Sun: Plasmajets as "heating" of the corona?

The first direct observation of millions of degrees is called "spiculae" to revive old theory

Extreme UV image of the sun (colors = wavelength ranges) with marked observation region. In it, researchers discovered the super hot spicules © Bart De Pontieu
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Why is the sun's atmosphere so much hotter than its surface? Astrophysicists have now for the first time a promising "suspect": In "Science" they prove for the first time the existence of millions of degrees hot plasma jet, which shoot at high speed from the surface into the atmosphere. They could be the long sought "heating" of the corona. However, where these "spicules" take their heat, is still puzzling.

One of the most persistent mysteries of solar physics is the question of why the outer atmosphere of the sun, the corona, is millions of degrees hotter than the "only" 6, 000 Kelvin warm solar surface. Although numerous theoretical models on possible coronary heating mechanisms have been discussed in recent decades, there was no direct evidence of the postulated mechanisms. For the first time, a new study by an American-Norwegian research team has made observations that could definitively confirm one of the theories.

Plasmajets too cold for coronary heating?

In their study, the researchers focused on the observation of spicules, narrow fountains of hot plasma shooting up from a region near the surface of the sun to the outside atmosphere. These "jets" were already in the 1980s as a possible heating of the corona, but were largely neglected in further research, since they did not seem to be hot enough at that time observations. "Spicules heating up to millions of degrees has never been directly observed before, so their role in coronary heating has been considered unlikely, " explains Bart De Pontieu, principal author of the study and solar physicist at Lockheed Martin's Solar and Astrophysics Laboratory. LMSAL).

New type of superhot spicules discovered

However, in 2007, De Pontieu and his colleagues made a pivotal discovery: they identified a new, previously unknown type of spikulae that moved much faster and had a shorter lifespan than the traditional plasma jet. These "Type II" spicules shot up more than 100 kilometers per second before suddenly disappearing. Exactly this fast disappearance was already a first indication for the astrophysicists that the jets could be very hot.

Plasmajets on the solar surface. Among them, researchers have now discovered the superhepatic spicules. Solar Dynamics Observatory / NASA

But only now could new observations with instruments onboard the solar observatories "Solar Dynamics Observatory" of NASA and "Hinodo" of the Japanese Space Agency confirm these assumptions: they prove that the spicules millions of degrees are actually hot, while normal jets only reach between 20, 000 and 100, 000 Kelvin. "Our observations reveal, for the first time, the one-to-one connection between the plasma heated to millions of Kelvin and the spicules that bring the plasma into the corona, " explains McIntosh. The high spatial and temporal resolution of the new instruments was crucial to the realization of this previously hidden mass delivery of the corona. Display

New riddle about the origin of spicules

"It has always been a mystery why the sun's atmosphere is hotter than its surface, " adds his colleague Scott McIntosh of the National Center for Atmospheric Research ( NCAR). By discovering that these jets shoot hot plasma into the outer solar atmosphere, we have gained more knowledge about the corona and can also use our amplification To improve the understanding of the effects of the sun on the upper atmosphere of the earth.

However, it is still unclear where the spicules take their energy and heat from. "One of our biggest challenges now is to understand what drives and heats the material in the jets, " says De Pontieu. As a next step, the researchers want to investigate the transition region between the solar surface and the corona. Launching in 2012, the NASA Observatory Interface Imaging Spectrograph (IRIS) will provide critical high-resolution data on temperature, magnetic field, and junction density.

(National Center for Atmospheric Research / University Corporation for Atmospheric Research, 07.01.2011 - NPO)