The Edge of Town Learning Objectives ! What physical qualities make Pluto like a planet? What objects in the Solar System have those same qualities? ! What physical qualities make Pluto unusual compared to the planets in our Solar System? Is Pluto a planet? ! What is unusual about the size and rotation of Charon compared to the other moons in the Solar System? ! What are Eris, Sedna, Quaoar, Haumea and Makemake? ! What are the Oort Cloud/Kuiper Belt? What is their size/ shape? How do they relate to long/short period comets? ! What are comets? In what direction do comet’s tails point? Why and how fast do comets evaporate? What causes meteor showers? The Discovery of Pluto ! Astronomers calculated that another body could be perturbing the orbits of Uranus and Neptune ! Percival Lowell calculated that this “Planet X” must have a mass 7 times that of the Earth ! In 1930, Clyde Tombaugh found Planet X, using Lowell’s observatory ! In honor of Lowell, the planet was named Pluto (P.L.) ! A fortunate bit of serendipity... Clyde Tombaugh (1906 – 1997) Pluto Facts!
Pluto has five known moons, Charon being by far the largest Radius 0.19 Earth Surface gravity 0.06 Earth Mass 0.002 Earth Average Distance from Sun 39.5 AU Tilt of Rotation Axis 123 degrees Orbit eccentricity 0.249 Year 248 Earth years Sidereal day 6.39 Earth days (“backwards” like Venus) How Does Pluto Measure Up? Pluto’s Orbit
! Highly eccentric ! Highly inclined with respect to the other planets ! We sometimes think of Pluto as the “outermost planet” but from 1979 to 1999, Pluto was closer to the Sun than Neptune! Pluto’s Atmosphere ! Until 2015 our best view of Pluto came from the Hubble Space Telescope ! The New Horizons spacecraft made the first flyby of Pluto in July 2015 ! Pluto’s atmosphere is almost all nitrogen with trace amounts of methane and carbon monoxide ! Pluto’s current surface temperature is about 40oK (-230oC, -390oF)! Pluto’s Largest Moon, Charon
! In 1977, Pluto was found to have a large moon ! Largest moon relative to its host planet ! About 600 km in radius ! Half the radius of Pluto ! Surface of water ice ! Both rotate synchronously Charon ! Pluto and Charon each keep the same face pointed towards the other ! We now know that Pluto has at least 5 moons Interior & Composition
! Pluto’s density (~ 1.9 g/cm3) is smaller than the Earth’s (~ 5.5 g/cm3) ! So, Pluto is likely made of lighter rocks and water ! Pluto likely has a subsurface ocean comprised of liquid water, with a little ammonia ! Charon is less dense (~ 1.7 g/cm3) and may be differentiated like Pluto, or a uniform rock/ice mix Trans-Neptunian Objects to 75AU ! Essentially all objects past planet Neptune ! Below are those discovered as of 2010 Eris (The former 10th planet) ! Currently the most massive known TNO ! Found 21 Oct 2003 ! Variously called planet X (for “10th planet”), Persephone, Xena, Lila, by media ! About Pluto’s size ! Orbits the Sun directly ! Eris has at least one moon (Dysnomia) orbiting it Eris (The former 10th planet) ! Highly Elliptical and Inclined Orbit
Beyond Pluto – The Kuiper Belt
! A “reservoir” of icy bodies beyond Pluto ! Proposed to explain short-period comets ! The first Kuiper Belt Object (KBO) was detected in 1992 ! Typical sizes 10-50 km, very faint ! The small ones are potential comets ! A few are large…hundreds of km across Quaoar ! Orbital distance ~ 43 AU ! About half Pluto’s size ! Has a moon, Weywot
Pluto’s Orbit
Quaoar’s Discovery images Orbit Sedna ! About half the size of Pluto ! Currently about 90 AU from the Sun ! Its orbit takes it over 900 AU from the Sun ! An orbital period of about 11,500 years! What is a Comet? ! Dirty icebergs in space ! 10-50 km across ! Composed mostly of water ice, with some solid dust, rock, and metal ! When a comet approaches the Sun, sunlight evaporates material from the comet’s surface Comet Halley Comets
Note Tail Direction! Where Do Comets Lurk? Where Do Comets Lurk?
! The vast majority live far out in the Solar System, beyond the planets ! Short period comets: The Kuiper Belt ! Orbital periods of hundreds of years ! Around and beyond the orbit of Pluto (30-50 AU) ! Long-period comets: The Oort Cloud ! From 2,000-200,000 AU…out to the edge of the Sun's gravitational influence Life & Death of a Comet ! Even comets on short orbits live mostly in the outer Solar System ! Kepler’s 2nd Law ... when far from the Sun they move slowly ! Every orbit, they lose 1% of their masses to solar evaporation ! When they become too small, they break apart Meteor Showers
! Meteors hit the Earth’s atmosphere all the time ! In the early morning, you typically see ~3 per hour ! Several times a year, the rate increases ! To about one meteor per minute ! Called meteor showers
! Seem to originate from a S. Numazawa single point in the sky Meteor Showers
! When a comet enters the inner Solar System, it leaves a trail of dust ! When Earth passes through this dust, we get a meteor shower ! Meteor showers typically don’t produce impacts with the Earth ! It’s all dust, not rocks Next Time
Review Lecture