4: PLUTO
What is notable about Pluto's rotation?
Rotational period is thought to be -6.4 days, aka RETROGRADE MOTION
How do astronomers think Pluto & its moons formed?
result of a GIANT COLLISION b/w two objects (1600 - 2000 km in size) in a similar process that formed the Earth & Moon
What is notable about Pluto's atmosphere? (3)
1) Pluto's weak surface gravity = its atmosphere extends further into space than Earth's atmosphere 2) the presence of Pluto's atmosphere is not constant: at its aphelion, Pluto receives so little solar energy & is so cold that the atmospheric methane freezes, aka Pluto's atmosphere only forms as it nears the Sun (near perihelion); 3) observation of successive stellar occultation events indicate that Pluto's atmosphere is undering GLOBAL COOLING, while its SURFACE is getting SLIGHTLY WARMER (this can only be partly caused by Pluto's eccentric orbit, other causal factors remain a mystery)
How is Pluto influenced by Neptune? (1 + 2)
1) Pluto, as a Kuiper Belt object, is in 3:2 orbital resonance w/ Neptune; at perihelion, Pluto is 30 AU from Sun & comes w/in Neptune's orbit but never nears Neptune itself 2) Pluto's current position was likely influenced by a migrating Neptune early in the history of the solar system
Describe two notable features about Charon's orbit.
1) SYNCHRONOUS, 1:1 spin-orbit resonance w/ Pluto so that Charon's orbital & rotational period synchronized w/ Pluto's rotational period, 6.4 days 2) orbit is tilted around 60 degrees to Pluto's orbit around the Sun
Describe two notable features about Pluto's surface
1) temperature is not uniform across surface: varies from -235 C to -210 C 2) a complex distribution of FROST migrates across Pluto's surface w/ orbital & seasonal cycles; frost = byproduct deposited out of Pluto's nitrogen-methane atmosphere; responsible for Pluto's surface features, incl. its prominent northern polar cap
List Pluto's five moons in descending size.
Charon: by far the largest; Pluto & Charon thought to be a double-planet system; NIX & HYDRA P4 & P5
Describe two notable features about Pluto's orbit.
ECCENTRIC: 30 - 50 AU (avg. distance to Sun = 40 AU) HIGHLY INCLINED: 17 degrees from ecliptic (rest of planetary orbits tilted < 8 degrees)
Why does Pluto not satisfy IAU's definition of a "planet"?
IAU's definition of planet = a celestial body that... 1) orbits the Sun; 2) has enough mass to assume a spherical shape; 3) has cleared the neighborhood around its orbit; *discovery of objects in Kuiper Belt which are larger than Pluto / Charon = Pluto does not satisfy the 3rd condition*
Why was Pluto's discovery an accident?
Neptune was discovered based on irregularities in Uranus' orbit (Neptune accounts for 98% of irregularity); search for Planet X to account for remaining 2%; TOMBAUGH: BLINK COMPARATOR: discovered Pluto but accidental b/c astronomers soon realized Pluto's mass is too small to account for irregularitiess in Uranus' orbit & 2% was simply the built-in margin of error in calculations
What do we know about Charon's interior structure / composition?
ROCKY CORE w/ a CRUST mixed of ROCK & ICE
Are there any seasonal changes on Pluto? If so, explain and describe them.
YES WHY: seasonal changes caused by both Pluto's AXIAL TIL & its ECCENTRIC 248-year orbit WHAT: the northern polar region has gotten brighter; Pluto's atmospheric mass has doubled b/c 1994 - 2003 due to the warming & melting of nitrogen ice
Does Pluto have an atmosphere? If so, how do we know and what is it composed of?
YES, Pluto's atmosphere was detected during stellar occultation; spectroscopic analysis of light from Pluto indicates the presence of NITROGEN w/ traces of METHANE & carbon monoxide
What do all 5 of Pluto's moons have in common? Does Pluto share these characteristics? Why or why not?
all share the same NEUTRAL COLOR & REFLECT sunlight with EQUAL EFFICIENCY AT ALL WAVELENGTHS (like our Moon); in contrast; sunlight interacts w/ the nitrogen & methane surface ices on Pluto & give it its reddish hue
What causes Pluto's reddish color?
byproduct of carbon-rich residue which forms as the Sun's UV radiation breaks up the methane on Pluto
What notable observation has been made about Charon? What does this tell us?
observations of Charon suggest that liquid water, w/ the help of ammonia, is pushed to the surface from deep w/in the interior; b/c Charon is a typical Kuiper Belt object, it's likely that other objects in the Kuiper Beltg of similar size and composition also have water resevoirs underneath their surface
