the non-rules

speculate and guess the stuff uncovered by the remote backhoe like
thing
not limit, so, if ya wanna name every substance that exists, then do
it
in the case of tie, the dealer wins, ya gotta a problem with that?
when they figure-out what the white stuff is, i'll probably not exist
& maybe not ye
chemistry, geology and astronomy buffs are not automatically
disqualified
the grand prize might be the personal regards of some martian organic
and/or inorganic molecules
you are allowed to change the rules at anytime, because contests are
probably often rigged

My guesses

chalk residue, calcium carbonate from water/weathering for 13 lillion
light years

sodium bicarbonate, a mega hangover antidote for an unknown drunk who
thinks he's deity

bad batch of latex paint, from that memorable time when the sherwin
williams mars plant was on strike and management dumped the stuff
before it firmed-up

baking soda------>sodium bicarbonate

oven cleaner, as long as they use rubber gloves the stuff won't eat-up
their hands too badly

septic tank residue, an imperialist-racist roto rooter driver dumped
it up there before daylight savings time began, and
his translator explained the benignity of the product to the martians

more salt storage for mcdonalds fries