Sky & Telescope - January 2022 - 19

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Chiron
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Gateway
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Average distance from the Sun (astronomical units)
THE ROAD TRAVELED Over time, Centaurs can migrate through the outer solar system to near Jupiter, experiencing more intense sunlight (shown
here as lighter shading) as they travel sunward. Their orbits also circularize (y-axis). The arrow shows the likely path that ATLAS (P/2019 LD2) has taken
in the last few thousand years, and the white dots mark current orbits of the Centaurs Chiron and S-W 1, the latter of which orbits in the so-called
Gateway (purple triangle) and is en route to becoming a Jupiter-family comet. The white contour curves indicate how the amount of solar heating in a
particular orbit compares to that received by a Jupiter-family comet.
should detect Centaurs at sizes that overlap with the observed
JFC sizes in a systematic way that allows us to better estimate
the intrinsic population. The long time scale of the survey
should also help identify brightness variations that indicate
activity, yielding a new set of active Centaurs
that astronomers can then study in more detail
with other observatories.
LSST's increased sensitivity compared to current
surveys should turn up more examples of
Centaurs on the cusp of transitioning to JFCs.
Recent dynamical studies of the Centaur-to-JFC
transition identified a region just exterior to
Jupiter's orbit, dubbed the JFC Gateway, that the
vast majority of inbound JFCs traverse. Gateway
objects have temporary, nearly circular orbits in
between Jupiter and Saturn that allow Jupiter
to scatter them inward. This orbital region,
expected to contain several hundred objects larger than
1 km, coincides with the solar distance at which we expect
significant cometary activity to begin in earnest. The recently
discovered active Centaur ATLAS (P/2019 LD2), which should
enter the JFC population mere decades from now, is likely just
the first of many transitional objects we can look forward to
discovering. These will help us better understand the early
stages of cometary activity.
Future spacecraft missions could also help reveal the
secrets of Centaurs. After the New Horizons mission's initial
exploration of the Kuiper Belt at Pluto and Arrokoth, and
Lucy's upcoming tour of the Jupiter Trojans, the Centaurs
remain a key unexplored outer-solar-system population. In
2019, researchers proposed two missions to Centaurs for
the latest round of NASA Discovery missions.
They were not selected (this time!), but perhaps
Centaurs will fare better in the future, especially
if they are featured in the next decadal
recommendations from the planetary science
community, expected in 2023.
Whether through spacecraft or additional
29P/SchwassmannWachmann
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July 2016 outburst
ground- and space-based observations, exploration
of the Centaurs will continue to provide
critical insights into how primordial icy bodies
formed and are transformed as they journey
into the inner solar system as comets.
¢ KAT VOLK is a planetary scientist at the University of Arizona's
Lunar and Planetary Laboratory. She studies the dynamics
and evolution of small solar-system bodies.
JOIN THE CAMPAIGN: Astronomers have begun a pro-am
campaign to catch as many outbursts from the Centaur 29P/
Schwassmann-Wachmann 1 as they can. Read page 57 of our
September 2021 issue or go to https://is.gd/observing29p
for more information. You'll need access to at least a 6-inch
scope; imaging capabilities are a plus.
sk yand tele scope .o r g * JANUARY 2022 19
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MIGRATION GRAPH: GREGG DINDERMAN / S&T; SOURCE: J. K. STECKLOFF
ET AL. / ASTROPHYSICAL JOURNAL LETTERS 2020; 29P/SCHWASSMANNWACHMANN
1 IN OUTBURST: PEPE MANTECA / CC BY-NC-ND 2.0
Orbital eccentricity (0 is a perfect circle)
Jupiter
Saturn

https://www.is.gd/observing29p https://skyandtelescope.org/

Sky & Telescope - January 2022

Table of Contents for the Digital Edition of Sky & Telescope - January 2022