The Solar System: One star,
nine eight planets. Right? Not really. Our Solar System is a treasure trove of more quaint destinations as well. Let the Ministry give you a short tour.
Virtually everyone has heard about the ex-planet Pluto
, and some may even have heard about it’s moon Charon. Charon is special: it’s the biggest moon in the solar system, relative to the “parent” body (followed by the Earth-Moon system). Less well known are the three other moons: Nix, Hydra and (the poetically named) S/2011 P1. Nothing much is known about these nuggets of ice in deep space, but the NASA space probe “New Horizons” is scheduled to visit in July 2015, so we may learn much more then…
Technically, Pluto is a dwarf planet, and it’s not alone. At the time this is written, there are at least eight dwarf planets in addition to Pluto. Ceres was discovered on January 1st 1801, and was immediately recognized as a planet (an honour shared with asteroids Pallas, Vesta and Juno). Located in what would later be known as the asteroid belt, it is by far the largest asteroid. In a close parallell to the demotion of Pluto, Ceres was demoted to an asteroid after astronomers found more and more other rocks in the same area, realizing it wasn’t all that unique after all.
Unlike Ceres, planet Pluto appeared to be alone for a long time after it was discovered in 1930. That all changed in 2002. In the course of a few years we discovered Quaoar, Sedna, Orcus, Haumea, Makemake and 2007 OR10, in addition to a number of smaller objects. Naturally Pluto wasn’t so special anymore. Rather than doubling the number of planets (not counting the large numbers which they suspect are yet to be discovered), they let Pluto take the hit and demoted it from a proper planet to one of the dwarven ones. Ironically, the schoolteachers and armchair astronomers who should be happy not having to teach their pupils the name of 17 planets were pissed, rebelling against the decision.
So, what about these newcomers? Well, we don’t actually know much about them. They’re pretty far out there, pretty small and pretty cold. Most lie around 40 – 70 times as far away from the sun as our planet does (scientists dub the Earth-Sun distance 1 astronomical unit or AU), but Sedna is different: right now, at it’s closest, it is 70 AUs away – but it goes all the way out to 937 AU.
Sedna begs an interesting question. If we just happen to see it now, how many other planets are out there, too cold and small to see? It could be dozens, hundreds, even more. We know there are many – because that’s where the comets come from. Scientists predict there’s a whole cloud of comets and dwarf planets out there – the Oort cloud. Sedna might be an inner object in this cloud, which is believed to be as far out as 50 000 AU. In deed, some claim there might be planets as big as Earth, or even Jupiter somewhere out there. In other words, the time of solar system planet hunting may not be over after all.
Top banner depicts an artist’s imagining of Pluto’s surface. Picture is courtesy of ESO/L. Calçada (Source).