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The Viking program ended on May 21, 1983. To prevent an imminent impact with Mars the orbit of Viking 1 orbiter was raised on August 7, 1980 before it was shut down 10 days later. Impact and potential contamination on the planet's surface is possible from 2019 onwards.[4]
Does this mean Viking 1 is set to impact Mars at any time?
First of all, the standards in 1970 were quite a bit higher for planetary protection of Mars than they are today. The Viking Landers were sterilized in a giant oven, a step which is not done today. We can build a lander to the same standards as an orbiter back in the day, which basically involve constructing in a clean room. In the 1970s things were sterilized completely that landed.
It is entirely possible that Viking 1 is still orbiting Mars, or it may have impacted. We just don't know. The way to figure this out would be to somehow search the orbit of Mars for a small object, which is theoretically possible using the spacecraft orbiting Mars now. They would be able to find a tiny asteroid orbiting, or a dead spacecraft. This hasn't been done, it just isn't considered enough of a priority to make it happen.
