This Is Why Scientists Think Planet Nine Doesn’t Exist
“Of course, this study isn’t enough to rule out Planet Nine; it still could be out there. As a counterpoint, Mike Brown has contended that a different survey strategy could have been definitive, and OSSOS simply isn’t a good survey for indicating yea or nay on Planet Nine. But remember, the old saying goes, “where there’s smoke, there’s fire,” indicating that if you observe an effect, it likely has a cause.
If you all of a sudden discover that what you thought was smoke was a figment of your imagination, it doesn’t mean there wasn’t a fire, but it sure does make the hypothesis that there ever was a fire a lot less compelling. The OSSOS study doesn’t rule out Planet Nine, but it does cast doubt on the idea that the Solar System needs one. Unless a deeper, better survey indicates otherwise, or Planet Nine serendipitously turns up, the default position should be its non-existence.”
Is there another massive planet in the Solar System? Do we have a super-Earth after all, between the masses and sizes of Earth and Neptune? And has it only gone undiscovered until now owing to our telescopic limitations, and the fact that it’s so much more distant than the presently known planets?
It’s possible. That’s the radical idea behind Planet Nine, proposed nearly three years ago by Konstantin Batygin and Mike Brown. They looked at the unusual orbits of a number of Kuiper Belt objects, and conjectures that a ninth planet, located hundreds of times as distant as Earth is from the Sun, could be the culprit. But on closer inspection, the evidence that they’re looking at might just be biased, and there may be no Planet Nine at all.
Our Motion Through Space Isn’t A Vortex, But Something Far More Interesting
“We know exactly how the Earth moves through the Universe, and it’s both beautiful and simple. Our planet and all the planets orbit the Sun in a plane, and the entire plane moves in an elliptical orbit through the galaxy. Since every star in the galaxy also moves in an ellipse, we see ourselves appear to pass in-and-out of the galactic plane periodically, on timescales of tens of millions of years, while it takes around 200-250 million years to complete one orbit around the Milky Way. The other cosmic motions all contribute, too: the Milky Way within the Local Group, the Local Group in our Supercluster, and all of it with respect to the rest-frame of the Universe.
The Solar System isn’t a vortex, but rather the sum of all our great cosmic motions. Thanks to the incredible science of astronomy and astrophysics, we at last understand, to tremendous precision, exactly what that is.”
There are images, GIFs, and videos that claim to show our motion through the galaxy. A great many of them are incredibly visually appealing; stunning, even. But are they scientifically accurate visualizations, or are they simply pseudoscience gussied up in the language of science, along with pretty-but-misleading visuals? Rather than nitpick the work of what someone else has created, let’s just go all the way and learn about what our actual cosmic motion through the Universe is, and get it as accurate as modern-day science actually knows!
“But the Sun will be so hot and so bright that much of the outer Solar System will be absolutely destroyed. Each of the gas giants has a ringed system; although Saturn’s is the most famous, all four of them have rings. These rings are mostly made of various ices, such as water ice, methane ice, and carbon dioxide. With the extreme energies given off by the Sun, not only will these ices melt/boil away, but the individual molecules will be so energetic that they will be ejected from the Solar System.”
When the Sun becomes a red giant, lots of changes are going to happen. Mercury and Venus will surely become engulfed; Earth and Mars will lose their atmospheres and oceans, becoming barren and charred. But even beyond that, the outer worlds and structures in the Solar System will melt and lose their volatiles. Asteroids will lose mass and become rocky/metallic cores; moons like Europa and Enceladus will melt away; the rings around the gas giants will disappear; even Pluto and the other large Kuiper Belt objects will lose their atmospheres and top layers, melting away until they’re only a rock-and-metal core.
Ask Ethan: How Do We Know The Age Of The Solar System?
“How do we know the age of our solar system? […] I have a loose grasp on the concept of dating the time elapsed since a rock was liquid, but 4.5 Billion years is roughly how long ago Theia hit proto-Earth liquefying a massive amount of everything. […] How do we know we’re actually dating the solar system and not just finding dozens of ways to date the Theia collision?”
You’ve probably heard the estimates before: that the Earth, the Sun, and the rest of the Solar System are all about 4.5 or 4.6 billion years old. But why be so imprecise? We don’t have to be! In fact, we know that there are slight variations, and based on the fact that we think that the Earth-Moon system formed from a giant impact tens of millions of years after the rest of the Solar System did, we shouldn’t get the same answer for everything! It turns out that we’ve now advanced to the point where we can actually give answers that are extremely accurate: the Earth-Moon system should be 4.51 billion years old; the oldest meteorites show an age for the rest of the Solar System of 4.568 billion years, and the Sun may be a little older at 4.6 billion years.
Remnants Of Our Solar System’s Formation Found In Our Interplanetary Dust
“Our naive picture of a disk that gets very hot, fragments, and cools to then form planets may be hopelessly oversimplified. Instead, we’ve learned that it may actually be cold, outer material that holds the key to our planetary backyard. If the conclusions of the Ishii et al. paper stand the test of time, we may have just revolutionized our understanding of how all planetary systems come into being.”
How did Earth (and the other planets) form? According to conventional wisdom, a molecular cloud collapsed, formed a protoplanetary disk, funneled material into the center, and gave birth to a star. This star then blew off the gas and light elements from the inner Solar System, with the planets we have today representing the survivors from these hot, early stages. Only, what if that picture weren’t correct after all? What if the material that gave rise to our (and other) worlds wasn’t forged in an inferno, but in a colder, more distant environment that only fell into the inner reaches at a later time?
Is Humanity Ignoring Our First Chance For A Mission To An Oort Cloud Object?
“In 2003, scientists discovered an object beyond Neptune that was unlike any other: Sedna. While there were larger dwarf planets beyond Neptune, and comets that would travel farther from the Sun, Sedna was unique for how far it always remained from the Sun. It always remained more than twice as distant from the Sun as Neptune was, and would achieve a maximum distance nearly 1,000 times as far as the Earth-Sun distance. And despite all that, it’s extremely large: perhaps 1,000 kilometers in diameter. It’s the first object we’ve ever found that might have originated from the Oort cloud. And we’ll only get two chances if we want to send a mission there: in 2033 and 2046. Right now, there isn’t even a proposed NASA mission looking at the possibility. If we do nothing, the opportunity will simply pass us by.”
Out beyond the eight planets of our Solar System, a large number of regions, all containing frozen objects, are theorized to exist. Innermost is the Kuiper belt, consisting of a wide variety of bodies, but all of which come quite close to Neptune’s orbit and feel its gravitational influence. Beyond that are the scattered disk objects: objects kicked by one of the gas giants out to greater distances. Beyond that are the detached objects, which have undergone multiple gravitational interactions and no longer come close to Neptune. And finally, there are the sednoids: objects that never come within double the Sun-Neptune distance of the Sun. There are only two known, and the first one, Sedna, is so large that it’s surely a dwarf planet. With an aphelion of approximately 1000 A.U., it may well have an origin in the inner Oort cloud, which is hitherto only theorized.
Ask Ethan: What Happens When Stars Pass Through Our Solar System?
“How bad would it be if a star passed near the Sun? How close/large would it have to be to pose serious danger? How likely would such an event be?”
Space is a pretty empty place; it’s more than four light years to the nearest star. But despite this, we’re moving through the galaxy at around 220 km/s, passing and being passed by other stars at about 10% of that speed. Over long periods of time, stars occasionally make close passes by our own, meaning that they could pertub the Oort cloud, the Kuiper belt, or (if they got close enough) even the orbits of the planets themselves. Which of these is a realistic concern, and how often do these events actually occur? Moreover, when they do occur, what are the implications for what we’ll experience here on Earth? Will there be a pretty light show? A series of cometary impacts? Or a complete disruption of our orbit?
Ask Ethan: If Dark Matter Is Everywhere, Why Haven’t We Detected It In Our Solar System?
“All the evidence for dark matter and dark energy seem to be way out there in the cosmos. It seems very suspicious that we don’t see any evidence of it here in our own solar system. No one has ever reported any anomaly in the orbits of the planets. Yet these have all been measured very precisely. If the universe is 95% dark, the effects should be locally measurable.”
You know the deal with dark matter: it makes up 85% of the mass of our Universe, it has gravitational effects but no collisions with normal matter or itself, and it explains a whole slew of cosmological observations. But why, then, if it’s everywhere, including in an enormous, diffuse halo around our Milky Way, doesn’t it affect the motion of our Solar System in an observable way? Surely, when you say that matter is distributed all throughout our galaxy, that will include the Sun’s neighborhood, right? The truth is, it actually does! Dark matter must exist throughout the Solar System, but that doesn’t mean its effects are observable. Contrariwise, you have to do the calculation to know what its density is, and to quantify the effects it would have on the planets. We can actually do this ourselves, and the results we find tell us, under a variety of conditions, exactly what we’d expect. Dark matter should be in our Solar System, and our best observations aren’t yet able to test whether it exists or not!
“So why are all the planets in the same plane? Because they form from an asymmetric cloud of gas, which collapses in the shortest direction first; the matter goes “splat” and sticks together; it contracts inwards but winds up spinning around the center, with planets forming from imperfections in that young disk of matter; they all wind up orbiting in the same plane, separated only by a few degrees — at most — from one another.”
When we look out not only at our own solar systems, but at the solar systems we’ve found around other stars, we find they have a remarkable feature in common: their planets all appear to rotate in the same plane. They might be off by a handful of degrees, but as far as we can tell, they all align with one another. This isn’t some mere coincidence, but seems to be a consequence of how solar systems form in the first place. Just as spiral galaxies orbit in the same, single plane, so do solar systems. Remarkably, it seems to be the same process at play: large structures collapse, which they do faster in one direction, and then angular momentum takes over, forming a disk. Over time, imperfections in the disk fragment, causing clumps to form and grow over time. When all is said and done, the survivors are all left in the same, single plane.