The New Horizons probe was the first spacecraft to study Pluto and its satellite system in detail, and the station collected a huge amount of scientific data. Astronomers revealed a rare shot of the night side of the planet compiled from 360 individual images.
The team of the interplanetary station New Horizons has published an image of the southern hemisphere of Pluto, which was hidden at night during a close flyby of the spacecraft past the dwarf planet. On it, the researchers found a bright area that could be an accumulation of nitrogen or methane ice.
Scientists compiled and analyzed an image of the night side of Pluto
New Horizons was launched into space in 2006, and in 2015 made a close flyby past Pluto for the first time in history. This encounter gave us images of both the dwarf planet and its satellites. In early 2019, the station approached the Kuiper Belt object Arrocot for the first time, receiving detailed images of it. Now the device is heading to the borders of the solar system, exploring the environment and other objects in the Kuiper Belt.
While flying past Pluto, New Horizons received detailed images of only the part of the planet that was well lit. The station also took pictures of the night side of Pluto when it flew away from it, but it was not possible to see so many surface details on them.
The night side of Pluto
A group of researchers from a team led by Tod Lauer of the NOIRLab (National Optical-Infrared Astronomy Research Laboratory) presented images of the invisible part of Pluto, which was illuminated only by the scattered surface of Pluto’s largest moon Charon by sunlight. At the time of filming, Pluto’s southern hemisphere was in winter, similar to the polar night on Earth. The seasons change on a dwarf planet every 62 years.
Composing the image of Pluto’s night side
The final image of Pluto’s night side was compiled from 360 LORRI images of Pluto itself, and another 360 images taken with the same geometry but without Pluto. This allowed scientists to remove as many artifacts from the image as possible, leaving only the details of Pluto’s surface.
In the resulting image, the researchers identified several areas. Scientists noted a dark crescent to the west, where neither sunlight nor light from Charon has fallen, and a large bright area that could potentially be deposits of nitrogen or methane ice. Scientists also found that the south polar region at the time of the survey had a significantly lower albedo than the north polar region of the planet, which may be due to the sublimation of nitrogen ice or the deposition of haze particles during the recent summer.
Past discoveries about Pluto
An hour and two minutes after the closest approach to Pluto, New Horizons observed a rare event, the covering of the Sun by a planetoid. This “eclipse” allowed scientists to obtain more accurate data on the atmosphere of the dwarf planet. According to NASA experts, it was previously observed at altitudes not exceeding 270 kilometers.
New observations have discovered Pluto’s atmosphere for the first time at an altitude of at least 1,600 kilometers above the surface. The transmission spectra obtained with the Alice spectrograph show that the upper layers are composed mainly of molecular nitrogen, while the lower ones contain some amounts of methane and more complex hydrocarbons.
New Horizons also found that Pluto is followed by a nitrogen “tail”. Measurements of the planet’s magnetosphere have shown that the solar wind, made up of high-energy charged particles emitted by our Sun, continually “blows away” the upper atmosphere of the planetoid, leaving behind a plume tens of thousands of kilometers long, consisting of ionized nitrogen.
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• Lauer, T. R., Spencer, J. R., & Bertrand, T. (2021, October 20). The Dark Side of Pluto. The Planetary Science Journal.
• Talbert, T. (2021, October 27). Researchers image pluto’s dark side in faint moonlight. NASA.