the strange temperature difference
between the surface of the sun, which is
a toasty 5500°, and the several-million-
degree corona. This spike may be due to
vibrating magnetic field lines heating up
material in the corona, or jets of material
from the sun’s surface that inject energy
into its atmosphere (SN Online: 8/20/17).
Parker could also help explain where solar
wind particles get the energy to speed up
as they escape the sun’s immense gravitational pull (SN Online: 8/18/17).
The enigmatic coronal heat and acceleration of the solar wind probably have
a common cause, says David McComas,
a space plasma physicist at Princeton
University. McComas is the principal investigator for one of the probe’s
instruments, the Integrated Science
Investigation of the Sun. There are many
competing theories to explain these two
problems, but Parker’s views of the sun
should help winnow down the list of possible explanations.
Parker’s observations should also give
new insight into the origins of those
highly energetic particles that escape the
sun into the solar wind, McComas says.
The solar wind washes over Earth at
hundreds of kilometers per second, and
disturbances in this cosmic breeze can
mess with satellites, spacecraft and
power grids (SN: 8/19/06, p. 120). A better
understanding of the sun’s tumultuous
atmosphere and solar wind could lead to
better forecasts for potentially danger-
ous space weather events.
On top of all that, Parker’s zoomed-in
view of the sun will undoubtedly raise
new mysteries about our home star,
McComas says. The data haul from “one
mission [often] just whets our appetites
for even more observations down the
road,” he says.
Fortunately, another spacecraft
bound for the sun is launching right
on the heels of the Parker probe. The
European Space Agency’s Solar Orbiter,
set to take flight in 2020, will provide
the first direct images of the sun’s poles.
Paired with Parker’s observations closer
to the sun’s midriff, Solar Orbiter data
may reveal how the solar wind varies at
These missions aren’t just about
getting to know our own solar system.
“Once you know about how our star
works, you’re going to know a lot more
about … other stars,” Fox says.
Whatever scientific discoveries come
from the mission, it’s difficult not to
get excited for the sheer “wow” factor
of the probe’s impending expedition.
“This is really freaking cool,” DeForest
says. “We’re launching a probe and flying it through [several-] million-degree
plasma on the periphery of a star. I
mean, how cool is that?” s
ATOM & COSMOS
Mars got its crust
before Earth did
Red Planet’s exterior hardened
by 4.547 billion years ago
B Y CAROLYN GRAMLING
Mars was a fully formed planet — crust
and all — within 20 million years of the
solar system’s birth. That rapid formation means the Red Planet probably got a
100-million-year jump on Earth in terms
of habitability, new research suggests.
Geochemical analyses of zircon crystals extracted from Martian meteorites
reveal that Mars had formed its earliest
crust by 4.547 billion years ago, planetary
scientist Laura Bouvier of the University
of Copenhagen and colleagues report in
the June 28 Nature.
The emergence of an outer shell, or
crust, is the final stage in the formation
of rocky planets. The process begins
with the accretion of particles from the
disk of gas and dust that surrounds an
infant star. Eventually, those particles
form molten material that makes up
a magma ocean. As the magma ocean
cools and crystallizes, it forms a dense
metallic core, and then an outer crust.
Simulations suggest that the whole process usually occurs on timescales of
30 million to as long as 100 million years.
“Having Mars cool so quickly puts limits on how massive its atmosphere could
have been,” says planetary scientist Linda
Elkins-Tanton of Arizona State University
in Tempe. Going by how quickly a planet
cools and how quickly the sun can strip
away its atmosphere, researchers can
estimate how much water and carbon
dioxide might have been released by the
magma. In Mars’ case, that atmosphere
would have been pretty thin to allow for
such rapid heat loss, Elkins-Tanton says.
Around the time Mars solidified,
Earth was almost certainly molten, possibly thanks to a giant whack that formed
the moon and remelted the entire planet
(SN: 4/15/17, p. 18), Elkins-Tanton says.
Earth had to wait another 100 million
years to fully harden. s
Round and round The Parker Solar Probe will circle the sun 24 times over the next seven
years, using the gravitational tug of Venus to gradually shrink its own orbit. On its final few loops,
beginning in 2024, the probe will skirt within about 6 million kilometers of the sun’s surface.
Closest approach on
November 3, 2018
Closest approach on
December 21, 2024
First Venus flyby
September 30, 2018
August 4, 2018 Sun