NASA is celebrating the 50th anniversary of the Apollo 11 mission this month.

Astronauts on each of NASA's six Apollo missions planted an American flag on the moon.

Brilliant sunlight and a lack of atmosphere to filter it have likely bleached all of the Apollo flags bone-white. It's possible some of the flags are also disintegrating.

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The photos have stood the test of time: A spacesuit-clad Apollo astronaut stands proudly next to a red-white-and-blue American flag on the moon, his national trophy saying: "The United States was here."

Unfortunately, the six flags planted on the lunar surface from 1969 through 1972 haven't fared so well.

Images taken by NASA's Lunar Reconnaissance Orbiter in 2012 showed that at least five out six flags were still standing. However, scientists think decades' worth of brilliant sunlight have bleached away their emblematic colors.

The result? The flags are probably completely bone-white by now, as we first learned from Gizmodo.

Their condition may now be even worse: On the 50th anniversary of NASA's Apollo 11 moon landing (July 20), some of the flags are likely starting to disintegrate.

A company called Annin Flagmakers wove the flags out of rayon, and each one cost NASA a paltry $5.50 (more than $33.00 today when adjusted for inflation). On the surface of Earth, such flags fade in sunlight. That's because ultraviolet light — the same wavelength that causes sunburn — excels at breaking down fibers and colors.

On Earth, some UV light gets absorbed by our planet's atmosphere, though not all of it. But the moon has no atmosphere at all to absorb sunlight, and outside of craters, there is no shade. This means the flags planted by the Apollo astronauts are exposed to constant, glaring sunlight and solar radiation for two-week stretches at a time, since one "day" on the moon lasts about 27 Earth days.

Read more: There is a 'dark side' of the moon, but you are probably using the term incorrectly

In a July 2011 article for Smithsonian Air & Space magazine, lunar scientist Paul Spudis explains:

"Over the course of the Apollo program, our astronauts deployed six American flags on the moon. For 40-odd years, the flags have been exposed to the full fury of the moon's environment – alternating 14 days of searing sunlight and 100° C heat with 14 days of numbing-cold -150° C darkness. But even more damaging is the intense ultraviolet (UV) radiation from the pure unfiltered sunlight on the cloth (modal) from which the Apollo flags were made. Even on Earth, the colors of a cloth flag flown in bright sunlight for many years will eventually fade and need to be replaced. So it is likely that these symbols of American achievement have been rendered blank, bleached white by the UV radiation of unfiltered sunlight on the lunar surface. Some of them may even have begun to physically disintegrate under the intense flux.

"America is left with no discernible space program while the moon above us no longer flies a visible US flag. How ironic."

Will we return to the moon?

An illustration of the spaceship of SpaceX's Big Falcon Rocket, or BFR, flying around the moon. SpaceX

Much has changed since Spudis' lament, but a lot hasn't: As of yet, no human being has returned to the moon.

However, NASA is working hard to fly astronauts into deep space by developing ultra-powerful Space Launch System rockets. The goal is to build a "gateway" space station at the moon that would reach lunar orbit in the early 2020s. A five-year plan that the Trump administration recently announced, called Artemis, endeavors to land astronauts on the lunar surface in 2024.

The lunar space station would be crewed with astronauts, who'd at first fly landers and robots to the moon's surface (perhaps to scout for water deposits that could be mined and turned into rocket fuel). They'd use the facility as a way point to send people to and from the lunar surface on regular missions. However, some Apollo astronauts — while excited — are skeptical about whether NASA can stick to its timeline.

In any case, the commercial sector is increasingly looking like an integral part of NASA's plans to reach the moon.

Tech mogul Elon Musk and his aerospace company, SpaceX, are developing a giant steel rocket called Starship that should be capable of reaching the moon or Mars. By 2023, Musk hopes to launch the company's first space tourist — a Japanese billionaire named Yusaku Maezawa — in one of the spaceships, along with a small crew of hand-picked artists. The plan is to fly them around the moon, but not land on it.

Amazon founder Jeff Bezos, who owns the rocket company Blue Origin, is also eager to move industry into space and colonize the moon. The billionaire recently unveiled Blue Moon, a spacecraft he hopes will help return astronauts to the lunar surface.

Read more: Elon Musk and Jeff Bezos have profound visions for humanity's future in space. Here's how the billionaires' goals compare.

An illustration of "Sparrow," a 1,300-lb robotic lunar lander that could make Israel the fourth country ever to touch the moon's surface. SpaceIL Smaller companies are trying to reach the moon, too. The non-profit SpaceIL, for instance, recently tried to deposit a small lander there, yet tragically failed.

NASA has also launched a competition to select small commercial moon landers that would carry government-sanctioned experiments to the moon (alongside private payloads). Some of these companies might even try to land near the sites of Apollo 11, 12, 14, 15, 16, or 17 and record live views of what the historic areas of the moon look like today.

If that comes to pass, there may be a flag in the frame — and we might settle the question of what happened to them after spending more than 46 years under the sun.

Jennifer Welsh contributed reporting to a previous version of this article.

This story has been updated with new information. It was originally published on April 9, 2017.