Scientists have been using a key tracer, isotopes of oxygen, to try and figure out how much atmosphere Mars lost. The problem they have had is that previous measurements have disagreed significantly. New observations by NASA-funded scientists have found that the amount of isotopes of oxygen vary depending on the time of day and the surface temperature of Mars.
Isotopes of oxygen are important to scientists because they help to estimate how much of an atmosphere Mars may have once had, and if the planet could have once been habitable. The tracer also gives scientists an indication of what surface conditions might have been like on the Red Planet early in its life.
Scientist know that while Mars is a dry and cold desert now, there are dry riverbeds and minerals that only from with liquid water that indicate it once had an atmosphere thick enough to retina the heat needed for liquid water. Scientists want to know how Earthlike the ancient Mars environment was and how long these conditions existed.
The team says that isotopes of oxygen are an important indicator of the atmosphere in the past because they have different weights. The lighter isotopes escape to space faster than the heavier isotopes. This means that the remaining atmosphere gets enriched in the heavier isotope. Scientists are measuring 18O and 16O.
The team is measuring the heavier 18O versus the lighter 16O to see how much more atmosphere was on ancient Mars along with an estimate for how much faster the lighter 16O escapes. The team is assuming that the amount of each isotope on Earth and Mars was once similar.
The measurement of those isotopes hasn’t been consistent with different missions measuring different ratios resulting in different understandings of the ancient atmosphere. The team has found that the measurements using a single method vary within a single day. The variance in isotope ratio is about 9% depleted in heavy isotopes at noon versus being about 8% enriched in heavy isotopes by about 1:30 pm compared to normal isotope ratios for Earth oxygen. The new work will help to refine measurements of the Martian atmosphere.