Sky & Telescope - September 2020 - 19

u EARTH (Top) Klyuchevskaya is the tallest and most active volcano on
the Kamchatka Peninsula of eastern Russia. It emitted this small plume
on January 10, 2018. The volcano has erupted more than 100 times in
the past 3,000 years.
u VENUS (Middle) Overlapping lava flows cover the flanks of Sapas
Mons and extend for hundreds of kilometers in this radar image. The
summit's two flat-topped mesas appear dark.
u MARS (Bottom) This mosaic shows Olympus Mons, the largest known
volcano in the solar system. It is more than twice as tall as Mount Everest.

orlds

The Red Planet is similarly endowed with shield volcanoes
and vast lava plains. It has two enormous volcanic provinces,
Tharsis and Elysium. It's within Tharsis that the biggest
shield volcanoes in the solar system are situated - with the
largest of them, Olympus Mons, rising to a summit elevation
of almost 22 km (14 miles). Expansive lava plains cover much
of the northern third of the planet. Some of these plains
formed in the last few hundred million years, but even the
very oldest terrains in the south likely also have a volcanic
origin. Indeed, Mars's volcanic record suggests a protracted
history of eruptions, both effusive and explosive, from
almost 4 billion years ago through as recently as the last few
million years.
Comparing these three worlds, we find some striking similarities. Volcanic activity has played a major role in shaping
their surfaces, has persisted for billions of years, and is widespread. Shield volcanoes and other types of edifices are the
rule, not the exception. These planets are clearly variations
on the same pattern. But as similar as these three surfaces
are, they paint a very different picture than those of Mercury
and the Moon, in terms of not only types but also distributions and ages of volcanic landforms.

E A RTH: JOSHUA STE V ENS A ND JEFF SCHM A LT Z / N ASA E A RTH
OBSERVATORY; V ENUS: N ASA / JPL; M A RS: N ASA / JPL / USGS

Exploring the Innermost Planet
It's hard to explore Mercury. Nestled deep in the Sun's gravity well, and orbiting too close to our star to safely point
a telescope at for very long, the innermost planet was the
last of the five rocky worlds to be visited with a flyby during
the opening act of our exploration of the inner solar system. When NASA's Mariner 10 spacecraft finally flew past
Mercury thrice in 1974 and 1975, it returned images of an
ancient, impact-scarred, and geologically dormant planet.
Then NASA's Messenger (Mercury Surface, Space Environment, Geochemistry, and Ranging) mission flew past
Mercury in 2008 and 2009 before entering orbit in 2011. The
craft's observations dramatically improved our understanding of the planet. Chief among Messenger's discoveries was
sk yandtelescope.org * SEP TEMBER 2 02 0

19



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Sky & Telescope - September 2020

Table of Contents for the Digital Edition of Sky & Telescope - September 2020

Contents
Sky & Telescope - September 2020 - Cover1
Sky & Telescope - September 2020 - Cover2
Sky & Telescope - September 2020 - 1
Sky & Telescope - September 2020 - Contents
Sky & Telescope - September 2020 - 3
Sky & Telescope - September 2020 - 4
Sky & Telescope - September 2020 - 5
Sky & Telescope - September 2020 - 6
Sky & Telescope - September 2020 - 7
Sky & Telescope - September 2020 - 8
Sky & Telescope - September 2020 - 9
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Sky & Telescope - September 2020 - Cover3
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