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- We lost Pluto. Pluto is no longer the 9th planet in our solar system. Our solar system has gotten smaller. Now we are down to 8 planets, 4 rocky planets and 4 giant gaseous planets. I'm writing this from the 3rd rock from the Sun.
- Or, has our solar system got larger? The reason Pluto got demoted to a dwarf planet was because astronomers have found 1,000 more dwarf planets, or, asteroids, or, Kuiper Belt Objects, or, what do we want to call these things that are part of our larger solar system beyond the planet Neptune?
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- Pluto's orbit is inclined by 17 degrees to the plane of the rest of the planets. Its orbit is in 2:3 resonance with Neptune's orbit. Pluto orbits the Sun twice for every three times Neptune orbits the Sun. Pluto is 1,467 miles diameter and it takes 248 years to orbit the Sun. Its gravity is 6% that of Earth’s. Average temperature is - 380F.
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- Since the advent of Charged Couple Devices, CCD’s, astronomers have found many more objects having orbital resonances with Neptune. These Kuiper Belt Objects are 38 to 48 astronomical units from the Sun. The Earth - Sun distance is 1 astronomical unit. 1AU = 93,000,000 miles. About 30 percent of these objects have moons, or satellites of their own. Pluto has 5 moons.
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----------------- Eris with moon Dysnomia
----------------- Pluto with moons Charon, Kerberos, Nix, Hydra, Styx
---------------- Makemake
---------------- OR10
---------------- Haumea with moons Hi’Iada, Namaka
--------------- Quaoar with moon Weywot
---------------- Sedna
---------------- Orcus with moon Vanth
--------------- MS4
--------------- Salacia
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- Moons are great for astronomers because they can be used to find the mass of the object they are orbiting. By measuring their radius of the orbit. And, the period of their orbit we can use Kepler's 3rd law to calculate the mass of the object. His 3rd law says that the square of the period is equal to the cube of the radius.
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------------------------ p^2 = a^3
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---------------------period * period = radius * radius * radius
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-------------------- when the period is in years and the radius is in AU
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- Newton generalized Kepler’s 3rd law to:
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---------------------------- p^2 = 4*pi^2 * a^3 / G * ( M1 + M2)
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----------------------- 4*pi^2 = 39.44
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---------------------- G = gravitational constant = 7.67*10^-1 m^3 / ( kg*sec^2)
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---------------------- 4*pi^2 /G = (5.9*10^11) which is the constant of proportionality needed to make the proportionality an equality. When the mass of the planet is much, much larger than the satellite the formula reduces to:
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------------------ M = (5.9*10^11) a^3 / p^2
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-------------- For Example : Mars Reconnaissance Orbiter is at 3,700 kilometer radius with a period of 114 minutes.
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------------------- M = (5.9*10^11) (3.7*10^6)^3 / 6.84*10^3)^2
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------------------ M = 6.3 * 10^23 kilograms, the mass of Mars, about 10% the mass of the Earth.
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- Once we have the diameter of the object we calculate the density as mass / volume. What we learn is that these objects are all over the map. The colors range from bright white to pitch black. The densities range from pure ice to rocks with a thin coat of ice. The size ranges from bigger than Pluto to small asteroid size.
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- What can we say by Pluto's neighborhood? Called the Kuiper Belt Objects these represent a “large variety” of new discoveries.
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- Most objects are less than 190 miles diameter, dark red in color. We can't call these Dwarf Planets. They resemble more like Saturn's moon Phoebe, which is 137 miles in diameter. Phoebe is pockmarked with craters and not perfectly spherical.
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- Many of the larger objects, greater than 250 miles in diameter, are brighter and lighter in color. Larger bodies have self-gravity that pulls them into a round shape. They may have even heated up to cover their surface with fresh, bright ice. Maybe these should be called Dwarf Planets. There are about 100 of them and 10 of them have names shown in the above paragraph
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- Pluto has an atmosphere of nitrogen, methane, and carbon dioxide. The atmosphere could mean that it has weather. Liquid nitrogen could rain into rivers and lakes on the surface. See photo above on how Pluto’s seasons change color.
- Pluto's moon Charon is large enough that if it was on its own it would be a Dwarf Planet as well.
- Eris is the same size of Pluto and has a moon Dysnomia . It is 3 times further from the Sun than Pluto, 38 to 90 AU.
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- Triton is a moon of Neptune. It is in retrograde orbit and was once probably a Dwarf Planet in the Kuiper Belt very similar to Pluto and Eris. Somehow , Neptune just happened to capture Triton.
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- The Makemake is half the size of Pluto, 0.05% the size of the Earth and traveling 9,843 miles per hour.. It's surface is most mostly methane ice, -402F.
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- Quaoar has a methane ice surface as well. It has a 783 mile diameter
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- Haumea spins so rapidly one day is 3.9 hours.
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- Sedna the is the oddball. It bears methane ice surface too and is 76 astronomical units away from the sun, more than twice the distance as Neptune. It's enormous orbit in 5,000 years will put it out to 1,000 astronomical units away. Sedna is half the size of the Moon, 1,000 miles diameter. At 8,000,000,000 miles distance it is like trying to see a soccer ball 900 miles away. It takes 11,500 years to orbit the Sun. It has a slow rotation of 40 days.
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- There is most certainly other objects past Neptune that are larger than Pluto. They are just too dim and distant to have been discovered by now. An announcement will be made shortly stay tuned.
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(1) See these reviews for more learning on Pluto and the other Dwarf Planets. 1364, 1129, 685, 1279
(2) See Review 502 on Sedna.
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RSVP, with comments, suggestions, corrections. Index of reviews available ---
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