Editor’s Note: This post highlights data from Webb science in progress, which has not yet been through the peer-review process.
Image of Saturn and some of its moons, captured
by the James Webb Space Telescope’s NIRCam instrument on June 25, 2023. In this
monochrome image, NIRCam filter F323N (3.23 microns) was color mapped with an
orange hue. Download the
full-resolution image, both labeled and unlabeled, from the Space Telescope
Science Institute. Credits:
NASA, ESA, CSA, STScI, M. Tiscareno (SETI Institute), M. Hedman (University of
Idaho), M. El Moutamid (Cornell University), M. Showalter (SETI Institute), L.
Fletcher (University of Leicester), H. Hammel (AURA); image processing by J.
DePasquale (STScI)
On June 25, 2023, NASA’s James Webb Space Telescope turned to famed ringed
world Saturn for its first near-infrared observations of the planet. The
initial imagery from Webb’s NIRCam (Near-Infrared Camera) is already
fascinating researchers.
Saturn itself appears extremely dark at this infrared wavelength observed
by the telescope, as methane gas absorbs almost all of the sunlight falling on
the atmosphere. However, the icy rings stay relatively bright, leading to the
unusual appearance of Saturn in the Webb image.
This image was taken as part of Webb Guaranteed Time Observation program 1247. The program
included several very deep exposures of Saturn, which were designed to test the
telescope’s capacity to detect faint moons around the planet and its bright
rings. Any newly discovered moons could help scientists put together a more
complete picture of the current system of Saturn, as well as its past.
This new image of Saturn clearly shows details within the planet’s ring
system, along with several of the planet’s moons – Dione, Enceladus, and
Tethys. Additional deeper exposures (not shown here) will allow the team to
probe some of the planet’s fainter rings, not visible in this image, including
the thin G ring and the diffuse E ring. Saturn’s rings are made up of an array
of rocky and icy fragments – the particles range in size from smaller than a
grain of sand to a few as large as mountains on Earth. Researchers recently
used Webb to explore Enceladus, and found a large plume jetting from the
southern pole of the moon that contains both particles and plentiful amounts of
water vapor – this plume feeds Saturn’s E ring.
Saturn’s atmosphere also shows surprising and unexpected detail. Although
the Cassini spacecraft observed
the atmosphere at greater clarity, this is the first time that the planet’s
atmosphere has been seen with this clarity at this particular wavelength (3.23
microns), which is unique to Webb. The large, dark, diffuse structures in the
northern hemisphere do not follow the planet’s lines of latitude, so this image
is lacking the familiar striped appearance that is
typically seen from Saturn’s deeper atmospheric layers. The patchiness is
reminiscent of large-scale planetary waves in the stratospheric aerosols high
above the main clouds, potentially similar to those seen in early Webb NIRCam
observations of Jupiter.
When comparing the northern and southern poles of the planet in this image,
the differences in appearance are typical with known seasonal changes on
Saturn. For example, Saturn is currently experiencing northern summertime, with
the southern hemisphere emerging from the darkness at the end of a winter.
However, the northern pole is particularly dark, perhaps due to an unknown
seasonal process affecting polar aerosols in particular. A tiny hint of
brightening towards the edge of Saturn’s disk might be due to high-altitude
methane fluorescence (the process of emitting light after absorbing light),
emission from the trihydrogen ion (H3+) in the
ionosphere, or both; spectroscopy from Webb could help confirm this.
Missions like NASA’s Pioneer 11, Voyagers 1 and 2, the Cassini spacecraft, and
the Hubble Space Telescope have
tracked Saturn’s atmosphere and rings for many decades. These observations from
Webb are just a hint at what this observatory will add to Saturn’s story in the
coming years as the science team delves deep into the data to prepare
peer-reviewed results.
Science Credits
NASA, ESA, CSA, STScI, Matt Tiscareno (SETI Institute), Matt Hedman (University
of Idaho), Maryame El Moutamid (Cornell University), Mark Showalter (SETI
Institute), Leigh Fletcher (University of Leicester), Heidi Hammel (AURA)
Image Processing Credits
J. DePasquale (STScI)
About the Authors
- Heidi B. Hammel is a Webb interdisciplinary scientist leading Webb’s
Cycle 1 Guaranteed Time Observations (GTO) of the solar system. She is the
vice president for science at the Association of Universities for Research
in Astronomy (AURA) in Washington, D.C.
- Leigh Fletcher is a professor of planetary science at the University
of Leicester in England. Leigh is the principal investigator for several
of Webb’s Guaranteed Time Observation Programs, including Program 1247
highlighted here.
- Matt Tiscareno is a Senior Research Scientist at the SETI Institute,
California, where he studies the dynamics of planetary systems, including
planetary rings. He is an integral member of the Webb Guaranteed Time
Observation team for the study of Saturn.
Unannotated Version of Image:
Source: Saturn’s Rings Shine in Webb’s Observations of Ringed Planet – James Webb Space Telescope (nasa.gov)
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