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Ulysses Takes The High Ground As Messenger Takes The Flanks

A Ulysses "clock plot" of solar wind speed vs. latitude reveals a high-speed wind blowing from the sun's poles.

MESSENGER Flyby of Mercury
At 2:04 p.m. EST MESSENGER skimmed 200 kilometers (124 miles) above the surface of Mercury in the first of three flybys of the planet. Initial indications from the radio signals indicate the spacecraft is still operating nominally. The first science data return from the flyby was received today, just minutes before the closest approach point with the planet, as planned. "The engineers and operators at the Deep Space Network (DSN) in Goldstone, Calif., in conjunction with engineers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., pulled off a tremendous feat, acquiring and locking onto the downlink signal from the spacecraft within seconds, providing the necessary Doppler measurements for the Radio Science team" said MESSENGER Mission Systems Engineer Eric Finnegan, of APL.

" The spacecraft is continuing to collect imagery and other scientific measurements from the planet as we now depart Mercury from the illuminated side, documenting for the first time the previously unseen surface of the planet." Tomorrow at noon EST, the spacecraft will turn back towards the Earth to start down-linking the on-board stored data. Measurements of this Doppler signal from the spacecraft will allow improve knowledge of Mercury's gravity field.

by Dr. Tony Phillips
for NASA Science News
Huntsville AL (SPX) Jan 15, 2008
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 "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.

This week, "Ulysses will measure the sun's magnetic field above the North Pole to see what it's like during the change of solar cycles," says Posner.

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.

One big puzzle 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: data."

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.

Related Links
Ulysses
Solar Science News at SpaceDaily



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NASA Satellites Capture Start Of New Solar Cycle
Huntsville AL (SPX) Jan 14, 2008
NASA scientists say a new solar cycle is beginning, and this could have important repercussions for space-based technology ranging from GPS navigation to weather satellites. On Jan. 4, a reversed-polarity sunspot appeared, signaling the start of Solar Cycle 24. A sunspot is an area of magnetic activity on the surface of the sun that appears as a dark spot on its surface.







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