Some science behind the scenes

Jupiter

Jupiter, the physical planet as opposed to the symbolic planet, is the fifth planet from the Sun and the largest planet within the Solar System. It is two and a half times as massive as all of the other planets in our Solar System combined.

Jupiter, along with Saturn, Uranus and Neptune, is classified as a gas giant. Together, these four planets are sometimes referred to as the Jovian planets, where Jovian is the adjectival form of Jupiter.

The planet Jupiter is primarily composed of hydrogen with a small proportion of helium; it may also have a rocky core of heavier elements under high pressure. Because of its rapid rotation, Jupiter's shape is that of an oblate spheroid (it possesses a slight but noticeable bulge around the equator). The outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence and storms along their interacting boundaries. A prominent result is the Great Red Spot, a giant storm that is known to have existed since at least the seventeenth century.

Surrounding the planet is a faint planetary ring system and a powerful magnetosphere. There are also at least 63 moons, including the four large moons called the Galilean moons that were first discovered by Galileo Galilei in 1610. Ganymede, the largest of these moons, has a diameter greater than that of the planet Mercury.

Jovian radio storms, first noticed in 1955, are beamed to Earth by radio lasers near Jupiter's magnetic poles. Lasers on Earth, in labs and classrooms, are man-made from wires, crystals and other electronics. Jupiter's radio lasers are natural, made of plasmas (ionized gases) and magnetic fields. High speed streams of magnetized plasma flowing downward into Jupiter's polar regions emit radio waves--a process known as the "cyclotron maser mechanism." When this mechanism is operating, Jupiter can outshine even the sun as a radio source.

The lasers are powered, in part, by Jupiter's moon Io. Volcanoes on Io hurl electrically conducting gas into Jupiter's magnetosphere (the region of space controlled by Jupiter's magnetic field), where it collects in a doughnut-shaped region, the "Io torus." As Io travels around Jupiter, it ploughs through the torus and makes waves, like the wake of a boat. These "Alfven waves," guided by magnetic forces, carry about 40 trillion watts of power to Jupiter's polar regions--more than enough to fuel the radio storms.

Jupiter's Io-controlled radio emissions don't go in all directions. The radio laser beam has the shape of a wide hollow cone. If Earth is inside the cone, we hear nothing. If Earth is outside the cone, we also hear nothing. But if Earth is in the narrow edge of the cone, we can hear some strong radio bursts.  Jupiter rotates once every 10 hours and the cone rotates with it like a lighthouse beam. To catch a radio storm you have to know when Earth will be aligned with the edge of the cone and when Io is in the right position to pour electrical energy into the storm zone.

Professional astronomers study these storms because they reveal a lot about Jupiter--especially its rotation and magnetism. Jupiter's cone-shaped radio beam is attached to the planet's magnetic field, which emerges from deep inside Jupiter. By tracking the radio beam as it turns, astronomers have managed to measure the rotation rate of the planet's hidden interior with a precision of milliseconds.

Jupiter's magnetosphere is huge. It's about 10 times wider than the sun, and its tail, stretched out by the solar wind, extends far beyond Saturn. One day, astronomers expect, this vast magnetosphere is going to flip. The Sun's magnetic field reverses polarity every 11 years; Earth's magnetic field flips, too, every 300,000 years on average. This seems to be normal behaviour for magnetic dynamos in stars and planets. When will Jupiter's field flip?

Radio listeners might be the first to know. When the magnetic field begins to change, so will Jupiter's radio beam. Earth will enter the cone at unexpected times, surprising listeners with unscheduled storms. And, maybe, the usual pecks and whale calls will turn into something new--barks and howls?--as the vast magnetic field rearranges itself.

“Listening online is not the only way to tune into Jupiter. NASA also supports an education program for kids (young and old) called Radio JOVE. Join, and you can buy a radio telescope kit, build your own observatory, and start listening from your own back yard or school yard.
Peck-peck. Pop. Swoosh. This is too much fun for professionals alone”.

Observations

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