Convert from petameter to mark twain

Unit Definition (petameter)
The petameter is a metric unit of distance equal to 10E12 kilometers. This is equivalent to about 621.371 billion miles or 0.1057 light year. The distance from the earth to the nearest star (other than the sun) is about 40 petameters.

Unit Definition (mark twain)
The mark twain or twain is an old word for the number two, derived from the Anglo-Saxon twegen. The American author Samuel Clemens (1835-1910), who had been a riverboat pilot on the Mississippi in his youth, took his literary name from a traditional riverboat phrase "mark twain", meaning "exactly two" fathoms of water. This was the minimum depth needed for the boats to operate safely without running aground.