# How much light would be reflected from Jupiter to Europa (in Europas night)?

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Suppose Europa is found habitable and humans start living on it. Europa is close to Jupiter and during the night Jupiter would be reflecting light to Europa, just like our full moon reflects light to earth. Our moon is small compared to Jupiter. Would humans still need artificial light during Europas nights?

It's a pretty straight forward calculation of 3 factors. Distance from the sun, apparent size and albedo. I'm going to compare Jupiter to our full moon, since we're all familiar with that.

Jupiter averages between 4.95 and 5.45 AU from the sun. That puts it, in comparison with our full moon (about 1.02 AU on average), that means individual square meters on Jupiter would receive between 1/23.5 and 1/28.5 the light that hits our moon. I'm going to round and say between 1/24 and 1/28.

Brightness is also important. The Moon is very dark with an albedo of about 12% - about the color of worn or greyish asphalt. Jupiter's bond albedo is about .34, so it would reflect nearly 3 times more light. That means per square meter, Jupiter is up to about 1/8th to 1/10th as bright.

The big difference is size. From Earth, the Moon takes up about 1/2 of 1 degree of arc. Jupiter's diameter is about 37 times the Moon's diameter. It's distance to Europa is about 1.73 times Earth's distance to the Moon, so it's apparent size would be about 21 times the diameter (about 10 degrees of arc), the reflective area is closer to 450 times. If you divide that by the ratio of 8 to 10 depending on how close or far Jupiter is to the Sun in it's orbit, A full Jupiter would be the brightness of roughly between 45 and 55 average full moons. It wouldn't glow as brightly, though some of it's lighter bands would be almost half way there. But the entire package would be 45 to 55 times as bright (ignoring any atmospheric reflection, which would make it appear even brighter).

That's probably bright enough to read under, but not so bright that it would hurt your eyes if you stared at it.

This only answers your question for a full jupiter, but the ratio, 45 to 55 times brighter should be about right for all the phases. And about 450 times larger than an average Moon. The Moon's size varies fairly significantly from Earth, though we don't always notice. Europa has a much more circular orbit around Jupiter, so it's size would stay about the same from the surface of Europa.

This is based purely on Stellarium's simulation, so may not be accurate.

From Europa, full Jupiter has a magnitude of almost -17 and an angular diameter of 12 degrees:

This makes it about 56 times brighter and 24 times larger (in diameter, not area-- it's about 600 times larger in area) than our full moon (magnitude -12.3), more than good enough for reading.

It's still not as bright as the Sun on Europa, which clocks in at a magnitude of -23.06:

If you accept the quarter moon (magnitude -10.0) provides sufficient reading light, two of Jupiter's other moons (Io and Ganymede; Callisto is very dark and has a low albedo) can do this as well:

So it seems Europa's sky is fairly well lit, even at solar night. But don't get your hopes too high: I performed this simulation at the intersection of Europa's equator and prime meridian. An earlier simulation in the northern hemisphere showed that Jupiter doesn't rise at all there.

## The Weird Plumes of Jupiter's Moon Europa Are Spewing Water Vapor

Europa's plumes appear to be real, but very sporadic.

The Jupiter moon Europa's elusive and enigmatic water-vapor plumes do indeed seem to be real.

NASA's Hubble Space Telescope has spotted indirect evidence of such plumes emanating from Europa, which is thought to harbor a huge, salty ocean beneath its ice shell. And researchers have now detected one such plume's water vapor directly for the first time, a new study reports.

"Essential chemical elements (carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur) and sources of energy, two of three requirements for life, are found all over the solar system. But the third &mdash liquid water &mdash is somewhat hard to find beyond Earth," study lead author Lucas Paganini, a planetary scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and American University in Washington, D.C., said in a statement.

"While scientists have not yet detected liquid water directly, we've found the next best thing: water in vapor form," Paganini added.

Paganini and his colleagues used the W.M. Keck Observatory in Hawaii to study the 1,900-mile-wide (3,100 kilometers) Europa, which astrobiologists regard as one of the solar system's best bets to host alien life.

The researchers observed Europa for 17 nights, from February 2016 through May 2017. On one of those nights &mdash April 26, 2016 &mdash they got a strong signal of water vapor, in the form of a characteristic wavelength of emitted infrared light.

And there was quite a bit of the stuff &mdash about 2,300 tons (2,095 metric tons), according to the researchers' calculations. That's almost enough to fill an Olympic-size swimming pool (which contains about 2,750 tons, or 2,500 metric tons, of water).

The researchers think the source of this water is a plume, which could be coming from the buried ocean or from a reservoir of melted ice within Europa's shell. For starters, the observed volume is much higher than what is predicted to result from "exogenic" processes, such as the stripping of water molecules from Europa's surface by Jupiter's powerful radiation belts. And such stripping would likely occur fairly regularly, or at least often enough to be noted more than one night out of 17, Paganini and his team wrote in the new paper, which was published online today (Nov. 18) in the journal Nature Astronomy.

Multiple lines of evidence now point to the existence of plumes on Europa. For example, in addition to the new results and Hubble's detection of atomic hydrogen and oxygen (which presumably came from water molecules split apart by radiation), NASA's Galileo Jupiter probe measured a big increase in the density of plasma, or ionized gas, during a Europa flyby in 1997.

And it's becoming increasingly clear that Europa's plumes are sporadic. In that regard, they're very different from the constant plume wafting from the south pole of Saturn's icy, ocean-harboring moon Enceladus, which is generated by more than 100 powerful geysers that are always on.

"For me, the interesting thing about this work is not only the first direct detection of water above Europa, but also the lack thereof within the limits of our detection method," Paganini said.

Plumes like those emanating from Enceladus and Europa are very exciting to astrobiologists, because they're sending "free samples" from potentially habitable environments out into space for potential snagging by robotic probes. And there's a possibility that a NASA spacecraft could soon do just that, if everything works out just right.

NASA is developing a mission called Europa Clipper, which is scheduled to launch in the mid-2020s. Clipper will orbit Jupiter but study Europa up close on dozens of flybys, characterizing the moon and its ocean and hunting for spots where a potential life-hunting lander could touch down in the future. Clipper could end up zooming through the plume on one or more of those flybys, if mission team members learn enough about the feature in the coming years &mdash or if they just get really lucky.

## Europa Glows: Radiation Does a Bright Number on Jupiter’s Moon

As the icy, ocean-filled moon Europa orbits Jupiter, it withstands a relentless pummeling of radiation. Jupiter zaps Europa’s surface night and day with electrons and other particles, bathing it in high-energy radiation. But as these particles pound the moon’s surface, they may also be doing something otherworldly: making Europa glow in the dark.

New research from scientists at NASA’s Jet Propulsion Laboratory in Southern California details for the first time what the glow would look like, and what it could reveal about the composition of ice on Europa’s surface. Different salty compounds react differently to the radiation and emit their own unique glimmer. To the naked eye, this glow would look sometimes slightly green, sometimes slightly blue or white and with varying degrees of brightness, depending on what material it is.

This illustration of Jupiter’s moon Europa shows how the icy surface may glow on its nightside, the side facing away from the Sun. Variations in the glow and the color of the glow itself could reveal information about the composition of ice on Europa’s surface. Credits: NASA/JPL-Caltech

Scientists use a spectrometer to separate the light into wavelengths and connect the distinct “signatures,” or spectra, to different compositions of ice. Most observations using a spectrometer on a moon like Europa are taken using reflected sunlight on the moon’s dayside, but these new results illuminate what Europa would look like in the dark.

“We were able to predict that this nightside ice glow could provide additional information on Europa’s surface composition. How that composition varies could give us clues about whether Europa harbors conditions suitable for life,” said JPL’s Murthy Gudipati, lead author of the work published Nov. 9 in Nature Astronomy.

That’s because Europa holds a massive, global interior ocean that could percolate to the surface through the moon’s thick crust of ice. By analyzing the surface, scientists can learn more about what lies beneath.

Shining a Light

Scientists have inferred from prior observations that Europa’s surface could be made of a mix of ice and commonly known salts on Earth, such as magnesium sulfate (Epsom salt) and sodium chloride (table salt). The new research shows that incorporating those salts into water ice under Europa-like conditions and blasting it with radiation produces a glow.

That much was not a surprise. It’s easy to imagine an irradiated surface glowing. Scientists know the shine is caused by energetic electrons penetrating the surface, energizing the molecules underneath. When those molecules relax, they release energy as visible light.

“But we never imagined that we would see what we ended up seeing,” said JPL’s Bryana Henderson, who co-authored the research. “When we tried new ice compositions, the glow looked different. And we all just stared at it for a while and then said, ‘This is new, right? This is definitely a different glow?’ So we pointed a spectrometer at it, and each type of ice had a different spectrum.”

To study a laboratory mockup of Europa’s surface, the JPL team built a unique instrument called Ice Chamber for Europa’s High-Energy Electron and Radiation Environment Testing (ICE-HEART). They took ICE-HEART to a high-energy electron beam facility in Gaithersburg, Maryland, and started the experiments with an entirely different study in mind: to see how organic material under Europa ice would react to blasts of radiation.

They didn’t expect to see variations in the glow itself tied to different ice compositions. It was – as the authors called it – serendipity.

“Seeing the sodium chloride brine with a significantly lower level of glow was the ‘aha’ moment that changed the course of the research,” said Fred Bateman, co-author of the paper. He helped conduct the experiment and delivered radiation beams to the ice samples at the Medical Industrial Radiation Facility at the National Institute of Standards and Technology in Maryland.

A moon that’s visible in a dark sky may not seem unusual we see our own Moon because it reflects sunlight. But Europa’s glow is caused by an entirely different mechanism, the scientists said. Imagine a moon that glows continuously, even on its nightside – the side facing away from the Sun.

“If Europa weren’t under this radiation, it would look the way our moon looks to us – dark on the shadowed side,” Gudipati said. “But because it’s bombarded by the radiation from Jupiter, it glows in the dark.”

Set to launch in the mid-2020s, NASA’s upcoming flagship mission Europa Clipper will observe the moon’s surface in multiple flybys while orbiting Jupiter. Mission scientists are reviewing the authors’ findings to evaluate if a glow would be detectable by the spacecraft’s science instruments. It’s possible that information gathered by the spacecraft could be matched with the measurements in the new research to identify the salty components on the moon’s surface or narrow down what they might be.

“It’s not often that you’re in a lab and say, ‘We might find this when we get there,'” Gudipati said. “Usually it’s the other way around – you go there and find something and try to explain it in the lab. But our prediction goes back to a simple observation, and that’s what science is about.”

Missions such as Europa Clipper help contribute to the field of astrobiology, the interdisciplinary research on the variables and conditions of distant worlds that could harbor life as we know it. While Europa Clipper is not a life-detection mission, it will conduct detailed reconnaissance of Europa and investigate whether the icy moon, with its subsurface ocean, has the capability to support life. Understanding Europa’s habitability will help scientists better understand how life developed on Earth and the potential for finding life beyond our planet.

## Europa’s icy surface may glow in the dark

Understanding the chemical composition of ice on Jupiter’s intriguing moon could reveal hints about its habitability.

This illustration of Jupiter's moon Europa shows how the icy surface may glow on its nightside, the side facing away from the Sun. NASA/JPL-Caltech

The night side of Jupiter’s moon Europa may glow in the dark, scientists reported this week in the journal Nature Astronomy.

When researchers fired beams of electrons at ice samples to simulate the radiation that regularly lashes Europa’s frigid surface, they noticed that the ice emitted a faint glow that varied depending on which minerals were present in the ice. NASA’s Europa Clipper probe may be able to observe this same phenomenon when it reaches the distant moon in a few years—and perhaps use it to investigate whether Europa has conditions amenable for life.

Until now, the only object in our celestial neighborhood known to emit light from its nighttime side is Earth the electricity humans use to light our dwellings can be seen from the International Space Station, says Murthy Gudipati, a laboratory astrophysicist at the NASA Jet Propulsion Laboratory in Pasadena, California. “Because of its position and the geological aspects of Europa, it could be very similar to Earth in the sense that we have a second object in our system that also glows in the night,” says Gudipati, who published the findings on November 9.

Europa is covered by an icy crust several miles thick, which scientists believe covers a vast ocean that is 40 to 100 miles deep. The moon also receives deluges of charged particles from Jupiter’s strong magnetic field this radiation would be lethal for a human standing on Europa’s surface. And that would only be relevant if humans were somehow able to withstand the moon’s surface temperatures of, on average, 100 Kelvin (-279.67 Farenheit). “This is a very unique place in our solar system,” Gudipati says. “It is one of the highest contenders for potential habitability [because of] these oceans and it is also very uniquely placed in one of the harshest outside environments.”

He and his colleagues wanted to understand what happens when charged particles strike Europa’s surface. They fired beams of electrons at ice cores representing different possibilities for Europa’s surface and filmed the results with a video camera. When the electrons struck pure water ice, the researchers saw, the frozen liquid gave off a whitish glow with a faint blue-green tinge. This glow was brighter when the irradiated ice contained magnesium sulfate (Epsom salt). Ice containing sodium chloride (sea salt) had a much dimmer glow without any colorful tinge. Upon further investigation, the scientists found that the light coming off the ice was predominantly white, but green wavelengths were slightly more prevalent in the light coming from the water ice, red in the Epsom salted ice, and blue-green in the sea salt ice.

This glow occurs because when electrons plow into the ice, they energize the material. The frozen water then releases some of this energy in the form of light, with different atoms and molecules giving off light at different wavelengths.

A similar process occurs in the northern lights, Gudipati says. To our eyes, the aurora has an intense green hue because the oxygen in the atmosphere has plenty of room to emit light without interacting with other materials. The composition of the luminescent ice is denser and more varied there may be several compounds constantly emitting light that muddles together to form a mostly whitish glow.

“In the ice there is no space between one atom and the other atoms it is like sea lions sunbathing, they cannot move around,” Gudipati says. “It is totally crowded and each of these excited atoms or molecules interacts with its surroundings.”

He and his colleagues estimate that, if Europa’s surface glows in the night like the ice in their experiment, the Europa Clipper’s planned instruments would likely be able to detect it as the spacecraft zooms past. The mission, which will launch in the mid-2020s, could give scientists an opportunity to figure out how suitable Europa might be for life by analyzing the glow coming off the night side of the moon.

As it sloshes against the seafloor, Europa’s ocean likely interacts with the rocky substrate to produce minerals that may be vital for life. Some of these minerals will eventually make their way into the ice covering Europa’s ocean. This frigid shell is scarred by relatively few craters, indicating that its surface is young. “Those impact craters are somehow cleaned up, and that cleaning up would only happen if there is an exchange between the interior and surface,” Gudipati says.

Depending on how brightly the ice glows and what wavelengths of light it emits, scientists could determine its chemical composition. “The material on the surface could bear some fingerprints from what the material was in the oceans [over] time,” Gudipati says.

## Europa glows: Radiation does a bright number on Jupiter's moon

This illustration of Jupiter's moon Europa shows how the icy surface may glow on its nightside, the side facing away from the Sun. Variations in the glow and the color of the glow itself could reveal information about the composition of ice on Europa's surface. Credit: NASA/JPL-Caltech

As the icy, ocean-filled moon Europa orbits Jupiter, it withstands a relentless pummeling of radiation. Jupiter zaps Europa's surface night and day with electrons and other particles, bathing it in high-energy radiation. But as these particles pound the moon's surface, they may also be doing something otherworldly: making Europa glow in the dark.

New research from scientists at NASA's Jet Propulsion Laboratory in Southern California details for the first time what the glow would look like, and what it could reveal about the composition of ice on Europa's surface. Different salty compounds react differently to the radiation and emit their own unique glimmer. To the naked eye, this glow would look sometimes slightly green, sometimes slightly blue or white and with varying degrees of brightness, depending on what material it is.

Scientists use a spectrometer to separate the light into wavelengths and connect the distinct "signatures," or spectra, to different compositions of ice. Most observations using a spectrometer on a moon like Europa are taken using reflected sunlight on the moon's dayside, but these new results illuminate what Europa would look like in the dark.

"We were able to predict that this nightside ice glow could provide additional information on Europa's surface composition. How that composition varies could give us clues about whether Europa harbors conditions suitable for life," said JPL's Murthy Gudipati, lead author of the work published Nov. 9 in Nature Astronomy.

That's because Europa holds a massive, global interior ocean that could percolate to the surface through the moon's thick crust of ice. By analyzing the surface, scientists can learn more about what lies beneath.

Scientists have inferred from prior observations that Europa's surface could be made of a mix of ice and commonly known salts on Earth, such as magnesium sulfate (Epsom salt) and sodium chloride (table salt). The new research shows that incorporating those salts into water ice under Europa-like conditions and blasting it with radiation produces a glow.

That much was not a surprise. It's easy to imagine an irradiated surface glowing. Scientists know the shine is caused by energetic electrons penetrating the surface, energizing the molecules underneath. When those molecules relax, they release energy as visible light.

"But we never imagined that we would see what we ended up seeing," said JPL's Bryana Henderson, who co-authored the research. "When we tried new ice compositions, the glow looked different. And we all just stared at it for a while and then said, 'This is new, right? This is definitely a different glow?' So we pointed a spectrometer at it, and each type of ice had a different spectrum."

To study a laboratory mockup of Europa's surface, the JPL team built a unique instrument called Ice Chamber for Europa's High-Energy Electron and Radiation Environment Testing (ICE-HEART). They took ICE-HEART to a high-energy electron beam facility in Gaithersburg, Maryland, and started the experiments with an entirely different study in mind: to see how organic material under Europa ice would react to blasts of radiation.

They didn't expect to see variations in the glow itself tied to different ice compositions. It was—as the authors called it—serendipity.

"Seeing the sodium chloride brine with a significantly lower level of glow was the 'aha' moment that changed the course of the research," said Fred Bateman, co-author of the paper. He helped conduct the experiment and delivered radiation beams to the ice samples at the Medical Industrial Radiation Facility at the National Institute of Standards and Technology in Maryland.

A moon that's visible in a dark sky may not seem unusual we see our own Moon because it reflects sunlight. But Europa's glow is caused by an entirely different mechanism, the scientists said. Imagine a moon that glows continuously, even on its nightside—the side facing away from the Sun.

"If Europa weren't under this radiation, it would look the way our moon looks to us—dark on the shadowed side," Gudipati said. "But because it's bombarded by the radiation from Jupiter, it glows in the dark."

Set to launch in the mid-2020s, NASA's upcoming flagship mission Europa Clipper will observe the moon's surface in multiple flybys while orbiting Jupiter. Mission scientists are reviewing the authors' findings to evaluate if a glow would be detectable by the spacecraft's science instruments. It's possible that information gathered by the spacecraft could be matched with the measurements in the new research to identify the salty components on the moon's surface or narrow down what they might be.

"It's not often that you're in a lab and say, 'We might find this when we get there,'" Gudipati said. "Usually it's the other way around—you go there and find something and try to explain it in the lab. But our prediction goes back to a simple observation, and that's what science is about."

Missions such as Europa Clipper help contribute to the field of astrobiology, the interdisciplinary research on the variables and conditions of distant worlds that could harbor life as we know it. While Europa Clipper is not a life-detection mission, it will conduct detailed reconnaissance of Europa and investigate whether the icy moon, with its subsurface ocean, has the capability to support life. Understanding Europa's habitability will help scientists better understand how life developed on Earth and the potential for finding life beyond our planet.

## Jupiter’s Moon Europa Glows In The Dark, Say Scientists

This artist's impression of Jupiter's moon Europa shows how the icy surface may glow on its . [+] nightside.

Jupiter is a powerful source of radio waves in the night sky.

When space agencies send spacecraft to the giant planet they have to make sure that their orbits are calculated carefully so that they don’t spend too long inside the radiation belts of Jupiter. The zone’s high-energy particles are just too much.

So what happens if you’re a moon in orbit of Jupiter having to constantly withstand a relentless pummeling of high-energy radiation?

You glow in the dark, that’s what.

New research from scientists at NASA’s Jet Propulsion Laboratory suggest that Europa—the fourth largest of Jupiter’s 79 moons—may glow shades of green, blue and white even on its nightside.

The glow could reveal much about the composition of ice on Europa’s surface, say scientists—and the glow could be observed by a NASA spacecraft headed to the moon in just a few years.

Europa has been described as looking like a "veiny eyeball."

Europa is smaller than our Moon. It’s about 1,900 miles/3,100 kilometers in diameter and has a thin oxygen-rich atmosphere, a liquid iron core and a magnetic field. Fractures in its icy surface make Europa look like a “veiny eyeball”.

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However, most remarkably, Europa is known to have a global ocean of water beneath an 11 mile/18 kilometer thick crust of ice. It’s thought (and hoped) that this ocean could harbor simple forms of life.

It’s thought that these new models of how Europa glows will tell scientists about the composition of that ice—and what lies beneath it—because of how the differing salty compounds on the moon’s surface react differently to radiation.

Each compound emits its own unique glimmer, which scientists can separate into wavelengths using a spectrometer.

Usually the light that scientists study from somewhere like Europa would be reflected sunlight on the moon’s dayside, but these new results show what Europa would look like in on its night-side.

“We were able to predict that this nightside ice glow could provide additional information on Europa’s surface composition,” said Murthy Gudipati at JPL and lead author of the work published today in Nature Astronomy. “How that composition varies could give us clues about whether Europa harbors conditions suitable for life.”

It’s thought that Europa’s surface is comprised of magnesium sulfate and sodium chloride—Epsom salt and table salt—which the researchers incorporated into ice under Europa-like conditions and blasted with radiation to produce an unexpected glow.

“We never imagined that we would see what we ended up seeing,” said Bryana Henderson of JPL, who co-authored the research. “When we tried new ice compositions, the glow looked different and we all just stared at it for a while and then said, ‘This is new, right? This is definitely a different glow?’ So we pointed a spectrometer at it, and each type of ice had a different spectrum.”

NASA’s Europa Clipper mission will launch in 2023.

Scheduled to launch in 2023, NASA’s Europa Clipper mission will perform about 45 flybys, in each pass photographing the moon's icy surface in high resolution. Will it detect Europa’s glow? Mission scientists are now reviewing these new findings to find out.

If so then NASA will soon know exactly what Europa is made of—and take a step closer to discovering what lurks in the watery depths below the ice.

## Europa Glows: Radiation Does a Bright Number on Jupiter’s Moon

This illustration of Jupiter’s moon Europa shows how the icy surface may glow on its nightside, the side facing away from the Sun. Variations in the glow and the color of the glow itself could reveal information about the composition of ice on Europa’s surface. Image credit: NASA/JPL-Caltech

As the icy, ocean-filled moon Europa orbits Jupiter, it withstands a relentless pummeling of radiation. Jupiter zaps Europa’s surface night and day with electrons and other particles, bathing it in high-energy radiation. But as these particles pound the moon’s surface, they may also be doing something otherworldly: making Europa glow in the dark.

New research from scientists at NASA’s Jet Propulsion Laboratory in Southern California details for the first time what the glow would look like, and what it could reveal about the composition of ice on Europa’s surface. Different salty compounds react differently to the radiation and emit their own unique glimmer. To the naked eye, this glow would look sometimes slightly green, sometimes slightly blue or white and with varying degrees of brightness, depending on what material it is.

Scientists use a spectrometer to separate the light into wavelengths and connect the distinct “signatures,” or spectra, to different compositions of ice. Most observations using a spectrometer on a moon like Europa are taken using reflected sunlight on the moon’s dayside, but these new results illuminate what Europa would look like in the dark.

“We were able to predict that this nightside ice glow could provide additional information on Europa’s surface composition. How that composition varies could give us clues about whether Europa harbors conditions suitable for life,” said JPL’s Murthy Gudipati, lead author of the work published Nov. 9 in Nature Astronomy.

That’s because Europa holds a massive, global interior ocean that could percolate to the surface through the moon’s thick crust of ice. By analyzing the surface, scientists can learn more about what lies beneath.

Shining a Light

Scientists have inferred from prior observations that Europa’s surface could be made of a mix of ice and commonly known salts on Earth, such as magnesium sulfate (Epsom salt) and sodium chloride (table salt). The new research shows that incorporating those salts into water ice under Europa-like conditions and blasting it with radiation produces a glow.

That much was not a surprise. It’s easy to imagine an irradiated surface glowing. Scientists know the shine is caused by energetic electrons penetrating the surface, energizing the molecules underneath. When those molecules relax, they release energy as visible light.

“But we never imagined that we would see what we ended up seeing,” said JPL’s Bryana Henderson, who co-authored the research. “When we tried new ice compositions, the glow looked different. And we all just stared at it for a while and then said, ‘This is new, right? This is definitely a different glow?’ So we pointed a spectrometer at it, and each type of ice had a different spectrum.”

To study a laboratory mockup of Europa’s surface, the JPL team built a unique instrument called Ice Chamber for Europa’s High-Energy Electron and Radiation Environment Testing (ICE-HEART). They took ICE-HEART to a high-energy electron beam facility in Gaithersburg, Maryland, and started the experiments with an entirely different study in mind: to see how organic material under Europa ice would react to blasts of radiation.

They didn’t expect to see variations in the glow itself tied to different ice compositions. It was – as the authors called it – serendipity.

“Seeing the sodium chloride brine with a significantly lower level of glow was the ‘aha’ moment that changed the course of the research,” said Fred Bateman, co-author of the paper. He helped conduct the experiment and delivered radiation beams to the ice samples at the Medical Industrial Radiation Facility at the National Institute of Standards and Technology in Maryland.

A moon that’s visible in a dark sky may not seem unusual we see our own Moon because it reflects sunlight. But Europa’s glow is caused by an entirely different mechanism, the scientists said. Imagine a moon that glows continuously, even on its nightside – the side facing away from the Sun.

“If Europa weren’t under this radiation, it would look the way our moon looks to us – dark on the shadowed side,” Gudipati said. “But because it’s bombarded by the radiation from Jupiter, it glows in the dark.”

Set to launch in the mid-2020s, NASA’s upcoming flagship mission Europa Clipper will observe the moon’s surface in multiple flybys while orbiting Jupiter. Mission scientists are reviewing the authors’ findings to evaluate if a glow would be detectable by the spacecraft’s science instruments. It’s possible that information gathered by the spacecraft could be matched with the measurements in the new research to identify the salty components on the moon’s surface or narrow down what they might be.

“It’s not often that you’re in a lab and say, ‘We might find this when we get there,'” Gudipati said. “Usually it’s the other way around – you go there and find something and try to explain it in the lab. But our prediction goes back to a simple observation, and that’s what science is about.”

Missions such as Europa Clipper help contribute to the field of astrobiology, the interdisciplinary research on the variables and conditions of distant worlds that could harbor life as we know it. While Europa Clipper is not a life-detection mission, it will conduct detailed reconnaissance of Europa and investigate whether the icy moon, with its subsurface ocean, has the capability to support life. Understanding Europa’s habitability will help scientists better understand how life developed on Earth and the potential for finding life beyond our planet.

## Radiation Does A Bright Number On Europa

As the icy, ocean-filled moon Europa orbits Jupiter, it withstands a relentless pummeling of radiation. Jupiter zaps Europa's surface night and day with electrons and other particles, bathing it in high-energy radiation.

But as these particles pound the moon's surface, they may also be doing something otherworldly: making Europa glow in the dark.

New research from scientists at NASA's Jet Propulsion Laboratory in Southern California details for the first time what the glow would look like, and what it could reveal about the composition of ice on Europa's surface. Different salty compounds react differently to the radiation and emit their own unique glimmer. To the naked eye, this glow would look sometimes slightly green, sometimes slightly blue or white and with varying degrees of brightness, depending on what material it is.

Scientists use a spectrometer to separate the light into wavelengths and connect the distinct "signatures," or spectra, to different compositions of ice. Most observations using a spectrometer on a moon like Europa are taken using reflected sunlight on the moon's dayside, but these new results illuminate what Europa would look like in the dark.

"We were able to predict that this nightside ice glow could provide additional information on Europa's surface composition. How that composition varies could give us clues about whether Europa harbors conditions suitable for life," said JPL's Murthy Gudipati, lead author of the work published Nov. 9 in Nature Astronomy.

That's because Europa holds a massive, global interior ocean that could percolate to the surface through the moon's thick crust of ice. By analyzing the surface, scientists can learn more about what lies beneath.

Scientists have inferred from prior observations that Europa's surface could be made of a mix of ice and commonly known salts on Earth, such as magnesium sulfate (Epsom salt) and sodium chloride (table salt). The new research shows that incorporating those salts into water ice under Europa-like conditions and blasting it with radiation produces a glow.

That much was not a surprise. It's easy to imagine an irradiated surface glowing. Scientists know the shine is caused by energetic electrons penetrating the surface, energizing the molecules underneath. When those molecules relax, they release energy as visible light.

"But we never imagined that we would see what we ended up seeing," said JPL's Bryana Henderson, who co-authored the research. "When we tried new ice compositions, the glow looked different. And we all just stared at it for a while and then said, 'This is new, right? This is definitely a different glow?' So we pointed a spectrometer at it, and each type of ice had a different spectrum."

To study a laboratory mockup of Europa's surface, the JPL team built a unique instrument called Ice Chamber for Europa's High-Energy Electron and Radiation Environment Testing (ICE-HEART). They took ICE-HEART to a high-energy electron beam facility in Gaithersburg, Maryland, and started the experiments with an entirely different study in mind: to see how organic material under Europa ice would react to blasts of radiation.

They didn't expect to see variations in the glow itself tied to different ice compositions. It was - as the authors called it - serendipity.

"Seeing the sodium chloride brine with a significantly lower level of glow was the 'aha' moment that changed the course of the research," said Fred Bateman, co-author of the paper. He helped conduct the experiment and delivered radiation beams to the ice samples at the Medical Industrial Radiation Facility at the National Institute of Standards and Technology in Maryland.

A moon that's visible in a dark sky may not seem unusual we see our own Moon because it reflects sunlight. But Europa's glow is caused by an entirely different mechanism, the scientists said. Imagine a moon that glows continuously, even on its nightside - the side facing away from the Sun.

"If Europa weren't under this radiation, it would look the way our moon looks to us - dark on the shadowed side," Gudipati said. "But because it's bombarded by the radiation from Jupiter, it glows in the dark."

Set to launch in the mid-2020s, NASA's upcoming flagship mission Europa Clipper will observe the moon's surface in multiple flybys while orbiting Jupiter. Mission scientists are reviewing the authors' findings to evaluate if a glow would be detectable by the spacecraft's science instruments. It's possible that information gathered by the spacecraft could be matched with the measurements in the new research to identify the salty components on the moon's surface or narrow down what they might be.

"It's not often that you're in a lab and say, 'We might find this when we get there,'" Gudipati said. "Usually it's the other way around - you go there and find something and try to explain it in the lab. But our prediction goes back to a simple observation, and that's what science is about."

Missions such as Europa Clipper help contribute to the field of astrobiology, the interdisciplinary research on the variables and conditions of distant worlds that could harbor life as we know it. While Europa Clipper is not a life-detection mission, it will conduct detailed reconnaissance of Europa and investigate whether the icy moon, with its subsurface ocean, has the capability to support life. Understanding Europa's habitability will help scientists better understand how life developed on Earth and the potential for finding life beyond our planet.

## Does Europa glow in the dark?

This artist’s concept of Jupiter’s moon Europa shows how the icy surface may glow on its nightside, the side facing away from the sun. Variations in the glow and the color of the glow itself could reveal information about the composition of ice on Europa’s surface. Image via NASA/JPL-Caltech.

New lab experiments that re-created the environment of Jupiter’s large moon Europa suggest that the icy world shines, even on its nightside.

As icy, ocean-filled Europa – one of Jupiter’s 79 known moons – orbits the planet, Jupiter bombards Europa’s surface night and day with electrons and other particles, bathing it in high-energy radiation. As the electrons penetrate the moon’s surface, they energize the molecules underneath. According to the new study, published November 9, 2020, in the peer-reviewed journal Nature Astronomy, when those molecules relax, they release energy as visible light, making Europa glow in the dark.

Variations in the glow and the color of the glow itself could reveal information about the composition of ice on Europa’s surface, say the scientists. That’s because different salty compounds react differently to the radiation and emit their own unique glimmer, so color will vary based on the real composition of Europa’s surface.

The new analysis, from scientists at NASA’s Jet Propulsion Laboratory (JPL) in Southern California, details what the glow would look like, and what it could reveal about the composition of ice on Europa’s surface. According to a NASA statement:

Different salty compounds react differently to the radiation and emit their own unique glimmer. To the unaided eye, this glow would look sometimes slightly green, sometimes slightly blue or white and with varying degrees of brightness, depending on what material it is.

Scientists use a spectrometer to separate the light into wavelengths and connect the distinct “signatures,” or spectra, to different compositions of ice. Most observations using a spectrometer on a moon like Europa are taken using reflected sunlight on the moon’s dayside, but these new results illuminate what Europa would look like in the dark. JPL’s Murthy Gudipati, lead author of the study, said in a statement:

We were able to predict that this nightside ice glow could provide additional information on Europa’s surface composition. How that composition varies could give us clues about whether Europa harbors conditions suitable for life.

That’s because Europa holds a massive, global interior ocean that could percolate to the surface through the moon’s thick crust of ice. Scientists have inferred from prior observations that Europa’s surface could be made of a mix of ice and commonly known salts on Earth, such as magnesium sulfate (Epsom salt) and sodium chloride (table salt). The new research shows that incorporating those salts into water ice under Europa-like conditions and blasting it with radiation produces a glow.

That much was not a surprise, said the researchers, because it’s easy to imagine an irradiated surface glowing. Scientists know the shine is caused by energetic electrons penetrating the surface, energizing the molecules underneath. When those molecules relax, they release energy as visible light. But the study researchers didn’t expect to see variations in the glow itself tied to different ice compositions. JPL’s Bryana Henderson, a study co-author, said:

But we never imagined that we would see what we ended up seeing. When we tried new ice compositions, the glow looked different. And we all just stared at it for a while and then said, ‘This is new, right? This is definitely a different glow?’ So we pointed a spectrometer at it, and each type of ice had a different spectrum.

Does Europa glow in the dark? A new @NASAJPL lab experiment finds that the icy moon shines, even on its nightside. This ice glow could provide insights on Europa's composition, giving us clues about whether the moon harbors conditions suitable for life: https://t.co/UuoSN6lNWz pic.twitter.com/9alExylEGp

&mdash NASA Astrobiology: Exploring Life in the Universe (@NASAAstrobio) November 9, 2020

A moon that’s visible in a dark sky may not seem unusual we see our own moon because it reflects sunlight. But Europa’s glow is caused by an entirely different mechanism, the scientists said. Imagine a moon that glows continuously, even on its nightside, the side facing away from the sun. Gudipati said:

If Europa weren’t under this radiation, it would look the way our moon looks to us, dark on the shadowed side. But because it’s bombarded by the radiation from Jupiter, it glows in the dark.

Bottom line: A new study suggests Jupiter’s large moon Europa shines, even on its nightside, thanks to a relentless pummeling of radiation from the planet.

## Hubble spies Jupiter and its icy moon Europa

The Hubble Space Telescope has produced two images of Jupiter: one showing moon Europa and another in wavelengths invisible to the human eye.

Published: October 3, 2020 at 8:16 am

The Hubble Space Telescope has captured a beautiful new image of Jupiter and its moon Europa, taken when the gas giant was 653 million km from Earth.

The new image, captured on 25 August 2020, is giving astronomers a fresh look at the tempestuous planet’s stormy atmosphere, including a new storm that appears to be brewing among the Jovian clouds.

Can you spot the white, elongated storm occurring at mid-northern latitudes on Jupiter’s disc? This single plume popped up on 18 August 2020 and was recorded as moving at 560 km per hour.

See more beautiful Hubble images:

Planetary scientists say this particular storm seems to have more structure behind it than previous storms observed in the region. Trailing it are a few dark clumps, which may be the early beginnings of a longer-lasting ‘spot’ in the northern hemisphere, much like the Great Red Spot that can be seen clearly in the southern hemisphere.

The Great Red Spot is Jupiter’s most striking feature, and one of the objects that makes the gas giant so visually iconic. Telescopic observations of the spot have been recorded since 1930, providing evidence that the storm is shrinking over time. Nevertheless, it currently measures 15,800 km across: large enough to swallow Earth whole!

To the left of Jupiter appears its moon Europa: an icy body thought to have a liquid ocean below its crust. Just like Saturn’s moon Enceladus, the presence of a liquid subsurface ocean makes it a prime target for search for signs of life.

And just like the Cassini mission at Saturn, which studied Enceladus, a new mission called Europa Clipper is primed to launch in the mid 2020s to do just that.

The rainbow-coloured image of Jupiter you can see above is a multiwavelength observation in ultraviolet/visible/near-infrared light also carried out by the Hubble Space Telescope on 25 August 2020.

In the image, the parts of Jupiter’s atmosphere that appear red are at higher altitude (note how the planet’s poles are both red). This is a result of atmospheric particles absorbing ultraviolet light. Blue areas, on the other hand, represent ultraviolet light being reflected off the planet.

This unique view of Jupiter is giving astronomers the chance to look at the gas giant and its mysterious atmospheric features like never before.

Credit: NASA, ESA, A. Simon (Goddard Space Flight Center), and M. H. Wong (University of California, Berkeley) and the OPAL team.

### Image stats

Release date 17 September 2020

Observatory Hubble Space Telescope

Image credit NASA, ESA, A. Simon (Goddard Space Flight Center), and M. H. Wong (University of California, Berkeley) and the OPAL team.

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