Curiosity's tunable laser spectrometer and quadrupole mass spectrometer, which make up part of Curiosity's Sample Analysis at Mars (SAM) laboratory, took separate readings of the Martian atmosphere to sort out the elements and measure the pattern of carbon, oxygen, and hydrogen isotopes, the papers report.

"As atmosphere was lost, the signature of the process was embedded in the isotopic ratio," said Paul Mahaffy of NASA Goddard Space Flight Center and the principal investigator for SAM and lead author of one of the two papers about Curiosity.

The results were compared with the very crude readings taken from the 1976 Viking probes and with analysis of the isotope variation found in meteorites that have been blasted off Mars by eruptions or impacts. The new data fits current climate models, and NASA says it's confident about the results.