Wednesday, June 11, 2008

Journey to the Sun

As the Northern hemisphere's climate warms in annual event called Summer, thoughts return again to the Sun. Tuesday NASA announced the Solar Probe Plus. The spacecraft will pass within 7 million km, or 9 solar radii. The conical shield will protect the spacecraft from extreme temperatures. Solar variablility affects Earth's climate in the most direct way. Though humans have wondered about our star for thousands of years, they are just beginning to understand the Sun

As late as the 1920's most physicists would lecture that the Sun is made of iron, and burns in the sky like a red-hot poker. Quantum mechanics was new, and physics of the Sun's interior had yet to be figured out. A young woman named Cecilia Payne first suggested that the spectral lines could be interpreted as hydrogen. As a woman, Payne was ignored but eventually she was proved right. Sincer we have no direct samples, the Sun's composition is still a matter of conjecture.

The "Faint Young Sun" has long been a paradox. According to models of astrophysics, life should not have evolved here because at Earth's formation the Sun was only about 75% as bright. Earth would have been frozen solid, making evolution of life impossible. Geology and the fossil record contradict the model, telling us that Earth had both liquid water and life billions of years ago. Because the Sun turns fuel into energy according to E=mc^2, change in c precisely accounts for this paradox. If c had not changed in precisely the amounts predicted, life would not have evolved to read this post.

Today there is plenty of evidence that the Sun fuses hydrogen into helium, but few understand how this reaction is maintained. Sustained nuclear fusion in a reactor is a dream that has eluded humans for decades. Scientists have yet to understand how the reaction is triggered in billions of stars. While stars are known to condense from gas clouds, those clouds should dissipate before fusion is triggered. Something else is needed to trigger a cloud's collapse into a star.

Photos of infant stars show twin jets reminiscent of those produced by Black Holes. If the Sun and other stars formed around them, Black Holes' gravity would draw gas inward until fusion began. Their presence in stars would maintain those immense pressures indefinitely. A Black Hole could easily exist in the second last place humans would expect, in front of our faces each morning.

Temperature of the Sun's surface is measured in thousands of degrees yet in the corona it is million of degrees. Scientists can not agree why the corona is so hot, though the answer is related to transfer of energy by magnetic field lines. The magnetic field lines originate in the Sun's mysterious core. The 11-year sunspot cycle is still a mystery. If launched in 2015, Solar Probe Plus will arrive at the end of Solar Cycle 24 and finish near the maximum of Cycle 25. It will pass directly through the hot corona. We can wish this mission the best of luck.

TOMORROW: NASA is scheduled to announce a decision on the Constellation Spacesuit system. The suit system will be used for decades, supporting flights to the Moon. Wednesday the US House of Representatives will vote on a NASA authorization bill that will order one additional Shuttle flight to take the Alpha Magnetic Spectrometer into Space. This is a very exciting time in Washington!



Blogger Stephen said...

Updating the old joke:

NASA is sending a probe to the Sun (in maybe 2015).

Won't it burn up?

They're sending it at night.

8:28 AM  
Blogger Stephen said...

It seems that there are other ideas on why early Earth had liquid water, that do not require changes to the speed of light.

For example, early Earth might have had lots of methane, etc., in the atmosphere, like Titan. This is a greenhouse gas, and could have kept things toasty enough.

Of course, the geologic record on Earth is complicated, due to plate tectonics, etc. Absence of evidence is not evidence of absence. It's no excuse to jump to your favorite hypothesis, even if that is "God did it".

8:34 AM  

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