Title: The Oblique Orbit of WASP-107b from K2 Photometry,
Abstract: Observations of nine transits of WASP-107 during the {\it K2} mission reveal
three separate occasions when the planet crossed in front of a starspot. The
data confirm the stellar rotation period to be 17 days --- approximately three
times the planet's orbital period --- and suggest that large spots persist for
at least one full rotation. If the star had a low obliquity, at least two
additional spot crossings should have been observed. They were not observed,
giving evidence for a high obliquity. We use a simple geometric model to show
that the obliquity is likely in the range 40-140$^\circ$, i.e., both spin-orbit
alignment and anti-alignment can be ruled out. WASP-107 thereby joins the small
collection of relatively low-mass stars hosting a giant planet with a high
obliquity. Most such stars have been observed to have low obliquities; all the
exceptions, including WASP-107, involve planets with relatively wide orbits
("warm Jupiters", with $a_{\rm min}/R_\star \gtrsim 8$). This demonstrates a
connection between stellar obliquity and planet properties, in contradiction to
some theories for obliquity excitation.