A solar eruption is pictured from the sun in the year 2014. (Image credit: NASA Goddard)
A fiery conundrum concerning the sun might be nearing resolution.
For several decades, researchers have been endeavoring to determine why the solar atmosphere is considerably warmer than the sun’s surface, despite being situated farther from the center. While the surface, recognized as the photosphere, reaches millions of degrees Fahrenheit, the atmosphere registers at roughly 10,000 F (5,500 C).
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Recent data originating from the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST) stationed in Hawaii — the most substantial ground-based solar telescope ever constructed — is enabling researchers to comprehend the means by which solar energy gets transported throughout the sun’s atmosphere.
A solar puzzle
Researchers previously took note of the elevated temperature of the sun’s corona, along with the highly energized movement of heated gasses, identified as the solar wind, which is emitted from the sun at velocities surpassing 1 million mph (1.6 million km/h), as indicated by Richard Morton, a solar physicist and professor at Northumbria University in the U.K. who spearheaded the research, speaking to Live Science through email.
Both of these occurrences demand energy, and scientists initially postulated that swirling convection at the surface of the sun generated the required propellant. Nevertheless, complications surfaced during initial analyses dating back several decades.
“It is unclear how this [energy] gets conveyed into the atmosphere and solar wind, and by what means the energy converts into heat and momentum,” Morton expressed.
In the year 1942, Swedish plasma physicist (and eventual Nobel laureate) Hannes Alfvén posited that magnetic waves may be the underlying cause. However, these waves, which we now know as Alfvén waves, had previously never been identified within the corona, until recently.
An illustration depicting twisting magnetic waves (inset) as captured by the Inouye Solar Telescope. These rising waves may play an integral role in resolving the riddle of why the sun’s corona is so intensely hot.
“This stemmed from the fact that the sensitivity of previous devices hadn’t been adequate for the purpose of resolving the movements of Alfvén waves,” Morton mentioned. “Despite this obstacle, a multitude of numerical experiments and space weather forecasting resources presuppose the existence of Alfvén waves within the corona. All the same, the attributes of the waves incorporated in such models have been formulated through well-informed estimations.”
‘Unprecedented’ observations
DKIST is outfitted with a 4-meter (13 feet) mirror and an “unprecedented” degree of solar resolution, Morton explained, offering “cleaner measurements” (reduced noise) than any former solar observation station. During this new research, researchers availed themselves of the telescope’s Cryogenic Near Infrared Spectropolarimeter (Cryo-NIRSP) with the goal of discovering the coronal Alfvén waves.
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Cryo-NIRSP possesses the capability to chart the motions within the corona through visual representations, as Morton explained, coupled with examining variations within the sun’s plasma (superheated gasses) utilizing an occurrence recognized as the Doppler shift — the apparent variance in wave frequency as the wave’s source and the observer shift toward or away from each other. (A typical instance within real life involves variations to an ambulance siren as it travels past a pedestrian along a road.)
“Cryo-NIRSP furnished the information required for observation regarding the tell-tale mark left by Alfvén waves, which, within plasma analogous to that of the corona, manifest as a back-and-forth distortion of the magnetic field,” Morton specified. “This presents as an alternating array comprised of red and blue Doppler displacement upon opposite sides of magnetic fields. We observed a persistent existence of these waves all through the duration of our observations, and in light of the absence of any particular exceptional trait exhibited by the observed region, this may imply their pervasive prevalence across the remainder of the solar atmosphere.”
“Potentially most significantly,” he went on, “our analysis points towards the high likelihood of these waves conveying a notable degree of energy.”
That holds significant import, he observed, on account of astronomers being engaged in debate between solar waves and magnetic reconnection — a scenario where solar magnetic fields intertwine and rupture, thereby liberating energy — when trying to identify the mechanism that underpins intense coronal heating.
While a variety of spacecraft have yielded indications that magnetic reconnection functions as a driver that facilitates coronal heating, the new information obtained via DKIST points towards a more elaborate and intricate picture. Solar observation facilities, including NASA’s Parker Solar Probe and the European Space Agency’s Solar Orbiter, along with current data obtained through DKIST, indicate that “both waves and reconnection occur frequently across the entirety of the Sun’s atmosphere,” said Morton.
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“Our research validates the occurrence of Alfvén waves, along with their transmission of substantial magnitudes of energy, potentially constituting at least half of the total energy budget mandated for coronal heating,” he elaborated. “Even so, assessments concerning the specific degree of energy linked with these waves continue posing considerable difficulty.”
The proportional relationship between magnetic reconnection and Alfvén waves exerts influence not only on solar heating, but likewise on the light (or in more precise terms, radiative output) released by the sun, coupled with light emanating from stars situated beyond our solar framework. Scientists harbor aspirations of harnessing this research to enhance knowledge pertaining to how planetary systems have evolved over extended periods, and to enhance immediate forecasts pertaining to solar wind generation. “Expectations involve subsequent investigations paralleling the endeavor we’ve publicized will shed added insight pertaining to Alfvén wave attributes, so that the models are enriched and prognostications attain elevated precision,” he mentioned.
Elizabeth HowellLive Science Contributor
Elizabeth Howell functioned as a staff journalist at Space.com from 2022 to 2024 and became a frequent writer to Live Science and Space.com encompassing the period spanning 2012 up until 2022. Elizabeth’s press activity comprises diverse unique reports emanating directly from within the White House, spanning multiple interactive sessions through the International Space Station, encompassing eye-witnessing of five human spaceflight launches upon two different continents, undertaking parabolic flights, functioning from within a spacesuit, coupled with involvement within a simulated mission to Mars. Her culminating novel, “Why Am I Taller?” (ECW Press, 2022) maintains co-authorship with astronaut Dave Williams.
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