UNIT 6 – Plutoids, TNOs, and Comets
o Beyond Neptune are million of icy bodies called Trans-Neptunian Objects
Pluto is one of them, and Eris, Makemake, and Haumea (all dwarf
When Pluto changed over from a planet to a dwarf there was much commotion for their
termed it a Plutoid:
o A celestial object that satisfies three conditions:
It orbits around the sun at an average distance greater than Neptune
It is massive enough that its own gravity beings it to equilibrium, making it
It has NOT cleared the neighborhood around its path from other orbiting
Comets: aggregates of ice, frozen gasses and rock dust/fragments travelling through the
o Usually on paths that are anchored with the Oort Cloud (long-period comets).
o Tiny fragnets falls off and that is bright light we see
o Most live for hundreds of passes.
Chapter 17: pLuToIdS and TNOs
Introduction: Definitions and Locations
o Pluto had to be dwarf because so many like it very being discovered that we
couldn’t have 50 planets.
o Plutoids: Pluto, Makemake, Haumea, and Eris.
o TNOs: any size object in te solar system that orbit Sun at a greater distance than
Neptune. Includes the Kuiper Belt and Oort Cloud.
o Tombaugh used a blink comparer
o 1930 he discovered it – but it was not as large as they thought
o Highly elliptical orbit – goes from 49 to 29 Au distance from the Sun o 2.03 density
o Tilt: 119 degrees
o Satellites: 3 (Charon is the biggest)
o Rings: None
o Usually the farthest from the Sun, b/c Pluto’s orbit is not circular, it is elliptical. It
swings inside the orbit of Neptune sometimes.
o The planets will never collide though.
o Very cold. 50K (-223)
o Best guess at the interior
Frozen nitrogen, water icce, mic of silicate rock and water ice.
It must have a component of rock (2/3 the size of the moon but twice as
dense as water)
Nitrogen makes up most of the atmosphere.
o 1979 discovery
o Orbits Pluto in a nearly circular orbit
o Tidally locked to each other
o Must contain 35% ice and 65% rock (both Pluto and Charon)
o Surfaces contrast
o Both go through dramatic seasons
o Most of the surface is covered with ices from seasonal freezings. New Horizons
will figure this out for us.
o Charon doesn’t fit the label of satellite
Why? Because the centre of gravity of a planet-satellite system is within
the parent planet. But the centre of gravity is in the space between Pluto
o Where dwarf planets are classified.
o Eris: orbits the Sun in a space farther out that Pluto, but closer than the main part
of the Kuiper Belt. Scattered Disc: the inner section f the Kuiper Belt – indicates the
population of objects it in
Eris originally called the 10 planet as it is bigger than Pluto.
Dysnomia orbits Eris as it’s satellite.
The first object of the Kuiper belt was not found until 1992.
o Now TNOs are being found at a high rate.
o The Kuiper Belt will be a much bigger version of the Asteroid Belt.
Chapter 18 – CoMeTs
o What are comets? Small icy objects that streak throught he Solar system, along
sun-orbital elliptical tracks
The frozen gases begin to vaporize as they go along and leave visible
tracks across space.
o Why study comets?
They brought evidence that comets brought water to Earth, providing life.
They brought the amino acids to Earth – 40, 000 tons of particles from
comets fall to Earth every year.
Comet nucleus is cold
Life cannot start ON them
o Diagram of a comet: (replace plasma tail with Ion Tail)
The Nucleus: o Nucleus + coma are called the heat of the comet.
o Centrally located, contains dust and frozen gases. Not solid objects.
o Irregular bodies with voids.
o Can fragment into more than one piece
o An atmosphere surrounding the nucleus
o Dominated by water then CO2
o Sprout 2 tails when close to Sun
o One: Dust tail
It reflects sunlight – made of dust
o Two: Ion Tail
Made of glowing gas because it is releasing light energy
Pushed away from the sun by solar wind
Points ina different direction
o Long-period comets – majority take thousands of years to go around the sun
o Short-period comets – 200 years or less orbital period, they dotn go much past
o Don’t follow a strict orbit
Life and Death
o Active comets (short-life) – mass loss at rates that cannot be sustained forever.
o The active comets are under the gravitational control of the planets