Sky and Telescope - September 2018 - 21

G EER: N ASA; INFOG R A PHIC: TERRI DUBÉ / S&T; V ENUS: N ASA / JPL- CA LTECH; E A RTH: S&T
ILLUSTR ATION; M A RS: N ASA / GODDA RD SPACE FLIG H T CEN TER SCIEN TIFIC VISUA LIZ ATION
ST UDIO; PA NCA K E DO ME BACKG ROUND: N ASA /JPL

says. "You can go from a habitable environment to a runaway
greenhouse. But you can't go from a runaway greenhouse
back to a habitable environment. It's a one-way street."
But scientists won't know the exact ratio of Venus-like to
Earth-like worlds until they uncover Venus's evolutionary
path. "We have no hope of making sense of those observations without getting a handle on the Venus-Earth dichotomy," Grinspoon says. Nor will scientists know if there are
other key characteristics that might hint at a planet's current
status, allowing them to pour their precious resources into
worlds that are more likely to harbor life.
"The exoplanet community is having a very slow and gradual realization that we can't do this on our own - we need
the planetary-science community," says Kane. And that has
caused some Venus proponents to regain hope. "I think that
constituency is already starting to gather, it may help come to
the rescue of the small-but-determined Venus community,"
Grinspoon says. "I'm still cautiously - perhaps foolishly -
hopeful that NASA will come around."
And he is not alone. "I think it's inevitable that we'll go
back there eventually," Kane says. "But I certainly do hope
that people will see the immense importance of it so that it
can be sooner rather than later."
Until that time comes, U.S. scientists will keep kicking at
Lucy's ball by writing one mission proposal after the next.
And there is some cause for optimism: NASA recently selected
a mission concept called Venus In Situ Composition Investigations (VICI) for further technology development. Meanwhile, the European Space Agency, Russia, and India are all
researching future missions to send to our sister planet.
"Look at the history of Magellan - that didn't get handed
to us at all," says James Head (Brown University), who fought

Avg. surface
temperature
(range)
Diameter

225

Diameter

12,756 km (7,926 mi)

400°C

hard to include the orbiter in Jimmy Carter's campaign and
later in President Reagan's budget. "It was a long, hard slog
to get that mission funded. We just have to keep ﬁghting
because it's the right thing to do."

¢ Freelance science journalist SHANNON HALL was watching
Venus's dark shadow dance across the surface of the Sun six
years ago when her niece was born. So, when she later taught
her niece the names of the planets, Venus was first on the list.
Dive into historic exploration images of Venus's surface:
https://is.gd/venusgallery.

Atmospheric
composition

Atmospheric
pressure

Sidereal day
(Earth units)

Inclination
of equator

(~0)

96 CO2
3.5% N2
<1% Other

-224 : 17

108
million km

92
bars

days hours
(retrograde)

300°C

23.4°

200°C

Year (Earth days)

365

p TO HELL AND BACK
NASA Glenn engineer Kyle
Phillips removes samples
from GEER after they were
exposed to Venus surface
conditions for 80 days.

2.6°
464°C/
867°F

Surface gravity

8.9 (m/s2)

NASA's Glenn Extreme
Environments Rig (GEER)
enables researchers to
simulate various planetary
conditions in a chamber a
little smaller than a refrigerator. Last year, they exposed
various mineral, rock, and
glass samples to Venusian
conditions for 80 days to
see what reactions would
take place. Researchers
have also exposed different
kinds of high-temperature
electronics, some of which
survived, says NASA's Jim
Green. That success might
open the door to small, longlived landers.

500°C

12,104 km (7,521 mi)
Year (Earth days)

Average
distance
from Sun

Venus on Earth

14°C/57°F
100°C

Surface gravity

(-88°C to 58°C
-126°F to 136°F)

150
million km

78% N2
21% O2
1% Other

1
bar

23 : 56
hours

mins

9.8 (m/s2)
0°C

Diameter

6,792 km (4,220 mi)

-100°C

Year (Earth days)

687

-63°C/-81°F

Surface gravity

(-140°C to 30°C
-220°F to 86°F)

3.7 (m/s2)

-200°C

228
million km

96% CO2
<2% Ar
<2% N2

25.2°

0.006
bar

24 : 37
hours

mins

<1% Other

sk yandtelescope.com * S E P TE M B E R 2 018

https://www.is.gd/venusgallery http://www.skyandtelescope.com

Sky and Telescope - September 2018

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