My photo collage above was inspired by Steven Gildea’s “Planetary Suite” oil painting, which thousands of people are sharing on social media (a) without credit and (b) without realizing it’s a painting. It’s beautiful, but it’s not strictly accurate, especially since it was made before we reached Pluto.
So I set out to make a collage of the real thing. This proved much more difficult than I’d anticipated. It turns out that most photos of planets aren’t true color!
You may have seen a collage like this one posted by Business Insider. They’re real NASA photos, but they’re not necessarily what the human eye would see.
Space probes and telescopes have sensitive cameras that pick up wavelengths beyond the range of human vision. This lets these instruments “see” many details invisible to the human eye, helping to distinguish different kinds of rocks, ices, gases or other materials on the surface.
Most spacecraft can “see” into infrared and/or ultraviolet wavelengths:
To help us “see” hidden details, scientists convert non-visible wavelengths into colors we can see. Either they’ll represent infrared and ultraviolet with bright colors (below right), or they’ll convert the image to show colors visible to human eyes (below left).
The Martian atmosphere is very dusty. Photos taken from the surface of Mars often look like they were taken during a dust storm at sunset.
To overcome this problem, researchers adjust photos from Mars missions using a color calibration patch stuck on the spacecraft. Knowing what that patch looked like before it left Earth helps scientists adjust Mars photos to match Earth lighting. This makes it easier to compare Martian and Earth rocks.
NASA scientist Donald E. Davis, who worked on Mars missions, has a detailed article on The Colors of Mars, discussing the hows and whys of color in photos taken by the different rovers and landers.
Venus is another planet that’s usually shown in false-color. In reality, it’s covered in a thick layer of cream-colored clouds that are almost featureless. It looks like a pearl.
I’ve never seen a true-color image of Venus from any spacecraft. Instead, we get false-color photos using infrared or ultraviolet. For radar images, which are essentially elevation maps, the color is simulated, based on surface photos taken by Soviet landers.
It took a lot of hunting, but I finally found true-color, or adjusted to true-color, photos of the most well-known nine planets. (Sorry, Ceres, Eris, Haumea and friends).
Here’s the photos I used.
The Mercury MESSENGER spacecraft surveyed the planet in 11 different wavelengths, including near-infrared, to bring out color.
For the past few years, astrophotography enthusiasts like Mattias Malmer have been sifting through old NASA mission files, looking for color data and photos which they can combine and adjust into true-color images.
NASA respects the work of the image processing community, most of whom are professional photographers and/or astronomers. In fact, I first found Malmer’s color-adjusted Venus photo on a NASA scientific article.
Here’s more true-color image-processed photos of Venus and Mercury.
Japan’s new Himawari-8 weather satellite, perched in geosynchronous orbit over the Pacific ocean, takes the highest-resolution true-color photos I’ve ever seen. The above screencap does not do it justice.
It takes multiple photos every day, resulting in absolutely incredible animations like those showcased by the New York Times.
Surprisingly, finding a true-color photo of Mars was my biggest challenge.
First, Mars is not always the same color: it varies due to massive dust storms (Surveyor, Hubble) and/or minute amounts of water ice in the atmosphere (see planetary scientists’ comments on this post). Second, we have photos from several decades of spacecraft, some better calibrated than others. Also, the Hubble website sometimes uses the term “true color” loosely to mean “natural color, as opposed to false color like this.“
So I scoured various images and had to make a judgement call:
- NASA calls this “true color”, a Viking photomosaic projected on an elevation map: butterscotch.
- Here’s the STUNNINGLY GORGEOUS Viking photomosaic used in #1, minus elevation data: butterscotch.
- National Geo’s award-winning, independently-praised true-color map of Mars, using Mars Global Surveyor data: butterscotch.
- Hubble calls this image “true color”: brick red.
- NOT true color, but “stretched” to bring out details: brick red.
I’ve decided to go with the Mars Global Surveyor images used by National G. That library is maintained/color-calibrated by Malin Space Science Systems, responsible for cameras on most Mars missions for the past 20 years (NASA also tapped MSS to make the Juno camera for its next-generation Jupiter mission).
Yes, I know. There’s either more or less than nine planets.
For puposes of my collage above, the “dwarf planet” debate is moot: we’re not going to have detailed photos of Eris or Pluto’s other siblings any time soon. I’ll add Ceres when the spacecraft currently orbiting it gets around to sending color photos.
For what it’s worth, here’s Hubble photos of Ceres with color. If you mentally lower the saturation on those, it’ll probably be about right.
Finally! Here’s a straightforward one.
NASA’s Cassini spacecraft snapped several beauty shots of the giant planet on the way out to Saturn. Here’s another gorgeous Cassini photo of Jupiter showing a little more detail, and one closer still.
Jupiter is a beefy 88,846 miles in diameter, yet its day is less than 10 Earth hours. Its fast rotation causes it to bulge sideways. Jupiter is 11.2 Earths wide but only 10.5 Earths tall, a difference of about 5,764 miles.
The Cassini Mission is responsible for a decade plus of amazing science, discovering the rivers and seas of Titan, the giant geysers of Enceladus, and the iconic photo of Earth seen behind the rings of Saturn. Cassina also dropped the first probe to photograph the surface of Titan!
You may have noticed some faint blue-gray stormcloud spots, more visible in the hi-res version of this image. In 2011, Saturn had massive thunderstorms at about that latitude in the northern hemisphere.
Like Jupiter, Saturn is squashed due to its fast rotation; its day is 10.5 Earth hours.
Tranquil, isn’t it? In infrared, you can see that Uranus has faint smoky rings and wispy clouds.
Once again, this took some work. I knew from the Neptune images that Voyager 2 images tend to be a little over-saturated, making Uranus look like spearamint.
To correct this, I overlaid a lower-resolution, “natural-color” Hubble image of Uranus [NASA/ESA, Erich Karkoschka] and borrowed the Hue. Dr. Erich Karkoschka is one of the foremost atmospheric scientists for Neptune and Uranus, so I’m a little more confident in his “natural color.” Also, I compared my result with Björn Jónsson’s image processing, and the color is quite close.
ETA: And here’s a tiny but uber-cool natural-color photo of Uranus peeping behind Saturn’s rings, taken by the Cassini spacecraft.
Neptune photos from Voyager 2 tend to be over-saturated, making the planet look like lapis lazuli. It’s remarkably blue, but it’s not quite that intense.
When I reached out to Dr. Emily Lakdawalla, planetary scientist and blogger for the Planetary Report, she recommended Neptune image processing by Björn Jónsson. See this post explaining how he combined Voyager 2’s high-resolution b&w data with lower-resolution color data to make the beautiful mosaic above.
New Horizons, built 30 years after Voyager, has better low-light optics, so it can see even when the sun is 3 billion miles away.
Like Uranus, Pluto rotates knocked on its side. From New Horizon’s perspective, Pluto’s north pole is tipped slightly towards us, in that yellowish area near the top of the photo.