Final answer:
Jupiter has a lower density of 1.3 g/cm³ compared to Mercury's 5.4 g/cm³. Jupiter's density is due to the extreme compression of light gases like hydrogen and helium at its core.
Step-by-step explanation:
The density of the planet Jupiter is lower than that of the planet Mercury. Jupiter's average density is 1.3 g/cm³, which is quite low compared to terrestrial planets like Mercury, which has a much higher density of 5.4 g/cm³. Despite being composed mainly of hydrogen and helium, which are light gases, Jupiter achieves its density through the tremendous compression of these gases in its center, leading to a central density of about 31 g/cm³ under extreme pressures greater than 100 million bars. Conversely, Mercury's higher density implies a substantially different composition from that of Jupiter or Earth's moon.