1. Migrating Planets!
28 October 2016

2. Origin of the Solar System
Elements were made inside stars
Stars formed from giant molecular clouds
Planets form in a disk around the protostar
Giant planets form from accretion onto cores
Terrestrial planets are only the cores
The giant planets form far away
Terrestrial planets form close to the star

5. Characteristics of our Solar System
Regular planet orbits
Planets are closely spaced
Terrestrial and Jovian planets
Asteroids and comets leftover
Satellites and rings imitate a miniature Solar System

6. Stages in planet formation
Dust collects in the mid-plane of the protoplanetary disk
Grows by mutual collisions: ‘accretion’
Planetesimals (about 1km across) grow and collide
Giant collisions are the final stage
Giant planet cores are bigger outside the frost-line: they attract gas to become gas giants like Jupiter
Star ignites: the gas and dust blown away

8. Leftovers
Near the Sun (inside frost-line, also known as snow line or ice line) rocky objects become asteroids
Far from the Sun (outside frost-line) icy objects form the comets and Kuiper Belt Objects

9. The first exoplanets discovered were labelled ‘Hot Jupiters’
The first exoplanets discovered were labelled ‘Hot Jupiters’. These planets, although similar in radius to Jupiter, orbit their stars so close that they are tidally locked in place with one side in permanent daylight and the other in perpetual darkness. The close proximity to their star means it can get incredibly hot. The hottest thus far is WASP-12b with a dayside temperature of around 2,500°C that is hotter than some stars. This orbital distance also means that a year on these worlds is just a matter of days allowing us to take multiple measurements of the planet and the star over short periods of time

10. Exoplanets: Hot Jupiters
"Hot Jupiters" — massive planets that orbit very close to their parent stars — have been found to be abundant outside Earth's solar system.
But how did these gas-giant planets in other solar systems get so close to their parent stars?
Because Earth's solar system does not host any hot Jupiters (the giant planets are further out, and smaller planets orbit closer to the star), scientists have to rely on observations of distant planetary systems to solve this mystery.

11. Where Hot Jupiter’s Form
Hot Jupiters are similar to planets such as Jupiter and Saturn.
These exotic worlds form relatively far away from their stars, as our solar system's gas giants did, but then move inward over time in a process that remains poorly understood
We're fortunate that Saturn and Jupiter didn't do this, for such migrations can boot smaller, rocky planets out of the way, sometimes ejecting them out of the solar system entirely

12. But how do they get close?
Consider Saturn’s rings, that resemble a protoplanetary disk
Moons in and near the rings create waves
Motion of the waves changes the rings and moon’s orbits (Newton’s Third Law strikes again!)
The moons move (migrate)
The same can happen to a planet, moving closer to the star

13. Density waves and
propellers in a
forming disk

14. Pan closeup

15. Propeller, but moon causing it still unseen

18. Figure 13.17
© 2014 Pearson Education, Inc.

20. Planet Migration
Density waves and gaps allow angular momentum transfers
These move the planets (like moons within rings) around
Some end up in the proto-star! Some stop, but why?
This infant mortality removes planets, like musical chairs…
What we see now are just the survivors. Was Earth lucky?

21. Summary: Exoplanet facts
The known exoplanets fall along a range of sizes, masses, and orbital positions. Sizes and masses range from smaller and less massive than Earth to super-Jupiter types of worlds. Orbital positions range from very close to the parent star to very distant.
The region around a star where liquid water could exist on the surface of a solid planet is called the habitable zone. Worlds orbiting in that zone are considered to be prime candidates where life could be supported.

22. More than 22 percent of Sun-like stars have Earth-sized planets in their habitable zones. These are important places to concentrate a search for possible life-bearing worlds.
The Kepler Mission was launched to search out distant worlds. It continues its search today.

23. Famous Exoplanets
51 Pegasi b: The first planet around a star like the Sun. Astronomers found it using the Observatoire de Haute-Provence in France, a ground-based facility. This planet is also known as a “hot Jupiter” because it appears to be a very warm gas-giant-type world.
Kepler 186-f: the first Earth-size planet circling in the habitable zone of its star. Found by the Kepler Mission in 2014.
Kepler 11-f: orbits a Sun-like star and has at least 2.3 times the mass of Earth. It may be a gas dwarf, due to its low density and possible hydrogen-helium atmosphere.