Comet 46P/Wirtanen. Image Credit: By Stub Mandrel at English Wikipedia, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=75160399
TESS, the Transiting Exoplanet Survey Satellite, has imaged an outburst from the comet 46P/Wirtanen. It caught the outburst in what NASA is calling the clearest images yet of a comet outburst from start to finish. A comet outburst is a significant but temporary increase in the comet’s activity, outside of the normal sunlight-driven vaporization of ices that creates a comet’s coma and tail.
Astronomers aren’t certain what causes them, but a new study based on this observation is shedding some light on them.
Left: A new image of the interstellar comet 2l/Borisov. Right: A composite image of the comet with a photo of the Earth to show scale. (Pieter van Dokkum, Cheng-Han Hsieh, Shany Danieli, Gregory Laughlin)
On August 30th, 2019, astronomers with NASA, the ESA, and the International Scientific Optical Network (ISON) announced the detection of the interstellar comet C/2019 Q4 (2I/Borisov). News of the object was met with a great deal of excitement since it was only the second interstellar object to be detected by astronomers – the first being the mysterious object known as ‘Oumuamua (which astronomers are still unsure about)!
After a lot of waiting and several follow-up observations, 2I/Borisov is about to make its closest approach to Earth. To mark the occasion, a team of astronomers and physicists from Yale University captured a close-up image of the comet that is the clearest yet! This image shows the comet forming a tail as it gets closer to the Sun and even allowed astronomers to measure how long it has grown.
Images from the Hubble Space Telescope of activated asteroid P/2013P5 where the dust tail can be seen. Source: NASA/ESA.
In the 18th and 19th centuries, astronomers made some profound discoveries about asteroids and comets within our Solar System. From discerning the true nature of their orbits to detecting countless small objects in the Main Asteroid Belt, these discoveries would inform much of our modern understanding of these bodies.
A general rule about comets and asteroids is that whereas the former develop comas or tails as they undergo temperature changes, the latter do not. However, a recent discovery by an international group of researchers has presented another exception to this rule. After viewing a parent asteroid in the Main Belt that split into a pair, they noted that both fragments formed tails of their own.
The reason asteroids do not do behave like comets has a lot to do with where they are situated. Located predominantly in the Main Belt, these bodies have relatively circular orbits around the Sun and do not experience much in the way of temperature changes. As a result, they do not form tails (or halos), which are created when volatile compounds (i.e. nitrogen, hydrogen, carbon dioxide, methane, etc.) sublimate and form clouds of gas.
Images of the P/2016 J1 asteroid pair taken on May 15th, 2016. They show a central region, the asteroid, and a diffuse blot corresponding to the dust tail. Credit: IAA
As astronomical phenomena go, asteroid pairs are quite common. They are created when an asteroid breaks in two, which can be the result of excess rotational speed, impact with another body, or because of the destabilization of binary systems (i.e. asteroid that orbit each other). Once this happens, these two bodies will orbit the Sun rather than being gravitational bound to each other, and progressively drift farther apart.
However, when monitoring the asteroid P/2016 J1, an international team from the Institute of Astrophysics in Andalusia (IAA-CSIC) noticed something interesting. Apparently, both fragments in the pair had become “activated” – that is to say, they had formed tails. As Fernando Moreno, a researcher at IAA-CSIC who led the project, said in an Institute press release:
“Both fragments are activated, i.e., they display dust structures similar to comets. This is the first time we observe an asteroid pair with simultaneous activity… In all likelihood, the dust emission is due to the sublimation of ice that was left exposed after the fragmentation.”
While this is not the first instance where asteroids proved to be an exception to the rule and began forming clouds of sublimated gas around them, this is the first time it was observed happening with an asteroid pair. And it seems that the formation of this tail was in response to the breakup, which is believed to have happened six years ago, during the previous orbit of the asteroid.
An artist’s conception of two tidally locked objects orbiting the Sun from afar (2010 WG9). Credit: zmescience
In 2016, the research team used the Great Telescope of the Canary Islands (GTC) on the island of La Palma and the Canada-France-Hawaii Telescope (CFHT) at Mauna Kea to confirm that the asteroid had formed a pair. Further analysis revealed that the asteroids were activated between the end of 2015 and the beginning of 2016, when they reached the closest point in their orbit with the Sun (perihelion).
This analysis also revealed that the fragmentation of the asteroid and the bout of activity were unrelated. In other words, the sublimation has happened since the breakup and was not the cause of it. Because of this, these objects are quite unique as far as Solar System bodies go.
Not only are they two more exceptions to the rule governing comets and asteroids (there are only about twenty known cases of asteroids forming tales), the timing of their breakup also means that they are the youngest asteroid pair in the Solar System to date. Not bad for a bunch of rocks!
The force of gravity can cause comets to rip apart.
[/caption]There are many interesting facts about comets. Some are about the different parts of the comet, others are about the effects that comets have had on humans and their behavior. This article will let you know about the different parts of the comet, the orbital habits of a comet, and the effects that comets have had on human behavior.
There are several interesting facts about comets. The first ones involve their nucleus. Comet nuclei can range from about 100 meters to more than 40 kilometers across. They are composed of rock, dust, ice, and frozen gases such as carbon monoxide, carbon dioxide, methane, and ammonia. They have been described as “dirty snowballs”, but recent observations have revealed that they have dry dusty or rocky surfaces, suggesting that the ices are hidden beneath a crust. Comet nuclei also contain a variety of organic compounds in addition to the gases already mentioned, these may include methanol, hydrogen, hydrogen cyanide, formaldehyde, ethanol, and ethane. It is also thought that they may contain more complex molecules such as long-chain hydrocarbons and amino acids. Because of their low mass, comets cannot become round under their own gravity and will have irregular shapes. Surprisingly, cometary nuclei are among the darkest objects known to exist in the solar system. They often reflect approximately 4% of the light that falls them . In comparison, asphalt reflects 7% of the light that falls on it. It is thought that complex organic compounds are the dark surface material. The very darkness of cometary surfaces allows them to absorb the heat necessary to drive their outgassing.
The most visible part of a comet is the coma. As a comet approaches the inner solar system, radiation causes the volatile materials within the comet to vaporize and stream out of the nucleus, carrying dust away with them. The streams of dust and gas form a huge, extremely tenuous atmosphere around the comet called the coma, and the force exerted on the coma by the Sun’s radiation pressure and solar wind cause an enormous tail to form, which points away from the Sun.
The coma and tail are illuminated by the Sun and may become visible from Earth when a comet passes through the inner solar system, the dust reflecting sunlight directly and the gases glowing from ionization. The streams of dust and gas each form their own distinct tail, pointing in slightly different directions. The tail of dust is left behind in the comet’s orbit in such a manner that it often forms a curved tail called the antitail. At the same time, the ion tail, made of gases, always points directly away from the Sun. This is because gas is more strongly affected by the solar wind than is dust, following magnetic field lines rather than an orbital trajectory. While the solid nucleus of comets is generally less than 50 km across, the coma may be larger than the Sun, and ion tails have been observed to extend 1 AU or more.
Most comets have elongated elliptical orbits that take them close to the Sun for a part of their orbit, and then out into the further reaches of the Solar System for the remainder. Comets are often classified according to the length of their orbital period, the longer the period the more elongated the ellipse. Short period comets are generally defined as having orbital periods of less than 200 years. They usually orbit more-or-less in the ecliptic plane in the same direction as the planets. Their orbits typically take them out to the region of the outer planets at aphelion. Short-period comets are further divided into the Jupiter family (periods less than 20 years) and Halley family (periods between 20 and 200 years).
Long-period comets have highly eccentric orbits and periods ranging from 200 years to thousands or even millions of years. Their orbits take them far beyond the outer planets at aphelia, and the plane of their orbits need not lie near the ecliptic. Single-apparition comets are similar to long-period comets, but have parabolic or hyperbolic trajectories which will cause them to permanently exit the solar system after passing the Sun once.
Comets have been instilling fear and awe into us since man first began to look toward the sky. As early as 240 B.C. the Chinese began to document the appearance of Halley’s Comet. Ancient Greeks believed that comets resembled stars with hair flowing behind them. In ancient times, before scientists discovered what exactly comets are, many people believed that comets were a curse or a harbinger of tragedy and misfortune. It was this belief that comets were a sign of a curse that led the Roman Emperor Nero to order all of his potential successors to be executed. More recently, in 1910, as the Earth passed through Halley’s Comet’s tail, businessmen took advantage of people’s fears of impending doom and sold items such as gas masks, anti-comet pills, and umbrellas to protect users from the dangers of the comet.
