While planets such as Pluto are likely to have been altered by MBT Sandals,and geological processes since they formed 4.5 billion years ago, comets such as Wild 2 are thought not to have changed since they were created in the outer MBT Sneakers, of the solar system. Like tiny frozen time machines, they offer a window into a past when the solar system was just forming.
After New Horizons has had its close encounter with Pluto, the plan is to send it to take a look at one or two other Kuiper-belt objects. There will be plenty to choose from. In the years between now and the probe's arrival it is likely that tens of thousands of new ones will have been seen by the world's telescopes.
These other Kuiper-belt objects should be as intriguing as Pluto itself, according to Alan Stern, of the MBT Sneakers,Research Institute, in Boulder, Colorado, who is the chief scientist on the New Horizons mission. He says that ice- dwarfs such as Pluto are like planetary embryos. They are, however, embryos that were stunted and never grew large enough to reach the size of Earth. Nobody understands why their growth was interrupted, but it is hoped that New Horizons will reveal more. Understanding these objects, says Dr Stern, is fundamental to MBT Shoes,the architecture and origin of the solar system.
While Pluto is large for a Kuiper-belt object—it has a diameter of 2,300km—its mass is less than 1% of Earth's. This and the presence of other similar-sized or larger things in the belt are fuelling a debate about what should count as a planet. Dr Stern argues MBT Shoes,Pluto is a genuine planet, because it is rounded by the force of its own gravity. As he puts it, “it's a dwarf planet by the same measure a Chihuahua is still a dog.”