It moves through the darkness on a path so long that humans had only begun to farm the first grains when it last came close to the Sun.
Sedna, a distant dwarf planet three-quarters the size of Pluto, is inching toward the brightest star in our sky — and in 2076, it will reach its closest point in more than 11,000 years. Astronomers say that if we want to study this mysterious body on the outer edge of the Solar System, this is our one shot.
But visiting Sedna isn’t like sending a probe to Mars or even Pluto. Even at its nearest, Sedna will still be nearly three times farther from the Sun than Neptune. Reaching it would require a spacecraft to traverse more than 11 billion kilometers through the coldest, most remote region of the Solar System. And to make it before the moment passes, scientists say, we’ll need to seriously revamp how we travel through space.
A Cold World With A Weird Orbit
First spotted in 2003, Sedna stunned astronomers with its orbit. It doesn’t sit comfortably in the Kuiper Belt like Pluto or Haumea. Instead, it swings in a stretched-out ellipse that takes it as far as 937 astronomical units (AU) from the Sun — that’s 937 times the distance between Earth and the Sun. Its closest approach, or perihelion, lies at about 76 AU.
That extreme path suggests Sedna might not even belong to the Kuiper Belt at all. It may be the first known resident of the inner Oort Cloud, the shell of icy bodies that marks the outermost boundary of our Solar System. Or, even more provocatively, Sedna might be a captured rogue: an exoplanet ensnared by our Sun long ago during a stellar close encounter.
“If confirmed, Sedna would represent the first known exoplanetary body accessible to in situ investigation,” wrote Dr. Elena Ancona of Politecnico di Bari, and her colleagues in their 2025 study. “The mere possibility of accessing exoplanetary material at such close range provides strong justification for a dedicated mission.”
And Sedna’s surface (one of the reddest ever seen) might be rich in complex organic molecules. Its composition could offer clues to how planetary building blocks formed in the cold vacuum of deep space, and how chemistry may have unfolded in the early days of the Solar System.
Getting There Fast — or Not at All
The trouble is time. A probe relying on conventional rockets could take 25 to 30 years just to do a quick flyby. That would mean launching around 2045 or sooner.
To meet that challenge, Ancona’s team evaluated two radically different propulsion technologies. One is a solar sail, using the gentle but constant pressure of sunlight to accelerate. The other is the Direct Fusion Drive (DFD), a conceptual engine that uses thermonuclear fusion (the same process that powers the Sun) to produce thrust.
Each system comes with trade-offs. A solar sail could reach Sedna in just 7 years, assuming a precisely timed gravitational slingshot past Jupiter and a risky dive near the Sun to trigger additional acceleration through thermal desorption. But it could only carry a payload of about 1.5 kilograms — the mass of a two-slice toaster. That limits the science.
The fusion drive would be slower, taking around 10 years, but could deliver up to 1,500 kilograms into orbit around Sedna. That’s enough for a full suite of scientific instruments, including spectrometers, magnetometers, and possibly even radar systems for probing the subsurface.
“Due to the limitations of traditional methods, innovative propulsion systems are crucial to reach distant targets like Sedna,” the authors wrote. “Chemical propulsion… suffers from low efficiency and high fuel mass requirements for long-duration missions.”
Risks at the Edge
Neither propulsion system is ready for launch. Fusion engines like the Princeton Field-Reversed Configuration (PFRC) are still in experimental phases and have never flown. They promise clean, aneutronic fusion using helium-3, but helium-3 is rare, both on Earth and off it. Only about 30 kilograms exist on Earth today.
Solar sails, meanwhile, are further along in development. Japan’s IKAROS probe demonstrated basic solar sailing in 2010. The Planetary Society’s LightSail-2 built on that with maneuvering. And in 2024, NASA’s ACS3 mission deployed a composite solar sail from a CubeSat.
But the approach proposed for Sedna is novel: coating the sail with a material that vaporizes when heated during a near-Sun dive, adding extra thrust via thermal desorption. That method is still untested. And flying that close to the Sun poses risks of material degradation and structural failure.
There are also communication hurdles. At Sedna’s distance, signals from Earth would take up to 13 hours to arrive. The spacecraft would need to operate autonomously for much of the mission, including maneuvers, data collection, and problem-solving.
What Would We Learn?
Even a flyby mission could answer pressing questions about Sedna’s origins. What is it made of? Are there signs of a tenuous atmosphere? Does it have moons?
An orbiter, however, would unlock far more. It could map the surface over months, analyze its gravitational field, and potentially identify subsurface layers. It could also search for signs of past geological activity or ice volcanoes, features seen on other distant worlds like Pluto and Triton.
Most tantalizingly, Sedna’s surface may hold clues about prebiotic chemistry or even material from beyond our Solar System.
“This information… is of extreme interest in the current debate regarding the primary chemical reactions at the origin of life,” the authors wrote.
The Clock Is Ticking
Scientists estimate that Sedna will remain within a reachable range — under 100 AU from the Sun — for about 200 years. But that’s a narrow window in astronomical terms, and the time needed to develop the mission, test the propulsion system, and launch will eat into that fast.
In an ideal scenario, a spacecraft could be ready to launch between 2035 and 2045. That would allow it to rendezvous with Sedna in the 2070s, just as the distant dwarf planet swings past its solar low point before retreating into darkness once again.
It’s a voyage that would stretch the limits of human technology — and our patience. But if we succeed, it could be the first time we touch something possibly alien.
Sedna waits. The question now is whether we’ll reach it in time.
