Tuesday, 22 April 2014

The Hourglass Sea

As the red planet reached opposition earlier this month, shining brightly over my garage roof, I thought I would do a post on significant moments in our relationship with our celestial neighbour.

The red planet

The ancient Greeks looked up and puzzled at the peculiar behaviour of Mars during its periods of apparent retrograde motion as the Earth, supposedly the fixed centre of their universe, passed it on the inside, making it appear from Earth as though Mars was moving in the opposite direction. Hipparchus of Nicaea, who compiled the earliest known catalogue of the stars in the 3rd Century BC, set out to explain this phenomenon through the theory of epicycles. These were small circular orbits traced out by the planets as they moved in larger circular orbits; known as deferents, around the Earth. Along with the misguided concept of an Earth-centric universe, the idea that the universe must possess a perfect nature and that the orbits of the planets must therefore be perfectly circular, caused the ancients to overcomplicate their explanation for the motion of the planets.

The great Alexandrian scholar Claudius Ptolemy, (90-168AD) whose vision of the cosmos would dominate for over a millennium, added further layers of complexity in his efforts to make the erratic motions of the planets fit within the framework of a perfect universe; centring their orbits around an imaginary central point known as the equant. With hindsight, it was all a case of trying to make the facts fit the theory, but until Nicolaus Copernicus looked up and pondered the heavens anew, no-one had a better idea.

 Copernicus' assertion in his seminal work of 1543, De revolutionibus orbium coelestium, published shortly before his death, that the sun and not the earth was the central point about which the planets moved, was not universally accepted. One man who had trouble letting go of the idea of an earth-centric cosmos was the larger than life and magnificently moustached  Danish scholar Tycho Brahe, (pictured right).
Brahe was not a man to let go of an argument easily. The gold prosthetic that covered his nose was testament to that. He had lost part of his nose in a duel over a mathematical dispute. So the story goes. I bet there was a woman involved somewhere.

Brahe fell out with the king of Denmark too and left in 1597 to serve as court astronomer to Emperor Rudolph II in Prague. Tycho had his own ideas about the universe. Through his observations of a supernova he had shown the cosmos to be dynamic and evolving, dispelling classical notions of unchanging perfection. Nevertheless he clung to the idea of a universe with the earth at its centre but came up with a new model in which the sun circled the earth but the other planets circled the sun. Brahe amassed copious amounts of data from detailed observations of the heavens in the hope of lending empirical weight to his theory. In 1600 Brahe was joined by the young Johannes Kepler, fleeing religious persecution in Graz. Brahe put Kepler to work studying his observations of Mars with the object of elucidating its orbit. After five years of work, in which he proved that Tycho's observations could not be fitted to a circular orbit, Kepler would publish his seminal Astronomia Nova, in which he announced that the orbit of Mars was elliptical, as must be the orbits of all planets; a conclusion enshrined as his first law of Planetary Motion. The solution was simple in its elegance and the Ptolomaic universe of equants and epicycles was consigned to the dustbin of history, where it would soon be joined by the Tychian model, though mercifully Brahe did not live to see this. Doubtless he would not have taken it well.

The apparent orbit of Mars as drawn by Cassini

As the telescope age dawned, further details of the nature of Mars were revealed. The first to observe the Martian polar ice caps was Christiaan Huygens who produced a sketch of the planet in 1659, showing three distinct views featuring different surface features. Between 1704 and 1720 Giacomo Maraldi, nephew of Gian Domenico Cassini, was following in his uncle's footsteps at the Paris observatory when he decided to take a particular interest in Mars. Maraldi too observed the polar caps and noted that they grew and shrank at different times. He was also able to observe other surface features on the planet, describing the shadowy band made by larval seas, although he believed the shadow to be a result of clouds in the Martian atmosphere rather than any solid entity. Through observation of the feature now known as Syrtis Major, 'the Hourglass Sea', Maraldi was able to determine Mars' rotation period at 24 hours and 40 minutes.

The advent of the 'Newtonian' reflector telescope brought better views of Mars than ever before. In the early 1780's William Herschel turned his attention to Mars with a 20 foot long reflector and observed with interest the changing nature of the poles. Herschel proposed that the growth and shrinkage of the polar caps was seasonal. He also demonstrated that Mars had very little atmosphere by observing that there was no discernible dimming of stars immediately before they passed into the shadow of the red planet. It was in the course of such observations in 1881 that Herschel made his most famous discovery; the planet Uranus. The moment of discovery is immortalised in this contemporary engraving (left) showing William and Caroline Herschel at work.

By 1862 the largest telescope in the world was the 26 inch reflector at the US Naval Observatory in Washington DC. Here the resident professor of astronomy was Asaph Hall, who sometimes received visits from Abraham Lincoln, who was fascinated by the work at the observatory. Hall enjoyed a prodigious career, publishing 500 papers on matters astronomical and determining the rotational period of Saturn. Hall's greatest quest was his search for satellites orbiting Mars. Finally he despaired and was ready to abandon the search but was encouraged to continue by his wife. And so he pressed his eye to the telescope once more and in 1877, within the space of a week after years of searching, he identified not one but two moons circling Mars. He named them Deimos and Phobos after the sons of Mars. Both moons are tiny, at just 14 and 8 miles across and are believed to be captured asteroids.

Drawings of Martian canals by Percival Lowell
It was a splendid achievement but would be overshadowed, in the public imagination at least, by the announcement in the same year by Milanese astronomer Giovanni Schiaparelli that he had observed 'canals' on Mars. Schiaparelli was an accomplished astronomer and had published his observations using the term 'canali' literally 'channels' to describe the features that he was seeing. These are now known to have been an optical illusion caused by the chance alignment of craters when viewing the Martian surface at the limit of resolution of Schiaparelli's telescope. Enter wealthy businessman and astronomy enthusiast Percival Lowell. Seizing upon the mistranslation of Schiaparelli's 'canals' Lowell embarked upon an obsession with the non-existent features, building a state of the art observatory in Arizona to aid his quest to explain the mystery of these Martian canals, suggesting that they had been created by intelligent beings living on Mars. The observatory that Lowell founded was nevertheless a great legacy and it was here in 1930 that Pluto was discovered. The proof of the existence of an outer planet had become Lowell's new quest although he did not live to see the vindication of his theory.

The idea of Martians was firmly embedded in the public consciousness and in 1898 HG Wells' classic War of the Worlds was published, inspired in part by Lowell's ideas. Illustration right is from a 1908 edition. Legend has grown up around the mass panic that was suddenly sparked by Orson Welles' radio dramatization of War of the Worlds for the Mercury Theatre on Air in 1938.  The story goes that Welles began his broadcast with an explanation that it was a fictional dramatization but that most people were listening to the popular Edgar Bergen show on another station. When Edgar's show finished, people belatedly tuned in to Orson Welles' ultra realistic news bulletin style War of the Worlds and wrongly assumed that it was all really happening, with mass hysteria resulting. Sadly it seems that this is a myth and that stories of the panic were wildly exaggerated by the American press, with the newspapers taking the opportunity to show the arriviste wirelessmen in a bad light as reckless purveyors of misinformation. They of all people should have known however that there is no such thing as bad publicity. After all, has anyone these days heard of Edgar Bergen?

Man has yet to set foot on Mars but has done the next best thing by landing probes and rovers on the surface. The United States has led the way with its Mariner and Viking  missions of the 1960's and 70's and the redoubtable Curiosity and Opportunity rovers that have brought us such wonderful images in recent years. Appropriately enough however, it was the Soviet Union that first landed a craft on the surface of the red planet, albeit not very successfully.

Soviet efforts to reach Mars began in 1962, just as the US Mariner programme was also beginning. The Soviets launched four missions to Mars, only the last of which made it out of Earth orbit and out into interplanetary space for a distance of over one hundred million kilometres from earth before losing its way. Two more efforts to launch an orbiter in 1969 both exploded shortly after launch.

Efforts were nevertheless stepped up and continued with the ambitious launch in 1971 of Mars 2 & 3 which were combined orbiter/lander craft. Both craft successfully reached Mars and went into orbit around the red planet in the summer of 1972. The US Mariner 9 had already become the first craft to successfully make it into orbit around Mars the previous year. Now however the Soviets had the opportunity to move ahead of their rivals. The landers were released into the teeth of a fearsome Martian dust storm and the Mars 2 lander crashed on the surface. Mars 3 made a successful landing on the surface but may have sustained some damage. It reportedly sent a 20 second transmission including one grainy image before communications were lost, though some have questioned whether the transmission occurred. The orbiters continued their mission, sending back images and details of the atmospheric temperatures, pressures and chemical composition.

Follow up missions launched in 1973 were largely disappointing. The Mars 4 mission failed to enter Mars orbit and flew right by the red planet. Its twin Mars 5 was more successful and orbited the planet, gathering images and more details of the atmosphere, surface temperature and composition and magnetic field. Two more missions were launched with the intention of landing more modules on the surface. Mars 6 released its lander successfully but a likely failure of the landing retro boosters caused it to slam into the surface. Mars 7 was an identical mission but a fault caused the landing module to be released too soon and it missed the planet altogether. The inability of the Soviets to prevent the degradation of their computer chips during the flight to Mars has been blamed for the majority of the failures. In 1975 the successful US Viking missions were launched and both subsequently made successful landings on the surface and sent back sustained transmissions, effectively ending the Cold War race to explore Mars.

In a post script NASA's Mars orbiter last year took a picture of what is believed to be the Soviet Mars 3 lander, sitting on the Martian surface in the Ptolomais crater, providing potential proof that the Soviets did indeed make it to the red planet first.

The Cold War propaganda poster is not especially related to the Mars programme but I liked it.

Read more space related posts on Slings and Arrows

Kepler and Mars
Maraldi and Herschel

Asaph Hall and the moons of Mars

Canals on Mars

War of the Worlds Mass Panic

The Soviet Mars Programme

Mars 3 Found?

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