It's Pluto time.
After a nine-year journey, NASA's New Horizons spacecraft is nearing its closest approach of Pluto. The event will be humankind's first ever encounter with the dwarf planet, which will mark the end of "firsts" in our exploration of the original solar system.
Here's a quick-and-dirty guide to enjoying the momentous occasion:
Where are we going?
New Horizons is zipping toward Pluto, the smallest and most distant "planet" in our solar system (736 miles across and 3 billion miles away, orbiting the sun only every 248 years).
These days Pluto is classified as a "dwarf planet," a.k.a "oh jeez there are a lot of weird planet-like things out there, what even are they," and we now know it sits on the inner edge of the Kuiper Belt.
Pluto may be our official destination, but the Kuiper Belt in general is no less exciting: It's the farthest region of our solar system, discovered in 1992, and it contains the cold debris of our system's formation. Scientists estimate that it could have hundreds of thousands of bodies larger than 62 miles across, many of them perhaps close to Pluto in size. We already know that one, Eris, is more massive than Pluto -- just not as wide across. Comets probably number in the trillions.
When New Horizons zips past Pluto at over 30,000 miles per hour on Tuesday, it's going to give us our first good look at a very interesting neighborhood.
If Pluto is so cool, shouldn't it become a planet again?
Noooo, stop asking this, please.
Look: There are a lot of worthwhile things in our solar system that aren't planets. Maybe New Horizons will find something so interesting that the powers that be will decide to redefine what makes a "planet" yet again.
But it probably won't, and that really doesn't matter, and please don't get hung up on it! Dwarf planets are no less exciting than planets. The categorization is just humankind's way of trying to understand the multitude of amazing and unique objects in the solar system. Love Pluto for what it is -- Pluto. Call it whatever you want. Keep it in your heart as the unofficial ninth planet in the solar system. Refuse to drop the "p" from your planetary mnemonic devices.
Just please, please, don't think that Pluto's importance hinges on how scientists classify it. And don't think that Pluto's reclassification in any way diminishes New Horizons -- Pluto hasn't changed since the spacecraft launched, and it hasn't gotten any less interesting! We've just come to understand the solar system a little bit better -- and hopefully, after this week, we'll understand it just a little bit more.
When does this happen?
Good question! It's complicated.
The flyby itself -- that is, the closest approach to Pluto, after which the spacecraft will keep shooting into the Kuiper Belt -- is set to occur at 7:49 a.m. Eastern time on Tuesday, July 14.
But we won't know for sure that it happened until later for a couple of reasons: First of all, when an object is 3 billion miles away, it's not going to be able to send an instantaneous report back to Earth. Right now New Horizons has a communications delay of a little over four hours.
But there's a bigger problem: To get its best pictures and observations of Pluto, the spacecraft has to point its equipment away from Earth. It can't look at Pluto and look at us at the same time. Once it's done doing science, it has to readjust so it's capable of communicating with mission control again.
If everything goes as planned, mission control will get a small packet of data sometime around 9 p.m. Eastern time on Tuesday. Keep an eye on the blog -- we'll make sure you know how to watch live.
There is of course a chance that something will go wrong, and that we'll never actually hear back from New Horizons after it meets Pluto for the first time. That's why Tuesday is going to be so suspenseful, and also why I'll definitely be crying at some point no matter what happens.
The Planetary Society's Emily Lakdawalla explains the downlink process (and the actual data we'll be waiting for) in more detail on her blog.
When will we see Pluto?
We already have! The photos are getting better and better. Over the course of the past few months, Pluto and its moons have gone from points of light in Hubble photos to real, beautiful, fascinating worlds. Here are links to a few images:
But it's true that the photos taken during the actually flyby will blow these out of the water. You can expect one last pre-flyby pic at around 8 or 9 a.m. Eastern time on Tuesday (just when we're starting to really bite our nails), and the first official flyby pic will come online sometime on Wednesday, July 15 -- we hope around 3 p.m. Eastern time.
Why are we doing this?
Spirit of exploration isn't a good enough reason for you? Fine.
Pluto and the other objects in the Kuiper Belt are considered remnants of the very first days of the solar system. They've also stayed very, very cold for the past 4.6 billion years, which means they haven't changed as much as objects closer to the sun. By examining the atmosphere and composition of Pluto and its moons, scientists may learn things that can inform our models of the formation of the solar system. You can read more about that here.
If New Horizons stays healthy during its flyby, it might get funding for an extended mission. NASA has already picked a few Kuiper Belt objects that might be good targets, and if the extension is approved, then New Horizons may burn some of its remaining fuel to reorient itself toward a new destination. We'll be getting a close look at Pluto and its largest moon Charon, and a glimpse of the dwarf planet's tinier moons -- but the more Kuiper Belt objects we can see, the better.
If you're wondering why we're flying by instead of orbiting, check out this earlier post.
How do I make sure I don't miss anything?
I'm soooo glad you asked. You can start by following me on Twitter, because I'll be hustling to give you constant Pluto updates all week. I also retweet a lot of the other space dorks you should be following, so you can make your social media feeds as Pluto-centric as you please.
You should also follow WashingtonPost on Snapchat, because we'll be sending you some fun updates that way on Tuesday. Consider downloading Periscope as well, so you can make sure you don't miss my livestreams from the mission center (though we'll be putting a lot of those online later, so don't worry if you're not glued to your phone).