PH 205

Jupiter

Jupiter is the largest planet in our solar system. It is a gas giant planet, and so important to us that we describe all gas giants as Jovian planets. It has an extremely varied atmosphere with complex structure, a large, strong magnetosphere and set of four large moons that comprise something like a miniature solar system. There are many smaller outlying moons as well. We will study Jupiter carefully, then compare and contrast other gas giants in our solar system with it.

Jupiter is made of differentially rotating gas. This means that the gas rotates at different speeds at different radii. Jupiter is about 320 times as massive as Earth, giving it a strong gravitational field that holds onto at least 67 moons, with four notably large inner moons. The Great Red Spot in Jupiter's atmosphere is a storm, much like a hurricane, that has existed for at least 150 years.

This graphic indicates the relative sizes of the planets. Jupiter is considerably larger than any other planet in our Solar system, and dwarfs the terrestrial planets, though it should be noted that we have discovered considerably larger gas giant planets orbiting other stars.

Since Jupiter is not a solid body, it tends to flatten as it rotates, as this graphic indicates. If Jupiter were not rotating, it would be spherical. The force due to gravity would be exactly balanced by pressure. Since Jupiter is rotating, the rotation also works against the gravitational force, producing a polar flattening and equatorial bulge.

Jupiter also exhibits differential rotation. A solid body rotates at a single angular speed, but a liquid or gaseous body need not rotate as a solid. In the case of Jupiter, rotation is slightly faster at the equator than at the poles. The rotation period at the equator is about 90 hours and 50 minutes, whereas the rotation period at the poles is about 90 hours and 56 minutes.

This image of the cloud tops of Jupiter taken by NASA's Voyager 1 spacecraft (with its moon Io in the foreground) shows details of the colored zonal structure of Jupiter's atmosphere. The swirling spots are vortices, much like hurricanes on Earth.

This diagram shows what we believe the structure of Jupiter's atmosphere to be, with its complex organization of various materials. Since different chemicals condense at different temperatures and pressures, they would tend to stratify in Jupiter's atmosphere. Note that the temperature is given as the blue line, decreasing upward until a pressure one tenth that of Earth, and then increasing. It is not clear what causes the temperature to increase upward, one theory is that it is a result of the Great Red Spot.

The largest feature to be seen on Jupiter is the Great Red Spot. We believe it is a very long-lived cyclonic storm, like a hurricane on Earth. On Earth, hurricanes exist because of hot air rising, forming convection currents, on the surface of a rotating planet. Hurricanes gather strength as they form over the ocean, and typically lose strength over land, since the land offers friction to the winds. On Jupiter, there is no solid surface to offer any resistance, so the storms can last much longer. The Great Red Spot has lasted for at lease 150 years, that we have been watching, and possibly much longer.

We think it is possible that the red color of the Great Red Spot can be caused by ammonium hydrosulfide interacting with cosmic rays or UV radiation from the sun. We have clocked the wind speeds at about 400 mph. The structure is about twice the size of Earth.

Jupiter radiates more energy to space than it receives from the Sun. At Jupiter's orbital distance from the Sun, it should have a temperature of about 105 Kelvin at the cloud tops, if it was radiating energy at the same rate that it received energy from the Sun. However, the temperature is measured to be about 125 Kelvin instead. Energy emitted by a planet is proportional to the fourth power of temperature, so a large difference in energy results from a small difference in temperature. We calculate that Jupiter radiates about twice the energy that it receives from the Sun. This energy must be coming from Jupiter itself.

What is the source of this energy? We believe it is leftover heat of formation of the planet still escaping to space.

This schematic of Jupiter's interior is currently our best guess of what lies inside the giant planet. Jupiter is made of mostly hydrogen, the most abundant kind of normal matter in the universe. Underneath the brightly colored cloud bands lies a thick layer of liquid metallic hydrogen. When hydrogen is under a great deal of pressure, the electrons can become unbound from the protons. When this happens, hydrogen can conduct electricity, as the electrons are free to flow. The rotation of this metallic hydrogen layer is believed to give rise to Jupiter's powerful magnetic field.

This is an artist's depiction of the Juno spacecraft, which is currently orbiting Jupiter. Juno orbits Jupiter every 53 days, taking high resolution photographs and gathering other kinds of data on each close approach.

We do not know if a dense core exists at the center of Jupiter or not. NASA’s Juno mission is focused on studying the properties of Jupiter, with the goal of understanding its origin and evolution. Juno will measure the magnetosphere of Jupiter as well as examine material in its atmosphere, with the hope of learning more about the deep interior of Jupiter.

This close-up image of Jupiter's south polar region was taken by the Juno spacecraft, on its fourth pass of the planet. The reasons behind the formations and colors of the swirling clouds is currently unknown. Hopefully, these images and other kinds of data gathered by Juno will help astrophysicists to unravel the mechanisms responsible.

While flying through Jupiter's magnetosphere on August 27, 2016, Juno's Wave sensor recorded radio waves it passed through. This remarkable video offers a glimpse into what Jupiter's magnetic field would sound like, with the radio waves converted to sound waves.

Looking straight down on Jupiter's north pole, we can see auroras impacting the northern region. These auroras are similar to those seen on Earth, created by charged particles entering along the magnetic field lines interacting with charged particles in the planet's atmosphere. The top inset was taken in ultraviolet light. The bright spots are places where electric current flows in along flux tubes that electrically connect Jupiter's moons to the planet.  The bottom inset was taken using infrared light, with the auroras in blue and the underlying clouds shown in red.

This illustration of Jupiter's magnetosphere shows the effect of the solar wind pushing it outward. The magnetosphere is so large that several of Jupiter's moons lie within it. The light from the aurora is created when electrons in the atmosphere are excited and relax to re-emit photons.