Ulysses Flyby of the Sun's North Pole

January 15, 2008
Ulysses Flyby of the Sun's North Pole
A Ulysses "clock plot" of solar wind speed vs. latitude reveals a high-speed wind blowing from the sun's poles.

Consider it a case of exquisite timing. Just last week, solar physicists announced the beginning of a new solar cycle and now, Jan. 14th, the Ulysses spacecraft is flying over a key region of solar activity--the sun's North Pole.

"This is a wonderful opportunity to examine the sun's North Pole at the onset of a new solar cycle," says Arik Posner, NASA Ulysses program scientist. "We've never done this before."

Launched in Oct. 1990 from the space shuttle Discovery, Ulysses is a joint mission of the European Space Agency and NASA. Unlike other spacecraft, Ulysses is able to fly over the sun's poles, looking down on regions that are difficult to see from Earth: diagram.

Ulysses has flown over the sun's poles three times before in 1994-95, 2000-01 and 2007. Each flyby revealed something interesting and mysterious, but this one may be most interesting of all.

"Just as Earth's poles are crucial to studies of terrestrial climate change, the sun's poles may be crucial to studies of the solar cycle," explains Ed Smith, Ulysses project scientist at NASA's Jet Propulsion Laboratory.

Many researchers believe the sun's poles are central to the ebb and flow of the solar cycle. Consider the following: When sunspots break up, their decaying magnetic fields are carried toward the poles by vast currents of plasma. This makes the poles a sort of "graveyard for sunspots." Old magnetic fields sink beneath the polar surface two hundred thousand kilometers deep, all the way down to the sun's inner magnetic dynamo. There, dynamo action amplifies the fields for use in future solar cycles.

One big puzzle revealed by previous flybys is the temperature of the sun's poles. In the previous solar cycle, the magnetic north pole was about 80,000 degrees or 8% cooler than the south. Why should there be a difference? No one knows.

The current flyby may help solve the puzzle because it comes less than a year after a similar South Pole flyby in Feb. 2007. Mission scientists will be able to compare temperature measurements, north vs. south, with hardly any gap between them.

Ulysses also discovered the sun's high-speed polar wind. "At the sun's poles, the magnetic field opens up and allows solar atmosphere to stream out at a million miles per hour," says Smith.

By flying around the sun, covering all latitudes in a way that no other spacecraft can, Ulysses has been able to monitor this polar wind throughout the solar cycle--and it is acting a bit odd.

Posner explains: "Eleven years ago, during a similar 'sea change' between solar cycles, the polar wind spilled down almost all the way to the sun's equator. But this time it is not. The polar wind is bottled up, confined to latitudes above 45 degrees."

Is this a detail of little importance or a major anomaly, signaling new things to come? Again, no one knows, and that's why now is a good time to visit the sun's North Pole. "We'll be monitoring the magnetic field above the north pole to see what it's like during the change of solar cycles."

Source: by Dr. Tony Phillips, Science@NASA

Explore further: Researchers develop a new technique to forecast geomagnetic storms

Related Stories

This summer's solar eclipses from the ends of the Earth

July 9, 2018

Solar eclipses will occur at opposite ends of the Earth this summer, 2018. Both will be merely partial solar eclipses as seen from the Earth's surface, not as dramatic as last summer's total solar eclipse whose path of totality ...

Recommended for you

Dust storms on Titan spotted for the first time

September 25, 2018

Data from NASA's Cassini spacecraft has revealed what appear to be giant dust storms in equatorial regions of Saturn's moon Titan. The discovery, described in a paper published on Sept. 24 in Nature Geoscience, makes Titan ...

Tracking the interstellar object 'Oumuamua to its home

September 25, 2018

A team of astronomers led by Coryn Bailer-Jones of the Max Planck Institute for Astronomy has tracked the interstellar object 'Oumuamua to several possible home stars. The object was discovered in late 2017 – this was the ...

Four extremely young asteroid families identified

September 25, 2018

Four families of extremely young asteroids have been identified by researchers affiliated with São Paulo State University (UNESP) in Guaratinguetá, Brazil. An article on the discovery has been published in Monthly Notices ...

A new classification scheme for exoplanet sizes

September 24, 2018

There are about 4433 exoplanets in the latest catalogs. Their radii have generally been measured by knowing the radius of their host star and then closely fitting the lightcurves as the planet transits across the face of ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.