Some experts believe the discovery of the elusive ‘Planet Nine’ could be just a few years away – or the hypothetical world’s existence ruled out for good.
But if we find it, how long would it be before we can send a spacecraft to the distant world? And could humans ever make the journey?
Planet Nine is the name given to a proposed planet believed to lurk nearby edge of the solar system. If it exists, Planet Nine is probably a dark, gas or ice giant planet somewhere between five and ten times the mass of the Earth which orbits the sun in a highly elliptical or elongated orbit – out of sync with the rest of the planets.
Researchers suspect Planet Nine is out there because about a dozen objects move outside Neptune’s orbit as if a large object is pulling on it. However, finding this missing world has proven extremely difficult.
But some astronomers believe Planet Nine could be discovered within a few years, once the state-of-the-art Vera C. Rubin Observatory begins surveying the night sky in late 2025.
Related: The elusive Planet Nine could be surrounded by hot moons, and that’s how we would find it
If Planet Nine is ever discovered, space agencies like NASA will want to send a probe to visit the distant world. But first they will have to plan such a mission and get approval.
‘This will take at least ten years or more’ Andreas Hein, a space systems engineer at the University of Luxembourg, told LiveScience in an email. This is mainly because missions have to go through a lengthy and rigorous government selection process, he added.
But this process can be accelerated depending on how strange the world looks in the first readings. Manasvi Lingam, a theoretical astrobiologist at the Florida Institute of Technology, told LiveScience in an email. “If Planet 9 is anomalous in some respect, there could be more interest in expediting such a mission.”
It’s also possible that a private space exploration company, such as SpaceX, could launch missions sooner — possibly as early as five years after discovery — because they aren’t hampered by so much bureaucracy, Hein said.
Reaching Planet Nine
Once a probe is sent to Planet Nine, the next question is: how long will it take for it to arrive?
In 2022 Hein, Lingam and part-time astronomer Adam Hibberd tried to answer this question in a theoretical article posted in the pre-print database arXiv. In this paper, which has not been peer-reviewed, researchers estimate that it would likely take between 45 and 75 years for a spacecraft similar to NASA’s Voyager probes to reach Planet Nine.
These calculations were based on the assumption that Planet Nine is on average about 400 astronomical units from the Sun, or 400 times further from the Sun than Earth. That’s also about 13 times further away from the sun than Neptune, the farthest known planet in the solar system.
But later studies suggest that Planet Nine’s true average distance from the sun is actually closer to 500 astronomical units. And the most recent research, that diminished the potential hiding place of the elusive worldalso indicates that the planet may currently be more than 550 astronomical units away, close to its farthest point from the Sun.
However, these developments do not dramatically change the timeline set out in the 2022 paper, Lingam said. The team’s estimates were “conservative,” meaning the top end of their uncertainty range “still appears sustainable,” he added.
Pushing boundaries
Seventy-five years may seem like a long time for a one-way trip. But this is quite fast compared to the travel of existing probes; For example, Traveler 1 – Earth’s most distant spacecraft – has been traveling through space for 46 years and is located according to NASA. As a result, a Planet Nine probe would have to travel about three times faster than Voyager 1 to reach Planet Nine within the researcher’s time frame.
This may seem unlikely, but it is possible, Lingam said.
Probes traveling to the outer solar system must be shot by gravity around the sun, planets and their moons to propel them across the vast distances. Voyager 1’s trajectory was carefully planned so that it could fly close Jupiter, Saturn, Uranus and Neptune, as well as some of their respective moons. To do this, Voyager 1 also had to be shot around objects to slow it down and redirect it to where it needed to go. However, a Planet Nine probe could go straight to the mysterious planet as directly as possible, allowing it to pick up more speed and travel much further in the same time.
Related: The elusive Planet Nine could be an alternative form of gravity masquerading as a planet, the study claims
Mike Brownan astronomer at Caltech who studied the Planet Nine hypothesis in 2016, originally estimated that a probe could potentially reach Planet Nine within twenty years using a similar method. However, it is “difficult” to see how a probe with current technology could reach Planet Nine so quickly, Lingam said.
But it might be possible to reach Planet Nine faster if we could crack more advanced propulsion technologies, such as light sails — giant sails that capture sunlight or lasers to accelerate spacecraft, Hein and Lingam said.
In the 2022 study, researchers suggested that a light sail could take just seven years to reach Planet Nine. However, the team estimates that it could take at least 20 years before light sails become a reality.
As a result, if we find Planet Nine tomorrow, it would be better to send an actual probe than wait for alternative technologies to become available, Lingam said. “Laser sails can be launched later, if and when they become practical and cost-effective.”
As propulsion systems continue to develop, it may also be possible to send humans to Planet Nine. But probably not so soon.
“I am convinced that in the distant future, humans will be able to visit Planet Nine,” possibly even while en route to other stars, Hein said.