Sky & Telescope - December 2019 - 26

Red Planet Forecast

can dramatically affect the planet's surface and atmospheric
signiﬁcantly shorter than the duration of southern winter:
temperatures. Scientists can monitor storms on all these
154 Martian days versus 178, where a Martian day, or sol,
scales using telescopes, orbiters, and surface landers and
lasts 24 hours and 39 minutes.
rovers. These instruments measure the way that the storms
The large increase in solar energy input during southern
create and move clouds of both dust and water ice. They also
spring and summer increases the average surface temperahelp us study the way that movement of dust and sand can
ture, driving stronger daily winds, fueling more frequent
change the surface albedo over time.
storms, and helping to occasionally raise surface temperaDespite some superﬁcial similarities to terrestrial storms,
tures at latitudes near the equator above the freezing point of
however, Martian storms are signiﬁcantly different from the
water. Conversely, the long polar nights during each hemikinds of storms that we are used to. For example, even though
sphere's winter season enable the surface temperatures to
the planet's dust devils and dust storms can spin or move
drop low enough (down to around −125°C) for up to about
across the surface with hurricane-like wind speeds, the force
1 meter (3 feet) of those famous CO2 snow and ice deposits
exerted by those winds is extremely weak because the planet's
to accumulate. Sadly, the physics of dry ice and even water ice
atmosphere is so thin. Indeed, even the most
at Mars polar temperatures and pressures means
extreme Martian storms, with wind speeds of
that traditional skiing or sledding isn't possible;
Midday
Temperatures
up to about 180 kph (112 mph), would feel to us
fans of such winter sports will have to ﬁnd other
on Mars
like a gentle breeze of around 21 kph (13 mph).
pastimes, or invent new Mars-speciﬁc equipment
Astronauts' heads would
That might disappoint those of us who imagtechnologies to feed their passions.
be about 20° colder than
ine our neighboring planet's tempests clobbering
their feet.
the surface like in the famous sandstorm scene
Uniquely Martian Storms
early in the movie The Martian. Although the
Just like on Earth, storms represent an important
-30ºC
storm provided a dramatic introduction to the
component of Martian weather on daily and
ﬁlm's compelling "human vs. nature" theme,
seasonal time scales. Storms on Mars come in
it's actually pure ﬁction. Rather than ﬁghting
a range of sizes, from small house-size vortices
intensely blowing sand and ﬂying debris ripped
comparable to terrestrial dust devils, to larger
off their habitats, astronauts like Matt Damon's
city-size moving walls of dust similar in some
character, Mark Watney, would instead have
ways to terrestrial desert haboobs, to large-scale
experienced something more like fast-moving
fronts that travel across major fractions of the
-10ºC
feathers or dandelion seeds "pummeling" their
surface, to fully planet-encircling systems that

Dust devil

26

D EC E M B E R 2 019 * SK Y & TELESCOPE

ASTRON AU T ICON: A RTEM KOV YA ZIN / THE NOUN PROJECT;
MID -DAY TEMPER AT URES: TERRI DUBÉ / S&T;
DUST DE VIL: N ASA / JPL / MSSS

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Sky & Telescope - December 2019

Table of Contents for the Digital Edition of Sky & Telescope - December 2019
