Gas Giants in our Solar System

Jupiter is by far the biggest planet in our solar system. It has over 2½ times the mass of all the other planets combined. Jupiter’s diameter is about 11 times that of Earth. Over 1,300 Earths could fit inside Jupiter, but Jupiter has only 318 times Earth’s mass. Jupiter has the shortest day of any planet; despite its size, it takes only 10 hours to rotate on its axis!

Jupiter is 5.2 times further from the sun than the earth, i.e. 5.2. astronomical units (AU) away. So its surface is a sub-freezing – 108°C (-162°F). Jupiter’s upper atmosphere is about 90% hydrogen and 10% helium. But Jupiter’s interior is 71% hydrogen, 24% helium, and 5% other elements. This is because all other atoms are heavier than hydrogen atoms.

Jupiter is really cold at the surface! But as one goes further into Jupiter, the pressure rises, causing it to get hotter. At Jupiter’s core, the pressure is about 735,000 tons per square inch or 100 million times our atmosphere’s pressure. It is like 160,000 cars stacked on top of your body! The temperature there is about 24,000°C (43,000°F)—about four times hotter than the sun’s surface! At such enormous pressure, hydrogen becomes a metal and conducts electricity. So Jupiter has a very powerful magnetic field, 20,000 times stronger than Earth’s.

Jupiter is so large that it’s the third brightest object in the night sky, after the moon and Venus. However, the planet does not emit its own light, but reflects the sun’s light. Jupiter’s most famous feature is its red spot—a storm that has been going continuously for hundreds of years! The spot is much smaller now than it was in the past—but still bigger than Earth!

In the early 2000s, Jupiter grew a new red spot that formed from several smaller storms. This spot is about the diameter of the earth and is informally called Red Spot Junior!

Jupiter’s moons

Jupiter has four large moons, named Io, Europa, Ganymede, and Callisto. They are called the Galilean satellites, after the astronomer Galileo who discovered them in 1610 with his telescope. Galileo showed that they were orbiting Jupiter as it moved through the night sky. This showed that not everything moved around the earth. This contradicted the science of the day.

Io is about the same size as Earth’s moon. However, it is the most volcanically active body in the solar system. Over 400 volcanoes have been identified on its surface, and at least 150 of them are active. This is evidence that it is relatively young—if it were billions of years old, it would have cooled and become inert long ago.

Callisto is almost a twin for Mercury in both size and appearance. It is the most crater-covered moon in the solar system.

Ganymede is the largest moon in the solar system—even 8% larger than the planet Mercury!

Europa is the smoothest body in the solar system, and it is covered by a layer of ice. It has very few impact craters.

Besides these 4 main moons, there are at least 75 smaller moons and orbiting bodies. But even the smallest Galilean moon, Europa, is about 7,000 times more massive than the largest of the remaining moons.

Saturn’s diameter is about 9 times Earth’s. Over 750 Earths could fit inside Saturn, which has only 95 times Earth’s mass. Saturn’s day is only slightly longer at 10 hours, 39 minutes. Saturn is 9.5 AU from the sun, so is very cold: – 178°C (-288°F).

Jupiter and Saturn are by far the biggest planets in our solar system. They are called gas giants because they are made up of elements that remain gaseous at the temperatures found in outer space. These are two of the most beautiful objects in the sky, and they show us God’s majesty in creation. However, you wouldn’t want to visit them up close!

Saturn is very like Jupiter, both in composition and structure. Saturn’s defining feature is its striking rings, which are easily seen with a small telescope. They might look like one solid ring. However, in reality, Saturn has thousands of rings in seven major groups which orbit at different speeds. They are composed of billions of pieces orbiting the planet together, ranging in size from dust particles to house-sized boulders. The rings are only an average of 20 m thick.

Saturn, like Jupiter, has a banded pattern in its outer atmosphere. But at its north pole, the clouds form a slowly rotating and color-changing hexagon. Each side is longer than Earth’s diameter.

Saturn has 62 moons as well as hundreds of moonlets. The largest moon is Titan, the second-largest moon in the solar system. It is also the only moon with an atmosphere.