Final answer:
The new study suggests that methane gas is responsible for ice-capped mountaintops on Pluto, as the frozen nitrogen in its lowland basins can persist for a long time.
Step-by-step explanation:
According to a recent study, methane gas may be the cause of Pluto's ice-capped mountaintops. The bright regions visible on Pluto's surface are lowland basins, which could be kilometers deep frozen nitrogen seas. When Pluto gets closer to the Sun, it can release both methane and nitrogen gas, but they do so very slowly, which keeps a large bowl of frozen nitrogen in place. Thus, the new study suggests that methane gas is responsible for ice-capped mountaintops on Pluto.