The new findings are an independent line of evidence that hydrothermal activity is taking place in the subsurface ocean of Enceladus. Earlier results, published in March 2015, indicated hot water is interacting with rock beneath the sea of this distant moon. The new discoveries support that conclusion and add that the rock appears to be reacting chemically to produce the hydrogen.
A moon is defined as a natural satellite that orbits a larger body--such as a planet--that, in turn, orbits a star. The moon is kept in its position both by the gravity of the object that it circles, as well as by its own gravity. Some planets are orbited by moons; some are not. Some dwarf planets--such as Pluto--possess moons. In fact, one of Pluto's moons, named Charon, is almost half the size of Pluto itself, and some planetary scientists think that Charon is really a chunk of Pluto that was torn off in a disastrous collision with another object very long ago. In addition, some asteroids are also known to be orbited by very small moons.
The team of astronomers used the same HST technique to observe the little moon as they did for discovering the small moons of Pluto in 2006, 2011, and 2012. Several earlier hunts around Makemake had not succeeded in spotting it. "Our preliminary estimates show that the moon's orbit seems to be edge on, and that means that often when you look at the system you are going to miss the moon because it gets lost in the bright glare of Makemake," commented Dr. Alex Parker in an April 28, 2016 Hubble Press Release. Dr. Parker, who led the image analysis for the observations, is of the Southwest Research Institute in Boulder, Colorado.