The Vikings were Amongst the First on Mars

The Vikings of Yesteryear

There are several hypotheses relating to the origin of the word "Viking". It is an ancient word as it appears on Rune stones which are contemporaneous with the Viking age. Like words in other languages, its meaning and use have evolved over the centuries. Ancient Runic inscriptions suggest that a Viking was a man who left his homeland to seek adventure and profit elsewhere (Runic is an  ancient alphabet script, also called futhark, used to write various Germanic languages before the adoption of the Latin alphabet). 

There was also an expectation that the Viking would return to his home with fortunes that had been amassed during these travels. However this is not the exclusive definition of the word.  Some language scholars propose that the word originates from the word "vik"" which means "creek" or "bay" with a "Vikingr" being "King of the creek''. or "King of the bay". Other researchers of the subject contend that to be a Viking also required  participation in acts of plunder, pillage and terror.  Viking warriors were reputed to be fierce, trained in archery, spear-throwing and swordplay from the young age of ten years. The most fanatical warriors were called "berserkers"

The "Viking Age"  really comes to prominence in the late 8th century.  Then, the  Kings of the bay started leaving their Scandinavian  homelands and using  the Norwegian and Baltic Sea to provide maritime access, raided and  traded across wide areas of Europe. They were facilitated by advanced sailing  techniques and navigational skills with their "longship" being a key enabler of their maritime voyages, at times to new lands across unchartered waters. 

The stamp above is from the Faroe Islands show the route of the Vikings out of their homelands to new frontiers. 

The stamp above is from the island of Jersey and is a good representation of a Viking longship.

One of the pivotal moments in their history occurs when  a group of Viking  armed raiders attack the defenceless monastery of St. Cuthbert in Lindisfarne, on the coast of Northumbria, England in 793 AD.   This was the first Viking invasion of England. At the time, present day England comprised four separate and independent kingdoms which were East Anglia, Wessex, Northumbria and Mercia. Mercia was the strongest in military might.  

Led by the brothers, Halfdan and Ivar the Boneless, the Vikings  picked off the Anglo-Saxon kingdoms of England one by one until only the kingdom of Wessex remained, unconquered. Wessex  was ruled by King Alfred. 

Alfred was a king by default as his older brothers had died from sickness or in prior Viking battles. In January 878 AD, Alfred was caught by surprise in a Chippenham estate by the army of Guthrum but he escaped, regrouped and a little later, returned to defeat the Vikings at Edington, a small village in Wiltshire. For this achievement in saving his kingdom, he is the only native English ruler to be given the title "the Great". So, until today, he is acclaimed  as King Alfred the Great.

For nearly a century England was controlled by the Vikings in the Midlands and the North whilst the Kings of Wessex ruled in the South and South-west. It was only in 954 AD that the King of Wessex expelled the last Vikings and unified England under the House of Wessex. 

This First Day Cover below from the island of Jersey commemorates its Viking heritage.

As historians would later realize, it was not only the Anglo-Saxon kingdoms that were targeted by the Vikings. Within a few years of their Lindisfarne attack, Viking raiding parties had struck in Scotland, Ireland and France. It is also estimated that the Vikings arrived in the Faroes in the mid 8th century, subsequently using this as a base to sail further west across the Atlantic. In addition, there are detailed historical records of the Vikings arriving in Iceland in the year 872 AD where they set up an independent society, owing no formal allegiance to the Kings of Norway. Many years later, in 1960 AD, strong evidence of Viking settlements were discovered in the northernmost tip of Newfoundland in Canada, demonstrating that there was already northern European discovery of the Americas many centuries before the legendary travels of Columbus.

The series of stamps above commemorate the Viking presence discovered in Canada.

Present Day Mariners and Vikings 

Seafarers, adventurers, mariners, warriors, settlers, explorers and innovators are just some of the many words that have been used to describe the historical Vikings. Thus, when Edgar Cortwright, a  scientist, engineer and senior NASA administrator was contemplating a concept to name inter-planetary missions to Mars, Mercury and Venus, he paralleled his thinking to the maritime world and this resulted in the selection of  "Mariner" and "Viking" as names for the American robotic craft that were going to "travel to great distances and remote lands" within our Solar System. 

The First Proposals 

The first credible technical study for a mission to Mars was made by Wernher von Braun between 1947 and the early 1950s. Von Braun, developer of the V-2 ballistic missiles that so terrorized Western Europe at the end of World War II but anointed the ''Father of Rocket Science" for his work on the Saturn V multi-stage rocket that took American astronauts to the moon,  was a reader of the works of Hermann Oberth, himself one of the founding fathers of rocketry and astronautics. Oberth was a disciple of the fictional works of Jules Verne, particularly the classics, "From Earth to the Moon" and "Around the Moon" so it is not difficult to understand the links that inspired this generation of physicists and engineers to dream of journeys to the celestial bodies that seemingly floated in the space high above our heads.

The Mars Race 

I will write about this period between the launch of the Sputnik 1 in 1957 and the Apollo-Soyuz Test project in 1975 in a further post. Many call this period "the Space Race". Within this Space Race, there were other "high-stakes" competitions ongoing simultaneously, on the ground, at sea, in the air and in space. During this period, which was the height of the "cold war", it was the sovereign  pride and military might of the two protagonists nations, the United States and the Soviet Union,  which were at stake. Commendable achievements in the conquest of space were critical in the claim for global political, technological and military leadership. 

Once the Soviet Union had sent robotic missions to orbit Earth,  it was only natural for targets further away to become the objective of the nation. Even before Yuri Gagarin had made his first orbit of the Earth in 1961, the Soviets were already planning for a robotic mission to other planets. By October 1960 they launched the "Marsnik 1" spacecraft for a flyby of Mars. Sadly for them, it was destroyed on take-off. Four days later, "Marsnik 2" suffered the same fate. 

In 1962, with the Americans busy emulating the Soviet achievement of putting a man into orbit (John Glenn orbited Earth in February 1962), two further robotic spacecraft were launched by the USSR. The second probe, named  "Mars 1" traveled more than 106 million kilometres from Earth before a technical  glitch caused ground control to loose communications with it.  Later in 1962, a third Soviet probe was launched, but to no avail. It also failed in Earth orbit. The obsession to achieve objectives quickly (and almost frantically) did not seem to be yielding the much sought-after national pride and international respect that was being domestically demanded.

It was only in 1964 that the Americans  joined the race to Mars. In November 1964, "Mariner 3" was launched but one hour after lift-off, the curse of the Mars probes struck and the mission failed. It was then the turn of  "Mariner 4" which was launched in November 1964. It  reached Mars in July 1965 and was deemed a success for its time as twenty-one  photographs of the Red Planet were relayed back to Earth.  

The stamps above commemorate the successful Viking flyby of Mars of Mariner 4

Two days after the American launch of Mariner 4, the Soviets launched  "Zond 2" which also targeted Mars. Unfortunately for the Soviets, Zond 2 made it to the Red Planet but at a critical stage of the mission, its radios failed and it was unable to send back any planetary data or images. So far away and yet so close, all at the same time!

On 25th February and 27th March 1969, NASA launched Mariner 6 and 7 respectively. They reached Mars in late July and early August the same year, sending back a total of 201 photographs of the equatorial and polar regions of  the planet. Given that the United States had only just landed humans on the moon, the USA closed the decade in the pole position of a two nation space race. 

Landing on Mars 

Once it was demonstrated that it was possible to reach Mars, the next objective was to aim for a successful soft landing of a robotic spacecraft  on the surface of the planet. Once again, the quest for global political and military leadership motivated the actions of the cold war actors. Between 1969 and 1971 several attempts to launch space vehicles to Mars were made by both the USA and USSR but both nations were thwarted. 

On 30th May 1971, the United States launched the robotic spacecraft, "Mariner 9" which successfully arrived and orbited Mars just weeks ahead of the Soviet twins of "Mars 2" and "Mars 3". After its first orbit, Mariner 9 became the first spacecraft to successfully circle another planet. Mariner 9 arrived at a time when severe dust storms enveloped the Red Planet. After patiently orbiting Mars for several months, it relayed back to Earth more than 7300 clear photographs, covering approximately 85 percent of the Red Planet. These photographs captured high altitude volcanoes, riverbeds, long networks of canyons (one, even  more than 4,000 kilometres long) and the small Martian moons of Phobos and Deimos. Most spectacularly, the largest known volcano in the Solar System (Olympus Mons) was photographed. 

Mars 2 and Mars 3

Mars 2 and Mars 3 were twin robotic spacecrafts launched by the Soviet Union nine days apart with the objective of being the first probes to land on the Martian surface. Mars 2 was launched on 19 May 1971 whilst Mars 3 followed nine days later. Both spacecraft successfully orbited the Red Planet but the lander deployed by the Mars 2 spacecraft to touch down on the planet, crashed on the surface of Mars. The same was not true of the lander deployed by Mars 3. It successfully soft-landed on the planet but the lander failed  technically some fifteen seconds after landing. In that short time, it  relayed one image from the planet's surface which was not well defined. Notwithstanding the failure, this event is still recorded as the first controlled landing of a spacecraft on Mars.

Cometh the Hour, Cometh the Vikings

Like the Russian Mars 2 and Mars 3 spacecrafts, the design configuration of the Viking robotic probe combined  an orbiter with a lander module, with the lander being deployed for touch down after arrival at the planet. At that stage, the orbiter would be applied for remote areal imaging and also used to relay data back to Earth. 

Viking 1 was launched in August 1975. It was planned for a landing on Mars on 4th July 1976 in conjunction with the 200th anniversary of the adoption of the American Declaration of Independence. Unfortunately things did not proceed as planned as areal images of the primary landing site, received from the orbiter,  showed that the selected terrain was too rough for a safe landing. Consequently, the descent was delayed until 20th July 1976 (the seventh anniversary of the American moon landing). On that day, the lander deployed by the Viking 1 orbiter became the second spacecraft to soft-land on Mars and almost immediately commenced relaying clear images of the planet back to Earth. The Viking 1 lander (later renamed the Thomas Mutch Memorial Station) operated for 2307 days (over 6.25 years or 2245 sols; i.e. Martian solar days). 

The series of stamps above: These are from the island of Nevis and they commemorate the 30th anniversary of the Viking 1 landing on Mars on 20th July 1976.

The eventual fate of the Viking 1 orbiter is not explicitly known. When operations were terminated in August 1980, it had already made 1485 orbits around the planet and relayed back more than 57,000 images. A study in 2009  concluded that whilst it may have crashed onto the Martian surface, it was more likely to be still in orbit around the planet. 

This stamp is from the Central African Republic and it commemorates the landing on the moon (July 1969) and the landing on Mars by the Viking 1 Lander (July 1976).

A month after the successful touch down by the Viking 1 lander on the Mars surface, the lander deployed by the Viking 2 orbiter also successfully soft-landed. The Viking 2 lander  operated on the surface of Mars for 1316 days or 1281 sols (i.e. until 12 April 1980) whilst the orbiter remained functional until 25 July 1978, returning more than 16,000 images while orbiting the planet more than 700 times.

The stamp above: There were several failures and problems encountered during the many attempts to successfully land a robotic spacecraft onto the surface of Mars. This stamp, from the Central African Republic honours those who were in the front-line of spacecraft operations and suffered success and failure. 

This is another stamp from the Central African Republic commemorates the landing on the moon (July 1969)  and the landing on Mars by the Viking 1 Lander (July 1976).

The Lessons

In retrospect, the stories and statistics above, many of them representing major and expensive failures, may seem inconsequential after all these years. But I am certain that at the time, there were many tears. To me, these failures demonstrate the vision and single-minded perseverance of leaders, engineers, scientists and patriots to build a deep platform of knowledge and understanding of our universe, and our role and place within it. From Galileo to Newton, from Einstein to Lemaitre, from Hubble to Hawking and even Oberth, Korolev and von Braun and many others who turned theoretical dreams into a practical reality, they understood that not all questions could be answered from the planet and place that we inhabit. For some answers, we needed to move our frame of reference. 

The quest of the Vikings of Scandinavia, when exploring, conquering and pillaging far away lands may have been driven by economic necessity or personal greed but unequivocally, they were explorers and innovators, led by the overhead stars into the maritime unknown. 

History has recorded that the Viking Age lasted about three hundred years and that they reached the shores of NewFoundland in Canada. I wonder; the Space Age has only had a life of sixty-five years. Already, we have landed robots and rovers on Mars several times and we now are contemplating a manned mission in the next decade. Other probes like the Voyager 1 and 2, launched in 1977, are leaving the Solar System after decades of exploration in space. In fact, in 2012, data received from Voyager 1 indicated that it had become the first man-made object to enter inter-stellar space. In 2019, similar data was received from Voyager 2. 

When I look at the stars each night, I wonder where we will all be after 300 years of space exploration? How will the Space Age have rewarded our quest for knowledge and understanding? What will we find? And what will be recorded in the digitized history books, holograms and blog posts of tomorrow?

This stamp is issued by the island of Pulau and it commemorates the Mars Pathfinder mission.

End of blog post.

Note: All stamps and the First Day Cover are from my personal collection.

Terminator Rex: A Few Seconds That Changed The Future of Earth

My last post was about meteoroids. Prior to that, I wrote about comets. I must now fill the third apex of this triangle of space nomads and write something about asteroids. The bulk of my post will feature one asteroid that probably changed the course of evolution on planet Earth but  I will also cover a couple more in less detail. They need to be mentioned as they are interesting in their own right. First, some stamps about asteroids.

The stamp above: This stamp is issued by Luxembourg on 30th June 2018 in commemoration of "Asteroid Day"

The stamp below:  This is an unusual stamp, issued by the nation of Bhutan. When studied, it shows a space ship traveling through a field of asteroids. It is unusual because, when observed, there is a 3 dimensional effect that has been included in the stamp. 

Timelines

Before I get into the details about asteroids, it is important to be apprised of some basic facts. 

It is estimated that the age of our planet is 4.5 billion years. There is credible historical evidence in the form of fossils found in Western Australia which demonstrate that forms of life have existed on Earth since at least 3.7 billion years ago. Furthermore, there are cohorts of researchers who believe that life may have existed on Earth even earlier, say 4.3 billion years ago. 

In this timeline of events, the dinosaurs dominated most parts of the planet about 200 million years ago whilst human beings (homo sapiens) only appeared approximately 250,000 years ago. These are certainly unfathomable lengths of time when compared to the lifespan of an average human being. 

To fully appreciate some of the points I present in this post, it is also important to have a 30 second primer in geologic time scales. 

Here goes.....In order to describe the timing and relationship of events that have occurred over a long period of time (such as the Earth’s history), geologists, paleontologists and other Earth scientists have developed a geologic time scale (GTS). This is a system of chronological dating that relates strata in the geology of the Earth (stratigraphy) to time. For the purpose of this post, we only need to know that within the GTS, the Cretaceous is a geological period that lasted from about 145 to 66 million years ago whilst the Tertiary is a geologic period from 66 million to 2.6 million years ago. 

The Alvarez Theory

Now, let's apply some of this knowledge and understand the basis of Alvarez's Theory. In a previous post I had written briefly on how a comet could "die" by plunging onto a planet and I highlighted the devastating example of the comet Shoemaker Levy impact into Jupiter which occurred in July 1994. If a comet could plunge into a planet, then surely, also could an asteroid with an equally catastrophic effect.

The Alvarez hypothesis, attributed to Nobel laureate Luis Alvarez and his son Walter, held that an asteroid, the size of San Francisco, traveling so fast that it compressed the air beneath it so violently that the air temperature was briefly several times hotter than the surface of the Sun, plunged through the atmosphere of Earth and crashed into the planet approximately 65 million years ago. The asteroid itself was so large (estimated at between 10.6 km and 80.9km in diameter) that even at the instant of contact with the surface of the shallow water of the sea, the top of the asteroid would have towered nearly two kilometres above the notional flying altitude of a passenger aircraft. The impact set off earthquakes greater than 11 in magnitude, widespread tsunamis and the shrouding of the globe in a thick cocoon of sky-blackening dust and debris for many years. This cataclysmic event not only claimed nearly 75 percent of all the species of life on our planet, including the dinosaurs (leaving only birds to carry their legacy), but also most varieties of flora and fauna and many types of microscopic organisms. It effectively ended the reign of the domination of the dinosaurs and opened the door for the ascension of mammals.

The Coverscape below: This coverscape, with a relevant stamp captures this life extinction event.

The Alvarez hypothesis was accepted as theory by an international panel of 41 experts in geology, paleontology, and other related fields after an exhaustive review of the relevant data in March 2010. Seminal evidence substantiating the theory was initially obtained in 1977 from Gubbio, Italy where a thin layer of red clay, found (by Walter Alvarez, a geologist) between the limestone, marking the end of the Cretaceous period and the beginning of the Tertiary period, was about 600 times richer in iridium than the surrounding limestone. Iridium, a silvery-white metal is virtually absent from the Earth’s crust, but high concentrations are common in extra-terrestrial objects, such as asteroids.The evidence became more convincing when this same “iridium anomaly” was subsequently discovered in clay layers at locations in Denmark and New Zealand, and later, more than a dozen other sites around the world. The iridium-spiked layers of clay also contained an abundance of soot. Comparisons of ratios between iridium and several other key elements in the clay layers indicated that the widely scattered iridium anomalies all came from the same source – one that was not of this earth.

This asteroid that caused this life extinction event is called the the Chicxulub Impactor.

A Few Seconds More ...

Our planet rotates on its axis every 24 hours. It is this rotation that gives us day and night. If the Chicxulub Impactor had arrived a few moments earlier, it would have plunged into the deep sea of the Atlantic Ocean, somewhere between Africa and the Americas. Alternatively, if it had arrived a little later, it would have plunged into the waters of the Pacific Ocean (to the left of the Americas on the map below). The depth of the water would have absorbed some of the force of the impact and limited the expulsion of much of the associated toxic fumes that choked the atmosphere for many of the subsequent months and years. Large dinosaurs may have survived such an impact and homo sapiens may not have had a chance to evolve, many eons later. It must be recalled that 65 million years ago, the relative positions of the continents, due to plate tectonics movement were different as shown in the map below. It is the simplest, relevant map I could retrieve that explains the position.

Apophis

Now let's fast forward to present day.......

Apophis is an asteroid with an estimated diameter of 370 metres. It caused a brief period of concern in December 2004 as initial observations indicated a probability of up to 2.7% that it would hit our planet on 13th April 2029. 

Apophis was discovered on 19th June 2004 by R. Tucker, D. Tholen and F. Bernardi. Additional observations provided improved predictions that eliminated the possibility of an Earth or Moon impact in 2029. However, until 2006, a possibility remained that during its 2029 close encounter with Earth, Apophis would pass through a gravitational keyhole that would set up a future impact exactly seven years later on 13th April, 2036. It was only in August 2006 that Apophis's rating on the Torino scale was lowered to zero (a rating of 0 indicates an object has a negligibly small chance of collision with the Earth whilst a rating of 10 indicates that a collision is certain, and the impacting object is large enough to precipitate a global disaster). 

As things stand today, the closest known approach of Apophis will occur on 13th April 2029, when the asteroid comes within a distance of approximately 31,000 kilometres from Earth's surface. That distance is ten times closer than the Moon, and even closer than some man-made satellites. It will be the closest asteroid of its size in recorded history. It will be quite an event for the those interested in astronomy (and probably for many who are not!).

Hayabusa & Itokawa

The word "Hayabusa" translated in the Japanese language refers to a Peregrine falcon, a bird renowned for its speed in flight, having been recorded diving at more that 320 km/hr. Then in 1999, the Japanese motorcycle manufacturer, Suzuki, launched the Hayabusa (or GSX 1300R), which immediately won global acclaim as the world's fastest production sport motorcycle.

On 9th May 2003, the "Mu Space Engineering Spacecraft C", a robotic spacecraft developed by the Japan Aerospace Exploration Agency (which also adopted the "Hayabusa" name), was launched with the objective of making a complex rendezvous with a small near-Earth asteroid named Itokawa (discovered on 26th September 1998). Hayabusa was also to land on the asteroid, collect a sample of asteroidal material and return the collected sample back to Earth. The asteroid itself was named after rocket scientist Hideo Itokawa (1912 -1999), who is regarded as the father of Japanese rocketry. In mid September 2005, the Hayabusa spacecraft arrived at the rendezvous point. It then landed on the asteroid in November 2005, performed its sampling objectives and lifted-off from the asteroid. It returned the collected samples to Earth on 13th June 2010. Hayabusa is legendary because it was the first robotic spacecraft to land on an asteroid, collect a sample, lift off, and then, successfully return the sample to Earth. 

The stamps below: These are issued by the nations of The Gambia (African continent) and again, also by Guyana (Latin America) commemorate the achievements of the Japanese Hayabusa mission. The series of stamps from Guyana are particularly instructive as they depict major milestones being achieved.

It is worthwhile to mention a few words about Guyana. There is a trend that some small countries issue beautiful stamps to commemorate a variety of international achievements and events as a means of raising national income. It was a relatively poor country but in 2015, ExxonMobil discovered vast quantities of oil in its offshore areas. The capital of Guyana is Georgetown. 

Shooting Stars

Introduction

When I prepared my previous posts earlier this month, I hardly expected there to be much interest in comets as there has been. I thought it would be a good topic to write about as I had some interesting postage stamps on Halley's comet and May is the month during which we are able to see the Eta Aquariids. This will be my last post on the topic of comets for a while so I hope to close off with a few stories and some (hopefully) interesting facts.

Shooting Stars

I promised myself to avoid too much astronomical jargon and to write something comprehensible for all readers so let's start with something that we all know or have heard about; "shooting stars". Exactly what is  a "shooting star"? In simple language, it is a meteoroid that enters the earth's atmosphere (after which it is then called a meteor).  As it plunges through the atmosphere, it vaporizes, the friction it encounters causing it to heat up and normally, it does not manage to reach the surface of the earth.  This is the ''shooting star" that we strive to momentarily observe.  If the meteor actually impacts the surface of the earth, it is then called a meteorite. 

Meteoroids

There is still one item to outline further. We need to explain how a meteoroid originates. So, here goes. A meteoroid is a small rocky or metal object, as small as a grain of sand or a boulder that orbits the sun. It originates from a comet or an asteroid which invariably leave a trail of debris as they move through space on their orbital paths. If you wish to know more about comets or asteroids, please read my earlier posts.

Eta Aquariids and Orionoid meteor showers

I mentioned the Eta Aquariids earlier in this post. Now it is the time to return to this topic. We have mentioned in a previous post that Halley's comet orbits the sun every 75-76 years. Our earth, on the other hand,  orbits the sun every 365.25 days. Twice a year, the orbit of earth intersects the orbital path of Halley's comet. During those periods, when our planet makes those intersections, we encounter debris (i.e. meteoroids), that Halley's comet has left behind during its many journeys to and from the sun every 75-76 years. As these meteoroids encounter and plunge through our atmosphere, they become meteors  and we are able to observe meteor showers ("shooting stars''). 

Our planet encounters these meteoroids  in late April to the mid of May and in October each year. The meteor shower which peaks in early May is called the Eta Aquariids because it appears to an earth-based observer to originate (i.e. it has its ''radiant") from the constellation of Aquarius whilst, the meteor shower which peaks in October, creates the Orionid meteor shower as it appears to have its radiant from the Orion constellation. 

Other comets are also responsible for meteor showers or shooting stars. As an example, the "Southern Delta Aquariids" (which are visible from mid July to mid August each year)  originated from the break-up of the what are now the Marsden and Kracht Sungrazing comets. 

Stamps from Sri Lanka and Australia

The island of Sri Lanka, in the Indian Ocean, issued a series of stamps to mark the return of Halley's comet in the mid-eighties. I like this particular stamp as it clearly shows the orbit of earth, intersecting the orbital path of Halley's comet which then gives us the Eta Aquariids and Orionoid meteor showers. Australia also issued a stamp showing the same data.

Gifts of Halley's comet

Both the Eta Aquariids and the Orionid meteor showers are 'gifts' of Halley's comet that we are able to observe each year as a reminder of the comet itself which is racing around the Solar System. There is one more gift of Halley's comet that I personally like a great deal. I studied for my undergraduate degree at Bath University. In Bath, there is an artisan area called Walcot Street and in a house on that street once  lived (and died, in 1772) Samuel Scott, a celebrated English landscape artist. Whilst he is known for many maritime paintings, my particular favourite is shown below: 

This painting is called 'Return of Halley's Comet 1759'. 

Halley's comet can clearly be seen in the sky above the River Thames, its reflection majestically lightning up the water and waves of the river.

A stamp from the Cook Islands

A special moment in time, captured in a painting by an artist who died in 1772 shows the same scene issued on a postage stamp to commemorate the return of the same comet more than two hundred years later. History, geography, astronomy and art, all converging into a story brought to all of us by a mere (?) postage stamp!

Comet Kohoutek

I will close off this section on comets with a short story about how I came to know about the existence of these space nomads. In 1973, I was fifteen years old and I recall my father telling me that a Czech astronomer, L. Kohoutek, had discovered a new comet which would be visible from earth with the naked eye.Before its close approach, Kohoutek was promoted by the media as the "comet of the century".

At that time our family lived in Penang, a beautiful island in Malaysia. I did not much about comets was but I spent a little time doing some background research.

One of the highest points in Penang Island is Penang Hill at 833 meters above sea level. The only way up (at that time) to its peak was by funicular railway. My research told me that the peak of Penang Hill  would be a great vantage point to get an outstanding view of the approaching comet of the century. At my behest, my father agreed to take the family up the hill a particular Sunday evening to sight the comet as dusk approached. On the designated day, we went up the hill but comet Kohoutek hardly made a visual impression. In fact, Kohoutek's display was considered a let-down not only by our family but by many media commentators as well.  Comet Kohoutek was observed by the crews of Skylab 4 and Soyuz 13 and it thus became the first comet to be observed by manned spacecraft,.

A stamp from Gambia

A stamp from Gambia commemorates comet Kohoutek being observed by Skylab 4.

All stamps shown above are from my personal collection and were photographed using a HUAWEI P30 telephone / camera.

Sunskirters, Sundivers and Sungrazers Are Not Cocktails!: Fundamental Facts About Comets

Introduction

In a previous post, I presented some information and stamps mostly about Halley's comet. If you are interested in some of the science around comets in general (peppered with some stamps on the subject) this post might be for you.

What is a Comet?

In short, a comet is a cosmic snowball of frozen gases, rock and dust that orbits the sun. A comet goes around the sun in an highly elliptical orbit and can spend hundreds and thousands of years in the outer depths of the solar system before it returns to the Sun at its perihelion (the point in an orbit when a comet or planet is closest to the Sun). As the comet approaches the Sun, the warming of its surface causes its materials to melt and vaporize in a process called "outgassing". The streams of dust and gas thus released 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. This tail points away from the Sun and even after a comet has passed the Sun, it actually travels tail first! This phenomenon was first noted in the 1530s by Petrus Apianus (Peter Apian), a German mathematician and astronomer. To provide an idea of scale, the tail of a comet can be as long as the distance between the Earth and the Sun (which is about 93 million miles).

This stamp from the Bermuda, a British Territory and an island located in the North Atlantic Ocean honours the discovery of Peter Apian.

A stamp from Grenada Grenadines, showing the 'outgassing' of a comet. Grenada is an island nation member of the British Commonwealth comprising the island of of Grenada and the six smaller islands located at the southern end of the Grenadines in the Southeastern Caribbean Sea. It is reported that Grenada ranks among the countries that have issued the most stamps in the world. Stamps inscribed with the words 'Grenada Grenadines' were issued from 1973 to 1999 for the islands of the Grenadines located to the north of Grenada. Since 1999, stamps for the Grenadines are marked 'Grenada Carriacou & Petite Martinique'.

Kepler's Laws

Like all orbiting bodies, comets follow Kepler’s Laws; i.e. the closer they are to the Sun, the faster they move.

Johannes Kepler, a German astronomer formulated the three laws of planetary motion:

+ Law of Orbits: planets move in elliptical paths with the Sun at one focus;
+ Law of Areas: a line that connects a planet to the Sun sweeps out equal areas in equal times; and
+ Law of Periods: The square of the period of any planet is proportional to the cube of the semi-major axis of its orbit.

Kepler's laws have an important place in the history of astronomy as they mark a key step in the revolution which moved the center of the solar system (and indeed the Universe as it was then thought) from the Earth (geocentric) to the Sun (heliocentric). These laws were published by Kepler between 1609 and 1619.

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A stamp honouring Johannes Kepler from the Republic of Sierra Leone. The Republic of Sierra Leone is a country situated on the southwest coast of West Africa. It was a British Colony until 1961.

And, what is the difference between an asteroid and a comet?

The main difference between asteroids and comets is their composition, as in, what they are made of and where there were formed. Asteroids are made up of metals and rocky material, while comets are made up of ice, dust and rocky material. Both asteroids and comets were formed early in the history of the solar system about 4.5 billion years ago, but asteroids formed much closer to the Sun, where it was too warm for ices to remain solid. Comets, on the other hand, formed farther away from the Sun where ices would not melt. Comets which approach the Sun lose material with each orbit because some of their ice melts and vaporizes to form a tail.

Where do comets come from?

Comets are believed to have two sources. Long-period comets (those which take more than 200 years to complete an orbit around the Sun) originate from the Oort Cloud. Short-period comets (those which take less than 200 years to complete an orbit around the Sun) originate from the Kuiper Belt.

Any 'Breaking News' on comets?

In September 2019, Astronomy Magazine reported that astronomers had discovered an orbital region just beyond Jupiter that appears to act as a kind of gateway for some objects entering the inner solar system from the Kuiper Belt. Their discovery could offer a solution to a puzzle that has long confused astronomers: How does a certain class of objects from the Kuiper Belt become comets?Many comets take a straightforward path into the solar system’s inner regions. They come from the Kuiper Belt or the Oort Cloud – regions beyond Neptune containing millions of icy leftovers from the solar system’s beginning. Gravitational nudges send them plunging inward until they swing around the Sun and out again.The puzzle comes from space rocks called Centaurs. First discovered in 1977, these objects from the Kuiper Belt have been gravitationally jostled into unstable orbits between Jupiter and Neptune. Close encounters with one of the giant planets can send a Centaur back to the Kuiper Belt or out to interstellar space, or send it deeper into the inner solar system. As Centaurs come closer to the Sun they begin to develop comas, telltale signs of cometary activity.

Sir Isaac Newton and the discovery of Halley's comet

The stamp below was issued by Ascension Island during the 1985-86 return of Halley's comet. It shows the images of Newton's Reflector Telescope and the comet in the background, indicating a link between the work of Halley and Newton. Indeed there is a link which was best described  in October 1985 when the New York Times reported the following;"it was Halley who encouraged the retiring Newton to write down the principles of gravitation he had developed after years of thought supposedly inspired by the legendary falling apple. Newton recognized that gravity on Earth represented the same law of force as that affecting the motion of planets around the Sun. Halley edited the manuscript and arranged financing for publication in 1687 of Newton's great book, ''The Mathematical Principles of Natural Philosophy.''

Halley's encouragement of Newton was perhaps his greatest contribution to science, according to Alan Cook, a professor of natural philosophy at Cambridge University in England. But in applying Newton's laws of gravitation in making his comet prediction, Halley went an important step further. His correct prediction turned out to be the first direct confirmation of Newton's theories."

Ascension Island is a British Overseas Territory and is an isolated island located  just south of the Equator in the South Atlantic Ocean.

What is special about a comet?

Based on observations from spectroscopy and findings of the Miller-Urey experiments, comets contain all the substances and conditions thought to be necessary for the synthesis of living organisms on Earth. This has led to the hypothesis that life may have originated elsewhere and hitched a ride on a comet to Earth!

How many comets are there?

As of July 2019, Wikipedia reports that there are 6,619 known comets but this number is increasing as they are discovered. Note that it is estimated that more than a trillion potential comets could reside in the Oort Cloud. For those with a deeper level of interest, the Gaia Space Telescope has identified a number of stars in the Milky Way that could cause more frequent comet activity. In 2018, it was announced that a star called Gliese 710 could actually barge into the Oort Cloud itself in 1.3 million years. This would likely dislodge many of the icy rocks in the Oort Cloud and send some of them into cometary orbits around the Sun.

The largest comet

There does not seem to be a consensus on this point as astronomers have yet to decide how the largest comet should be measured! As an example, comet Hyakutake's tail measured 500 million km from its nucleus. Thus it is the longest known tail on a comet. The Hale-Bopp comet had a nucleus of more than 60 miles in diameter. This is the biggest nucleus ever measured. Recently, a new definition has been proposed; i.e. the region of space disturbed by the presence of the comet. In this regard, comet McNaught wins the title of the largest comet ("space disturbed" being a function of the outgassing of a comet).

Near-Sun comets

The orbital paths of some comets take them very close to the Sun and hence they are exposed to conditions that are extreme. Researchers of these type of comets have termed them "near-Sun comets".  Within this broad categorization, there are "sunskirters, sungrazers and sundivers". The orbital path of a sundiver intersects the solar photosphere so they have little chance of surviving their perihelion passage. The sunskirter on the other hand, experiences less violent conditions with a perihelion passage that passes between 3.45 solar radii and 33 solar radii of the Sun's center and depending on its size and physical properties, has a chance of surviving. The sungrazer has a perihelion passage that takes it inside 3.45 solar radii of the Sun's center.  Small sungrazers can completely evaporate during such a close approach to the Sun whilst larger sungrazers can survive many perihelion passages. However, the strong evaporation and tidal forces they experience often lead to their fragmentation. Until the 1880s, it was thought that all bright comets near the Sun were the repeated return of a single sungrazing comet.Then, German astronomer Heinrich Kreutz and American astronomer Daniel Kirkwood determined that, instead of the return of the same comet, each apparition was a different comet, but each was related to a group of comets that had been separated from each other at an earlier passage near the Sun (at perihelion).

When does a comet die?

Once a comet has outgassed or exhausted all available volatile substances, its coma and tail will disappear and the remaining inert nucleus will take on the characteristics of a low albedo asteroid.  Sometimes, the comet completely disintegrates (as in the case of a sundiver or a sungrazer mentioned in the previous section). Although comets seem long-lived from a human perspective, on an astronomical time scale, they evaporate quite rapidly. Bearing in mind that a typical comet nuclei may range in size from a small mountain to a large city, it is not difficult to understand why it takes many years for all that ice to evaporate! The stamp presented below commemorates the recent demise of a comet that was observed by many astronomers on Earth.

Comet Shoemaker-Levy

The most spectacular demise of a comet in recent years occurred in July 1994. Comet Shoemaker-Levy was discovered on 24 March 1993. It had been captured by the gravitational effects of Jupiter (probably 20 or 30 years earlier) and Jupiter's tidal forces had acted to tear the comet apart. The comet disintegrated into a number of fragments, one piece up to 2 kilometers in diameter and approximately 21 fragments collided with Jupiter's southern hemisphere between 16 - 22 July 1994.  The scars from the multiple collisions remained visible on Jupiter's gaseous surface for many months afterwards. The comet was closely observed by astronomers worldwide and this event also provided the first direct observation of an extraterrestrial collision of objects in the Solar System. The stamp below, part of a series of five on a First Day Cover, was issued by Germany in 1999 and shows the collision of the comet with the planet.

All stamps presented in this post are from my personal collection and were photographed using a HUAWEI P30 telephone / camera.