NASA has selected the CubeSat Imaging X-Ray Solar Spectrometer (CubIXSS),
led by Southwest Research Institute, to measure the elemental composition of
hot, multimillion-degree plasmas in the Sun’s corona – its outermost
atmosphere. The nanosatellite is expected to be launched in 2024 as a
secondary payload on another satellite launch. CubIXSS will determine the
origins of hot plasma – highly ionized gas – in solar flares and active
regions.
Concentrations of strong and complicated magnetic fields at the surface of
the Sun are called “active regions.” These regions frequently spawn strong
solar activity including explosive “solar storms” such as solar flares and
coronal mass ejections (CMEs).
“A solar flare happens because the magnetic field in that active region has
become so twisted and tangled that it basically ‘snaps’ back into a less
tangled shape,” said SwRI Principal Scientist Dr. Amir Caspi, the mission’s
leader. “That snap releases a lot of energy, which we see as a solar flare.”
The solar flare heats the Sun’s plasma in that region to heat up to tens of
millions of degrees Celsius. That is considerably hotter than the rest of
the Sun’s corona, which typically ranges from 1 to a few million degrees,
and much hotter than the Sun’s surface, which is only about 6000 degrees.
“One of the interesting things we don’t really know is how much plasma in
solar flares is heated directly in the corona, and how much is heated in the
Sun’s lower atmosphere and then transported up to the corona,” Caspi said.
“CubIXSS will measure the X-rays that come from these phenomena, to allow us
to unravel this mystery.”
A standard CubeSat is a 10-centimeter cube with a one-liter volume, referred
to as “1U.” CubIXSS takes up six of these units, or 6U, about the size of a
shoebox or two loaves of bread. It will carry multiple spectrometers to
measure different wavelengths, or “colors,” of X-rays from the Sun,
including a new kind of X-ray imaging spectrometer to determine the amounts
of certain key elements in the Sun’s corona, which will in turn allow Caspi
to identify where that plasma was heated.
“Some elemental species – certain ions – can only exist in a specific range
of temperatures, so seeing which elements are more prevalent helps us to
create a temperature map,” Caspi said. “Previous observations have shown a
higher proportion of certain elements in the corona than other regions of
the Sun. By measuring the abundances of these elements at each temperature,
we’ll be able to tell where the heated plasma came from.”
CubIXSS will be the first device of its kind to routinely measure certain
wavelengths of solar X-ray emissions, which not only help to determine the
abundances of solar elements but also have a direct impact on the Earth.
X-rays from the Sun can contribute to expansion of Earth’s upper atmosphere,
which can cause increased drag on satellites in low orbits and alter their
trajectories. They also cause changes in Earth’s ionosphere, a charged
region in the upper atmosphere, that can affect radio communications.
“Even though it might seem like what we’re doing is very academic, studying
the Sun is very important for people living on Earth. It drives almost
everything that happens on our planet,” Caspi said. “CMEs and solar flares
can impact satellites and radio frequencies, disrupting communications both
on Earth and to satellites in space. Understanding how these things happen
is very important to understanding why they happen, which will help us
predict these ‘space weather’ events and mitigate their effects.”
Work is set to begin on CubIXSS in late 2021, with a projected launch date
of late 2024.
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