1. Asteroids and Meteors Physics 1800 Lecture
updated May 17, 2014

2. 2
Titius-Bode Law (1766)
The distances between the planets gets bigger as you go out.
Titius & Bode came up with a law that predicted the size of the orbits
BIG gap between Mars (1.6 AU) & Jupiter (5.2 AU).
Predict planet at 2.8 AU
Johann Daniel Titius ( 1729 – 1796)
Johann Elert Bode ( )
Missing Planet

3. Ceres Discovered 1801 at 2.77 AU from sun!3
Ceres Discovered 1801 at 2.77 AU from sun!
First Asteroid discovered by accident by Piazzi 1801
It’s the biggest, 950 km in diameter (small compared to moon)
Contains 32% of mass of entire asteroid belt!
Combined mass of all asteroids is only 4% of earth’s moon
Giuseppe Piazzi.

4. Ceres (Hubble Space Telescope)4
Ceres (Hubble Space Telescope)

5. 5
Structure of Ceres
Mass determined from perturbations on another asteroid [348 May] which make 3 close approaches between 1891 and 1984.
Interior is possibly rocky core with icy mantle 60 to 120 km thick (containing about as much as all the fresh water on the earth).
Dawn Mission (2007) will arrive at Ceres in Feb 2015

6. More “Minor Planets” discovered6
More “Minor Planets” discovered
Sizes determined from occultations of stars by the asteroid
Name
Date
Orbit AU
Size (km)
Notes
1 Ceres
1801
2.76
950
Biggest
2 Pallas
1802
2.77
500
Share orbit with Ceres
3 Juno
1804
2.67
235
Stony
4 Vesta
1807
2.36
530
Brightest, Calcium on surface

7. 7
Dawn Mission (2007)

8. 8

9. Vesta: Recent Data (Dawn Mission)9
Vesta: Recent Data (Dawn Mission)
Dawn Mission entered orbit around Vesta on 16 July 2011 for a one-year exploration, and left Vestan orbit on 5 September 2012

10. Vesta: Recent Data (Dawn Mission)10
Vesta: Recent Data (Dawn Mission)
July 17, 2011

11. Vesta: Recent Data (Dawn Mission)11
Vesta: Recent Data (Dawn Mission)
July 24, 2011
Range 5200 km

12. 12
Vesta: Recent data
It lost some 1% of its mass less than a billion years ago in a collision that left an enormous crater occupying much of its southern hemisphere. Debris from this event has fallen to Earth as howardite–eucrite–diogenite (HED) meteorites, a rich source of information about the asteroid

13. 13
Vesta probably is Differentiated Meteorites with Calcium in them possibly come from Vesta!

14. In 1830 more discovered (1 per year)14
No more found for 38 years
In 1830 more discovered (1 per year)
Now several hundred thousand are known between Mars and Jupiter

15. 90% of asteroids are in the Asteroid Belt between Mars and Jupiter15
90% of asteroids are in the Asteroid Belt between Mars and Jupiter
136,000 cataloged
13,500 have official names.

16. Jupiter’s gravity helped shape the asteroid belt16
Jupiter’s gravity helped shape the asteroid belt
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

17. Apollo Asteroids 17 First Discovered 1932 Cross Orbit of Earth
Icarus goes closer to sun than Mercury!

18. 18
Jupiter’s gravity also captures asteroids in two locations, called Lagrangian points, along Jupiter’s orbit

19. Hilda Asteroids are in a 3/2 resonance with Jupiter19
Hilda Asteroids are in a 3/2 resonance with Jupiter

20. Spacecraft have visited a few asteroids. Several small bodies20
Spacecraft have
visited a few
asteroids.
Several small bodies
(asteroids, satellites
of Mars, and a
comet nucleus)
shown in their
relative sizes

21. Asteroid Ida has its own little moon, Dactyl, which is21
Asteroid Ida has its own little moon, Dactyl, which is
1.5 km in diameter
Ida is 56 km long

22. 22
Gaspra is 18 km long

23. Mars’ satellite Phobos23
Mars’ satellite Phobos
Phobos is cratered, but has an overall smooth surface.
Note the long grooves and chains of craters.
The chains of craters are probably caused by gas
coming out of the interior of Phobos.
The other craters are from impacts.
Phobos is probably an asteroid.

24. 24
Asteroid #216 Kleopatra, mostly made of metal, mapped by reflection of radar signals (2000) 217x94 km.

25. 25
Japanese Hayabusa mission at asteroid Itokawa, landed Nov 2005, returned samples to earth June 2010 [chondrite type asteroid]
Itokawa is about 500 meters long – it is a Near-Earth asteroid (NEA)

26. 26
Another Near-Earth
asteroid, 433 Eros,
was visited by an
orbiting spacecraft in 2001
The spacecraft was
called NEAR
(Near Earth Asteroid
Rendezvous)

27. 27
After orbiting 433 Eros for about a year, the spacecraft settled down onto the surface in a “controlled crash” landing.

28. 28
NEAR took pictures all the way down to the surface.
This frame shows an area about the size of our classroom.
Boulders in the bottom of a
depression on Eros’ surface.

29. Asteroids occasionally collide with one another29
Asteroids occasionally collide with one another
Asteroids undergo collisions with each other, causing them to break up into smaller fragments

30. Asteroids collide with one another …30
In these sketches, an asteroid is shattered by a large
impact (C). It then reassembles into a broken mass (E), and is again hit by a big impactor (F) and flies apart. A B C E D F

31. Asteroid fragments hit the planets and sometimes fall to the ground as31
Asteroid fragments
hit the planets and
sometimes fall to
the ground as
METEORITES
Meteorites are
free samples
of other worlds.

32. asteroids also produce very fine dust particles. These 32
The Zodiacal Light
Milky Way
Collisions among the
asteroids also produce very
fine dust particles. These
are illuminated by sunlight
and form a faint band
across the sky, visible
at sunrise and sunset.
This is the Zodiacal Light
Horizon

33. NEA: Near Earth Asteroids33
NEA: Near Earth Asteroids
The asteroids that have orbits that cross the orbit of the Earth have the possibility to collide with our planet
The Apollo and Amor family asteroids are most likely to hit Earth
About 2200 Near-Earth (NEA) asteroids are known
There are more NEAs that have not yet been found
PHA: Potentially Hazardous Asteroids, 836 known, that come closer to Earth than 0.05 AU and about 100m in size, i.e. can cause a global catastrophe.

34. The 1 mile diameter Barringer Crater (Arizona) was probably created by a 45 meter object, 50,000 years ago. 34

35. Formation of an impact crater35
Formation of an impact crater
Impacts occur
at velocities
some 10-20
times the speed
of a rifle bullet.
This produces a
powerful
explosion. 35

36. Meteors – Comet dust particles entering our atmosphere and burning36
Meteors –
Comet dust
particles
entering our
atmosphere
and burning
up from the
friction.
Every year
about Nov. 18
the Earth goes
through the
path of an old
comet.

37. Meteorites are … Most come from the asteroids, but some are chips from37
Meteorites are …
Most come from
the asteroids, but
some are chips from
the Moon and some
are from Mars.

38. 1992 The Peekskill, NY Meteorite Fall38
1992 The Peekskill, NY Meteorite Fall
A meteor streaked across the skies of for 40 minutes, then hit a car

39. Peekskill Meteorite The car and the meteorite39
Peekskill Meteorite The car and the meteorite
Now in the Smithsonian!

40. 40
A meteorite the size of a car streaks across the sky, headed for Canada, but doesn’t strike the ground. It “skips” off the atmosphere.

41. October 17, 2012, a car-sized meteor passed northward over the Hayward hills.41

42. Feb 15, 2013, Russian Meteor Event42
Feb 15, 2013, Russian Meteor Event
Videos:

43. Some meteorites are big43
Some meteorites are big
15-ton meteorite found in the
Willamette Valley, Oregon
Known to native Americans,
but “discovered” in Now
in the Hayden Planetarium,
New York City.
1906 photo
This is an iron meteorite

44. Many meteorites have been recovered in Antarctica44
Many meteorites have been recovered in Antarctica
Meteorites are preserved
in the Antarctic ice cap.
The are concentrated in
certain areas by the
motion of the ice.
Meteorites are easier
to find in the ice
because there are very
few “native” rocks.
A few thousand have
been found so far.

45. Melted and unmelted meteorites come from different kinds of asteroids45
Melted and unmelted meteorites come from different kinds of asteroids
This is an asteroid
that has melted
and differentiated.
The iron has mostly
gone to the core.
These two asteroids
have not melted, and
have not differentiated.

46. Chondrites are meteorites that contain chondrules 46
Chondrite meteorites
Chondrites are meteorites that contain chondrules
Chondrules are little BB-size blobs of minerals and mineral glass that were once melted and quickly solidified. They look like gravel.

47. Ordinary chondrites contain metal (iron and 47
Ordinary chondrites contain metal (iron and
nickel). Note the tiny shiny flakes in this
meteorite.

48. 48
Very important !
The ordinary chondrites have the overall composition (metal + silicate minerals) of the Earth and the other terrestrial planets.
If we put the Earth in a giant blender and ground it all up (core, mantle, and crust) into small pieces, it would have the overall composition of an ordinary chondrite. + =

49. differentiated asteroid49
This sketch shows a cut through an asteroid that
has melted and mostly differentiated. The iron
and other metals were sinking to form a core,
and the lighter silicate minerals were floating to
the top. The asteroid was small, and solidified
before differentiation was entirely complete.
The outer layer is made of silicate
rocks.
The core is made of iron + nickel.
The intermediate zone is a mix of
metal and silicate minerals.
We can call this a
differentiated asteroid

50. 50
When differentiated asteroids are shattered, they produce at least three kinds of meteorites.
Two iron
meteorites
from the core
of an asteroid

51. A stony-iron meteorite from the region near the core. Note the green 51
When differentiated asteroids are shattered, they produce at least three kinds of meteorites.
A stony-iron meteorite
from the region near the
core. Note the green
olivine crystals.

52. A basaltic meteorite from the volcanic crust of a 52
When differentiated asteroids are shattered, they produce at least three kinds of meteorites.
A basaltic meteorite from
the volcanic crust of a
differentiated asteroid

53. The Importance of Meteorites53
The Importance of Meteorites
They are the oldest material that we have.
Their ages are consistently 4.45 to 4.57 billion years.
Meteorite ages are determined from the radioactive atoms in them.
You have seen these two figures before …