Did Pluto’s gravity affect the trajectory of New Horizons when it flew past? 

This artist’s concept depicts the New Horizons spacecraft during its encounter with Pluto and its moon Charon. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Key Takeaways:

• Pluto imparted a slight but measurable alteration to the New Horizons spacecraft's trajectory (both bending and acceleration) during its 2015 flyby.
• The minimal nature of this trajectory change was due to the spacecraft's substantial flyby distance (10 Pluto radii), its high velocity (10 times Pluto's escape speed), and Pluto's relatively low mass and gravitational influence.
• These combined factors resulted in a directional modification for New Horizons that amounted to a small fraction of a degree.
• Despite the minor degree of alteration, its precise calculation and integration into subsequent trajectory corrections were critical for the spacecraft's successful targeting of the Kuiper Belt object Arrokoth in 2019.

Key takeaways sponsored by The Space Store

As New Horizons passed Pluto in July 2015, did the dwarf planet alter the probe’s trajectory?

Douglas Kaupa
Council Bluffs, Iowa

Pluto did in fact both bend and accelerate the trajectory of New Horizons when the spacecraft reconnoitered the dwarf planet in 2015, but only very slightly.

There are three reasons the trajectory changes caused by Pluto were so small. One was that the spacecraft flew by fairly far from the world, about 10 Pluto radii (7,380 miles [11,880 kilometers]). Another reason was the spacecraft’s very fast speed of 9 miles (14 km) per second, which is 10 times more than Pluto’s escape speed. Finally, there was Pluto’s low mass and therefore low gravitational influence.

All three factors conspired to reduce Pluto’s influence on the New Horizons trajectory, resulting in a directional change for the spacecraft of a small fraction of a degree. Had we gone closer or been flying slower, the change would have been greater. But it’s worth adding that despite the change being small, it still had to be very precisely calculated and measured, and then factored into the trajectory change we made a few months later with the spacecraft’s propulsion system to target the flyby of the Kuiper Belt object Arrokoth in 2019. Had we not taken that into account, we would have considerably missed the aim point for Arrokoth.

S. Alan Stern
New Horizons Principal Investigator, Boulder, Colorado