Section 5 EO C440.03 – DISCUSS CHARACTERISTICS OF THE PLANETS IN THE SOLAR SYSTEM

The planet Mercury, named for the Roman messenger god, is the closest planet to the sun. It is the smallest planet and a cratered wasteland. Since it is so close to the sun it means the planet is completely at the mercy of solar radiation, solar flares, and other solar weather phenomena. The planet is also battered by the many asteroids that float through space. The sun's gravitational pull means that these free floating bodies of rock accelerate towards the sun. Depending on Mercury's position in orbit, these asteroids may impact its surface. There are craters on Mercury that are 600 km wide. Our knowledge of this planet is still incomplete. Only one man-made satellite has ever passed by Mercury, and it was able to collect information about only a small portion of the planet's surface.

Mean Distance From the Sun

Mercury is the closest planet to the sun. The range varies from 46 million to 69.8 million km. The mean distance is 57.9 million km.

Mercury's diameter is a mere 4 879 km. The planet's diameter is only 0.383 times that of Earth.

Mercury is the smallest planet in our solar system. Its mass is 0.0553 times the mass of Earth.

Despite the quick pace that the planet travels around the sun, Mercury does not rotate around its own axis very quickly. It takes 58.65 days for the planet to rotate around its axis, or two-thirds of a Mercurian year.

The axis of Mercury sits at an angle of 0.01 degrees relative to the sun's axis.

Orbit Characteristics

Mercury has what is known as an eccentric orbit. This means that the distance the planet is from the sun varies throughout its revolution around the sun. The actual shape that the planet would travel around the sun would be an ellipse. This can be seen in the extreme range in the planet's distance from the sun. Mercury travels around the sun once every 88 days. This means that the Mercurian year is 88 days long. Mercury's synodic period is 115.9 days.

Synodic period. The time it takes for a planet to return to a specific spot in the night sky as observed from Earth.

Mercury has an average orbital velocity of 47.9 km / s. This means that the planet travels in its orbit around the sun at an average speed of 47.9 km / s or 172 440 km / h.

Travelling from the sun past Mercury, the next planet is Venus. Named for the Roman goddess of love and beauty, Venus is constantly cloaked in cloud. This permanent cover means that scientists know very little about the surface of the planet. Observed from Earth, Venus is the brightest planet in the night sky. The Space Age has greatly enhanced our understanding of this planet. Prior to the 1960s, it was thought that Venus was an oceanic planet equivalent in vegetation to Earth during pre-historic periods. Since the 1960s, several satellites have been sent to Venus or on a path near Venus. These satellites have included Mariner 2 and 10, and the Russian Venera 7, 9, and 13 landings.

Mean Distance From the Sun

Venus is the second closest planet to the sun at a mean distance of 108.2 million km. The distance can range from 107.5 million to 108.9 million km.

Venus is very similar in size to Earth. Many scientists refer to Venus and Earth as near-twins. The diameter of the planet at the equator is 12 104 km, approximately 0.949 times that of Earth.

The mass of Venus is approximately 0.815 times the mass of Earth.

Venus is unique in that it is the only planet in our solar system which rotates east to west, or clockwise. All other planets, including Earth, rotate west to east or counter-clockwise. It takes just over 243 days for Venus to rotate around its axis. It should be noted that this is longer than the Venusian year.

The axis of Venus sits at an angle of 177.4 degrees. This means that the planets north pole is actually at the bottom of the planet.

Orbit Characteristics

Venus' orbit around the sun is almost perfectly circular which explains the small range of distance from the sun. It takes 224.7 days for Venus to complete one revolution around the sun. This means that one year on Venus is 224.7 days long. Venus' synodic period is 583.92 days, meaning that the planet will return to the same point in the Earth's sky almost every two years. Venus has an orbital velocity of 35.02 km / s or 126 072 km / h.

The Earth is the third planet from the sun and is the only planet known to support life. The Earth's atmosphere is composed mainly of nitrogen and oxygen. The temperatures are moderate, due to the ozone layer found in our atmosphere. There is water on Earth, which in current scientific belief is an absolute requirement for life.

Earth has one naturally occurring satellite, Luna. Usually, Luna is simply referred to as the moon. The moon has a profound effect on Earth. Not only is it a constant feature in the night sky, but being the brightest object means that it can provide light on a clear night. Being so close to the Earth (384 000 km) and with a diameter of 3 475 km, the moon also has a gravitational effect on our planet. This effect is most apparent in the tidal patterns of our oceans.

Distance From the Sun

The Earth's average distance from the sun is 149.6 million km. Due to the orbit this can range from 147.1 million to 152.1 million km.

Since humans have studied the Earth in depth, we tend to base all of our concepts of planet size relative to the Earth. Earth is therefore the standard by which we measure the size of other planets. Earth's diameter is 12 756 km at the equator.

Earth's mass is 5.97 x 10²¹ tonnes. Earth's ratio values for both size and mass are one, since we use the Earth as the standard for measurement.

The Earth rotates west to east around its axis. It takes 23h 56m 04s for the Earth to complete one rotation. This means that the standard Earth day is approximately 24 hours in length.

Earth's axis is tilted at an angle of 23.5 degrees.

Orbit Characteristics

The Earth's orbit is very circular as seen by the small range in distance from the sun. It takes 365.2 days for the Earth to revolve once around the sun. As such, our standard year is 365 days in length with a leap year every four years to take into account the 0.2 days. The Earth has an orbital velocity of 29.8 km / s or 107 280 km / h.

Mars is the fourth planet from the sun. Named after the Roman god of war due to its red colour, there are many legends that claim this planet was bright in the sky on the eve of many great victories. Mars has taken a central place in many of today's space programs. At its closest, Mars is 59 million km away from Earth, making it the second-closest planet after Venus. During the space race of the 1960s, the goal was to be the first to set foot on the moon. Now, there is a collaborative effort by many international space agencies to send a manned mission to Mars. The planet itself is currently deemed uninhabitable without the use of artificial environment resources. There have been many probes sent to Mars in recent years to assess the natural environment and evaluate what equipment would be needed in order to sustain human life on the planet.

Mean Distance From the Sun

Mars is nearly twice the Earth's distance from the sun. The mean distance the planet is from the sun is 227.9 million km. This ranges from 206.6 million to 249.2 million km depending on its position in its orbit around the sun.

The diameter of Mars at the equator is 6 792 km, which is 0.532 times that of Earth.

The mass of Mars is 0.107 times that of Earth.

Like Earth, Mars' rotation is west to east and takes 24h 39m 35s. In other words, a standard Earth day is very close in duration to a Martian day.

The axis of Mars is also very similar to Earth's. The axis of Mars is tilted at an angle of 25.2 degrees.

Orbit Characteristics

The orbit of Mars is eccentric, as shown by the large range in distance from the sun. Mars will revolve around the sun once every 687 days (a little less than two years). Mars has an orbital velocity of 24.1 km / s or 86 760 km / h.

After passing through the ring of the asteroid belt, the next planet past Mars is Jupiter, the innermost gas giant planet. Named after the leader of the Roman gods (Zeus to the Greeks), Jupiter is the largest planet in our solar system. Despite its distance from the Earth, the only planets that can outshine it in the night sky are Earth's neighbours, Venus and Mars.

Jupiter has 63 known natural satellites. Of these, 47 are less than 10 km in diameter, and only 4 are large enough to be considered moons. These are identified as Galilean moons and include:

Mean Distance From the Sun

Though Jupiter is the fifth planet in our solar system, the separation provided by the asteroid belt means that Jupiter is a great distance from the sun. The mean distance of Jupiter from the sun is 778.4 million km. Due to its orbit this distance can range from 740.5 million to 816.6 million km.

The diameter of Jupiter at its equator is 142 984 km, 11.21 times that of Earth. Due to the rotation of Jupiter, there is a significant difference between the diameter at the equator and the diameter at the poles. The polar diameter is 133 700 km, almost 10 000 km less than the equatorial diameter. By comparison, the difference in diameter between the Earth's equator and poles is a mere 42 km.

Jupiter's mass is 317.8 times the mass of Earth.

Jupiter rotates at an immense speed which causes the equator to bulge out. This is the reason for the large difference between the equatorial and polar diameters. One day on Jupiter is only 9h 55m 30s.

Jupiter's axis is only 3.1 degrees from the perpendicular, meaning that Jupiter is almost straight up and down.

Orbit Characteristics

Jupiter has a slightly eccentric orbit. Due to its distance from the sun, it takes the planet 4 331 days (11.86 years) to revolve around the sun. The orbital velocity of Jupiter is 13.1 km / s or 47 160 km / h. Jupiter's synodic period is 398.9 days.

Saturn is a very distinct planet in our solar system. It is the second of the gas giants from the sun, the sixth planet in the system. Named after the Roman god of time because of the length of time it takes for the planet to cross the night sky, Saturn is said to be the most beautiful object in the sky when viewed through a telescope.

Mean Distance From the Sun

Saturn is more remote than Jupiter. Orbiting at a mean distance of 1 433.5 million km, Saturn is almost twice as far from the sun as Jupiter.

Saturn's equatorial diameter is 120 536 km, which is more than nine times that of the Earth. Saturn is the second largest planet in the solar system.

Saturn's mass is 95.2 times the mass of Earth.

Saturn rotates on its axis once every 10h 13m 59s. Like Jupiter, the speed at which this occurs causes a slight bulging at the equator, causing the large distortion between the equatorial diameter and the polar diameter.

The axis of Saturn tilts at an angle of 26.7 degrees.

Orbit Characteristics

Saturn has a slightly eccentric orbital path. It travels around the sun in 10 747 days or 29.43 years. Saturn's synodic period is 378.1 days. The orbital velocity of Saturn is 9.7 km / s or 34 920 km / h.

Uranus is a very distinct planet which shares some of the characteristics of Saturn. Most prominent of these are the rings which orbit the planet, but even here there is uniqueness. Uranus is barely visible to the naked eye and the study of Uranus actually led to the discovery of the next planet in the solar system. The planet is named after the mythological father of Saturn.

Mean Distance From the Sun

Uranus is the second-furthest planet from the sun. The mean distance is 2 872.5 million km with a maximum of 3 003.6 million km and a minimum of 2 741.3 million km. Compared to Saturn, Uranus is twice as far from the sun and four times as far as Jupiter.

Uranus is just over one third the size of Jupiter, but is still the third largest planet in the solar system. It has an equatorial diameter of 51 118 km, which is 4.01 times that of Earth.

Uranus' mass is 14.5 times that of Earth.

Uranus rotates around its axis once every 17h 14m.

The axis of Uranus tilts at an angle of 97.8 degrees. This means that it is technically on its side and the rings of Uranus look like they are vertical compared to Saturn's rings. Also, the satellites orbit Uranus on a vertical plane instead of a horizontal plane like the other planets.

Orbit Characteristics

Uranus has an irregular orbit. There is a point in the orbit where Uranus, as viewed from Earth, performs two 180-degree turns. This would look like a giant Z in the orbital path. It takes Uranus 83.76 years to orbit the sun once. Its mean orbit velocity is 24 607 km / h. The synodic period of Uranus is 369.7 days.

Named after the Roman god of the sea, Neptune was found as a result of scientific study of Uranus. Almost all of our knowledge of Neptune comes from one spacecraft, Voyager 2, which flew past the planet in 1989. The atmosphere is made up predominantly of hydrogen, helium and methane. The planet is a very windy place, with equatorial winds in excess of 450 m / s or 1 620 km / h.

Mean Distance From the Sun

Neptune is approximately half again as far as Uranus from the sun. Orbiting at a mean distance of 4 495.1 million km, it is 20 times as far as Mars. Neptune is the last planet in the solar system, keeping in mind that Pluto has been down-graded to a dwarf-planet.

Neptune is nearly identical in diameter to Uranus at 49 528 km, 3.88 times the diameter of the Earth.

Neptune's mass is more than 18 percent greater than Uranus' and 17.1 times the mass of the Earth.

It takes Neptune 16h 7m to rotate once around its axis. This is the third fastest rotation of all of the planets.

The tilt of Neptune's axis is 28.3 degrees, slightly more than Earth's.

Orbit Characteristics

Neptune's orbit is almost perfectly circular. It takes Neptune 163.7 years to orbit the sun, almost twice as long as Uranus. Its mean orbit velocity is 19 720 km / h. Neptune's synodic period is 367.5 days.