AI-imagined view of Planet X, a dim blue ice giant with faint rings, far from a distant star-like Sun
AI-imagined artwork

Planet X

A hidden giant that may circle the Sun far beyond Neptune. No one has seen it yet, so this is how an AI imagines it.

See it on the live map

At a glance

Estimated mass ~6 Earths
Average distance ~380 AU from the Sun (model range ~300–520)
One orbit takes ~7,400 years (example orbit)
Surface temperature ~−230 °C (about 40 K)
Sunlight it receives ~1/250,000 of what Earth gets
Status Not yet found still hypothetical
AI-imagined close-up of Planet X with banded blue clouds, a dark storm and thin rings
An AI portrait: a cold ice giant wrapped in methane clouds.

What might it look like?

If Planet X is real, it is probably a smaller cousin of Uranus and Neptune: a ball of rock and ice wrapped in a thick hydrogen and helium atmosphere. Traces of methane would absorb red light, giving it a deep blue-teal colour.

So far from the Sun, daylight there would be dimmer than a full moon on Earth. The Sun would look like little more than an unusually bright star.

These pictures are imagined by AI. They are artistic guesses, not real photos.

Why astronomers think it exists

In 2016, astronomers Konstantin Batygin and Mike Brown proposed Planet Nine to explain some strange patterns at the edge of the Solar System.

01

Clustered orbits

Several of the most distant icy bodies, such as Sedna, have long oval orbits that all point in roughly the same direction. By chance alone, that would be very unlikely.

02

Tilted paths

Some far-off objects travel on orbits tilted steeply, or even backwards, compared to the planets. A massive unseen planet could tug them into those angles over millions of years.

03

A predicted hiding place

Computer models suggest it spends most of its time near the far end of its orbit, so faint that only the biggest telescopes, such as the Vera C. Rubin Observatory, have a chance of spotting it.

One possible orbit

Diagram of one possible orbit of Planet Nine: a blue ellipse about 760 AU across, with the Sun off-centre at a focus, Neptune's small 30 AU orbit, a closest distance of 300 AU and a farthest distance of 460 AU
Illustrative example based on Brown and Batygin (2021). Not a discovery or a prediction of where the planet is now.

Here is one possible orbit, not a confirmed orbit or the planet’s current location. It uses representative values from Brown and Batygin’s 2021 study. arxiv.org

The blue line is the hypothetical orbit; the small green circle is Neptune’s orbit. The Sun sits off-centre, so the planet’s distance changes even though the ellipse looks almost circular.

For this example, the farthest distance is 460 AU. The “around 500 AU” used on the live map is a rounded model estimate.

How scientists calculated it

They worked backwards from the objects they could observe:

  1. Measure distant objects’ orbits

    Repeated telescope observations reveal how small icy bodies beyond Neptune move, including their orbital shapes, orientations and tilts.

  2. Test an additional planet

    Computer simulations add a hypothetical planet and calculate how its gravity changes those small bodies’ paths over millions to billions of years. Some simulations reproduce the observed orbital alignment. caltech.edu

  3. Try different masses and orbits

    Researchers vary the hypothetical planet’s mass, distance, tilt and orbital shape, then compare the resulting patterns with observations.

  4. Account for telescope selection

    Objects are easier to discover in some locations than others. The 2021 study included those observational biases and used statistical sampling, called Markov Chain Monte Carlo, to estimate ranges of possible parameters. arxiv.org

The underlying physics is Newton’s gravity:

F = GMm r2

Here, M and m are the objects’ masses, r is their separation, and G is the gravitational constant. A simulation repeatedly adds the gravitational pulls from the Sun and planets and updates each object’s motion. NASA Science

The calculation behind this drawing

The drawing uses an orbital half-length, or semimajor axis, of a = 380 AU and a closest distance of q = 300 AU, the study’s reported central estimates. These produce an illustrative ellipse; combining central estimates does not establish a uniquely preferred orbit. arxiv.org

QuantityCalculationResult
Orbital stretch, e1 − q/a = 1 − 300/3800.211
Farthest distance, Q2a − q = 760 − 300460 AU
Closest distance in kilometres300 × 149.6 million44.9 billion km
Farthest distance in kilometres460 × 149.6 million68.8 billion km

Kepler’s third law gives the approximate time for one orbit around the Sun, using AU and Earth years:

P = a3 = 3803 ≈ 7,408 years

That law calculates the period once we assume an orbit; it does not prove a planet exists. NASA Science: Kepler’s Laws

The evidence remains indirect: a model can explain the observed patterns without being the only possible explanation. Finding the planet and tracking its movement would provide much stronger confirmation.

AI-imagined view from an icy moon, with Planet X filling the sky above frozen ridges
Imagined from one of its possible icy moons: the giant planet hangs over a frozen landscape.

Find it among the planets

Turn on "Planet Nine" on the live solar system map to see where it might be right now.

Open the live map