AST 248. Is Pluto a Planet?

Size: px

Start display at page:

Download "AST 248. Is Pluto a Planet?"

Mary James
5 years ago
Views:

1 AST 248 Is Pluto a Planet? And what is a planet, anyways? N = N * f s f p n h f l f i f c L/T

2 What is a Star? A star supports stable Hydrogen fusion Upper mass limit: about 120 M above that radiation pressure blows the star apart Lower mass limit: M below that core temperatures are too low for fusion

3 Stars Brown Dwarfs Planets

4 Brown Dwarfs Below M, H cannot undergo stable nuclear fusion But, Deuterium ( 2 H) fuses at lower temperatures Brown dwarfs are objects that fuse all the D in their cores have masses between and M burn their D quickly, then slowly cool. form like stars.

6 Planets Do not support Deuterium fusion Less massive than Brown dwarfs M < M ~ 13 M Jupiter Form in disks surrounding stars Questions: Can planets form in isolation (like stars?) What is the minimum planetary mass

7 Exoplanets

8 Planet Formation

9 Planet Formation

10 Planet Formation Planet formation in flattened disks, dictated by conservation of angular momentum, explains the shape of our Solar System

11 Fraction of Stars with Disks Hernandez et al 2007, ApJ 662, 1067

12 Planet Formation in a Disk Temperature decreases outwards Density decreases outwards At high enough temperatures, everything is gaseous As temperatures fall, gases condense into solids

13 Condensation Sequence Temperature (K) Condensate 1500 Fe 2 O 3, FeO, Al 2 O Fe, Ni 1200 Silicates 1000 MgSiO FeS 175 H 2 O 150 NH CH 4 65 Noble gases

15 Solar System Small rocky planets close to Sun Large gaseous planets further from Sun

16 Gas Giant Planets Also known as Jovian planets Large rocky core surrounded by gaseous envelope Form outside the ice line Planet M core (M ) M atm (M ) Jupiter Saturn Uranus Neptune

17 Rocky Planets Also known as terrestrial planets Metallic core plus rocky mantle Minimal atmospheres

18 Debris Disks

19 Kuiper Belt Objects Also known as Trans-Neptunian Objects (TNOs) Dwarf Planets Sedna ~900 km radius 80 AU from Sun

20 Eris (2003 UB313) Radius: 1200 km Mean distance from Sun: 68 au e=0.44, i=44 o

23 Debris: Minor Planets 951 Gaspra 19 x 12 x 11 km 241 Ida 58 x 23 km 443 Eros 40 x 14 x 14 km

24 Debris: Comets

25 Comets Comet Wild-2 Stardust mission flyby January 2006 Nucleus: 5 km

27 Comet Churyumov-Gerasimenko from Rosetta at 62 km, 12 September 2014

28 How Big?

29 Comets

30 Take-Aways Comets are primitive material from the outer solar system Comets are dirty snowballs Comets can be the largest objects in the SS Comets are rich in volatiles Did comets return volatiles to the inner SS? Comets can evolve into asteroids

31 Meteors It is easier to believe that Yankee professors would lie than that stones would fall from heaven. -- attributed to Thomas Jefferson

32 Meteors Meteoroids: small objects outside the Earth's atmosphere. Meteors: small bodies traversing the atmosphere, and (generally) burning up. Meteorites: Meteors that survive the atmosphere and land on the Earth. Irons Chondrites Carbonaceous Chondrites

33 Fireballs and Bolides Very bright meteors May leave a persistent trail Due to impacting object bigger than about 1m

34 Chelyabinsk 2/15/2013

35 Is Pluto a Planet? The real issue is that we need to know precisely what we mean when we use the word planet. It all depends on what the meaning of is is William Jefferson Clinton

36 Let s define a planet as: Is Pluto a Planet? A body that: Orbits a star Is large enough for its gravity to make it round Is neither a star nor a satellite of a planet Consequences: Pluto is a planet So are Ceres, Charon, and Eris (2003 UB313, a.k.a. Xena) And an estimated 40+ Kuiper belt objects!

37 The IAU Compromise A planet is a body that: Orbits a star Is large enough for its own gravity to make it round Has cleared the neighborhood of smaller objects Consequences: Pluto is not a planet

38 Consequences of the IAU Compromise The Moon is not a planet It orbits the Earth Asteroids are not planets The biggest are round, but they do not dominate their orbits Pluto is not a planet It does not dominate its orbit Does Neptune dominate its orbit?

39 What is Pluto? The runt of the major planets? The king of the dwarf planets? The largest of the Kuiper belt objects (maybe)? Or a cartoon dog? And what does it really matter? Today Pluto is the same physical entity as it was last year.

40 What is the value of f p? Our Sun has planets. Based on that, we can set the fraction of stars with planets to 1. We ll reassess in week 10, when we look for planets around other stars.

41 N Update N = N * f s f p n h f l f i f c L/T N * = 4 x f s ~ 0.2 f p ~ 1 N = 8 x n h f l f i f c L/T

AST 105. Overview of the Solar System

AST 105. Overview of the Solar System AST 105 Overview of the Solar System Scale of the Solar System Earth Voyager 1, 1991, distance = 4 billion miles Recap: The Solar System in Scale If the Solar System were the size of a football