By Prasad Ganti

NASA’s Juno spacecraft traveled for five years before reaching Jupiter on July 4, 2016. It will orbit around for 20 months studying Jupiter’s atmosphere before crashing into it. The last spacecraft to visit and study Jupiter was Galileo.

Jupiter, named after the King of Gods in Roman mythology, is the fifth planet from the Sun and the first gas giant. There is supposedly very little core or “land” inside its thick atmosphere. Juno in Roman mythology is Jupiter’s wife. The spacecraft Juno was travelling to meet her husband!

Like any space trajectory, the spacecraft does not travel in straight line from Earth to Jupiter partly because both the planets are moving all the time. The launch platform as well as destination are moving at the same time. A circular trajectory is the most most natural one in space. When launched in 2011, Juno was put into an orbit around the Sun. In 2012, deep space maneuvers, by firing the thrusters, brought it closer to the Earth again. In 2013, it received gravity assist from Earth and was flung towards Jupiter. This maneuver is difficult to imagine but it is like the action of a slingshot. The picture of the trajectory is shown below. Courtesy NASA.

Path of Juno from Earth to Jupiter.

Juno is armed with 3 solar sails on its outward journey. The sails provide power for propulsion as well as the contained electronic instruments. It was also spinning as it sped along. The spinning allows for more stability and orientation. As massive as the planet is, next to the sun, it is the largest body in our solar system. Although it consists mostly of gas, it has an intense gravitational field. Understandably so because huge masses have surrounding gravitational fields of more intensity. The gravitational field is enough to support a structure of about seventy moons, the most significant and largest of which are the Galileans – Ganymede, Europa, Io, and Callisto. Along with its mighty gravity, it also has a very strong magnetic field presumably due to the metallic hydrogen it harbors. Metallic hydrogen is the liquid form of hydrogen which exists under the intense pressure of Jupiter’s atmosphere. It does not exist anywhere on Earth, but has been produced only in laboratories under extreme pressure and temperature for a tiny fraction of a second.

Juno’s mission is to map out Jupiter’s gravitational and magnetic fields. Additionally, it will try to find more about the interior structure of the gas giant. Its findings might reveal if the planet has a rocky core or none at all. There is a great red spot on the planet which is supposed to be a storm raging for more than a thousand years. Juno will try to ascertain its depth.

All the electronic equipment aboard the spacecraft is enclosed in a Titanium vault to shield it from the intense radiation. In addition to the data from the sensors, the JunoCam will also send back close up pictures of the planet.

The famous science fiction writer Arthur C. Clarke has speculated that there is an Earth sized diamond in the middle of Jupiter’s core. Is it really there ? Is it just metallic hydrogen ? Well, hopefully, Juno will provide the answers !