Sky and Telescope - September 2018 - 17

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ia

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Mo n s

500 km

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niti

a
Qu etz al p e t l a t l
Corona

270°

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At the end of the day, our toxic twin - which is eerily
similar to our planet in some regards and yet worlds apart
in others - could easily help explain our changing climate,
the initiation of plate tectonics, and what made our world
habitable. "Venus is uniquely positioned and equipped to
give us answers in a way that no other planet that we can
explore can," Grinspoon says. "And yet we've been completely
neglecting it. It's criminal."

ia

Type 1 coronae

A . DAVAILLE E T A L. / NATUR E GEOSCIENCE 2017

upt

adi

Pla

2

p ARTEMIS CORONA This image combines radar (gray) and topographic
(color scale) views of Artemis Corona, a 2,600-km-wide hotspot in Venus's
southern hemisphere. Scientists think coronae form when a large molten
plume wells up from the mantle, fracturing the crust above it and exuding
onto the surface. The weight from the spreading lava bends the underlying crust, forcing it to subduct back into the mantle. This process would
explain the rifts radiating out from the corona and its encircling trench and
buckled terrain. In Artemis's case, there also appear to be several smaller
corona-like features inside the large one.

Themis Regio

len

4

t VOLCANISM Venus has widespread signs of recent (perhaps active)
volcanic activity. Expansive lava flows cover its surface, and giant hotspots
(circled) are the surface manifestations of upwelling mantle plumes. These
can span more than 1,000 km and likely underlie the roughly 500 circular
features called coronae. (Type 1 coronae have concentric rings of cracks.)
Representative features and those mentioned in the article are labeled.

Venera 14

Phoebe Regio

He

t

Elevation (km)

la

Beta
Regio

Plan

en

P

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ch

Sed

ere

Tr

Guinev

Rift

Type 2 coronae

315°

Flow fields

360°

the role we play in those changes. "It's not just an academic
question," Grinspoon says. "Understanding how climate
works on Earth-like planets is now a matter of survival."
If scientists could pinpoint the factors that tipped Venus
away from becoming a habitable world and toward a noxious
one, then they would also be able to pinpoint the factors that
kept Earth on the other course. "We want to know when in
the 4.5 billion years of the history of the solar system, the
destiny of the two planets was written - and when did it
diverge," says Thomas Widemann (Paris Observatory).
Only then can we understand what truly makes a world
habitable. Or as Lori Glaze (NASA Goddard) says: "If we don't
understand that, we don't know what makes Earth Earth."

A Planet Left in the Dust
With so much to learn from our neighboring planet, many
planetary geologists find it inconceivable that NASA hasn't
sent a dedicated mission there since the 1990s. And it's not
like Venus was a one-hit wonder back then. When scientists
first started to explore the solar system, they set their eyes
on Venus. Not only was it the target of our first successful
encounter beyond Earth, but it also was frequently visited
throughout the 1960s and '70s.
But after Magellan, no new probe embraced its skies for
more than 10 years, until European and Japanese orbiters
launched in 2005 and 2010, respectively. So, James Green,
NASA's new Chief Scientist, argues that there are more Venus
missions happening than disgruntled researchers let on. "You
don't have to lead the mission to do Venus science," he says.
sk yandtelescope.com * S E P TE M B E R 2 018

17

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

Contents
Sky and Telescope - September 2018 - Cover1
Sky and Telescope - September 2018 - Cover2
Sky and Telescope - September 2018 - 1
Sky and Telescope - September 2018 - Contents
Sky and Telescope - September 2018 - 3
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