Evaluation of Example 14: Elemental Composition of Jupiter

Passage:

“The elemental composition of Jupiter is known to be similar to the sun. … The core would be composed mainly of iron and silicates, the materials that make up most of the earth's bulk. Such a core is expected for cosmogonic reasons: If Jupiter's composition is similar to the sun's, then the planet should contain a small portion of those elements.”

John H. Wolfe, “Jupiter,” Scientific American 230 no. 1, (Jan. 1974), 121.

Analsyis:

Petitio Principii as an argument occurs since the author reasons:

The composition of Jupiter includes elements similar to the sun.
Therefore Jupiter's elemental composition should be like the sun.