Solar System/Terrestrial Bodies


 * For general information about the event, see Solar System.

Terrestrial Bodies is the topic of the Division B Solar System for the 2018 season. The topic covers the terrestrial planets (excluding Earth), the Earth's Moon, several other rocky bodies such as Io, Phobos, and Deimos, and asteroids. The specific focus of the event is the history, formation, and geology of these rocky bodies.

Mercury
Mercury is the smallest planet in the solar system with a radius of about 2439 km. It is also the planet closest to the sun at an average distance of about 57.9 million kilometers, or about 0.39 AU. (Mercury has a highly elliptical orbit.) The length of a year on Mercury is 88 Earth days long, and a day on Mercury is 59 Earth days long. The surface gravity of Mercury is 1/3 of Earth's, so it can only hold an extremely thin atmosphere consisting of small amounts of hydrogen, helium, and oxygen. Mercury’s surface is scarred with the craters of impacted meteors. The surface temperatures at day and at night are very different, because of the thin atmosphere. The temperature during the day is 227°C and the temperature at night is -173°C. The most noticeable feature is the largest impact crater on its surface, the Caloris basin.

Venus
Venus is the third smallest planet in the solar system with a radius of 6051 km. It is also the second closest to the sun at a distance of 108.2 million kilometers. It is the only planet whose day is longer than its year. Its day is 243 Earth days, and its year is 225 Earth days. The extremely long rotation periods of Venus and Mercury is thought to be caused by mutual gravitation pull; Mercury is sometimes thought to be an escaped moon of Venus. Venus is often called Earth's sister planet because of its close proximity to Earth, and because of its similar diameter and mass. People even thought it could hold life, but sadly people discovered that the greenhouse effect on Venus raised the surface temperature to the highest in the Solar System.

Earth
NOTE: Earth is not included as a major part of the event for 2018; however, a basic knowledge of how Earth fits in the context of the Solar System will likely be of use.

Earth is the third planet from the Sun. It is also the fifth largest planet at a radius of 6378 km, ranking below the gas giant planets. It is the only planet in the universe currently known to support intelligent life. It is used as a basis for many measurements of planets and other things in the solar system, for example, the AU (Astronomical Unit), the average distance between the Earth and the Sun, 93,000,000 miles or 149,600,000 km. The year on Earth is equal to about 365.256 Earth days, and a corresponding day is equal to one 1 earth day, hence the definition.

Mars
Mars is the fourth planet from the Sun at a distance of about 227,392,000 km, with a highly elliptical orbit. It is often called the Red Planet due to the large quantities of iron oxide present in its soil. The Romans saw it as blood, so they named it for their god of war, Mars. It is the second smallest planet, with a radius of 3397 km. It has a day length of about 25 hours, and a year equal to 687 Earth days. It has been suggested that Mars may hold life, but it has not been proven. Mars contains two polar ice caps consisting of frozen ice and carbon dioxide located on the southern and northern poles.

30% of the polar ice caps are made up of dry ice or CO2. The dry ice then sublimates creating large gusts sweeping across the polar ice caps creating cirrus clouds in the atmosphere. Mars has two tiny moons, Phobos and Deimos, believe to be captured asteroids.

Earth's Moon
Earth's Moon is known as the Moon. It is Earth’s only known permanent natural satellite. It takes 27 Earth days for the Moon to fully orbit the Earth. The moon is widely thought to have formed 4.51 million years ago, not too long after Earth, supposedly after a Mars-sized body collided with Earth. The moon is in synchronous motion with Earth, and always shows the same face, although about 59% of it can be seen over time due to libration.

The moon appears the same size in the sky as the sun, resulting in total solar eclipses, but the moon’s distance from Earth is slowly increasing.

Io
Io is the third largest of Jupiter's four Galilean moons, and is the most volcanically active body in our solar system, with over 400 volcanoes, the result of tidal heating from the pull of Jupiter and its other moons. It is the innermost of the four Galilean moons, and has the highest density of all the moons.

Phobos and Deimos
Phobos and Deimos are moons of Mars, discovered in 187 by astronomer Asaph Hall. Phobos is the inner moon and seven times as massive as Deimos, the outer moon. They are both believed to be captured asteroids.

It is possible for Mars to have moons smaller than 100 meters in diameter and a dust ring between Phobos and Deimos, but neither have been discovered so far.