If there is a planet beyond Neptune, what is it like?

A new computer model may show more hypothetical specifics about the proposed Planet Nine. The specifics include estimates on size, temperature, and brightness.

Esther Linder, Christoph Mordasini, Universität Bern
An illustration of a new computer model of Planet Nine. It details temperature, brightness, and possible size.

Scientists may not have been able to spot the proposed ninth planet in our solar system, or even confirm that it exists, but that hasn't stopped them from imagining how it looks.

Astrophysicists from the University of Bern recently showed off a new model of the possible evolution of Planet Nine, a planet hypothesized to explain the movement bodies at our solar system's edge.

Published in the Journal Astronomy and Astrophysics, the model shows the possible size, temperature, and brightness of the mysterious planet.

"With our study, candidate Planet Nine is now more than a simple point mass, it takes shape having physical properties," said Prof. Christoph Mordasini, lead author of the study, said in the university press release.

In January, Astrophysicists Michael Brown and Konstantin Batygin of the California Institute of Technology in Pasadena proposed the existence of a large planet orbiting the sun in the far reaches of the solar system.

The planet is so far from the sun that it would be too difficult to spot with a telescope, but computer models suggest the planet exists and is shaping the orbits of objects in the Kuiper Belt, a ring of icy space rocks beyond Neptune, The Christian Science Monitor's Ben Thompson reported.

Professor Mordasini and his PhD student, Esther Linder, also from the University of Bern, sought to discover the specifics of the planet, if it indeed exists. With backing from the Swiss National Science Foundation and the National Center for Competence in Research, the duo plugged in size estimates and possible orbits to model a clearer picture.

Their study concludes that if Planet Nine exists, it has a mass equal to 10 times that of Earth and a frost temperature of 47 degrees Kelvin (-375 degrees Fahrenheit).

Why has no one seen the hypothetical planet yet? Mordasini and Ms. Linder may have found an answer to that question as well: The planet is bigger than Earth, but still too small for our telescopes.

The study concludes that previous surveys looking for planet sized objects in the solar system have only a small chance to detect anything 20 Earth masses or less. But scientists may be able to increase the odds of a sighting by switching to infrared telescopes, according to Mordasini and Linder.

The 47 Kelvin temperature "means that the planet's emission is dominated by the cooling of its core," Linder said. In other words, if the planet was relying only on the sun for warmth, it would be far cooler. Since it has another source of heat, its core, it would be much more visible in infrared than the cooler objects around it.

Planet Nine's existence is still not confirmed, as only indirect evidence points to its existence. And there is an astronomically long history of scientists proposing the existence of planets past Neptune.

In 1985, a theory that a mystery planet similar to Planet Nine may have been regularly causing extinction events on Earth gained popularity after it was published in a Time magazine article entitled, "Did Comets Kill the Dinosaurs? A Bold New Theory About Mass Extinctions."

So far that and other proposals have remained unproven, and have been largely dismissed by the scientific community. But some scientists believe Planet Nine could be the outlier.

"It's such a long history of people being basically wrong that standing up and saying we're right this time makes us almost look crazy," Brown told the Associated Press in January. "Except I'm going to stand up and say we're actually right this time. The evidence for the first time is actually very good that this thing is actually out there."

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