June 29, 2022
The image shows the "dark side" of Pluto, illuminated by the moon Charon

The image shows the “dark side” of Pluto, illuminated by the moon Charon

I 2006, a NASA The New Horizons probe bound for Pluto was launched, and after nearly a decade of travel, it was launched He reached the dwarf planet, Take close-up photos of the surface of Pluto and its moons. Now, a team of researchers led by Tod Lauer of the National Infrared Optical Astronomy Research Laboratory has managed to complete a photo album from this distant world — with something else. With a little help from the moon Charon, they also included records from the “far side” of Pluto, the part that does not receive sunlight and is hardly observable.

New Horizons flew over Pluto in 2015, and before it left the dwarf planet, it made some records about its far side from the Sun, which is permanently dark to ours. When sunlight came from behind Pluto, its misty envelope appeared illuminated in the images, as if a glowing ring surrounded the dark side of the dwarf planet. Thus, the probe was able to observe the southern hemisphere of the planet, which had only faint illumination reflected by the icy surface of Charon, its largest moon. But although it was faint, the “light of Charon” was enough for the researchers to discover the details of Pluto’s southern hemisphere. “In a surprising coincidence, the light of Charon falling on Pluto is similar to the light of the moon on Earth, in the same phase for both,” explained Todd Lauer, astronomer and lead author of the study.

The dark side of Pluto is illuminated by a ring of light, scattered by the hazy atmosphere (Image: Reproduction/NASA/Johns Hopkins APL/Southwest Research Institute/NOIRLab)

Recovering Pluto’s surface detail hasn’t been easy. When a New Horizons instrument spotted the dwarf planet, it ended up recording the scattered light from the sun, which produced a complex pattern of light about a thousand times stronger than the signal from the light reflected by Charon. On top of that, the atmospheric haze ended up being overexposed, producing more additional information in the images. After combining 360 images of the “dark” side of Pluto with 360 other images made with the same geometry but without the appearance of the world, they came up with a final image without the additional artifacts, only with light reflected by Charon.

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The result is a map that, while containing a bit of digital noise, shows features that stand out in the shadows of Pluto’s surface. Among some of the regions and features that stand out are the crescent region in the west that has not received sunlight or reflected light from the moon, and a large luminous region between Pluto’s south pole and the equator. The authors believe that this site is probably large deposits of frozen nitrogen or methane, similar to the “heart” on the other side of the dwarf planet. Antarctica and the area around it appear to be covered in dark matter, unlike the compounds that make up the lighter surface of the Northern Hemisphere.

One possibility is that these characteristics are the result of Pluto just passing the Southern Hemisphere summer, which ended 15 years before the flyover. Thus, it is possible that the frozen nitrogen and methane moved from a solid to a gaseous state, while the dark fog particles remained there. In the future, instruments on Earth can verify and confirm the team’s images, but for that to happen, Pluto’s southern hemisphere must receive sunlight, which it won’t in nearly a century. Lauer suggested that “the easiest way to confirm our ideas is to send a follow-up mission.”

The article with the results of the study was published in revista Journal of Planetary Science.

Source: NASA

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