Just what is #UltimaThule?
A) A little-known building block of our solar system
B) A Kuiper belt object
C) The Jan. 1 flyby target for @NASANewHorizons
If you picked "all of the above," well done! 🌟 Send us #askNASA questions now on Facebook Live: https://t.co/KKGXt7aMeg pic.twitter.com/rWia1yH6Fm

— NASA (@NASA) December 19, 2018

Mars' Olympus Mons, the tallest known volcano in the solar system, has such a gradual slope that someone standing at the base couldn't see the summit because it's beyond the horizon. pic.twitter.com/cKjWpKGhIR

— Fermat's Library (@fermatslibrary) December 13, 2018