cometsanother major class of solar system objects
DESCRIPTION
Principal Observational Features Coma Dust Tail Ion tail Ion tail glows with light of molecular ions, CO +, N 2 +, CO 2 +TRANSCRIPT
![Page 1: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/1.jpg)
Comets…another major class of solar system objects
![Page 2: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/2.jpg)
Comets appear at irregular intervals and are not confined to the ecliptic
Observed features noted in “De Cometis” by Seneca, ~ A.D. 62 “Ratio terrorem prudentibus
excutit”
![Page 3: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/3.jpg)
Principal Observational Features
• Coma• Dust Tail• Ion tail
Ion tail glows with light of molecular ions, CO+, N2
+, CO2+
![Page 4: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/4.jpg)
Question for the august assembly: Why would you
expect the ion tail to move on a different trajectory than the dust
tail????
![Page 5: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/5.jpg)
Tail of a comet can stretch a substantial fraction of an a.u.
![Page 6: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/6.jpg)
Point to keep in mind: Comets obey Kepler’s Laws: they move
on elliptical orbits around the Sun. They can be perturbed by gravitational force from planet.
![Page 7: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/7.jpg)
The Structure of a Comet
• Deduced about 40 years ago
• Nucleus of solid matter in center of coma
![Page 8: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/8.jpg)
Ice in nucleus sublimes to form coma
![Page 9: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/9.jpg)
A remarkable thing about comets is that a prominent structure
extending over 1 astronomical unit has its origin in a solid
object which can be from 1 – 10 km in diameter. Even a very
large one would have a diameter of 50 kilometers.
![Page 10: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/10.jpg)
Nucleus forms coma and tails by sublimating ice gas.
Cometary nucleus must be ices such as water, CO2, and CH4. Ions are produced by photoionization of molecules by UV light
![Page 11: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/11.jpg)
Until 20 years ago these were (well established) theoretical predictions. Starting in 1986, there have been a
number of spacecraft visits to comets, and images have been made of the cometary nuclei. See p171 of text
![Page 12: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/12.jpg)
Comet Halley (about 15 km long)
![Page 13: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/13.jpg)
Comet Wild 2 (visited by Stardust about one year ago)
![Page 14: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/14.jpg)
Orbits of Comets
![Page 15: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/15.jpg)
Recall properties of the orbits of the major planets
• Semimajor axis a: 0.4- 30 au.
• Eccentricity: 0.00 – 0.090 – 0.20
![Page 16: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/16.jpg)
A cometary orbit (Halley’s Comet)
“I’m a believer…” (in ellipses)
![Page 17: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/17.jpg)
Properties of cometary orbits (see Table 7-1, p156)
• Table gives a, eccentricity, and q (perihelion distance) for a whole bunch of comets
• Short Period Comets: a ~ few au, ecc ~ 0.39 – 0.96 (highly eccentric compared with major planets)
• Long Period Comets: a~ 160, 200, or greater, ecc ~ 0.996, 0.990, 1.0
Question: why do these classes have the names they do?
![Page 18: Cometsanother major class of solar system objects](https://reader033.vdocument.in/reader033/viewer/2022051105/5a4d1b877f8b9ab0599bd2ac/html5/thumbnails/18.jpg)
The Oort Cloud: vast repository of comets