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Jovian Wrapup – Uranus and Neptune● Uranus was discovered by accident● Neptune was found via predictions from gravitational

physics.

Uranus Neptune

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William Herschel's Discovery of Uranus● In 1781 William Herschel noticed a moving object

(moving night-to-night) that he supposed was a comet.● He reported the “comet” and people around the world

began to observe it. – They soon realized that the object was in a circular orbit

around the Sun beyond Saturn – a new planet!

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Neptune's Discovery● By the mid-1800's Uranus had completed an orbit

around the Sun since its discovery.– Astronomers noted that it was not quite following the path

predicted by Newton's physics and gravitation

– It was likely that a massive unknown planet beyond Uranus was tugging Uranus off of its expected path.

– Working backwards English mathematician Adams and French mathematician LeVerrier independently calculated the location of the unknown planet.

– LeVerrier contacted astronomers in Berlin who found Neptune within an hour of the start of the search (only a finger's width away from the predicted position).

Adams

LeVerrier

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Uranus and Neptune● Uranus and Neptune are Jovian worlds dominated by

Hydrogen/Helium mantles.

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Uranus and Neptune

● Jupiter and Saturn have “solar” composition.– Uranus and Neptune are more dominated by ice (and rock).

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Uranus and Neptune

● Jupiter and Saturn have “solar” composition.– Uranus and Neptune are more dominated by ice (and rock).

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Uranus and Neptune

– Methane gas absorbs red light but lets blue light pass into the atmosphere, off the particulates, and back to us giving them their blue-green color.

– Since they are colder than Jupiter and Saturn the high white clouds are made of methane ice crystals.

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Uranus and Neptune

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Uranus and Neptune

● Uranus and Neptune both have systems of thin rings

Infrared views reveal/exaggerate the Uranian rings since the planet is quite dark at these wavelengths.

Visible light views hardly show them at all.

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Uranus and Neptune

● Uranus and Neptune both have systems of thin rings

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Uranus and Neptune

● Uranus and Neptune both have systems of thin rings

Neptune's Rings

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Uranus/Neptune Wrapup● Uranus and Neptune both have systems of icy moons

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Uranus/Neptune Wrapup● Uranus and Neptune both have systems of icy moons

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Triton

● Triton is a Pluto-sized world with a “youthful” icy surface.

● It holds on to a thin nitrogen atmosphere.

● It orbits Neptune “backwards” and is likely a captured cousin of Pluto

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Triton● Like Enceladus and the

Uranian satellites, Triton is dominated by water/ice and is rich in volatiles like ammonia, nitrogen and methane. This mix enables geological activity at the frigid temperatures of the outer Solar System with only modest interior warmth.

● Triton is likely to be representative to what we will find when we arrive at Pluto in 2015.

Frozen lakes on Triton?

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● Triton's south pole is just coming out of a decades-long winter where it is so cold the thin nitrogen atmosphere has frozen solid on the surface.

● The dark streaks arise from nitrogen/ice geysers that shoot material into the atmosphere.

● The nitrogen atmosphere freezes out at the poles in winter. Warmed in the summer, the gas bursts out from below the frozen surface layers.

Triton's Atmosphere, Ice Caps and Geysers

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● The dark streaks arise from nitrogen/water/ice geysers that shoot material into the atmosphere.

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Pluto: Major Planet or Minor Nuisance?● Pluto/Charon is a double world at the outskirts of the

Jovian Planet region of the Solar System

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Pluto: Major Planet or Minor Nuisance?● Smaller than the Earth's Moon, it's status as a “major”

planet, secure for 70 years, was recently lost.

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Pluto: Major Planet or Minor Nuisance?● From its discovery in 1930 until its demotion in 2006

Pluto was regarded as one of nine major planets in the Solar System.

Pluto and its satellite Charon

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Pluto: Major Planet or Minor Nuisance?● The formal definition of Pluto as a “dwarf planet” by the

International Astronomical Union in 2006 brought strong reaction from both astronomers and non-scientists.

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Pluto: Major Planet or Minor Nuisance?● The formal definition of Pluto as a “dwarf planet” by the

International Astronomical Union in 2006 brought strong reaction from both astronomers and non-scientists.

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Solar System Debris:Comets and Asteroids

● Primarily found in two zones in the solar system.

The AsteroidBelt (rocky, between Jupiter and Mars)

The Edgeworth/Kuiper Belt (beyond Neptune) and Oort Cloud (way out there) – sources of comets (icy)

If you want to understand the issues surrounding Pluto's planetary status, then you first must understand...

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Solar System Debris

● Why do comets and asteroids exist?.... Solar system formation is a messy process.

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Solar System Debris● During the accretion of the planets, the planets sweep

up and fling out most of the debris but stable/protected zones remain.

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Solar System Debris: Asteroids● Jupiter interfered with the formation of a planet

between Mars and Jupiter. Some fraction of the debris remains today as the asteroid belt.– Jupiter stirred up the planetesimals so that collisions were violent

rather than gentle.

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Asteroids● Asteroids are small, rocky, cratered and irregularly

shaped.– They are the collisionally modified remains of leftover

planetesimals between the orbits of Mars and Jupiter.

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Asteroids● Asteroids are small, rocky, cratered and irregularly

shaped.– They are the collisionally modified remains of leftover

planetesimals between the orbits of Mars and Jupiter.

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Asteroids● Asteroids are small, rocky, cratered and irregularly

shaped.– They are the collisionally modified remains of leftover

planetesimals between the orbits of Mars and Jupiter.

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Asteroids● Millions of these objects orbit in the Asteroid belt –

staying between Mars and Jupiter.– Some have orbits that cross the inner planets.

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Asteroids● Millions of these objects orbit in the Asteroid belt –

staying between Mars and Jupiter.– Some have orbits that cross the inner planets.

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Asteroids● Some asteroids are “binary” objects.

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Asteroids● The original “parent bodies” that were the predecessors of

the asteroids were large enough to differentiate.– some asteroids are metallic, consisting of the core fragments of a

large parent body.

– the largest asteroids may be intact parent bodies. The DAWN mission, now in orbit around Ceres targets two of the largest – Ceres and Vesta.

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The Dawn Mission

● The Dawn spacecraft, launched in 2007, arrived at Ceres (2011) and will travel on to Vesta (arriving in 2015).

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The Dawn Mission● Ceres and Vesta are thought to

represent substantially intact planetesimals from the early Solar System.

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Vesta from Dawn

Click on the image for a movie of Vesta's rotation

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Vesta from Dawn

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Asteroids and Meteorites● Meteorites that fall to Earth are just small asteroids. They

tell the story of the differentiation and fragmentation of the asteroids.– Some are entirely metallic, some are stony, some appear to come

from unmodified undifferentiated objects.

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Asteroids and Meteorites● Meteorites that fall to Earth are just small asteroids.

They tell the story of the differentiation and fragmentation of the asteroids.– Some are entirely metallic, some are stony, some appear to come

from unmodified undifferentiated objects.

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Meteorites● If you want to find a meteorite, go to a place on Earth

where Earth-rocks are rare.– Antartica and the Sahara Desert are good choices.

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Asteroids and Meteorites● Meteorites that fall to Earth are just small asteroids.

They tell the story of the differentiation and fragmentation of the asteroids.– Meteorites are often spectral fingerprint matches to distant

asteroids. You can hold a piece of Vesta in your hand with certainty.

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Meteorites● There are four major classes of meteorites

– Stones: rocky meteorites with iron flecks.

– Stones represent the majority of “falls” but are found in equal numbers with “iron” meteorites.

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Meteorites● There are four major classes of meteorites

– Stones tend to be composed of chondrules – glassy beads making up most of the mass of the rock.

– Astronomers still argue about the origin of chondrules – how did these glassy beads form during the formation of the Solar System?

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Meteorites● There are four major classes of meteorites

– Irons represent the other significant type of meteorite.

– Only about 6% of “falls” are irons, but they represent the majority of “finds” because they are so recognizable as something completely odd.

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Meteorites● There are four major classes of meteorites

– Irons represent the other significant type of meteorite.

– When etched with nitric acid a crystalline patter appears in cross sections of iron meteorites.

– This pattern can only arise from the slow cooling of molten iron (one degree every million years) consistent with formation in the center of a huge differentiated asteroid!

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Meteorites● There are four major classes of meteorites

– “Stony-iron” meteorites (a.k.a. Pallasites) appear to have come from the core-mantle boundary in a differentiated asteroid. They are quite rare.

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Meteorites● There are four major classes of meteorites

– “Carbonaceous chondrites are possibly the most interesting of meteorites of all. They represent about 1% of falls.

– Carbonaceous chondrites are undifferentiated and largely unprocessed. They must come from small parent objects too small to become hot and melt and differentiate.

– Some carbonaceous chondrites contain amino acids formed in the Solar Nebula – the building blocks of protiens.

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Meteorites● Meteorites are important astronomically because they

represent material preserved from the time of the origin of the Solar System. – Recall that radioactive dating uniformly finds an age of 4.56

billion years for all of these objects.

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Pluto: Major Planet or Minor Nuisance?● The formal definition of Pluto as a “dwarf planet” by the

International Astronomical Union in 2006 brought strong reaction from both astronomers and non-scientists.

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The Discovery of the Asteroids (ca. 1800)● On January 1, 1801 an object (Ceres), much smaller

than the Earth's Moon, was discovered orbiting the Sun between the orbits of Mars and Jupiter.

● At first it was thought to be the 8th planet (only 7 were known at the time), but...– On March 28, 1802 another object (Pallas) was discovered in

nearly the same orbit, and another (Juno) in 1804, and yet another (Vesta) in 1807.

– In 1828 textbooks listed 11 planets, however by 1851 twelve(!) more of these objects had been found.

● Finally, in 1852, astronomers recognized these “asteroids” as a separate class of object and went back to a Solar System with eight planets (Neptune having been discovered in 1846).– The asteroids were tiny compared with the “classical” planets

See http://aa.usno.navy.mil/hilton/AsteroidHistory/minorplanets.html

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The Discovery of Pluto in 1930● Pluto was discovered in 1930 during a deliberate search

for a planet beyond Neptune. – When it was discovered it was thought to be larger than the

planet Mercury.

– All hailed it as the Ninth Planet in the Solar System.

– That designation stuck until 1992 when the first of hundreds of similar objects were found orbiting the Sun beyond Neptune.

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Pluto's Stock Plummets

● By 2000 it was apparent that Pluto was simply the largest object yet discovered in an outer (icy) asteroid belt.– Astronomers counted the days until an object larger than Pluto was

discovered in this region.

– It happened with the discovery of 2003UB313 (now Eris) in 2003.

● Astronomers now had to cope with the issue. Was 2003UB313 Planet 10, or was it time to demote Pluto to non-planetary status?– In 2006 the vote was official – The Solar System has Eight planets.

Eris and Dysnomia

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Pluto's Demotion● The Solar System now officially contains 8 major

planets. Pluto, along with Ceres and Eris are “dwarf” planets.– The body that governs the naming of astronomical objects has

officially decided:● "A planet is a celestial body that (a) has sufficient mass for its self-

gravity to overcome rigid-body forces so that it assumes a hydrostatic-equilibrium (nearly round) shape, and (b) is the dominant object in its local population zone, and (c) is in orbit around the Sun."

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Why Pluto Never Had a Chance

● Bottom line – the Solar System has Four well defined zones

– The rocky terrestrial planets – Mercury, Venus, Earth, Mars

– The asteroid belt

– The immense gas giant worlds – Jupiter, Saturn, Uranus, Neptune.

– The outer icy asteroid (Kuiper) belt – containing Pluto and hundreds of thousands of other objects.

57But Pluto's Status as an Interesting World has not Changed

● Pluto has a large moon, Charon, and an atmosphere.– Two new smaller moons were discovered in 2005. One or maybe

even two even smaller ones turned up recently.

● The “New Horizons” spacecraft (the fastest thing ever launched by Humans) will arrive in 2015.

– Pluto is getting farther from the Sun at present

– New Horizons hopes to arrive before the atmosphere freezes out.

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Detecting Pluto's Atmosphere● How do you tell that a world that is just a dot in a

telescope has an atmosphere?– Watch it pass in front of a star...

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Spending on Space

● Guiding principle: All federal investments should maximize societal benefit

● Direct return– The information returned may directly benefit us all

● Protection against rogue asteroids● Perspective on Earth climate

– Earth orbit is the ideal platform for Earth monitoring.● Finding resources or a future refuge.... unfortunately not.

– Exploration for exploration's sake... the data themselves are worth the cost.

● Products of space exploration (pictures of Titan) are of intrinsic worth equal to expenditure.

– A definition/expectation of a great civilization.

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Spending on Space● Guiding principle: All federal investments should

maximize societal benefit● Indirect return

– Economic stimulus on steroids

– Note that NASA does not launch gold bars into space valued at billions of dollars

● Funding spent on NASA ( ½ a percent of the federal budget) gets spent here on the ground employing people and developing our high-technology infrastructure.

– 100 times more than the NASA budget is already spent on social programs. Savaging NASA would make the smallest dent here on Earth.

● Of the $4 billion spent on the Cassini mission, the salvage value of the spacecraft is maybe $100,000 the rest went into jobs and technology development in the US.

● Even spectacular NASA failures (e.g. the recent Orbiting Carbon Observatory) are economic successes.

61We Should Solve Our Problems Here on Earth First

● This is exactly the outcome of spending on space exploration.

– Development of new practical technologies (why do you think you have an iPhone?)

– High quality highest-technology jobs here in the U.S.

– Significant budgetary multiplier – Every dollar of NASA spending is estimated to provide several dollars of return to the economy.

– Inspiration ● Fostering the next generation of scientists is possibly the

most important outcome of NASA spending● Astronomy is the most visually compelling and thus instantly

inspiring of the sciences.● If you want to lift a child out of poverty make him/her want

to be a scientist (and provide the opportunities to pursue that goal – maybe the hardest part, back to social programs....).

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Investing in the Future– Today's high-tech society and its resultant wealth-generating

power can be tied in many ways to the significant investment made in space exploration in the 1960s.

– How can we afford not to take as aggressive an approach to science today??? We're not...

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Bottom Line(s) ● Investment in Space drives technology innovation

benefiting all of society.– Technology is the ultimate engine of our economy in the

present era.

– World leadership is the outcome.

● Space Exploration, in many ways is the ultimate economic stimulus.

● How can we afford NOT to invest in space exploration in the midst of a recession or at any other time???