. ▁It ▁is ▁w ides p read ; ▁it ▁does ▁not ▁seem ▁to ▁have ▁a ▁point ▁source . ▁ ▁The ▁surface ▁appearance ▁of ▁some ▁regions ▁of ▁Mars ▁is ▁due ▁to ▁how ▁this ▁unit ▁has ▁de grad ed . ▁ ▁It ▁is ▁a ▁major ▁cause ▁of ▁the ▁surface ▁appearance ▁of ▁lo b ate ▁de br is ▁apr ons . ▁The ▁layer ing ▁of ▁the ▁upper ▁pla ins ▁mant ling ▁unit ▁and ▁other ▁mant ling ▁units ▁are ▁believed ▁to ▁be ▁caused ▁by ▁major ▁changes ▁in ▁the ▁planet ' s ▁climate . ▁ ▁Mod els ▁predict ▁that ▁the ▁ob liqu ity ▁or ▁t ilt ▁of ▁the ▁rot ational ▁axis ▁has ▁varied ▁from ▁its ▁present ▁ 2 5 ▁degrees ▁to ▁maybe ▁over ▁ 8 0 ▁degrees ▁over ▁ge ological ▁time . ▁ ▁Period s ▁of ▁high ▁t ilt ▁will ▁cause ▁the ▁ice ▁in ▁the ▁polar ▁caps ▁to ▁be ▁red ist ributed ▁and ▁change ▁the ▁amount ▁of ▁dust ▁in ▁the ▁atmosphere . ▁ ▁Linear ▁R idge ▁Network s ▁ ▁Linear ▁r idge ▁networks ▁are ▁found ▁in ▁various ▁places ▁on ▁Mars ▁in ▁and ▁around ▁cr aters . ▁▁ ▁R id ges ▁often ▁appear ▁as ▁mostly ▁straight ▁segments ▁that ▁intersect ▁in ▁a ▁lattice - like ▁manner . ▁ ▁They ▁are ▁hundreds ▁of ▁meters ▁long , ▁tens ▁of ▁meters ▁high , ▁and ▁several ▁meters ▁wide . ▁ ▁It ▁is ▁thought ▁that ▁impact s ▁created ▁f ract ures ▁in ▁the ▁surface , ▁these ▁f ract ures ▁later ▁acted ▁as ▁channels ▁for ▁flu ids . ▁ ▁Fl u ids ▁c ement ed ▁the