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-be-discovered) 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

Unlike observations of far away stars, they move even over a short duration of few minutes!

Different tracking of telescope is needed!

Observation of Solar System objects

Separation is only 19,640km (5% of the Earth-Moon distance) 6.4 days of orbit

Pluto’s satellite, Charon

impact origin of Charon?

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.

Discovered by Chad Trujillo and Michael Brown in 2002.

Quaoar : “Kwawar”

… and the quest for larger, more distant KBOs contunued…

Binary KBOs

Discovered by M. Brown +

Even larger than Pluto (by ~30%).

2003 UB313 = “Xena” = Eris

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

Haumea

About 500 known KBOs

Currently known KB objects

Larger (or similar) objects kept discovered even at larger distances…

They are similar in size and composition.

What should we call them?

A slew of new discoveries…

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 objectsPlanet:• 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 timesa 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

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.

Astronomy Picture of the Day2010 September 13

Using coronagraph, images of dozens of debris disks were obtained (mostly with Hubble Space Telescope).

Imaging Debris Disks with Coronagraph

Some images of Debris Disks

Debris Disks are signposts of exoplanetary systems

Outermost edge of the Solar System

Kuiper Belt Objects

Oort Cloud

In summary…

Important ConceptsRelation between KBOs and Debris

DisksDefinition of IAU PlanetReasons behind the name of

“Dwarf Planets”

Important TermsTrans-Neptunian ObjectsKuiper Belt ObjectsDwarf PlanetsZodiacal light

Chapter/sections covered in this lecture : sections 14-9 and 14-10