Climate change
Modelling by Peter Buhler, a planetary scientist at
NASA’s Jet Propulsion Laboratory, is attempting to
explain its longevity. Each time Mars warms up,
some of the dry ice remains trapped under the
water ice. The carbon dioxide that does escape is
eventually deposited back on top of the water ice
when temperatures plummet. That leads to the
layering we see. Studying these layers should allow
researchers to more accurately construct a picture
of Mars’ climate stretching back billions of years to
a time when the planet may have been habitable.
Ultimately we may get a better answer to the
question of whether there’s ever been life on Mars.
According to Michael Way from NASA’s Goddard
Institute for Space Studies, it could also help work
out where to land when planning future human
missions to the Red Planet. “They’d definitelywant
to talk to the climate modellers,” he says. “Itcould
tell you where to place your settlements orwhere
the sub-surface water is most likely to be.” Wayand
his colleagues have been adapting NASA’s model
of Earth’s climate and applying it to other bodies
in the Solar System, including Mars. It’s knownas
a general circulation model. “It combines factors
such as ocean circulation, wind circulation,cloud
dynamics and different types of cloud,” Waysays.
“It also estimates how many photons of lightenter
our atmosphere and are absorbed or ref lected.”
Porting this model over to other worlds is notan
easy task. “Applying it to modern Mars is very
challenging,” he says. It should get easier withthe
passage of time as improvements in computing
power allow more intricate models to run ina
shorter amount of time.
If Mars is hard, then modelling Venus’
climate is even tougher. The world called
Earth’s ‘twin’ is an unforgiving hellhole.
Thick clouds of carbon dioxide trap the
Sun’s heat, sending temperatures soaring
beyond 400 degrees Celsius (752 degrees
Fahrenheit). The atmospheric pressure is
nearly one hundred times greater than Earth’s
and over 15,000-times higher than on Mars.That
has severely restricted our ability to land space
missions on Venus. Those that did make it to the
surface succumbed very quickly to the mayhem.
“We have very few data points for Venus,” says Way.
Unlike Mars you can’t just run rovers around, taking
lots of temperature measurements. “Our models
struggle as a result,” he says.
The models that have been devised so far point
to two different possible climatic histories for Venus,
depending on how long the planet’s early magma
ocean hung around. The rocky planets were formed
when lumps of rock and metal called planetesimals
smashed into one another with such ferocity that
the solid materials melted. Being closer to the
Sun, whose light was more intense at the time,
combined with the presence of a hot magma ocean,
created an atmosphere of steam and carbon dioxide.
“The atmospheric pressure would have been one
thousandtimesgreaterthanthe
modernEarth,”saysWay.Amolecule
ofwaterisH2O– twoatomsofhydrogenbonded
tooneatomofoxygen.Ona hotVenusthisbond
wouldhavebeenbrokenregularly.Thehydrogen
islosttospaceandtheoxygenbecomestrapped
insidethemagmaocean.“Ifthat’sthecasethen
Venushasbeena dry,desiccatedworldformostof
thelast 4 billionyears,”saysWay.Thealternative
isthatthemagmaoceanwasa muchshorterlived
phase.“Thenitwouldhavebeencoolenoughto
condensewaterintolakes,riversandoceans,”says
Way.Inotherwords,farmoreEarth-likethantoday.
PerhapstheSolarSystemhadtwohabitableplanets
atthesametime.
Ifit’sthelatterthenVenushasexperienceda
hugechangeinclimateoverthelast 4 billionyears,
largelythankstotheroleofcarbondioxide.Given
ourcurrentclimatepredicamentonEarth,isthereanything we can learn from our neighbour? “It’s
a compelling idea,” says Way, “but it is a difficult
comparison to make.” The driver of Venusian
climate change is largely thought to have been
large-scale volcanism dumping huge quantities of
carbon dioxide into the atmosphere, far more than
we’ve added to the Earth’s since the Industrial
Revolution. “Unlike Venus, the Earth will eventually
adjust to this increase in carbon. We just may not
be around to see it,” Way says.
Along with Venus and Mars, Way and his
colleagues have also secured funding to model
the climate of Titan – Saturn’s largest satellite and
the only moon in the Solar System with a thick
atmosphere. “Titan is interesting as the density of
its atmosphere is only 1.5 times Earth’s,” Way says.
“A lot of its climate dynamics are similar too.” Part
of the attraction of studying Titan is the wealth
of data that came back from the Cassini missionRight: One
day it may
be possible
to engineer
Mars’ climate
to be more
hospitableBelow: The
ESA’s Huygens
probe touched
down on
Saturn’s largest
moon Titan
in 2005What
killed the
dinosaurs?
It’s famously attributedtoan
asteroid impact, whichthr
huge volumes of debrisinto
sky and blocked out theSu
A rapid change followed
which put pressureon
the big lizards.Source: Wikimpedia © Daein BallardSource: Wikimpedia © David Monniauxan
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