Chapter 5 - 5

05 Astronomy

Jovian Planets

Jovian planets, or “gas giants,” are distant planets that share similar compositions.

These planets include Jupiter, Saturn, Uranus, and Neptune.

Jovian planets are different from the other planets of the solar system and form their own subcategory.

However, each one possesses unique qualities relating to composition and formation.

The four planets are placed into the category of Jovian planets due to their composition.

Unlike the planets that make up the inner solar system such as Mercury, Venus, Earth, and Mars (also known as terrestrial planets) that have solid surfaces, Jovian planets consist mainly of the gases hydrogen and helium, with traces of methane, water, and ammonia.

Since the outer solar system is far from the sun, it is a cold region where ice is plentiful.

Its low temperatures affected the formation of the Jovian planets.

First, planetesimals formed from tightly packed flakes of ice as well as metal and rock slivers.

The planetesimals expanded as ice flakes accumulated, forming the cores of Jupiter, Saturn, Uranus, and Neptune.

Since these cores were large enough to have their own gravitational pull (equal to at least fifteen times the mass of the Earth), they were able to attract hydrogen and helium gas from around them in a process called nebular capture, leading to the formation of a denser atmosphere.

The cores heated up as the particles falling inward generated more heat.

The heavier elements sank to the core, which in turn became denser.

Thus, the planets, dense with gases, formed.

Jupiter, which is five angstrom units a.u. from the sun, is chemically and compositionally different from the other Jovian planets.

Jupiter has a high proportion of hydrogen and helium in its upper atmosphere.

Its outer layer is made of molecular hydrogen covering a layer of metallic liquid hydrogen, which then surrounds a denser solid core.

The layer of metallic hydrogen underneath the layer of molecular hydrogen (which can be seen from afar as a layer of tumultuous clouds) makes up most of Jupiter and is responsible for the planet’s powerful magnetic field.

Its interior is extremely hot, averaging at around 20,000 Kelvin (K).

Jupiter’s surface is rendered different shades of reds, yellows, oranges, and browns due to sulfur reactions.

Saturn, which is twice as far from the sun as Jupiter, also has a unique composition.

In contrast to the vivid red of Jupiter, Saturn can be described as a dull yellow.

This color is due to the presence of ammonia in the atmosphere.

The ammonia covers the atmosphere as either a solid or a liquid.

Saturn’s atmosphere is made up of about ninety-four percent hydrogen, with very small amounts of helium, methane, and ammonia.

The lower levels of Saturn’s atmosphere contain many of the same red colors as Jupiter.

However, due to the dense covering of ammonia clouds, this layer is rendered invisible.

Uranus, which is nineteen a.u. away from the sun, is relatively featureless.

The planet lacks cloud bands and forceful weather patterns, instead appearing as a solid bluish-green color.

Uranus is considered to be an “ice giant,” since it consists mostly of ice and rock, whereas Jupiter and Saturn are made up primarily of gases.

While all of the Jovian planets started out with red and yellow colorations due to the initial domination of ammonium hydrosulfide, Uranus later developed its blue color when its temperatures dropped below seventy K during its process of formation.

This caused ammonia gas to freeze and eventually leave the atmosphere.

Methane become more dominant over time.

Though its outer layer consists mostly of hydrogen, the amount of methane (also present) gives Uranus its blue color.

Neptune, thirty a.u. away, is also considered an “ice giant”.

Neptune has a similar blue color to Uranus, though the blue is much brighter.

The atmosphere of Neptune contains a higher concentration of methane gas than Uranus.

Thus, due to the higher concentration, Neptune appears bluer than Uranus.

Atmospheric features, such as clouds, are more easily seen on Neptune than on Uranus, presumably due to the planet’s heat allowing the clouds to rise higher in the atmosphere.

The weather patterns on Neptune, which are characterized by winds in excess of 1,500 kilometers per hour, lead to the frequent appearance of colored bands.

Winds more easily move storm systems, which tend to wrap around the planet.