Images from IRIS show the tadpole-shaped jets containing pseudo-shocks streaking out from the Sun
Credits: Abhishek Srivastava IIT (BHU)/Joy Ng, NASA’s Goddard Space Flight Center
For 150 years scientists have been trying to figure out why the wispy upper atmosphere of the Sun — the corona — is over 200 times hotter than the solar surface. This region, which extends millions of miles, somehow becomes superheated and continually releases highly charged particles, which race across the solar system at supersonic speeds.
When those particles encounter Earth, they have the potential to harm
satellites and astronauts, disrupt telecommunications, and even
interfere with power grids during particularly strong events.
Understanding how the corona gets so hot can ultimately help us
understand the fundamental physics behind what drives these disruptions.
In recent years, scientists have largely debated two possible
explanations for coronal heating: nanoflares and electromagnetic waves.
The nanoflare theory proposes bomb-like explosions, which release energy
into the solar atmosphere. Siblings to the larger solar flares, they
are expected to occur when magnetic field lines explosively reconnect,
releasing a surge of hot, charged particles. An alternative theory
suggests a type of electromagnetic wave called Alfvén waves might push
charged particles into the atmosphere like an ocean wave pushing a
surfer. Scientists now think the corona may be heated by a combination
of phenomenon like these, instead of a single one alone.
The new discovery of pseudo-shocks adds another player to that
debate. Particularly, it may contribute heat to the corona during
specific times, namely when the Sun is active, such as during solar
maximums — the most active part of the Sun’s 11-year cycle marked by an
increase in sunspots, solar flares and coronal mass ejections.
The discovery of the solar tadpoles was somewhat fortuitous. When
recently analyzing data from NASA’s Interface Region Imaging
Spectrograph, or IRIS, scientists noticed unique elongated jets emerging
from sunspots — cool, magnetically-active regions on the Sun’s surface
— and rising 3,000 miles up into the inner corona. The jets, with bulky
heads and rarefied tails, looked to the scientists like tadpoles
swimming up through the Sun’s layers.
“We were looking for waves and plasma ejecta, but instead, we noticed
these dynamical pseudo-shocks, like disconnected plasma jets, that are
not like real shocks but highly energetic to fulfill Sun's radiative
losses,” said Abhishek Srivastava, scientist at the Indian Institute of
Technology (BHU) in Varanasi, India, and lead author on the new paper in
Nature Astronomy.
Using computer simulations matching the events, they determined these
pseudo-shocks could carry enough energy and plasma to heat the inner
corona.
The scientists believe the pseudo-shocks are ejected by magnetic reconnection — an explosive tangling of magnetic field lines, which often occurs in and around sunspots. The pseudo-shocks have only been observed around the rims of sunspots so far, but scientists expect they’ll be found in other highly magnetized regions as well.
Related Links:
By Mara Johnson-Groh
NASA’s Goddard Space Flight Center, Greenbelt, Md.
A computer simulation shows how the pseudo-shock is ejected and becomes disconnected from the plasma below (green)
Credits: Abhishek Srivastava IIT (BHU)/Joy Ng, NASA’s Goddard Space Flight Center
The scientists believe the pseudo-shocks are ejected by magnetic reconnection — an explosive tangling of magnetic field lines, which often occurs in and around sunspots. The pseudo-shocks have only been observed around the rims of sunspots so far, but scientists expect they’ll be found in other highly magnetized regions as well.
The tadpole-shaped pseudo-shocks, shown in dashed white box, are ejected from highly magnetized regions on the solar surface. Credits: Abhishek Srivastava IIT (BHU)/Joy Ng, NASA’s Goddard Space Flight Center
Over the past five years, IRIS has kept an eye on the Sun in its
10,000-plus orbits around Earth. It’s one of several in NASA’s
Sun-staring fleet that have continually observed the Sun over the past
two decades. Together, they are working to resolve the debate over
coronal heating and solve other mysteries the Sun keeps.
“From the beginning, the IRIS science investigation has focused on
combining high-resolution observations of the solar atmosphere with
numerical simulations that capture essential physical processes,” said
Bart De Pontieu research scientist at Lockheed Martin Solar &
Astrophysics Laboratory in Palo Alto, California. “This paper is a nice
illustration of how such a coordinated approach can lead to new physical
insights into what drives the dynamics of the solar atmosphere.”
The newest member in NASA’s heliophysics fleet, Parker Solar Probe,
may be able to provide some additional clues to the coronal heating
mystery. Launched in 2018, the spacecraft flies through the solar corona
to trace how energy and heat move through the region and to explore
what accelerates the solar wind as well as solar energetic particles.
Looking at phenomena far above the region where pseudo-shocks are found,
Parker Solar Probe’s investigation hopes to shed light on other heating
mechanisms, like nanoflares and electromagnetic waves. This work will
complement the research conducted with IRIS.
“This new heating mechanism could be compared to the investigations
that Parker Solar Probe will be doing,” said Aleida Higginson, deputy
project scientist for Parker Solar Probe at Johns Hopkins University
Applied Physics Laboratory in Laurel, Maryland. “Together they could
provide a comprehensive picture of coronal heating.”
Related Links:
- Learn more about NASA’s IRIS Mission
- NASA’s Parker Solar Probe and the Curious Case of the Hot Corona
- Learn more about NASA's Parker Solar Probe
By Mara Johnson-Groh
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Editor: Rob Garner
Source: NASA/IRIS
