This article originally appeared on The conversation.
Humans have been exploring the surface of Mars for more than 50 years. According to the United Nations Office for Outer Space Affairs, countries have sent 18 man-made objects to Mars during 14 separate missions. Many of these missions are still ongoing, but over the decades of Mars exploration, humanity has left a lot of debris on the planet’s surface.
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I am a postdoctoral researcher studying ways to track Mars and lunar rovers. In mid-August 2022, NASA confirmed that the Mars rover Perseverance had spotted a piece of debris thrown out during its landing, this time a tangled mess of nets. And this isn’t the first time scientists have found trash on Mars. That’s because there is a lot.
Where does the debris come from?
Debris on Mars comes from three main sources: scrapped hardware, idle spacecraft, and crashed spacecraft.
Any mission to the surface of Mars requires a module to protect the spacecraft. This module includes a heat shield for when the craft passes through the planet’s atmosphere and a parachute and landing hardware so it can land softly.
The craft discards pieces of the module as it descends, and these pieces can land in different locations on the planet’s surface – there may be a lower heat shield in one place and a parachute in another. When this debris falls to the ground, it can break into smaller pieces, as happened during the Perseverance rover landing in 2021. These small pieces can then be blown around by Martian winds.
Over the years, much small, wind-blown debris has been found, such as the netting material recently found. Earlier in the year, on June 13, 2022, the Perseverance rover discovered a large, shiny thermal blanket wedged into some rocks 2 km from where the rover landed. Both Curiosity in 2012 and Opportunity in 2005 also encountered debris from their landing vehicles.
Dead and Crashed Spacecraft
The nine idle spacecraft on the surface of Mars make up the next type of debris. These craft include the Mars 3 lander, Mars 6 lander, Viking 1 lander, Viking 2 lander, the Sojourner rover, the previously lost Beagle 2 lander, the Phoenix lander, the Spirit rover and the most recently deceased spacecraft, the Opportunity rover. These are largely intact and should be regarded as historical relics rather than rubbish.
Wear and tear takes their toll on everything on the surface of Mars. Some parts of Curiosity’s aluminum wheels have broken off and are believed to be scattered across the rover’s track. Some of the waste is targeted, with Perseverance dropping a drill on the surface in July 2021, leaving it trade in a new pristine bit so it could keep collecting samples.
Crashed spacecraft and their pieces are another major source of waste. At least two spacecraft have crashed and another four have lost contact before or just after landing. Descending safely to the planet’s surface is the hardest part of any Mars landing mission — and it doesn’t always end well.
If you add up the mass of all the spacecraft ever sent to Mars, you get about 22,000 pounds (9979 kilograms). Subtract the weight of the currently operational craft on the surface — 6,306 pounds (2,860 kilograms) — and you’re left with 15,694 pounds (7,119 kilograms) of human debris on Mars.
Why is waste important?
Today, the biggest concern scientists have about debris on Mars is the risk it poses to current and future missions. The Perseverance teams are documenting all the debris they find and checking to see if it could contaminate the monsters the rover collects. NASA engineers also considered whether Perseverance could become entangled in debris from the landing, but have concluded that the risk is low.
The real reason debris on Mars is important is because of its place in history. The spacecraft and their pieces are the early milestones for human planetary exploration.