1
Jovian Wrapup – Uranus and Neptune
●
●
Uranus was discovered by accident
Neptune was found via predictions from gravitational
physics.
Uranus
Neptune
2
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!
3
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
4
Uranus and Neptune
●
Uranus and Neptune are Jovian worlds dominated by
Hydrogen/Helium mantles.
5
Uranus and Neptune
●
Jupiter and Saturn have “solar” composition.
–
Uranus and Neptune are more dominated by ice (and rock).
6
Uranus and Neptune
●
Jupiter and Saturn have “solar” composition.
–
Uranus and Neptune are more dominated by ice (and rock).
7
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.
8
Uranus and Neptune
9
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.
10
Uranus and Neptune
●
Uranus and Neptune both have systems of thin rings
11
Uranus and Neptune
●
Uranus and Neptune both have systems of thin rings
Neptune's Rings
12
Uranus/Neptune Wrapup
●
Uranus and Neptune both have systems of icy moons
13
Uranus/Neptune Wrapup
●
Uranus and Neptune both have systems of icy moons
14
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
15
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?
16
Triton's Atmosphere, Ice Caps and Geysers
●
●
●
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.
17
●
The dark streaks arise from nitrogen/water/ice
geysers that shoot material into the
atmosphere.
18
Pluto: Major Planet or Minor Nuisance?
●
Pluto/Charon is a double world at the outskirts of the
Jovian Planet region of the Solar System
19
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.
20
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
21
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 nonscientists.
22
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 nonscientists.
23
If you want to understand the issues surrounding Pluto's
planetary status, then you first must understand...
Solar System Debris:
Comets and Asteroids
●
Primarily found in two zones in the solar system.
The Asteroid
Belt (rocky,
between
Jupiter and Mars)
The
Edgeworth/Kuiper
Belt (beyond
Neptune) and
Oort Cloud (way
out there) –
sources of comets
(icy)
24
Solar System Debris
●
Why do comets and asteroids exist?.... Solar system
formation is a messy process.
25
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.
26
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.
27
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.
28
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.
29
30
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.
31
Asteroids
●
Millions of these objects orbit in the Asteroid belt –
staying between Mars and Jupiter.
–
Some have orbits that cross the inner planets.
32
Asteroids
●
Millions of these objects orbit in the Asteroid belt –
staying between Mars and Jupiter.
–
Some have orbits that cross the inner planets.
33
Asteroids
●
Some asteroids are “binary” objects.
34
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.
35
The Dawn Mission
●
The Dawn spacecraft, launched in 2007,
arrived at Ceres (2011) and will travel on
to Vesta (arriving in 2015).
36
The Dawn Mission
●
Ceres and Vesta are thought to
represent substantially intact
planetesimals from the early Solar
System.
37
Vesta from Dawn
Click on the image for a movie of Vesta's rotation
38
Vesta from Dawn
39
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.
40
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.
41
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.
42
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.
43
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.
44
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?
45
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.
46
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!
47
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.
48
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.
49
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.
50
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 nonscientists.
51
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
52
53
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.
54
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
55
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 selfgravity to overcome rigid-body forces so that it assumes a hydrostaticequilibrium (nearly round) shape, and (b) is the dominant object in its
local population zone, and (c) is in orbit around the Sun."
56
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.
But 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.
57
58
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...
59
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
–
●
–
Finding resources or a future refuge.... unfortunately not.
Exploration for exploration's sake... the data themselves are
worth the cost.
●
–
Earth orbit is the ideal platform for Earth monitoring.
Products of space exploration (pictures of Titan) are of
intrinsic worth equal to expenditure.
A definition/expectation of a great civilization.
60
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.
We 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....).
61
62
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...
63
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???