Bell Tone
Bell Tone
Narrator: All the comets that we can see from Earth are orbiting the sun, but some belong to a special group called sungrazing comets. Sungrazers are comets that come very close to the sun at their nearest approach, a point called perihelion. To be considered a sungrazer, a comet needs to get within about 850,000 miles from the sun at perihelion. Many come even closer, even to within a few thousand miles. Being so close to the sun is very hard on comets for many reasons. They are subjected to a lot of solar radiation which boils off their water or other volatiles. The physical push of the radiation and the solar wind also helps form the tails. And as they get closer to the sun, the comets experience extremely strong tidal forces, or gravitational stress. In this hostile environment, many sungrazers do not survive their trip around the sun. They don't actually crash into the solar surface, but the sun destroys them anyway. Many sungrazing comets follow a similar orbit, called the Kreutz Path, and collectively belong to a population called the Kreutz Group. In fact, close to 85% of the sungrazers seen by the SOHO satellite are on this orbital highway. Scientists think one extremely large sungrazing comet broke up hundreds, or even thousands, of years ago, and the current comets on the Kreutz Path are the leftover fragments of it. As clumps of remnants make their way back around the sun, we experience a sharp increase in sungrazing comets, which appears to be going on now. Comet Lovejoy, which reached perihelion on December 15, 2011 is the best known recent Kreutz-group sungrazer. And so far, it is the only one that NASA's solar-observing fleet has seen survive its trip around the sun. Comet ISON, an upcoming sungrazer with perihelion on November 28, 2013, is not on the Kreutz Path. In fact, ISON's orbit suggests that it may gain enough momentum to escape the solar system entirely, and never return. Before it does so, it will pass within about 40 million miles from Earth on December 26th. Assuming it survives its trip around the sun. All comets are great laboratories for scientists to learn more about our solar system, but sungrazing comets can also help us learn about the sun. Their tails of ionized gas illuminate invisible magnetic fields, so they can act as a tracer, helping scientists observe these normally unseeable features. Such fields have even ripped off comet tails, allowing astronomers to watch them blowing in the solar wind. A wind that abruptly accelerates between one and five million miles from the sun. Because of this, researchers will be watching ISON, and other sungrazing comets very closely. And since we are in a period of high sungrazing comet activity, scientists can expect many more chances to watch these beautiful, natural research satellites in the coming years.
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