ESA title
X-ray jets from the Sun
Science & Exploration

Hinode: new insights on the origin of solar wind

07/12/2007 2196 views 1 likes
ESA / Science & Exploration / Space Science

Spectacular images and data from the Hinode mission have shed new light on the Sun's magnetic field and the origins of solar wind, which can disrupt power grids, satellites and communications on Earth.

The results are published in the 7 December issue of the journal Science.

Data from Hinode, a Japanese (JAXA) mission with ESA participation, shows that magnetic waves play a critical role in driving the solar wind into space. The solar wind is a stream of electrically charged gas that is propelled away from the Sun in all directions at speeds of almost 1.5 million km/h. Better understanding of the solar wind may lead to more accurate prediction of damaging radiation waves before they reach satellites.

How the solar wind is formed and powered has been the subject of debate for decades. Powerful magnetic waves in the electrically charged gas near the Sun (called Alfvén waves) have always been a leading-candidate force in the formation of solar wind. In principle, such waves can transfer energy from the Sun's surface up through its atmosphere, or corona, into the solar wind.

The Sun's north pole
The Sun's north pole

In the solar atmosphere, Alfvén waves are created when convective motions and sound waves push magnetic fields around, or when dynamic processes create electrical currents that allow the magnetic fields to change shape or reconnect.

"Until now, Alfvén waves have been impossible to observe because of limited resolution of available instruments," said Alexei Pevtsov, Hinode program scientist, at NASA Headquarters, Washington, USA. "With the help of Hinode, we are now able to see direct evidence of Alfvén waves, which will help us unravel the mystery of how the solar wind is powered."

Using Hinode's high resolution X-ray telescope, a team led by Jonathan Cirtain, a solar physicist at NASA's Marshall Space Flight Center, Alabama, USA, was able to peer low into the corona at the Sun's poles and observe record numbers of X-ray jets. The jets are fountains of rapidly moving hot plasma. Previous research detected only a few jets daily.

Close-up of the solar corona
Close-up of the solar corona

With Hinode's higher sensitivity, Cirtain's team observed an average of 240 jets per day. They conclude that magnetic reconnection, a process where two oppositely charged magnetic fields collide and release energy, is frequently occurring in the low solar corona. This interaction forms both Alfvén waves and the burst of energized plasma in X-ray jets.

"These observations show a clear relationship between magnetic reconnection and Alfvén wave formation in the X-ray jets." said Cirtain. "The large number of jets, coupled with the high speeds of the outflowing plasma, lends further credence to the idea that X-ray jets are a driving force in the creation of the fast solar wind."

The Sun's south pole
The Sun's south pole

Another research team led by Bart De Pontieu, a solar physicist at Lockheed Martin's Solar and Astrophysics Laboratory, California, USA, focused on the Sun's chromosphere, the region sandwiched between the solar surface and its corona. Using extremely high-resolution images from Hinode's Solar Optical Telescope, De Pontieu's team found that the chromosphere is riddled with Alfvén waves. When the waves leak into the corona, they are strong enough to power the solar wind.

Simulation of the Sun's atmosphere
Simulation of the Sun's atmosphere

"We find that most of these Alfvén waves have periods of several minutes, much longer than many theoretical models have assumed in the past," says De Pontieu. Comparisons with advanced computer simulations from the University of Oslo, Norway, indicate that reconnection is not the only source of the Alfvén waves. "The simulations imply that many of the waves occur when the Sun's magnetic field is jostled around by convective motions and sound waves in the low atmosphere," continued De Pontieu.

Notes for editors:

Hinode was launched in September 2006 to study the Sun's magnetic field and how its explosive energy propagates through the different layers of the solar atmosphere.

Hinode is a Japanese mission developed and launched by ISAS/JAXA, with NAOJ as domestic partner and NASA and STFC as international partners. It is operated by these agencies in co-operation with ESA and the Norwegian Space Centre.

Since 27 May 2007, European scientists have free access to spectacular data and images from Hinode. This free access is possible thanks to the opening of the Hinode Science Data Centre in Norway, developed and run by the Institute of Theoretical Astrophysics at the University of Oslo on behalf of ESA and the Norwegian Space Centre. It is part of ESA and Norway’s joint contribution to this solar mission.

The other part of the joint contribution to Hinode consists of ground station coverage through the SvalSat downlink station at Svalbard, which nearly quadruples the data rate and thus significantly increases Hinode’s science return. Svalsat is the only station in the world that can receive Hinode’s data during each of its 15 daily orbits. Hinode's operations centre is located at JAXA's facility in Sagamihara, Japan.

For more information:

Bernhard Fleck, ESA SOHO and Hinode Project Scientist
Email: Bfleck @ esa.nascom.nasa.gov

Related Links

Science & Exploration

Hinode (Solar-B) overview

01/01/1970 10104 views
Open item
Science & Exploration

Hinode (Solar-B) in a nutshell

989 views 2 likes
Read
Science & Exploration

SOHO overview

01/01/1970 58332 views
Open item
Hinode in orbit
Science & Exploration

Hinode helps unravel long-standing solar mysteries

22/08/2007 1447 views 0 likes
Read
Dynamic solar corona seen by Hinode in X-rays
Science & Exploration

Hinode’s solar data ready for Europe’s access

30/05/2007 1289 views 0 likes
Read
Structure of the Sun's magnetic field
Science & Exploration

Hinode sees the dynamic and violent sun as sharply as never…

21/03/2007 2407 views 0 likes
Read
Solar corona as imaged by Hinode
Science & Exploration

Hinode’s first images of our violent Sun

22/12/2006 2216 views 1 likes
Read
Hinode (former Solar-B) launched
Science & Exploration

Solar-B renamed ‘Hinode’ after launch

25/09/2006 1385 views 0 likes
Read
Hinode (Solar-B) mission to study the dynamic Sun
Science & Exploration

Solar-B – a new solar mission to study the dynamic Sun

20/09/2006 3990 views 6 likes
Read
Animation showing far-side imaging of the Sun
Science & Exploration

Nowhere to hide from SOHO

10/03/2006 1129 views 6 likes
Read
SOHO's image of the Sun
Science & Exploration

ESA’s SOHO will lead a fleet of solar observatories

24/05/2006 2511 views 1 likes
Read
SOHO's components
Science & Exploration

How we see the far side of the Sun

18/11/2003 6703 views 17 likes
Read
Science & Exploration

What are solar flares?

176495 views 708 likes
Read
Composite image of CME from SOHO instruments
Science & Exploration

Scientists weather a space storm to find its origin

02/08/2005 1174 views 1 likes
Read
Sun-Earth day events
Science & Exploration

How the Sun affects us on Earth

26/06/2003 36405 views 221 likes
Read