Curiosity Kills Uncertainty On Mars

Scientists believe Mars has lost most of a once-far-thicker atmosphere. But molecular composition data supporting that hypothesis have suffered high levels of experimental uncertainty: Error bars in graphs of data from the Red Planet often exceed the measured values themselves. Measurements from NASA’s Curiosity rover now bolster the atmospheric loss idea by greatly reducing the uncertainty, according to researchers led by the space agency’s Paul R. Mahaffy and Christopher R. Webster (Science 2013, DOI: 10.1126/science.1237966 and 10.1126/science.1237961). The rover’s Sample Analysis at Mars suite analyzed atmospheric samples with its quadrupole mass spectrometer and tunable laser spectrometer. The atmosphere has more of the heavy carbon isotope ¹³C than predicted, both instruments found, with far less experimental uncertainty than data from previous Mars landers, martian meteorites recovered on Earth, and Earth-based telescopes. The finding supports the atmospheric loss idea, the researchers say, because as gases escape, the molecules with heavier isotopes are the last to go. Separately, hydrogen, carbon, and oxygen isotopic ratios in martian carbon dioxide and water vapor mirror those of nearly 4 billion-year-old martian meteorites. That suggests most of the atmospheric loss occurred earlier, near the beginning of Mars’s history, the researchers say.