Aliens are Out There! Lisa Kaltenegger (#294)

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https://www.surveymonkey.com/r/intotheimpossible Lisa Kaltenegger
is the founding director of the Carl Sagan Institute at Cornell. In
2009, Kaltenegger realized that a telescope like JWST would see
only tiny signals from atmospheric gases during each transit, so in
order to achieve any statistical certainty, astronomers would need
to observe dozens or even hundreds of transits, which would take
years. Acting on this insight, astronomers started to seek Earths
in close orbits around dimmer, colder red dwarf stars, where
atmospheric signals will be less drowned out by starlight and
transits repeat more frequently. In 2017, astronomers announced the
discovery of seven rocky planets around a red dwarf star called
TRAPPIST-1. Then in September, the SPECULOOS-2 system emerged as a
backup. These stars are close. They’re dim and red. They each have
multiple rocky planets that transit. And as of the summer, the JWST
is up and running even better than expected. It will spend a
sizable fraction of the next five years staring hard at these messy
globes of rock and chemicals spinning around their strange stars.
For theoreticians like Kaltenegger who went from daydreaming of
alternate Earths to churning out predictions about their
atmospheric chemistry, decades of anticipation have given way to a
slow fade-in of squiggly spectra on computer monitors. The goal at
the time was to compare spectra from rocky, temperate planets to
what Earth’s spectrum would look like from far away, seeking
conspicuous signals like a surplus of oxygen due to widespread
photosynthesis. Kaltenegger’s objection was that, for the first 2
billion years of Earth’s existence, its atmosphere had no oxygen.
Then it took another billion years for oxygen to build up to high
levels. And this biosignature hit its highest concentration not in
Earth’s present-day spectrum, but during a short window in the late
Cretaceous Period when proto-birds chased giant insects through the
skies. Without a good theoretical model for how Earth’s own
spectrum has changed, Kaltenegger feared, the big planet-finding
missions could easily miss a living world that didn’t match a
narrow temporal template. She needed to envision Earth as an
exoplanet evolving through time. To do this, she adapted one of the
first global climate models, developed by the geoscientist James
Kasting, which still includes references to the 1970s magnetic-tape
era it originated in. Kaltenegger developed this code into a
bespoke tool that can analyze not only Earth through time but also
radically alien scenarios, and it remains her lab’s workhorse.
Follow Lisa https://twitter.com/KalteneggerLisa Join the Carl Sagan
Inst: https://carlsaganinstitute.cornell.edu Read How to
Characterize Habitable Worlds and Signs of Life
https://www.annualreviews.org/doi/abs/10.1146/annurev-astro-082214-122238
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