ASTR-1010ASTR-1010Planetary AstronomyPlanetary Astronomy

Day - 35

Solar Surface Close UpSolar Surface Close Up

Course AnnouncementsCourse AnnouncementsNext Lab: 51 Pegasi: Discovery of a New Planet

Homework Chapter 10: Due Monday April 19.

Homework Chapter 11: Due Friday April 23.

Homework Chapter 12: Due Wednesday April 28.

Homework Chapter 21: Due Wednesday April 28.

-this is extra credit.

The last 1st Quarter moon observing nights are:

Tuesday (April 20) & Thursday (April 22)

8:00 pm both nights.

Exam 4 and “Final”: Friday, April 30 – 1030 am

Uranus has thin rings and Uranus has thin rings and several moonsseveral moons

The Moons of UranusThe Moons of Uranus

Miranda: a broken worldMiranda: a broken world

The ChevronThe Chevron

Grooves and CracksGrooves and Cracks

ArielAriel

UmbrielUmbriel

TitaniaTitania

OberonOberon

The Moons of NeptuneThe Moons of Neptune

TritonTriton

Triton has a thin Triton has a thin atmosphereatmosphere

Nitrogen Geysers on TritonNitrogen Geysers on Triton

ProteusProteus

PlutoPluto

• Very small – 1/6 the mass of Earth’s Moon.

• Binary planet: Pluto/Charon.

• Has properties like comets:– Eccentric orbit– Icy composition (probably)

• Member of the Kuiper Belt Objects, maybe not even the largest one.

Pluto and CharonPluto and Charon

Dr. R. Albrecht, ESA/ESO Space Telescope European Coordinating Facility/NASA

Pluto: distant ice worldPluto: distant ice world

Pluto FactsPluto Facts

Pluto was discovered by Pluto was discovered by Clyde Tombaugh in 1930Clyde Tombaugh in 1930

Charon was discovered by Charon was discovered by James Christy in 1978James Christy in 1978

Pluto & Charon System by Pluto & Charon System by HSTHST

Pluto & Charon are not bigPluto & Charon are not big

Pluto and Pluto and Charon Charon Eclipsed Eclipsed

each each other from other from

1985-1985-19901990

Like Uranus, Pluto orbits Like Uranus, Pluto orbits on its sideon its side

Pluto Has Pluto Has An An

AtmosphereAtmosphere!!

Pluto is covered in Pluto is covered in Methane FrostMethane Frost

Interior of Pluto & Charon?Interior of Pluto & Charon?

All is speculation until the New All is speculation until the New Horizons mission arrives in Horizons mission arrives in

20162016

© 2007 W.W. Norton & Company, Inc. © 2007 W.W. Norton & Company, Inc. 21st CENTURY ASTRONOMY, 2/e 21st CENTURY ASTRONOMY, 2/e 3636

Concept Quiz – PlutoConcept Quiz – Pluto

Pluto is very different from the gas giants in all ways but:

A. Its mass.

B. Its composition.

C. Its location in the Solar System.

D. The shape of its orbit.

Chapter 12Chapter 12Lecture OutlineLecture Outline

Asteroids, Meteorites, Comets, Asteroids, Meteorites, Comets, and other Debrisand other Debris

The Debris of the Solar The Debris of the Solar SystemSystem

Titus-Bode Law is a Titus-Bode Law is a mathematical coincidencemathematical coincidence

Orbital radius = 0.4 + 0.3x2n-2 where n =2, 3, 4, 5, 6, …

The “missing” planet The “missing” planet Ceres was discovered in Ceres was discovered in

18011801

Diameter 934 km

Numerous other asteroids Numerous other asteroids were discovered in the were discovered in the

early 1800’searly 1800’s

Most (but not all) asteroids Most (but not all) asteroids orbit between Mars & orbit between Mars &

JupiterJupiter

Asteroid BeltAsteroid BeltAstronomers first discovered the asteroids while searching for a “missing planet”. There was no planet, but there were thousands of asteroids with diameters ranging from a few kilometers up to 1000 kilometers orbiting within a belt between the orbits of Mars and Jupiter. It was first thought that these must be the remains of a planet that was destroyed by a collision. But, the combined mass of these asteroids is nowhere near being enough for a planet-sized object. They are simply debris left over from the formation of the solar system.

Locating asteroidsLocating asteroidsAsteroids are being continually discovered at a rate of 10-100 per month. Asteroids are generally discovered using photographic techniques - take a very long exposure of a star field; if something moves, it is probably an asteroid. NASA also has a relatively new program for tracking all known NEOs (Near Earth Objects), in the hopes that we might be able to avoid a collision (http://neo.jpl.nasa.gov).

Formation of the belt - Jupiter’s Formation of the belt - Jupiter’s influenceinfluence

Supercomputer simulations indicate that the formation of the asteroid belt was drastically affected by Jupiter’s gravity - in fact, without Jupiter, a 5th terrestrial planet probably would have formed!

However, Jupiter’s gravity can’t explain the fact that the asteroids have eccentric inclined orbits rather than circular. Recent theories include a Mars-sized object that did form in the region of the belt, but was then ejected by Jupiter’s gravity.

This object would have interacted with the asteroids to produce the observed orbits. Perhaps this is the same object that collided with Earth to produce the Moon!

Continuing influence from Continuing influence from JupiterJupiter

Even today, gravitational perturbations by Jupiter deplete certain orbits within the asteroid belt. The resulting gaps, called Kirkwood gaps, occur at simple fractions of Jupiter’s orbital period.

Trojan asteroidsTrojan asteroids

The combined effect of the Sun’s and Jupiter’s gravity also captures asteroids in two locations, called Lagrangian points, along Jupiter’s orbit. These are known as trojan asteroids.

Appearance and compositionAppearance and composition1 Ceres is by far the largest asteroid (it makes up almost one-third of the mass of the asteroid belt by itself). Several of the larger asteroids are able to hold themselves together in a roughly spherical shape. These larger asteroids even show signs of chemical differentiation due to the heat of the impacts that formed them. Some even have “moons” like Ida.

Appearance and compositionAppearance and composition

Most asteroids, however, are quite irregular, frequently loosely bound conglomerations of material. This is because of the billions of years of occasional collisions that they have undergone, causing them to break up into smaller fragments. Even though there are a great number of asteroids, they are spread out over a lot of space, so they are not actually that close together (as The Empire Strikes Back would have you believe).

Most asteroids Most asteroids are small and are small and

irregular irregular shapedshaped

Asteroids tumbleAsteroids tumble

Some asteroids are piles Some asteroids are piles of debrisof debris

253 Mathilde

Collisions with EarthCollisions with EarthSome asteroids (the near-Earth objects), move in elliptical orbits that cross the orbits of Mars and Earth. If such an asteroid strikes the Earth, it forms an impact crater whose diameter depends on both the mass and the speed of the asteroid. It is thought that several particularly large collisions led to the multiple mass extinctions that are observed in the fossil record. The top picture is Barringer Crater in Arizona, the bottom is the aftermath of an “almost collision”. The asteroid exploded in the atmosphere due to the extreme heating above the Tunguska region of Siberia before it actually hit the ground.

AsteroidsAsteroids

• Asteroids are small, irregular bodies.

• Most are composed of rock or metal.

• Most orbit between Mars and Jupiter.

• Some can cross Earth’s orbit.

• Model conditions in the early Solar System.

Asteroids and MeteoritesAsteroids and Meteorites

• Meteorites are pieces of asteroids that have fallen to Earth.

• In space it is called a meteroid.

• While passing through the atmosphere, it is a meteor.

• Meteorites have different types.

• The types reflect different physical conditions during formation.

Types of MeteoritesTypes of Meteorites

• Most are stony, like Earth rocks.

• Iron meteorites have high concentrations of metal.

• Stony-irons are a combination.

• Some stony meteorites are carbonaceous (they have a lot of carbon).

• Can date meteorites to the age of the Solar System (4.5 billion years).

Types of MeteoritesTypes of Meteorites

Courtesy of Ron Greeley