Some experts believe we could be just a few years away from discovering the elusive ‘planet nine’ – or definitively ruling out the hypothetical world’s existence.
But if we find it, how long would it take us to send a spacecraft to a distant world? And could humans ever make the journey?
Planet Nine is the name given to the planet that is said to be hiding nearby the 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 Earth which orbits the Sun in a highly elliptical or elongated orbit – out of sync with the rest of the planets.
Researchers suspect that Planet Nine is out there because about a dozen objects beyond Neptune’s orbit move as if they are being pulled by a large object. However, finding this missing world proved to be extremely difficult.
However, some astronomers believe that Planet Nine could be discovered within the next few years, once the modern Vera C. Rubin Observatory begins scanning the night sky in late 2025.
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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 have to plan and get approval for such a mission.
“This will take at least ten years or more,” Andreas Hein, a space systems engineer at the University of Luxembourg, told Live Science in an email. This is mostly because the mission has to go through a lengthy and rigorous government selection process, he added.
However, this process could be accelerated depending on how strange the world appears in the initial 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 way, there might be more interest in expediting such a mission.”
It’s also possible that a private space exploration company like SpaceX could launch missions sooner — potentially as early as five years after discovery — because they’re not hindered by as much red tape, Hein said.
Reaching Planet Nine
Once the probe is sent to planet nine, the next question is how long will it take to arrive?
In 2022, Hein, Lingam and a part-time astronomer Adam Hibberd attempted to answer this question in a theoretical paper that was placed in the preprints database arXiv. In that paper, which was not peer-reviewed, the researchers estimated that it would likely take 45 to 75 years for a spacecraft similar to NASA’s Voyager probes to reach Planet Nine.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 an average of about 400 AU from the Sun, or 400 times farther from the Sun than Earth. It is also about 13 times farther from the Sun than Neptune, the most distant known planet in the Solar System.
However, subsequent studies suggest that the actual average distance of planet nine from the Sun is actually closer to 500 AU. And the latest survey which narrowed down the potential shelter of the elusive worldalso suggests that the planet could currently be more than 550 AU away, near its furthest point from the Sun.
However, these developments do not dramatically change the timeline set out in the 2022 document, Lingam said. The team’s estimates were “conservative,” meaning the upper end of their range of uncertainty “still looks 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 paths of existing probes; for example, Voyager 1 — the farthest spacecraft from Earth — has been traveling through space for 46 years and is estimated to be only about 163 AU from Earth. NASA. As a result, the Planet Nine probe would have to travel about three times as fast as Voyager 1 to reach Planet Nine in the researcher’s time frame.
That may seem unlikely, but it is possible, Lingam said.
Probes moving toward the outer solar system must be gravitationally flung around the Sun, planets, and their moons to propel them enormous distances. Voyager 1’s trajectory was carefully planned for a close flyby Jupiter, Saturn, Uranium and Neptune, as well as some of their respective moons. In order to do this, Voyager 1 also had to be bombarded around the objects to slow it down and redirect it to where it needed to go. However, the Planet Nine probe could go as directly as possible directly to the mysterious planet, allowing it to increase speed and travel much further in the same amount of time.
Related: Elusive Planet Nine could be an alternative form of gravity masquerading as a planet, study claims
Mike Browna Caltech astronomer who co-designed Planet Nine Hypothesis in 2016, originally an estimate that a probe could potentially reach planet nine in just 20 years using a similar method. But it’s “difficult” to see how a probe could reach Planet Nine that quickly using current technology, Lingam said.
But it might be possible to reach Planet Nine faster if we could break out more advanced propulsion technologies like light sails — giant sails that capture sunlight or lasers to accelerate the spacecraft, Hein and Lingam said.
In a 2022 study, scientists suggested that a light sail could take as little as seven years to reach planet nine. But it could take at least 20 years before lightweight sails become a reality, the team estimated.
As a result, if we were to find Planet Nine tomorrow, it would be better to send an actual probe rather than wait for alternative technologies to become available, Lingam said. “Laser sails may be launched later if and when they are practical and cost effective.”
As propulsion systems progress further, it may also be possible to send humans to planet nine. But probably not anytime soon.
“I’m sure that in the distant future, people will be able to visit planet nine,” Hein said.