Pluto and Charon in their natural colors


NASA has published new images of the dwarf planet Pluto and its largest moon Charon which reproduce with the greatest possible accuracy their natural colors. This processing celebrates the 3rd anniversary of the New Horizons space probe’s July 14, 2015 flyby, but also the 40th anniversary of the discovery of Charon, identified by the astronomer James Christy on June 22, 1978 and confirmed in the following days thanks to other observations.

The new images (NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute / Alex Parker) are the result of refined calibrations performed on the data collected by the New Horizons space probe’s Multispectral Visible Imaging Camera (MVIC) instrument. The problem comes from the fact that MVIC’s color filters don’t match the light wavelengths perceived by the human eye. The consequence is that the mission scientists processed the images to create an approximation of what an instrument replicating the human eye would see.

The result was the creation of images of Pluto and Charon that have rather subdued colors compared to the more vivid ones we have become used to over the past three years. The colors are delicate due to the fact that the wavelengths perceivable by the human eye have a narrower range.

Both images were captured on July 14th 2015 during the moments of maximum approach to Pluto, from a distance of 35,445 kilometers (22,025 miles). At that point, Charon was 74,176 kilometers (46,091 miles) away. They were created using only data obtained with the MVIC instrument, without adding data detected by other instruments. The various areas of Pluto and Charon remain clearly visible.

In the case of Charon, the celebration is double thinking of the fantastic New Horizons space probe’s flyby and the fact that it was discovered only 40 years ago. Trying to get more precise data on Pluto’s orbit, on June 22, 1978 the astronomer James Christy noticed a strange bump in an image of what was then classified as a planet and started investigating to understand its origin.

Examining other images of Pluto, James Christy noticed that the bump appeared on different sides and seemed to move around it in a cycle of 6.39 Earth’s days. The chances were that Pluto had either a really gigantic mountain or a satellite.

With the help of his colleague Robert Harrington, James Christy looked for other images in the archive and waited for new observations to be carried out. On July 2, 1978 new images showed a bump where the two astronomers’ calculations predicted. On July 7, they announced their discovery.

That moon was called Charon and is about half the size of Pluto. There are arguments to change its classification because it would be more correct to define Pluto and Charon as binary dwarf planets. It wouldn’t be the first time that Pluto is involved in classification changes after many arguments.

Today we know that Pluto has other, much smaller, moons but it’s thanks to the discovery of Charon that the interest in the dwarf planet increased. This led to the New Horizons mission project and within 40 years we passed from seeing a smudge on a photo with a bump that moves around to the magnificent high definition photos, now also with natural colors.



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