We live in a very strange neighbourhood

When I was a youngster we learned a bit of basic stuff about our solar system at school and, because I was a voracious reader, in encyclopedias. They used to be the hard-cover equivalent of Google back then. 😊

The solar system and how the planets formed was all very logical. The sun started as a spinning accretion of gas clouds that condensed until it kind of 'turned on' and started to produce light and energy as a fusion reactor. During this process it spat out concentric rings of material which in turn started their own cycle of condensation. The first planets, those closest to the sun, were comprised of the heavier materials. Thus we had Mercury, Venus, Earth, and Mars. We skipped over the asteroid belt. I don't remember the explanation back then. Not enough material to coalesce into a new planet? Disrupted by Jupiter's massive gravity field? Then it was on to the gas giants – Saturn, mighty Jupiter, Uranus, and Neptune. Then, as an afterthought of left-overs, Pluto. They all danced around the sun in a pretty much flat plane and some of them had moons of their own. Back then the moonless planets were Mercury, Venus, and Pluto.

All this was a simplified view of the solar system, suitable for kids and people not interested in science and astronomy, which was just about everybody. That superficial veneer of uniformity drops off fairly quickly when start to look more closely. Venus and Uranus rotate in the opposite direction to all the other planets (ie the sun rises in the west). Venus's day is longer than its year. Uranus rotates on its side (ie the axis of the poles points at the sun). Pluto turned out to be a binary system with its large moon, Charon, and was demoted to a dwarf planet. Oh – and Pluto does not orbit in the same plane as its erstwhile siblings. Its orbit is at a 17° angle from the plane. It's also more circular, so sometimes Pluto is closer to the sun than Neptune. However, there's no chance of a collision between Pluto and Neptune because "for every two orbits that Pluto makes around the Sun, Neptune makes three, which prevents close encounters between them that would otherwise destabilize their orbits." [1]

We knew there were thick clouds blanketing Venus's atmosphere – but it wasn't until space craft visited that we learned that Venus isn't covered with lush jungles as depicted in many SF stories of the '50s and '60s. 

Another popularly supported myth, originating from Italian astronomer Giovanni Schiaparelli, who observed Mars in 1877, was the network of canals on the planet's surface. We now know that's not true. Mars might have supported water and life eons ago but not anymore. But that myth inspired writers like HG Wells and Edgar Rice Burroughs to write his books.

We knew very little about the outer planets until the seventies when the Voyager missions visited. Astronomers found many, many more moons, marvelled at the rings of Saturn and the moonlets that acted as shepherds of the rings. We found out there are volcanoes on at least one of Jupiter's moons and that moons might have oceans. We learned that ALL of the gas giants – Saturn, Jupiter, Uranus, and Neptune – have rings. In the recent New Horizons visit to Pluto astronomers were astonished to find evidence of lava flows on the planet, since it's so cold out there.

Now we know Jupiter's famous Red Spot, a massive cyclonic storm larger than the diameter of the Earth, is shrinking. Over time Saturn's iconic rings will disappear. And an object (named Kiku) has been spotted in the solar system beyond Neptune's orbit that orbits in the opposite direction to all the other satellites of the sun. Scientists, as they say, are baffled.

There is so much more to learn.

I was delighted to hear Mike Pence say that the US wants humans to return to the Moon by 2024. [2] It's regrettable that the reason is very likely much the same as the reasons for the space race in the 'sixties – rivalry with Russia and I suspect more importantly today, with China. But it hardly matters. Space exploration has languished for too long. It has been forty-seven years since a man stood on the lunar surface and that probably has to happen before we even think about landing anyone on Mars. I'm glad I have a chance of being around when that happens again.