- 4192 -
KUIPER BELT PLANETS
- The Kuiper Belt is the vast
region at the edge of our solar system populated by countless icy objects, is a
treasure trove of scientific discoveries. The detection and characterization of
Kuiper Belt Objects (KBOs), sometimes referred to as Trans-Neptunian Objects
(TNOs), has led to a new understanding of the history of the solar system.
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- Studying bodies in
the outer solar system is one of the many objectives of the James Webb Space
Telescope (JWST). Using data obtained by Webb's Near-Infrared Spectrometer
(NIRSpec), an international team of astronomers observed three dwarf planets in
the Kuiper Belt: Sedna, Gonggong, and Quaoar.
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- These observations
revealed several interesting things about their respective orbits and
composition, including light hydrocarbons and complex organic molecules
believed to be the product of methane irradiation.
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- Despite all of the
advances in astronomy and robotic explorers, what we know about the
Trans-Neptunian Region and the Kuiper Belt is still very limited. To date, the
only mission to study Uranus, Neptune, and their major satellites was the
Voyager 2 mission, which flew past these ice giants in 1986 and 1989, respectively.
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- The New Horizons
mission was the first spacecraft to study Pluto and its satellites in July 2015
and the only one to encounter an object in the Kuiper Belt, which occurred on
January 1st, 2019, when it flew past the KBO known as Arrokoth.
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- In addition to
studying exoplanets and the earliest galaxies in the universe, JWST's powerful
infrared imaging capabilities have also been turned toward our backyard,
revealing new images of Mars, Jupiter, and its largest satellites.
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- The three planetoids
in the Kuiper Belt—Sedna, Gonggong, and Quaoar, are about 620 miles in diameter, which places them
within the designation for “Dwarf Planets”.
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- Other
Trans-Neptunian bodies—like Pluto, Eris, Haumea, and Makemake—have all retained
volatile ices on their surfaces (nitrogen, methane, etc.). The one exception is
Haumea, which lost its volatiles in a large impact (apparently). As Emery said,
they wanted to see if Sedna, Gonggong, and Quaoar have similar volatiles on
their surfaces.
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- Sedna is an inner
Oort Cloud object with perihelion of 76 AU and aphelion of nearly 1,000 AU,
Gonggong is in a very elliptical orbit also, with perihelion of 33 AU and
aphelion 100 AU, and Quaoar is in a relatively circular orbit near 43 AU.
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- These orbits place
the bodies in different temperature regimes and different, irradiation
environments. Sedna spends most of its
time outside the sun's heliosphere.
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- Using data from
Webb's NIRSpec instrument, the team observed all three bodies in low-resolution
prism mode at wavelengths spanning 0.7 to 5.2 micrometers (µm) placing them all
in the near-infrared spectrum. Additional observations were made of Quaoar from
0.97 to 3.16 µm using medium-resolution gratings at ten times the spectral
resolution. The resulting spectra revealed some interesting things about these
TNOs and the surface compositions.
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- We found abundant
ethane (C2H6) on all three bodies, most prominently on Sedna. Sedna also shows
acetylene (C2H2) and ethylene (C2H4). The abundances correlate with the orbit
(most on Sedna, less on Gonggong, least on Quaoar), which is consistent with
relative temperatures and irradiation environments. These molecules are direct
irradiation products of methane (CH4).
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- If ethane (or the
others) had been on the surfaces for a long time, they would have been
converted to even more complex molecules by irradiation. Since we still see
them, we suspect that methane (CH4) must be resupplied to the surfaces fairly
regularly.
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- JWST data of
smaller KBOs cluster into three groups, none of which look like Sedna,
Gonggong, and Quaoar. That result is consistent with our three larger bodies
having a different geothermal history.
- These findings
could have significant implications for the study of KBOs, TNOs, and other
objects in the outer solar system. This includes new insight into the formation
of objects beyond the Frost Line in planetary systems, which refers to the line
beyond which volatile compounds will freeze solid.
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- In our solar
system, the Trans-Neptunian region corresponds to the nitrogen line, where
bodies will retain large amounts of volatiles with very low freezing points
(i.e., nitrogen, methane, and ammonia).
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- These findings
also demonstrate what type of evolutionary processes are at work for bodies in
this region. The primary implication may
be finding the size at which KBOs have become warm enough for interior
reprocessing of primordial ices, perhaps even differentiation.
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- We should also be
able to use these spectra to better understand irradiation processing of
surface ices in the outer solar system. And future studies will also be able to
look in more detail at volatile stability and the possibility for atmospheres
on these bodies over any parts of their orbits.
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- The JWST data
enabled us to get spectra at longer wavelengths than we can from the ground,
which enabled the detection of these ices. Often, when observing in a new
wavelength range, the initial data can be pretty poor quality. JWST not only
opened up a new wavelength range but also provided fantastically high-quality
data that are sensitive to a suite of materials on the surfaces in the outer
solar system.
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October 21, 2023 KUIPER BELT
PLANETS 4192
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Saturday, October 21, 2023 ---------------------------------
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