Rubin Planetarium Video - Planet 9

Some astronomers have hypothesized the existence of a “Planet 9,” a massive, Neptune-sized object in the far outer solar system whose gravitational effects would explain the unusual orbits of distant trans-Neptunian objects. Planet 9 is thought to have a mass 5 to 10 times that of Earth, with an orbit that takes it 400 to 800 astronomical units from the Sun.

If it exists, Planet 9 may be hard to find for two reasons. Its extreme distance from the Sun means there will likely be little sunlight for it to reflect back to Earth. Also, Planet 9 may have a dark surface. Both of these conditions would make the object extremely faint.

So far, searches for Planet 9 have been unsuccessful; however, most surveys have lacked the ability to search the large volume of space in which Planet 9 might reside. The wide coverage and sensitivity of the LSST survey should enable it to detect — or definitively rule out — the existence of Planet 9 in about 60% of the sky.

Storyboard

This animation shows a hypothetical large body in the outer solar system far beyond the orbit of Neptune. It can represent “Planet 9,” or another substantive, faint object that would only be detected with a large and sensitive sky survey.

From this viewpoint the Sun looks more like a very bright star because of our large distance from it. An extended haze around the Sun represents, in part, the diffuse glow from zodiacal dust in the inner system and asteroid belt. As this vantage point is significantly far from the ecliptic, the distribution is more circular, not edge-on and flattened.

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Initially Planet 9 is almost impossible to see, a dark object silhouetted against the Milky Way, left of center of the front of the dome.

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The object is now very close and can be seen transiting the Sun. It is still mostly in silhouette, but has some faint illumination of features from the glow of the surrounding stars and the Milky Way.

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We are now pulling away from the objectʼs dark, illuminated side, losing view of it against the star field of the Milky Way.

Additional References

https://iopscience.iop.org/article/10.3847/1538-3881/aabfc0/meta