Monkey Head Nebula HD

Imagine, a frigid, distant shadow-region in the far suburbs of our Solar System, where a myriad of twirling icy objects--some large, some small--orbit our Sun in a mysterious, mesmerizing phantom-like ballet within this eerie and strange swath of darkness. Here, where our Sun is so far away that it hangs suspended in an alien sky of perpetual twilight, looking just like a particularly large star traveling through a sea of smaller stars, is the Kuiper Belt--a mysterious, distant deep-freeze that astronomers are only now first beginning to explore. Makemake is a denizen of this remote region, a dwarf planet that is one of the largest known objects inhabiting the Kuiper Belt, sporting a diameter that is about two-thirds the size of Pluto. In April 2016, a team of astronomers announced that, while peering into the outer limits of our Solar System, NASA's Hubble Space Telescope (HST) discovered a tiny, dark moon orbiting Makemake, which is the second brightest icy dwarf planet--after Pluto--in the Kuiper Belt. Ganymede: Ganymede is both the largest moon of Jupiter, our Solar System's planetary behemoth, as well as the largest moon in our entire Solar system. Observations of Ganymede by the HST in 2015 suggested the existence of a subsurface saline ocean. This is because patterns in auroral belts and rocking of the magnetic field hinted at the presence of an ocean. It is estimated to be approximately 100 kilometers deep with a surface situated below a crust of 150 kilometers. A billion years ago, our Moon was closer to Earth than it is now. As a result, it appeared to be a much larger object in the sky. During that ancient era, if human beings had been around to witness such a sight, it would have been possible to see the entire Moon--not merely the one near side face that we see now. A billion years ago, it took our Moon only twenty days to orbit our planet, and Earth's own day was considerably shorter--only eighteen hours long. Stupendous, almost unimaginably enormous tides, that were more than a kilometer in height, would ebb and flow every few hours. However, things changed, as the lunar orbit around our primordial planet grew ever wider and wider. Annually, Earth's Moon moves about 1.6 inches farther out into space. Currently, the lunar rate of rotation, as well as the time it takes to circle our planet, are the same.