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Why Are Planets Different Colors?

Why Are Planets Different Colors

More now than ever before we are seeing amazing images of our neighboring planets. We can see a kaleidoscope of colors spanning across our solar system. But why are planets different colors? It all comes down to what they are made of and how their atmospheres interact with light from the Sun.

planets

Image Credit: NASA/JPL

Inner Planets

Inner planets are the planets that lie between the asteroid belt and the Sun. These planets are made up of rocky material and sometimes have a gaseous atmosphere. 

Mercury

Mercury looks a lot like our Moon. It is rocky and covered in a thick layer of dust, giving it a dark grey appearance. While to the naked eye it all looks one color, astronomers can overlay images in different artificial color bands to highlight key features in Mercury’s surface, giving it an alien look.

Image Credit: (left) MESSENGER Space Craft. (right) NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Venus

Venus has a thick atmosphere made up of carbon dioxide and sulfuric acid clouds. This gives Venus a yellowish appearance. 

venus

Image Credit: ARTUR PLAWGO / SCIENCE PHOTO LIBRARY via Getty Images

Earth

Earth has three main colors when viewed from space. Blue is Earth’s dominant color; this comes from the oceans and the composition of our atmosphere. Greens and browns come from the land and foliage on the surface. White is very commonly seen from the ice at the North and South Poles and from the clouds. Unlike Venus, our clouds are white because they are made up of water droplets. 

earth

Image Credit: Appollo 17 Crew

Mars

Mars’ red color is so prominent that it even looks orange red to the naked eye. But what gives it this strong color? Many rocks on Mars are made of iron, when these rocks get exposed to the atmosphere they oxidize, or in other words rust. Just like an old car gets rusty when left to the elements.  In newer images we are able to see that Mars has white ice caps on it’s poles just like Earth. 

mars

Image Credit: NASA

Outer planets

Outer planets are outside of the asteroid belt. These planets are made up of entirely gas.

Jupiter

Jupiter is one of the gas giants and may be one of the most spectacular looking planets. Its outer atmosphere is made up of mainly hydrogen and helium with small amounts of other elements. Clouds of these elements have varying shades of white, orange, brown, and red. These clouds can be seen in bands caused by winds rotating around the planet at different rates, with round storms speckled throughout. Jupiter’s most recognizable feature, its giant red spot is actually a large storm, larger than the Earth. While we have seen this red spot for as long as we have been observing Jupiter, the spot is shrinking. While many things could change and affect the growth of this storm, if it continues its path of reduction it could disappear in the next 20 years according to researchers at NASA’s JPL in California. 

jupiter

Image Credit: NASA, ESA, A. Simon (Goddard Space Flight Center), and M. H. Wong (University of California, Berkeley) and the OPAL team.

Saturn

Saturn is most recognizable for its magnificent rings. It is also one of the gas giants and its atmosphere is mainly made up of hydrogen and helium. It’s yellowish-brownish color comes from trace elements of ammonia, phosphine, water vapor, and hydrocarbons in its atmosphere. 

saturn

Image Credit: NASA/JPL-Caltech/Space Science Institute

Uranus

Uranus has a greenish blue color due to the methane gas mixed with its atmosphere, which is mainly hydrogen and helium. Though not as prominent as Saturn’s, Uranus also has rings. 

uranus

Image Credit: Lawrence Sromovsky, University of Wisconsin-Madison/W.W. Keck Observatory

Neptune

Neptune’s atmosphere has a very similar makeup to Uranus’s atmosphere. It too is mainly hydrogen and helium with some methane, resulting in a very similar color as well. 

neptune

Image Credit: NASA/JPL

Moons

If each planet’s unique makeup determines its color, can the same be said for the moons of planets? Of course! Not only moons, but asteroids, comets, and anything we see has its color determined by what it’s made of and how the light interacts with it. 

Many moons are made of rocky material and appear grey like our Moon. Our Moon can appear bright white on a clear night because it is so close to the Sun and reflecting bright light back to us, lightening its appearance, but in reality it is a greyish color. 

Jupiter’s Moon Europa is quite interesting to look at. Its surface is almost pure ice so most of it appears white or blueish. Additionally, there are reddish streaks across its surface made up of non-ice components. These color variations are associated with the differences in geological features in an area. Astronomers believe these cracks and ridges across Europa’s surface are caused by the massive gravitational pull from Jupiter. 

jupiter moon

Image Credit: NASA/JPL-Caltech/SETI Institute

Another one of Jupiter’s moons has a very interesting surface. Io’s surface is covered in more than 100 active volcanoes, with at least six always erupting. This constant volcanic activity causes its surface to be continuously changing. In fact, its entire surface is covered with lava every few thousand years. 

jupiter moon io

Image Credit: NASA/JPL/University of Arizona

Jupiter’s Callisto also shows signs of a violent past. It has numerous markings and craters, scars of its collisions with objects in space throughout its lifetime. Callisto is the most heavily cratered object in our solar system. Astronomers believe the different colors on Callisto’s surface are due to ice and ice erosion. 

jupiter callisto

Image Credit: NASA/JPL/DLR

Exoplanets

Exoplanets are planets that are outside of our solar system. Since the color of a planet or a moon depends on the makeup of the object, it is reasonable to hypothesize that exoplanets can be any number of colors. In 2013 astronomers determined the color of an exoplanet for the first time. Planet HD 189733b is a rich blue. Though we do not have any real images of this planet yet, below is an artist’s rendering of what this planet could look like. 

exoplanets

Image Credit: NASA/ESA

References

https://www.space.com/39764-jupiter-great-red-spot-could-disappear.html
https://www.space.com/jupiter-moon-europa-atmosphere-water-vapor
https://www.theatlantic.com/technology/archive/2013/07/for-the-first-time-astronomers-have-determined-the-color-of-an-exoplanet/277710/
https://solarsystem.nasa.gov/planets/neptune/overview/
https://solarsystem.nasa.gov/planets/uranus/overview/
https://solarsystem.nasa.gov/news/814/scientists-finally-know-what-time-it-is-on-saturn/
https://cosmosmagazine.com/space/astronomy/whats-happening-to-jupiters-great-red-spot/
https://www.jpl.nasa.gov/edu/learn/video/mars-in-a-minute-is-mars-really-red/#:~:text=Well%2C%20a%20lot%20of%20rocks,the%20martian%20sky%20look%20pink.
https://www.space.com/44-venus-second-planet-from-the-sun-brightest-planet-in-solar-system.html
https://www.spacecentre.nz/resources/faq/solar-system/earth/colour.html#:~:text=Short%20answer%3A%20Mostly%20blue%2C%20with,blue%20light%20from%20the%20atmosphere.
https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-are-clouds-k4.html
https://astronomy.com/news/2012/03/data-from-messenger-spacecraft-reveals-new-insights-on-planet-mercury
https://solarsystem.nasa.gov/resources/771/colors-of-the-innermost-planet-view-1/
https://astronomy.com/magazine/weirdest-objects/2015/05/34-jupiters-moon-io
https://www.treehugger.com/spectacular-moons-in-our-solar-system-4869170
https://coolcosmos.ipac.caltech.edu/ask/203-Why-do-the-planets-have-different-colors-#:~:text=Planets%20have%20the%20colors%20that,igneous%20silicate%20rocks%20and%20dust.

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Cassie Hatcher

Cassie is a lifelong learner with a passion for communicating high level science in a conversational matter. She holds a B.S. and M.S. in physics and has written two astronomy theses, one of which is published. She earned an internship at NASA’s Goddard Space Flight Center in 2016 and got the chance to see the James Webb Space Telescope while it was being built.
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