comets & history of cometary science tamil nadu science forum for eyeson ison campaign 1

Comets&

History of Cometary science

TAMIL NADU SCIENCE FORUM

ForEyeson ISON campaign

1

History and philosophy of cometsHistory of Cometary astronomy can be divided into five major periods.1. Before 1600, comets were usually viewed as heavenly omens, or

possibly meteorological phenomena in the terrestrial atmosphere, and were not yet clearly established as astronomical bodies.

2. 17 th – 20th century : Evolution of cometary science – positional measurements and prediction of comets were established.

3. 1835 -1950: Evolution of Cometary physics- spatial structures in a comet were described in detail.

4. 1950 – 1985 : the emergence of the modern picture of comets as an ensemble of solar system objects composed of primordial ice and dust.

5. After 1985 : Use of space missions for in-situ measurements and close up images of comets

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History and philosophy of comets

• COMET – from Greek meaning ‘hairy star’

• The recorded earliest observation of a comet– 1000BCE in China and in

Chaldea (Iraq)

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• Chinese astronomers kept extensive records on the appearances, paths, and disappearances of hundreds of comets.

• The Mawangdui silk Texts, a 'textbook' of cometary forms and the various disasters associated with them, was compiled sometime around 300 B.C.

• Image credit: NASA/JPL


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• Prediction of a comet was not possible for ancient people as they did for planets.

• So they considered them as heavenly omens of disaster and messengers of the gods.

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• Pythagoras (550 BCE) – a kind of planet visible near horizon

• Aristotle (330 BCE) – Dry and warm exhalation in the upper atmosphere

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• The first recorded efforts to study the paths of comets across the heavens as an astronomical exercise- by Paolo Toscanelli

Comet of 1449-50 observed by Toscanelli

History and philosophy of cometsPath of a comet (1449)

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• In the 1530s Peter Apian in Germany discovered that the tail of a comet always points away from the Sun.

History and philosophy of cometsComets – Sun connection (1530)

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• The Aristotelian thought of comet as ‘sublunary’ object ( celestial object below the moon) which prevailed for many centuries , was broken by Tycho Brahe

• From the parallax observation of the Great Comet of 1577, he showed that its distance from the earth was 4 times the distance to the Moon.

History and philosophy of cometsComets far away from the earth (1578)

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• Kepler thought comets to be spherical transparent objects refracting the sun’s rays.

• He assumed that the head of a comet is a globe of transparent nebula-like matter which is denser than the surrounding ‘ether’, but is not solid and indissoluble.

• When the sun’s rays pass through the head they expel a stream or effluvium of the nebulous matter of the head in the opposite direction.

• This stream, which obviously is denser than the pure ether, reflects the sun’s rays and becomes visible as the tail of the comet.

History and philosophy of cometsLight source of Comets (1604)

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• Galileo argued that comets were optical phenomena (1623)

• Descartes thought that comets were bodies

that travelled from one solar system to

another.

• In Descartes’ philosophy, comets are the

final products of the cosmos and contain the

densest substance in the universe. They

have a planet-like head, but their tails are

optical.

• But both these were not accepted

History and philosophy of cometsLight source of Comets

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Path of a comet

• In 17th centuary the path of the comet was thought to be an elongated ellipse or parabolic.

• Georg Dörffel was the first to specifically state that the two bright comets seen in 1680 and 1681 are one and the same before and after its perihelion passage, and that it moved along a parabola with the Sun in the focal point.


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Path of a comet

• Newton, by introducing comets as members of the

solar system, opened the modern era of cometology.

• In this era, it was accepted that comets were planet-

like objects orbiting around the sun (although in

highly elongated orbits) and obeying the same laws

governing the motion and trajectory of other planets.


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Path of a comet

Newton in his Principia (1687):

• If comets are made of matter, then they are attracted to the Sun just as the planets are.

• Given rectilinear inertia and a centrally directed force, the moving body's (comet) path must be a conic section.

• Thus the predictive astronomy of Newton made it possible to calculate and predict the path of comets precisely


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• Edmond Halley (1705) took Newton’s notion and drew up a table of the parameters of the twenty-odd brightest comets that had been seen over the previous several centuries.

• He pointed out that the parameters of the comets of 1533, 1607 and 1682 were the same and concluded that this was a periodic comet.

• He predicted its return in 1758. In that year (Halley had died in 1742) the comet appeared as predicted and has been called Halley's Comet ever since.

History and philosophy of cometsPrediction of Comets (1705)

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• Johann Palitzsch , a German astronomer recovered the ‘Halley Comet’ in 1758 ( on a Christmas Day), as predicted by Edmond Halley.

• Thus the era of philosophy of comet came to an end and the Science of Comet began


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Second successful prediction of comet

• Johann F. Encke , suspected one of the three comets discovered in 1818 to be the same one already discovered by him in 1805.

• Encke predicted its return for 1822, but this return was observable only from the southern hemisphere and was seen by Carl Ludwig Christian Rümker (a German astronomer) in Australia .

• This comet now carries his name and has the shortest period of all known comets ( just 3.3 years).

Comet Encke, on its 59th documented visit on 2003

Carl Ludwig Christian Rümker

History and Science of comets

Johann F. Encke

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• François Arago directed his polariscope toward the tail of Comet Tralles (the great comet 1819 -II) and found the light to be polarized, hence it was “reflected” sunlight.

• Later observations of comet Halley made in 1935 confirmed the polarization of light from comets.

History and Science of cometsLight source of Comets

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• French Astronomer Charles Messier discovered a comet on June 14, 1770 , while looking at Jupiter and Sagittarius.

• He decided to name this one after the fellow who did the orbital calculations, Anders Lexell.

• Andres Johan Lexell (1740–1784) calculated that the comet was moving on an elliptical orbit with a period of only 5 ½ years.

History and Science of cometsMass of Comets

• He also showed that the comet had had a much larger perihelion before the encounter with Jupiter in 1767

• And predicted that after encountering Jupiter again in 1779 it would be altogether expelled from the inner Solar System.

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• Since Lexell’s comet passed the earth within a very short distance (almost six times that of the moon, just 24,00,000km, ever closest approach of a comet)

• Laplace calculated that the earth’s action decreased the time of the sidereal revolution of the comet by 2.046 days.

History and Science of cometsMass of Comets (1805)

• But the more exciting question was to what extent the comet affected the earth’s motion.

• Laplace calculated that the mass of the Laxell’s comet was less than 1/5000 part of that of the earth.

• Laplace believed that if a comet impact a planet or its satellites, the result would not be so destructive

• Laplace started a new era in cometology in which comets were treated as physically insignificant bodies in the solar system 20

Heinrich Olbers (German amateur astronomer)

Discoverer of five comets and the asteroids vesta and Pallas

He proposed that pressure of light* is responsible for comet's tails always pointing away from the Sun (1811)

Bessel ( Bessel functions fame), German astronomer and mathematician.

Following olbers, Bessels, in 1836 postulated the ejection of solid particles in the direction of the Sun, and that these particles were somehow forced back into a “tail” by an unknown repulsive force acting in the anti-sunward direction

History and Science of cometsExplanation of Comet tails

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• Feodor A. Bredikhin further developed the comet tail theory based on an ad hoc repulsive force from the Sun that varied with the square of the heliocentric distance. This became known as the Bessel-Bredikhin mechanical model and was widely used and remained in use until the late 1950's.

• This mechanical theory of comet described movements of matter not only in the head of a comet, but also in its tail.

Explanation of Cometary tailsHistory and Science of comets

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• By 1877, Bredikhin introduced a scheme for classifying cometary tails into three types, depending on whether the repulsive force was more than 100 times the gravity of the Sun (Type I) or less than one solar gravity (Types II and III).

• By 1879 he had distinguished between them on the basis of their constitution. Type I – hydrocarbons dominate. Type II – light metal such as sodium predominant. Type III- iron molecules

History and Science of cometsExplanation of Cometary tails

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• One of the repulsive forces acting on the dust was identified by Svante Arrhenius (1900) as the radiation pressure by sunlight.

• The theory was further developed by Karl Schwarzschild (1901).

• In 1903, Ernest Fox Nichols (1869–1924) and Gordon Ferrie Hull (1870–1956), equipped with the data produced by Arrhenius, Lebedev, and Schwarzschild imitated cometary tails in an interesting experiment


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• They calcined spores of a funguss by heating to redness and produced sponge-like charcoal spheres with a density of about one-tenth that of water.

• They mixed these particles with some emery sand particles and placed them in an evacuated long hour-glass.

• When the tube was held vertically and a fine stream of powder started to fall down, a beam of light with approximately known intensity was directed horizontally to the stream.

• While the sand particles were falling vertically, the spores were deflected from the stream by the light pressure!


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• The close connection between comets and meteors was demonstrated by Giovanni Schiaparelli (1866, 1867)

• He found that the orbits of the Perseid and the Leonid meteor streams coincide with those of comets P/Swift-Tuttle (1862 III) and P/Tempel-Tuttle (1866 I), respectively.

Comets and meteor showers


• These observations led the Italian astronomer to formulate the hypothesis, subsequently proved to be very exact, that the meteor showers could be the trails of comets.

• This was the proof that comets were indeed losing solid particles.

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• The Comet 2P/Encke was subsequently found to arrive systematically at perihelion about 0.1 days earlier than predicted, even when taking planetary perturbations into account.

• Bessel suggested that a non-gravitational effect might arise due to the rocket-type impulse imparted by an outflow, possibly explaining perihelion shifts such as those observed for Comet 2P/Encke.

Perihelion shift and Non-gravitational effects


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• Usherwood, a commercial photographer of England took the first photograph of a comet ( Donati's comet, The great comet of 1858) on 27 Sep 1858.

• On the very next day (28sep) George philip Bond (2nd director of Harvard Observatory) took the photograph of the same comet.( but he could take only the nucleus)

History and Science of cometsThe earliest phototography of a Comet (1858)

Usherwood, Bond and Donati

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• Drawing of Comet Donati by George Phillips Bond on October 10, 1858.

• The drawing shows four jets coming off of the nucleus that are connected to and feeding two parabolic hoods, or envelopes as he referred to them, as well as two outer parabolic hoods.

The fine details of a Comet (1858)History and Science of comets

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• Donati pioneered spectroscopy of comets to determine their physical composition.

• He discovered that the spectrum changed when a comet approached the Sun, and that heating caused it to emit its own light rather than reflected sunlight:

• He concluded that the composition of comets is, at least in part, gaseous.

Gaseous Composition of Comets – Spectroscopy- (1864)History and Science of comets

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• Huggins was the first person to record a photographic spectrum of a comet.

• The bands recorded by Huggins, known as the “carbon” or “Swan” bands, were found in all subsequent observations of comets.

• The Swan bands so strongly dominated cometary spectra that carbon was immediately believed to be an important constituent of comets.

History and Science of cometsCarbon Composition of Comets – Photograpic Spectra (1868)

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• H2O was also considered as a potential parent molecule, following the discovery of the OH 3090 Å UV emission in 1941

• Karl Wurm (1930) and Pol Swings (1948) showed that the parent molecules of CO+, CN, CH, CO2+ , N2+, and NH emissions found in enkey comet were CO or CO2, C2N2, CH4, N2, and NH3 molecules

History and Science of cometsComposition of Comets – Photograpic Spectra

Visible spectrum - coma of comet NEAT

Courtesy: http://www.physics.sjsu.edu

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http://www.physics.sjsu.edu/

• A major evolution in cometary science took place in 1950–1951 with the formulation of three very important ideas within a short time span.

1. The icy-conglomerate (“dirty snowball”) model of the cometary nucleus was proposed by Whipple (1950).

2.Then, came the identification by Oort (1950) of a distant population of comets now known as the Oort cloud.

3.Finally, Biermann (1951) gave the correct explanation for the

motions of features in cometary plasma tails caused by their interactions with a flow of charged particles emanating from the Sun’s surface (i.e., the solar wind).

History and Science of cometsModern Era : After 1950

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• Building on the ideas of Bessel (1836a), Whipple described the nucleus as a mixture of ices from which the gases in the coma are produced by sublimation in increasing quantities as the comet approaches the Sun and the surface temperature of the nucleus rises.

• ( In his terminology icy means melting point < 300K )

History and Science of cometsDirty Snowball Model – Whipple (1950)

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Whipple’s model was hugely influential because of its ability to successfully explain within a single conceptual framework many observed cometary phenomena, such as

(1) the large gas production rates [200 kg/s of C2 for 1P/Halley in 1910 derived by Wurm (1943)], for which the desorption model was totally inadequate;

(2) the observed jet-like structures in the coma and the erratic activity, impossible to produce if the source of gas and dust was a cloud of particles;

(3) the fact that most comets that pass extremely close to the Sun, e.g., the Kreutz Sun-grazing comet group, apparently survive such approaches; and

(4) the fact that comets are the sources of meteor streams.

History and Science of cometsDirty Snowball Model – Whipple (1950) –why widely accepted?

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• Then why the highly volatile material is not removed from the surface layer of the nucleus long before perihelion?

• Delsemme and Swings (1952) noticed that almost all parent molecules explained the observed radicals and ions in comets could coexist in the nucleus in the form of solid clathrate hydrates of H2O, where the volatile “guest molecule” occupies a cage in the H2O crystal lattice.

History and Science of cometsDirty Snowball Model – Whipple (1950)

Methane molecule inside a cage formed by the water molecules

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In 1932, the Estonian astronomer Öpik suggested that stellar

perturbations would raise the perihelia of comets, resulting in a

cloud of objects surrounding the solar system

However, he specifically rejected the idea that comets in the cloud

could ever be observed, even indirectly, because he did not

recognize that stellar perturbations would also cause some orbits

to diffuse back into the planetary region. Öpik concluded that the observed Long period comets (LPCs) came

from aphelion distances of only 1500–2000 AU

History and Science of cometsOrigin of Comets – Oort clouds (1950) -2

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• If the reciprocal of “original” semi-major axis ( i.e. without the influence of planets) 1/a(orignal) is < 0, then comet's “original” orbit is hyperbolic in nature.

• The work by Strömgren (1914, 1947) and colleagues demonstrated that there were no original hyperbolic orbits among the observed comets; all apparently hyperbolic orbits were actually perturbed into those states by planetary effects, mainly the influence of Jupiter.

• This showed that comets were not originating from inter-stellar space.

History and Science of cometsOrigin of Comets – Oort clouds (1950) -2

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In 1948, the Duthch astronomer Van Woerkom ( Research Student of Oort) showed that there should be continues source of new, near parabolic comets to explain the relative numbers observed.

In 1950, Jan Oort, worked on the distribution of comets in the solar system and he observed that

the inclination of all 'new' comets (or LPCs) were randomly distributed in all possible directions around the sun.

Among the distribution of semi-major axes of 19 observed long period comets, ten comets had an average aphelion distance of 110,000 AU.

History and Science of cometsOrigin of Comets – Oort clouds(1950) - 3

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If the distance of Oort cloud is nearly half of the distance of th nearby star, then why a comet should visit the inner solar system?

Oort replied that the perturbation caused by the nearby passing star causes a comet to follow a parabolic orbit towards the Sun.

History and Science of cometsOrigin of Comets – Oort (1950)

•In 1950, he based on these dynamics of the long-period comets, concluded that the “new” long-period comets originate in a general cloud of comets surrounding the sun in a distance from 50,000 to 150,000 AU.• This accumulation of comets which is called the Oort cloud is estimated to

contain 1011 comets of observable size. •The entire mass of the Oort cloud is about 1/10 to 1/100 of that of the earth.

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In 1951, Gerard Peter Kuiper (student of Oort) suggested that a closer reservoir of comets lay just outside of the solar system, composed of the leftovers of the cloud from which our planetary system was formed.

He suggested that in a distance starting from the orbit of Neptune and extending as far as 50 AU a great population of comets is distributed in a flattened disk which acts as the source of the short period comets.

This distribution of comets, called the Kuiper belt, contains probably 107 to 109 comets larger than 5 km in size.

History and Science of cometsOrigin of Comets – Kuiper (1951)

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•Even after the discovery of the radiation pressure and development of tail theories based on the pressure of the sun’s light, there were left several comets whose rapid increase of tails was not explainable by the new theory.

•The German astronomerBiermann suggested that a continuous flow of high-speed particles from the sun accelerates the ions (mainly CO+) in a comet’s tail through the momentum transfer.

History and Science of cometsOrigin of Comet tails – Biermann (1951

• This flow of particles, which is called the solar wind, though it has a very low density (~10−23 g cm−3), travels at the high speed of about 500 km/s.

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•Due to the action of the high speed particles of the solar wind, ionized molecules of cometary substance form a tail that is aligned almost with the radius vector of the comet’s orbit.

•This tail which is distinguished by its extended length, straightness and bluish color is called the plasma tail.

•On the contrary, the second type of cometary tail, the dust tail, is composed of dust particles swept from the nucleus and is distinguished by its white to yellow color, relatively short length, and curved shape.

History and Science of cometsOrigin of Comet tails – Biermann (1951)

Ion tail

Dust tail

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•On 1985 International Cometary Explorer (ICE) passed within 7,862 kilometers of the Comet Giacobini-Zinner 's core.

•It was the first spacecraft to fly past a comet.

•The spacecraft returned excellent data on the comet's tail, confirming theories that comets are essentially "dirty snowballs.”

History and Science of cometsMissions to Comets ICE – Confirmation of “Dirty Snowball”

Ion tail

Dust tail

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•Giotto mission goal was to take photographs of Halley comet’s nucleus.

•It s Closest encounter was at a range of 605 kilometers on1986.

•Giotto returned 2,000 images of Halley’s comet on its surface

History and Science of cometsMissions to Comets Giotto (1986)– the first closest encounter

Ion tail

Dust tail

Findings:

The nucleus size was just 10x15 km

It was darker than the coal, reflecting

just 4% of the light falling on its surface

Activity (dust emission) from the

nucleus is restricted to between 10-15% of

the surface area.

The surface had features like craters,

mountains, ridges etc.

Water represents 85% in the gas phase45

• The main goal of the DS1 mission was to test the new spacecraft’s technologies .•The nearest encounter with the comet Borrelly was 2,200km on Sep 2001.•It returned detailed photos of the comet nucleus.

History and Science of cometsMissions to Comets : Deep Space-1 (2001)

Ion tail

Findings:

The age of the comet

was older than the

planets.

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• The probe Star Dust encountered comet Wild -2 in 2004 and captured particles surrounding the comet. •After collecting the samples it returned the samples to the Earth.

History and Science of cometsMissions to Comets : Star Dust (2004) – A Return sample mission

Ion tail

Findings: the comet came into being about 1.7 million years after the solar system was formed, contradicting the belief that comets were the earliest materials to be transported to the edges of the solar system.Scientists discovered glycine, a fundamental building block of life, in samples of comet Wild 2 returned by the Stardust spacecraft.

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• Deep Impact mission,the first attempt to peer beneath the surface of a comet. •July 4, 2005 , DI made a planned impact with comet Tempel 1

History and Science of cometsMissions to Comets : Deep Impact (2005)

Ion tail

Findings: a cloud of fine powdery material was released when the impactor slammed into the nucleus of comet the comets contain a substantial amount of organic material ( may have brought that material to Earth at one time)

the comet's interior is well shielded from solar heating

After impact

Water Ice

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•This is a recycled mission of Deep impact spacecraft

•The image taken of comet Hartley 2 by NASA's EPOXI mission, shows many features across the comet's surface.

History and Science of cometsMissions to Comets : EPOXI (2010) – A recycled mission

Ion tail

Findings: The EPOXI mission flyby reveals that comet Hartley 2's rocky ends spew out tons of golf-ball to basketball-size fluffy ice particles

Hartley 2 has an 'excited state of rotation' because it spins around one axis, but also tumbles around a different axis.

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•Rosetta is the first mission designed to orbit and land on a comet•Launched in March 2004 and will meet its target, comet 67P/Churyumov-Gerasimenko, in 2014•After entering orbit around Comet in 2014, the spacecraft will release a small lander (Philae) onto the icy nucleus, then spend the next two years orbiting the comet as it heads towards the Sun.

History and Science of cometsMissions to Comets : Rosetta (2014) – A comet landing mission

Ion tail

Goal: Rosetta's main objective is to help understand the origin and evolution of the Solar System.

Rosetta orbits comet with lander on its surface

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History and Science of cometsMissions to Comets : Visited Comets

Ion tail

7.6km

15 km

2 km

5.5km

8.7 km

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1. Nucleus 2.Coma 3.Tails Ion TailDust Tail

Anatomy of Comet

Dust tail 30 million km

Upto 1lakh km

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Comet ISON – the Great comet of the century?!

• C/2012 S1, also known as Comet ISON, is discovered on 21 September 2012 by Vitali Nevski and Artyom Novichonok .

• Since the discovery was made using the 0.4-meter (16 in) reflector of the International Scientific Optical Network (ISON) in Russia, it got the name ISON.

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• C/2012 S1 will come to perihelion (closest approach to the Sun)

• C/2012 S1 will pass approximately 1,100,000 km above the Sun's surface.

• Its trajectory is nearly parabolic, i.e. a new comet coming freshly from the Oort cloud.

• it will pass about 0.429 AU (64,200,000 km) from Earth on 26 December 2013.

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Inclination to the Earth’s orbital plane: 62.39°

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The path of C/2012 S1 (ISON) from December 2012 through October 2013

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• Since it is a sungrazing comet, there is probability for tidal forces and solar radiation may destroy the comet.

• Since the nucleus is believed to be large enough, many astronomers hope it will survive .

• If the comet survives it could emerge glowing as brightly as the Moon, briefly visible near the sun in broad daylightHubble image of ISON comet

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Aristotle – Comets are the Earth’s atmosphereic phenomenaTycho Brahe – Comets are far away from the EarthNewton–Comets are part of solar system having parabolic orbitsHalley – First prediction of appearance of comet Laplace – Mass of a comet is 5000 times smaller than the Earth.Arrhenius – Sun’s radiation pressure cause the dust to form tail.Donati – First spectroscopic observation of comet to find composition

Whipple – Dirty snowball modelOort – Origin of long period comets from Oort cloudsKuiper – Origin of short period comets from Kuiper beltBiermann – Solar wind causes the plasma (ion) tail

History and Science of cometsSummary

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The comets - primordial remnant objects of the solar system.The short period comets ( period < 200yrs) originate from Kuiper

belts or beyond the Jupiter orbit.The long period comets (P > 200yrs) originate from Oort clouds. When they approach the Sun (~450 million km), they start to develop coma and tail. The solar heat cause the volatile components in nucleus to

sublime , resulting the coma. The solar wind from the push the ions away, forming the ionic tail The radiation pressure push the dust particles away, forming the dust tail. The ions of CO or cyanogen in the ion tail make them to glow in blue or green colors.


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Since the size and mass of a comet (nucleus) is small, they will make only a local disaster for few thousand Km and not for the whole earth.

Since the comets carry water ice and organic substances, they may be the seed for the life in the Earth.

Since comets are just rocky bodies, we need not to believe the superstitions ( religious & pseudo-scientific) about it.


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AKWNOLEGEMENT

The EyesOn ISON campaign team• VIGYAN PRASAR• ALL INDIA PEOPLES’ SCIENCE NETWORK• NAVMRITI

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ReferenceBooks and Articles:

• A History of Physical Theories of Comets, From Aristotle to Whipple by Tofigh Heidarzadeh• Comets II , edited by Michel C Festou, et al, University of Arizona press • Introduction to Comets By John C. Brandt Cambridge University Press, 2004• Babylon to Voyager and Beyond: A History of Planetary Astronomy

– By David Leverington Cambridge University Press, 2003• Encyclopedia of the Solar System edited by Lucy-Ann McFadden, Paul Weissman, Torrence Johnson,

academic Press, 2007 • On the Theory of Comet Tails By H. ALFVGN. • Cosmic Dust – Mc Donnell, Wiley, 1978• Solar System Evolution – S Ross Taylor, Cambridge, 1994

Websites:• http://www.nasa.gov/mission_pages/deepimpact/media/f_ancient.html• http://solarsystem.nasa.gov/deepimpact/science/comets.cfm• http://www.lcas-astronomy.org (for biography of astronomers)• http://solarsystem.nasa.gov/missions ( for missions)• http://www.jpl.nasa.gov/missions/• Wikipedia

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http://www.grahamphillips.net/

http://solarsystem.nasa.gov/deepimpact/science/comets.cfm

http://www.lcas-astronomy.org/

http://solarsystem.nasa.gov/missions

http://www.jpl.nasa.gov/missions/

THANK YOU

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comets & history of cometary science tamil nadu science forum for eyeson ison campaign 1

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