The Earth has a magnetosphere. So does Jupiter. But Jupiter's has a million times the volume of ours. As a result, Jupiter slams its moon, Europa, with a steady blast of high-energy radiation. This can't help but have an effect on the satellite, and new research from NASA's Jet Propulsion Laboratory has an idea what that effect is: Europa glows, in shades of green, blue, and white. The moon's night side even glows in the dark. The discovery was made by exploring the behavior of a Europa laboratory model bombarded with radiation.
The research is published in the journal Nature Astronomy.
Europa
Enhanced closeup of the "chaos terrain" that is the icy surface of Europa
Credit: NASA/JPL-Caltech/SETI Institute
Europa is believed to have an ocean of water or slush beneath its chaotically-featured water-ice surface. According to NASA, it's suspected that the moon's ice layer is 10 to 15 miles thick and floats atop an ocean 40 to 100 miles deep. Europa is just a quarter the size of Earth, but its vastness and depth may mean that it has twice as much water as all of our oceans combined.
With water considered to be a prerequisite for life, scientists' interest in Europa is obvious. NASA is sending the radiation-resistant Europa Clipper there to have a look. The spacecraft will conduct 45 flybys at different distances, ranging from 1,675 miles to 16 miles above the ice. The Europa Clipper will carry cameras, spectrometers, ice-penetrating radar, magnetometer, thermal instruments, a device for measuring gravity, and more.
NASA has previously detected what may be vapor plumes extending outward from Europa. If the Europa Clipper confirms their existence, it may be possible in the future to sample the moon's escaping vapors without needing to land or drill through the ice.
ICE-HEART
Artist's impression of Europa against a backdrop of Jupiter
Credit: NASA/JPL-Caltech
The researchers modeled Europa's response to Jupiter's radiation using a special instrument they constructed called the Ice Chamber for Europa's High-Energy Electron and Radiation Environment Testing (ICE-HEART). To blast it with radiation, they took it to the Medical Industrial Radiation Facility at the National Institute of Standards and Technology in Gaithersburg, Maryland, a high-energy electron beam facility.
Expecting that Europa's oceans would contain a mix of water and salts similar to those on Earth, they were investigating the response of various materials to radiation. They began with magnesium sulfate and sodium chloride — essentially Epsom salt and table salt — both believed to be in Europa's ice.
They weren't surprised to see some glowing caused by energetic electrons getting through the moon's ice and energizing molecules beneath it. The glow is generated when the molecules relax after exposure.
However, the variety of colored glows emitted by radiated compounds was a surprise, according to co-author Bryana Henderson. "We never imagined that we would see what we ended up seeing," Henderson said. "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." (Spectrometers divide light into wavelengths that can signify specific compounds.)
"Seeing the sodium chloride brine with a significantly lower level of glow was the 'aha' moment that changed the course of the research," said co-author Fred Bateman.
Both sides now
We can see our own moon because it reflects sunlight. Most spectrometer readings of Europa have thus far been derived from observations of its light-reflecting bright side.
"If Europa weren't under this radiation," said Gudipati, "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."
This means that the moon's dark side also emits light in the form of its glow, so here come the spectrometers. Gudipati said of the research, "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."
He adds, "It's not often that you're in a lab and say, 'We might find this when we get there. 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."
NASA scientists announced its Cassini spacecraft found evidence that the ocean on Enceladus, one of Saturn’s 62 moons, may contain all the ingredients necessary for the emergence of life.
Cassini flew through plumes of gas bursting out from under the ice covering the oceans and detected a clear presence of molecular hydrogen. This might indicate the existence of hydrothermal vents on the moon’s ocean floor. Such vents would be similar to Earth’s hydrothermal vents where some scientists believe life on our planet originated.
In the new findings, described the journal Science, scientists consider the possibility of a chemical reaction called methanogenesis taking place in the moon’s underwater vents. This reaction has been shown to be crucial to the development of microbial life by providing an energy source for the microbes.
The researchers cannot at this point conclusively state if methanogenesis is indeed taking place under Enceladus’s ice. It is also possible that this moon may be too young to have undergone the life-creating process.
“Although we can’t detect life, we’ve found that there’s a food source there for it. It would be like a candy store for microbes,” said the study’s lead author Hunter Waite of the Southwest Research Institute in San Antonio.
Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate in Washington, was also optimistic about the scope of Cassini’s current achievement.
"This is the closest we've come, so far, to identifying a place with some of the ingredients needed for a habitable environment," stated Zurbuchen.
Since 2004, the Cassini spacecraft provided no shortage of discoveries. As its head of imaging science Carolyn Porco explained, Cassini conducted over a 100 more “close flyby maneuvers” than have been done so far in the entire planetary program.
It has given us an unprecedented understanding of Saturn, with stunning new images, insights into its rings, atmosphere and moons.
In 2005, the spacecraft landed the Huygens probe on Titan, Saturn’s largest moon, a historic first for landing human machines in the outer solar system. The probe discovered a wealth of information, including an underground super-salty ocean. The Cassini-Huygens mission was carried out in cooperation between NASA, the European Space Agency and the Italian Space Agency.
Here’s a film made by compiling imaging data from Cassini and the probe’s instruments as it descended towards Titan:
Cassini also came amazingly close to Jupiter, providing us with the best photos we have of the gas giant.
Composite photo of Jupiter, comprised of images taken by Cassini on December 29, 2000. Credit: NASA.
The spacecraft will be decommissioned on September 15, 2017 by being plunged to burn in Saturn’s atmosphere. The reason for just a drastic demise lies in the fear that Cassini will soon run out of fuel and crash into one of Saturn’s moons, the ones we now think may contain life. It’s safer for it to burn up on entry than possibly contaminate the moons.
On its way down, the spacecraft will transmit more data and images. These will include new maps of Saturn’s magnetic and gravity fields, and details on the composition of the planet’s rings.
"It’s inspiring, adventurous and romantic — a fitting end to this thrilling story of discovery," wrote NASA.
Watch this beautiful new film from NASA on Cassini’s final journey:
Notably, another NASA team just published findings on a different ocean world that might have some form of life. Their paper on observations from the Hubble Space Telescope program showed new evidence of water vapor plumes found on Jupiter’s moon Europa. In fact, they think they spotted a huge 62-mile-high plume over Europa’s equator, in the same place a plume candidate was spotted in 2014.
These warm plumes are thought to be potential hosts for life. Considering that Europa is billions of years older than Enceladus, the chances for life to have emerged there could actually be greater.
Europa. Credit: NASA
As always, Bill Nye is on standby to explain the workings of the world and universe around us. The widely accepted theory on how Earth’s moon was created is known as the Giant Impact Hypothesisis. It states that a very young proto-Earth was struck by an asteroid, and in that collision both Earth and the debris that chipped off it became molten. They both cooled off, and now we have a moon; nicely spherical (although not perfectly) and solid, in orbit around us.
So why don’t gas giants have gas moons? The simple answer: gravity. When Jupiter or Saturn have undergone similar collisions or events that resulted in a fragment being spun off into their orbits, those new moons were too small to sustain themselves in a gaseous state. Gravity pulled the gas down until it formed a solid sphere. A gas giant, on the other hand, stays gaseous because of its size; there is so much heat generated from its spin that it cannot cool down into a solid state. Jupiter, for example, has 67 known moons and even the bigger ones like Io, Callisto, Europa and Ganymede, have cooled off – they're non-gaseous, unlike Jupiter itself.
Much can be learned after we know the state of moons; we now know that Europa has twice as much seawater as Earth, but that the water is under a crust of ice. One day, we may find life in those oceans – they’ve been around for 4.5 billion years, so it’s likely Europanians may be living there, says Nye.
Bill Nye's most recent book is Unstoppable: Harnessing Science to Change the World.
