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It could. As posted by the original authors on their blog pages findplanetnine.com it might be ~5 earth masses https://arxiv.org/abs/1902.10103 and the answer to this thread

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Short answer: the Earth is closer to the Sun than to Mars about 77.9% of the time. Methodology I wrote https://github.com/barrycarter/bcapps/tree/master/ASTRO/bc-compdist.c to compute when and how long Mars was further from the Earth than the Sun. In the ~30,000 year period covered by DE431, this happens 14,231 times for an average duration of 607.93 days, ...

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For a diagramatic answer, draw a circle around the Earth of 1AU radius, place the Sun on that circle then draw Mars' orbit. The part of Mars' orbit that is outside the 1AU circle is the part where Mars is farther away than the Sun. I expect that the two current answers are equivalent.

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Let us first consider the Earth a fixed point and Mars moving around the Sun on a circular orbit with angular velocity equal to the relative angular velocity ($\omega_\bigoplus - \omega_♂)$ The distance between Mars and the Earth can be described as the square root of $R_E^2+R_M^2-2R_ER_Mcos(\theta)$, and when this is equal to $R_E^2$: \$cos(\theta) = \frac{...

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Variable star observers can obtain 0.1 magnitude accuracy by comparing the brightness of a star with 2 nearby stars of known magnitude; one a bit brighter and one a bit fainter. Most estimates are done telescopically with all 3 stars in view at the same time. The accuracy is much worse when doing this by naked eye and red stars are more difficult. So the ...

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While the eye is terrible at determining apparent magnitude or brightness of stars due to our adaptive iris, it's perfectly capable of discerning relative brightness between two objects in the same visual field. Also, the ancient Greeks could discern six magnitudes of star brightness by realizing that brighter stars look bigger in the night sky. The word ...

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