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---------------------- 2270 - How Many Planets?
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- Our Solar System has nine planets. That is the way I learned it and I’m sticking to it. Then, they told me eight planets because Pluto had to be redesigned as a Dwarf Planet along with a half dozen other sub-planets, some that were just recently discovered. They even wanted to redesigned the Ceres Asteroid as a Dwarf Planet And, it orbits in the asteroid belt between Mars and Jupiter.
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- Reviews written over the past dozen years have changed our vision of our Solar System. Here are some Reviews that have tracked our progress to this one, 2270.
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- 2061 - Our Solar System started out with a cloud of dust and gas coalescing round the Sun some 5 billion years ago. After the rocky planets formed there were 300 million years of bombardment from asteroids.
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- 1933 - How big is our Solar System ? The math does not work. Why?
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- 1916 - New discoveries at the edge of the Solar System are causing a renewed search for the answer.
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- 1872 - Our Solar System appears to be unique compared to the over 3,000 exoplanets that have been discovered in other solar systems. This Review list 5 more reviews about our Solar System.
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- 2270 - Yet, redefining our Solar System seems to be just getting started. The outer reaches of our Solar System are still remarkably unmapped. We have to date discovered 840 new small worlds in the distant and hard-to-explore region of space beyond Neptune.
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- Let that sink in. 840 new planets, sub-planets, or asteroids? How many of these new discoveries are going to be designated as Planets, Dwarf Planets or just asteroids. How can we go from 8 to 8 hundred in a single jump. Live and learn:
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- These little icy worlds are important as they help us tell the Solar System’s history. They can also help us test the idea that there is a yet unseen planet lurking in the outer solar system. Is there a large Planet Nine out there somewhere?
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- Our planetary system as we see it today is not as it formed. When the Sun was newborn, it was surrounded by a massive disk of material. Encounters with tiny, growing planets, including some of the worlds we’ve just discovered, moved the giant planets outward from the Sun until they settled into their present locations. The growing number of planets went everywhere, scattering both inward and outward in their orbits.
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- Planetary migration , as they call it, also happened in far away exoplanet systems around many other stars. Fortunately, the celestial bodies in our own planetary system are comparatively close by, making it the only place where we can see the intricate details of how our migration might have happened. Mapping the minor planet populations that are left over from the disk lets us reconstruct the history of how the big planets were pushed into place.
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- Astronomer’s surveys have looked for faint, slow-moving points of light within eight big patches of sky near the plane of the planets and away from the dense star fields of the Milky Way. With 840 new discoveries made at distances between 6 and 83 astronomical units the survey gives us a very good overview of the many sorts of orbits these planet-like objects have beyond the orbit of Neptune.
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- An Astronomical Unit (au) is a measure of distance. It is the average distance between the Sun and the Earth which is 93,000,000 miles.
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- Earlier surveys have suffered from losing some of their distant discoveries. When too few observations occur, the predicted path of a minor planet in the sky will be so uncertain that a telescope can’t spot it again, and it is considered “lost”. This happens more to objects with highly tilted and elongated orbits, producing a bias in what’s currently known about this population of many different orbits.
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- This new survey successfully tracked all its distant discoveries. The frequent snapshots made of the 840 objects over several years meant that each little world’s orbit could be determined very precisely. In total, more than 37,000 measurements of the hundreds of discoveries precisely pinned down their arcs across the sky. From the arc the orbits are calculated.
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- This project has also created a software computer model which provides a powerful tool for testing the inventory and history of our solar system‘s objects. This lets theorists test out their models of how the solar system came to be in the shape we see it today, comparing calculations with these actual real discoveries.
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- The new icy and rocky objects fall into two main groups. One includes those that reside in nearly round orbits in the Kuiper belt. The Kuiper Belt was originally thought to be only asteroids and comets extending from 37au to approximately 50au from the Sun.
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- The other consists of worlds that orbit with Neptune as it travels around the Sun. These “resonant” trans-Neptunian objects, which include Pluto, were pushed into their current elongated orbits during Neptune’s migration outwards from the center of the Solar System.
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- In the Kuiper belt they have discovered 436 of these small worlds. Their orbits confirm that a concentrated “kernel” of the population nestles on almost perfectly round, flat orbits at 43 to 45au.
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- These quiet orbits may have been undisturbed since the dawn of the solar system, a leftover fraction of the original disk. Soon, we will see a member of this group up close: the New Horizons spacecraft, which visited Pluto in 2015, will be flying by a new world that’s about half the size of Britain on New Year’s Day 2019.
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- This dwarf planet candidate 2015 RR245 is on an exceptionally distant orbit, but is one of the few dwarf planets that could one day be reached by a spacecraft mission.
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- The survey has found another 313 resonant trans-Neptunian objects showing that they exist as far out as an incredible 130au. Among these discoveries is this dwarf planet 2015 RR245, which is about half the size of Britain. It may have hopped onto its current orbit at 82au after an encounter with Neptune hundreds of millions of years ago. It was once among the 90,000 scattered objects of smaller size that we estimate currently exist in this part of our Solar System.
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- Among the most unusual of the discoveries are nine little worlds that are on incredibly distant orbits, never coming closer to the Sun than Neptune’s orbit, and taking as long as 20,000 years to travel around the Sun. Their existence implies an unseen population of hundreds of thousands of trans-Neptunian objects on similar orbits.
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- How these objects got on their present paths is unclear. Some orbit so far out that, even at their closest approach, they are barely tugged by Neptune’s gravity. One explanation that has been put forward is that a yet unseen large planet, sometimes called “Planet Nine”, could be causing them to cluster in space.
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- However, our nine minor planets all seem to be spread out smoothly, rather than clustering. Perhaps the shepherding of such a large planet is more subtle ,or, these orbits instead formed in a different way.
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- The history of our solar system is just beginning to be told. We hope discovering some 840 new planet-like objects will help piece together the story. Stay tuned, we still have a lot t learn. Your education is incomplete.
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- February 13, 2019
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-------------------------- Thursday, February 14, 2019 --------------------------
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