Hour 3: Star and Planet Formation, History of our Solar System, Planets Around Other Stars Interstellar Clouds & Star-Forming Regions Protoplanetary Disks & Solar System Formation Two Kinds of Planets & the Condensation Sequence Era of Heavy Bombardment - Frustration of Life ? Extrasolar Planets & the “Hot Jupiter” Puzzle

Take-aways: Clouds of material between the stars are sites of stars formation Earth plus the other planets in our solar system evidently formed from a disk around the Sun as it formed; such protoplanetary disks are seen around many young stars Planets like Earth are believed therefore to form as normal by- products of stars forming There are two types of planets in our solar system, Earth-like and Jupiter-like, results of a process we think we understand Almost 200 planets have now been found around other stars, but those planetary systems often have “hot Jupiters” - is our solar system weird, or are those systems weird ? All the planets sustained heavy bombardment from remnant construction material soon after they formed; that may have set the timescale for the beginning of life on Earth

Interstellar Clouds and Star-forming Regions

The Orion Nebula: An Active Star-Forming Region

Constellation Orion left: visual wavelength image right: far-infrared image

p.194c

p.195b

p.194b

Globules Evaporating gaseous globules (“EGGs”): Newly forming stars exposed by the ionizing radiation from nearby massive stars

p.177b

p.177d

Globules Bok globules: ~ 10 – 1000 solar masses; Contracting to form protostars

Shocks Triggering Star Formation Henize 206 (infrared)

Protoplanetary Disks & Solar System Formation

Fig. 1-7, p.7

p.364a

Table 16-1, p.367

Fig. 16-1, p.357

Fig. 16-2, p.358

Fig. 16-3, p.358

Two Kinds of Planets & The Condensation Sequence

Two Kinds of Planets Planets of our solar system can be divided into two very different kinds: Terrestrial (earthlike) planets: Mercury, Venus, Earth, Mars Jovian (Jupiter-like) planets: Jupiter, Saturn, Uranus, Neptune

Table 16-3, p.369

Asteroids Last remains of planetesimals that built the planets 4.6 billion years ago! Small, irregular objects, mostly in the apparent gap between the orbits of Mars and Jupiter.

Fig. 16-7, p.363

The Geology of Comet Nuclei Comet nuclei contain ices of water, carbon dioxide, methane, ammonia, etc.: Materials that should have condensed from the outer solar nebula. Those compounds sublime (transition from solid directly to gas phase) as comets approach the sun. Densities of comet nuclei: ~ 0.1 – 0.25 g/cm 3 Not solid ice balls, but fluffy material with significant amounts of empty space.

Fig. 16-4c, p.359

Extrasolar Planets & the “Hot Jupiter” Puzzle

Fig. 16-5, p.360

Artist’s Conception HD Planet passing in front of parent star -- size indicates density like Jupiter

Hot Jupiters: They seemingly go against the neat “Condensation Sequence” theory that seems to explain our solar system’s arrangement Did the “Hot Jupiters” form “cold”, i.e. at the expected location beyond the “ice line”, and then migrate toward the Sun ? If so, wouldn’t that destroy any Earth-like planets ? In our system Jupiter did NOT migrate -- is our system weird or are the Hot Jupiter systems the unusual ones, but just easier to detect with present technology ?

Era of Heavy Bombardment - Frustration of Life ?

Fig b, p.374

p.389c

Fig. 17-9, p.394

Fig. 18-3, p.424

Take-aways: Clouds of material between the stars are sites of stars formation Earth plus the other planets in our solar system evidently formed from a disk around the Sun as it formed; such protoplanetary disks are seen around many young stars Planets like Earth are believed therefore to form as normal by- products of stars forming There are two types of planets in our solar system, Earth-like and Jupiter-like, results of a process we think we understand Almost 200 planets have now been found around other stars, but those planetary systems often have “hot Jupiters” - is our solar system weird, or are those systems weird ? All the planets sustained heavy bombardment from remnant construction material soon after they formed; that may have set the timescale for the beginning of life on Earth