The news media had fun last summer with the notion of a NASA Planetary Protection Officer. Here’s an example from the BBC.In reality, the position is quite interesting and would be an important part of Extraterrestrial Contact. First, let’s get the obvious question out of the way: is this person in charge of preparing defensive weaponry to respond to dangerous aliens? The answer is no. Planetary Protection refers to biological contamination. That could go either of two ways- humans bringing Earth contamination to other planets or Humans visiting other planets and bringing back biological contamination to Earth. Humans visiting another planet and bringing back an organism would be what is called back-contamination. It was closely monitored with the lunar landings.
Given that focus, planetary protection would be a big issue if aliens visited Earth. Biological contamination from an alien world could be quite dangerous here on Earth. In the settlement of Australia Europeans brought rabbits to the continent. Unfortunately, those rabbits did not have any natural predators there and soon Australia was overrun with rabbits. It may sound funny, but it was a serious problem for agriculture. Organisms here on Earth are controlled by the environment- an environment the organism has been a part of for thousands or even millions of years. An Earth organism is unlikely to run amok due to the checks and balances of our ecology. But there would be nothing in place to control an alien organism. Something as seemingly innocuous as a single-celled alien organism could cause terrible problems here on Earth. NASA would want to study a visiting alien craft quite carefully for alien organisms, radiation and other potentially harmful tag-alongs. The aliens themselves could be quite benign, but their contamination could be dangerous.
So, yes, the NASA Planetary Protection Officer would be one of the first scientists called if aliens do land on Earth someday. But they won’t be in charge of nuclear weapons- they will be using electron microscopes and other scientific instruments. Hopefully visiting aliens would have done their homework before landing and made sure their craft, and whatever else touches the Earth atmosphere, is clean and free of foreign contaminants. If not, they better be prepared to answer to NASA.