Transcript Life in the Universe

Pluto and Kuiper Belt
Lecture 26
Discovery of Pluto
 Like Neptune’s influence on Uranus’ orbit, in late 19th century, many astronomers
believed that Neptune’s orbit was also perturbed by an unseen (yet-to-bediscovered) planet.
 Percival Lowell installed a wide-field camera in 1929.
 in 1930, Clyde Tombaugh discovered an object beyond Neptune’s orbit but 250
times fainter!
Method of discovering planets
Pluto
 Pluto’s orbit is very different from those of other planets
 eccentricity = 0.25  sometimes, Pluto gets closer to the Sun than Neptune!
 inclination = 17.15°
 Pluto is so far away, and its apparent diameter is only 0.15 arcsecond
 makes it harder to understand Pluto even in the 21st century.
Image of Pluto
Observation of Solar System objects
Unlike observations of far
away stars, they move even
over a short duration of few
minutes!
Different tracking of telescope
is needed!
Pluto’s satellite, Charon
impact origin of Charon?
Separation is only 19,640km
(5% of the Earth-Moon
distance)  6.4 days of orbit
Pluto in the Sky
If Pluto and Charon were created from a
collision of two large rocks, there should be a
large population of similar objects near (or
beyond) Neptune’s orbit.
 Search began.
Discovery of KBOs
 Discovery image of 1992 QB1 (1992 Aug
30) by Dave Jewitt
 First object beyond Pluto’s orbit
= Kuiper Belt Object
= Trans-Neptunian Object
Another KBO : 1993 SC
 This image is shows a small part of
the discovery frames of 1993 SC,
one of the brightest Kuiper-Belt
objects so far discovered. It was
taken using the 2.5m Isaac Newton
Telescope on La Palma by Alan
Fitzsimmons, Iwan Williams and
Donal O'Ceallaigh on 17th
September 1994. The two images
are separated in time by 4.6 hours,
and by comparing them it is clear
that one of the objects has moved
from upper left of center to almost
merging with the image of a distant
galaxy. This motion marks it as
being a distant member of our solar
system, further away than the
planet Neptune.
Quaoar : “Kwawar”
 Discovered by Chad Trujillo and Michael
Brown in 2002.
… and the quest for larger, more distant KBOs contunued…
Binary KBOs
2003 UB313 = “Xena” = Eris
Discovered by M. Brown +
Even larger than Pluto (by
~30%).
Haumea
Why is Haumea shaped like a
potato? Although the dwarf
planet has never been directly
observed, its elongated shape
has been calculated from its
light curve. Haumea’s length
is twice that of its width.
Discovery conspiracy b/w
Caltech and Spanish team:
- discovered in Dec 2004
from an image on May 6,
2004
- Spanish team reported a
discovery of on July 2005
from an image taken on
Mar. 2003
Currently known KB objects
About 500 known KBOs
A slew of new discoveries…
Larger (or similar) objects
kept discovered even at larger
distances…
They are similar in size and
composition.
What should we call them?
Orbit of Sedna
Starting at the inner Solar System, which includes the orbits of Mercury, Venus,
Earth, and Mars (all in yellow), the view pulls away through the asteroid belt and
the orbits of the outer planets beyond (green).
Dwarf planets
'planet' gets more press attention than 'large Kuiper belt object’
Plutons : suggested by the IAU before they realized that this is a well-established
geological term for an intrusive rock mass.
Plutoids : suggested by some astronomers.
Dwarf Planets : the IAU's half-way suggestion. Not a real planet, but still has
'planet' in the name, like 'minor planets' (a.k.a asteroids).
Dwarf Planet
 Accepted in the IAU meeting in 2006 from the pressure of ever-increasing number
of Trans-Neptunian objects
Planet:
• an object orbiting the Sun (i.e., no satellites)
• massive enough to be spherical (large enough gravity)
• cleared its neighboring region (i.e., no embedded large asteroids)
Dwarf Planet:
• an object orbiting the Sun
• sufficient mass to be round-shaped (or nearly)
• has not cleared its surrounding region
• not a satellite
Small Solar System Bodies: all other objects except satellites.
Strongest objections  school teachers and astrologers (and some US Astronomers)…
Dusty Disks
 KBOs collide among themselves and create a myriad of small dust grains
 Breaking on 100km object into 1micron particles  1027 particles
increase the surface area by billion times
a disk is billion times easier to discover than a large KBO around other star
This disk of dust grains is known as Debris Disk  disk made of debris of planet formation
Astronomy Picture of the Day
2010 September 13
An unusual triangle of light is visible this time of year just before dawn, in the
northern hemisphere. Once considered a false dawn, this triangle of light is actually
zodiacal light, light reflected from interplanetary dust particles. The bright reflecting
triangle is clearly visible on the right of the above horizontally-compressed image
taken just after sunset from Namibia in the southern hemisphere in 2009 June.
Imaging Debris Disks with Coronagraph
Using coronagraph, images of
dozens of debris disks were
obtained (mostly with Hubble
Space Telescope).
Some images of Debris Disks
Debris Disks are signposts of exoplanetary systems
Outermost edge of the Solar System
Oort Cloud
Kuiper Belt Objects
In summary…
Important Concepts
Important Terms
 Relation between KBOs and Debris
Disks
 Definition of IAU Planet
 Reasons behind the name of
“Dwarf Planets”
 Trans-Neptunian Objects
 Kuiper Belt Objects
 Dwarf Planets
 Zodiacal light
Chapter/sections covered in this lecture : sections 14-9 and 14-10