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Beautiful and tragic

Using crater counting of the Northern Hemisphere and the ages from some Martian meteorites I don't think it has been billions of years since Mars died.

Crater counting and some basalt meteorites indicate that the Northern Hemisphere might be less than 200 million years old.

Does anyone know of a phenomena that can resurface half a planet?

What effects would an interstellar comet like Borisov have done if it had struck a planet?

A very fast interstellar comet (of modest size) can have the same energy as a much larger slower moving comet from this neighborhood.

Oumuamua and Borisov, oh my.
Main stream science acknowledges that the Northern Hemisphere is buried in basalt (lava). What is contested is that it is just 200 million years old. This is related to a self-contradictory theory called the Late Heavy Bombardment produced by Houston.

Until the appearance of an interstellar asteroid and comet no impact would have had the velocity/energy necessary to produce massive quantities of molten rock. In the absence of a mechanism explaining the seas of basalt on the Moon, Houston moved the impacts backward in time until the Moon was still partially liquid. With the arrival of Oumuamua and Borisov the Late Heavy Bombardment became a failed hypothesis.

The worse case velocity for an interstellar impact appears to be about 500 kilometres per second. The Hipparcos and Tycho Catalogues Table 3.6.3. The 150 Stars with Largest Transverse Velocities . . . . . . 486

(conjecture) If an interstellar comet punched through Mars (entering at Hellas Planitia and exiting somewhere in the Northern Hemisphere) it would have blown away most if not all of Mars’ atmosphere. There are sediments miles deep exposed on Mars, some of which were laid by water. The conditions we see now did not produce these sediments.