HALE-BOPP

                                                                  Comet Hale-Bopp. (Image credit: NASA)

Introduction

Hale-Bopp was a highly regarded comet of the 20th century and was visible for many decades. It had been observable for 18-months straight, twice as long as the Great Comet of 1811, the previous record holder. Therefore, Hale-Bopp was named ‘the greatest comet’ of 1997.

Discovery

The comet was discovered on July 23, 1995 by two observers, Alan Hale in New Mexico and Thomas Bopp in Arizona. The next morning, it was confirmed that it was a newly discovered comet and was given the name C/1995 O1.

Observations

Being the centre of attention, many scientists had shown keen interest in researching about it. And a lot of observations were made. Researchers inferred the age of the comet to be approximately 4 billion years old. Its position in the universe was calculated to be about 7.2 AU from the Sun which was the longest distance from Earth where a comet had ever been discovered before. Most comets in this range are extremely dim, but Hale-Bopp already had a visible coma. The analysis also showed that its comet nucleus was 60 ± 20 km wide. Its orbital period and size were probably the main reasons why Hale-Bopp remained illuminated for so long. It was a long-period comet, frozen in space for a long time, which enables the comet keep its structure stable during perihelion path around the sun. The orbit of the comet was also farther away from the plane of the solar system which placed the comet at a reasonable high position after perihelion, keeping it out of the sun’s twilight glare.

The inner coma of the comet was extremely strong, probably due to its high dust production. And the dust particles of the comet were smaller than seen in any other comet due to its high 

temperature, high albedo and powerful silicate emission feature.

Sodium tail

Sodium Tail

One of the most remarkable findings on the comet was that it had a third type of tail i.e., the sodium tail, in addition to the known gas and dust tails. Sodium extraction had been observed before in other comets as well but was not shown to occur in the tail. The sodium tail of Hale-Bopp had neutral atoms and stretched 30 million miles in length. But the tail was only visible through strong instruments with detector filters.

                                       

.                                                                              Comet Hale–Bopp's neutral 

 The source of sodium would have been its nucleus but it looked like an internal coma. There are many ways to produce a source of sodium atoms, such as the "pumping" of sodium from dust particles by ultraviolet light or collisions between dust particles around the nucleus.

Although the exact cause of Hale - Bopp sodium tail has not yet been determined. It is also concluded that sodium atoms are driven into the comets head under radiation pressure as the sodium tail appears to lie between the comet's dust tail and the gas tail.

Deuterium Abundance 

The amount of deuterium in the form of heavy water is found in the comet, about twice that of the earth's oceans. This also means that although the cometary impacts are thought to be the source of the world's water resources, they cannot be the only source.

Deuterium has also been found in many other hydrogen compounds in the comet. The levels of deuterium and hydrogen have been found to vary from compound to compound, suggesting that comet ices are formed in interstellar clouds. As suggested by the theoretical model of the formation of ice in the interstellar, comet Hale-Bopp was formed at temperatures of about 25 to 45 kelvins.

Detection of chemicals

.                                                                                         Image Credit- Google

Hale-Bopp also reveals the presence of many natural chemicals, a number of which had never been detected in comets before. Hale-Bopp was the first comet to have argon gas. Apart from the fact that the solar nebula was much cooler and richer in argon than it is commonly

believed, this suggests that the comet was built across Neptune in the Kuiper belt region and then moved out to the Oort Cloud.                      

Observations helped astronomers determine the orbit of the comet, which was found to be 11 hours and 46 minutes long.

Although information using adaptive optics has shown a double peak in the light of nucleus, the argument remains as to whether such observations can only be explained by a binary nucleus or not. And no cases of stable binary nucleus were found till that date. Although the size of the comet is no different compared to other large comets before it. Most of the substances detected in the comet have been found in dust clouds and interstellar gas and also in the formation of planetary disks within those clouds. Therefore, the study of this comet has helped us gain better knowledge about the formation of planets. There are many factors that have led to the appropriate title ‘The Great Comet of 1997’. 

After perihelion

As the comet neared the Sun, it continued to illuminate and show growing tails, the blue gas tail pointed directly away from the Sun and its dusty yellow tail orbiting it. Hale –Bopp was

Extremely close to Earth on March 22, 1997, Hale –Bopp was extremely close to Earth at a distance of 1.315 AU.

                                                                              Passing the perihelion on April 1, 1997, the comet developed into a spectacular view. Its dusty tail reached 40-45 degrees in the sky and it was dazzling bright than any star in the sky except Sirius. Even before it was dark, it could be seen clearly, and to spectators in the northern parts, it was seen all night long.

Conclusion

Hale-Bopp was probably the most recognizable comet in history. Making a big impact on the norm and is certainly seen by more people than any other comets. As Hale-Bopp abated it continued to disappear. But it has made several important advances in cometary sciences, which helps us to find and observe comets more accurately today.

Article by- Nehal Sharma