Review Questions for the Midterm:
1. Overview the details of Jupiter beginning to migrate inwards, including possible
causes and effects. Describe the final state of our Solar System in this case.
If, as we believe may have happened in some exosolar systems, Jupiter were to migrate
inwards, it could be due to a number of possible causes: gravitational interaction with
other stars, gravitational interaction with other planets, and gravitational drag (where an
in-spiraling body drags another along in its wake). The question then is what becomes of
Jupiter in this scenario. Possible results are:
a. It keeps going until it falls into the sun, or
b. It stops somewhere in a closer orbit.
Several mechanisms for the latter have been suggested, including
(1) Running out of disk with which to interact, possibly due to solar wind activity,
(2) Magnetic fields from the disk interacting with and braking the planet’s sun-
ward fall until it goes into close orbit, or
(3) Tidal locking with the sun acting to park the planet in close orbit.
Whether Jupiter kept falling in or slowed into near orbit, it would have huge effect upon
other planets on the way, clearing out other planets including our own as it goes, either
Colliding with them;
Tearing them apart with its gravitational field;
Capturing them and turning them into satellites;
Flinging them to larger orbits or even out of the solar system altogether.
2. What is the difference between proper motion and radial velocity of a star?
Proper motion is motion that can be traced on the sky; radial velocity is motion in the
same plane as the observer, i.e., towards and away from your p.o.v.
3. Describe the three most important properties for measuring a radial velocity
curve used for planet detection.
This is done by measuring the radial velocity of the star, that is, by examining the minute
fluctuations in its movement towards and away from us. Since the star’s motion would be
regular unless acted upon by some other body, any fluctuations that exhibit periodicity
are presumed to be caused by the gravitational pull of a body orbiting that star. To do this
we need a number of observations, with a high degree of sensitivity, over a period of time
long enough to detect periodicity. Through this we can look at the signal (the actual mo-
tion curve of the star including any fluctuations), noise (inaccuracies due to sampling er-
ror, lack of sensitivity in instruments, interference from other sources, e.g.
., our own at-
mosphere), and sampling (the number of samples over time).
Note that this is the only option discussed in the course. The others are my own suggestions.