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takyon [soylentnews.org] writes:

Astrophysicists from the Physics Institute at the University of Bern have calculated upper and lower limits [bbc.com] for the size, temperature, and luminosity [unibe.ch] of the hypothetical icy giant known as "Planet Nine" [wikipedia.org]:

In their paper accepted by the journal "Astronomy & Astrophysics" the scientists conclude that a planet with the projected mass equal to 10 Earth masses has a present-day radius of 3.7 Earth radii. Its temperature is minus 226 degrees Celsius or 47 Kelvin. "This means that the planet's emission is dominated by the cooling of its core, otherwise the temperature would only be 10 Kelvin," explains Esther Linder: "Its intrinsic power is about 1000 times bigger than its absorbed power." Therefore, the reflected sunlight contributes only a minor part to the total radiation that could be detected. This also means that the planet is much brighter in the infrared than in the visual. "With our study candidate Planet 9 is now more than a simple point mass, it takes shape having physical properties," says Christoph Mordasini.

The researchers also checked if their results explain why planet 9 hasn't been detected by telescopes so far. They calculated the brightness of smaller and bigger planets on various orbits. They conclude that the sky surveys performed in the past had only a small chance to detect an object with a mass of 20 Earth masses or less, especially if it is near the farthest point of its orbit around the Sun. But NASA's Wide-field Infrared Survey Explorer may have spotted a planet with a mass equal to 50 Earth masses or more. "This puts an interesting upper mass limit for the planet," Esther Linder explains. According to the scientists, future telescopes like the Large Synoptic Survey Telescope under construction near Cerro Tololo in Chile or dedicated surveys should be able to find or rule out candidate Planet 9. "That is an exciting perspective," says Christoph Mordasini.

Evolution and magnitudes of candidate planet nine [aanda.org] (open, DOI: 10.1051/0004-6361/201628350) and arXiv link [arxiv.org]

Previously: Closing in on Planet Nine [soylentnews.org]

Original Submission