Sky and Telescope - February 2017 - 11

SOLAR SYSTEM

More Evidence for
Volcanoes on Venus

Flank flows

Main
flow

PLANETARY SCIENTISTS haven't yet

V ENUS: N ASA / ESA / DLR; TR A NS-NEPT UNIA N: N ASA

witnessed an active volcano on Venus,
but they have little doubt that eruptions
occur there. NASA's Magellan orbiter,
which used radar to map the planet's
surface in the early 1990s, found lots
of fresh-looking flows. Years later, ESA's
Venus Express found several hot spots
that came and went. And both Venus
Express and NASA's Pioneer Venus
Orbiter detected surges in the atmosphere's level of sulfur dioxide (SO2), a
gas likely released during eruptions.
Now a new study pinpoints a likely
set of still-warm lava flows on the
slopes of Idunn Mons, a massive volcano in the planet's southern hemisphere that's about 200 km across and
2½ km tall. In 2006 and 2007, Venus
Express detected excess heat coming
from the mountain's eastern flank, but
the atmosphere's opaque clouds blocked
any direct view from orbit.
A team led by Piero D'Incecco (German Aerospace Center, Cologne) dove
into the Magellan archives to identify

Artist's concept of a
trans-Neptunian object.

SOLAR SYSTEM

Retrograde Rock
"Stands Up" in Orbit
THE RECENTLY DISCOVERED object

471325 (formerly 2011 KT19) hints that
a distinct new class of high-inclination
Centaurs lurks in the distant solar system. Centaurs are objects whose orbits

Idunn
Mons

50 km

S Radar-brightness maps from NASA's Magellan orbiter, acquired in 1990-92, reveal several
fresh-looking flows on the summit and eastern flank of Venus's Idunn Mons.

high-resolution radar maps of Idunn
Mons. The researchers identified five
distinct lava flows: an extensive one that
blankets the summit, and four others
that trail down the mountain's eastern
flank. All five look fresh. The team first
modeled how much heat could be radiating from each flow, then determined
that a combination of three flows on
the eastern flank (outlined with purple,
blue, and orange in the map above)
matches the heat distribution best.
These flows also appear to be superimposed on other slope features, suggesting
they're the most recent additions.

D'Incecco reported these findings
during October's joint meeting of the
European Planetary Science Congress
and the American Astronomical Society's Division for Planetary Sciences.
So what will it take to prove that
volcanoes on Venus continue to spout
off? More capable spacecraft - and
luck. Some European scientists hope
to launch an orbiter called EnVision in
2025, while a NASA-sponsored team
has proposed an orbiter called Veritas
that could start high-resolution radar
mapping in 2021.

cross those of one or more outer planets. They generally lie between Jupiter
and the Kuiper Belt.
Observers with the Catalina Sky
Survey first spotted 471325 in 2011.
It turned up again last year in images
taken in the constellation Serpens
Caput with the Pan-STARRS 1 telescope
in Hawai'i. Based on its 22nd-magnitude brightness, this object should be
70 to 200 km in diameter - at most
one-sixth the diameter of Pluto's large
moon, Charon.
But it's the orbit derived by Ying-Tung
Chen (Academia Sinica, Taiwan) and
others that shows what a strange little
world this is. Reported in the August
20th Astrophysical Journal Letters, the
unusual, 212-year circuit takes 471325
inside the orbit of Neptune and out
to just inside the aphelion of Pluto.
Furthermore, the orbit's inclination to

the ecliptic is 110°, nearly perpendicular
to the plane of the major planets' orbits
around the Sun. The object loops around
our star in a slow retrograde orbit - one
moving "backward" with respect to the
motions of the major planets.
Just one other known trans-Neptunian object has a retrograde orbit: 2008
KV42, whose path is inclined 103°. These
two objects - along with four other
small Centaur asteroids in prograde
orbits - share a common orbital plane.
Based on simulations, Chen's team
calculates that the likelihood of getting
all six objects in the same orbital plane
is only 0.016% - and the alignment
isn't stable, since orbital precession
should scatter these objects in just a few
million years. Dynamicists don't know
what sort of mechanism is keeping
these objects in the same plane.

■ J. KELLY BEATTY

■ DAVID DICKINSON

s k y a n d t e l e s c o p e .c o m

* FEBRUARY 2017

11


http://www.skyandtelescope.com

Sky and Telescope - February 2017

Table of Contents for the Digital Edition of Sky and Telescope - February 2017

Contents
Sky and Telescope - February 2017 - Cover1
Sky and Telescope - February 2017 - Cover2
Sky and Telescope - February 2017 - 1
Sky and Telescope - February 2017 - Contents
Sky and Telescope - February 2017 - 3
Sky and Telescope - February 2017 - 4
Sky and Telescope - February 2017 - 5
Sky and Telescope - February 2017 - 6
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