Patrick Moore and David A. Hardy compared Pluto's solitude to no lunar landscape or Martian desert.
Announcements
Important deadlines for homework assignments:
Homework 12 due today, June 11.
Homework 13 available online, due Thursday, June 12.
Homework 14 due Monday, June 16.
Homework 15 due Tuesday, June 17.
Reminder to add to Portfolio, including sky observations and simulations.
Final Exam scheduled for Wednesday, June 18.
Notable quote by Michael E. Brown: "I may go down in history as the guy who killed Pluto." (Associated Press, 2006-08-24)
Topics for Today
Comparison of icy moons and comets.
Characteristics of large objects in the Kuiper belt.
Discovery and classification of Pluto.
Definition of a dwarf planet.
Insights from satellite missions regarding Pluto, Charon, and Ceres.
Overview of asteroids and the reason for the asteroid belt.
Origins of meteorites.
Types of meteorites and their significance.
Description and origin of comets.
Explanation of the current locations of comets.
Rings of Jovian Planets
Hypothesis on Rings Formation:
Formed from dust generated by impacts on moons orbiting jovian planets.
Evidence for Hypothesis:
Rings cannot be remnants of planet formation due to the small size of particles.
Continuous replacement of tiny particles is necessary.
Most likely source of these particles is impacts with the jovian moons.
Ring Formation Characteristics
Jovian planets all possess rings due to numerous small moons nearby.
Random impacts on these moons contribute to ring formation.
Saturn’s remarkable rings might be considered an “accident” of the current epoch.
Comets: Definition and Characteristics
Comets Defined:
Formed beyond the frost line, they are icy planetesimals known as "dirty snowballs" consisting of ice and rock.
Most comets do not manifest tails.
Majority remain frozen in the outer solar system; only a few venture into the inner solar system to develop tails.
Locations of Comets
Oort Cloud: Comets in random orbits extending to approximately 50,000 AU.
Kuiper Belt: Comets on orderly orbits ranging from 30-100 AU in the disk of the solar system.
Kuiper Belt Comets
Proposed as an explanation for short-period comets.
Considered remnants from the Solar System's formation.
Typical sizes range from 10-50 km; categorized as faint objects (first detected in 1992).
Some are much larger, measuring hundreds of km across.
Discovery of Pluto
Plutonic Discovery:
Astronomers deduced another body must be affecting the orbits of Uranus and Neptune.
Percival Lowell hypothesized a “Planet X” with a mass seven times that of Earth.
Clyde Tombaugh, tasked to locate it, discovered Pluto in 1930; it was named in honor of Lowell.
Fortunate Mistaken Identity
Pluto was ultimately determined not to be Lowell’s “Planet X.”
Pluto has only 0.2% of Earth’s mass rather than the hypothesized seven times.
Too small to impact the orbits of Uranus & Neptune.
In 1977, it was discovered that Pluto has a moon, Charon, which is about 1200 km across and constitutes 12% of Pluto's mass.
Pluto and Charon rotate synchronously, always showing the same face to each other.
Pluto’s Condition and Atmosphere
Pluto has a thin nitrogen atmosphere, which refreezes on its surface as it moves away from the Sun.
Charon, Pluto's moon, is nearly equal in size to Pluto, likely resulting from a significant impact.
Pluto's surface temperatures are extremely low, around 40 K.
Pluto’s Orbit Dynamics
Pluto's orbit does not intersect with Neptune's orbit due to a 3:2 orbital resonance, meaning Neptune completes three orbits for every two Pluto orbits.
Exploration of Kuiper Belt Objects (KBOs)
Many KBOs have been recently discovered, knowledge of which remains limited.
NASA’s New Horizons mission conducted a flyby investigating Pluto and KBO Arrokoth.
Pluto's Classification Issues
Traditionally recognized as a planet due to its size, which is greater than most comets and KBOs.
Pluto has one primary moon (Charon) and four smaller moons.
In 2006, the International Astronomical Union established three criteria to determine if an object is a planet:
Must orbit the Sun.
Must possess enough self-gravity to form a spherical shape.
Must have "cleared" its orbit of other large bodies.
Any celestial objects meeting the first two criteria but not the third are classified as dwarf planets.
Pluto and Eris Comparison
Initially, Pluto's size was overestimated, leading to its classification as a planet.
With the discovery of Eris and other massive KBOs, scientific debates arose about the definitions of planets and dwarf planets.
Historical Views of Dwarf Planets
2006 saw heated debates among astronomers regarding the classification of celestial bodies, determining whether they could all be viewed as planets or dismissed entirely.
Characteristics of Dwarf Planets
Most dwarf planets (like Pluto and Eris) share similar characteristics, such as size and orbital features, even though they originate from the Kuiper belt and are not classified as full planets.
Insights from the New Horizons Mission
New Horizons conducted a flyby of Pluto and its moons in July 2015, providing high-resolution imagery and spectra. This mission aimed to gather new data for refined models of these celestial bodies.
Discoveries of Active Ice Geology on Pluto
Findings from New Horizons indicated dynamic characteristics in Pluto’s surface:
Variability in surface ages, some less than 10 million years.
Presence of H2O ice mountains, frozen nitrogen glaciers, and varied geological features including dunes, valleys, and plains.
Suggested potential seasonal changes in nitrogen and methane cycles and presence of cryovolcanism.
Charon's Geological Features
Charon exhibits large rift belts indicating tectonic activity.
Beneath the rifts lie smoother areas that suggest extensive resurfacing.
The dark red “Mordor” region indicates interactions with Pluto's atmosphere resulting in the formation of complex chemistry like tholins.
Minor Moons of Pluto
Pluto has several minor moons, including Nix and Hydra, sized between 60-200 km and are significantly fainter (5000 times) than Pluto.
Charon remains larger than these smaller moons, raising possibilities of being remnants from a collision that created Charon.
Ceres Exploration via Dawn Mission
Ceres, the largest asteroid, is now classified as a dwarf planet.
The 2015 Dawn mission uncovered insights about its cratered icy surface and enigmatic bright spots of unclassified origin.
Summary of Key Learning Points
Comets: Defined as icy planetesimals or "dirty snowballs" orbiting the Kuiper Belt and Oort Cloud.
Comets stay frozen until they enter the inner solar system, leading to tail development.
Kuiper Belt Objects: Larger icy bodies in the Kuiper Belt include dwarf planets like Pluto and Eris, which share similarity in physical characteristics and composition but differ in orbital dynamics.
Asteroids: Formed through rocky leftovers of planetary formation, primarily found in the asteroid belt, ranging in size significantly, with most artifacts being smaller.
Meteorites: Objects surviving atmospheric entry provide insights into the nature of early solar system materials, including both primitive and processed forms.
Meteor Showers: Result from Earth intersecting the orbits of comets, leading to meteor display appearances from Earth’s perspective.
Differentiation in Bodies: Evidence suggests past geological activity through processed meteorites and icy world surfaces, revealing the history of asteroid and dwarf planet formation.