Figure 3.
Exclusion zones for
each of the planet
candidates in the
Kepler-186 system.
Prior to validation,
the star was known
as KOI (Kepler Object
of Interest) 571, and
Kepler-186f (KOI571.05) is shown in
the lower middle
panel. The shaded
regions indicate the
parameter space
that can be ruled
out for having
an astrophysical
source (like a binary
star system) that
is inducing light
variations that could
mimic a planet signal.
The region shaded in
green is excluded by
Gemini speckle imaging,
the pink is from the
Keck-II adaptive optics
observations, the blue
is based on modeling
the transit light curve,
and the yellow is based
on pixel centroids
data (measures of the
movement of the pixels
which can indicate if
the primary source is a
binary star system, not
shown in the Kepler-186f
panel). Observational
constraints rule out all
regions of the figure
except for the white
areas, which then go
through additional
statistical analysis.
The additional shaded
region provided by
Gemini — looking for
sources very close to the
star — was crucial
in our validation of
Kepler-186f.
Credit: Thomas Barclay
20
planet’s blocking of some light from the star.
Kepler measurements of the brightness decrease, and the frequency of transit, as well as
knowledge of the star’s size, are used to determine the size of the planet and the planet’s
distance from its star.
The Kepler mission has contributed more
than 950 exoplanet discoveries to the current
count of about 1700, in addition to the 38000
potential planets that await confirmation.
Several key milestones have been reached
by Kepler towards the goal of finding potentially habitable planets. A small number of
Earth-sized planets, such as Kepler-20e, have
been found, however they all orbit close to
their star, making them extremely hot and
therefore inhospitable to life. About a dozen
planets have been found to orbit in their star’s
habitable zone, however they are all larger
than Earth and most have a thick atmosphere
of gas like Jupiter. Kepler-186f is the first
“Goldilocks planet,” it has the right size, and
orbits at the right distance, to allow the existence of water, thought to be a key ingredient
for supporting life.
GeminiFocus
Gemini’s Role
One way to verify claims of exoplanet detection is to look for a signature “wobble” in the
host star, as gravity from orbiting planets tug
on it. However, Earth-sized planets, like Kepler-186f, are too small to create a detectable
wobble with existing technology. Confirmation had to come in a new way.
To prove that the signals in the star’s light are
due to planets and not other nearby astrophysical sources, high-contrast images were
obtained from both Gemini North and Keck II
telescopes. Some common sources of apparent variability, which can trigger a false planetary detection, include a binary star system
in the background or foreground that introduces small variations in the total measured
light. Alternatively, if we are truly looking
at a binary star system, but a third star is so
close that it dilutes the signal, or if the binary
stars barely eclipse each other, then these are
other scenarios that could cause a small dip
in the light curve and be misinterpreted as a
planetary eclipse.
2014 Year in Review
January 2015