WHAT I REALLY WANT TO KNOW IS…
What secrets will Ultima Thule reveal?
When New Horizons launched in January 2006, with a specific mission to explore Pluto and the Kuiper Belt, it became the fastest spacecraft ever launched. So, when I tell you that it took us nine and a half years to get to Pluto, then another three and a half to Ultima Thule, it’s not because we were dawdling.
We are travelling over one million kilometres a day which is the distance from Earth to the Moon and back again, and then some. New Horizons reached Pluto in July 2015, and that autumn we fired our engines to redirect our course to Ultima Thule (pronounced ‘ultima too-leh’). We are just about to intercept this unique world on 1 January 2019. It is six billion kilometres from Earth and about 30km in diameter.
Ultima Thule is a world unlike any other that has been explored by spacecraft. It is located in the third zone of our Solar System – in the realm beyond the giant planets called the Kuiper Belt – and it’s about the size of London. We know very little about it except that it formed at the birth of our Solar System, four and a half billion years ago.
It has never left the Kuiper Belt, meaning that Ultima Thule has always existed at a temperature near absolute zero. It’s scientifically valuable because it’s a frozen relic of the ancient Solar System and we have never had a chance to study something so well preserved from that early era. It will tell us about how planets like Pluto formed.
Checking the coast is clear
Before we get to Ultima Thule we will be using the onboard telescopes and cameras to search for hazards, because the spaceship is travelling so fast (50,000km/h) that even striking something the size of a rice pellet could be fatal.
We will use our cameras to navigate to the target, making course corrections based upon their imagery and we will transmit (by radio) the flyby instructions. During the flyby we will be using all seven science instruments aboard New Horizons to collect valuable data. We will map Ultima Thule; search for moons and rings; take its temperature; determine how it interacts with the solar wind and the local environment; and see whether it’s surrounded by any dust (icy grains). We are going to find out about its geology and composition, and whether it is orbited by anything or has an atmosphere. We will study Ultima Thule at a higher resolution than Pluto. Our closest approach to Pluto was about 13,000km. At Ultima, we will travel within 3,500km – almost four times closer than we got to Pluto. Hopefully, these findings will help us decide between models of planetary formation. For example, if we find that Ultima Thule is a monolithic structure that would point towards one theory of how planets were formed. Or we may find it is made up from different compositions which would indicate another theory.
Reporting back
We’ve decided that the spacecraft will spend its time making science observations and not communicating with Earth. We are only close to Ultima Thule for less than a day and New Horizons won’t report back until about four hours after the closest approach. The signal takes about six hours to reach us and that first report will have no imagery or science data. Then it will begin to download imagery and, each day for four days, send home better and better data.
It will take about 20 months to transmit this all back. During this time, in addition to analysing the results, our team will start searching for another target to propose to NASA. As New Horizons has the fuel to operate into the mid 2030s, a visit to another Kuiper Belt object is very likely before 2027.
Looking ahead to Ultima Thule, it’s a very challenging mission. No spacecraft in history has ever conducted a flyby of a world so far away, so we are breaking all the records. The team is feeling excited and we are raring to go.