Jupiter’s icy moon Europa is considered one of only a few bodies in our solar system that has the potential to host some form of life.
It has a ocean deep beneath a frozen crust, which like Earth’s, may contain salt, and plumes of water vapor have been discovered above the surface.
现在, scientists say the moon may visibly glow green in the dark as high levels of radiation from Jupiter’s powerful magnetic field interact with its moon’s icy surface.
Laboratory simulations found that irradiated ice emits a greenish light in a process called “electron-stimulated luminescence.”
“The night-time ice glow occurring on Europa may be very unique and unlike any other phenomenon in our solar system,” 研究说.
The findings were published in the journal Nature Astronomy on Monday.
An upcoming mission by NASA’s Europa Clipper spacecraft, which is expected to launch later this decade, could observe the glow and map the chemical composition of Europa’s surface by measuring how much ice glow is seen at different wavelengths, the authors of the study said.
A lab simulation shows how Jupiter’s moon Europa might glow in the dark.
Habitable environment?
These observations may also allow scientists to figure out the chemical make-up of the moon’s sub-surface ocean — for example, its salinity — something that Murthy Gudipati, lead of author of the study and a principal scientist at NASA’s Jet Propulsion Laboratory at the California Institute of Technology, said would be “important for potential habitability.”
Europa’s interior could be made of oceans of liquid water that separate the moon’s rocky core and outer ice shell, 根据来自的数据 NASA’s Galileo Mission in the 1990s, said Murthy.
“Imagine a full coconut, with its hard shell outside and then coconut meat (which are similar to Europa’s ice shell) and then inside we have water in the coconut,” he said via email.
“It is thought that this liquid ocean tens of kilometers beneath the ice shell could have (一个) habitable environment.”
The Europa Clipper, named for the streamlined sailing ships of the 1800s, could launch as early as 2023, but a targeted launch has been set for 2025. It is expected to reach Europa after a journey lasting several years.
Europa Clipper will carry cameras and spectrometers to capture images and determine the composition of the moon.
Ice-penetrating radar will measure the thickness of the ice shell covering the ocean, and help search for the subsurface lakes believed to be there — much like those in Antarctica on Earth. A magnetometer can determine the strength and direction of magnetic fields and could help us understand how deep the ocean goes and its salinity.
Understanding the barrage of radiation on Europa is key because the particles could be a source of energy for the basic chemical reactions needed for life.
“Radiation is indeed a form of energy, like sunlight reaching Earth — that is critical for life on Earth,” Murthy said. “Radiation in the form of electrons, protons, and ions with high-energy may also be one of the requirements for Europa’s potential habitability.
“Radiation reaching to the surface breaks the bonds of water molecules, salts, and organics — if present — generating more energy-rich molecules such as, 例如, hydrogen peroxide…which is stable at Europa’s temperature conditions,” 他解释.
“These energy rich materials may get into the oceans over geological time scale (millions of years), which may increase the chances of Europa’s habitability.”
On Europa, which is around the same size as Earth’s moon, temperatures range from as high as about 140 Kelvin (关于 -210 华氏度) at the moon’s equator to as low as about 50 Kelvin (-370 华氏度) in icy patches at the moon’s poles.
