Geeks Are Outraged: Why Didn’t We Orbit Pluto?

It’s been over a month since New Horizons completed its flyby of Pluto, and many astronomers and space cadets are feeling ennui at the prospect of withdrawing from the dwarf planet’s system. After all of those years of anticipation, isn’t it sad that the probe only did a flyby, and did not remain in orbit around the heart-toting body?


It’s actually a technological, mathematical and financial marvel that we were able to get the probe to Pluto and Charon at all, or so Robert Frost, instructor and flight controller at NASA believes. If we were to make New Horizons an orbiter mission, the complexity and cost would have increased many-fold.


Firstly, in order for a spacecraft to lift off of the Earth’s surface at all, we need some way of propelling it off of the surface. Presently we use chemical rockets, which burn hot and fast. The downside is that the fuel itself has weight, and therefore we actually have to load extra fuel to launch fuel into space, which leaves no room for course changes once the spacecraft is spacebound. This creates a sort of rocket-paradox that NASA solved long ago: by using other planets’ gravity wells as a means of slingshotting around the solar system, we can add velocity to any body in space without the extra fuel.


This allows us to greatly reduce transit time in between planets of our solar system. However, this also means that only planetary bodies with a relatively large mass have any hope of capturing our spacecraft and gently guiding it into orbit. For all its charms, Pluto is still a dwarf planet, which means its gravity is fairly weak. At less than a ninth of our own gravity on Earth, we would have either needed to pack a lot more fuel for a major deceleration, or forgone the entire slingshot method to keep New Horizons from going too fast to enter orbit with Pluto–but this would have made the probe’s trip so long that public interest may have totally died out.

And none of these reasons listed so far accounts for the pull of the Sun’s gravity, which, being strong enough to hold the likes of Jupiter and Saturn in orbit, means that New Horizons literally had to be the fastest vehicle ever launched out of Earth orbit, further compounding the challenge of Plutonian orbit.

Unfortunately, every mission to space is ultimately governed by the money we can muster to launch them. Even acquiring approval to launch the flyby took NASA two years, and two previous plans to visit Pluto were cancelled. It’s a complicated issue, but remember that despite all the challenges, we did make it to Pluto, after all.

Does news of New Horizons and Pluto excite you? Learn more about space with Space Scouts: