  Aeronomy, the study of Earth's upper atmosphere and its interaction with the
local space environment, has long traced changes in the thermospheres of Earth
and other solar system planets to solar variability in the X-ray and extreme
ultraviolet (collectively, "XUV") bands. Extending comparative aeronomy to the
short-period extrasolar planets may illuminate whether stellar XUV irradiation
powers atmospheric outflows that change planetary radii on astronomical
timescales. In recent years, near-infrared transit spectroscopy of metastable
HeI has been a prolific tracer of high-altitude planetary gas. We present a
case study of exoplanet aeronomy using metastable HeI transit observations from
Palomar/WIRC and follow-up high-energy data from the Neil Gehrels Swift
Observatory that were taken within one month of the WASP-69 system, a K-type
main sequence star with a well-studied hot Jupiter companion. Supplemented by
archival data, we find that WASP-69's X-ray flux in 2023 was less than 50% of
what was recorded in 2016 and that the metastable HeI absorption from WASP-69b
was lower in 2023 versus past epochs from 2017-2019. Via atmospheric modeling,
we show that this time-variable metastable HeI signal is in the expected
direction given the observed change in stellar XUV, possibly stemming from
WASP-69's magnetic activity cycle. Our results underscore the ability of
multi-epoch, multi-wavelength observations to paint a cohesive picture of the
interaction between an exoplanet's atmosphere and its host star.
