Jezero's less-altered floor rocks complicate a lake-only explanation
Contrasts with the Séitah formation leave shielding and groundwater pathways in play. Lake level alone cannot settle how the Margin unit changed.
Jezero once held a lake, but that does not establish which waters altered rock. A September 21 study of its Margin unit sets out both lake-linked and groundwater-only explanations.
One complication lies on the crater floor. The Séitah formation is less altered than the East and West Margin and Western fan. The authors say this is unexpected if lake water caused alteration throughout the units below lake level.
Earlier studies proposed that overlying rocks, since eroded away, shielded Séitah from lake water. The new paper also notes that Séitah lacks the ridges found in the Margin unit. Less fracture-related permeability could have restricted groundwater contact with its rocks.
Neither explanation is a dated account of water moving through the crater. The comparison shows why elevation alone cannot identify the fluid source. The researchers retain lake water and evolving groundwater as alternatives for the silica between grains, while other minerals record later water-rock reactions.
프리즘코리아 편집국 > Alex Rowan
