The not yet discovered "ninth planet", presumably located in the distant regions of the solar system, is acquiring its physical appearance. According to new estimates, it should be 3.7 times larger than the Earth and have a hydrogen-helium atmosphere cooled to –220 ° C.
Ever since astronomers at the California Institute of Technology reported circumstantial evidence for the existence far beyond Pluto's orbit - on the dark outskirts of the solar system - a still unknown "ninth planet", interest in it has not waned. And while some scientists are pondering what instruments and telescopes could allow it to be examined and discovered, others have already begun to investigate the mysterious planet, however, so far only theoretical.
You can recall, for example, the recent results of computer simulations, which showed that the "ninth planet" may be an alien in our solar system - an exoplanet born in a completely different star, once near ours, and captured from a former neighbor. The new theoretical work, which physicists from the University of Bern, Switzerland, report in the journal Astronomy & Astrophysics, looks at other possible aspects of the prehistory and even the structure of the incredible planet.
Art by Esther Linder, Christoph Mordasini, Universität Bern
Computer simulations of the evolution of exoplanets are a common method for studying them. However, Christoph Mordasini and Esther Linder have never worked with such a close (albeit hypothetical) object: it is estimated to be only 700 times farther from the Sun than Earth. Most likely, it is a smaller copy of the solar system's ice giants, Uranus and Neptune, and, like them, is surrounded by an atmosphere of light gases, hydrogen and helium. Based on these assumptions, the Swiss astronomers got down to work. They abandoned the version with the capture of the "ninth planet" from another star, simulating its possible evolution within our stellar system - that is, in the last 4.6 billion years.
“With our work, candidate planet 9 ceases to be a“point mass”, it takes shape and physical properties,” the scientists say. Indeed, they showed that today the "ninth planet" may have a radius of 3.7 times that of Earth and a mass 10 times that of Earth. Its atmospheric temperature is a measly 47 Kelvin - that's below –220 degrees Celsius.
Among other things, this means that the weak radiation of the planet should appear not as a result of the reflection of the rays of the distant and dim Sun, but during the slow cooling of its heavy iron core. This energy heats up the atmosphere, without which its temperature would drop by another couple of tens of Kelvin. “This internal energy of hers is about a thousand times greater than what she receives from the Sun,” added Esther Linder in an interview with the press service of the University of Bern.
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These calculations may affect the planned search for the "ninth planet". If Linder and Mordesini are right, then it should radiate much brighter in the infrared than in the visible. Indeed, scientists have also considered the question of why the so far distant planet has eluded observation. They calculated the luminosity that would be expected from planets of different masses and sizes in different distant orbits, in which the "ninth planet" may be located.
It turned out that with a mass of less than 20 Earth masses, there was very little chance of detecting it, especially while it is in the distant parts of its orbit. Well, we would have found it reliably if its mass was 50 times greater than that of the Earth: according to the authors' calculations, in this case, the "ninth planet" was necessarily noticed by the WISE space infrared telescope. “These numbers set some kind of upper limit on the possible mass of planet nine,” adds Esther Linder. Swiss astronomers pin their main hopes for confirming its existence on new, more powerful telescopes, and above all on the wide-angle LSST with an 8.4-meter reflector, which is being built in the Chilean Andes.
