Final answer:
If the solar nebula had cooled to 50 K, the inner planets might have included more ices and organic compounds, potentially increasing their sizes and altering their compositions significantly.
Step-by-step explanation:
If the entire solar nebula had cooled to 50 K before the solar wind cleared away the surrounding gas, the compositions and sizes of the inner solar system planets would likely be different from what we observe today. At this lower temperature, it is possible that more volatile materials like ices and carbonaceous organic compounds could have condensed closer to the Sun, including in the inner solar system. Therefore, the terrestrial planets might have been able to incorporate these substances into their compositions, potentially leading to larger sizes due to the increased availability of building materials.
This, in turn, could have affected the planets' densities, atmospheres, and even their potential for hosting life, as the presence of more volatiles and organic materials is significant in these respects. The formation of planets in such a cooler solar nebula might have resulted in a more homogenous composition of planets throughout the solar system, blurring the distinction we currently see between the rocky inner planets and the gas and ice giants further out.