Space photo of the week: 1st-ever close-up of Neptune is Voyager 2's final portrait of a planet

What it is: One of the final photographs of Neptune taken by NASA's Voyager 2 probe

Where it is: 2.8 billion miles (4.5 billion kilometers) from the sun

When it was taken: Aug. 25, 1989

When it was shared: Aug. 19, 2024

Why it's so special: Only one spacecraft has ever visited the eighth and most distant planet from the sun.

On Aug. 25, 1989, NASA's Voyager 2 spacecraft took the first-ever close-up images of Neptune. This one — among the last full-disk photos taken before the probe ended its "Grand Tour" of the planets — became one of the most iconic. It revealed Neptune as a deep azure blue, which colored the public's perception of the planet for decades. (That is, until a new treatment of Voyager 2's images earlier this year revealed Neptune's true color to be a much lighter blue green.)

Voyager 2's original images were taken in false color using filters — a standard technique used by planetary astronomers. In this case, blue and green filters were used alongside one that passes light at a wavelength absorbed by methane gas. According to scientists, hydrogen and helium dominate Neptune's atmosphere, but methane gives it its blue appearance by absorbing red light. The filters make methane look dark blue in this image, but they also reveal a semitransparent haze layer across the planet. The bright-red edge around Neptune is caused by the haze scattering sunlight at higher altitudes, above most of the methane.