When I started working with NASA in 1989 as part of a mission to send spacecraft to Pluto, I knew it would take at least 10-15 years to see results of my efforts.

There was a time when Pluto - which NASA's New Horizons spacecraft at last explored in 2015, a mission I led - was considered the last planet. We now know there are thousands of other - possibly inhabited - planets.

Pluto is just the brightest of the many objects in the Kuiper Belt. It's a fossil relic of the formation of our solar system.

I have July 14, 2015, emblazoned on my calendar. That's our arrival date at Pluto. We are now quite certain of that.

The Kuiper Belt is the largest structure in the solar system. We used to think Pluto was a misfit.

Every mission has life-or-death moments.