10 Mistérios do Cosmos

10 Mysteries of the Cosmos

10. Is there a mass extinction cycle on Earth?
The West African rhinoceros is gone. So is the Madeiran Large White butterfly. Poachers finally wiped out the rhinos in 2006. The following year, the Portuguese insect was listed as extinct, partly due to human encroachment on its habitat.

Loss of species is on the increase. That's distressing for environmentalists but anticipated by scientists. In 2005, U.C. Berkeley physicists examined an exhaustive list of marine fossils and identified a strong pattern of extinction for the last 500 million years. Approximately every 62 million years (some scientists argue 26 million years), 50 to 95 percent of Earth's species die off -- and we're due. But don't give up and quit your job: These losses occur over the course of a few million years.
What has caused species eradication in the past? Scientists aren't sure, but they have some theories:
  • A giant asteroid could have sent up clouds of dust that blocked the sun's rays and lowered global temperatures.
  • Extensive volcanic eruptions could have led to global warming.
  • A reduction of sea level caused by glacier formation may have wreaked havoc, especially on marine species.
  • Gamma rays (high levels of radiation) caused by a collapsing star could have instigated a global drop in temperature.
  • A supernova (stellar explosion) may have sent galactic cosmic rays to Earth, interfering with climate stability and leading to an ice age.
  • Currently, many scientists blame human intervention for the alarming pace of extinctions, which is, at minimum, 100 times the expected natural rate of species loss.

9. What caused the "Wow!" signal?
Picture this: You receive an unanticipated but welcome phone call. What might you say? "Yea! Wahoo! About time!"

"Wow!" That was the stunned reaction Jerry Ehman wrote on a computer printout that may have been evidence of a signal from space. In 1977, Dr. Ehman, a professor at Ohio University and a volunteer for the SETI project (Search for Extraterrestrial Intelligence), was studying data from the Ohio State University Radio Observatory when he noticed a loud signal that lasted two-and-a-half minutes. Why was this reading so special?

Almost two decades earlier, physicists from Cornell hypothesized that non-terrestrial beings searching for other intelligent life forms would use universal systems, such as mathematics and science, to communicate. Hydrogen, the most abundant element in the universe, resonates at 1420 megahertz. The SETI radio telescope, therefore, monitored that frequency, and Dr. Ehman's "Wow!" printout nearly matched that resonance.

The signal was traced to an area in the Sagittarius constellation, but no planet or star was located. There has been considerable speculation about the source, and scientists have a few suggestions:
  • A signal from a moving spaceship
  • Noise from a black hole, pulsar or gamma ray
  • A plane, jet or satellite signal or Earth broadcast (These suggestions have been discarded, however, because such broadcasting is not permitted at 1420 megahertz.)

8. What caused the Pioneer anomaly?
If you're balancing your checkbook and you're a few cents off, do you worry about that? Some people let it pass; it's only spare change. Other folks find it important to account for every penny. You have your records and you've kept track; it should make sense. That's the way many astronomers feel about the Pioneer anomaly.

In 1972, NASA launched the space probe Pioneer 10 to observe Jupiter; Pioneer 11 was launched the following year to investigate Saturn. They were to leave the solar system eventually, but their journey appeared nonstandard. In 1998, NASA realized that both probes were traveling at speeds slightly slower than anticipated. The difference was relatively tiny, but considering the scientific, technological and mathematical precision needed for space travel, the anomaly should not have existed.

It could simply have been a gas or heat leak, but what if the source was not so mundane? What if gravity was affecting the rate, and it was not recognized because we don't have a full understanding of the force? What if gravity doesn't always act as we expect?

NASA researchers initiated a study in 2006 to try to identify the cause of the incongruity. Using decades of temperature and power readings from both probes, scientists began analyzing data, hoping to determine a few things:
  • Exactly when the anomaly began
  • The location of the anomaly
  • The nature of the anomaly
  • Similarities and differences between the anomalies of each probe

7. What is Saturn's polar hexagon?

Saturn is a fascinating planet, with seven icy rings traveling around it. It also has another special feature: a huge hexagon located in the atmosphere over the planet's north pole. Initially reported in the 1980s by the Voyager 1 and 2 probes, its existence was confirmed 20 years later by the Cassini spacecraft (a joint project between NASA, the European Space Agency and the Italian Space Agency).

This phenomenon has never been observed on any other planet, nor is it seen elsewhere on Saturn -- the south pole has an apparent hurricane. The hexagon is precise; its sides are straight and equal. It's also enormous, with a width of 15,000 miles (24,140 kilometers). That's almost twice the diameter of Earth.

Scientists are not certain of the cause of the hexagon, but researchers at the University of Oxford hypothesize that it may be the result of "fluid dynamics." They created a laboratory simulation that mimicked a jet stream flowing through a planet's rotating atmosphere. The shape of the jet stream depended upon speed: The greater the difference between the rotation of the planet and the spinning of the jet stream, the more sides the stream developed. A very rapidly moving stream created a hexagon.

6. What is dark matter?
Dark matter sounds like something from an espionage story: "The spy realized he was in the midst of a very dark matter." It may seem vaguely sinister, but it's actually a term used to describe a large component of the universe that we don't understand yet.

Our world is made up of atoms (baryonic matter, to astronomers), but does that hold true in space? Scientists wondered and began estimating the mass of galaxies by monitoring the relative velocities of its planets, stars and gases. Supporting evidence was obtained by observing gravitational lensing (the bending of light), which is demonstrated when the appearances of farther galaxies are changed by nearer ones.

In 2001, the Wilkinson Microwave Anisotropy Probe (WMAP) was launched to gather diverse data. One of its functions is to measure density of the universe, identifying amounts of baryonic and non-baryonic matter. Added to those earlier observations, scientists can estimate the substance of the universe accurately: Less than five percent is baryonic matter (atoms). Most of the remainder is dark matter (23 percent) and dark energy (72 percent).

Dark matter is affected by the push and pull of gravity, yet it can't reflect or produce light. So what is it? Brown dwarfs (small stars) have been proposed because they're so dim they can only be identified by their gravitational pull. Perhaps gigantic black holes (collapsing stars) are taking up a lot of space. It could even be a type of matter with which we are unfamiliar -- something altogether new.

5. What is dark energy?
Dark energy is not the burst of vigor toddlers seem to get as twilight approaches and their parents unwind. Rather, it's a comprehensive scientific explanation for some insufficiently understood features of the universe. For instance, scientists had believed that, due to the presence of gravity and the large amount of matter, the universe would eventually stop expanding. However, observations made around the turn of the 21st century indicated that expansion was actually speeding up. Why?

Another feature requiring clarification is the shape of the universe, which depends on the amount of matter and energy within it. A great deal of matter and energy would result in a spherical universe, which would ultimately collapse. With much less matter and energy, the universe would be saddle-shaped and expand at a decreasing rate. Amounts somewhere in between the two produce a flat universe. Recent observations made by WMAP revealed this last scenario, but scientists can't detect enough matter to form a flat universe. So why is it flat?

The answer to both questions is energy, specifically dark energy. Astronomers believe it composes 72 percent of the universe, but other facts are scarce. There are hypotheses, though:
  • It may be a property of space.
  • It may be a previously unknown energy field that operates quite differently from familiar energy or matter.
  • Einstein's theory of gravity is wrong. If so, the increasing expansion of the universe would need a new explanation. Could dark energy be part of this new theory of gravity?

4. How do galaxies form?
The Milky Way: not just a tasty candy bar, but the galaxy for our very own sun. Not that it makes us special -- there are 100 billion stars in that galaxy.

And that's one galaxy out of a projected 200 billion in the entire universe. Where did all these galaxies come from?

Scientists don't know for certain how galaxies were formed after the Big Bang, but there are at least two possibilities. Both would have been extremely slow processes:
  • Smaller to larger: Small particles and radiation combined to create stars, then combined into galaxies. If the center of the galaxy developed first, it would eventually expand into a disk with spiral extensions. (Thus, a spiral galaxy.) If the stars formed more or less simultaneously, an elliptical galaxy would materialize. (Huge ellipticals may also emerge after galaxies collide and unite.)
  • Larger to smaller: Massive collections of cosmic materials eventually separated into galaxies. Gravity and the motion of the matter would have caused the masses to divide and reform.

3. Is there other life in the universe?
There's a story that one day in 1950, Enrico Fermi, the Nobel prizewinning physicist, asked his lunch companions, "Where are they?" This became known as Fermi's paradox: Why are we not aware of life on other planets? There are so many solar systems, so many planets and so many possibilities.

So where are they?

The Milky Way galaxy has been in existence for more than 10 billion years; hominids have inhabited Earth during a fraction of that. Considering how far we've come in a relatively short time, why don't we see evidence of life in older solar systems? Several hypotheses attempt to explain the lack of contact, but none are terribly satisfying:
  • Extraterrestrials have visited Earth, but we failed to recognize the signs. (No evidence.)
  • Extraterrestrials are our ancestors. (No evidence.)
  • Extraterrestrials have not had time to contact us yet. (No long-distance messages? No space probes?)
  • Extraterrestrials are trying to contact us, but we are oblivious to the signs. (We know a lot of basic ways to communicate, such as electromagnetic radiation. Why wouldn't they?)
  • Extraterrestrials don't understand our mathematics; they employ a different system. (There's no evidence of any strange messages.)
  • We are the first civilization. (Our sun, however, is not particularly old. Other stars are far older and thus have the opportunity to provide energy for other life forms.)
  • Extraterrestrials have all died off; we are the only civilization left. (Maybe we are alone.)

2. Are there other universes out there besides ours?
In "The Wizard of Oz," Dorothy (and her little dog, too) travels to an unearthly land, which she immediately knows is "not in Kansas." Surrounded by talking animals, animated objects and magic, she's clearly not in our world. She may be in a dream, or she may be in an alternate reality. Some scientific models, such as string theory, propose that there are many universes that cannot be seen by us, perhaps even an infinite number. This is known as multiverse theory.

How could this be possible? One hypothesis suggests that within a black hole (a collapsing star), there is a spot where our understanding ends: The physical laws we know and love no longer function as expected. One possible result of this could be a wormhole, a shortcut to another part of the universe. Suddenly, space seems smaller, and traveling to another star system is conceivable.

However, if all physical laws are up for grabs, there could be another consequence.

Imagine a place with no gravity, no magnetism and no friction. If there was a location where even one of our physical laws didn't exist, it could legitimately be described as a different universe. Would separate wormholes lead to diverse sites, essentially allowing us entry to multiple universes?

Would there be any life? Even slight deviations from our universe's norms would make life as we know it impossible.

1. What came before the Big Bang?
When you picture the Big Bang, do you envision a tremendous explosion of material? It's an awesome image, but the scientific depiction differs. At the moment of the Big Bang, all energy and matter were concentrated in one spot. There was no colossal blast; matter and energy simply appeared everywhere at once. Particles didn't burst away from a central point; there was no middle.

That's the Big Bang -- but what happened before it? With no data to guide them, many scientists avoid speculation. Others have suggestions:
  • Time is not infinite. It has a specific beginning, and that was the Big Bang.
  • Quantum physics replaces the usual cause-and-effect approach of science with a chaotic framework. Therefore, the Big Bang happened, because, well, it happened.
  • Quantum cosmology proposes that time was, at one point, simply another dimension of space. Time separated out on its own at the moment of the Big Bang; consequently, there was no before.
  • Fluctuations of microwaves (electromagnetic waves) recorded by a space probe indicate that the level of microwaves varies throughout the universe rather than being uniform. Do the areas of the more intense waves indicate remnants of whatever existed before the Big Bang?
The Big Bang is the best explanation scientists have for the creation of the universe, but it's incomplete. There's still plenty more to discover about space, and scientists will continue to explore. As Albert Einstein said, "The important thing is to not stop questioning. Curiosity has its own reason for existing".

Source: NASA by discoverychannel.com


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