I have to come to the defense of Ms. Brennan here…
Margaret Brennan is perhaps the most competent news anchor in the business. I’m sure she meant to say “a mile a second”, which would be at the threshold of hypersonic speed. The phrase, “a mile a minute” is an old expression which goes all the way back to the early railroad days, when a train was the fasted vehicle around. It was even faster than a pony express rider. So the expression “a mile a minute” was used for over a century to mean “fast.” I’m sure Ms. Brennan is well read in history and knows that, and that’s how that phrase got crossed up in her neurons.
Also, “a mile a minute” is alliterative, which forms stronger neuro-links and is more likely to be followed by the language processing centers in the brain than a non-alliterative phrase such as “a minute a second.”
Isn’t neuro-linguistics fun (and sometimes embarrassing)?
Still, reporters on average, usually struggle with math and science topics.