thought was unusual for a moon. They thought maybe this was because the surface was constantly refreshing itself. Perhaps the dark lines were from new material welling up from below the icy surface. We would need to wait about 20 years to find any more answers.

In 1995, the Galileo spacecraft arrived in orbit around Jupiter, taking pictures of the giant planet and its moons. The team of scientists behind the mission thought Europa’s surface was so fascinating they extended the mission an additional two years. The moon’s surface was covered with ridged plains, bumps, pits, and domes called lenticulae, and features they called “chaos,” which looked like jumbled chunks of ice that might have been icebergs.

But that’s not all the Galileo team learned. One of the mission’s goals was to study Jupiter’s magnetic field. While they were observing the giant’s field, however, they saw that it was disrupted wherever Europa was in its orbit. The only explanation they could come up with for this was if Europa had a magnetic field of its own. And in order for that to be possible, there had to be something conductive inside Europa.

Now, Earth has a magnetic field as well, and scientists are pretty certain it is because of the planet’s molten iron-nickel outer core. This fluid metal is conductive, creating a magnetic field. Something similar must be happening on Europa, but that moon is too small and too cold for its core to behave like Earth’s. But there is something else that Europa might have that would be conductive: a liquid salt water layer under it’s thick crust of ice. In other words, an interior ocean!

The idea of a fluid interior layer also supports all the cracking and lines on Europa’s surface. The Earth has “cracks” as well, or fault lines, which move over time as the plates in Earth’s crust move over its pliable rock mantle under the crust. It might be possible that between a hard, brittle ice crust and a liquid interior ocean, there is a layer of pliable ice that behaves like Earth’s mantle, expanding in some areas, subducting or going underneath the surface in other areas. This would explain why the surface doesn’t show as many craters as might be expected, because the surface is being renewed. Scientists thought perhaps there might even be icequakes or even ice volcanoes, much like we have volcanoes with lava on Earth. If the mechanism is the same, why not?

Fast forward to 2014. Scientists pointed the Hubble Space Telescope at Europa to make some observations. In one of the images, they saw a bulge on the side of the moon. Then, in 2016, they saw a similar bulge in the same spot! When they looked back at data from the Galileo mission, they learned that there was a “hot” spot there that was warmer than the surrounding areas (though it was still very, very cold, much colder than anywhere on Earth). The scientists had found their ice volcanoes! This supported the idea that Europa has an interior salt water ocean, containing two times the amount of water on Earth.

Why Is This Important?

So, why is this so important and exciting? It’s just water, right? Well, the only place we are positive there is liquid water is Earth. The only place we know there is life is also Earth. Water is a major building block of life as we know it. If there is water on Europa, perhaps there could be life as well.

In addition to water, life also needs to have certain chemicals as well as energy to metabolize them. Looking at Earth again, our ocean life gets its chemistry from where the water meets the floor of the ocean. The currents of the water mixes up the dirt down there, spreading out nutrients like calcium, sulphur, carbon, oxygen, phosphorous, and more. Microorganisms eat this, and it goes up the whole food chain. It’s not hard to imagine the same thing happening on—or in—Europa. Energy, however, is a little trickier.

On Earth, we get our energy from the sun. The plants use the sun’s energy to carry out photosynthesis, animals eat the plants, and we eat both the plants and the animals. Europa is very far from the sun, however, and receives much less of its energy. But it has a much closer neighbor that releases a lot of energy as well: Jupiter. The problem is, Jupiter sends off a bit TOO much energy for life to be able to survive on the surface of Europa without becoming completely irradiated. Once again, though, let’s use Earth as an example.

On Earth, we have a nice thick atmosphere that protects us from the sun’s harmful amounts of radiation. We get just the right amount of energy from the sun to survive. If we think about Europa, once more, as a much colder version of Earth, rather than having a gaseous atmosphere, a solid rock crust, and a liquid rock inner layer, Europa could have an ice layer behaving like Earth’s atmosphere over its inner ocean. The ice could protect the ocean below from Jupiter’s harmful radiation. Furthermore, the radiation could break apart molecules on the surface of the ice on Europa, and as the crust on Europa moves and renews, these molecules and ions are brought beneath the surface and into the interior ocean, providing needed chemistry and energy as well. This would provide life in the interior ocean of Europa with everything it needs!

Of course…all of this is basically guesswork. We have good ideas, but how could we prove these ideas true or false? Well…I guess we’re going to have to go back to Europa! But to learn more about that, you’ll have to wait until next week!

Humans have been looking for the possibility of life on Mars since it became clear that the red speck traveling across the night sky was another world like Earth. Percival Lowell thought Martian-built canals criss-crossed the planet. Classic science fiction authors like Jules Verne, Edgar Rice Burroughs, Ray Bradbury, and beyond dreamed up civilizations on the Red Planet. We’ve visited Mars via spacecraft and rovers more than any other planet, but we’ve never found any definitive proof that any life ever existed on Mars. Until...now?

On July 21, 2024, the Mars Perseverance rover took a picture of a rock that had scientists quite excited. The rock is in Neretva Vallis, the ancient river bed that is thought to have once fed the hypothetical lake in Jezero Crater, the landing spot of Perseverance. River beds and deltas are notorious places on Earth for finding signs of life, both past and present, and there is no reason to think this would be any different on Mars. This is one of the main reasons NASA specialists chose this area for Perseverance to study. Detecting “potential biosignatures,” signs that point to the possibility that life once existed in an area, is one of the mission’s main priorities, so the rover has specialized equipment to analyze for these things. The rock in question, called Cheyava Falls, had tiny dark spots on it which looked similar to markings found on Earth rocks in similar environments. On Earth, these markings are often the result of chemical reactions caused by living things. But this rock isn’t on Earth. It’s here, on Mars:

Now, scientists can’t just jump up and say, “Holy cow! We’ve found signs of life on Mars!” First of all, if these spots are indeed analogous to those on Earth (in other words, the Mars version of the same process as on Earth), they are most likely from long, long ago, from when there was still liquid water on the Martian surface. Whatever caused those marks is likely not still alive. No one wants to cause a panic—the news would need to be handled carefully so that there aren’t misconceptions and confusion about what was found. Second of all, scientists weren’t positive about what Perseverance found, and they might not be for a very long time yet. So, let’s back up and look at exactly what Perseverance found and what it might mean.

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Many of us had to memorize the scientific method at some point in our schooling adventures, and there was a good reason for that, though perhaps we all didn’t understand it at the time. Scientists (and people in many other fields) actually DO use this method to answer questions. Here’s a refresher in case you forgot it, or in case your school didn’t cover it:

NASA scientists and others used the scientific method to come up with Perseverance’s mission objectives and a landing site that would give them the greatest chance of accomplishing those goals (you can read more about that in my article here). Now, what you might not have learned in school is that there can be multiple levels of the scientific method within one project. In this case, we have the overall Perseverance mission, the landing site, the goals, the actual observations of the rover, etc. When Perseverance showed us those dark spots on the rock, it started a new round of scientific questioning within the larger scope of its mission. What were those dark spots?

Scientist Joel A. Hurowitz and his team thought the spots, which they called “leopard spots,” looked a lot like the spots on similar rocks on Earth, so they started the process of scientific examination. They put the rover to work, using its many scientific instruments to gather information. The rover scraped the rock to see what was under the surface, and it drilled a hole to get a sample of the rock, sample #25 called Sapphire Canyon. It also used its scanners and special instruments to find out what the rock was made of, and what the composition of the spots might be. They found that the rock, which they named “Cheyava Falls,” was made of silt, clay, and fine-grained mudstone, just like what they would expect to find in a dried river bed. But they also found that the rock was rich in organic carbon, sulfur, oxidized iron (rust), and phosphorous—all things that are present on Earth in places that have microbial life.

“The combination of chemical compounds we found…could have been a rich source of energy for microbial metabolisms,” Hurowitz, a geoscientist at Stony Brook University said. “But just because we saw all these compelling chemical signatures in the data didn’t mean we had a potential biosignature. We needed to analyze what that data could mean.”

In other words, his team had to analyze the data and think about all the other possible explanations for the chemicals. Then they would need to see if they could rule any of those things out. Only after they ruled the other explanations out could they say “these might point to life.” Iron phosphate and iron sulfide minerals like those observed by Perseverance can be created by what are called “redox reactions” involving organic carbon, and occur after mud and silt are deposited by a river. But these chemicals can be made in ways that don’t involve life as well as those that do, and the team of scientists had to rule those other ways out before they could draw any conclusions.

First, they determined that the iron phosphate spots—the leopard spots—were formed after the mud that formed the rock itself was deposited by the river. They could see that the spots were on the rock. Rather than being incorporated into the grains of mud that made the rock itself, the reactions that caused the markings happened “in situ”—in the place they were observed on the surface of the rock. So the scientists asked themselves what abiotic reactions, reactions that did not involve life, could have caused these spots at the low temperatures they seemed to have happened in?

One abiotic process that could explain the reaction involves a mineral called pyrite. If pyrite is rusted by iron and water, it could result in the chemicals found at the Mars site. But after analyzing the site more, scientists didn’t find any pyrite around.

Another process involved high temperatures that would have required magma or a hydrothermal event (think geysers or hot springs) interacting with the deposited stone, because those events produce sulfide gas that could leave a deposit on stone. But there is no evidence for any kind of hydrothermal or magmatic situations near the formation. And in order for the reactions involving sulfide to happen, there would need to be intense heat. There is no evidence that anything heated the rocks in the area to the temperatures that would have been necessary for the reactions to take place that way.

Without these explanations for the chemical reactions that made the leopard spots, scientists did see that a biological cause may indeed have been responsible. They referred to these same markings on rocks on Earth that are created at low temperatures by microbial life in sites with water long ago. These spots are considered evidence for some of the earliest life on Earth. The scientists working on this project are using these very similar conditions on Mars to propose that the same thing was possible on the Red Planet. The problem with this hypothesis, though, is that scientists—many different teams of scientists—would have to be able to examine the rock in person to confirm it.

There was good news on this front. A mission called the Mars Sample Return was planned to launch this summer in order to bring the samples collected by the Perseverance Rover back to Earth. It would have been a partnership between NASA and the European Space Agency and would have been a two part mission, one to collect the samples and put them in Martian orbit, and the other to collect them from orbit and bring them home. This mission is in severe jeopardy, however, because the White House recently declared it wanted to kill the program, and with the support of the conservative congress, it is pretty much a done deal. This is extremely unfortunate, especially in light of the new, possibly world-changing, discoveries Perseverance is making. Such discoveries could put the United States back into the forefront of space science. While we can try to replicate Martian conditions or try to find more evidence on Earth that is like that on Mars, there is no true way to confirm what the rocks on Mars could tell us without having them in hand.

“Ultimately, the return of the samples from Mars for study on Earth…would provide the best opportunity to understand the processes that gave rise to the unique features described here,” Dr. Hurowitz and his colleagues state in their paper about this discovery. Sadly, in addition to the cut of the Mars Sample Return mission, the White House has also announced an avalanche of other funding cuts for science in the next year.

If you don’t agree with these funding cuts, which are crippling programs and missions across the board, there are a few things you can do:

Part of science is being comfortable with saying, “We don’t know.” But another, equally important part of science is saying, “But let’s try to find out!” and being curious enough to explore. I know I’d like to find out if life existed on Mars, especially since we have this clue practically in our hands. Wouldn’t you?

The Mars Perseverance Rover landed on Mars in 2021, and it’s been an extremely successful mission over the past five years. One reason for its success was the landing site: scientists were very picky about where the rover would land to give it the greatest chance of accomplishing its four main objectives. In this article, I’ll explain how scientists and mission specialists decided where to land this rover.

This was a mission like no other, and a lot of care was taken to find just the perfect landing site for the rover. With a $2.4 billion price tag on the building and launching of the rover, NASA wanted to give the mission every chance for success. That included landing the rover safely and making sure there were the right conditions for it to find and collect data. But how did NASA pick the landing site for the Mars Perseverance Rover, when the planet is 69.5 million miles away? They used remote sensing technology.

Remote sensing is a way to observe things and take measurements when you aren’t there to collect data in situ, or in person. Here on Earth, we’ve used remote sensing to make maps, predict the weather, track climate change, and study the ocean floor. We’re getting better at it all the time, and we’re constantly developing new technology. Every mission we’ve done to other planets involves remote sensing. We use the information sent back to us from probes and orbiters to form hypotheses about the planets, to map their surfaces, and to share beautiful images with people on Earth. From a planet’s orbit, we can now tell what the rocks on the surface of that planet are made of by looking at the wavelengths of light those rocks reflect. This allows us to see where water might have been present, and where life might have developed at one point in history. That is exactly what NASA scientists were interested in when they started to plan the Perseverance mission.

Because Perseverance is an unmanned robotic rover, a vital part of NASA’s prelaunch procedure was to find a safe landing spot with few travel hazards and a wealth of scientific data for the rover to sample, test, and record. For the site to be viable, it had to allow for the rover to accomplish the four main objectives of the mission. Geologically, the site should be diverse, showing signs of the different processes that formed it. The site should be astrobiologically interesting, to help scientists look for signs of ancient life. There should be enough suitable material at the site for the rover to collect and cache in the hope it can be collected at some point. And finally, the site should contribute to the knowledge that will allow human travel to Mars.

Fortunately, remote sensing technology has made it possible for us to visit planets in our solar system without ever setting foot on them. The Mars Reconnaissance Orbiter, which has been collecting data from Mars since 2006, has three specialized cameras on board that allow us to see the red planet like we never have before. The resolution of these cameras is so fine that the resulting images are like works of art. Yet they are so much more than that.

The Compact Reconnaissance Imaging Spectrometer, or CRISM, and the High-Resolution Imaging Science Experiment, or HiRISE, both send back images that can be processed by scientists so they can see what minerals are present at a certain site, where those minerals came from (whether on the surface or brought up from beneath the surface by volcanism or impacts), and if those minerals are the types that are present where there is or was water, like clays and carbonates. This is done by examining the wavelengths of light these minerals reflect (software is used to divide the image into bands of different wavelengths, so these things can be seen easily). Below is an example of an image from CRISM, with bands of reflected light set to be different colors so scientists can see the difference between various minerals. In this case, yellow is olivine, blue is pyroxene.

Image: NASA/JPL/JHUAPL

And below, here is an image from HiRISE, where its high-resolution imagery helped scientists discover lava coils on Mars for the first time. I highly recommend looking at other HiRISE imagery. The hi-def pictures will take your breath away.

Image: NASA/JPL/UArizona

The third camera, the Context Camera, or CXT, takes images that are intended to be used as a background for the information gathered by the other two instruments and is useful for seeing the big picture. The table below gives more information about each of the cameras and what they are used for.

Table: Melanie R. Meadors

All three of these instruments remove much of the guesswork from what’s going on at particular sites on Mars. In short, we’ve never had better access to potential landing sites than we do now. NASA was in a position to make a really educated decision as to where to land the new Mars Perseverance Rover.

Scientists met several times to discuss over thirty possible sites, dissecting them to see which sites would offer the best chance to achieve the mission objectives. Eventually, it came down to three final sites: Northeast Syrtis, Jezero Crater, and Midway. You can see below that these sites are relatively close to one another, and Midway was named such because it is mid-way between the other two sites. It was a last-minute addition to the site list.

Image: NASA/JPL; Map created using ArcGIS by Melanie R. Meadors

All three of these sites had pros and cons that NASA considered, but it was very hard to choose between them. In fact, if it hadn’t been for the detailed information scientists were able to get via remote sensing, the decision wouldn’t have been clear at all.

Northeast Syrtis (below) had minerals that suggested past habitability, and there were clear signs of the processes that formed the area. But it was decided that it would take too long for scientists to accurately classify some things there that were harder to make out—if they were able to make them out at all.

Image: NASA/JPL, Map created using ArcGIS by Melanie R. Meadors

Midway (below) could be reached from either of the other two sites, which made it an interesting secondary possibility. It holds some interesting possibilities for potential subsurface life, but the origins of some of the rocks were deemed too uncertain to make it the primary site.

Image: NASA/JPL, Map created using ArcGIS by Melanie R. Meadors

This left Jezero Crater (below), which was the site ultimately decided upon to be the landing site for the Perseverance rover. It had scientific characteristics and points of interest pertinent to the mission objectives, as well as terrain on which it would be safe for the rover to land and operate, increasing the odds of mission success.

Image: NASA/JPL, Map created using ArcGIS by Melanie R. Meadors

It doesn’t take a highly trained scientist to notice Jezero Crater has a very interesting feature on its west side—a delta from an ancient river that flowed into what scientists believe was a lake that filled the crater. One of the landing site criteria was that the geologic processes that made the site had to be discernible, and while there is some disagreement about the age of these features in Jezero, it’s well agreed that this delta was formed by an ancient river. Because deltas on Earth are known to be very rich in nutrients and organics, the building blocks of life, and so the same is thought to be true on Mars. Upon closer examination, teams of scientists found clays, carbonates, and possible hydrosilicates, all of which are good indicators that signatures of organic matter might be found at the site. Jezero has been deemed safe for the landing and operating of the Mars Perseverance Rover, and there are a wide variety of rocks and minerals here for collecting. It’s also close enough to Midway where the rover could potentially travel out to that site as well.

Image: NASA/JPL, Map created using ArcGIS by Melanie R. Meadors

Planning a mission to a planet we’ve never seen in person always has risks involved. But remote sensing makes it possible for scientists and engineers to make these plans with a clearer vision than ever before, and it takes a lot of guesswork out of the planning phases. All of this planning paid off, and the Mars Perseverance Rover has collected a lot of new information to teach us more about the Red Planet than ever, using a different type of remote sensing--the instruments on the rover itself!

In future articles, I will talk about what the Mars Perseverance Rover has found so far, as well as future plans for Mars exploration!