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Is the solar system a fat ninth dark planet is drifting somewhere far beyond Neptune’s orbit?
Since 2016, many astronomers have said it is possible, pointing to evidence of a large gravity source in deep solar space. But a new article argues that this source of gravity is nothing more than a statistical mirage, the consequence of where in the night sky astronomers point their telescopes. The first physical clue (CK) of this hypothetical Planet Nine was a group of space rocks with similar orbits that appeared to be grouped together unusually close together. These dark, distant, and hard-to-spot objects orbit beyond Neptune and are known as “trans-Neptunian objects” (TNO).
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Because these icy little worlds in the distant solar system reflect so little sunlight, they tend to blend into the brighter backgrounds of stars and galaxies that occupy the attention of most astronomers, and only a handful have been identified and cataloged. (The most famous of these is the retrograde dwarf planet Pluto, which orbits relatively close to the sun compared to many of its TNO cousins.)
But in 2016, astronomers Konstantin Batygin and Mike Brown of the California Institute of Technology noticed that six TNOs, including the dwarf planet Sedna, all had long, elliptical, “eccentric” orbits pointing in the same direction. Eccentric here means that their aphelions, or most distant points, are much further from the sun than their perihelions, or points closest to the sun. And the six had aphids on pretty much the same side of the solar system. In a 2016 article published in The astronomical journal Batygin and Brown wrote that a planet with a mass about 10 times that of Earth, much further than Pluto, and following a long elliptical path around the sun, could explain the apparent grouping. Over time, they argued, its great gravity would have dragged these six TNOs into their clustered orbits.
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But in this new article, published on February 12 in arXiv database, though not yet peer-reviewed, a large collaboration of researchers suggests the NWT is not particularly clustered – it just looks that way because of where Earthlings are pointing their telescopes. The researchers took a sample of 14 known “extreme” TNOs (that is, in very distant orbit, belonging to the family of objects that most influenced the research of Planet Nine) and assumed that they were part of a larger family of invisible objects, which they almost certainly are. Next, they analyzed the time the telescopes spent pointing at different parts of the sky. They discovered that astronomers could detect this particular collection of objects if all of the TNOs outside the solar system actually had a fairly uniform distribution – from 17% to 94% uniform. (A 100% uniform distribution would mean that the TNO orbits are evenly spaced around the sun.) In other words, the extreme TNOs (ETNOs) may appear to cluster together, but that’s only because telescopes have, on average , focused their attention on that. part of space. Such a uniform distribution would not correspond to the Planet Nine hypothesis.
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This statistical analysis is similar to the kind of gut checks that opinion polls do all the time. If a survey of a few hundred Americans found country music to be 55% of people’s favorite genre, but a closer look at the data found 40% of respondents were from Nashville, the pollster might adjust the data to account for the fact that this sample was so heavily weighted towards one region of the country. In doing so, the pollster might find that the overwhelming preference for country music disappears.
Dave Tholen, a University of Hawaii astronomer who searches for the NWT using the Subaru telescope atop Mauna Kea in Hawaii, and who was not involved in the study, said there was still too little data for anyone to draw firm conclusions about Planet Neuf.
“We have a classic situation that I could describe as ‘small number statistics’. A discovery cannot align with anything. Two aligned orbits could easily be a coincidence. Three eye sockets in a row might raise the question, but it’s definitely not enough to hang your hat, ”Tholen told Live Science in an email. “How many aligned orbits do you need before the odds of it being a coincidence drop to a convincing small number? And what constitutes an ‘alignment’? Do they have to be? less than 10 [degrees] one of the other? 30 [degrees]? 90 [degrees]? My own feeling is that we are still at the “suggestive” stage. “
The regrouping of the TNOs suggests that there might be a planet shooting them, making this a hypothesis worth exploring. But the clustering seen so far is not solid evidence. On the flip side, the new study can’t rule out Planet Nine either, Tholen said.
Current efforts will significantly expand the catalog of known NWTs and provide a more solid ground for any claims on the matter, Tholen said.
“Progress comes slowly,” he said. “Any paper reports of simulated polls will always be out of date as long as we continue our observational work, as they will not include our latest sky coverage.”
His team, Tholen said, are working to observe the sky in a uniform fashion “specifically to avoid the kind of … bias” at the heart of the new newspaper’s case.
Scott Sheppard, an astronomer who studies the NWT at the Carnegie Institution for Science in Washington, DC, and was one of the first researchers to propose that a large planet could exist in the distant solar system, largely agreed with Tholen’s point of view.
“We just don’t have enough authentic remote ETNOs to have a good statistical argument for or against clustering,” he told Live Science.
The new article ignores some well-studied objects, like Sedna, and says it makes the results less convincing, Sheppard noted. And some of the objects studied by the new document are likely influenced by the gravity of Neptune, which makes them poor candidates for studying Planet Nine, he added.
“I would say we need to triple the current sample size of very distant ETNOs to have reliable statistics on the angles of the orbits of these objects,” Sheppard said. “If you don’t have a large enough sample size, even if things are heavily clustered, the statistics will still be consistent with a uniform distribution just because the sample size is too small.”
Kevin Napier, a University of Michigan astronomer and lead author of the new paper, told Science magazine he somewhat shared concerns about the sample size of his article. Napier told Science that the statistical power of their methods is inherently low with only 14 objects involved, and that when the sensitive Vera C. Rubin observatory in Chile goes live in 2023, it is expected to reveal hundreds of new TNOs that can shed light on the Planet Nine Question.
Originally posted on Live Science.
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