My first Magazine Sky & Telescope - 01.2019 | Page 54

JANUARY 2019 OBSERVING
Exploring the Solar System by Sean Walker
Mars at Opposition
2016
2018
A Dusty Apparition
Mars was bustling with activity during the close opposition of 2018.
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JA N UA RY 2 019 • SK Y & TELESCOPE
p Mars normally sports high-contrast albedo features and white clouds near opposition (left), but
the global dust storm that erupted in late May 2018 (right) obscured many of the familiar features
around Sinus Meridiani, seen at center in both of these Hubble Space Telescope images.
At the time, the planet had just expe-
rienced equinox days before, with the
north entering autumn while its south
began its long spring. Seasons on Mars
last roughly twice as long as we experi-
ence them here on Earth.
Within days, the storm moved
south and spread out, obscuring most
of Sinus Meridiani, Oxia Palus, and
Margaritifer Sinus. Dust storms are
a double-edged sword, at least from
an observer’s perspective. While it’s
exciting to spot these unpredictable
changes in a telescope, they can often
grow strong enough to encircle the
entire planet, rendering it a featureless,
salmon-hued ball. But on the positive
side, these storms paradoxically can
make hard-to-discern features easily
visible for a short time. For example,
as the storm poured into the great
canyon system of Valles Marineris, it
rendered this normally invisible feature
cutting across Aurorae Sinus visible in
even small telescopes. Amateurs with
telescope apertures as small as 6 inches
were able to clearly resolve the dust-
choked valleys as conditions permitted
in early June.
For several weeks, the storm grew to
global proportions, completely encir-
cling the planet in the north, while
some albedo features remained visible
in the south, particularly in the region
of Mare Cimmerium. Glimpses of Syrtis
Major were had throughout late June
and into early July. The South Polar
Cap, hidden from view by its seasonal
M
ars continues to grace the eve-
ning skies, long past its perihelic
opposition last July. Although the Red
Planet has shrunk to a diminutive 7.4
arcseconds diameter, at the time of this
writing in mid-October it’s still show-
ing off lots of detail in the eyepiece.
That wasn’t the case in the months
before its closest approach in 15 years.
As the planet was poised to put on a
great show for observers at opposition
with a respectable disk size of 24.3
arcseconds, its atmosphere had other
plans, at least for a while.
When the planet was transitioning
from a morning to an evening target in
the last days of May, observers spotted
a yellowish dust storm over the dark
albedo feature Mare Acidalium. While
Martian dust storms are not an uncom-
mon occurrence, they most often tend
to kick up during the summer months
in the planet’s Southern Hemisphere.