Neptune is cooler than we thought: Study reveals unexpected changes in atmospheric temperatures
Date:
April 11, 2022
Source:
University of Leicester
Summary:
New research has revealed how temperatures in Neptune's atmosphere
have unexpectedly fluctuated over the past two decades.
FULL STORY ==========================================================================
New research led by space scientists at the University of Leicester
has revealed how temperatures in Neptune's atmosphere have unexpectedly fluctuated over the past two decades.
==========================================================================
The study, published today (Monday) in Planetary Science Journal, used observations in thermal-infrared wavelengths beyond the visible light
spectrum, effectively sensing heat emitted from the planet's atmosphere.
An international team of researchers, including scientists from Leicester
and NASA's Jet Propulsion Laboratory (JPL), combined all existing thermal infrared images of Neptune gathered from multiple observatories over
almost two decades.
These include the European Southern Observatory's Very Large Telescope
and Gemini South telescope in Chile, together with the Subaru Telescope,
Keck Telescope, and the Gemini North telescope, all in Hawai'i, and
spectra from NASA's Spitzer Space Telescope.
By analysing the data, the researchers were able to reveal a more complete picture of trends in Neptune's temperatures than ever before.
But to the researchers' surprise, these collective datasets show a
decline in Neptune's thermal brightness since reliable thermal imaging
began in 2003, indicating that globally-averaged temperatures in Neptune's stratosphere -- the layer of the atmosphere just above its active weather
layer -- have dropped by roughly 8 degrees Celsius (14 degrees Fahrenheit) between 2003 and 2018.
Dr Michael Roman, Postdoctoral Research Associate at the University
of Leicester and lead author on the paper, said: "This change was
unexpected. Since we have been observing Neptune during its early
southern summer, we would expect temperatures to be slowly growing warmer,
not colder."
========================================================================== Neptune has an axial tilt, and so it experiences seasons, just like Earth.
However, given its great distance from the Sun, Neptune takes over 165
years to complete an orbit around its host star, and so its seasons
change slowly, lasting over 40 Earth-years each.
Dr Glenn Orton, Senior Research Scientist at JPL and co-author on the
study, noted: "Our data cover less than half of a Neptune season,
so no one was expecting to see large and rapid changes." Yet, at
Neptune's south pole, the data reveal a different and surprisingly
dramatic change. A combination of observations from Gemini North in
2019 and Subaru in 2020 reveal that Neptune's polar stratosphere warmed
by roughly 11?C (~20?F) between 2018 and 2020, reversing the previous globally-averaged cooling trend. Such polar warming has never been
observed on Neptune before.
The cause of these unexpected stratospheric temperature changes is
currently unknown, and the results challenge scientists' understanding
of Neptune's atmospheric variability.
==========================================================================
Dr Roman continued: "Temperature variations may be related to seasonal
changes in Neptune's atmospheric chemistry, which can alter how
effectively the atmosphere cools.
"But random variability in weather patterns or even a response to the
11-year solar activity cycle may also have an effect." The 11-year solar
cycle (marked by periodic variation in the Sun's activity and sunspots)
has been previously suggested to affect Neptune's visible brightness,
and the new study reveals a possible, but tentative, correlation between
the solar activity, stratospheric temperatures, and the number of bright
clouds seen on Neptune.
Follow-up observations of the temperature and cloud patterns are needed
to further assess any possible connection in the years ahead.
Answers to these mysteries and more will come from the James Webb Space Telescope (JWST), which is set to observe both ice giants, Uranus and
Neptune, later this year.
Leigh Fletcher, Professor of Planetary Science at the University of
Leicester, will lead such observations with allocated time of JWST's
suite of instruments.
Professor Fletcher, also a co-author on this study, said: "The exquisite sensitivity of the space telescope's mid-infrared instrument, MIRI,
will provide unprecedented new maps of the chemistry and temperatures
in Neptune's atmosphere, helping to better identify the nature of these
recent changes." This study was funded by a European Research Council
grant to the University of Leicester, known as GIANTCLIMES. This project
has previously discovered long- term changes in atmospheric temperatures
and clouds on the gas giants, Jupiter and Saturn, and it provided the
first maps of the stratospheric temperatures of Uranus. GIANTCLIMES has
paved the way for new discoveries on all four giant planets from JWST
in the years to come.
Additional co-authors on this work include Thomas Greathouse (Southwest Research Institute), Julianne Moses (Space Science Institute), Naomi
Rowe- Gurney (Howard University / NASA Goddard Space Flight Center),
Patrick Irwin (Oxford), Arrate Antun~ano (UPV/EHU), James Sinclair (JPL), Yasumasa Kasaba (Tohoku University), Takuya Fujiyoshi (Subaru Telescope),
Imke de Pater (UC Berkeley), and Heidi Hammel (Association of Universities
for Research in Astronomy).
'Sub-Seasonal Variation in Neptune's Mid-Infrared Emission' is published
in Planetary Science Journal.
========================================================================== Story Source: Materials provided by University_of_Leicester. Note:
Content may be edited for style and length.
========================================================================== Related Multimedia:
* Images_of_Neptune ========================================================================== Journal Reference:
1. Michael T. Roman, Leigh N. Fletcher, Glenn S. Orton, Thomas K.
Greathouse, Julianne I. Moses, Naomi Rowe-Gurney, Patrick
G. J. Irwin, Arrate Antun~ano, James Sinclair, Yasumasa Kasaba,
Takuya Fujiyoshi, Imke de Pater, Heidi B. Hammel. Subseasonal
Variation in Neptune's Mid- infrared Emission. The Planetary
Science Journal, 2022; 3 (4): 78 DOI: 10.3847/PSJ/ac5aa4 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/04/220411101321.htm
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