Wednesday, February 27, 2008

Shot Down in Midair!

3/2/08 - 3/8/08
by C. Zaitz

I’m not usually picky about why people get interested in science. But when my spouse came to me excited about the fact that the US Navy had shot down one of our own satellites with an unarmed missile launched from a ship out in the middle of the ocean, I felt smug. “Oh that’s nothing” said I. “We went to the moon six times, when we had to launch incredibly huge Saturn V rockets, figure out how to slip three astronauts into orbit, plunge two of them down to the surface to play, then scoot them back into a tiny aluminum foil launch vehicle, blast them off the moon, rendezvous with the orbiting vehicle, and have them burn themselves back into a tricky return to earth, with just the right trajectory to ensure they neither would skip off the atmosphere nor burn up in re-entry. No easy feat!” He rolled his eyes.

Meanwhile, I was just being cynical, and he was right, the destruction of the satellite was pretty interesting. Launching a missile from a rocking, moving ship is no easy feat, and hitting a fast-moving target is trickier still. Shooting down satellites is a controversial affair, due to China’s demolishing of a weather satellite last year. Nations get nervous when other nations send missiles shooting into the sky. But they did it, and so did we. How? Why?

The “why” of shooting down our own satellite was apparently due to the tank of hydrazine on board. Hydrazine is a toxic substance which once gained fame as being a product of a compound called Alar which was sprayed on apples to keep them on the tree to ripen them. The fear of this substance falling to earth as a cold slush, possibly killing or injuring people within 30 feet of it, was reason enough for the US to destroy it before reentry. The satellite had died, leaving no energy to keep the hydrazine warm, and hydrazine has a freezing point above water, so the threat of it surviving reentry as a half-frozen substance was real. Some say we did it just to see if it could be done, which leads up to the “how” of hitting a satellite moving at 17,000 km/second.

Breaking up a satellite before reentry poses problems. We have a pretty good understanding of orbits and trajectories of objects, once we know their mass and velocity. But when conditions like weather are uncertain, or change rapidly, problems of math and physics become very complex. So we use guiding systems which can track infrared, or heat signals. Unfortunately the satellite was dead so it wasn’t producing much heat. When China blew up one of its spy satellites, a cloud of debris was left behind in orbit that still exists and will remain for years, creating hazards for other orbiting bodies. We needed to hit the satellite in the hydrazine tank, which upon impact, even without explosives, would smash both the missile and the satellite, the pieces of which would reenter the atmosphere and burn up within weeks. And apparently that’s what happened.

Without knowing all the military details, but knowing that we are target practicing, as are other countries, I’m kind of glad that some of us are very interested in science.

Until next week, my friends, enjoy the view.

Wednesday, February 20, 2008

Spelunking in Space

2/24/08 – 3/1/08

by C. Zaitz

The planet Mars currently has a flotilla of spacecraft either orbiting or crawling on it. Interest has always been high when it comes to Mars, due to the strange landscape and its earth-like features, as well as the fact that it may have harbored life in its history. Recently, orbiting spacecraft have found holes the size of football fields in Mars’ landscape. After careful study, speleologists (scientists who study caves) say it is most likely that the holes are cave entrances, similar to caves on earth.

The fact that Mars has caves is interesting for a couple of reasons. First, caves can be safe havens for any life that might have taken hold on the planet. Mars is a harsh place, though it is the more earth-like than other planets. Its atmosphere is much thinner than earth’s and the weather is significantly meaner as a result. The thin atmosphere allows more killing solar radiation to reach the surface of Mars, even though it is farther away from the sun than we are. If life did form on Mars, it wouldn’t last long in the sizzle of the sun’s energy.

Caves provide protection from the more dangerous forms of radiation, and can also be shelter from raging wind and dust storms that often blast across the surface. Scientists think that caves are an excellent place to look for evidence of life on Mars. But even if life never did exist on Mars, there is another reason caves interest us. We humans have lived in caves for much of our history. They are perfect protection from fierce weather and from marauding neighbors. Though we don’t expect to have to hide from Martians, we will need protection from the elements on Mars that caves afford.

Scientists wonder how the caves formed. We know what can cause caves on earth. Falling rain water absorbs carbon dioxide. Water and carbon dioxide combine into a weak form of carbonic acid. The acid eats away rocks that are made of calcium carbonate, or limestone, and caves form as rock is dissolved and carried away in underground streams. Hollow chambers are left behind.

Caves on Mars may not be limestone, however. Mars has a very different atmosphere. It is mostly carbon dioxide, not nitrogen and oxygen. 95% of the air is poison to us, but would be very useful to plants. However, it isn’t clear that Mars has the right chemistry for the karst formations and caves we find on earth. So if the caves on Mars aren’t eroded limestone, what are they?

What Mars does have is volcanoes, like those on earth. The caves may be hollow lava tubes from ancient volcanoes. If it turns out that they are, they would provide excellent shelter for future spelunkers from earth. There might be magnificent chambers with sky lights and protected rooms for equipment and living space. These volcanic mansions might provide the right environment for exploring humans to survive on the foreign planet. Work is currently being done to design and build robots that could explore the caves on Mars, These robots could not only look for signs of past life, but could pave the way for future inhabitants to move in.

If you’d like to see Mars tonight, look to your southern sky for a bright, peach-colored light among the stars.

Until next week, my friends, enjoy the view.

Wednesday, February 06, 2008

Spring on the Sun

In January, solar scientists found their first robin of the sun’s spring. It was a sun spot, a little black dot on the visible surface of the sun. This spot was somehow different from the spots that had come before and from spots still on the sun. This spot had a different magnetic polarity, and was in a different place than previous spots. The news was clear: the long awaited first sign of Solar Cycle 24 had arrived. The sun’s winter, known as “solar minimum,” was midway through and the new solar cycle had begun.

The analogy of spring can only be taken so far. The sun does go through activity level changes, just like we do in different seasons, and these changes are related to the sun’s average temperature. But the sun doesn’t have seasons, just an ongoing 11 year cycle of magnetic storm activity. It turns out that the sun’s average temperature is lower during the multi-year lull in sunspot activity, and is greatest during the peak, called solar maximum.

Like a human going through puberty, the sun face is always changing, and its most noticeable feature is the scattering of spots on its face. The spots indicate areas where the turbulent and twisted magnetic field lines are organized and the normally bright plasma of the sun is slightly cooled and darkened. They appear darker against the bright background of hotter plasma, and that is what we see as a sunspot. Sunspots form often form in pairs or groups. They have a system of polarity, just like magnets have south and north poles. They form in somewhat predictable ways throughout an entire solar cycle. One of the clues scientists have been looking for is the switch in polarity of spots that form in in either the northern or southern hemisphere of the sun. This is one of the clues that indicate the official end of cycle 23 and the beginning of the new solar cycle.

Another clue is where the spots form on the sun. New solar cycles always begin with a high-latitude, reversed polarity sunspot. Old cycle spots form near the sun's equator. New cycle spots appear higher on the sun, around 30 degrees above the sun’s equator. The new spot was high and backward, indicating cycle 24 had begun. Now the sun’s activity would grow day by day over the course of the next 4-6 years.

Though we’ve turned the corner in the sun’s growing activity, it takes years to peak. Scientists predict that the upcoming solar cycle will be quite fierce when it peaks around 2011. What that means is that we will be vulnerable to the effects of solar storms, like power grid overloads causing power outages, cell phone and other communication interruptions due to satellite malfunction, GPS malfunctioning and air traffic problems. One pretty side effect caused by excess solar particles in our atmosphere is the Northern Lights. Scientists predict this solar cycle will be famous for Northern Light displays. We‘ll have to wait for solar max to see these spectacular Auroral displays, however. Meanwhile we can enjoy the heightening daily path of the sun, and that it lingers longer as the days go by. Spring is indeed coming.

Until next week, my friends, enjoy the view.