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.
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.
New Horizons is a very high-tech, small, roughly 1,000-pound spacecraft with the most powerful battery of scientific instrumentation ever brought to bear on a first reconnaissance mission.
Are governments the only entities that can build human spacecraft? No - actually, every human spacecraft ever built for NASA was built by private industry.
To try to really land a spacecraft really on another world is really difficult, and if we lose that ability, it's going to be heartbreaking.
If somebody had told me when I was in graduate school, 'Brian, in 35 years you'll get a chance to fly the first commercial spacecraft with no computers,' I'd have said, 'I don't think so. People are not going to be that stupid.'
The need for a detailed, comprehensive examination of the Saturn system became clear during the early 1980s, after the two Voyager spacecraft made flybys of the planet. These celebrated events were the opening acts in the story of humanity's exploration of Saturn.
When the Voyager 2 spacecraft sped through the Saturnian system more than a quarter of a century ago, it came within 90,000 kilometers of the moon Enceladus. Over the course of a few hours, its cameras returned a handful of images that confounded planetary scientists for years.
I think that, a lot of times, people have this idea that the solar system is entirely explored, that we have sent spacecraft to every planet, we've taken beautiful pictures of everything, and that it's kind of done.
I think every time we send a spacecraft to an asteroid or comet, we learn more.
