The motion of the tectonic plates is driven by A) the ...

[storky111]

The motion of the tectonic plates is driven by
 
  A) the gravitational pull of the Moon and Sun.
  B) the elliptical nature of Earth's orbit.
  C) heat moving by convection.
  D) magnetic repulsion.
  E) Earth's subsurface convection cycle.

Question 2

How can astronomers be confident that the larger exoplanets discovered are not simply brown dwarfs?
 
  What will be an ideal response?

[macagnavarro]

Answer to Question 1

E

Answer to Question 2

Unless the majority of the planets detected are in orbits that we are seeing nearly face on, the objects found are not massive enough to fall into the brown dwarf category. The large number of planets detected by the transit method are in orbits that are nearly edge on, making the minimum mass estimates likely to be fairly close to the actual mass. Many of these have masses much lower than the estimated dividing line between planets and brown dwarfs of about 12 Jupiter masses.

[storky111]

Excellent

[sailorcrescent]

Gracias!