Comet Hyakutake

Comet Hyakutake

Comet Hyakutake , officially called C / 1996 B2 (Hyakutake), is a long-period comet discovered on January 30, 1996 by the Japanese amateur astronomer Yuji Hyakutake . In March 1996, the comet passed relatively close to the Earth (its approach was one of the closest approaches of comets to the Earth in the last 200 years). The comet was very bright and easily observed with the naked eye in the night sky, due to which it was named the " Big Comet of 1996" . For some time, comet Hyakutake eclipsed comet Hale - Bopp , which at that time was approaching the inner region Solar system .

The observation of Comet Hyakutake has led to several scientific discoveries. The most surprising for scientists was the first discovered X-ray emission from a comet, probably caused by the interaction of the ionized solar wind with neutral atoms in the comet's coma... In addition, the Ulysses spacecraft unexpectedly crossed the tail of comet Hyakutake at a distance of more than 500 million km from the nucleus .

Until the last passage of Comet Hyakutake through the solar system, its orbital period was 17,000 years, but after interacting with the gravitational field of the giant planets, it increased to 70,000 years or more.

Timeline

Opening

The comet was discovered on January 30, 1996 by the Japanese amateur astronomer Yuji Hyakutake . By that time, he had been searching for comets for several years, which largely determined his move to Kagoshima Prefecture for the darker sky of rural areas. His usual place of sighting was a mountain about 15 km from his home. To observe the starry sky, he used a powerful wide-angle astronomical binoculars with 6- inch objectives (150 mm ) Fujinon 25x150 MT-SX mounted on a mount .

This comet became the second in a row discovered by Hyakutake. He discovered the first, C / 1995 Y1on December 26, 1995 , but in the end it did not reach high brightness: it could only be observed through a telescope . Five weeks later, while observing C / 1995 Y1 and the surrounding space, he noticed another comet, just 4 ° from the part of the sky where he had previously found the first one . Recalling his condition at the time of the discovery of a new comet, Hyakutake wrote:

 

To be honest, I was a little confused. My reaction was somewhat difficult to understand, as I originally intended to travel [to my usual place] to take a picture of the first comet. I found the second comet in the same place as the first, near the constellations Libra and Hydra .

 

Hardly believing in his luck, Hyakutake announced the opening to the National Astronomical Observatory of Japan . On the same day, the discovery was confirmed by independent observers. At the time of detection, the comet was at a distance of about 2 AU. e. from the Sun , having an apparent magnitude of 11.0 and an angular diameter of 2.5-3 minutes . After its discovery, comet Hyakutake was found in the image taken on January 1, 1996 (that is, before it was discovered), when it was at a distance of 2.4 AU. e. from the Earth and had a brightness of 13.3 .

The first calculations of the comet's orbit, performed by the head of the Central Bureau of Astronomical Telegrams Brian Marsden on February 3 , showed that on March 25, 1996, the comet would pass approximately 0.1 AU. ie from the Earth . For comets, this is a very small distance: in the last century, only four "tailed wanderers" passed closer: C / 1983 H1 (IRAS - Araki - Alcoca) , 7P / Ponsa - Winnecke , 73P / Schwassmann - Wachmann and C / 1983 J1 (Sugano - Saigus - Fujikawa) .

At the beginning of 1996, bright comets had not appeared for almost 20 years: the last "Big" was Comet West (C / 1975 V1) . Since mid- 1995, astronomers have already anticipated the appearance of another comet, C / 1995 O1 (Hale-Bopp) , which was predicted to break this long "comet-free" period in 1997 . The discovery of comet Hyakutake gave reason to assume that it will outstrip Hale-Bopp and become the next in a series of bright comets, if only its activity continues .

Comets that first arrive in our system from the Oort cloud often "flash" brightly at first, but then their brilliance subsides as soon as their upper layer of volatiles evaporates. So, for example, it happened with the comet Kohoutek in 1973 : it was initially believed that it would be very bright, but the comet did not live up to the forecasts, reaching only moderate indicators . From the very beginning, orbital calculations showed that comet Hyakutake is not "new", but long-period : the last time it was in the solar system about 17,000 years ago, and it approached the Sun more than once ...These data indicated that the brightness of C / 1996 B2 would not change dramatically, and that the comet's appearance would be very memorable.

The passage of a comet past the Earth

By mid-February, the comet reached a brightness of 8.5 , and it became possible to observe it with small binoculars, and by the end of February, it could already be seen with the naked eye. Until mid-March, it was still not very noticeable, reaching only 4th magnitude and having a 5 ° tail. However, the closer the comet approached the Earth, the faster its brightness, coma diameter and tail length increased. So, if on March 13 the angular diameter of the C / 1996 B2 coma was estimated at 20 minutes, then on March 19 it exceeded 1 °, which is twice as large as the apparent diameter of the Moon . By March 24, thecomet had become one of the brightest objects in the night sky, and its tail was already 35 ° long. The comet was a remarkable bluish-green color.

On March 25, comet Hyakutake approached the Earth as close as possible (0.1018 AU = 15.2 million km) . The comet was moving so fast (about 50 km / s) that its movement could be seen in just a few minutes of observing the starry sky; in 30 minutes it covered a distance equal to the full diameter of the moon (0.5 °). Observers reported that its brightness is equal to 0th magnitude, and the length of the tail has grown to 80 ° (the absolute record for the apparent size of a comet's tail). Her coma , which by that time is almost at the zenith for observers of mid-northern latitudes , reached about 1.5-2 ° in diameter (that is, about 3-4 full diameters of the moon).Even with the naked eye, it was easy to see that the comet's head has a greenish color (a consequence of the strong emission of diatomic carbon C ₂ ).

During the passage of the comet near the Earth, the inhabitants of the northern hemisphere had the opportunity to observe it all night, since, due to its large inclination, the visible trajectory of comet Hyakutake ran along the polar constellations . Such observation conditions are unusual for comets: the brightest comets of the 20th century were observed at twilight , and most of the other comets open near the Sun in the so-called "Everhart zone" .

Unlike other "Big" comets , in particular, the same comet Hale - Bopp , which appeared in the next 1997 , C / 1996 B2 became noticeable precisely because of its approach to the Earth, and not because of its size therefore, it was bright for only a few days. In addition, in some European countries (in particular, England) due to unfavorable weather conditions in March 1996, its observation was very difficult .

Perihelion and the path after it

After a close approach to the Earth, the comet's brightness dropped to 2nd magnitude, and stayed near this value near perihelion ( May 1, 1996 ), after which it continued to decline. In addition to the previously observed ionic tail, the comet has a dusty tail. True, now its proximity to the Sun made observation difficult. The study of the comet during its perihelion passage continued with the SOHO satellite , which at the same time recorded a large coronal mass ejection . The distance between the comet and the Sun at that time was 0.23 AU. ie

After passing the perihelion, comet Hyakutake quickly lost its brightness, and by the end of May it became inaccessible to the naked eye. Now the comet has moved to the southern hemisphere, but such extensive studies have not been carried out as before. The last known observation was made on November 2, 1996 .

Scientific results

Orbit

Comet Hyakutake's orbit has a number of features. In addition to the fact that the comet's trajectory allowed it to approach the Earth, another unusual fact was discovered: the comet's orbital plane has an inclination of 125 ° , that is, it is located almost perpendicular to the ecliptic plane . This fact, as well as the long period of the comet, indicate that it was formed in the Oort cloud , and not in the Kuiper belt .

The comet's original orbital period around the Sun was estimated at 17,000 years, but in 1996 the comet's orbit was heavily influenced by the gravity of the giant planets , and now estimates of the comet's return time range from 70,000 to 110,000 years. In this case, the point of maximum distance from the Sun ( aphelion ) is located at 4560 AU. e. (or 0.072 sv.g . )>.

The passage of a spacecraft through the tail of a comet

On May 1, 1996, an unexpected event occurred: the Ulysses research vehicle passed through the tail of comet Hyakutake . At this moment he was at a distance of 3.73 AU. e. from the Sun, and the angle of inclination to the ecliptic was about 45 °. No evidence of the meeting was found until 1998 . A group of astronomers studying archival data from Ulysses drew attention to a sharp increase in the level of protons , as well as changes in the strength and direction of the magnetic field around the spacecraft during flight . This meant that Ulysses crossed the trail of some object, it was assumed that comets.

In 2000, two independent groups of scientists began to find out what kind of object it was . The magnetic measurement group has been building on the fact that such changes in magnetic field are similar to phenomena thought to occur in comet ion tails. Finding no registered comets near Ulysses, the group expanded their search. She soon found out that on April 23, 1996, Hyakutake crossed the orbital plane of the device, being at a distance of 500 million km from it. Under the action of the solar wind at a speed of about 750 km / s, the tail displacement to the point of meeting with the spacecraft would take exactly 8 days.Based on Ulysses' data, it was also established that the source of the trace was in the plane of the orbit of comet Hyakutake .

At the same time, another group, working on data obtained from the Ulysses ion spectrometer, found a sharp jump in the ion level. The relatively high abundance of chemical elements meant that the source was definitely a comet . Thanks to the meeting with Ulysses, it was found that the length of the tail of this comet was at least 570 million km (3.8 AU). This is almost 2 times more than the previous record of 2 amu. e., belonging to the tail of the Big Comet in 1843 .

Composition

Observations made from Earth have revealed the presence of various compounds of hydrocarbons , nitrogen and sulfur , in particular, cyanide (HCN) and isocyanide (HNC) hydrogen, H CN, isocyanic acid (HNCO), carbon monoxide (CO), methyl alcohol ( CH ₃ OH), formaldehyde (H ₂ CO) , carbon monosulfide (CS), hydrogen sulfide (H ₂ S) . For the first time organic gases were discovered for comets - ethane (C₂ H ₆ ) and methane (CH ₄ ). Chemical analysis showed that the relative content of the latter was approximately equal. This indicates that the comet was born in interstellar space far from the Sun, whose radiation would have evaporated these volatile compounds . Comet Hyakutake's ice masses must have formed at temperatures of 20 K or less. Most likely, the medium “native” for the comet was denser than an ordinary interstellar cloud .

The deuterium content of the comet's ice was determined by spectroscopic methods . It was found that the D / H (deuterium to hydrogen ) ratio is approximately 3.0⋅10 , while in the oceans on Earth it is only 1.6⋅10 . There is a theory according to which the main source of water on Earth was comets that fell on the planet , but a similar higher D / H ratio found in comets Hyakutake, Hale-Bopp and Halley gives reason to doubt it ...

X-rays

One of the biggest surprises from Comet Hyakutake was very strong X-rays . It was recorded by the ROSAT apparatus on March 27, 1996 . This was the first time that comets had such radiation, but astronomers soon became convinced that almost every comet had it. The strongest radiation came from the comet's head on the "sunny" side.

It is assumed that the cause of this phenomenon is a combination of two processes. An important role is played by the interaction between charged particles of the solar wind and matter evaporating from the comet's nucleus . Although the phenomenon of reflection of solar X-rays has been observed in other space objects (for example, the Moon ), simple calculations show that, even with the highest reflectivity of a molecule or dust particle, it is impossible to explain such a strong radiation, whereas the "atmosphere" of a comet Hyakutake is rather thin and sparse. Observations of comet C / 1999 S4 (LINEAR)by the orbiting X-ray observatory " Chandra " in 2000 made it possible to establish that the main cause of X-ray radiation was the exchange of charges during the collision of highly active ions of carbon monoxide and nitrogen in the solar wind with neutral molecules of water , oxygen and hydrogen in a coma .

The comet nucleus and its activity

Radar observations at the Arecibo Observatory showed that the nucleus of comet Hyakutake was about 2 km across and was surrounded by a "swarm" of pebble- sized particles ejected at a speed of several meters per second. These measurements were confirmed by conclusions drawn from infrared and radio observations .

The small size of the nucleus (for comparison, the nucleus of Halley's comet is about 15 km across, the Hale-Bopp comet is about 40 km) with a high brightness of the comet itself means that the nucleus must be very active. Most comets release matter only in certain areas of their surface, but it seems that comet Hyakutake had all (or almost all) of the surface layer active. At the beginning of March, the dust release rate was 2 t / s, and as the comet approached perihelion, it increased 150 times. At the same time, the velocity of the ejection itself increased from 50 m / s to 500 m / s .

Observations of the ejection of matter allowed astronomers to establish the speed of rotation of the comet's nucleus. It was noted that, passing by the Earth, the comet ejected a large mass of matter with a period of 6.23 hours. A similar, but smaller eruption, occurring with the same frequency, confirmed that this was the rotation period of the comet's nucleus .

The legacy of the comet

After it became clear that Hyakutake would pass close to Earth, there were reports in some tabloids that the comet would actually hit Earth. The Weekly World News called the discovered comet a “doomsday comet”, confusing, however, almost all the details of its discovery. Nevertheless, the reaction of the masses to Hyakutake was still calmer than to the same Hale-Bopp a year later .

Comet Hyakutake is mentioned in some feature films. The main heroine of melodrama 2002 " A Walk to Remember " ( Engl.  A Walk to the Remember ), removed Adam Shenkmanom , wanted to assemble a telescope to see the comet , is the desire to perform its young people closer to the end of the film . In one of the scenes of the film "Hurricane" by Leonardo Pieracchioni, members of the Quarini family are looking for a comet in the sky .

The comet was not ignored by astrologers either . So, she is mentioned in the book of Pavel Globa "The Teachings of the Ancient Aryans", where a chapter entitled "The Savior's Comet" is devoted to her .

In 1997, the studio Cyanogen Productions withdrew Comet yakutake documentary "the Comet Odyssey: the Comet Hyakutake Brought to Life with Time The Lapse Movies" .