In Nature Geoscience's article Independent confirmation of a methane spike on Mars and a source region east of Gale Crater is announced that the reported methane spike on sol 305 by the Tunable Laser Spectrometer-Sample Analysis at Mars (TLS-SAM) on Curiosity was confirmed by Planetary Fourier Spectrometer (PFS) observations onboard the Mars Express spacecraft in the spot-tracking mode. The combination of PFS and TLS-SAM observations strongly suggested that the emission took place outside the crater.
Using wind fields simulations with a general circulation model (GCM) and independently from this trying to find potential methane release structures around Gale crater led the authors to conclude that the Aeolis Mensae region a few hundred km east of the crater was the most likely source of the methane spike.
In this article the authors used the Mars Regional Atmospheric Modeling System for methane transport simulations and concluded that a methane source just outside Gale crater could be excluded to explain the observed methane spikes and even the lower background methane levels.
In the recent article Mars Methane Sources in Northwestern Gale Crater Inferred From Back Trajectory Modeling the authors used new modeling techniques to identify upstream methane emission regions at an unprecedented spatial resolution. The outcome supports surface emission sites in the vicinity of the Curiosity rover. Only if fast methane removal mechanisms would exist, emission sites could be outside Gale crater, most likely to the north.
From the Conclusions chapter:
Methane concentration data from future in situ measurements, especially those collected in consecutive measurements performed within a few hours, could further improve the emission site identification.
So, after having examined the sulfate unit, instead of going further up Mount Sharp, could not Curiosity turn around and head for the northern plains in Gale crater ?
Travelling just 50 m a day, while doing TLS-SAM measurements every day and/or night, it could reach the northern rim in less than 4 years.
Could the scientific value of going up Mount Sharp and that of intensive methane measurements while going north be quantified scientifically and be weighed against each other ?
And if not, could not the fact that the Curiosity rover will be the only one for a long, long time that can do in situ methane measurements on Mars be an extra motive to change to this new, main scientific objective ?