The Planets

The word planet probably comes from a greek word meaning wanderer.

Since prehistoric times, people have watched these enigmatic star like lights move against the skyscape of the seemingly never-changing stars.

Today, we know planets are large, rounded astronomical bodies that are not stars. They do not (usually) emit light, so they are visible only by light reflected from stars. The planets in the solar system are illumiated by the Sun.

The Terrestrial Planets

Mercury, Venus, Earth and Mars are known as the terrestrial, telluric or rocky planets.

They orbit the Sun in the inner solar system and all have rocky surfaces. All except Mercury have atmospheres.

Mercury

Venus in an ultraviolet image to show clouds.

The telescope images show each planet’s disc and features. The composite image shows their relative sizes to scale.

Earth with Tracy Caldwell Dyson on the IIS (2011)

Mars (2021)

Jupiter and Europa (2020)

Saturn (2012)

The Gas Giants

Gas giants, Jupiter and Saturn, are huge planets that are mostly (90%) made up of hydrogen and helium. These elements are also the main constituent of stars. Some scientists even call Jupiter a failed star.

The Ice Giants

Ice giants, Uranus and Neptune, are similar in appearance to the gas giants. They also contain a lot of hydrogen but only to about 20% of their total mass. The rest is expected to be oxygen, carbon, nitrogen and sulphur in compounds like water, methane and ammonia.

Uranus by Voyager 2 (1986)

Neptune by Voyager 2 (1989)

Find Out More

Nasa Science - The Planets

Wikipedia - The Solar System

In Purple Mash

Data is a vital resource for astronomers and other space scientists. They collect it with their telescopes, their spacecraft and with many other experiments. Names numbers, measurements, images and text are stored in databases that the scientists access to analyse and interpret our Universe.

Purple Mash has a space database too. Launch 2Investigate and you’ll find an example Planets database.

Your challenge is to research the planets to check and improve on this example. Look for Improve the Planets Database in your 2Dos.

Watch this video to see how to add a new Type field so that the dwarf planets can be included.

Open this video in a new tab

Here is a checklist of improvements you can make:

• Add a field for the type of a planet (see video).
• Research the dwarf planets and add records for each.
• Find or draw a better picture of each planet.
• Show how eliptical a planet’s orbit is by recording its perihelion and apehelion distances. These are its minimum and maximum distances from the Sun.