Sky & Telescope - December 2024 - 4

SPECTRUM by Peter Tyson
A Spectral Surprise
EVEN THOUGH IT LIES 700 light-years away, we know a lot about
WASP-39b. In the first decade after astronomers reported the exoplanet's
discovery in 2011, our land- and space-based instruments
supplied valuable data with which to infer much about it.
We know it's a scalding, bloated gas giant larger than Jupiter but
bearing less than one-third as much mass. It takes just four Earth days to orbit
its G-type star, being closer to its host than Mercury is to the Sun. As a result,
its dayside temperature is a broiling 900°C (1600°F). So life as we know it is
not a possibility for WASP-39b.
But astronomers are interested in it for reasons other than the search for
life. The exoplanet can tell us a lot about how gas giants like it form and evolve
as well as what kind of atmosphere it has. In 2018, scientists used the Hubble
and Spitzer space telescopes to study starlight
sieved through WASP-39b's skies. They
detected a large amount of water vapor -
three times as much as Saturn has. They
decided that the gas giant must have formed
far away from its star, where lots of icy material
would have bombarded it early on.
By the end of the 2010s, scientists could
The exoplanet WASP-39b in an
artist's concept
feel rightly proud of how much they knew
about this far-off giant - a world we can't
even image with our best telescopes.
Then the James Webb Space Telescope secured its own spectrum of WASP39b's
atmosphere (see page 38) - and, as Shannon Hall recounts in her cover
story beginning on page 34, the new data set scientists back on their heels.
Theorists, in particular, felt humbled. JWST's spectra were so exquisitely rich
- revealing a plethora of atoms and molecules along with evidence of active
chemistry and clouds - that their computer models suddenly proved inadequate.
They found themselves confounded by what they saw.
Hall does a masterful job explaining precisely how and why theorists are
laboring to make sense of what JWST is revealing about WASP-39b and other
exoplanets. Using phrases like " to make matters more difficult " and " in reality,
it's not so simple, " Hall guides us through the gauntlet that modelers are running
- and, in so doing, she provides a fascinating look at how science works.
Are the theorists daunted? Not as much as they're jazzed. Scientists are never
so happy as when they have a problem to solve - especially when the problem is
excellent data that need explaining. Here's to some, well,
model remodeling.
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Sky & Telescope - December 2024

Table of Contents for the Digital Edition of Sky & Telescope - December 2024

Contents
Sky & Telescope - December 2024 - Cover1
Sky & Telescope - December 2024 - Cover2
Sky & Telescope - December 2024 - 1
Sky & Telescope - December 2024 - Contents
Sky & Telescope - December 2024 - 3
Sky & Telescope - December 2024 - 4
Sky & Telescope - December 2024 - 5
Sky & Telescope - December 2024 - 6
Sky & Telescope - December 2024 - 7
Sky & Telescope - December 2024 - 8
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Sky & Telescope - December 2024 - 10
Sky & Telescope - December 2024 - 11
Sky & Telescope - December 2024 - 12
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Sky & Telescope - December 2024 - Cover3
Sky & Telescope - December 2024 - Cover4
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