We’re only a day from reaching everyone’s favorite demoted planet—a Pluto Day, that is. The icy dwarf world rotates once every 6 days, 9 hours, and 22 minutes, meaning that at 10:28 p.m. EST tonight, Pluto will have itself just one more spin before the New Horizons spacecraft makes its closest approach on July 14th.

We typically think of a day as being 24 hours long, but that’s a very Earth-centric perspective. The length of time it takes to complete a full, 360 degree rotation varies widely across the planets in our solar system, from Venus’s interminable 243 Earth-days to Jupiter’s zippy 9.9 Earth-hours. That’s because a planet’s rotational rate depends on many different things, from the angular momentum it picks up during its formation to gravitational interactions with moons to geologic activity and even weather events. Day length can also change over time, which is why scientists have to keep inserting leap seconds into Earth’s clock and breaking the Internet.


As alien as Pluto may seem, the dwarf world’s day length is actually fairly Earth-like compared with some of our other neighbors. What’s more, at 3.67 billion miles from the sun, Pluto still receives enough light at midday to be comparable to Earth at dawn and dusk. NASA’s dubbed this special time of interplanetary connectedness “Pluto Time.”

Whether or not Pluto bears any other similarities to Earth—such as a nitrogen-rich atmosphere, complex seasons, and volcanic activity—is all part of of what we’ve shipped New Horizons off to find out. We’ll know a lot more in a Pluto day.

[Science News]

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Top image: Artists depiction of Pluto’s surface, via Wikimedia