Could it be that the
Mysterons like their Vindaloo and pints after a hard day of scoping out Earth for conquest?
Its just possible. Also there have been suggestions that Mars is in fact geologically active as there have been recent signs of
some level of seismic fluctuation suggesting underground magma.
My hypothesis: the magma superheats pockets of methane dating back from a time when Mars did support life (about 1B years ago)
during the late Hesperian, resulting in it leaking to the surface through existing micro fractures in the rock.
In fact it is now believed that lakes on Mars persisted even longer as recently as 230M years ago in a few small areas where the salt
content was particularly high.