Science journalist: Brown dwarfs are celestial objects with more mass than planets but less mass than stars. They are identified by their mass and whether or not lithium is present in their atmospheres. Stars at least as massive as the Sun have lithium remaining in their atmospheres because the mixing of elements in their internal nuclear furnaces is incomplete. Stars with less mass than the Sun have no lithium because the element has been fully mixed into their nuclear furnaces and consumed. A brown dwarf does not have a fully functional nuclear furnace and so its lithium cannot be consumed.
Summary
Brown dwarfs are more massive than planets but less massive than stars. They are identified by their mass and whether or not lithium is present in their atmospheres. A brown dwarf’s lithium cannot be consumed because they do not have a functional nuclear furnace.
Strongly Supported Conclusions
If a celestial object does not have lithium in its atmosphere, then it is not a brown dwarf.
A
Any celestial object without lithium in its atmosphere is a star with less mass than the Sun.
This answer is unsupported. We don’t know from the stimulus that any celestial object without lithium must be a star. We only know from the stimulus that some stars do have lithium in their atmospheres.
B
Any celestial object with lithium in its atmosphere has a nuclear furnace that has incompletely mixed the object’s elements.
This answer is unsupported. We know that this is true of stars at least as massive as the sun, but saying this is true of any celestial object is too strong.
C
No celestial object that has no lithium in its atmosphere is a brown dwarf.
This answer is strongly supported. We know that brown dwarf’s must have lithium in their atmospheres because it cannot be consumed by a nuclear furnace.
D
No celestial object with lithium in its atmosphere has less mass than the Sun.
This answer is unsupported. This is the reverse relationship from the stimulus. The stimulus tells us that if a star is at least as massive as the sun, then there is lithium in that star’s atmosphere.
E
No celestial object less massive than a brown dwarf has lithium in its atmosphere.
This answer is unsupported. We don’t know anything about celestial objects with less mass than brown dwarfs from the stimulus. The stimulus is limited to brown dwarfs and celestial objects with greater mass.