Five of the strangest asteroids and dwarf planets...

Above: Pluto, a world half the size of the US but stranger than anything dreamed up by sci-fi writers.

Most people thinking of space exploration think of the planets - Mars, Venus, even Jupiter and its Moons. But that's missing something - hundreds of somethings in fact: The large asteroids and dwarf planets make up a collection of worlds as varied and compelling as the terrestrial planets. So here are a few of the oddest...

Ceres:
The king of the asteroid belt, Ceres is a dwarf planet nearly a thousand kilometres across. It's also one of the relatively few asteroids to have been visited by a human space craft - in fact the Dawn space probe is still in orbit, surveying this small world. Despite its small size Dawn has shown that there's still recent signs of geologic activity on that 4 billion year old surface, and perhaps even hints of subsurface water.

Above: A simulated flight over Ceres, assembled from data supplied by the Dawn probe.

Vesta:
The first small world visited by the Dawn probe, Vesta proved to be a world with a history of cataclysmic violence. Already suspected to have been a hot, churning, volcanic world in its youth, Dawn found that the tiny world’s entire South Pole had been obliterated, not once but twice, by gigantic asteroid impacts. The largest of these was so huge it left the 'ripples' caused by the shockwave permanently imprinted in the Vestan rock.

 

Above: Dawn's greatest finds at Vesta

Psyche:
Although we've only ever seen this world at a distance, through telescopes, it is due to be visited by a unique space probe (also called 'Psyche') in 2026. Why? Because it's a solid chunk of metal the size of the state of Massachusetts. The only sensible explanation anyone has come up with (so far) is that Psyche was once the core of a planet - a planet that suffered some terrible fate which stripped down to its metal core...

 Above: The bizarre metal asteroid Psyche, and the mission to explore it.

Sedna:
It's unlikely that Sedna, a world 8 billion kilometres from Earth with a year over 11,000 Earth years long, will get a visit from any spacecraft soon. Even so, it's playing a pivotal role in our exploration of the dim outer reaches of our solar system. The dwarf planet's odd shaped orbit could be the result of the gravity of a ninth major planet, far out in space. Or, perhaps even more intriguingly, it could be a sign that Sedna is not really a member of our solar system at all: It could have been a loosely bound dwarf planet of another star, kidnapped by our sun during a rare stellar flyby.

Above: Think you know how far a long way is? Well take a look at the orbit of Sedna...

Pluto:
I take it you've heard of this one? Although the debate still rages in parts as to whether its demotion from planet to dwarf planet was a fair one, I really don't think this immense and incredibly complex ice world cares. From it's weird hundred meter blades of ice, to its nitrogen ice glacier ocean on which mountains float like ice bergs, to the hints that rivers of liquid nitrogen once flowed on its surface and might well still run beneath its subsurface, Pluto has every reason not to give a damn what we teeny humans classify it as. But, thanks to the New Horizons space probe, this beautifully weird world has, been opened up to human eyes...

 
Above: A virtual fly over of Pluto, assembled using data from the New Horizons mission.

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