Comet, Oort cloud, Solar System, Astronomy, Star id Belt, Kuiper Belt, & Oort Cloud | Settle The Stars (Episode 18)
In our last episode, we ventured farther out than we ever had before out into the kuiper belt to visit some of the most distant dwarf, planets yet discovered. Those objects are notoriously difficult to find, usually with only the most powerful telescopes or by detecting tiny nudges in the orbits of other bodies. Today well put our astronomers to the test, flexing the might of their technologies and techniques to reveal objects that are even smaller. The clumps of rock and ice that litter the in between spaces within our solar system well find out about the elegant order. These objects follow as theyre shepherded, captured or flung about by the larger planets they might encounter all under the watchful eye and captivating orbit of our sun. For almost as long as astronomers have been fascinated by the bright shining points of light in the sky, theyve also wondered about the spaces between them. After all, smaller objects had been known to fall from the sky for thousands of years made of metal of otherworldly strength and mysterious magnetic properties. But where do these objects come from? And what about the rare and beautiful comets that cast their brilliant tales across the night sky during their regular visits? Where do they go when theyre, not here many early, astronomers hypothesized, that there was an order to the location of these dark objects and noticed large gaps? Where they might expect to find more objects to study, but in fact only found darkness in 1596, german astronomer and mathematician johann kepler pointed out that, among the mountains of observations and notes amassed by the elder dutch astronomer tycho bray, there seemed to be an inexplicable gap Between mars and jupiter, where no object had yet been discovered in his brave defense of heliocentrism, the astronomical model wherein the sun is the center of the solar system.
Kepler noted between mars and jupiter, i place a planet. Fellow german and fellow johann johann daniel tishas would jot a small but brilliant footnote in his translation of a text that would later come to be known as the tishus bode law. One can only guess how much astronomical data one would need to review before this became apparent, but tishus noted that if one began counting at zero with the sun and then counted out 3 6, 12 and so forth, doubling each number and then added four to each Of the numbers before dividing each by ten, you could predict with remarkable precision the radii of the orbits of the known planets, as measured in astronomical units, the average distance of earth to the sun. All of the known planets correspond to a node in this sequence, with a mysterious gap between 12 mars and 24 jupiter, even uranus discovered almost two decades after the discovery of this curious law, fit right into the sequence where the next planet was predicted. It isnt known what could cause the sequential spacing that tishas noted, but after the discovery of neptune, which sits outside of this sequence, it was decided that the sequence is an uncanny coincidence or at best a trend rather than a law. At last, an object was cited in 1801 by italian, giuseppe piazzi in the orbit predicted by tishius, which he named ceres after the roman patron goddess of his hometown sicily, about a year later, german physician and astronomer heinrich obers found another object in the same area to Be called palace, these two objects were a source of confusion for astronomers.
At the time they moved across the sky as a planet would, but the strongest telescopes in the world could not resolve the image of a disc to discern color or shape they were indistinguishable from stars, except for their planet. Like movement, a new class of objects was proposed to group. These new bodies called asteroids by william herschel in 1802 asteroid is derived from the greek word asteroids, which translates to star like in reference to their confounding appearance. The name didnt stick at first, though, and the objects were still referenced as planets by the wider community astronomers in lillianthal, germany took up the study of these curious objects and the unknown region they occupied lilianthal was home to the reason, telescope or giant telescope. A marvel of the latest and greatest optical technology with these resources, astronomers were able to identify two more new objects in the group juno and vesta within five years. Then the napoleonic wars found their way to lillianthal and, as so frequently happens in times of strife, science was an early casualty. Tragically, lilianthal was sacked and while the observatory was spared from the fires that destroyed the rest of the village, it was looted and the research was lost effectively ending the study of asteroids for almost 50 years in 1845. The search picked back up with the identification of estrella the first in a long list of newly found objects. Each and every one of them were included in the full list of planets until doing so became too burdensome for astronomers and herschels idea to group them all.
As asteroids gained wider acceptance in the following years, the region was referred to as the asteroid belt a term we still use today by 1921, a total of a thousand asteroids had been identified. 60 years later. In 1981, there were 10 000 as modern astronomy took off and with the aid of even better technologies and automated searching computers. By the year 2000, the number had grown to a hundred thousand asteroids. The asteroids are grouped into classes based on their composition, c type for carbonaceous s, type for silicates and m type for metallic. So how about we have a look ourselves to do so well need to take a short trip of around 18 months. Any direction will do the asteroids are pretty well evenly distributed across the belt, so well run into some eventually generally, we just want to head away from the sun. Fortunately, for us, the belt hugs, the orbit of mars closer than that of jupiter, so we wont need to go too far and as we reach our destination and slow to a stop, well see expanding before us, a gigantic expanse of nothing just empty space, contrary to Sci fi, depictions of crowded fields of rock there isnt much going on in the asteroid belt across the entire arc of the asteroid belt, is spread an amount of mass equaling only about four percent of the mass of our own moon. The area of the belt is so huge and the amount of mass within it is so small.
They will need to go hunting to see any asteroids put another way. Traveling through the asteroid belt would be less like dodging trees. In a forest and more like dodging islands in the south pacific sure there are a lot of them, but theyre, tiny and theyre spaced way out from each other. First, lets take a look at ceres. The largest object in the belt hogging up about a quarter of all the mass in the asteroid. Belt ceres resembles a miniature version of our moon, just shy of a thousand kilometers across spherical and grey and cratered its actually recognized. As a dwarf planet, the only known one to reside within the boundary of neptunes orbit. It probably even has a semi liquid interior with evidence of cryo volcanoes capable of spouting enough gas to form a transient. Exosphere vesta is the next down in size, but much smaller at just over 500 kilometers wide vesta is not large enough to support a spherical shape resembling an egg or a rugby ball. Its bright gray color make it highly reflective to light and, as a result, vesta is the brightest asteroid in the sky from earth just barely visible to the naked eye. It is believed that vesta is a protoplanet composed of leftover matter that collected to form the rocky planets and the only one confirmed. Yet these early bodies would have formed from the accretion disk early in the solar system gradually clumping into the larger planets if they werent slung out of the solar system by gravity or pulverized by a collision first, how do we know so much about vestas composition to Be able to guess that well, two huge craters reveal past collisions each apparently large enough to suggest massive fracturing within the last couple billion years.
The collision sprayed so much material that the fragments fell to earth as howardite ukrite diogenite meteorites. So we have pieces of vesta here at home to study. As a matter of fact, 99.8 percent of the meteorites that fall to earth are thought to have originated from the asteroid belt. So weve had a lot of help in studying asteroids in the form of direct sampling, palace and hygeia round out. The group of four largest objects in the belt, both slightly smaller than vesta and less well studied its believed. Pallas could be another proto planet like vesta, but without specimens this hasnt been confirmed. Hygiena is the largest of the carbonaceous c type asteroids and its hypothesized to have been fractured by past massive collisions and later reformed from the resulting debris. The outer reaches of the asteroid belt are rich, with c class asteroids like hygeia, while s type silicates are near the inner boundary and metallic m types are scattered throughout one outstanding mystery of the belt is the apparent rarity of a fourth type, the v type basaltic Asteroids prevailing thought is that the planets were formed by the conglomeration of v type asteroids in order to explain the high presence of basalt or olivine in the crust of the terrestrial planets. Today. Upon observation, however, 99 of the basalt material expected in the asteroid belt is missing. Actually only two v types have been discovered so far at all. These questions have been studied with the help of several spacecraft visits to the region, mostly by passers, by on their way farther out into the solar system.
As recently as 2015 nasas probe dawn visited vesta and ceres collecting valuable image and spectrometer data before depleting its hydrazine fuel in 2018., today the powered down dawn quietly orbits ceres, but will probably fall to the surface within the next 20 years. Visits are even more rare to the next collection of smaller bodies well visit out beyond the orbit of neptune out here, spanning a region from 30 to 50 times the distance of the sun to the earth. The kuiper belt circles similar to the asteroid belt. But over much greater space and with about 20 times as much mass another difference from the asteroid belt, is that most of the objects this far out are made of ices frozen methane, water and ammonia. There are other dwarf planets as well, including some which were snatched up to become moons of saturn and neptune. We visited the kuiper belt neighborhood in the previous episode journeying to pluto, along with some of the other dwarf planets that reside there. So we wont spend too much time here today, except to point out that, yes, there is more to explore to see the edge of the solar system well need to head out farther than weve traveled. Yet on this podcast to a place so mysterious and unknown that even the voyager probes, the farthest man made objects with a nearly 40 year head start havent. Even gotten close. This region was first hypothesized as a way to explain the intermittent visits of comets into the solar system.
As observed, many comets dive into the solar system from far out in space make a quick loop around the sun and then shoot back out into the blackness. This suggests large parabolic or oval shaped orbits with the sun, tucked in close at one end and a huge orbit. Bending out past the known solar system, estonian astronomer ernst, opic, suggested in 1932 that theres a large cloud of material outside the solar system from which these comets originate. But the idea was not widely accepted. It would take some puzzling and reintroduction by dutch astronomer, jan ort in 1950, to revive the theory after noting that the unstable orbits of comets and their volatile burning off of materials which produce their characteristic tales ort theorized, that over time, comets should have all either collided. With objects in the solar system, or been completely burned away by the sun, if there were an area outside the solar system in which these objects resided until eventually being pulled into an orbit as a comet, it could explain why they still exist so long after the Formation of the solar system. Today we call this theoretical region, the oort cloud or the opec oort cloud, defining the boundary of the known solar system. The oort cloud is thought to be home to billions of comets drifting, more or less aimlessly in a loose spherical area. Around the solar system, unlike the donut, shaped orbits of the closer asteroid and kuiper belts as far as two thousand to two hundred 000 times as distant as the earth from the sun, these objects would be bathed in almost perpetual darkness.
Aside from the backdrop of stars in every direction out here, the gravitational relationship with the sun is tenuous with other stars exerting as much influence as anything else. On the way, an object might be nudged, its even thought that objects in the oort cloud could stretch and morph, due to the tidal forces exerted by the milky way itself, almost in the same way that water on earth is pulled by the moon into tidal patterns. This kind of interaction, along with nudges from other nearby stars or even clouds of molecules, could theoretically be enough to get one of these objects. Drifting closer to the sun. With enough of a push, such an object would begin the inevitable fall toward the sun diving past and around it before gravitational forces. Hurl it back out into space to fall again and thus a comet is born. Comets exhibit a bright plume of gas and dust. We see as the tail this tail emanates from a thin atmosphere surrounding the comet called the coma. Sometimes the coma can become quite large, even larger than the sun comets 17p holmes and the great comet of 1811 both had comas as large or slightly larger than the diameter of the sun, although they can decrease significantly as they approach closer to the inner solar system. The suns radiation pushes the molecules within the coma into a smear behind it, forming the bright tail that we see because the force of the radiation is applied from the sun.
The tail of the comet is always facing away from the star, not trailing behind it. Like a dust cloud behind a car, that means that after a comet swings around the sun and retreats back out into space, its tail actually points forward ahead of the comets path. Short period. Comets are comets with orbits that take up to 200 years to complete. Most of these comets are thought to originate from much closer kuiper belt or the scattered disk of icy debris linked to it. Some comets, like the famous halleys comet and others like it, are believed to have originated in the oort cloud. Despite having short periods long period, comets have orbits that are longer than 200 years, with some lasting millions of years. Comet mcnaught is a long period. Comet that put on quite a show for the southern hemisphere recently in 2007, with a tail stretching almost a quarter of the way across the sky and visible in broad daylight. If you missed it, unfortunately youll have to wait another 92 700 years for it to come back. But if you dont feel like waiting that long im sure there will be other beautiful comments to see before then, and sometimes even if the comet itself isnt nearby. The trail it leaves behind can still put on a show. Many of the major meteor showers witnessed around the world at regular annual intervals are due to the passing of earth through the debris left behind by a comet sometime in the past.
The orionids in october, for example, are actually little bits left behind by halleys comet. Occasionally there can be collisions. Of course, diving through the solar system is always risky. Business comets have been known to impact the planets and moons of the solar system, notably the shoemaker levy 9 comet that collided with jupiter in 1992. We learned a great deal about both comets and jupiter by watching the massive impact safely here on earth. But earth is known to enter the line of fire too, sometimes with our fair share of comet impacts from time to time. In fact, its believed that repeated bombardment by comets could have delivered enough water to earth during its formation to fill our oceans and provide a likely beginning for life to evolve, along with some of its necessary organic ingredients. While exploration of the oort cloud isnt a viable possibility for humans, quite yet, given the incredible distance, we can appreciate that instead we receive these regular visits from some of its inhabitants. From time to time. In the past, comets were seen as omens of the gods or portents of great events, good and bad war, famine, prosperity and in france, even exceptionally, good wine have all been associated with the appearance of great comets in the sky now and hopefully continuing in the future. These rare events will be appreciated as opportunities for scientific study and the awe inspiring beauty of space available to us, even in our own backyard.
I hope youve enjoyed listening as weve learned more about the asteroids and comets that litter our solar system theyre an often overlooked feature, but offer a fascinating glimpse into how solar systems like ours form and what forces and characteristics can lead to the incredible diversity of environments. We have observed so far next week. Well continue our exploration of the solar system as we return back home and revisit some of the most familiar locations with fresh eyes in the meantime be sure to subscribe. If you havent already settle the stars is available on pretty much every podcasting platform and were also mirroring our episodes on youtube at youtube.com, edgeworks, entertainment and be sure to ring that bell. So you know when theres a new episode. We also have a patreon page at patreon.com, edgeworks entertainment, where you can get early episodes and tons of other great rewards. The support of listeners like you is what makes this show possible and im so grateful to the people who have already joined and be sure to leave a rating and a review on apple, podcasts, spotify or wherever youre listening leaving a review is the single easiest way That you can support indie podcasters like me.