A journey of nine years and 4.8 billion kilometers (three billion miles) finally came to its summit yesterday as NASA’s unmanned New Horizons spacecraft reached the dwarf planet Pluto for its long-awaited flyby.

Here are six fascinating facts we’ve learned about the dwarf planet this week:

1. Pluto’s heart does not stand still

Highly visible in the latest images, the landscape of Pluto's heart-shaped area – which is probably caused by frost – is constantly changing. New Horizons planetary scientist Bonnie Buratti said to Popular Science: “We have been monitoring what we now know as the heart for 60 years, and it does look like that heart thing has been eroding away over time.”

2. Pluto may be little - but it’s bigger than we thought

New Horizons is also recording more accurate measurements for Pluto. The latest and most accurate measurement sent back has Pluto with a diameter of 2,370 kilometers (about 1,473 miles), which is about the length of 56 marathons.

This measurement is about 70 kilometers (44 miles) more than what scientists previously estimated for Pluto’s middle. And this means Pluto is the largest object in our Solar System beyond Neptune’s orbit.

3. Oh, my! Pluto’s craters could be named after Star Trek characters

Craters on the surface of Pluto are likely signs of deep impact from smaller space rocks colliding with the planet. Researchers may name some of these craters after characters from Star Trek.

^{This screenshot from a Google+ Hangout in 2013 illustrates how some features on Pluto could have Star Trek names. SETI Institute/Space.com}

4. There’s something in the air

Excuse you, Pluto! New Horizons detected nitrogen emissions from Pluto as early as five days away from its closest approach, much earlier than researchers predicted.

Because New Horizons picked up these whiffy emanations from 6 million kilometers (3.7 million miles) away rather than the predicted 2.5 million kilometers (1.6 million miles), it suggests that the source of the gassy releases could be much stronger than estimated, the atmosphere of Pluto is much thinner than previously thought, or something else entirely. Fortunately, New Horizons should have collected sufficient data on its flyby to determine a definite reason.

5. The dark side of Pluto

Dark spots have been noticed on Pluto's surface. What’s strange about these irregularities is their similar size and spacing. Unfortunately, they had rotated out of view when New Horizons arrived, so we won't learn much more about them from this mission.

^{The last view of Pluto's dark spots as seen by New Horizons before the flyby. NASA} 

6. Those caps are definitely ice, ice baby

There were theories that Pluto had ice caps but nothing was for certain – until now. The ice has been confirmed as frozen methane and nitrogen ice.