Some experts estimate we could be just a few years away from discovering the elusive “Planet Nine” – or definitively ruling out the existence of a hypothetical world.
But if we find it, how long would it take us to send a spaceship to this distant world? And could humans ever make the journey?
Planet Nine is the name given to a proposed planet believed to be hidden near the edge of the solar system. If it exists, Planet Nine is probably a dark, gaseous, or icy giant planet somewhere. between five and ten times the mass of the Earth which circles the sun in a very elliptical or stretched orbit – out of sync with the rest of the planets.
Researchers suspect Planet Nine exists because a dozen objects beyond Neptune’s orbit move as if a large object is pulling them. However, finding this missing world proved extremely tricky.
But some astronomers believe Planet Nine could be discovered in the next few years, once the state-of-the-art Vera C. Rubin Observatory begins studying the night sky in late 2025.
Related: The elusive Planet Nine could be surrounded by hot moons, and that’s how we’d find it
If Planet Nine is ever detected, space agencies like NASA will want to send a probe to visit the distant world. But first they will need to plan and get approval for such a mission.
“It will take at least a decade, if not more,” Andreas Hein, a space systems engineer at the University of Luxembourg, told Live Science in an email. This is mainly because missions must go through a lengthy and rigorous government selection process, he added.
But this process could be accelerated depending on the strangeness of the world in the first readings, Manasvi Lingam, a theoretical astrobiologist at the Florida Institute of Technology, told Live Science in an email. “If Planet 9 is anomalous in some respect, there may be more interest in accelerating such a mission.”
It’s also possible that a private space exploration company, such as SpaceX, could launch missions sooner — potentially as early as five years after discovery — because they aren’t hampered by as much bureaucracy, Hein said.
Reach Planet Nine
Once a probe is sent to Planet Nine, the next question is how long will it take to arrive?
In 2022, Hein, Lingam and part-time astronomer Adam Hibberd attempted to answer this question in a theoretical article published in the preprint database arXiv. In this paper, which has not been peer-reviewed, the researchers estimate that it would likely take between 45 and 75 years for a spacecraft similar to NASA’s Voyager probes to reach Planet Nine.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. It’s also about 13 times farther 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 investigation, which reduces the potential hiding place of the elusive worldalso suggests that the planet could currently be more than 550 astronomical units away, near its farthest point from the sun.
However, these developments do not radically change the timeline presented in the 2022 document, Lingam said. The team’s estimates were “conservative,” meaning the upper limit of their uncertainty range “still appears tenable,” he added.
Push the limits
Seventy-five years may seem like a long time for a one-way ticket. But it is quite fast compared to the paths of existing probes; For example, Traveler 1 – the farthest spacecraft from Earth – has been traveling in space for 46 years and is only about 163 astronomical units from Earth, according to NASA. As a result, a Planet Nine probe would have to travel three times faster than Voyager 1 to reach Planet Nine within the researcher’s time frame.
It may seem unlikely, but it’s possible, Lingam said.
Probes heading to the outer solar system must be launched gravitationally around the sun, planets and their moons to propel them the vast distances involved. Voyager 1’s trajectory was carefully planned to allow it to fly close Jupiter, Saturn, Uranus and Neptune, as well as some of their respective moons. To do this, Voyager 1 also had to be launched around objects to slow it down and redirect it where it needed to go. However, a Planet Nine probe could most directly travel directly to the mysterious planet, allowing it to pick up more speed and travel much further in the same amount of time.
Related: The elusive Planet Nine could be an alternate form of gravity masquerading as a planet, a study suggests.
Mike Browna Caltech astronomer who co-proposed the Planet Nine Hypothesis in 2016, initially estimated that a probe could potentially reach Planet Nine within just 20 years using a similar method. However, it is “difficult” to see how a probe could reach Planet 9 so quickly with current technology, Lingam said.
But it might be possible to reach Planet Nine more quickly if we can master more advanced propulsion technologies, such as light sails – giant sails that capture sunlight or lasers to accelerate spacecraft , said Hein and Lingam.
In the 2022 study, researchers suggested that a light sail could take as little as seven years to reach planet nine. However, it may take at least 20 years for light sails to become a reality, the team estimates.
As a result, if we found Planet Nine tomorrow, it would be better to send a current probe rather than wait until alternative technologies become available, Lingam said. “Laser sails may be launched later, if and when they become practical and cost-effective.”
As propulsion systems advance, it may also be possible to send people to Planet Nine. But probably not anytime soon.
“I’m confident that in the distant future, humans will be able to visit Planet 9,” potentially even if they head to other stars, Hein said.