While SpaceX and Musk might have gotten all the calculations right as far as getting the car into space is concerned, the need to sterilise the car and the mannequin might have slipped their minds. When NASA generally prepares a spacecraft to land on other planets, its Office of Planetary Protection makes sure that the spacecraft is completely sterile. But in this case, the Tesla Roadster was never intended to land, which is why the Office of Planetary Protection did not deem cleaning the spacecraft necessary.
Jay Melosh, a professor of earth, atmospheric and planetary sciences at Purdue University said, "If there is an indigenous Mars biota, it’s at risk of being contaminated by terrestrial life.”
Talking about the microorganisms adapting to Martian conditions, he said, "Would Earth’s organisms be better adapted, take over Mars and contaminate it so we don’t know what indigenous Mars was like, or would they be not as well adapted as the Martian organisms? We don’t know.”
The lack of oxygen in space will ensure that Musk's Tesla Roadster does not ever rust, but the lack of reacting element also ensures that the bacteria and microorganisms stay potent for as long as the Tesla remains in space.
“Even if they radiated the outside, the engine would be dirty,” says Melosh. “Cars aren’t assembled clean. And even then, there’s a big difference between clean and sterile.”
The report by Purdue University states that extreme temperatures, low pressure and unfiltered cosmic radiation make space a difficult environment for the organisms. But this may not be enough to kill the bacteria.
A professor of aeronautics and astronautics at Purdue while also being an experienced worker at a lab that specialises in freeze-drying bacteria, Alina Alexeenko stated, "The load of bacteria on the Tesla could be considered a biothreat, or a backup copy of life on Earth.”
While this does raise concerns, it is unlikely that the Tesla Roadster will deviate from its path, enough to drive it into Martian lands.