AAS Nova
Gravitational microlensing
A planet betraying itself by briefly focusing the light of a star behind it.
When one star passes exactly in front of another, its gravity bends and brightens the background star's light for weeks. A planet orbiting the foreground star adds a short extra spike to that curve. It is the only method sensitive to planets far from their stars and to free-floating planets bound to no star at all, and it has a cruel property: the alignment never repeats, so anything found this way can never be observed again.
Where it has come up lately
Related terms
Transit method
Finding planets by watching a star dim slightly as one passes in front.
Radial velocity
Finding planets by the wobble they induce in their star's motion.
Habitable zone
The orbital band where a planet could hold liquid water — no more than that.
Sub-Neptune
The most common kind of planet in the galaxy, and there is not one in our solar system.
Questions
What is Gravitational microlensing?
A planet betraying itself by briefly focusing the light of a star behind it.
Why does it matter?
A planet orbiting the foreground star adds a short extra spike to that curve. It is the only method sensitive to planets far from their stars and to free-floating planets bound to no star at all, and it has a cruel property: the alignment never repeats, so anything found this way can never be observed again.