Ganymede Jupiter’s biggest moons were discovered 411 years ago by Galileo. Peering through his newly-improved 20-power homemade telescope at the planet Jupiter on Jan. 7, 1610,
Italian astronomer Galileo Galilei noticed three other points of light near the planet, at first believing them to be distant stars. Observing them over several nights, he noted that they appeared to move in the wrong direction concerning the background stars and they remained in Jupiter’s proximity but changed their positions relative to one another. He later observed a fourth star near the planet with the same unusual behavior. By Jan. 15, Galileo correctly concluded that they were not stars at all but moons orbiting around Jupiter, providing strong evidence for the Copernican theory that most celestial objects did not revolve around the Earth. In March 1610, Galileo published his discoveries of Jupiter’s satellites and other celestial observations in a book titled Siderius Nuncius (The Starry Messenger). As of today, astronomers have identified 79 satellites orbiting Jupiter, but the most known are still Io, Europa, Ganymede, and Callisto. They are fascinating worlds. Some could hide oceans that could hold life.
Nasa claimed that the Juno spacecraft has detected an FM radio signal coming from one of these giant moons. Where did the signal come from how did NASA find it? Something recently happened that caught everyone’s attention: NASA’s Juno spacecraft is still out there wandering space and for the first time since it was launched. It detected an FM radio signal, coming from Jupiter’s moon Ganymede. This is pretty the same kind of signal that we would detect here on Earth. We use this signal almost every day and know it as wi-fi. So did we just pick up an alien radio station broadcast from Ganymede? Is there wifi on Ganymede? To figure that out, we need to know more about this icy alien world. Ganymede is the largest moon in the entire solar system. If it was orbiting the sun, it would be a planet itself, since it is larger than Mercury! Although Ganymede doesn’t have an atmosphere, it's the only known moon to have a powerful magnetosphere, which sometimes produces auroras that are affected by the moon’s underground saltwater oceans. The rocking seen by the auroras gave researchers evidence that the underground oceans on Ganymede are possibly liquid and very salty. Far saltier than the Earth’s oceans. The FM signal that came from Ganymede originated from electrons in electromagnetic fields, a process causing the electrons to whirl and oscillate slower than their spin rate.
The Juno spacecraft detected a 5-second radio burst in late 2020 when the moon crossed a polar region of Jupiter, where the gas giant’s magnetic field interacts with Ganymede. Patrick Wiggins, a NASA Utah ambassador, cautioned it's probably not aliens. “It’s not E.T.,” Wiggins said. “It’s more of a natural function.” The Juno spacecraft was moving across a region of Jupiter where magnetic field lines can connect with the Ganymede moon. That's when Juno picked up the radio source. Juno was sent out to study how Jupiter formed and evolved over time. Juno's primary goal is to reveal the story of Jupiter's formation and evolution. Using long-proven technologies on a spinning spacecraft placed in an elliptical polar orbit, Juno will observe Jupiter's gravity and magnetic fields, atmospheric dynamics and composition, and evolution. It was electrons, not extraterrestrials, responsible for the radio emissions from the moon.
Through a process called cyclotron maser instability, electrons oscillate at a lower rate than they spin which causes them to amplify radio waves rapidly. Though a significant discovery, the orbiting spacecraft was only able to pick up the radio emissions for just five seconds. Juno hurtled at a blinding speed of 111,847 mph. That's fast enough to cross the entire United States coast to coast in just under two minutes. But why are radio signals so important? The researchers are interested in detecting radio emission from planets and other bodies because such information may help scientists decipher what's happening in the same worlds' magnetic fields. Those magnetic fields, in turn, influence conditions on the surface of the planet - Earth's magnetic field protects the atmosphere that makes the world one we can survive, for example. Such magnetic fields can also tell scientists about other qualities of a world, like its structure and history. A planet’s magnetic field emanates from its core and it deflects the charged particles of the stellar wind, protecting the atmosphere from being lost to space. Magnetic fields, born from the cooling of a planet’s interior, could also protect life on the surface from harmful radiation, as the Earth’s magnetic field protects us. It's such an important factor! Low-mass stars are among the most common in the universe. Planets orbiting near such stars are easier for astronomers to target for study because when they transit or pass in front of, their host star, they block a larger fraction of the light than if they transited a more massive star. But because such a star is small and dim, its habitable zone where an orbiting planet gets the heat necessary to maintain life-friendly liquid water on the surface also lies relatively close in. And a planet so close to its star is subject to the star’s powerful gravitational pull, which could cause it to become tidally locked, with the same side forever facing its host star, as the moon is with the Earth.
That same gravitational tug from the star also creates tidally generated heat inside the planet or tidal heating. Tidal heating is responsible for driving the most volcanically active body in our solar system, Jupiter’s moon Io. So could there be life on Ganymede? Well, we know for sure the signal didn’t originate from alien life, it’s also very cold on Ganymede, with temperatures around minus 186 degrees Fahrenheit. However, during one of its flybys, the Galileo spacecraft detected a dense stream of atomic hydrogen escaping from the moon’s very thin atmosphere. This means that there are large amounts of oxygen that are locked up or hovering over its icy surface. Atomic hydrogen is the lightest atom and Ganymede has a weak gravitational field, so the hydrogen escapes, and the atomic oxygen stays behind. Some researchers say that Ganymede could have as much oxygen on its icy surface as the earth has in its atmosphere. So could Ganymede have everything for life to exist in its subsurface oceans? Some scientists think the pressure at the base of any ocean here would be so high that it would turn to ice, but a mission is needed to find out more. Anyway, scientists say extremophile microorganisms capable of in Ganymede's core-mantle Boundary. Which, while not as exciting as finding full-blown intelligent life, would definitely be the biggest finding ever broadcast on Earth.
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