General Astronomy
The Solar System
The Dwarf Planets
Defining a Planet
• A dwarf planet is a celestial body that
– is in orbit around the Sun,
– has sufficient mass for its self-gravity to overcome
rigid body forces so that it assumes a hydrostatic
equilibrium (nearly round) shape,
– has not cleared the neighborhood around its orbit,
and
– is not a satellite.
Ceres
Ceres
• On January 1, 1801, Piazzi (a Sicilian
astronomer) noted a new object which he
watched until February 11. He wrote Bode of
his discovery, but by the time Bode looked
for it, the object was too near the direction
of the Sun for observation.
• In November, Gauss predicted the location
of this object based on Piazzi's
observations; it was found on Dec 31, 1801
• Piazzi named the object "Ceres" after the
protecting goddess of Sicily
• The missing planet had been found at a
distance of 2.77 AU
Ceres
• By 1890, over 300 more "planets" had
been discovered in the same region (in
regards to distance from the Sun) and
Ceres was stripped of its planetary
status.
• In 2006, Ceres was given a new
designation of "dwarf planet"
The bright spot on Ceres
Ceres – Occator Crater
Ceres
Ceres’ Statistics
Eccentricity
0.080
Orbital period
4.6 yr
Orbital Radius
2.7 AU
Inclination
10.6°
Size
975×909 km
Mass
9.5×1020 kg
Density
2.08 g/cm³
Escape velocity
0.51 km/s
Rotation
0.3781 d
Tilt of Axis
~4 °
Albedo
0.113
Mean surface temperature
~167 K
Max surface temperature
239 K (-34 ° C)
Ceres’ Interior
Vesta & Ceres versus the Moon
Pluto
Discovering Pluto
Pluto
Eccentricity
0.249
Orbital period
248 years
Orbital Radius
39.5 AU
Inclination
17.14 °
Size
1473 Km
Mass
9.5×1020 kg
Density
2.06 g/cm³
Escape velocity
1.2 km/s
Rotation
6.4 d
Tilt of Axis
119.6 °
Albedo
0.49–0.66 (varies by 35%)
Mean surface temperature
44 K
Max surface temperature
55 K
Discoverer
Clyde Tombaugh, 1930
Pluto
The Whale
The Heart
The Brass Knuckles
Pluto
Pluto’s Nitrogen Atmosphere
Pluto’s Haze, Mountains and Plains
Charon
Charon Map
Nix and Hydra
•
•
Two additional moons of Pluto were imaged by astronomers working with the
Hubble Space Telescope on May 15, 2005.
These small moons orbit Pluto at approximately two and three times the distance
of Charon
–
–
Nix at 48,700 Km
Hydra at 64,800 Km from the barycenter of the system.
•
They have nearly circular prograde orbits in the same orbital plane as Charon
•
Observations of Nix and Hydra are ongoing to determine individual
characteristics.
–
•
•
Hydra is sometimes brighter than Nix, speculating that it either is larger in dimension or
different parts of its surface may vary in brightness.
Sizes are estimated from albedos.
The moons' spectral similarity with Charon suggests a 35% albedo similar to
Charon's
–
–
–
this results in diameter estimates of 46 kilometers for Nix and 61 kilometers for
brighter Hydra.
Upper limits on their diameters can be estimated by assuming the 4% albedo of the
darkest Kuiper Belt objects; these bounds are 137 ± 11 km and 167 ± 10 km respectively.
At the larger end of this range, the inferred masses are less than 0.3% of Charon's
mass, or 0.03% of Pluto's.
Pluto’s newest moons
(2011 and 2012)
Eris and Dysnomia
Eris
Eris
Eris
(2003 UB313)
Eccentricity
0.438
Orbital period
557 years
Orbital Radius
38.2 – 97.6AU
Inclination
44°
Size
2400 Km
Mass
?
Density
?
Escape velocity
?
Rotation
>8h
Tilt of Axis
?
Albedo
0.86
Mean surface temperature
~ 30 K
Discoverer
Chad Trujillo, Dave
Rabinowitz and Mike Brown,
2002
Makemake
Makemake
• Makemake is the creator of humanity in
the mythos of Rapa Nui
• It is the third-largest known dwarf
planet in the Solar System
• No satellites have been detected around
Makemake so far
• The presence of methane and possibly
nitrogen suggests that Makemake could
have a transient atmosphere
Orbital characteristics
Makemake
Aphelion
53.1 AU
Perihelion
38.5 AU
Semi-major axis
45.8 AU
Eccentricity
0.159
Orbital period
309.88 yr
Average orbital speed
4.4 km/s
Inclination
28.96°
Physical characteristics
Dimensions
1300–1900 km
Mean radius
750 km
Mass
~4 × 1021 kg
Mean density
~2 g/cm³
Sidereal rotation
unknown
period
Axial tilt
unknown
Albedo
78.2
Temperature
30–35 K
Apparent magnitude
16.7
Haumea
Haumea
• The goddess of childbirth and fertility in Hawaiian
mythology.
– The name is particularly apt as the goddess Haumea also
represents the element of stone and observations of Haumea
hint that, unusually, the dwarf planet is almost entirely
composed of rock with a crust of pure ice.
• Haumea is joined in its orbit by two satellites that are
thought to have been created by impacts with it in the
past.
– The first and largest moon is to be called Hi'iaka, after the
Hawaiian goddess, the patron goddess of the island of Hawai'i.
– The second moon of Haumea is named Namaka, a sea goddess,
also Haumea's daughter
Orbital characteristics
Haumea
Aphelion
51.5 AU
Perihelion
35.2 AU
Semi-major axis
43.3 AU
Orbital period
285.4 yr
Inclination
28.2°
Satellites
2
Eccentricity
0.188
Physical characteristics
Dimensions
~1960 × 1518 × 996
Km
Mass
4.2 ×1021 kg
Mean density
2.6–3.3 g/cm³
Rotation period
3.9 hr
Albedo
0.7
Temperature
32K
Apparent magnitude
17.3
Haumea
Pluto
Makemake
Other Candidates
Quaoar
Quaoar
•
•
•
•
•
•
Distance from Sun = 50 AU
Orbital period = 285 years
Eccentricity = 0.04
Diameter = 1250 Km
Orbital Inclination = 8°
Discoverers: Chad Trujillo and Mike
Brown, 2002
Sedna
Sedna (2003 VB12)
Distance from Sun: 74 AU - 990 AU
Length of day:
10 hours
Orbital period:
~11,249 years
Eccentricity:
0.849
Diameter:
1800 Km
Discoverers: Chad Trujillo, Dave Rabinowitz and Mike Brown
Year of Discovery: 2002
Sedna
Easterbunny
Makemake
Santa
Haumea