Physics 101 - Astronomy - Spring 2019
Class notes for day 16, March 19, 2019
Ch. 12 – Pluto and Charon
There are several kinds of objects in our Solar System, and astronomers are
still working on ways to classify them all.
The planets are divided up into Terrestrial planets and Jovian planets (two gas
giants, Jupiter and Saturn, and two ice giants, Uranus and Neptune), and they
can have satellites (called moons).
Astronomical objects smaller than the eight planets are classified as dwarf
planets (which can also have moons) or small solar-system bodies (SSSBs) –
asteroids, comets and meteoroids
Some objects are still being classified:
Kuiper Belt Objects are objects in the Kuiper Belt. Kuiper is a Dutch surname and rhymes with "hyper."
Plutoids are objects "like Pluto."
Plutinos are smaller versions of Pluto.
Trans-Neptunian Objects (TNOs) are simply objects further from the Sun than Neptune.
Oort cloud objects are objects very far from the Sun, in the Oort cloud, named after another Dutch astronomer. The Oort cloud is not a flat donut-shaped object like the Kuiper Belt or the Asteroid Belt.
KBOs and Oort cloud objects are trans-Neptunian objects—they orbit farther from the Sun than the outermost planet Neptune.
Dwarf Planets
When the definition of planet was changed and the new term "dwarf planet" was
adopted by the international astronomical community in 2006, three objects,
Pluto, Ceres, and Eris, were classified as dwarf planets. Later we
discovered Haumea and Makemake, which are dwarf planets out in the Kuiper Belt.
So at present there are 5 dwarf planets.
Pluto can barely be resolved by telescopes from Earth, so we didn't know much
about its surface until the summer of 2015. The period of Pluto’s orbit is 248
years, and the orbit of Pluto is tilted and elliptical (e = 0.25). A moon of
Pluto, called Charon (pronounced like "Karen"), was discovered by noticing a bulge in some photos of
Pluto. Pluto and Charon are almost like a double planet. The Pluto–Charon Orbit
is so unusual that it probably means Charon is captured, and not co-evolved with
Pluto. The New Horizons spacecraft has now gone by Pluto and returned many
pictures and data. I showed several photos from the John Hopkins University -
Applied Physics Lab website (where they managed the mission):
http://pluto.jhuapl.edu/ These were too
big to put in the PowerPoint, so look at the website. Also see the NASA website http://www.nasa.gov/mission_pages/newhorizons/main/index.html
We obtained completely new images from the New Horizons spacecraft, which passed close to Pluto in the summer of 2015.
See the PowerPoint for some of the pictures. Many other Pluto images are best
seen in a web browser, so I showed these in class:
Methane snow on peaks
http://pluto.jhuapl.edu/Galleries/Featured-Images/image.php?page=1&gallery_id=2&image_id=231
High resolution pictures of Sputnik Planum, an ocean of solid nitrogen
http://pluto.jhuapl.edu/Galleries/Featured-Images/image.php?page=8&gallery_id=2&image_id=240
http://pluto.jhuapl.edu/Galleries/Featured-Images/image.php?page=10&gallery_id=2&image_id=277
http://pluto.jhuapl.edu/Galleries/Featured-Images/image.php?page=13&gallery_id=2&image_id=387
Mountains and plains, with haze layers
http://pluto.jhuapl.edu/Galleries/Featured-Images/image.php?page=11&gallery_id=2&image_id=300
http://pluto.jhuapl.edu/Galleries/Featured-Images/image.php?page=11&gallery_id=2&image_id=282
geology map with color to denote different types of surface
http://pluto.jhuapl.edu/Galleries/Featured-Images/image.php?page=15&gallery_id=2&image_id=409
The
New Horizons trajectory is shown in this graphic:
http://pluto.jhuapl.edu/Mission/Where-is-New-Horizons/index.php
I showed a slide with some Kuiper Belt Objects compared to Moon and Earth.
The known ones are somewhat smaller than the Moon. Notice that we think Triton
(now a moon of Neptune) was captured by Neptune, but was originally further away
in the Kuiper Belt. It is probably an object like Pluto and the KBOs. However, pictures of Pluto
taken in 2015 to compare with some
pictures of Triton taken by the Voyager spacecraft show that they are fairly
different.
For more information (if you are interested), see this web page about KBOs:
http://www2.ess.ucla.edu/~jewitt/kb.html
I mentioned a few KBOs, like Eris, which is a dwarf planet even further than
Pluto. The Keck telescope got an image of Eris and its moon Dysnomia.
Ch. 12 - Rings
Rings around planets are important to understand because they allow us to test theories about the formation of the solar system. The early solar system was a disk-shaped nebula around a protostar, and it very likely had some of the features that we see today in the rings of the Jovian planets. The capture of ring material by shepherd moons, or the clearing of gaps in the rings, are critically important to the accretion process that formed large objects in the solar system nebula.
For images of the rings of Saturn, and a few comments about the gaps, shepherd moons, etc., see the PowerPoint.
A planetary disk in formation around a distant star has been seen by the ALMA
observatory, see
http://www.almaobservatory.org/press-room/press-releases/771-revolutionary-alma-image-reveals-planetary-genesis
and
http://www.eso.org/public/news/eso1436/
These images show that the study of Saturn's rings and their shephard moons is
related to the study of protoplanetary disks.