Sky & Telescope - August 2020 - 38

Volcanism, Part II

Piccard Mons. Wright Mons is 155 km
across and 4 km high, with a pit some
45 km wide on top. Piccard Mons is
somewhat larger, but New Horizons
was unable to resolve its topography
as clearly. Concentric rings surround
both mountains' crowning depressions, which could be a sign of collapse
after cryomagma erupted. Although
the interpretation is still tentative,
these two structures are the best
candidates for cryovolcanic structures
on Pluto.
We know of potential cryovolcanoes
on Saturn's moon Titan, too, found
thanks to the Cassini spacecraft's radar instrument, which
penetrated Titan's smog-like haze to image about half of the
surface. The best example is a mountain called Doom Mons,
which is more than 1 km high and adjacent to a depression
more than 1 km deep called Sotra Patera. Sotra is an irregularly shaped pit rather than a circular depression, making it
unlikely that it is an impact crater. Giant features that look
like thick ﬂows emerge from Doom Mons and spread over
some 200 km. Based on spectra, these candidate cryovolcanic
ﬂows and Doom Mons itself both have a different composition than the surrounding regions, which are blanketed by
sand dunes. There are even hints that the region could still be
active, or at least venting gases from the interior: The Doom
Mons area doubled in brightness from 2005 to 2006, possibly

ROSALY LOPES is a senior research scientist at NASA's
Jet Propulsion Laboratory, Caltech. She was a member of the
Galileo and Cassini missions and studies volcanoes on Earth,
Io, Titan, and anywhere else she can find them.

S WRIGHT MONS Just south of Sputnik Planitia on Pluto sits this mountain. The giant depression on its summit appears to reach as deep as the
mountain is high - which is on par with Mauna Kea in Hawai'i.

S DOOM MONS Scientists combined radar and infrared spectrometry
data from the Cassini spacecraft to construct this view of the landscape
around Titan's Doom Mons and the pit at its side, Sotra Patera. Colors
mark different compositions: Blue is the surrounding sand dunes, while
the green and yellow regions are covered by material that appears to be
cryovolcanic in origin.

AUGUST 2 02 0 * SK Y & TELESCOPE

W TETHYS The vast crater Odysseus (some
450 km wide) mars the bright surface of this
icy Saturnian moon. An impact this size could
have shattered a solid body. That, combined
with the crater's subdued features, suggests
the moon was slushy when Odysseus formed.

TE TH YS: N ASA / JPL / SPACE SCIENCE INSTIT U TE; WRIG H T M ONS: N ASA
/ JHU A PL / SWRI; DOO M M ONS ON TITA N: N ASA / JPL- CA LTECH / USGS /
UNIVERSIT Y OF ARIZONA

due to erupted gas freezing and covering the ground in frost. Unfortunately,
Cassini did not detect a thermal glow,
so we have no "smoking gun."
Several other icy bodies in the solar
system show signs that cryovolcanism
has occurred there, from Jupiter's
Ganymede to Pluto's companion
Charon. Even the dwarf planet Ceres
in the asteroid belt has a lone mountain, Ahuna Mons, that
may have grown to its 4-kilometer height when a giant bubble
of muddy, salty water pushed up from below. Although the
furthest object ever explored, the Kuiper Belt object Arrokoth, does not show evidence of cryovolcanism, it is possible
that larger Kuiper Belt objects such as Eris might. As we keep
exploring, we will learn more about this still unfamiliar type
of volcanism and how it affects the evolution of surfaces in
the far reaches of the solar system.

Sky & Telescope - August 2020

Table of Contents for the Digital Edition of Sky & Telescope - August 2020