Image: Hot plasma
NASA/Solar Dynamics Observatory
Narrow jets of material, called spicules, streak upward from the solar surface at speeds often greater than 60 miles per second. Some of the spicules' plasma (ionized gas), which can reach temperatures in excess of one million degrees kelvin, is inserted into the corona (the sun's outer atmosphere).
updated 1/6/2011 2:49:42 PM ET 2011-01-06T19:49:42

Physicists who train their thoughts on the sun have long been perplexed by why its outer atmosphere is millions of degrees hotter than the surface. While theories abound, no direct observations have been made of the mysterious processes that heat the sun's atmosphere ... until now.

With the help of some state-of-the-art technology, a team of scientists thinks it has discovered an important piece of the puzzle. The results of the new study suggest that the scorching heat of the solar atmosphere is continuously replenished by jets of plasma that scream upward from the surface of the sun at supersonic speeds.

These plasma jets, called spicules, are "long, elongated fin features at the edge of the sun," Bart De Pontieu, the study's lead researcher, told The motion of the heated spicules could explain how the sun's atmosphere, or corona, is a few million degrees hotter than the surface, which has a temperature of about 10,800 degrees Fahrenheit (6,000 degrees Celsius).

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"The gas or plasma is originally pretty cool, but as the spicules are propelled upwards, some fraction of that gas gets heated to a few million degrees," said De Pontieu, a solar physicist at the Lockheed Martin Solar and Astrophysics Laboratory in Palo Alto, Calif.

Fountains of plasma
Scientists had previously examined spicules as a possible source of coronal heating, De Pontieu said, but many researchers dismissed the idea because they lacked observations of the jets' intense temperature.

In 2007, De Pontieu and his colleagues identified what they called Type II spicules, extremely fast but short-lived jets that burst upward faster than 60 miles (100 kilometers) per second.

The researchers combined data from NASA's recently launched Solar Dynamics Observatory and the Japanese Hinode satellite to make direct observations of these fast-moving jets of hot plasma for the first time.

"By identifying that these jets insert heated plasma into the sun's outer atmosphere, we gain a greater knowledge of the corona and possibly improve our understanding of the sun's subtle influence on Earth's upper atmosphere," said Scott McIntosh, a solar physicist at the National Center for Atmospheric Research in Boulder, Colo., who was also involved in the study.

Taking a different approach
The findings represent a departure from existing theories of coronal heating, but the keen eye of the Solar Dynamics Observatory, which captures a daily bounty of high-definition images of the sun, afforded scientists the clearest views yet of the magnificent star.

"The high spatial and temporal resolution of the newer instruments was crucial in revealing this previously hidden coronal mass supply," McIntosh said.

Still, there is much more to be learned about spicules and the mechanisms behind coronal heating.

"We're not saying this is the only way that the corona is heated, but our results show something that cannot be explained by the current theories," De Pontieu said. "Based on our current estimates, these jets likely play a significant role in coronal heating, but we have to be careful with our conclusion. It's very possible other mechanisms are at play – these observations show there's a lot of interesting stuff going on."

The road ahead
To expand upon this study, De Pontieu and his colleagues are hoping to obtain data on the composition of the jets and the mechanisms that take place between the solar surface and the corona.

"One of our biggest challenges is to understand what drives and heats the material in the spicules," De Pontieu said.

In 2012 NASA is scheduled to launch the Interface Region Imaging Spectrograph (IRIS), which will focus on the density, temperature and magnetic field between the surface of the sun and the corona. Researchers are hoping that data from this mission will lead to a better understanding of spicules and coronal heating.

"We want to understand the big picture, but we need to understand all the little details of how things work in order to understand that big picture," De Pontieu said.

The results of the study are published in today's (Jan. 6) issue of the journal Science.

You can follow Staff Writer Denise Chow on Twitter @denisechow.

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Photos: Month in Space: January 2014

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  1. Southern stargazing

    Stars, galaxies and nebulas dot the skies over the European Southern Observatory's La Silla Paranal Observatory in Chile, in a picture released on Jan. 7. This image also shows three of the four movable units that feed light into the Very Large Telescope Interferometer, the world's most advanced optical instrument. Combining to form one larger telescope, they are greater than the sum of their parts: They reveal details that would otherwise be visible only through a telescope as large as the distance between them. (Y. Beletsky / ESO) Back to slideshow navigation
  2. A balloon's view

    Cameras captured the Grandville High School RoboDawgs' balloon floating through Earth's upper atmosphere during its ascent on Dec. 28, 2013. The Grandville RoboDawgs’ first winter balloon launch reached an estimated altitude of 130,000 feet, or about 25 miles, according to coaches Mike Evele and Doug Hepfer. It skyrocketed past the team’s previous 100,000-feet record set in June. The RoboDawgs started with just one robotics team in 1998, but they've grown to support more than 30 teams at public schools in Grandville, Mich. (Kyle Moroney / AP) Back to slideshow navigation
  3. Spacemen at work

    Russian cosmonauts Oleg Kotov, right, and Sergey Ryazanskiy perform maintenance on the International Space Station on Jan. 27. During the six-hour, eight-minute spacewalk, Kotov and Ryazanskiy completed the installation of a pair of high-fidelity cameras that experienced connectivity issues during a Dec. 27 spacewalk. The cosmonauts also retrieved scientific gear outside the station's Russian segment. (NASA) Back to slideshow navigation
  4. Special delivery

    The International Space Station's Canadian-built robotic arm moves toward Orbital Sciences Corp.'s Cygnus autonomous cargo craft as it approaches the station for a Jan. 12 delivery. The mountains below are the southwestern Alps. (NASA) Back to slideshow navigation
  5. Accidental art

    A piece of art? A time-lapse photo? A flickering light show? At first glance, this image looks nothing like the images we're used to seeing from the Hubble Space Telescope. But it's a genuine Hubble frame that was released on Jan. 27. Hubble's team suspects that the telescope's Fine Guidance System locked onto a bad guide star, potentially a double star or binary. This caused an error in the tracking system, resulting in a remarkable picture of brightly colored stellar streaks. The prominent red streaks are from stars in the globular cluster NGC 288. (NASA / ESA) Back to slideshow navigation
  6. Supersonic test flight

    A camera looking back over Virgin Galactic's SpaceShipTwo's fuselage shows the rocket burn with a Mojave Desert vista in the background during a test flight of the rocket plane on Jan. 10. Cameras were mounted on the exterior of SpaceShipTwo as well as its carrier airplane, WhiteKnightTwo, to monitor the rocket engine's performance. The test was aimed at setting the stage for honest-to-goodness flights into outer space later this year, and eventual commercial space tours.

    More about SpaceShipTwo on PhotoBlog (Virgin Galactic) Back to slideshow navigation
  7. Red lagoon

    The VLT Survey Telescope at the European Southern Observatory's Paranal Observatory in Chile captured this richly detailed new image of the Lagoon Nebula, released on Jan. 22. This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. This image is a tiny part of just one of 11 public surveys of the sky now in progress using ESO telescopes. (ESO/VPHAS team) Back to slideshow navigation
  8. Fire on the mountain

    This image provided by NASA shows a satellite view of smoke from the Colby Fire, taken by the Multi-angle Imaging SpectroRadiometer aboard NASA's Terra spacecraft as it passed over Southern California on Jan. 16. The fire burned more than 1,863 acres and forced the evacuation of 3,700 people. (NASA via AP) Back to slideshow navigation
  9. Where stars are born

    An image captured by NASA's Spitzer Space Telescope shows the Orion Nebula, an immense stellar nursery some 1,500 light-years away. This false-color infrared view, released on Jan. 15, spans about 40 light-years across the region. The brightest portion of the nebula is centered on Orion's young, massive, hot stars, known as the Trapezium Cluster. But Spitzer also can detect stars still in the process of formation, seen here in red hues. (NASA / JPL-Caltech) Back to slideshow navigation
  10. Cygnus takes flight

    Orbital Sciences Corp.'s Antares rocket rises from NASA's Wallops Flight Facility on Wallops Island, Va, on Jan. 9. The rocket sent Orbital's Cygnus cargo capsule on its first official resupply mission to the International Space Station. (Chris Perry / NASA) Back to slideshow navigation
  11. A long, long time ago...

    This long-exposure picture from the Hubble Space Telescope, released Jan. 8, is the deepest image ever made of any cluster of galaxies. The cluster known as Abell 2744 appears in the foreground. It contains several hundred galaxies as they looked 3.5 billion years ago. Abell 2744 acts as a gravitational lens to warp space, brightening and magnifying images of nearly 3,000 distant background galaxies. The more distant galaxies appear as they did more than 12 billion years ago, not long after the Big Bang. (NASA / NASA via AFP - Getty Images) Back to slideshow navigation
  12. Frosty halo

    Sun dogs are bright spots that appear in the sky around the sun when light is refracted through ice crystals in the atmosphere. These sun dogs appeared on Jan. 5 amid brutally cold temperatures along Highway 83, north of Bismarck, N.D. The temperature was about 22 degrees below zero Fahrenheit, with a 50-below-zero wind chill.

    Slideshow: The Year in Space (Brian Peterson / The Bismarck Tribune via AP) Back to slideshow navigation
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