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Narrator: When it comes to finding planets outside our
solar system, no space mission to date can beat NASA's Kepler
in 5 years it has found more than a thousand confirmed exoplanets,
with thousands more awaiting confirmation. Kepler finds
exoplanets by carefully watching starlight, looking for slight dips in
brightness as a planet passes in front of, or transits, its star. This
technique, called time-series transit photometry, is most effective
for large planets in close orbits. This both maximizes the light
loss during a given transit and the number of transits we observe.
But how far can astronomers go with this technique? Can we
find a twin of Earth? Or even identify whether a planet has moons?
With two transit photometry missions on the horizon--NASA's
TESS and ESA's PLATO--some astronomers have examined the limits
of this technique, with surprising results. Daniel Angerhausen: For our study,
Michael Hippke and I combined the knowledge of the
lessons learned from Kepler with what we know about the future missions like
TESS and PLATO, and we asked ourself the question 'what would we be able
to see if we put these observatories outside our solar system and observed
our solar system.' And the results are that we
probably won't be able to see Mars, or Mercury, but
everything else in our solar system we definitely get a solid detection of
Earth, a solid detection of Venus. Also of the outer planets.
We might even be able to see ring structures like the one around
Saturn, and maybe even moons, Jupiter's moons.
Narrator: In another study, they pushed Kepler to the limit by cleverly
combining almost all extrasolar planet data collected by the telescope
using an understanding of orbital mechanics. Daniel: For example, Jupiter
has so-called trojan asteroids that collect in two
specific areas on its orbit, pretty symmetrically to its orbit.
And in the study that we did on the Kepler data, where we added up
all the phase curves of all 4,000 planets in the Kepler data set, we were even
able to see signatures of asteroids in extrasolar
systems. And with the future missions we might even be able to find that
in individual systems and not just by putting all the data together.
We wanted to figure out what the ultimate limit
is that we can do photometry with, and it turns out
with the next generation of instruments we're already hitting the technical limit and are
mostly limited by the variation of the host stars themselves,
by the huge noise that's coming from the host stars. Narrator: The way to push down
this noise is by observing stars for longer periods to improve
models of the star's behavior, allowing astronomers to tease out the smallest transits.
The work of Hippke and Angerhausen shows
that future missions will be able to detect Earth-size planets orbiting
sun-like stars at distances that would allow liquid water.
These systems will become prime targets for more detailed study, using other
missions, such as NASA's James Webb Space Telescope. Will we
find a copy of our solar system? How common are habitable
worlds, and particularly twins of Earth? The thousands of exoplanets
to be discovered by TESS and PLATO will go a long way to providing answers.
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