The Solar System - the Terrestrial Planets Quiz

Answer: Earth

The Moon is the fifth largest moon in the Solar System, and Earth's only natural satellite. The Earth is the only planet in our Solar System with one moon. The Moon has been a beneficial presence for life on Earth, moderating the Earth's "wobble" on its axis, and being responsible for the regular tides. The Moon is locked with Earth, so that one face is shown at all times.

As the largest and brightest object in the night sky, with changes of phases, solar and lunar eclipses, and an apparent size similar to the Sun, the Moon has captured the human imagination since pre-history. Twelve astronauts set foot on the Moon as part of the Apollo missions between 1969 and 1972.

Answer: Venus

As do all the planets, Earth and Venus orbit around the Sun in ellipses, with an average distance from the Sun of approximately 150 million km and 108 million km, respectively. Their distance from each other is constantly changing. Venus's nearest approach to Earth is approximately 38 million km, and the furthest distance they get apart is around 260 million km.

Mars comes within 55 million km of Earth, and Mercury approaches to around 77 million km.

Answer: Earth

Earth is the densest planet, with an average density of around 5,500kg per cubic metre. The chief constituents of Earth are: iron, oxygen, magnesium and silicon.

The order of planets by density, highest to lowest, is: Earth, Mercury, Venus, Mars, Neptune, Jupiter, Uranus, Saturn.

Answer: Mars

Mars is unique in the Solar System in having two natural satellites. Phobos and Deimos were discovered in 1877 by Asaph Hall. Their names come from the mythical Greek twins, the personification of "Panic" and "Dread" respectively, sons of Ares, the Greek equivalent of Mars.

The moons are small, and irregularly shaped - Phobos has a diameter of around 22km, and Deimos's is around 13 km. Their origin is uncertain - possibly they were asteroids captured by Mars, but this is disputed.

Mercury and Venus have no moons, Saturn has over eighty.

Answer: Mercury

Mercury is the smallest planet. Its mean radius is less than 2,500km. Jupiter's is 69,900 km. Due to tidal locking with the Sun, Mercury rotates oddly. It has one day for every two Mercury years. Mercury lacks an atmosphere, instead having an exosphere of atoms that have been blasted off the surface by meteorites or the solar wind.

The planets in order of increasing size: Mercury, Mars, Venus, Earth, Neptune, Uranus, Saturn, Jupiter.

Answer: Venus

As observed by Kepler, planets follow elliptical orbits around the Sun. Venus's is the least eccentric of all the planets, that is, the most like a circle. Venus has a very low eccentricity, at 0.007. At its nearest, Venus is around 107.7 million km from the Sun, and its farthest away is around 109.2 million km. Mercury has the most eccentric orbit, ranging from 47 to 71 million km away from the Sun.

The orbits of the planets in increasing eccentricity are Venus, Neptune, Earth, Uranus, Jupiter, Saturn, Mars, Mercury.

Answer: Venus

Most of the planets rotate on their axis in an anti-clockwise direction. Venus bucks the trend by having retrograde motion - it rotates clockwise. The rotation is very slow - so slow, in fact, that a day on Venus lasts longer than a year: 243 Earth days vs 225. Comparing speeds at the equator, whereas a point on Earth's equator moves at around 1700 km per hour, a point on Venus's equator moves at 6.5 km per hour.

Planets listed by length of rotation/day, longest to shortest: Venus, Mercury, Mars, Earth, Uranus Neptune, Saturn, Jupiter.

Answer: Mercury

Venus gets closest to the Earth, and Mars gets second closest. However, if you calculate over the full cycle of rotations of the planets, Mercury is on average the nearest planet to Earth. It seems counter-intuitive, but if you think of two planets at their furthest apart, Mercury's furthest distance from another planet is always going to be much nearer than any other planet's because it is so close to the Sun.

Not only is Mercury the nearest on average to Earth, it is the nearest on average to all the planets in the Solar System. It is even the nearest on average to dwarf planet Pluto, despite its highly eccentric and inclined orbit.

Answer: Venus

Despite not being the nearest to the Sun, Venus has the hottest surface temperature. Its atmosphere is very dense, is made up of more than 95% carbon dioxide, and is heated by the most intense greenhouse effect in the Solar System to temperatures of around 447C. Scientists point to Venus, in many ways a twin planet to Earth, as a warning example of the effects of greenhouse gases.

Looking at the planets by temperature, only Venus bucks the trend by being hotter than Mercury, although farther from the Sun. The order, hottest to coldest, is: Venus, Mercury, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.

Answer: Mars

Olympus Mons (Latin for Mount Olympus) is the biggest mountain and volcano in the Solar System. It is two and a half times the height of Mount Everest, at 22km tall.

In the nineteenth century, the astronomer, Giovanni Schiaparelli, observed what he thought must be very high mountains in the Tharsis plateau, where Olympus Mons is situated. It was identified by space probes as a mountain, with its height confirmed by the Mars Orbiter Laser Altimeter mission.

Answer: Earth

With an average radius of around 6,400 km, Earth is the largest terrestrial planet. It is near to being a sphere, but is slightly flattened at the poles. Its shape is termed an oblate spheroid. Earth's radius is about 20km smaller round the poles than round the equator. There are, of course, peaks and troughs, although they are small in relation to the Earth's size. The biggest dip in the Earth's sphere is the Marianas Trench, at 11km below sea level, and the biggest bit sticking up is Everest, at nearly 9km above sea level.

Neptune, the smallest of the non-terrestrial planets, has an average radius of just under 25,000 km.

Answer: Mars

Mars's average radius is around 3,400 km, just over half that of Earth. Its radius is about 20km lower at the poles compared to the equator. Mars has two polar ice caps, that are present permanently. These ice caps are made up primarily of water ice, which gets coated by frozen carbon dioxide, or dry ice. The dry ice freezes or sublimes depending on the seasons.

A lake of water has been discovered under the southern ice cap, and it is speculated that this may be a candidate area to search for evidence of life on Mars.

Answer: Mercury

The Caloris Basin, or Caloris Planitia, on Mercury is one of the largest impact craters in the Solar System. It is about 1500 km in diameter, and ringed by mountains 2km tall. It was formed by the impact of a meteorite early in the Solar System's history, around 3.9 billon years ago.

The Caloris Basin was discovered by the Mariner 10 mission in the 1970s. The name Caloris Planitia means "heat plain" in Latin, reflecting the level of heat on Mercury's surface.

Answer: Mars

Like geography on Earth, which comes from the Greek "writing about the Earth", areography is the study of Mars's physical features, deriving from Ares, the Greek god of war equivalent to the Romans' Mars. The earliest known aerographer, who drew a map of Mars's physical feature from telescopic observation, was Christiaan Huygens (1629-1695). Early areographers were convinced the features they saw on Mars were canals.

A similar word construction is used for selenography, the study of the Moon's physical features.

Answer: Mercury

Mercury is the quickest planet. Travelling at around 48 km per second, it completes a rotation around the Sun in 88 days. Early humans noticed the planets moving across the night sky. The name "planet", from the Greek "wanderer" was given to objects they thought were stars that wandered across the sky in relation to the other stars. Mercury was the quickest mover, and was therefore given the name of the fast-moving messenger god. For the ancient Babylonians, this was Nabu, for the Greeks, Hermes, and for the Romans, Mercury.

Speed of planet decreases with distance from the sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Neptune's speed is around 5km per second.