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Processed raw image of Metis captured by NASA’s Galileo spacecraft in 1997. (NASA/JPL/Jason Major)

Everyone’s heard of Jupiter’s four most famous moons Europa, Io, Callisto, and Ganymede—we’ve known about them for over 400 years, thanks to Galileo—but giant Jupiter has many more moons than that. To date there are thought to be 69 natural satellites orbiting Jupiter. 53 are officially named, while 16 are awaiting further confirmation. So you’d be forgiven for not being immediately familiar with all of them…it’s a big Jovian family!

The little world seen above is one of Jupiter’s smaller and lesser-known satellites and it holds a particular distinction. It’s called Metis (pronounced like “meet” in the present tense, not “met” in the past) and it’s only about 37 miles across and 21 miles high. It is the closest moon to Jupiter, orbiting within the planet’s main ring (yes, Jupiter has rings) at a distance of about 80,000 miles. It’s also Jupiter’s speediest moon—at 70,500 mph it completes a single orbit in just over 7 hours. That’s almost three hours less than a Jovian day!

The image above was captured by NASA’s Galileo spacecraft on November 6, 1997, two years into its 8 years in orbit at Jupiter. It’s a highly-upscaled version of a raw file I downloaded from NASA’s Planetary Data System (PDS) archive using SETI’s OPUS site. I’ve recently been looking into some raw data from older missions with the goal of processing better versions of things I had worked on in previous years using lower-quality preview JPEGs, and also finding some things I didn’t know about before. Metis is one of them!

Galileo wasn’t the first spacecraft to capture images of Metis; actually Voyager 1 was. The moon was discovered by JPL astronomer Stephen Synnott in data acquired by Voyager 1 in 1979 during its flyby of Jupiter. In March 4 of that year Metis was captured passing in front of Jupiter’s bands of swirling clouds…imagine its view!

The image below is a color-composite I assembled from Voyager 1 observations in red, green, and blue visible-light filters. 37-mile-wide Metis is a tiny speck near the lower right.

Color-composite of Metis and Jupiter from Voyager 1 in March 1979. (NASA/JPL/Jason Major)

Can you spot Metis? If not, here’s some help:

There are three other inner moons of Jupiter in addition to Metis, which is the closest—Adrastea (the smallest and the only other inner moon to orbit faster than a Jovian day), Amalthea (the largest and first-known), and Thebe (rhymes with Phoebe). All orbit between the rings and the orbit of Io, the innermost of the four Galilean moons.

(I processed a Galileo image of Thebe as well:)

Processed raw image of Thebe from Galileo on Jan. 3, 2000. (NASA/JPL/Jason Major)

We don’t know that much about Metis, other than like the other inner moons it’s quite dark (albedo of .06) and is probably made mostly of water ice, based on density.

Learn more about Metis here, and find a full list of Jupiter’s known moons here.

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Hand-colored data from Mariner 4, the “first TV image of Mars,” captured on July 15, 1965. Via Dan Goods.

In November 1964 NASA launched Mariner 4, the fourth of its ambitious series of robotic explorations of our three inner planet neighbors. Mariner 1 was lost during launch; Mariner 2 successfully flew past Venus; Mariner 3 failed to deploy; but on July 14–15, 1965, the 575-lb Mariner 4 became the first spacecraft to fly past Mars and capture close-up images of another planet from space.

Of course the pictures that Mariner 4 captured were in greyscale and not like the beautiful color views we are used to seeing from spacecraft today. But thanks to one creative scientist at NASA (and a box of crayons) our first scenes of Mars from space were in brilliant color.

The 21 images of Mars successfully captured by Mariner 4 were taken with its TV camera and stored on an onboard tape recorder to be transmitted back to Earth over the following three weeks as part of the 5.2Mb of data acquired during the flyby.

Scientists assemble a ticker-tape mosaic of Mars from Mariner 4 data in 1965. (NASA/JPL)

The first of these images, a curved view looking over the planet’s surface from space, was assembled into a large color mosaic by scientists at JPL by printing out the arriving data on long strips of ticker-tape paper and—get this—hand-colored with pastel crayons.

The reason this was done was partially to confirm that the drive containing the image data was indeed working, and to create an image as quickly as possible (since computers in 1965 took considerably longer to assemble an image from raw data than they do today!)

Richard Grumm, the scientist in charge of Mariner 4’s tape system, created a “Mars color palette” using pastel crayons he bought from an art store and assigned hues and values to specific numbers in the data, printed onto the ticker tape. By coloring them in and stapling the strips together, he and his team effectively created the first “color” image of Mars…and in fact it was the first close-up image of Mars to be shown on television since the media reporters were ravenous for something to show the public.

Once Mariner 4’s data were processed into actual images they showed how close Drumm’s handmade version really was…but of course they were in greyscale whereas his was in beautiful shades of Martian oranges and yellows.

Hand-colored image (L) and processed TV camera image (R) of Mars from Mariner 4. (NASA/JPL-Caltech. Via Dan Goods.)

“Though he used a brown/red color scheme, the thought that Mars was red did not enter his mind. He really was looking for the colors that best represented a grey scale, since that was what they were going to get anyway. It is uncanny how close his color scheme is to the actual colors of Mars.”
— Dan Goods, Visual Strategist for JPL

The color mosaic is currently displayed at JPL in Pasadena, CA.

Read more about this fascinating “interplanetary color-by-numbers” in this blog post by Dan Goods, visual strategist at NASA’s Jet Propulsion Laboratory, and learn more about the Mariner 4 mission here.

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Hand-colored data from Mariner 4, the “first TV image of Mars,” captured on July 15, 1965. Via Dan Goods.

In November 1964 NASA launched Mariner 4, the fourth of its ambitious series of robotic explorations of our three inner planet neighbors. Mariner 1 was lost during launch; Mariner 2 successfully flew past Venus; Mariner 3 failed to deploy; but on July 14–15, 1965, the 575-lb Mariner 4 became the first spacecraft to fly past Mars and capture close-up images of another planet from space.

Of course the pictures that Mariner 4 captured were in greyscale and not like the beautiful color views we are used to seeing from spacecraft today. But thanks to one creative scientist at NASA (and a box of crayons) our first scenes of Mars from space were in brilliant color.

The 21 images of Mars successfully captured by Mariner 4 were taken with its TV camera and stored on an onboard tape recorder to be transmitted back to Earth over the following three weeks as part of the 5.2Mb of data acquired during the flyby.

Scientists assemble a ticker-tape mosaic of Mars from Mariner 4 data in 1965. (NASA/JPL)

The first of these images, a curved view looking over the planet’s surface from space, was assembled into a large color mosaic by scientists at JPL by printing out the arriving data on long strips of ticker-tape paper and—get this—hand-colored with pastel crayons.

The reason this was done was partially to confirm that the drive containing the image data was indeed working, and to create an image as quickly as possible (since computers in 1965 took considerably longer to assemble an image from raw data than they do today!)

Richard Grumm, the scientist in charge of Mariner 4’s tape system, created a “Mars color palette” using pastel crayons he bought from an art store and assigned hues and values to specific numbers in the data, printed onto the ticker tape. By coloring them in and stapling the strips together, he and his team effectively created the first “color” image of Mars…and in fact it was the first close-up image of Mars to be shown on television since the media reporters were ravenous for something to show the public.

Once Mariner 4’s data were processed into actual images they showed how close Drumm’s handmade version really was…but of course they were in greyscale whereas his was in beautiful shades of Martian oranges and yellows.

Hand-colored image (L) and processed TV camera image (R) of Mars from Mariner 4. (NASA/JPL-Caltech. Via Dan Goods.)

“Though he used a brown/red color scheme, the thought that Mars was red did not enter his mind. He really was looking for the colors that best represented a grey scale, since that was what they were going to get anyway. It is uncanny how close his color scheme is to the actual colors of Mars.”
— Dan Goods, Visual Strategist for JPL

The color mosaic is currently displayed at JPL in Pasadena, CA.

Read more about this fascinating “interplanetary color-by-numbers” in this blog post by Dan Goods, visual strategist at NASA’s Jet Propulsion Laboratory, and learn more about the Mariner 4 mission here.

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This animation is comprised of three images acquired by ESA’s Mars Express spacecraft on Sept. 12, 2017 with its High Resolution Stereo Camera (HRSC). It shows parts of the grooved and pitted surface of Phobos, the larger of Mars’ two natural satellites.

The original images were captured in greyscale; I added color based on other images of Phobos taken by NASA’s Mars Reconnaissance Orbiter in March 2008.

Phobos orbits Mars at an altitude of about 6,000 km. Image: ESA

Unlike Earth’s relatively enormous Moon, Phobos is a tiny satellite only about 16 miles (26 km) across. It orbits Mars at a very low altitude of 3,721 miles (5,989 km) and travels rapidly, only taking 7 hours and 39 minutes to complete a single orbit.

See more images of Phobos captured by various missions over the years here.

Unlike our Moon which is slowly but steadily moving away from us, little Phobos’ orbit is degrading. Eventually (some estimates say in only about 10 million years) Phobos will either impact Mars or be ripped apart by tidal forces, forming a ring of material that would temporarily turn Mars into a miniature version of Saturn.

And speaking of Saturn, in 2016 Mars Express captured images of Phobos passing in front of the ringed planet, which at 650 million miles distant appeared as a small oval dot in the background blackness. Besides making for fascinating images, such observations are planned to help mission scientists calibrate the positioning of the spacecraft and better determine the precise location and orbit of Mars’ moons. Click here to watch the video and see more images from Mars Express.

Source: ESA. HT to Bill Dunford on Twitter.

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Infrared image of Deimos by THEMIS on Feb. 15, 2018 (NASA/JPL-Caltech/ASU/SSI)

Can you feel the heat? NASA’s Mars Odyssey can see it! This is an image of Mars’ smaller moon Deimos, captured with Odyssey’s THEMIS (Thermal Emission Imaging System) instrument on Feb. 15, 2018. Part of the 7-mile-wide Moon was in shadow, but the sunlit surface area reached temperatures up to 200 K (that’s still pretty cold for us, though… –100ºF / -73ºC!)

This was the first observation of Deimos by Mars Odyssey; the spacecraft first imaged Mars’ other moon, Phobos, on September 29, 2017. Researchers have been using THEMIS to examine Mars since early 2002, but the maneuver turning the orbiter around to point the camera at Phobos was developed only recently. (Source: NASA)

Mars isn’t a planet well-known for its natural satellites but it actually does have two small moons. The larger, Phobos, is an irregularly-shaped, heavily grooved and cratered world only about 17 miles (27 km) across at its widest. But Phobos has an even smaller companion: Deimos, which at 7.5 miles across is less than half Phobos’ size.

Deimos is much further away from Mars than Phobos too. With a mean distance of 13,268 miles (21,353 km) from the surface of Mars it’s over 2 1/2 times farther away. Little Deimos travels quickly though—it only takes it bout 30 hours to complete one orbit.

Deimos imaged by HiRISE aboard MRO (NASA/JPL-Caltech/ASU)

Mars Odyssey launched on April 7, 2001 and arrived at Mars on Oct. 24, 2001. The Thermal Emission Imaging System (THEMIS) is a special camera on the Mars Odyssey spacecraft developed and run by Arizona State University. Its main tasks are mapping rock mineralogies and detecting heat, which yields information on the physical and thermal properties of the Martian surface. (Via ASU)

Image credit: NASA/JPL-Caltech/ASU

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Infrared image of Deimos by THEMIS on Feb. 15, 2018 (NASA/JPL-Caltech/ASU/SSI)

Can you feel the heat? NASA’s Mars Odyssey can see it! This is an image of Mars’ smaller moon Deimos, captured with Odyssey’s THEMIS (Thermal Emission Imaging System) instrument on Feb. 15, 2018. Part of the 7-mile-wide Moon was in shadow, but the sunlit surface area reached temperatures up to 200 K (that’s still pretty cold for us, though… –100ºF / -73ºC!)

This was the first observation of Deimos by Mars Odyssey; the spacecraft first imaged Mars’ other moon, Phobos, on September 29, 2017. Researchers have been using THEMIS to examine Mars since early 2002, but the maneuver turning the orbiter around to point the camera at Phobos was developed only recently. (Source: NASA)

Mars isn’t a planet well-known for its natural satellites but it actually does have two small moons. The larger, Phobos, is an irregularly-shaped, heavily grooved and cratered world only about 17 miles (27 km) across at its widest. But Phobos has an even smaller companion: Deimos, which at 7.5 miles across is less than half Phobos’ size.

Deimos is much further away from Mars than Phobos too. With a mean distance of 13,268 miles (21,353 km) from the surface of Mars it’s over 2 1/2 times farther away. Little Deimos travels quickly though—it only takes it bout 30 hours to complete one orbit.

Deimos imaged by HiRISE aboard MRO (NASA/JPL-Caltech/ASU)

Mars Odyssey launched on April 7, 2001 and arrived at Mars on Oct. 24, 2001. The Thermal Emission Imaging System (THEMIS) is a special camera on the Mars Odyssey spacecraft developed and run by Arizona State University. Its main tasks are mapping rock mineralogies and detecting heat, which yields information on the physical and thermal properties of the Martian surface. (Via ASU)

Image credit: NASA/JPL-Caltech/ASU

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