ASTRONEWS
Diameter of all planets combined
248,982 miles (400,698km)Distance between Earth and the Moon
238,856 miles (384,402km)Jupiter Earth MoonSun’s diameter
864,576 miles (1,391,400 kilometers)
Saturn
NeptuneUranus
EarthVenusMars
MercuryTHE AMAZING COLOSSAL SUN
The Sun’s mass accounts
for 99.86 percent of all
mass in the solar system.Compared to each of us as an individual, Earth is big. Really big. But even in the setting
of our planetary system — to say nothing of the universe as a whole — Earth is quite
tiny. Take the word solar, as in solar system. It comes from sol, the Latin name for the Sun.
And when we consider our star and its system of planets, moons, asteroids, and comets,
nothing comes close to matching the size of the Sun in any way. — Michael E. BakichEIGHT ISN’T ENOUGH. The diameters of all eight planets combined (left) don’t come
close to matching the diameter of the Sun. Even the space between Earth and the Moon
(above) would span only slightly more than a quarter of the solar disk. ASTRONOMY: ROEN KELLYFAST
FAC T14 ASTRONOMY • SEPTEMBER 2017
After 20 years, Cassini is working through
its final chapter and is in the process of
completing 22 dives through the space
between Saturn and its rings before
plunging to its death in September.
During the first dive, the team was pre-
pared to use Cassini’s round antenna as
a shield, but surprisingly did not need
to use it. Scientists were amazed by how
little dust the craft encountered in the
1,200-mile-wide (2,000km) area, but they
counted it as a lucky break that Cassini
wouldn’t have to endure the treacherous
conditions for which they had prepared.
Images from Cassini’s first dive on
April 26 were stitched into a movie to get
a better look at what the spacecraft saw
as it passed through. The video, which
can be viewed at http://www.nasa.gov/feature/
jpl/new-movie-shows-cassinis-first-dive-
over-saturn, shows a closer look at the
vortex at Saturn’s north pole and itshexagon-shaped jet stream.
“I was surprised to see so many sharp
edges along the hexagon’s outer bound-
ary and the eye-wall of the polar vortex,”
said Kunio Sayanagi, an associate of the
Cassini imaging team. “Something must
be keeping different latitudes from mix-
ing to maintain those edges.”
The video also notes Cassini’s altitude
above the clouds, dropping from 45,
miles (72,400km) to 4,200 miles
(6,700km).
Now that the team knows what to
expect from the atmosphere and the
space that Cassini will travel through,
they plan to adjust camera settings for
better results on a similar opportunity
June 29.
Cassini is just under half-finished with
its dives through the rings and is sched-
uled to take its death plunge on
September 15, 2017. — N. K.An up-close view of Saturn’s atmosphere
AN OPPORTUNITY TO PERSEVERE. Mars rover Opportunity reached Perseverance Valley, an area carved
by some form of erosion, in May. The rover will study if wind or water was the culprit.GET A LITTLE CLOSER. Cassini’s first dive on April 26 brought
us this image of Saturn’s atmosphere. NASA/JPL-CALTECH/SPACE SCIENCE INSTITUTECuriosity spies active dunes on Mars
NASA/JPL-CALTECH/MSSS NASA/JPL-CALTECH/MSSS
DUNE BUGGY. Mount Sharp rises in the distance as NASA’s Curiosity Mars rover looks out over the Bagnold Dunes in this 360-degree mosaic, taken with the Mast
Camera on March 24 and 25. The rover is completing the second part of a two-phase study — the first close-up non-terrestrial investigation of active dunes in the
solar system. Between February and April, Curiosity sampled four sites near a linear dune on the northwestern side of Mount Sharp. These samples provide a comparison
for samples of crescent dunes taken in 2015 and 2016 from a site about 1 mile (1.6km) downhill. The study aims to compare how Mars’ winds shape dunes into different
patterns. Curiosity also nabbed a small sample of sand from both types of dunes to image over time and observe whether martian winds preferentially sort different
grains with varying mineral contents. — A. K.