Huygens Herschel Russell Jeffreys Kuiper Laplace Bessel BarnardB Ring Cassini Division A RingThey found that if the Sun had been
a fast rotator, with all the solar activity
that implies, there shouldn’t be any
potassium at all left in lunar samples.
The fact that there is means our Sun
was likely a quiet youngster, rotating
more slowly than the average star. But
the team can’t pinpoint exactly how
slowly the Sun rotated because it’s notclear how volatile-depleted the Moon’s
rocks were to begin with. Theories
about the event that formed the Moon
and its effect on volatiles still disagree.SPIN EFFECT
Regardless, the Sun did rotate faster
— some nine to 10 days per rotation,
instead of today’s 27-day average —
during the solar system’s first few
hundred million years. That means the
young Moon and planets were subject
to more solar activity than they endure
today. That’s likely the period when
Venus lost its hydrogen, and Mars
lost its atmosphere and then water.
Even Earth likely lost its first, thinner
atmosphere, until it made a new one
from volcanic gases, dense enough to
survive the Sun’s harsh activity with the
help of our planet’s magnetic field.
As NASA plans return visits to the
Moon, lunar scientists hope for more
samples from across the surface and
deep underground to learn more about
the early history of the solar system.
— KOREY HAYNESEND OF AN ERA
NASA’s Spitzer Space Telescope,
launched in 2003 to study the
infrared sky, will be permanently
retired January 30, 2020.METEOR CLOUDS
Vaporized space rocks can kick-
start cloud formation on Mars,
new research finds. Because
ancient Mars was pummeled by
meteorites, the discovery has
implications for the Red Planet’s
past water cycle.RING IT IN
ALMA spotted a never-before-
seen ring of cool hydrogen gas
wrapped around the Milky Way’s
central supermassive black hole,
providing fresh insight into how
black holes accrete matter.WRECKING BALL
A ball of dark matter may have
plowed through a line of stars
streaming around the Milky Way,
disrupting them. If confirmed, this
suggests dark matter is “cold,”
meaning it’s heavy, relatively slow
moving, and clumps together.MYSTERIOUS MASS
Scientists have discovered an
enormous mass of dense material,
possibly the remains of an
asteroid, buried a half-mile
(0.8 kilometer) under the Moon’s
largest, oldest impact feature: the
South Pole-Aitken Basin.BEWARE SUPERFLARES
Data indicate that every few
thousand years, the Sun should
emit “superflares” at least 100
times stronger than the 1859
Carrington Event, which wreaked
havoc on telegraph lines across
North America and Europe.SALTED MOON
Europa’s underground ocean is
brimming with table salt, finds a
new study. Scars on the moon’s
chaotic Tara Regio could allow
salty water to seep through cracks
in the crust. — JAKE PARKSQUICK
TAKE S
WWW.ASTRONOMY.COM 11
IN THE ROCKS. Samples of the lunar surface,
such as this rock brought back by Apollo 16
astronauts, allow scientists to estimate our
Sun’s activity levels during the solar system’s
early years. NASA/JSCNASA/JPL/
SS
I/DIA
GRAMBYEMILYLAKDAWAL
LAFrench astronomer Giovanni Cassini
discovered the division in 1675 through a 2½-inch
telescope at the Paris Observatory.FAST FACT
HIDDEN RINGS.
Through amateur
telescopes,
Saturn’s Cassini
Division looks
like a void. But
from 620,
miles (1 million
kilometers) away,
the Cassini space-
craft imaged
a number of
faint rings and
gaps within it.
In 2009, the
International
Astronomical Union announced
eight new names for the gaps in the
Cassini Division. — MICHAEL E. BAKICHCASSINI DIVISION DETAILS