With terrestrial predators, there are constant accusations these are being poached by herders without licences.
It is imperative, therefore, that we do not inadvertently contaminate Mars with terrestrial organisms.
"The difference is that with terrestrial livestock, we've had thousands of years of history to deal with," he said.
Competing head-to-head with terrestrial radio's armies of local sales staff members will not be easy.
As with terrestrial vertebrates, the number of olfactory receptor cells may be very large, up to 10 million.
In addition to a built-in high-tech compass, the service requires pinpoint accuracy available in urban areas only when satellite-based G.P.S. is augmented with terrestrial radio.
He long advised NASA on how to operate its probes to avoid contaminating foreign bodies with terrestrial microbes, as well as accidentally bringing alien ones back to Earth.
Ecosystems across the continent are in dire straits, with terrestrial and freshwater biodiversity rated as "red" based on current trends, and in the outlook for two decades hence.
The instinct to describe what were, necessarily, incredibly indistinct features with words with terrestrial connotations undoubtedly reinforced the sense that Mars was Earth's mirror.
But, compared with terrestrial radio or network TV, the Internet offers fewer direct boundaries to push against; there are no station managers to thumb your nose at.
In other words, humanity must limit itself to one chance in a thousand of seeding another planet with terrestrial life in the course of exploring it.
