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New Horizons could help us locate possible planets beyond Neptune

Artist's impression of NASA's New Horizons spacecraft encountering a Pluto-like object in the distant Kuiper Belt.

Artist’s impression of the New Horizons spacecraft encountering a Kuiper Belt Object, as part of an extended mission after the Pluto flyby. Image Credit: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI)

The recent discovery of evidence of a giant planet lurking in the outskirts of the Solar System made by Caltech astronomers has re-ignited the discussion about the existence of planets beyond Neptune. We could be really on the verge of confirming the presence of a hypothetical ‘Planet Nine’ and NASA’s New Horizons spacecraft, our messenger to Pluto and trans-Neptunian objects might have the final word in this debate.

New Horizons was launched in January 2006 and made its closest approach to Pluto on July 14, 2015. After the successful encounter with the dwarf planet, the probe entered the next phase of its mission dedicated to studying icy celestial bodies beyond Neptune’s orbit, called Kuiper belt objects (KBOs).

NASA now considers the time right – to make use of this spacecraft to hunt for possible planets in this area.

A study conducted by a scientist before New Horizons’ encounter with Pluto laid out perspectives of finding the location of massive objects by employing the spacecraft’s capabilities.

Lorenzo Iorio of the Italian Ministry of Education, Universities and Research, argued that radio tracking apparatus aboard New Horizons should be able to detect hypothetical planets hiding at the very fringes of the Solar System. A research paper detailing his study was published online on Jan. 29 on the arXiv pre-print server.

Mysterious Orbital Alignment of KBO objects with Hypothetical Planet 9

The six most distant known objects in the Solar System with orbits exclusively beyond Neptune (magenta) all mysteriously line up in a single direction. Also, when viewed in three dimensions, they tilt nearly identically away from the plane of the Solar System. Batygin and Brown show that a planet with 10 times the mass of the Earth in a distant eccentric orbit anti-aligned with the other six objects (orange) is required to maintain this configuration. Image & Caption Credit: Caltech/R. Hurt (IPAC)

New Horizons is equipped with the Radio Science Experiment (REX), an uplink radio science instrument with radiometer capabilities. It was designed to study surface conditions on Pluto; in particular, atmospheric temperature and pressure.

Iorio has suggested that REX could also be used for accurate radio tracking of anthropogenic objects beyond the Solar System’s outermost planet. The fact that the spacecraft is spin-stabilized would help in these observations and measurements.

The location of a possible unknown planet can be indirectly derived from its putative gravitational pull on known objects in the Solar System. According to Iorio’s research, New Horizons should be able to reach an accuracy of its range of 33 feet (10 meters) over distances up to 50 AU (astronomical units; 1 AU is equivalent to approximately 93 million miles or 150 million kilometers).

“This should allow to effectively constrain the location of a putative trans-Plutonian massive object, […] whose existence has recently been postulated for a variety of reasons connected with, e.g., the architecture of the Kuiper belt and the cometary flux from the Oort cloud,” the paper reads.

Iorio’s computations anticipate that New Horizons would be capable of detecting an Earth-sized rock-ice planetoid at some 100 to 200 AU as it would impact the range of the spacecraft at a kilometer level. The same applies to a Jovian-mass planet at 10,000 to 20,000 AU; it should be easily detectable by the REX instrument.

There is also a possibility of detecting a potential planet directly from its emitted electromagnetic radiation, either in the visible or in the infrared. However, as the author of the paper concludes, imaging so distant bodies would be quite difficult for New Horizons with present-day technology.

New Horizons is currently on course for a close flyby with a KBO designated 2014 MU69, located about a billion miles farther from the Sun than Pluto. It should arrive there on Jan. 1, 2019. This long and demanding journey could be a great opportunity for the spacecraft to look out for the hypothetical ‘Planet Nine’ by keeping its scientific ears and eyes open.

CGI depiction of hypothetical 'Planet Nine' with lightning.

CGI depiction of hypothetical “Planet Nine” with lightning. Image Credit: Caltech / R. Hurt


Tomasz Nowakowski is the owner of Astro Watch, one of the premier astronomy and science-related blogs on the internet. Nowakowski reached out to SpaceFlight Insider in an effort to have the two space-related websites collaborate. Nowakowski's generous offer was gratefully received with the two organizations now working to better relay important developments as they pertain to space exploration.

Reader Comments

We think we have found Planet Nine which we call Vulcan:

Estimates of its mass may be found here.

It’s orbital parameters can be found here:

And it’s orbital period verified here:

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