GAS GIANTS

Introduction:

Each time you look up to the sky and see a star you are looking at a sun in another galaxy. If you were on another planet looking back at our solar system, you would see our sun as a star.

It’s believed that every sun has planets orbiting it. Our Milky Way galaxy has more planets than it has stars. In our solar system we have eight planets: Mercury, Venus, Earth, and Mars are the inner rocky planets.

Jupiter and Saturn are the outer gas giants. Uranus and Neptune are the outer ice giants. In recent years, astronomers have designed a new class called the “dwarf planets.”

These are smaller worlds, not quite big enough to be considered a standard planet, and include Pluto.

To qualify as a gas giant planet it must be of a larger size and made up of mostly gases, such as helium and hydrogen, and have a small rocky core.

In our solar system, our four gas giants are also called “Jovian planets,” named after Jupiter as they live in the outer orbits of the solar system.

Gas Giant Statistics:

Jupiter:

• Distance from Sun: 483.8 million mi
• Rings: 4
• Radius: 43,441 mi
• Polar Diameter: 133,709 km
• Orbital period: 12 years
• Mass: 1.90 × 10^27 kg (318 Earths)
• Length of day: 0d 9h 56m
• Surface area: 23.71 billion mi²
• Effective Temperature: -148 °C
• Moons: (79, including (Io, Europa, Ganymede & Callisto)
• First Recorded: 7th-8th Century BCE by Babylonian astronomers

Saturn:

• Distance from Sun: 890.8 million mi
• Rings: (30 or more – in 7 groups)
• Radius: 36,184 mi
• Polar Diameter: 108,728 km
• Orbital period: 29 years
• Mass: 5.68 × 10^26 kg (95 Earths)
• Length of day: 0d 10h 42m
• Surface area: 16.49 billion mi²
• Moons: (62 including Titan, Enceladus, Iapetus & Rhea)
• First Recorded: 8th Century BCE by the Assyrians

Uranus:

• Distance from Sun: 1.784 billion mi
• Rings: 13
• Radius: 15,759 mi
• Polar Diameter: 49,946 km
• Orbital period: 84 years
• Mass: 8.68 × 10^25 kg (15 Earths)
• Effective Temperature: -216 °C
• Moons: (27, including Miranda, Titania, Ariel, Umbriel & Oberon)
• Date of Discovery: March 13, 1781 by William Herschel

Neptune:

• Distance from Sun: 2.793 billion mi
• Rings: 5
• Radius: 15,299 mi
• Polar Diameter: 48,682 km
• Orbital period: 165 years
• Mass: 1.024 × 10^26 kg (17.15 M⊕)
• Moons: (14, including Triton)
• Date of Discovery: September 23, 1846 by Urbain Le Verrier & Johann Galle

History of the Names:

We have four gas giants in our solar system: Jupiter, Saturn, Uranus, and Neptune.

Jupiter is the fifth planet from the Sun and is the largest planet in our Solar System. It was named after the roman king of the gods and the name fits its size.

Saturn is the sixth planet and was named after the Roman father of the god Jupiter, also the god of agriculture. Uranus is the seventh planet and is associated with the Roman god Caelus.

In Ancient Greek literature, Uranus or Father Sky was the son and husband of Gaia, Mother Earth. Neptune is the eighth planet and was named after the Roman god of the sea because it has such a beautiful color of blue.

Formation:

Using NASA’s Spitzer Space Telescope, astronomers have located evidence that showed that the gas giants may have formed within the first 10 million years of a sun-like star’s life.

They came to this conclusion when they were searching for gas traces around 15 different sun-like stars. They found that a majority ranged in age from 3-30 million years.

The Spitzer Space Telescope’s Infrared Spectrometer instrument allowed the scientists to search through the inner regions of these stars that had relatively warm gas.

In our solar system this area might be comparable to the zone between Jupiter and Earth. The astronomers also searched for cooler gases in these system’s outer reasons using ground-based radio telescopes.

In our solar system it’s believed that they may have finally settled into their current configuration around 4.5 billion years ago.

Scientists believe that planets such as Jupiter and Saturn were originally formed as icy, rocky planets that are similar to the terrestrial planets.

Their core size allowed them to capture helium and hydrogen from the gas clouds before the sun blasted most of it away.

The smaller sized Neptune and Uranus have greater orbits and it was more difficult for them to collect the vast amounts of helium and hydrogen efficiently.

Structure and Surface:

The gas and ice giant planets are all located in the outer perimeters of our solar system. Since they are so far out they take longer to complete their orbit around the sun.

Our terrestrial planets may be higher in density that the gas giants, but unlike the name, the gas giants aren’t completely made up of gas. Jupiter and Saturn have layers of molecular hydrogen and liquid metallic hydrogen under their atmospheres.

The liquid metallic hydrogen layers also conduct electricity. Neptune has a rocky core with a mantle of water-ammonia that overlays it. Uranus has an icy layer around the solid rock core and that is surrounded by its atmosphere of gas.

As scientists continue to study other solar systems, they are finding that a majority of the larger gas giants are closer to their sun than ours are.

These gas giant exoplanets are called “hot Jupiters, Giant Neptunes, or Super Jupiters,” and it’s thought that our gas giants may have originated close to our sun and over time, migrated to the outer areas of our solar system.

The cores of the gas giants are under very high pressures that crush the core to create the energy that keeps their temperatures so hot. The Kepler Space Telescope has allowed scientists to discover gas giants around over one thousand stars.

Scientists refer to Uranus and Neptune as “ice giants.” These are defined as planets that have at least ten times the Earth’s mass and have a higher percentage of the “ices” of volatile elements heavier than helium and hydrogen.

Astronomers are continuing to study other exoplanets and believe some of them could be ice giants.

Atmosphere. Magnetosphere, and Moon Status:

Jupiter’s atmosphere is difficult to define, mainly because it is a gaseous outer zone that transitions into the planet’s liquid layer. Scientists have designated that the atmospheric pressure on Jupiter’s “surface” is equal to 10 times that of the Earth at sea level.

The atmosphere is around 90% hydrogen and 10% helium, which is almost the same as that of the Sun. Due to this fact, it is believed that if Jupiter had grown just a little bit more it could have been a star

The atmosphere of Saturn is made up of around 96% hydrogen, 4% helium, and trace amounts of acetylene, ethane, ammonia, methane, and phosphine. Saturn has a layer of atmosphere that has up to 1,800 km wind speeds.

These are considered to be some of the fastest speeds in the Solar System. While it isn’t visible, Saturn does have a horizontally banded cloud pattern that are wider in the equator than even those found on Jupiter’s equator.

They were unknown until the 1970’s Voyager missions. The clouds on Saturn appear as faint jet streams, striped and storms and these have an array of colors including shades of brown, yellow, and grey.

Uranus has a blue-green color from all of the methane gas in its atmosphere. When sunlight passes through the atmosphere it reflects light back through the top of the clouds. Methane gas absorbs the red factors in light, leaving the blue-green shade

Very similar to the planet Uranus, Neptune’s upper atmosphere is made up of mostly hydrogen (80%), helium (19%), and trace amounts of the methane that gives it the blue coloring.

Neptune has a much deeper shade of blue that makes it different than Uranus in atmospheric composition.

The atmosphere of both Uranus and Neptune contain more heavier elements such as ammonia and methane

Jupiter has a powerful magnetic field that balloons 600,000 to 2 million mi/1-3 million km toward the sun.

This is 7-21 times the diameter of Jupiter itself and the field tapers into a tadpole-shaped tail that extends out behind the planet more than 600 million mi/1 billion km.

This extension goes as far as the orbit of Saturn. The intense magnetic field of Jupiter is 16-54 times as powerful as the magnetic field of Earth and rotates with the planet, picking up any particles that have an electric charge.

The magnetic field traps swarms of charged particles near the planet and then speeds them up to extremely high energies, creating high intensity radiation that bombards the innermost moons.

It’s this radiation that can cause a lot of damage to any spacecraft and why much of the exploration of Jupiter is often done from a distance. The magnetic field does create some of the most beautiful aurorae at its poles.

Although Saturn’s magnetic field is smaller than Jupiter’s, it’s still 578 times more powerful than our Earth’s. Saturn and its rings as well as a lot of its satellites all exist within its enormous magnetosphere.

Saturn’s magnetosphere is in the region of space where electrically charged particles are influenced less by solar wind and instead, controlled by Saturn’s magnetic field.

Magnetic fields are usually aligned with the rotation of the planet, but not so on Uranus. It has an irregular magnetosphere which is tipped over on an axis of almost 60 degrees from the axis of rotation of the planet.

Due to the lopsided magnetic field, the auroras are also not lined up with the poles, like they are on Earth, Jupiter, and Saturn.

The tail of Uranus’ magnetosphere extends into space for millions of miles and its magnetic field lines are twisted due to Uranus’ sideways rotation so that it’s shaped like a corkscrew.

A 1989 discovery of an oval-shaped storm in the southern hemisphere of Neptune was named its “Great Dark Spot.”

This spot is big enough to hold the entire Earth, and while this one disappeared, others have shown up on various areas of the planet.

Neptune’s magnetic field main axis is tipped to the side by around 47 degrees as compared to Neptune’s planetary rotation axis.

Both Neptune and Uranus have magnetic axis that are tilted and the tilt causes wild variations as the planet rotates.

Neptune’s magnetic field is around 27 time stronger than that of Earth.

The gas giants have dozens of moons and due to the matched rotation of the parent planet, most are thought to have been formed at the same time as the parent planet.

However, there are some moons that rotate in the opposite direction and these are believed to have been external bodies that were pulled in by the parent planet’s gravity

The gas giants in our Solar System all have some sort of ring system. The rings are made up of a number of elements including material chunks, dust, and ice in the outer areas of the Solar System.

The planet Saturn has the largest ring system in our Solar System and at least one asteroid is believed to have a small ring.

Could Life Exist?

None of the gas giants have an actual surface and the temperatures and pressures are so great that it is believed that life as we know it couldn’t survive, adapt, and thrive.

Interesting Information:

Space Visits:

Jupiter has been studied for many years, with the first observations detailed in 1610 by Galileo Galilei. Since then, we have sent a number of spacecraft, probes, and orbiters to take detailed images and collect data from Jupiter.

In the 1970’s we sent Pioneer 10 and 11 as well as Voyager 1 and 2 for flybys of Jupiter. The Galileo spacecraft orbited the gas giant and sent a probe into the atmosphere.

When Cassini was heading to Saturn it took an array of images of Jupiter, and New Horizon did the same as it headed to Pluto and the Kuiper Belt. In 2016 NASA’s June spacecraft arrived in the Jovian system to study the gas giant in orbit.

So far, there have been four robotic spacecraft that have visited Saturn. The first look was NASA’s Pioneer 11 in 1979. Then in 1980 and 1981, NASA sent Voyager 1 and Voyager 2 for flybys.

Each new trip exposed wonderful details about the ringed gas giant, however, it wasn’t until 2004 with the international Cassini mission that we learned so much more.

Cassini remained in orbit for 13 years, studying Saturn. Cassini’s last mission was to plunge it into the atmosphere of Saturn in 2017 to learn as much as possible.

Cassini had also carried the Huygens probe that had previously landed in 2005 on Saturn’s moon Titan.

There has been only one spacecraft that visited near Uranus. NASA’s Voyager 2 took 9 years and traveled 1.8 billion mi/3 billion km, gathering important information about our solar system.

It flew by Uranus, spending only six hours and collected much of the data that we know about the planet. Almost everything else that we have learned about Uranus has been thanks to the Hubble Space Telescope observations.

In 1989, NASA’s Voyager 2 spacecraft studied Neptune up close. This was over 140 years after the predictions made by Le Verrier about Neptune.

Voyager 2 remains the first-and-only spacecraft to study Neptune, and it sent back an incredible volume of information and data about the planet and its moons.

Voyager 2 also confirmed that the ice giant had faint rings like other gas giant planets. Since that time, scientists have relied on the Hubble Space Telescope for additional information about Neptune.

Facts about the Gas Giants:

• Gas giants are also called “Jovian planets,” named after Jupiter
• To be considered a gas giant, the planet has to be made up of mostly gas, be located in the outer area of the solar system, and have a mass that is ten times that of Earth.
• Scientists refer to the atmospheres of Saturn and Jupiter as being more “polluted” because they have larger percentages of heavy metals such as methane and ammonia.
• The gas giant planets have so many moons that it’s believed that the moons were originally independent travelers that got trapped by each gas giant’s gravity.
• If Jupiter had been a bit larger it could have become the second star in our solar system.

Pop Culture:

Jupiter:

Jupiter has made a presence in many television shows, movies, comics, and video games. In the science fiction “Jupiter Ascending” it was the main destination.

Jupiter’s moons have also been noted in “Cloud Atlas, Futurama, Power Rangers, and Halo.”

You might remember “Men in Black” when Will Smith, playing Agent J, comments that he thought his teacher was from Venus and Tommy Lee Jones, playing Agent K, corrects him to say that she was really from one of Jupiter’s Moons.

In the movie “2010: The Year we Make Contact,” Jupiter was ignited to become the second sun in our solar system and its moon Io was to be left alone to allow life to progress.

Saturn:

Saturn has played a role in many science fiction stories, television, movies, comics, and video games.

The planet’s usual rings have made it an icon for space travel. Some of the pop culture references include: “Cthulhu Mythos, WALL-E, 2001: A Space Odyssey, Star Trek, Dead Space 2, and Final Fantasy VII.

Tim Burton created the movie “Beetlejuice” where a fictional Saturn is home to giant sandworms, and the 2014 movie “Interstellar,” had a wormhole near Saturn that allowed astronauts to travel to another galaxy.

Uranus:

There is no getting around the “butt” of so many jokes about this planet, however, it’s also been the focus of quite a few science fiction stores, television shows, and games, including “Doctor Who” and the video game “Mass Effect.”

Neptune:

Neptune has been a frequent focus for quite a few science fiction and pop culture themes. The “Event Horizon” was a sci-fi/horror film in 1997 and Neptune was the backdrop for the storyline.

The animated series “Futurama” had Robot Santa Claus with a home based in the north pole of Neptune. The “Sleep No More” episode of Doctor Who was set on a space station that orbited around Neptune.

Star Trek: Enterprise had the episode “Broken Bow” where fans leaned that at the speed of warp 4.5 it would be possible to fly from Earth to Neptune and back in only six minutes.

https://www.space.com/30372-gas-giants.html
https://solarsystem.nasa.gov/resources/677/gas-giant-interiors-2003/
https://exoplanets.nasa.gov/resources/66/gas-giants-form-quickly/
https://solarsystem.nasa.gov/planets/overview/