There’s better equipment on Earth
For all the wonders robotic space missions have to offer, they are limited by mass, power, and size requirements. We can’t carry all our large, precise laboratory equipment to space. That limits us when we want to precisely know a rock’s age, the conditions in which it formed, and whether it carries signatures of past life, said Jeffrey Johnson, a planetary geologist at the Johns Hopkins University Applied Physics Laboratory.
“Many Martian science objectives can only be achieved by analyzing returned samples in laboratories on Earth,” he said. “The sophisticated instruments at such facilities can detect subtle chemical, mineralogical, and morphological signatures with greater precision and accuracy than is possible with miniaturized robotic instruments on the Martian surface.”
Whereas a single spacecraft instrument tends to be designed for one particular function, the samples we return from Mars can be subjected to the full range of current and future scientific tools available on Earth.
“It’s not that we can’t miniaturize and flight-harden one instrument, it’s that we can’t do it for all the instruments and analyses that we’d be able to perform on these rocks once they’re returned to Earth,” said Amy Williams, an assistant professor in geological sciences at the University of Florida.
Many important analytical tests performed on rock and soil samples require careful preparation using fluids or slicing at ultrafine, nanometer scales. That just can’t happen on Mars. Nor can we bring to Mars the full range of equipment found in a single geosciences department, let alone the scope of advanced laboratories around the Earth. With returned samples, multiple labs will work together to validate, verify, and confirm key findings — multiple lines of evidence for, and confidence in, important scientific discoveries. This level of certainty and reproducibility is critical for bombshell results such as a possible sign of past life.