Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.armaghplanet.com/pdf/Astronotes/Astronotes2010/Astronotes%202010-03.pdf Дата изменения: Tue Sep 20 18:49:36 2011 Дата индексирования: Tue Oct 2 01:33:24 2012 Кодировка: Поисковые слова: galactic collision

March 2010

ASTRONOTES
Incorporating FRIENDS' NEWSLETTER Great balls of fire! Smashing asteroids! The sky this month Measuring space Mars rocks!

ARMAGHPLANETARIUM


2 Astronotes March 2010

Great balls of fire!
By Martina Redpath, Education Support Officer There was an air of excitement in the Planetarium on Thursday 4 February as reports of a fireball travelling across Ireland the previous evening flooded in. The telephones were ringing continuously and a TV crew even arrived at the Planetarium to find out more information about this bright fireball. This excited the primary school visitors who were trying to get themselves on TV, however this was less exciting for the education staff, who were trying to avoid the camera! So what was this bright ball of light? From collated reports this sight is thought to have been a meteor, and chances are that some parts fell to the Earth's surface as a meteorite. A meteor, sometimes more commonly known as a shooting star, is a small particle of metallic or stony matter, about the size of a grain of rice or smaller, burning up in the Earth's atmosphere. When these particles are travelling through space they are known as meteoroids and very large meteoroids are known as asteroids. When space debris lands on Earth these fallen pieces are known as meteorites. The thought that a meteorite may have landed somewhere in Northern Ireland is very exciting as the last known time that this happened was 41 years ago in Bovedy, Co. Londonderry in 1969. Why do things burn up as they come through the atmosphere? Million of meteors occur in the Earth's atmosphere everyday. They are visible between 65 and 120 km (30-60 miles) above the Earth's surface. As these bits of space debris reach the Earth they are travelling at high speeds, usually between 12-70 km/s (7-43 miles per second). As meteoroids travel through the atmosphere air resistance creates friction causing the material to become heated until it is white hot and therefore giving out light. As the surface vaporises, a process known as ablation, due to the sudden heat, a glowing trail of gases and melted meteoroid fragments are visible for a few seconds. The ablation process which occurs for most of the flight is also an efficient method of removing heat from the meteorite, meaning the meteorite may reach the ground at air temperature rather than glowing red hot as depicted in so many movies.

"When space debris lands on Earth these fallen pieces are known as meteorites"
Spacecraft face the same difficulties with reentry into the atmosphere as air resistance generates a lot of heat. All spacecraft require a heat shield for protection. In the 1950s, engineers working for the National Advisory Committee for Aeronautics (NACA, the predecessor of NASA) discovered that a blunt shape made the most effective heat shield. The shape creates a shockwave ahead of the spacecraft deflecting the heat away. However, the extreme pressure between the shockwave and the heat shield turns the gas to hot plasma. Plasma is gas so hot that the very electrons are ripped off its atoms. An

Image Credit: NASA,

Apollo 8 reentry Artist's impression of the Apollo 8 capsule entering the Earth's atmosphere. The capsule has a blunt shape making a more effective heat shield.


March 2010 Astronotes 3 ablative heat shield is a simple way of dispersing the heat from the hot plasma, allowing it to vaporise, the heat being carried away in the plasma. As an aside, the plasma carries a positive electric charge, blocking radio communications to and from the re-entering craft. Although this ablative shielding method is simple and relatively inexpensive, it is only useful on a spacecraft that is not going to be re-used. Advanced spacecraft, like the Space Shuttle, are expected to fly many times therefore they have a specially designed Thermal Protection System (TPS). The Shuttle's TPS is Underside of Space Shuttle Discovery Space Shuttle Discovery was made up of individual silica photographed from the International Space Station of during a back flip tiles, designed to withstand manoeuvre showing the TPS. high temperatures and multiple re-entries into requires a lot of fuel; for a Space Shuttle to reach the atmosphere, with only minor repairs needed low orbit it must use almost two million litres between missions. (0.4 million gallons) of propellants. The Space Since spacecraft reach high temperatures and burning up on re-entry is a possibility, how come rockets don't burn up when leaving the atmosphere? Rockets have to reach orbital velocity, or even escape velocity, fast enough to break free of the Earth's gravitational pull. To leave the Earth, a Space Shuttle has to reach a speed of 40 000 km/h (24 900 mph). Launching straight upwards allows the Shuttle to travel through the denser parts of our atmosphere without gaining much heat from air resistance. This also Shuttle and other rockets are still gaining speed (so they are travelling relatively slowly) as they rise through the lower atmosphere where the air density is thickest and friction the highest. By the time they have burned most of their propellant, they are travelling much faster but have risen over 30 km (100 000 ft). At this altitude the air is much thinner, reducing the friction. Shooting stars are wonderful sights and now you know just how spectacular an event you have just witnessed!

Fire in the sky
By Colin Johnston, Science Communicator As you will have gathered from the previous article, about 1800 GMT on Wednesday 3 February something dramatic happened in our skies. I missed seeing it myself but within minutes of arriving at my desk on Thursday morning, I was quite green with envy as I received reports by telephone and e-mail from eye witnesses of a spectacular fireball the night before. Most reports came from witnesses along an arc

Image Credit: NASA


4 Astronotes March 2010 extending from Omagh to Moira, several reports came from motorists travelling along the M1 motorway. Every observer reported that the fireball made no sound, was moving towards the north and was brightly coloured, most saying green, but blue, turquoise and yellow were also claimed. Virtually everyone compared it to a burning aircraft. Most witnesses said it was very low in the sky and several believed they had seen it impact the ground at locations they named. Sadly no genuine fragments have come light. David Asher of Armagh Observatory has made me aware of the intriguing possibility that the fireball was actually a fragment of debris from a US military Delta 4 rocket launched in 2006, This theory suggested by amateur-astronomer Enrico Stomeo is supported by evidence. The debris' polar orbit is consistent with the north-south alignment of the meteor and its colourful appearance (burning metals or propellent?). Perhaps

Meteor map showing the locations of some of the witnesses who observed the meteor's dramatic descent. we will have an answer by the next issue of Astronotes.

Crash of the asteroids
By Sinead McNicholl, Education Support Officer Asteroids are rocky material left over from the formation of the Solar System and are mainly found orbiting the Sun within the Asteroid Belt which is located between Mars and Jupiter. One theory suggests that they are the remnants of an ancient planet that was destroyed in a massive collision in the distant past. Another, more likely, theory postulates that asteroids are material that never formed into a planet. Many believe the second theory to be more viable because if we collected all the asteroids in the belt to make a single object it would be less than 1500 kilometres (930 miles) across, which is less than half the diameter of our Moon. There are more than 100 000 asteroids in the Belt. However, they are so sparsely distributed that numerous unmanned spacecraft have travelled through it successfully without incident. The first spacecraft to make a journey through the Asteroid Belt was Pioneer 10 on its way to Jupiter back in 1972. So as you can imagine flying through the belt is not how the movies convey it, with duelling
Image Credit: NASA, ESA, and D. Jewitt (UCLA)

Close-up asteroid collision This is a NASA Hubble Space Telescope picture of the comet-like object called P/2010 A2. The long trail of debris behind the nucleus is quite obvious starfighters constantly dodging asteroids in flight; the truth is that it's quite empty. In reality the average spacing of asteroids is several million kilometres, so if you were able to land on one, the closest asteroid would be so faint you would have to use a telescope to see it. Because they are situated so far apart it means that asteroid collisions in space

Image Credit: Colin Johnston/GoogleEarth


March 2010 Astronotes 5 are extremely rare and infrequent, in fact there has never been evidence of these cosmic impacts before, well that is until now. NASA's Hubble Space Telescope has captured images of two colliding asteroids about 145 million km (90 million miles) from Earth. This amazing occurrence was discovered by the Lincoln Near-Earth Asteroid Research (LINEAR) sky survey on January 6, 2010. Only one asteroid survived the impact and has been named P/2010 A2 whilst the other asteroid disintegrated behind it forming a luminous trail of debris. On first viewing the image strongly resembles a comet; however on closer inspection it is actually quite different. within the Belt and there are even suggestions that asteroids are being slightly eroded and ground down due to the smashes, but to finally witness the immediate aftermath of such an event was truly astounding. Researchers estimate that this asteroid crash occurred at about 18 000 km per hour (11 000 mph) or five times the velocity of a rifle bullet. The main nucleus of P/2010 A2 would be the surviving remnant of this so-called hypervelocity collision.

"asteroid collisions in space are extremely rare"
Follow-up images taken by Hubble on January 25 and 29 uncovered a strange X-pattern structure near the nucleus. The images also revealed that the nucleus of P/2010 A2 is situated out of the halo of dust, which has never been seen before in a comet. This dust trail also lies within the warmer region of the inner Asteroid Belt, where comet nuclei are not known to reside. Groundbased research also indicates that there is no gas present which comets emit. This is because they are composed of ice which turns to gas near the Sun. Astronomers have concluded that the object may be the result of a head-on collision between two asteroids in the Asteroid Belt and the strange shape is actually a shower of rubble which forms a comet-like tail. "If this interpretation is correct, two small and previously unknown asteroids recently collided, creating a shower of debris that is being swept back into a tail from the collision site by the pressure of sunlight. The filamentary appearance of P/2010 A2 is different from anything seen in Hubble images of normal comets, consistent with the action of a different process", remarked David Jewitt, an astronomer at the University of California Los Angeles. Asteroid collisions are expected to be energetic and produce a kinetic explosion which is caused by the high-speed smash. Astronomers have long known that these impacts should occur

"there has never been evidence of these cosmic impacts before, well that is until now"
Now I don't intent to frighten you, but by sheer coincidence the orbit of P/2010 A2 suggests that it is part of the Flora asteroid family, a famous group of asteroids produced by other collisions more than 100 million years ago. About 65 million years ago a former member of the Flora family is thought to have been the asteroid that struck Earth at the YucatАn Peninsula in Mexico creating the Chicxulub crater. The impact was thought to have formed a huge dust cloud

Asteroid Belt The asteroid belt lies in the region between Mars and Jupiter and contains over 100 000 asteroids.

Image Credit: Artemio Urbina


6 Astronotes March 2010 which created a global cooling effect and may have been responsible for the extinction of the dinosaurs. To make it quite clear however, we are in no danger from the debris of this unique event as it happened so far away, approximately 140 million km (90 million miles) from Earth. You can sleep easy tonight as we have organisations such are LINEAR who are constantly monitoring the skies. Their research can educate us about the habits of asteroids and what happens if they do collide together. Events such as the P/2010 A2 collision provide data and a real-life scenario of what such an impact generates and the more that we observe and learn about these smash-ups then we can adapt our prevention methods to make sure that an asteroid will not hit Earth.

March Night Sky
By Tracy McConnell, Education Support Officer Welcome to this month's guide to the night sky, where we will mostly be looking at the constellations visible at approximately 11.00pm on 15 March 2010, however there will be little variation in position from night to night. Before looking at the constellations, there are three planets visible this month too. As the Sun sets between 7.00 and 7.30pm so does the planet Venus which will appear as the evening star. After sunset, Saturn rises in the east and Mars is visible in the south (for more information on Mars see February 2010 Astronotes). At 11.00pm Mars will have moved to the high SW and Saturn will have risen to the south-east mid way up the sky. There are also five zodiac signs visible at this time this month. Starting in the east and stretching to the south is the largest of the zodiac signs, second largest of all the constellations, Virgo the Maiden. (Saturn is in the head of Virgo). There are many ways of joining the stars in Virgo but one of them does outline what looks like a stick person, lying down. Virgo is often thought to be the Greek goddess of agriculture, Demeter, because the Sun passes through this constellation at harvest time. The constellation is home to the Virgo Galaxy cluster, containing up to 3000 galaxies and lying 70 million Light-years away (21.5 Mpc). High in the sky due south is the fierce constellation Leo the Lion, easily spotted due to the bright "sickle" shape of stars. This constellation was
Image Credit: XMM-Newton, ESA, NASA

Castor Sextuple star system Castor, made up of three binaries, bright visual stars Castor Aab and Bab and dim red flare stars YY Geminorum AB, which are much brighter in X-ray wavelengths. also mentioned in more detail in last month's guide to the night sky. In front of Leo, facing SW is Cancer the Crab, which contains 4 stars; one at the centre, and 3 around the centre which can be connected by radial lines. In Greek mythology Hera, the wife of Zeus, sent a crab to attack Hercules. Hercules squashed the crustacean by stepping on him, after which Hera placed the poor defeated shellfish in the heavens. Near the central star of Cancer the Crab, is the Messier object M44. It is an open cluster called Praesepe or "The Beehive" and even though it's located 580 light years (177pc) away and is 10 light years (3pc) across, it can still be seen with


March 2010 Astronotes 7 the naked eye. This cluster is thought to have formed over 600 million years ago and is larger and older than most open clusters. As it can be seen without the aid of a telescope, M44 has been known since prehistoric times and it has been observed and studied by many astronomers throughout the ages. So far with large telescopes over 200 stars have been confirmed as members of this cluster though there are still many others in the region. The planet Mars is mid way between the constellations Cancer and star system with six individual stars gravitationally bound together. In the mid sky in the east, is the constellation BoЖtes the Herdsman, who was placed into the heavens for creating the plough and appears as a pattern resembling an ice cream cone. Just above BoЖtes are his herding dogs Chara and Asterion, the constellation Canes Venatici. This constellation is home to five Messier objects, four of which are galaxies outside our own Milky Way. The most significant of these is the Whirlpool Galaxy, (M51, NGC 5194), which was first observed by the Irish astronomer Lord Rosse in 1845. Other galaxies include, the Sunflower Galaxy (M63, NGC 5055), Messier 94 (NGC 4736), and Messier 106 (NGC 4258). Messier 3 (NGC 5272) is a globular cluster, one of the largest and brightest, and is made up of around 500,000 stars. It is located at a distance of about 33,900 light years (10,400 pc) away from Earth. M3 has an apparent magnitude of 6.2, making it visible to the naked eye under dark conditions. From a moderate-sized telescope, the cluster is fully defined. It is estimated to be 8 billion years old. I hope this guide has been of some help to you, Happy stargazing!

Virgo galaxies This NASA GALEX telescope image shows a triplet of galaxies in the Virgo cluster in ultraviolet light: NGC 5560 (top galaxy), NGC 5566 (middle galaxy), and NGC 5569 (bottom galaxy). Gemini, which is in the mid-sky in the West. Gemini the Twins looks like two stick men star patterns with very bright stars marking their heads. This amazing pair sailed with the Argonaut crew in Greek mythology. Supposedly they calmed the savage waves that would have sunk their ship. The sea god Poseidon, made the twins the protectors of all sailors and placed them among the stars. The two crowning stars are called Castor and Pollux after the twins. Although Pollux is the brightest, Castor is by far the more interesting of the two, as it is a sextuple

Image Credit: NASA/JPL-Caltech

Moon Phases Mar 2010
Sunday 7 March Monday 15 March Tuesday 23 March Tuesday 30 March Last Quarter NEW MOON First Quarter FULL MOON

Measuring the void (part 1)
By Mary Bulman, Education Support Officer Here on Earth we use kilometres or miles to measure long distances. We can easily use kilometres for the distance to the Moon, it being roughly 380 000 km (236 000 miles). We can even use our familiar kilometres or miles for distances to the Sun which is 150 000 000 Km (93 million miles). However when it comes to distances to Neptune or Pluto we are into billions of kilometres and the zeroes become unmanageable.


8 Astronotes March 2010 In an effort to deal with this problem, astronomers in the seventeen century came up with a new unit of measurement, the Astronomical Unit (written as AU). An Astronomical Unit is roughly the distance from the centre of the Earth to the centre of the Sun. What is this distance? People have been calculating the distance between the Earth and the Sun since ancient times. Eusebius of Caesarea (263 AD ­ 339 AD) got very close to the present measure, his 804 million stadia converting to 149 million km. Our present calculation is based on the work of Giovanni Cassini (1625 ­ 1712). In 1672 he estimated the distance between the Sun and the Earth to be 140 million Km (87 million miles). In 1976 the Astronomical Unit was formally set at approximately 150 000 000 Km by the International Astronomical Union which is responsible for defining the units of measurement used by astronomers and scientists. The AU is the favoured unit of measurement within the Solar System. Neptune and Pluto are about 29 AU and 40 AU respectively from the

Compacted Solar System If the planets were so close together we would not need to use AU to measure their distances Sun. Venus is 0.7 AU from the Sun while Mars is 1.5 AU. It works well within the Solar System but when we move beyond the Solar System distances become mind boggling. Here we have to recourse to even greater units namely the Light Year and parsec. Both are used for deep space measurements, the parsec being favoured by professional astronomers and the Light Year used more in popular astronomy. I will tell you about these vast measures in the second part of this article (next issue).

Where have all the Martians gone? (part deux)
By Colin Johnston, Science Communicator In the last part of this article we saw how Mars had once been regarded as a home for life. Yet space missions had revealed the planet's surface to be utterly hostile, apart from the savage cold, the atmosphere was much, much thinner than had been thought (in fact it was virtually nonexistent), the terrain was scoured by both harsh ultraviolet (UV) radiation from the Sun and dangerous cosmic rays. Any astronaut who leapt outside their Mars lander without putting their spacesuit on first would last about as long as a drummer with Spinal Tap. The hapless human would choke in the thin poisonous carbon dioxide atmosphere until he passed out. Death would follow inside a couple of minutes The dead body would freeze rapidly in the deep cold while the intense UV radiation would then blacken the
Image Credit: NASA/JPL

Man meets robot A full-scale replica of a Viking spacecraft is displayed by Carl Sagan. The super optimistic Sagan hoped the Vikings might discover Martian fauna as big as bears and proposed that the probes carry bait to lure them for close up photography. This suggestion was not acted on.

Image Credit: NASA/JPL


March 2010 Astronotes 9 ment. When the Mars soil at the two Viking sites was analysed for organic molecules, the stuff any feasible living thing would be made of, none was found. The soil was sterile; unbelievably there was more organic material to be found in the lunar soil brought back by the Apollo missions. Hence the Viking experiments were less than conclusive. It appeared that the soil on Mars had some very peculiar chemical properties (it appeared to contain a powerful oxidising compound similar to hydrogen peroxide) but was lifeless. Or it contained life of a completely alien type. You may think that this meant it was time to launch Vikings 3, 4 and so on to investigate further but NASA abandoned landing on Mars for over twenty years, a decision forced on it not by choice but by economic necessity alas.

Image Credit: NASA

A little piece of Mars ALH 84001 photographed beside a 1 cm cube corpse, which would quickly dry out and shrink as its moisture was leeched out. The gruesome remains' wizened features would quickly resemble those of an Egyptian mummy or possibly those of Victoria Beckham. Nether the less, there remains the possibility that under the red sands hardy micro-organisms were clinging on to life (dare we call them "Clingons"?) In the mid-1970s NASA sent the twin Viking landers to explore this possibility. Each probe scooped up a handful of the surface material in its steely claw and poured on to it a rich nutrient broth, a sort of "chicken soup for the soil". Any Martian microbes would hopefully drink this in and in response belch out carbon dioxide. So what happened? Immediately after the broth was released, the test chamber swelled with carbon dioxide! Both Viking landers saw this. Was this proof of life on Mars? The mission scientists, no doubt trembling with excitement, ordered further experiments, and these caused doubts to rise. The initial belch of gas from the soil tapered off abruptly. If there were Mars bugs in the soil then they were not thriving on the food. Adding more broth did not spark a second release of gas, this never happened with terrestrial soils. There was one hopeful sign: when fresh soil samples were taken but baked at high temperature in the probes' tiny ovens before adding the nutrients, nothing happened. This result is just what you would expect if the heat had sterilised the soil, killing its microscopic inhabitants. It was another experiment which caused the final disappoint-

"about a billion tons of Mars rock have landed on Earth"
In the interest of fairness, I should point out that one of the designers of the Viking instruments, Dr. Gilbert V. Levin, has vociferously claimed that the spacecraft did indeed find life there. According to him, the mass spectrometer used to determine if there was organic matter in the soil was so poorly calibrated it could not even detect organic matter in terrestrial soil. His views have met with little support from the wider scientific community. Some of Levin's other suggestions, namely that muddy puddles and plant life are visible in some images from Mars landers have met with derision. No subsequent NASA Mars probe or rover since has carried any instruments to directly locate Martian life, being focussed on the planet's climate and geology. Over the decades, disillusionment over the possibilities of Martian life settled firmly over most of the scientific community. No one seriously expected to find life on Mars anymore (but on the other hand the rocks are absolutely fascinating!) This may seem odd: surely all these Pathfinders, Sojourners, rovers and so on are meant to look for signs of life? Well NASA is painfully aware since the Apollo years


10 Astronotes March 2010 In 1984, meteorite hunter, Roberta Score found an interesting specimen near the Allan Hills in Antarctica . She designated it ALH 84001, a name which became famous world-wide in 1996. NASA researchers led by Dr David McKay claimed to have discovered actual Martian lifeforms in ALH 84001! When ancient, apparently dead, alien organisms are found frozen in the Antarctic ice, the usual protocol is to take them imbedded in a block of ice to a nearby isolated and claustrophobic research base. Then all you have to do is wait for the aliens to thaw out (they will make occasional slight but ominous movements as the ice melts away but no one will notice until it's too late) and eventually they will grow slimy pseudopods and start eating or taking over the scientists.

Image Credit: NASA

Fossilised Martian? This structure found in ALH 84001 does look very biological. that the public are not interested in rocks and as a publicly funded body NASA relies on their support. The public (or at least some of them) are very interested in aliens. If the price of getting a MЖssbauer spectrometer to Mars is playing up the possibility that the mission might find an organism, well it's a price worth paying. In its news releases the space agency tends to play up the idea of each mission's purpose being to find life but (in my opinion) this is not a serious goal. By the mid-1990s, the Americans were planning a return to Mars with a series of new space missions (I'll talk about them in the next part of this article), but suddenly life on Mars seemed to have been discovered not by a probe on the Martian surface but in an unlikely corner of our own planet. Let's have a flashback. Once upon a time there was a little Martian rock quietly sitting on or just under the Vallis Marinaris. One day, fifteen million years ago a giant meteor impacted nearby throwing thousands of tonnes of the terrain skywards. Most of this debris fell back down, but some fragments, including our rock escaped their parent world's gravity altogether, and fell into orbits around the Sun. Millions of years passed until one day in about 13 000 BC our rock felt strangely drawn towards a warm blue planet mottled with cloud. After a hot and scary ride through a dense oxygenated atmosphere the rock crunched onto a frigid and desolate plain. Perhaps it thought it was back home again...

"...could life from early Earth have seeded Mars?"
McKay and his colleagues chose a more careful approach. After its discovery ALH 84001 lay in storage for eight years. On examination it was realised to be very unusual and was briefly thought to be a fragment of the asteroid Vesta, however by 1993 it was recognised to have originated on Mars (it has been estimated that about a billion tons of Martian rock have landed on Earth since the Solar System formed!) McKay and his team analysed the meteorite and discovered several interesting things in it, namely 1. Patches of carbonated minerals, suggesting that ALH 84001 had once been immersed in warm water 2. Chemical compounds called polycyclic aromatic hydrocarbons, usually a by-product of living organisms 3. Grains of magnetite crystals, commonly formed by bacteria on Earth 4. Tiny worm-like structures reminiscent of bacteria. There were possible non-biological explanations for 2 and 3, but this seemed conclusive evident of life from Mars. It was item 4 that caught the world's attention; it seemed NASA was saying we actually had in our hands fossilised Martian lifeforms. President


March 2010 Astronotes 11 Clinton even announced the discovery on live television. Extraterrestrial life exists QED! Sadly, there is a long tradition of respectable scientists throwing caution to the wind and announcing amazing discoveries which eventually turn out not to be so clear cut. One recalls N-rays, polywater, Nessiteras rhombopteryx and, above all, cold fusion. Was this another example? Microbiologists were quick to say so, pointing out that the alleged bacteria were too tiny to be viable. A small earthly bacterium would be a sphere 600 nanometres (nm) across, meaning that you could line up 5000 of them along this capital `I', yet the putative Martians were tubes just 380nm long. Contrary to popular opinion, bacteria are not `simple', and are in fact packed with the machinery required for life, and most microbiologists said organisms as small as have been found to be oddly crystallised globs of organic molecules and inorganic minerals. Interesting, yes, but not actually alive. Nanobacteria seem to be another example of an amazing discovery which turned out to be illusory. Today, the consensus is that the announcement of Martian life in ALH 84001 was highly premature. Inorganic processes could have created the magnetite grains, the PAH could be terrestrial contamination and the "fossils" oddly crystallised minerals. There simply is not enough hard evidence to say who is correct and the debate slowly rumbles on right up to the present (finding the evidence would require a full-scale exploration of Mars by astronauts). McKay and his colleagues have continued to minutely examine ALH 84001 and other Martian meteorites. They have observed more structures which they say are of extraterrestrial biological origin, but these claims have not been accepted by the wider scientific community. A century from now I imagine McKay (or indeed Gilbert Levin) will be filed either with Percival Lowell or with Charles Darwin. The possibility of life been carried between planets in the distant past opens up intriguing thoughts. There is excellent evidence that Mars some 3.5 billion years ago had a much denser atmosphere than it does today and that water splashed in lakes or seas on its surface. If life arose there in those distant days, could meteorite impacts have launched living cells towards our planet, making us the descendents of Martians? Alternately could life from the early Earth seeded Mars? We cannot answer these questions yet. Meanwhile there are those, dwelling on the wilder, wackier shores of the Internet who claim that evidence of Martian vegetation, cities and monuments is staring us in the face. We'll examine not only these amazing allegations but also the latest thinking on Martian life from sensible people in the third and final (I promise) part of this article. Further reading Young, John D. And Martel, J, The rise and fall of nanobacteria, Scientific American, January 2010

Image Credit: NASA/David Mackay

Martian graveyard? This is a scanning electron microscope image of a series of partly filled pits on the surface of a mineral grain from the Nakhla Martian meteorite. Similar pits are sometimes found on Earth minerals which have been attacked by organic acid generated by microbes. The pits in the Martian minerals are partly filled with debris, interpreted by some as the remains of the microbes. MacKay's `fossils' could not exist. Some more sympathetic scientists made the counter claim that the "Martians" were indeed genuine fossils and were examples of `nanobacteria' (from the Greek `nano' meaning "itsy-bitsy" and from the English `bacteria' meaning bacteria). These were recently discovered terrestrial organisms of startlingly small scale, but as time has passed these


12 Astronotes March 2010

Image of the Month

This composite image (from the Hubble Space Telescope, the Spitzer Space Telescope, and the Chandra X-ray Observatory- NASA's `Great Observatories') provides one of the most detailed views ever of our galaxy's mysterious core. Human eyes cannot see the Milky Way's core as it is obscured by lanes of dust. However observations using infrared light and X-ray light can see through this dust and reveal that the galactic core's vicinity is bustling with activity. The actual centre of the galaxy is located within the bright white region in the middle right of the image. The entire image width covers about onehalf a degree, about the same angular width as the full Moon, and contains more than a hundred thousand stars.

More than a beautiful picture, this image reveals stellar evolution: we can see regions of star birth, young hot stars, old cool stars and evidence of those sinister corpses. black holes. Beyond lies the crowded, hostile environment (the radiation levels would be lethal to creatures like ourselves) of the galaxy's core, dominated by a supermassive black hole millions of times larger than our Sun (not visible in the image). The diffuse blue haze of X-ray light seen across the image is emitted from gas that has been heated to millions of degrees by outflows from the supermassive black hole and winds from massive stars and by the blasts of stellar explosions. (Caption by Colin Johnston, Science Communicator)

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