When Hubble was launched, it became clear very shortly thereafter that there was a problem with the optics.The mirror was not quite the right shape. And the one program that I had really been looking forward to doing with Hubble was studying outer planets in our solar system, the planets Uranus and Neptune.
Our solar system is actually a wild frontier, teeming with different, diverse places: planets and moons, millions of objects of ice and rock.
There's no doubt that the search for planets is motivated by the search for life. Humans are interested in whether or not life evolves on other planets. We'd especially like to find communicating, technological life, and we look around our own solar system, and we see that of all the planets, there's only one that's inhabited.
I'm a fan of the planets in any combination. When I was born, Mercury, Venus, Jupiter, Saturn, Uranus, Neptune, Pluto, the Sun, and the Moon were all in the sky.
Before 1995, the only planets we knew about were the planets in our solar system.
As you go further from the sun, Jupiter, Saturn and Uranus are each colder in their upper atmosphere. But when you get to Neptune, it's just as warm as Uranus.
Every type of ring behavior we have seen around Jupiter, Uranus, or Neptune can be found in orbit around Saturn. And Saturn's ring system offers the greatest promise of understanding processes in operation within all disk systems, not just those found around planets.
No one planet can tell us everything about the universe, but Neptune seems to hold more than its share of information about the formation of our own solar system - as well as the solar systems beyond.
As our sensitivity improves, we are finally seeing planets with longer orbital periods, planetary systems that look more like our solar system.
When I grew up as a kid, we didn't know there were any other planets outside of our own solar system. It was widely speculated that planet formation was an incredibly rare event and that it's possible that other planets just don't exist in our galaxy, and it's just this special situation where we happen to have planets around our sun.
No matter how you measure it, whether you measure the amount of mass or you measure the number of bodies, most of our solar system exists out beyond the orbits of the asteroids. So we could not have claimed to know our own solar system until Voyager had toured the giant planets.
The planets and moons of our solar system are blatantly visible because they reflect sunlight. Without the nearby Sun, these planets would be cryptic and dark on the sky.
Hubble wasn't designed to look at objects in our solar system, but after it was launched, astronomers realized that with just a little bit of modification to the software, it could look at solar system objects.
Estimates are that at least 70 per cent of all stars are accompanied by planets, and since the latter can occur in systems rather than as individuals (think of our own solar system), the number of planets in the Milky Way galaxy is of order one trillion.
The gas-giant planets in our solar system all have large moons.
Pluto and its brethren are the most populous class of planets in our solar system.