WEIR: I am not a fan. And I’ve mentioned this a few times in the past.
My main concern is this. OK, so just run through a little flowchart in your mind. Start off by saying, “Is there anything that’s on Earth, any organism on Earth, that can survive an eight-month journey through the vacuum of space and the radiation of space, and all the other rigors of being just out in space, that can survive the trip from Earth to Mars?” OK, maybe some tardigrades could; it’s possible; maybe some bacteria inside of something could. OK.
But if your answer to that is no, then there’s no need for planetary protection.
If your answer is yes, then the next question is, “Is there any life native to Earth that could find anything to eat on Mars?” That there’s any, anything . . . “Would it be able to survive and reproduce on Mars?” I don’t think it would. So if the answer to that is no, then there’s no need for planetary protection.
If it’s yes, then ask yourself this: “Would that life that you accidentally introduced to Mars — ” Oh, sorry. Right at the top of this flowchart, ask, “Do you think there’s life on Mars?” If the answer is no, there’s no need for planetary protection. If the answer is yes, then move into these other steps.
Now, so since we’re assuming there’s life on Mars, move ahead to, “Would the Earth life somehow be more adept at surviving on Mars than naturally evolved Mars life to the point that it would displace it and ruin the Mars ecosphere?” Seems very unlikely to me, so I would say no.
But if your answer to that is yes, then ask yourself if the Soviets properly sterilize their probes.
But the atmosphere is very thin so that it is currently major challenge to use it to slow anything down before it slams the ground.
While the temperature is governed by the speed of reentry (large speed relative to atmosphere molecules == high temperature) the heat transfer is depending also on the pressure. Low pressure == lower efficiency of heat transfer. Martian surface is around 600Pa, only 0.6% of Earth surface pressure.
This means, that entire Mars reentry profile is comparable to reentering just 0.6% of Earth atmosphere mass. This happens at around 40km (25miles) on Earth. It means, that if it is able to reach 40km above surface of Earth it is as if it already crossed entire Mars atmosphere.
It is also worth noting that the altitude of peak heating depends heavily on angle of reentry. In a steep reentry the period of peak heating happens much lower. For example, the peak heating for Space Shuttle was at about 70km, but that was only because the profile was kept purposefully extremely shallow to be done with heating before it reaches dense atmosphere.
You be the judge if it is enough to completely burn up Tesla Roadster, I find it difficult to reach any scientific study of Tesla Roadsters being thrown into Mars gravity well to watch results.
Cassini was deorbited on Saturn specifically to minimize the chances of it crashing into one of its moons and contaminating it.
If the car would land on Mars it would be a whole other story but as long as the biggest risk is that it would burn in its atmosphere if it even stood a chance of being captured it doesn’t need any extraordinary sanitation other than the usual clean room treatment.