A Stellar Flyby Jumbled Up the Outer Solar System

This is a screenshot from a supercomputer simulation. It shows how an ancient stellar flyby shaped the Solar System. Among other things, the flyby can explain the Solar System's population of irregular moons. Image Credit: Forschungszentrum Jülich

An ancient passerby may have visited the Sun and inadvertently helped shape the Solar System into what it is today. It happened billions of years ago when a stellar drifter came to within 110 astronomical units (AU) of our Sun. The effects were long-lasting and we can see evidence of the visitor’s fleeting encounter throughout the Solar System.

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New Evidence for Our Solar System’s Ghost: Planet Nine

Artist's impression of Planet Nine as an ice giant eclipsing the central Milky Way, with a star-like Sun in the distance. Neptune's orbit is shown as a small ellipse around the Sun. The sky view and appearance are based on the conjectures of its co-proposer, Mike Brown.

Does another undetected planet languish in our Solar System’s distant reaches? Does it follow a distant orbit around the Sun in the murky realm of comets and other icy objects? For some researchers, the answer is “almost certainly.”

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If Planet 9 has Moons, Would That Help Us Find It?

Artist's concept of the hypothetical "Planet Nine." Could it have moons? Credit: NASA/JPL-Caltech/Robert Hurt

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.

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Dwarf Planet Quaoar has a Ring

This artist’s impression shows the dwarf planet Quaoar and its ring. Quaoar’s moon Weywot is shown on the left. Quaoar’s ring was discovered through a series of observations that took place between 2018 to 2021. Image Credit: http://www.esa.int/spaceinvideos/Terms_and_Conditions

Quaoar is one of about 3,000 dwarf planets in our Solar System’s Kuiper Belt. Astronomers discovered it in 2002. It’s only half as large as Pluto, about 1,121 km (697 mi) in diameter. Quaoar has a tiny moon named Weywot, and the planet and its moon are very difficult to observe in detail.

Astronomers took advantage of an occultation to study the dwarf planet Quaoar and found that it has something unexpected: a ring where a moon should be.

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Two Bizarre red Asteroids Somehow Migrated From the Kuiper Belt all the way to the Main Asteroid Belt

If asked to pick what color asteroids in the asteroid belt would be, red is likely not one that would come to mind for most people.  But that is exactly the color of two new asteroids found by Hasegawa Sunao of JAXA and an international team of researchers.  The catch is the objects don’t appear to be from the asteroid belt at all, but are most likely Trans-Neptunian objects that were somehow transported into what is commonly thought of as the asteroid belt. How exactly they got there is still up for debate.

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Astronomers Find a New Binary Object in the Kuiper Belt

This image is an artist’s impression of the trans-Neptunian object that two Southwest Research Institute scientists recently discovered is a binary object. Image Credit: SwRI

Scientists from the Southwest Research Institute (SwRI) have presented the discovery of a binary pair of objects way out in the Kuiper Belt. They’re Trans-Neptunian Objects (TNOs) which means their orbit is outside the orbit of Neptune, our Solar System’s outermost planet. This binary pair is unusual because of their close proximity with one another.

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Uranus’ Moons are Surprisingly Similar to Dwarf Planets in the Kuiper Belt

Ö. H. Detre et al./MPIA

Astronomer William Herschel discovered Uranus—and two of its moons—230 years ago. Now a group of astronomers working with data from the telescope that bears his name, the Herschel Space Observatory, have made an unexpected discovery. It looks like Uranus’ moons bear a striking similarity to icy dwarf planets.

The Herschel Space Observatory has been retired since 2013. But all of its data is still of interest to researchers. This discovery was a happy accident, resulting from tests on data from the observatory’s camera detector. Uranus is a very bright infrared energy source, and the team was measuring the influence of very bright infrared objects on the camera.

The images of the moons were discovered by accident.

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If Planet 9 is a Primordial Black Hole, We Might Be Able to See Flares When it Consumes Comets

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

A comet-eating black hole the size of a planet? It’s possible. And if there’s one out there in the distant Solar System, a pair of researchers think they know how to find it.

If they do, we might finally put the Planet 9 issue to rest.

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Over a Hundred New Large Objects Found in the Kuiper Belt

This is an artist's concept of a craggy piece of Solar System debris that belongs to a class of bodies called trans-Neptunian objects (TNOs).Credit: NASA, ESA, and G. Bacon (STScI)

Hey Pluto, Sedna, Haumea, Makemake Et al.: You’ve got company!

While searching for distant galaxies and supernovae, the Dark Energy Survey’s powerful 570-megapixel digital camera spotted a few other moving “dots” in its field of view. Turns out, the DES has found more than 100 previously unknown trans-Neptunian objects (TNOs), minor planets located in Kuiper Belt of our Solar System.

A new paper describes how the researchers connected the moving dots to find the new TNOs, and also says this new approach could help look for the hypothetical Planet Nine and other undiscovered worlds.

Guess you never know what you’ll find once you start looking!

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Evidence Mounts for the Existence of Planet Nine

Artist's impression of Planet Nine, blocking out the Milky Way. The Sun is in the distance, with the orbit of Neptune shown as a ring. Credit: ESO/Tomruen/nagualdesign
Artist's impression of Planet Nine, blocking out the Milky Way. The Sun is in the distance, with the orbit of Neptune shown as a ring. Credit: ESO/Tomruen/nagualdesign

In January of 2016, astronomers Mike Brown and Konstantin Batygin published the first evidence that there might be another planet in our Solar System. Known as “Planet 9”, this hypothetical body was estimated to be about 10 times as massive as Earth and to orbit that our Sun at an average distance of 700 AU. Since that time, multiple studies have been produced that either support or cast doubt on the existence of Planet 9.

While some argue that the orbits of certain Trans-Neptunian Objects (TNOs) are proof of Planet 9, others argue that these studies suffer from an observational bias. The latest study, which comes from a pair of astronomers from the Complutense University of Madrid (UCM), offers a fresh perspective that could settle the debate. Using a new technique that focuses on extreme TNOs (ETNOs), they believe the case for Planet 9 can be made.

Extreme Trans-Neptunian Objects are those that orbit our Sun at average distances greater than 150 AU, and therefore never cross Neptune’s orbit. As the UMC team indicate in their study, which was recently published in the Monthly Notices of the Royal Astronomical Society, the distances between the ETNOs nodes and the Sun may point the way towards Planet 9.

Artist’s impression of what the theoretical Planet 9 could look like. Credit: NASA

These nodes are the two points at which the orbit of a celestial body crosses the plane of the Solar System. It is at these points that the chances of interacting with other bodies in the Solar System is the greatest, and hence where ETNOs are most likely to experience a drastic change in their orbits (or a collision). By measuring where these nodes are, the team believed they could tell if the ETNOs are being perturbed by another object in the area.

As Carlos de la Fuente Marcos, one of the authors on the study, explained in an interview with The Information and Scientific News Service (SINC):

“If there is nothing to perturb them, the nodes of these extreme trans-Neptunian objects should be uniformly distributed, as there is nothing for them to avoid, but if there are one or more perturbers, two situations may arise. One possibility is that the ETNOs are stable, and in this case they would tend to have their nodes away from the path of possible perturbers, he adds, but if they are unstable they would behave as the comets that interact with Jupiter do, that is tending to have one of the nodes close to the orbit of the hypothetical perturber”.

For the sake of their research, Doctors Carlos and Raul de la Fuente Marcos conducted calculations and data mining to analyze the nodes of 28 ETNOs and 24 extreme Centaurs (which also orbit the Sun at average distances of more than 150 AUs). What they noticed was that these two populations became clustered at certain distances from the Sun, and also noted a correlation between the positions of the nodes and the inclination of the objects.

Animated diagram showing the spacing of the Solar Systems planet’s, the unusually closely spaced orbits of six of the most distant KBOs, and the possible “Planet 9”. Credit: Caltech/nagualdesign

This latter find was especially unexpected, and led them to conclude that the orbits of these populations were being affected by the presence of another body – much in the same way that the orbits of comets within our Solar System have been found to be affected by the way they interact with Jupiter. As De la Fuente Marcos emphasized:

“Assuming that the ETNOs are dynamically similar to the comets that interact with Jupiter, we interpret these results as signs of the presence of a planet that is actively interacting with them in a range of distances from 300 to 400 AU. We believe that what we are seeing here cannot be attributed to the presence of observational bias”.

As already mentioned, previous studies that have challenged the existence of Planet 9 cited how the study of TNOs have suffered from an observational bias. Basically, they have claimed that these studies made systematic errors in how they calculated the orientations in the orbits of TNOs, in large part because they had all been directed towards the same region of the sky.

By looking at the nodal distances of ETNOs, which depend on the size and shape of their orbits, this most recent study offers the first evidence of Planet 9’s existence that is relatively free of this bias. At the moment, only 28 ETNOs are known, but the authors are confident that the discovery of more – and the analysis of their nodes – will confirm their observations and place further constraints on the orbit of Planet 9.

A planetary mass object the size of Mars would be sufficient to produce the observed perturbations in the distant Kuiper Belt. Credit: Heather Roper/LPL

In addition, the pair of astronomers offered some thoughts on recent work that has suggested the possible existence of a Planet 10. While their study does not take into account the existence of a Mars-sized body – which is said to be responsible for an observable “warp” in the Kuiper Belt – they acknowledge that there is compelling evidence that such a planet-sized body exists. As de la Fuente Marcos said:

“Given the current definition of planet, this other mysterious object may not be a true planet, even if it has a size similar to that of the Earth, as it could be surrounded by huge asteroids or dwarf planets. In any case, we are convinced that Volk and Malhotra’s work has found solid evidence of the presence of a massive body beyond the so-called Kuiper Cliff, the furthest point of the trans-Neptunian belt, at some 50 AU from the Sun, and we hope to be able to present soon a new work which also supports its existence”.

It seems that the outer Solar System is getting more crowded with every passing year. And these planets, if and when they are confirmed, are likely to trigger another debate about which Solar bodies are rightly designated as planets and which ones aren’t. If you thought the “planetary debate” was controversial and divisive before, I recommend staying away from astronomy forums in the coming years!

Further Reading: SINC. MNRAS