Earth
Discover
The third planet from the sun, Earth is a waterworld, with two-thirds of the
planet covered by ocean. It’s the only world known to harbor life. Earth’s
atmosphere is rich in life-sustaining nitrogen and oxygen. Earth's surface
rotates about its axis at 1,532 feet per second (467 meters per second) —
slightly more than 1,000 mph (1,600 kph) — at the equator. The planet zips
around the sun at more than 18 miles per second (29 km per second).
- Diameter: 7,926 miles (12,760 km)
- Orbit: 365.24 days
- Day: 23 hours, 56 minutes
Orbital characteristics
Earth spins on an imaginary line called an axis that runs from the North Pole to
the South Pole, while also orbiting the sun. It takes Earth 23.439 hours to
complete a rotation on its axis, and roughly 365.26 days to complete an orbit
around the sun.
Earth's axis of rotation is tilted in relation to the ecliptic plane, an
imaginary surface through Earth's orbit around the sun. This means the northern
and southern hemispheres will sometimes point toward or away from the sun
depending on the time of year, varying the amount of light they receive and
causing the seasons.
Discover
The fourth planet from the sun, is a cold, dusty place. The dust, an iron oxide,
gives the planet its reddish cast. Mars shares similarities with Earth: It is
rocky, has mountains and valleys, and storm systems ranging from localized
tornado-like dust devils to planet-engulfing dust storms. It snows on Mars. And
Mars harbors water ice. Scientists think it was once wet and warm, though today
it’s cold and desert-like.
Mars' atmosphere is too thin for liquid water to exist on the surface for any
length of time. Scientists think ancient Mars would have had the conditions to
support life, and there is hope that signs of past life — possibly even present
biology — may exist on the Red Planet.
- Diameter: 4,217 miles (6,787 km)
- Orbit: 687 Earth days
- Day: Just more than one Earth day (24 hours, 37 minutes)
Orbital characteristics
The axis of Mars, like Earth's, is tilted with relation to the sun. This means
that like Earth, the amount of sunlight falling on certain parts of the planet
can vary widely during the year, giving Mars seasons.
However, the seasons that Mars experiences are more extreme than Earth's because
the red planet's elliptical, oval-shaped orbit around the sun is more elongated
than that of any of the other major planets. When Mars is closest to the sun,
its southern hemisphere is tilted toward the sun, giving it a short, very hot
summer, while the northern hemisphere experiences a short, cold winter. When
Mars is farthest from the sun, the northern hemisphere is tilted toward the sun,
giving it a long, mild summer, while the southern hemisphere experiences a long,
cold winter.
The tilt of Mars axis swings wildly over time because it is not stabilized by a
large moon, such as on Earth. This led to different climates on its surface
through its history. A 2017 study suggests that the changing tilt also
influenced the release of methane into Mars' atmosphere, causing temporary
warming periods that allowed water to flow.
Discover
The fifth planet from the sun, Jupiter is huge and is the most massive planet in
our solar system. It’s a mostly gaseous world, mostly hydrogen and helium. Its
swirling clouds are colorful due to different types of trace gases. A big
feature is the Great Red Spot, a giant storm which has raged for hundreds of
years. Jupiter has a strong magnetic field, and with dozens of moons, it looks a
bit like a miniature solar system.
- 86,881 miles (139,822 km)
- Orbit: 11.9 Earth years
- Day: 9.8 Earth hours
Physical characteristics
Jupiter is the most massive planet in our solar system, more than twice as
massive as all the other planets combined, and had it been about 80 times more
massive, it would have actually become a star instead of a planet. Its
atmosphere resembles that of the sun, made up mostly of hydrogen and helium, and
with four large moons and many smaller moons in orbit around it, Jupiter by
itself forms a kind of miniature solar system. All told, the immense volume of
Jupiter could hold more than 1,300 Earths.
Discover
The sixth planet from the sun is known most for its rings. When Galileo Galilei
first studied Saturn in the early 1600s, he thought it was an object with three
parts. Not knowing he was seeing a planet with rings, the stumped astronomer
entered a small drawing — a symbol with one large circle and two smaller ones —
in his notebook, as a noun in a sentence describing his discovery. More than 40
years later, Christiaan Huygens proposed that they were rings. The rings are
made of ice and rock. Scientists are not yet sure how they formed. The gaseous
planet is mostly hydrogen and helium. It has numerous moons.
- Diameter: 74,900 miles (120,500 km)
- Orbit: 29.5 Earth years
- Day: About 10.5 Earth hours
Physical characteristics Saturn is a gas giant made up mostly of
hydrogen and helium. Saturn is big enough to hold more than 760 Earths, and is
more massive than any other planet except Jupiter, roughly 95 times Earth's
mass. However, Saturn has the lowest density of all the planets, and is the only
one less dense than water — if there were a bathtub big enough to hold it,
Saturn would float.
The yellow and gold bands seen in Saturn's atmosphere are the result of
super-fast winds in the upper atmosphere, which can reach up to 1,100 mph (1,800
km/h) around its equator, combined with heat rising from the planet's interior.
Saturn spins faster than any other planet except Jupiter, completing a rotation
roughly every 10-and-a-half hours. This rapid spinning causes Saturn to bulge at
its equator and flatten at its poles — the planet is 8,000 miles (13,000
kilometers) wider at its equator than between the poles.
