Glossary term: inner planet

Description: In our Solar System, the inner planets are Mercury, Venus, Earth and Mars. Their orbits are inside the asteroid belt, and all of those planets are so-called terrestrial planets, with thin atmospheres compared to the giant planets with their puffy hydrogen and helium atmospheres.

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Term and definition status: This term and its definition is still awaiting approval

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

Related Media

The planet Mercury covered by many craters


Caption: This image is a composite of a picture mosaic of the planet Mercury's surface obtained by the MESSENGER (Mercury Surface, Space Environment, Geochemistry and Ranging) space probe. MESSENGER was launched by NASA in 2004 and explored Mercury from 2011 to 2015.
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington credit link
License: PD Public Domain icons
The planet Venus showing white clouds enshrouding the planet

Venus in visible light

Caption: This picture taken by NASA's Mariner 10 probe shows what the planet Venus looks like when looking at it with naked eyes. Venus is enshrouded inside a thick cloudy atmosphere dominated by carbon dioxide, never revealing its hot surface.
Credit: NASA/JPL-Caltech credit link
License: PD Public Domain icons
The planet Venus' surface with ridges and valleys

Venus' surface

Caption: This image is a computer-aided rendering of the surface of the planet Venus. Since visual light cannot penetrate the thick clouds in Venus' atmosphere, the image was obtained with radio waves. NASA's space probe Megallan, launched in 1989 mapped Venus' surface between 1990 and 1994.
Credit: NASA/JPL credit link
License: PD Public Domain icons
The Earth from space showing oceans and continents

Earth as observed from Apollo 17

Caption: Full disk view of the Earth taken on 7 December 1972, by the crew of the Apollo 17 spacecraft en route to the Moon at a distance of about 29,000 kilometres (18,000 mi). It shows Africa, Antarctica, and the Arabian Peninsula.
Credit: NASA/Apollo 17 crew/Project Apollo Archive
License: PD Public Domain icons
The planet Mars with a rusty red surface, volcanoes, valleys, craters, ice clouds and a white polar cap


Caption: This image of the planet Mars taken by NASA's Mars Global Surveyor Orbiter in 1999 shows its dry surface. The picture features the most spectacular geological regions on Mars. Besides the deep Valles Marineris valley we see four volcanoes. While three of them form the Tharsis ridge, the Olympus Mons is largest volcano we have so far discovered in the Solar System. Ice clouds cover parts of the Martian surface.
Credit: NASA/JPL/MSSS credit link
License: PD Public Domain icons