A hypothetical mysterious planet believed to be responsible for the strange orbits of the outer solar system has just received one of its biggest blows.
According to a comprehensive analysis of extremely distant objects, led by physicist Kevin Napier of the University of Michigan, the New Planet may not exist – because there is no evidence of its existence. Rather, what astronomers have considered the influence of a planet’s gravity is instead a selection bias in observations.
The preprinted paper has been uploaded to the archive and is awaiting peer review.
The New Planet erupted in 2016, when astronomers Konstantin Batygin and Michael Brown of Caltech published a work in Astronomical Journal showing the case of a planet still undiscovered in the outer edges of the solar system. The evidence, they said, is in other objects beyond Neptune’s orbit.
These objects are called Extreme Trans-Neptune Objects (ETNOs). They have huge elliptical orbits, which never cross closer to the Sun than Neptune’s orbit at 30 astronomical units and swing more than 150 astronomical units.
Batygin and Brown discovered that these orbits have the same angle at the perihelion, the point in their orbit closest to the Sun. They performed a series of simulations and discovered that a large planet could group orbits in this way.
The New Planet, according to their calculations, should be about five to 10 times the mass of the Earth, orbiting at a distance somewhere between 400 and 800 astronomical units.
Because this hypothetical planet would be so far away and the sky is so big, it would not be easy to find. So his search was continuous.
Just as the New Planet itself would be hard to find, however, so would ETNOs. These bodies are smaller than a planet and therefore weaker. When they move away from the Sun, we have almost zero chance of seeing them. And here some astronomers believe that there is a selection bias.
“Because ETNOs follow extremely elliptical orbits and their brightness decreases by 1 / r4, they are almost always discovered in a few decades of perihelion,” the researchers wrote in their paper.
“Moreover, telescopic surveys observe a limited area of the sky at certain times of the year at a limited depth. These effects lead to significant selection bias.”
The difficulty involved in seeing ETNOs means that I did not find many. The initial simulations performed by Batygin and Brown were based on only six ETNOs, which were collected from an assortment of surveys with unpublished selection functions; in other words, any selection biases were unclear.
More recent polls have been meticulous about their selection functions. And, although no survey found enough ETNOs to constitute a comprehensive statistical population, the combination of the surveys may lead scientists to a stronger conclusion. That’s what Napier and his team did.
They took five objects from the Study of the Origins of the Outer Solar System (OSSOS) (which previously found no evidence of clustering), five objects from the Dark Energy Study and four objects found by astronomers Scott Sheppard, Chad Trujillo and David Tholen, who led the search for the New Planet.
As all three surveys had quite different objectives, they therefore had different selection functions. The challenge was to resolve these differences so that the objects could be combined into one large survey. To do this, the team designed a survey simulator.
“In essence,” they wrote in their paper, “a survey simulator simulates the detection of a population model of solar system bodies using the history, depth, and tracking criteria of the survey. This allows us to calculate the selection function of a survey for a certain population, which allows us to explain the bias and therefore to understand the real underlying populations. “
If the ETNO group was caused by a physical effect, then it should have remained consistent with the larger sample of objects analyzed by Napier’s team. Instead, their results suggested that the ETNO sample was consistent with a uniform distribution of the parent body in space.
This does not mean that researchers have carefully observed that there is no new planet. It just means that the existence of the planet cannot be deduced from ETNO data. There is not enough information to confirm or exclude it.
Other lines of evidence also indicate its existence. For example, the strangely inclined orbits of Kuiper Belt objects in the outer solar system, such as Sedna – although astronomers have proposed other explanations for these behaviors.
A stronger decision will be possible with a larger population of ETNOs and objects in the Kuiper belt to be analyzed, which may mean waiting for objects in a more powerful telescope, such as the Vera Rubin Observatory, which is expected to begin operations. sometime this year.
Meanwhile, the avid hunt for the elusive planet results in some truly amazing discoveries, including a few possible dwarf planets that make their way to the outer limits of the solar system and a whole bunch of giant gas moons.
So, whether the New Planet exists or not, the debate itself is amazing for science – leading to discoveries that we may not have encountered otherwise.
The study was published on the pre-print website arXiv.org.