What is Halley’s comet?

We explain what Halley’s comet is, its characteristics, origin and discovery. Also, when will it happen again near Earth.

1. What is Halley’s comet?

Officially known as 1P / Halley and popularly as Halley’s Comet, it is a large and bright comet, which orbits our Sun every 75 years or so (between 74 and 79 years), meaning it has a short period. It is the only one of its kind that can be seen from the Earth’s surface, making it an extremely popular astronomical phenomenon.

The Halley has an irregular orbit around the Solar System . It is one of the best known astronomical objects from those that come from the Oort Cloud, a spherical conglomerate of trans-Neptunian objects.

Its irregularity is due to its orbit being distorted by the gravity of the planets (especially the outer giants) of the Solar System . It is also due to its changing mass, since the comet loses tons of frozen water with each step around the Sun.

This comet owes its name to British astronomer Edmund Halley, who in 1682 was the first to observe and detail it scientifically. However, Halley’s comet had been observed and recounted by diverse cultures since ancient times .

2. Origin of Halley’s Comet

The various comets that cross our solar system have two possible origins: the Kuiper belt, a set of frozen astronomical rubble located about 50 astronomical units (AU) from the Sun, beyond the orbit of Neptune; or the Oort cloud, a set of frozen bodies that is still a hundred times farther away, at the very edges of the solar system.

Although usually short period comets come from the Kuiper Belt. However, the case of Halley is strange, since it was born in the farthest body of the Oort cloud , as with other long-period comets, such as Hale-Bopp, whose orbit takes thousands of years.

This is because it was initially a long-cycle comet, which was captured in the gravity of the planets of the Solar System, especially Venus.

3. History and discovery

Halley’s comet was observed by mankind since time immemorial. It is estimated that the year 239 a. C. was the first record of its passage . That is why it is not accurate to talk about its discovery in the 17th century. However, his scientific discovery is attributed to Edmund Halley , who was also the first to calculate its orbit in 1705.

In fact, it is known that in 1456 the comet had been observed by German astronomer and mathematician Johann Müller Regiomontano; in 1531 by the German humanist Petrus Arpianus; and in 1607 by Johannes Kepler in Prague.

Thanks to all these documents Halley was able to deduce that the comet cycle was repeated every 76 years , thus predicting its appearance by 1757. A fairly accurate prediction, since the comet appeared on December 25, 1759, sixteen years after Halley’s death .

Since then the comet has frequented our planet in 1835, 1910 and 1986 .

4. Halley’s Comet Study

The Halley study was a recurring theme for Chinese, Babylonian and medieval European astronomers throughout history. It was associated with cyclic rites, changes of era, and it is even thought that this comet could have been the so-called Star of Bethlehem, which according to biblical mythology led the Three Wise Men to the birth of Jesus Christ.

The Halley is also the first comet to be observed from outside the atmosphere and studied in high degree of detail by various space probes, such as Vega 1 and 2, Giotto, Suisei (PLANET-A), Sakigake and the ISEE-3 / ICE.

This set of space probes is popularly known as the Halley Navy and we owe our extensive knowledge of the comet.

5. Halley’s comet characteristics

The Halley is composed of a relatively small core, peanut-shaped or peanut-shaped, 15km long and 8km wide and tall. It has a low mass of 2.2 × 10 ¹⁴ kg and a density of 0.6 g / cm ³ . It reflects only 4% of the light received, more or less the same as coal, so that it is a black body, although from the Earth it looks white and bright.

In addition, it has a comma or hair (gas cloud) that extends over millions of kilometers in space. This gas is emitted when the Sun’s energy heats its surface, and is composed of 80% water vapor, 17% carbon monoxide and between 3 and 4% carbon dioxide , with possible traces of hydrocarbons.

Halley’s scientific observation coincided with the predictions of American astronomer Fred Lawrence Whipple, who claimed in 1950 that the comets were “dirty snowballs.”

6. When will Halley’s comet happen again?

The orbit of Halley’s comet, as we said, is irregular and cannot be predicted too accurately, but considering that the last time to pass by Earth was in 1986, the most likely date it will return will be that of 2061 .

Experts warn that, within thousands of years, the orbit of Halley will change and will be influenced by Jupiter, being able to lengthen in orbits of 300 years instead of the usual 75.