Starship Asterisk*

Artist's concept of 'Planet Nine' -- Credit: NASA/JPL-Caltech/Robert Hurt

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A University of Michigan doctoral student has logged two pieces of evidence that may support the existence of a planet that could be part of our solar system, beyond Neptune.

Some astronomers think this alleged planet, called Planet Nine, exists because of the way some objects in space, called "Trans-Neptunian Objects," or TNOs, behave. These TNOs are rocky objects smaller than Pluto that orbit the sun at a greater average distance than Neptune. But the orbits of the most distant of these TNOs—those whose average distance from the sun is more than 250 times as far as Earth's distance—seem to point in the same direction. This observation first led astronomers to predict the existence of Planet Nine.

For these TNOs to be aligned in the orbits they currently occupy because of Planet Nine's influence, astronomers say, they would have been in the solar system for longer than a billion years. However, some astronomers think in that amount of time, some of these objects should have either smashed into another planet, been thrown into the sun, or ricocheted off into space by other planets' gravitational force.

The U-M research, led by Juliette Becker, a graduate student in the Department of Astronomy, consisted of a large set of computer simulations, which uncovered two findings about these TNOs. First, the researchers established a version of Planet Nine that would most likely cause our solar system to look the way it currently does, by preventing the TNOs from being destroyed or thrown out of the solar system. Second, the simulations predict that there is a process that they call "resonance hopping" by which a TNO jumps between stable orbits. This process can prevent the TNOs from being ejected from the solar system. ...

• Astronomical Journal 154(2):61 (2017 Aug) DOI: 10.3847/1538-3881/aa7aa2
  arXiv.org > astro-ph > arXiv:1706.06609 > 20 Jun 2017

The orbits of the new extreme dwarf planet, 2015 TG387, and its fellow Inner Oort Cloud objects, 2012 VP113 and Sedna, as compared with the rest of the Solar System. (Credit: Roberto Molar Candanosa, Scott Sheppard (CIS, DTM))

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Carnegie’s Scott Sheppard and his colleagues—Northern Arizona University’s Chad Trujillo, and the University of Hawaii’s David Tholen—are once again redefining our Solar System’s edge. They discovered a new extremely distant object far beyond Pluto with an orbit that supports the presence of an even-farther-out, Super-Earth or larger Planet X.

The newly found object, called 2015 TG387, was announced Tuesday by the International Astronomical Union’s Minor Planet Center. ... 2015 TG387 was discovered about 80 astronomical units (AU) from the Sun, a measurement defined as the distance between the Earth and Sun. For context, Pluto is around 34 AU, so 2015 TG387 is about two and a half times further away from the Sun than Pluto is right now.

The new object is on a very elongated orbit and never comes closer to the Sun, a point called perihelion, than about 65 AU. Only 2012 VP113 and Sedna at 80 and 76 AU respectively have more-distant perihelia than 2015 TG387. Though 2015 TG387 has the third-most-distant perihelion, its orbital semi-major axis is larger than 2012 VP113 and Sedna’s, meaning it travels much farther from the Sun than they do. At its furthest point, it reaches all the way out to about 2,300 AU. 2015 TG387 is one of the few known objects that never comes close enough to the Solar System’s giant planets, like Neptune and Jupiter, to have significant gravitational interactions with them. ...

• arXiv.org > astro-ph > arXiv:1810.00013 > 28 Sep 2018

Solar System distances to scale showing the newly discovered 2018 VG18, nicknamed 'Farout', compared to other known Solar System objects. Illustration: Roberto Molar Candanosa and Scott S. Sheppard/CIS

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A team of astronomers has discovered the most-distant body ever observed in our Solar System. It is the first known Solar System object that has been detected at a distance that is more than 100 times farther than Earth is from the Sun.

The new object was announced on Monday, December 17, 2018, by the International Astronomical Union’s Minor Planet Center and has been given the provisional designation 2018 VG18. The discovery was made by Carnegie’s Scott S. Sheppard, the University of Hawaii’s David Tholen, and Northern Arizona University’s Chad Trujillo.

2018 VG18, nicknamed “Farout” by the discovery team for its extremely distant location, is at about 120 astronomical units (AU), where 1 AU is defined as the distance between the Earth and the Sun. The second-most-distant observed Solar System object is Eris, at about 96 AU. Pluto is currently at about 34 AU, making 2018 VG18 more than three-and-a-half times more distant than the Solar System’s most-famous dwarf planet.

bystander wrote: ↑Mon Dec 17, 2018 7:04 pm Discovered: The Most Distant Solar System Object Ever Observed
Carnegie Institution for Science | 2018 Dec 17

Solar System distances to scale showing the newly discovered 2018 VG18, nicknamed 'Farout', compared to other known Solar System objects. Illustration: Roberto Molar Candanosa and Scott S. Sheppard/CIS

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2018 VG18, nicknamed “Farout” by the discovery team for its extremely distant location, is at about 120 astronomical units (AU), where 1 AU is defined as the distance between the Earth and the Sun. The second-most-distant observed Solar System object is Eris, at about 96 AU. Pluto is currently at about 34 AU, making 2018 VG18 more than three-and-a-half times more distant than the Solar System’s most-famous dwarf planet.

The strange orbits of some objects in the farthest reaches of our solar system, hypothesised by some astronomers to be shaped by an unknown ninth planet, can instead be explained by the combined gravitational force of small objects orbiting the Sun beyond Neptune, say researchers.

Kuiper Belt's Ice Cores ~ Credit: ESO/M. Kornmesser

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The alternative explanation to the so-called ‘Planet Nine’ hypothesis, put forward by researchers at the University of Cambridge and the American University of Beirut, proposes a disc made up of small icy bodies with a combined mass as much as ten times that of Earth. When combined with a simplified model of the solar system, the gravitational forces of the hypothesised disc can account for the unusual orbital architecture exhibited by some objects at the outer reaches of the solar system.

While the new theory is not the first to propose that the gravitational forces of a massive disc made of small objects could avoid the need for a ninth planet, it is the first such theory which is able to explain the significant features of the observed orbits while accounting for the mass and gravity of the other eight planets in our solar system. ...

Beyond the orbit of Neptune lies the Kuiper Belt, which is made up of small bodies left over from the formation of the solar system. Neptune and the other giant planets gravitationally influence the objects in the Kuiper Belt and beyond, collectively known as trans-Neptunian Objects (TNOs), which encircle the Sun on nearly-circular paths from almost all directions.

However, astronomers have discovered some mysterious outliers. Since 2003, around 30 TNOs on highly elliptical orbits have been spotted: they stand out from the rest of the TNOs by sharing, on average, the same spatial orientation. This type of clustering cannot be explained by our existing eight-planet solar system architecture and has led to some astronomers hypothesising that the unusual orbits could be influenced by the existence of an as-yet-unknown ninth planet. ...

• arXiv.org > astro-ph > arXiv:1804.06859 > 18 Apr 2018 (v1), 25 Nov 2018 (v2)

Orbits of the distant Kuiper belt and Planet Nine. Orbits rendered in purple are primarily controlled by Planet Nine’s gravity and exhibit tight orbital clustering. Green orbits, on the other hand, are strongly coupled to Neptune, and exhibit a broader orbital dispersion. Updated orbital calculations suggest that Planet Nine is an approximately 5 Earth mass planet that resides on a mildly eccentric orbit with a period of about ten thousand years. Image credit: James Tuttle Keane/Caltech.

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Seeing is believing, but when it comes to Planet Nine, complex calculations of space objects’ behavior, careful observation of orbital anomalies, and watchful observation of the region beyond Neptune will have to do for now.

“The strongest argument in favor of Planet Nine is that independent lines of evidence can all be explained by a proposed new planet with the same properties. In other words, there are multiple reasons to believe that Planet Nine is real, not just one,” said Fred Adams, the Ta-You Wu Collegiate Professor of Physics (and Astronomy) at the University of Michigan.

Three years ago, astronomers Konstantin Batygin and Mike Brown of Caltech hypothesized about the existence of a ninth planet in the solar system, beyond Neptune, that would explain why some objects in space, called “Trans-Neptunian Objects,” or TNOs, behave as they do.

Since then, astronomers have been busy gathering evidence of its existence. Batygin, Brown and Adams, along with doctoral candidate Juliette Becker from U-M’s Department of Astronomy, recently reviewed this evidence in the article “The Planet Nine Hypothesis,” published this month by Physics Reports.

“Although this analysis does not say anything directly about whether Planet Nine is there, it does indicate that the hypothesis rests upon a solid foundation,” said co-author Mike Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy at Caltech.

Adams said he’s optimistic that in the next 10 to 15 years we’ll either be able to observe Planet Nine or have enough data to rule it out. In the last two decades, the number of discoveries of both new solar system objects and extrasolar planets have increased exponentially. For example, the four authors of the report have collectively co-discovered dozens of such objects and the rate of detections is well-positioned to increase. ...

• Physics Reports (online 10 Feb 2019) DOI: 10.1016/j.physrep.2019.01.009
  arXiv.org > astro-ph > arXiv:1902.10103 > 26 Feb 2019

A pair of physicists think it’s possible that a tiny black hole left over from the universe’s early days lurks in the outer solar system.

An artistic rendering of Planet Nine, a hypothetical massive object that orbits the sun beyond Neptune. Two physicists now think it's possible Planet Nine is actually a primordial black hole. Image Credit: NASA/JPL-Caltech/Robert Hurt

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It’s been a little over 13 years since the once-planet Pluto was dethroned. But in the cold, distant reaches of our solar system, there may still lurk a massive body that orbits the sun—one that appears to exert a gravitational tug on some of the small space rocks that lie beyond Neptune.

No one has yet detected the so-called Planet Nine. But if its nicknames are any indication, researchers seem to have a good grip on the nature of this mysterious cosmic object, should it exist at all.

Then again, maybe not. Last week, a pair of physicists proposed an alternate theory in a paper published on the preprint server arXiv: Planet Nine might be less of a planet, and more of a grapefruit-sized black hole.

This possibility, the researchers acknowledge, isn’t terribly likely. But simply entertaining the notion, they argue, could change the way astronomers continue to search for the hypothetical object. ...

• arXiv.org > hep-ph > arXiv:1909.11090 > 24 Sep 2019

bystander wrote: ↑Wed Oct 02, 2019 6:00 pm Planet Nine probably isn’t a black hole.
But it might be worth checking.
NOVA | Public Broadcasting System | 2019 Oct 02

A pair of physicists think it’s possible that a tiny black hole left over from the universe’s early days lurks in the outer solar system.

Last week, a pair of physicists proposed an alternate theory in a paper published on the preprint server arXiv: Planet Nine might be less of a planet, and more of a grapefruit-sized black hole. This possibility, the researchers acknowledge, isn’t terribly likely. But simply entertaining the notion, they argue, could change the way astronomers continue to search for the hypothetical object. ...

https://en.wikipedia.org/wiki/Grapefruit#History wrote:

Capt. Shaddock brought pomelo seeds to Jamaica & bred the first grapefruit

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<<The genetic origin of the grapefruit is a hybrid mix. One ancestor of the grapefruit was the Jamaican sweet orange (Citrus sinensis), itself an ancient hybrid of Asian origin; the other was the Indonesian pomelo (C. maxima). One story of the fruit's origin is that a certain "Captain Shaddock" brought pomelo seeds to Jamaica and bred the first fruit, however, it probably originated as a naturally occurring hybrid between the two plants some time after they had been introduced there.

The hybrid fruit, then called "the forbidden fruit", was first documented in 1750 by a Welshman, Rev. Griffith Hughes, who described specimens from Barbados in The Natural History of Barbados. The grapefruit was brought to Florida by Count Odet Philippe in 1823 in what is now known as Safety Harbor. Further crosses have produced the tangelo (1905), the Minneola tangelo (1931), and the oroblanco (1984).

The grapefruit was known as the shaddock or shattuck until the nineteenth century. Its current name alludes to clusters of the fruit on the tree, which often appear similar to that of grapes. Botanically, it was not distinguished from the pomelo until the 1830s, when it was given the name Citrus paradisi.>>

Artist's conception of accretion flares resulting from the encounter of an Oort-cloud comet and a hypothesized black hole in the outer solar system. Credit: M. Weiss

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Scientists at Harvard University and the Black Hole Initiative (BHI) have developed a new method to find black holes in the outer solar system, and along with it, determine once-and-for-all the true nature of the hypothesized Planet Nine. The paper ... highlights the ability of the future Legacy Survey of Space and Time (LSST) mission to observe accretion flares, the presence of which could prove or rule out Planet Nine as a black hole.

Dr. Avi Loeb, Frank B. Baird Jr., and Amir Siraj have developed the new method to search for black holes in the outer solar system, based on flares that result from the disruption of intercepted comets. The study suggests that the LSST has the capability to find black holes by observing for accretion flares resulting from the impact of small Oort cloud objects.

"In the vicinity of a black hole, small bodies that approach it will melt as a result of heating from the background accretion of gas from the interstellar medium onto the black hole," said Siraj. "Once they melt, the small bodies are subject to tidal disruption by the black hole, followed by accretion from the tidally disrupted body onto the black hole." Loeb added, "Because black holes are intrinsically dark, the radiation that matter emits on its way to the mouth of the black hole is our only way to illuminate this dark environment."

Future searches for primordial black holes could be informed by the new calculation. "This method can detect or rule out trapped planet-mass black holes out to the edge of the Oort cloud, or about a hundred thousand astronomical units," said Siraj. "It could be capable of placing new limits on the fraction of dark matter contained in primordial black holes." ...

• arXiv.org > astro-ph > arXiv:2005.12280 > 25 May 2020 (v1), 29 Jun 2020 (v2)

Illustration of the hypothetical Planet 9. Credit: R. Hurt/IPAC, Caltech

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A faint integrated flux nebula near Polaris. Credit: Kush Chandaria

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We have a pretty good idea of what lurks within our solar system. We know there isn’t a Mars-sized planet orbiting between Jupiter and Saturn, nor a brown dwarf nemesis heading our way. Anything large and fairly close to the Sun would be easily spotted. But we can’t rule out a smaller, more distant world, such as the hypothetical Planet 9 (or Planet 10 if you want to throw down over Pluto). The odds against such a planet existing are fairly high, and a recent study finds it even less likely.

Many astronomers have wondered about the existence of planets that might hide at the edge of our solar system, particularly when the power of our telescopes were fairly limited. But as large sky surveys started to scan the heavens they found nothing beyond asteroid-sized worlds. But the orbits of the worlds we did find seemed to be clustered in a statistically odd way, as if they were being gravitationally perturbed by a larger object. If that were the case, this “Planet 9” would have a mass of about five Earths, and an orbital distance of a few hundred to a thousand astronomical units. In other words, just small enough and distant enough that it wouldn’t be easily seen in sky surveys.

Naturally, this motivated folks to search for the world, but it isn’t easy. Planet 9 would be too distant to be seen by reflected light, so you’d have to look for it by its faint infrared glow. And with a mass of only five Earths, it wouldn’t give off much heat. Adding to this is the fact that such a distant planet would orbit very slowly, such that within a single set of observations you wouldn’t notice it move at all. This is where this new study comes in.

To look for distant planets, the team used two infrared sky surveys, one from the InfraRed Astronomical Satellite (IRAS) and one from the AKARI Space Telescope. The two surveys were taken more than twenty years apart, giving any hypothetical planet plenty of time to move to a slightly different part of the sky. They assumed any distant planets would be fairly close to the equatorial plane, then combed through the data taking note of potential planets. ...

• Monthly Notices of the RAS (online 29 Jul 2022) DOI: 10.1093/mnras/stac2044
• arXiv > astro-ph > arXiv:2207.09985 > 20 Jul 2022

The orbits of several KBOs provide indications about the possible existence of Planet 9. Credit: Caltech/R. Hurt (IPAC)

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Planet 9 continues to remain elusive. This potential super-Earth-sized object in the outer Solar System is only hypothetical, as something out there appears to be gravitationally influencing several Kuiper Belt Objects into unusual orbits. Whatever or wherever it may be, Planet 9 has yet to be found, despite several different hypotheses and numerous observational searches.

But what if Planet 9 has moons? Could they help us find it? A new paper speculates that any moons orbiting the theoretical planet could provide indirect clues to the location of Planet 9, while revealing some basic properties of this mysterious object.

“In this article, we show that the probability of capturing large trans-Neptunian objects (TNOs) by Planet Nine to form a satellite system in the scattered disk region (between the inner Oort Cloud and Kuiper Belt) is large,” wrote astronomer Man Ho Chan ... “By adopting a benchmark model of Planet Nine, we show that the tidal effect can heat up the satellites significantly, which can give sufficient thermal radio flux for observations.” ...

• Astrophysical Journal 944(2):172 (2023 Feb 20) DOI: 10.3847/1538-4357/acb5a1
• arXiv > astro-ph > arXiv:2301.13471 > 31 Jan 2023