The Sky at Night Phần 6 pptx

It was only a year since our last programme about Saturn, but as the planet was high in the sky, and the Cassini spacecraft was sending exciting new data, we decided to return to it, but

20 Exploring Mars

drift, and extricated itself only with difficulty But Mars has been helpful too Dust accumulating upon their upper panels threatened to cut off all transmissions, but in the nick of time convenient winds blew the dust away

Both rovers have been photographed from orbit, and both have traversed fasci-nating and varied territory One of the most spectacular features is Victoria Crater, visited by Opportunity, with its bays and inlets, while Spirit scaled the Columbia Hills inside Gusev Crater, probably an ancient lake Everywhere there is evidence of past water activity – and, of course, past eruptions The giant volcanoes of Tharsis must indeed have been awesome, and we cannot be sure that they are now extinct They may merely be dormant

There was also the “Face on Mars”, originally imaged by the Viking orbiters of the 1970s One has to admit that it did look like a face – and predictably caused great excitement among flying saucer enthusiasts Perhaps disappointingly, new images taken from different angles show that it is a very ordinary rock structure There is nothing in the least unusual about it

Plans for returning to Mars are well advanced, both by NASA and by the European Space Agency The search for life will continue, and talk of a fully fledged Martian Base can no longer be dismissed as science fiction When this will

be possible depends partly upon progress in technology, and partly upon politics

Of one thing I am certain: the world of 2080 will not be the same as that of 2008

Either we will be preparing to set up bases on Mars, or else the remnants of Homo

sapiens will be trying desperately to survive in radioactive caves

I have always felt that the first travellers to Mars will not go straight there, but will stop-off first at Deimos which is after all a natural space-station and might have been put there especially for our benefit I would favour Deimos rather than Phobos mainly because it is further out, whirls along at a less giddy speed, and would give

us a better overall view However, the Russians prefer Phobos, and even hope to bring samples back for analysis Phobos is only about as far from the surface of Mars as London is from Aden, and it has even been suggested that when a Martian crater is formed some material may have been hurled upward violently enough to spatter on Phobos Studies of Stickney, the largest crater on Phobos, link it with the 300-mile impact crater Lyot on Mars, which is well-formed and is thought to be between 3 and 3½ million years old Whether this is true or not, Phobos and Deimos may eventually turn out to be remarkably useful

Next year – before this edition of the Sky at Night is published, I am sure that

we will have to do yet another Mars update Much of what I have written here will need modification, but I doubt whether much of it will be downright wrong, as our ideas of 1957 have turned out to be

P Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_21,

© Springer Science+Business Media, LLC 2010

Chapter 21

The Lakes of Titan

Lakes of Titan (Credit: NASA JPL)

It was only a year since our last programme about Saturn, but as the planet was high in the sky, and the Cassini spacecraft was sending exciting new data, we decided to return to it, but this time to concentrate upon Titan As before, John Zarnecki and Michelle Dougherty joined me.

I think it is fair to say that Cassini has been one of the most successful of all space missions up to the present time Quite apart from carrying the Huygens lander, it has carried out a prolonged survey of Saturn and its satellite system; it has imagined the clouds which look rather like “a string of pearls”, it has looked for the strange spokes

in Ring B, which seem to be very variable; it has given new information about the fountains of Enceladus, which are now thought to be fuelling the E Ring, and it has provided us with firm evidence about the existence of broad seas on Titan

Titan, remember, is much larger than the Moon, and slightly larger than Mercury, though not so massive Alone among planetary satellites, it has a thick atmosphere – denser than ours, made up largely of nitrogen, though the lack of free oxygen, together with the intense cold, rules out advanced life-forms of our type Huygens, which made a controlled landing, touched down upon a surface with “about the consistency of wet sand”, and there were indications of drainage channels It was thought possible that the area was part of a coastline, but there was no clear sign of

a sea or a lake within the range of the grounded probe’s cameras There had almost certainly been a fairly recent shower, not of water but of liquid methane; cloud-cover on Titan is constant (which is why we had never before been able to see the actual surface), and there may well be methane drizzle all the time

The Lake District of Triton (Credit: NASA JPL)

21 The Lakes of Titan

Long after Huygens had lost contact, Cassini itself went on with its programme, during which it flew past the satellites and sent back pictures and data On 22 July

2006 Titan was the target, and Cassini returned radar images of areas in high northern latitudes which caused great excitement at Mission Control – and beyond, because the images showed numerous very dark patches with sharply edged boundaries

A rough area will look bright in radar, while a smooth area will look black The Titan patches were so featureless that they could hardly be anything other than liquid areas: in other words, lakes They were of considerable size, in one case at least

40 miles long

Finer details could be made out At a second pass, on 23 September 2006, Cassini showed two lakes at latitude 73°N, 40°W, which were each about

15 miles across, and were joined by a narrow channel (somebody at JPL called them “kissing lakes”) The right-hand lake had lighter patches within it, indicat-ing that it may be startindicat-ing to dry out with the approach of northern summer, and patchy lakes were also found elsewhere, so that we are presumably seeing deep lakes, shallow lakes and lakes which have either dried up completely or else are

in the process of doing so

The Saturnian seasons are different from ours The tilt of the planet’s axis is much the same as that of Earth, but Saturn takes 29.5 years to complete one journey round the Sun so that the seasons are a great deal longer This also applies to Titan because like all the other major satellites (except Iapetus) its orbit lies almost in the plane of Saturn’s equator, and a lake there has ample time to form and then dry out again partially or completely Everything happens at a very leisurely pace

Let us admit that we have no final proof that the radar-smooth areas are lakes, but I would estimate that the odds in favour are around 99.9%, and it is very dif-ficult to suggest any other explanation At Titan’s surface temperature of −180°C, the lakes cannot contain water and must consist of methane mixed with a certain amount of ethane They are thought to be the source of the methane gas which accounts for 5% of the satellite’s atmosphere Over millions of years sunlight breaks down atmospheric methane, and there has to be a way of replenishing it Much more work remains to be done, both by Cassini and future missions, and

no doubt there will be other surprises in store, but at least we have found a world unlike any other in the Solar System It is a fascinating place – and one day, per-haps, astronauts will go there and explore the Lake District of Titan

Saturn was past opposition, but still prominent in the evening sky, with the rings practically edgewise on The Cassini probe was still orbiting, and in full order, sending back amazing data Clearly we should discuss it

I had two regular and distinguished guests: Carl Murray and Michelle Dougherty Carl had been making special studies of the rings, and of course the main revelation was the discovery of the new ring associated with Phoebe It is extensive and very tenuous, with retrograde motion, and formed from material knocked off Phoebe itself Some material is wafted inward and falls on Iapetus, darkening the leading hemisphere; at least this solves the problem of Iapetus yin-yang appearance But even more exciting are the chemical lakes of Titan, and here Michelle is the leading expert

What is the loveliest object in the sky? Opinions differ, but my vote would unhesi-tatingly go to Saturn It is not the only ringed planet, but it is in a class of its own

It is a gas giant, much larger than any other planet apart from the other gas giants Jupiter (Uranus and Neptune are better classes as ice giants) Its equatorial diameter is almost 75,000 miles, but its rapid rotation – less than 11 h – makes the equator bulge out so that in shape Saturn resembles a slightly squashed orange The orbital period is 29½ years The axial inclination is slightly greater than that

of the Earth, and the rings and the orbits of all the main satellites apart from Iapetus lie practically in the plane of the equator There is a strong magnetic field, and it is worth noting that the magnetic axis is virtually coincident with the axis

of rotation

The rings are made of water-ice particles, ranging in size from tiny pebbles up

to blocks at least as large as a car Three rings are within the range of a small tele-scope, two bright (B and A) and one semi-transparent (C) Others, much more elusive, lie closer in or further out The bright rings, A and B, are separated by a gap known as the Cassini Division in honour of its seventeenth century discoverer; the Italian astronomer G.D Cassini, a pioneer telescopic observer of Saturn The current spacecraft is also named after him

Glint from sunlight reflected from a lake adjoining Kraken Sea

21 The Lakes of Titan

Saturn has a wealth of satellites, but only a few are over 100 miles in diameter, and most of the rest are probably captured asteroids The larger members of the family have differing features of interest; tiny Enceladus with its geysers of ice particles, Mimas with its “death star” crater, Dione with its icy cliffs, Iapetus with its weird equatorial mountain range… But Titan is really big and actually larger than Mercury It has an atmosphere twice as dense as ours, made up chiefly of nitrogen, and it is of course bitterly cold Saturn’s mean distance from the Sun is 886,000,000 miles It is difficult to visualise any life, at least of our kind

The first spacecraft to pass by-pass Saturn were Pioneer 11 (1979), Voyager 1 (1980) and Voyager 2 (1981) Good images were obtained, but those of Titan were not particularly informative, because they could do no more than show the upper-most clouds of the dense atmosphere What the surface was like remained a mys-tery The existence of “seas” was not ruled out, but not filled with water; they would

be chemical, with methane and/or ethane

Cassini was the first Saturn orbiter It arrived in 2004, and was an immediate success It carried a small lander, Huygens (named after the Dutch astronomer who discovered Titan in 1655) which released and made a controlled landing on Titan’s surface It came down on solid ground, said to have the same consistency as damp sand There were features that looked like drainage channels Presumably, there had been a recent methane shower Contact could not be maintained for long, but the landing was certainly one of NASA’s greatest achievements to date

Cassini continued happily on its way, and regularly sent back data and images

of Saturn and the satellites Titan was a prime target It was expected to be fascinat-ing, and it did not disappoint us

The existence of chemical seas and lakes was proved beyond all doubt Radar results gave the essential clue Smooth areas are radar-dark, and a sea-surface is obviously, completely smooth Most of the seas and lakes seem to be in the polar regions Anything over about 250 miles in diameter is conventionally classed as a

sea (mare) anything smaller as a lake (lacus) In the north, there are three seas,

Kraken Mare, Ligeia Mare and Punga Mare – huge features filled with methane plus some ethane Kraken, the largest of them is about 730 miles in diameter, roughly the size of the Caspian Sea It was named after a legendary Norwegian sea monster It seems to be rather irregular in shape, and contains an island, Mayda Insula On 8 July 2009 Cassini’s instruments observed a spectacular reflection from

a lake Jingpo Lacus, adjoining the northern coast of Kraken Ligeia and Punga are

of the same type as Kraken, though smaller

The real “lake district” is far north There are more than a dozen named lakes, notably Jingpo Lacus (diameter 150 miles) There are fewer known lakes in the south, of which the largest is Ontario Lacus (145 miles), about equal to our Lake Ontario Ontario was actually the first lake to be identified, on 21 December 2008 However, we must remember that our mapping of Titan’s surface is very incom-plete, and the long seasons mean that there will be major changes in the seas and lakes over the course of a Saturnian year

Whether men will ever reach Titan remains to be seen, but it will certainly not

be yet awhile Frankly, it must be a gloomy place, with permanent cloud cover and

probably persistent methane drizzle There may be a gentle lapping of waves at the shore, but that is all, and indeed the calm may be constant I suppose that life in the chemical seas cannot be entirely ruled out, but it does seem highly unlikely Of one thing I can be certain; no future astronauts will be able to organise fishing parties

in the Kraken Mare!

P Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_22,

© Springer Science+Business Media, LLC 2010

When the first episode of the Sky at Night was transmitted (live!) on 24 April 1957,

it never occurred to me that I would still be broadcasting after an unbroken run of half a century But I was – and believe me, my Fiftieth was a joyous occasion There were in fact three programmes, one of which was organised separately by the BBC and about which I knew little before it was transmitted I was both honoured and staggered by the number of people who were on it – including most of our leading astronomers; some distinguished MPs – Charles Kennedy, Lembit Opik; equally distinguished public figures – Sir Richard Branson, Sir Tim Rice; musical and theatre figures – Dame Evelyn Glennie, Mylene Klass; pioneer astronauts – Neil Armstrong, Buzz Aldrin; space pioneer Sir Arthur Clarke, plus almost all my true, personal friends It was overwhelming There were also some who are no longer with us, notably one of the closest friends I have ever had, Michael Bentine I was seen doing a sketch with Morecambe and Wise, and there was even a clip taken during

Chapter 22

Fiftieth Anniversary

Fiftieth anniversary

a cricket match, just as I came on with my leg-breaks, delivered at the end of my long, leaping run On film I tiptoed through the tulips with Magnus Pyke Memories aplenty … Special tribute to Jonathan Ross for his expert comparing, and to Philip (Pip) Jennings, aged 12, who spoke on behalf of the British Astronomical Association I append here (a) a list of the people at my actual party

on 21 April; I hope I have not left anyone out, and (b) a list of the participants in the programme who were not actually present in person I am particularly proud because I doubt whether there has ever before been such a gathering organised

to pay tribute to one person – and an amateur astronomer at that What more can

I say – except “Thank you?”

There was a good deal of discussion about our actual Fiftieth programme, and eventually it was decided to look back and forward in a novel way First we would return to 1957 and give as accurate a reconstruction as we could; John Culshaw, well-known for his TV impersonations, would play me as I used to be then, and using a Time Machine the PM of 1957 could talk to the PM of 2007 Next, look forward at the next fifty years; a suitably age-increased Dr Chris Lintott would give reports from Lunar Base, and from Port Lowell on the surface of Mars There would follow

a broadcast from the Sky at Night studio in 2057, with Professors Chris Lintott, John

Zarnecki and Brian May… Initially I was afraid that the programme would end up something like out of Monty Python, but at the end most viewers felt that the recipe worked, even though I have to add that there were a few dissenters

John Culshaw was brilliant; he really did look like the 1957 version of me, and

he had all my mannerisms Chris Lintott and John Zarnecki demonstrated their very considerable acting skills, and of course Brian May is unique (incidentally he was

in the throes of completing his PhD thesis at Imperial College, London, put on hold years earlier when the Queen Group monopolised his main attention; his subject was Zodiacal dust) The programme was tricky to produce Jane Fletcher and her team coped admirably, and got everything absolutely right

I think that our reconstruction of the 1957 studio was accurate, and as a “Time Lord” I felt nostalgic The opening music, “At the Castle Gate” by Sibelius, has never changed; I chose it, and we have only twice used anything else, though for our last programme about Halley’s Comet in 1986, the Band of the Royal Transport Corps played us out with the march which I had composed for the Halley’s Comet Society (This flourished between 1968 and 1988 and was great fun, perhaps because it had no aims, objects or ambitions, and claimed to be the only completely useless society in the world with the obvious exception of the European Parliament

It really ought to be revived.)

Let me add here that one thing absent from an ordinary Sky at Night programme

is background music At the present moment, all producers seem to be obsessed with it; it destroys the credibility of a science programme, and dumbs it down to the level of Listen with Mother It also sounds so amateurish, and does its best to swamp the participants in the programme; even news bulletins are not immune We did once have a background “executive producer” who wanted to make extensive