Watch the Johns Hopkins University Applied Physics Laboratory mission control at the moment New Horizons finally reached Pluto after a mission a 9½-year mission. (NASATV)

With any luck, NASA’s New Horizons spacecraft just made its closest pass by Pluto. At 7:49 a.m. Eastern on Tuesday, the probe – which took off from Earth over nine years ago – was meant to be slipping past Pluto, marking humankind’s first encounter with the dwarf planet.

[This may be the second best photo we’ll ever see of Pluto]

But we won’t actually know if New Horizons did the deed until around 9 p.m. Here’s why: First of all, Pluto is more than 3 billion miles away from Earth. That’s a long way for the lil data packets that New Horizons sends home to travel. It takes about 4.5 hours for signals sent from New Horizons to reach Earth. So even if the spacecraft sent home word of its successful flyby immediately, we wouldn’t hear about it until lunch time. But wait, you say, that still leaves some eight hours and change unaccounted for!

[Everything you need to know about Tuesday’s Pluto encounter]

The extra time lag is by necessity and by design. New Horizons is going dark so it can do as much science for us as possible. New Horizons is zipping by Pluto at about 30,000 miles per hour, so the robot isn’t going to spend much time sitting right on top of the target dwarf planet. But as the spacecraft approaches Pluto’s immediate neighborhood – and keeps driving – we’ll be able to take amazing photos and readings, allowing scientists to determine the composition of Pluto, its atmosphere, and its largest moon, Charon.

It’s precious time, and NASA isn’t going to waste it by having New Horizons phone home immediately.

[Why did NASA spend 9 years getting to Pluto only to fly right past it?]

In fact, New Horizons will be facing the wrong direction through the peak of the flyby. It can’t look at us and at Pluto at the same time, so you better believe it’s going to give Pluto a hard stare for a good few hours.

NASA's Amy Shira Teitel explains why the New Horizons spacecraft is going dark as it passes Pluto. (NASA New Horizons/YouTube)

With all the data collection on the menu (and the incredibly slow download rate), NASA estimates that New Horizons will be sending home the data it collects on Tuesday for the next 16 months.

[Why the July 14 Pluto flyby will be a spectacular event for all of us]

For now, all we can do is cross our fingers and toes and wait. It’s possible that something will go wrong, and that New Horizons will reach out only to tell us the flyby somehow failed. Even worse, the spacecraft could just stay silent. There’s something like a 1 in 10,000 chance that New Horizons will be destroyed by errant space debris. But as of its last contact with Earth, New Horizons was in tip-top shape. Keep an eye on the blog – and follow us on Twitter – for the latest updates.

Final countdown!!!!! We have closest approach! #plutoflyby

A video posted by Rachel Feltman (@rafeltman) on

Read more:

Everything you need to know about Tuesday’s Pluto encounter

This is the last picture we’ll see of Pluto’s mystery spots for a long time

Why did NASA spend 9 years getting to Pluto only to fly right past it?

Graphic: 9 years and 3,000,000,000 miles to Pluto