Direct Imaging Earth and Moon from Mars

(NASA/ JPL-Caltech/ Univ. of Arizona)

Sometimes images arrive that make it clear that the space age is not a throw-away line, but a reality.

This one was taken by a satellite orbiting Mars, and it shows the Earth and the moon.  Kind of remarkable, given that the camera — the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter — was 127 million miles away

And HiRISE is not a far-seeing telescope, but rather a camera designed to look down on Mars from 160 to 200 miles away.  It’s job (among other tasks) is to image the terrain, measure the compounds and minerals below, and keep an eye on Mars dust storms, climate, and the downhill steaks that periodically appear on some inclines and may contain surface salty water.

The image is a composite image of Earth and its moon, combining the best Earth image with the best moon image from four sets of images acquired on Nov. 20, 2016 by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter.

Each was separately processed prior to combining them so that the moon is bright enough to see. The moon is much darker than Earth and would barely be visible at the same brightness scale as Earth. The combined view retains the correct sizes and positions of the two relative to each other.

This is how JPL described the details:

HiRISE takes images in three wavelength bands: infrared, red, and blue-green. These are displayed here as red, green, and blue, respectively. This is similar to Landsat images in which vegetation appears red. The reddish feature in the middle of the Earth image is Australia. Southeast Asia appears as the reddish area (due to vegetation) near the top; Antarctica is the bright blob at bottom-left. Other bright areas are clouds.

What I find especially intriguing about the image is that it is precisely the kind of “direct imaging” that the exoplanet community hopes to some day do with distant planets.  With this kind of imaging, scientists not only can detect the glints of water, the presence of land, the dynamics of clouds and climate, but they can also get better spectrographic measurements of what chemicals are present.

Some exoplanets are being painstakingly direct imaged, but the difficulty factor is high and the result is most likely one or two pixels.  And since the planets are orbiting stars that send out light that hides any exoplanets present, coronagraphs are needed inside the telescopes to block out the sun and its rays.

Enormous, unfolding “starshades” sent to space may some day perform the same function in tandem with a space telescope. Advocates for the technology say it will provide greater opportunity and sensitivity.

More on this in the weeks ahead.

Here is another Earth/moon image taken by HiRISE in 2007, when our distance Mars was 88 million miles.  Here the Earth diameter is about 90 pixels and the moon diameter is 24 pixels.

(NASA/JPL-Caltech/University of Arizona)


Marc Kaufman
Marc Kaufman is the author of two books about space: "Mars Up Close: Inside the Curiosity Mission” and “First Contact: Scientific Breakthroughs in the Search for Life Beyond Earth.” He is also an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer. While the “Many Worlds” column is supported and informed by NASA’s Astrobiology Program, any opinions expressed are the author’s alone.

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