Sky and Telescope - September 2018 - 20

The Case for Venus

q TESSERA TERRAIN Radar-bright and roughly textured, Fortuna Tessera and other tesserae have strange cracks and wrinkle-ridge folds. Lava
plains infiltrating the tessera's cracks indicate the fractured terrain is older.
Scientists aren't sure how tessera terrain formed.

S E P TE M B E R 2 018 * SK Y & TELESCOPE

t GROUND TRUTH Donald Mitchell
remapped and combined a spherically
projected Venera 14 panorama to create
this more intuitive view of the Venusian
surface. The spacecraft landed just south
of the equator, near the border of Phoebe
Regio and Navka Planitia.

But it doesn't have to be an
either-or endeavor. Many Venus
researchers say that there are
fundamental questions about our
neighboring planet that could be answered with the technology available today - even if those missions might not survive for long. "To say that we can't get to the surface of Venus
is just hogwash," Dyar says.
Finally, many planetary scientists argue that Mars has a
romantic appeal that Venus will never possess (despite the fact
that it's named after the Roman goddess of love and beauty).
Not only is Mars a world that might host evidence of past
life, but it also might host humans in the future, as we settle
on the Red Planet or use it as a stepping stone as we venture
outward beyond Earth. The same cannot be said of Venus.

All Hope Is Not Lost
But the tides might be turning. Despite the shrinking constituency of Venus scientists, a counter-trend seems to be
building within the ballooning ﬁeld of exoplanet astronomy.
There, researchers have uncovered thousands of planets
around other stars, dozens of which are Earth-size and in
their star's habitable zone. But because most observations
often only reveal a planet's size and distance from its host
star - and Venus and Earth are essentially twins in these
respects - there is no way
to determine whether these
THREE WORLDS Although
planets are true Earth anaVenus and Earth have similar
logs or if they're more akin
sizes, Mars is more akin to our
planet in terms of temperature,
to our hellish sister.
day length, and axial tilt. Mars
As such, many argue that
and Venus both have carbon
we must better understand
dioxide-dominated atmoVenus if we wish to better
spheres - but Venus has a lot
interpret exoplanets. "If
more CO2.
we really are interested in
studying Earth-size planets,
then we need to go to the
Venus
exoplanet laboratory right
Earth
next door, which is Venus,"
says exoplanet astronomer
Stephen Kane (University
of California, Riverside).
To boot, there might
simply be far more Venus
analogs than Earths. "It's
quite possible that Venus is
actually the end-state of all
Mars
terrestrial planets," Kane

V ENER A 14: DON A LD MITCHELL A ND Y URI G EK TIN;
TESSER A E: N ASA / JPL / M A PA PL A NE T.ORG / EMILY L A K DAWA LL A

search for life is still a high priority. Take the two mission proposals that were accepted last December for the ﬁnal assessment round.
Instead of exploring lifeless Venus,
Zurbuchen opted for studying a
ﬂying rotorcraft that would investigate the geology and prebiotic
chemistry on Saturn's largest
moon, Titan - which is thought
to be a great place for testing ideas
on how life arose on Earth - and a craft to return samples
from the nucleus of Comet 67P/Churyumov-Gerasimenko
(S&T: May 2017, p. 14), whose primordial cousins might have
delivered the essential building blocks of life to Earth. There's
no doubt that NASA has stayed true to its mantra.
Additionally, many Venusian critics argue that the current technology favors visits to Mars over infernal Venus.
The Red Planet won't melt lead, so rovers and landers placed
there have lifespans measured not in hours but in years.
Grinspoon thinks that could be a factor in the slew of Venus
mission rejections. "I believe there's a psychological bias that
we're not going to select a mission that essentially takes an
hour's worth of science data - no matter how important that
data is, no matter how vital the questions are that could be
addressed," he says. The other missions will seem like they
give a bigger bang for one's buck.
To be clear, no one is saying that NASA should stop going
to Mars. "One thing you'll never hear me do is put down the
cause of Mars exploration," Grinspoon adds. "It's just fantastic what we've learned."

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Sky and Telescope - September 2018

Table of Contents for the Digital Edition of Sky and Telescope - September 2018