good afternoon ladies and gentlemen can you hear me how are you guys doing e I am glad you guys are also doing well so this is our second last lecture for this module can you guys believe it so before we start I thought of showing you guys three videos of what we will be talking about today and hopefully it will give you a different perspective on metroids asteroids and comets diagram of the solar system you'll see a big gap between Mars and Jupiter a few centuries ago that Gap bugged astronomers they really wanted there to be a planet in there on the first day of the 19th century Janu AR 1st 1801 they got their wish kind of Italian astronomer jeppi piai found a point of light moving at just the right speed to be the desired Planet but it was just a DOT and too faint to physically be a terribly big object he suspected it might be a comet but follow-up observations showed it wasn't fuzzy the object was given the name series but was it really a planet well [Music] hopes were high that series was the wished for Planet between Mars and Jupiter but then something rather amazing happened a little over a year later in 1802 another one was found then in 1804 astronomer spotted a third one and a fourth in 1807 it was becoming clear that a new class of solar system object had been discovered given that they were all just dots in the telescopes of the time points of light like stars they were given the name asterid roids which literally means star-like by the end of the 19th century more than 450 had been found in total the rate of discovery has accelerated over the years and now today we know of hundreds of thousands there are probably billions yes billions of them larger than 100 meters across in the solar system and over a million larger than one kilometer in size so what are we dealing with here what are these asteroids there's not really a hard and fast definition of what's an asteroid and what is it but generally speaking it's a class of smaller bodies that are rocky or metallic that orbit the Sun out to Jupiter objects past Jupiter have special designations that we'll get to in the next episode over the centuries we've learned a lot about them by scrutinizing them with telescopes asteroids come in a few basic flavors most of them about 3/4 are carbonous which means they have lots of carbon in them about a sixth are silicious heavy on the Silicon based materials you know rock the rest are lumped into one catchall category but are dominated by metallic objects literally loaded with iron nickel and other metals so many of them orbit the sun between Mars and Jupiter that this region is now called the main belt the main belt has structure for example there are very few asteroids about 425 million kilometers from the Sun an asteroid at that distance would have an orbital period of about four years a simple fraction of Jupiter's 12year period any asteroid there would feel a repeated tug from Jupiter's Mighty gravity pulling it out of that orbit the resulting Gap is called the Kirkwood Gap and there are several such asteroid deserts all with simple multiples of Jupiter's period in this way the main belt is like Saturn's rings whose gaps are carved out by the gravity of the orbiting moons another way to group asteroids is by orbit some have similar orbits and may have formed from a bigger parent asteroid that got disrupted by an impact these groups are called families and there are a few dozen known for example the yomia family has over 400 members and are silicious rocky asteroids and probably all formed from a parent body that was about 300 km across when you watch movies they always show spaceships dodging and swooping through asteroid belts trying to evade the bad guys but in reality our asteroid belt is mostly empty space on average decent sized asteroids are millions of kilometers apart so far that if you stood on an asteroid odds are good you wouldn't even be able to see another one with your naked eye and despite their huge numbers they don't add up to much if you took all the asteroids on the main belt and lumped them together they'd be far smaller than our own Moon series is the biggest at about 900 km across it's round nearly spherical due to its own gravity crushing it into a ball a funny thing about series as we write and record this episode it's being visited for the first time by a spacecraft named Dawn that means everything I tell you about this asteroid is probably about to be obsolete but we do know a few things series probably has a rocky core surrounded by a water ice mantle the amount of water in it is staggering probably more than all the fresh water on Earth it may even be liquid under the surface like the oceans of Enceladus in Europa early images by Dawn as it approached the asteroid show its surface is heavily cratered and some craters are very bright they may be exposing ice under the surface or just fresher brighter material there are tantalizing observations of localized water vapor on the surface which may be from sublimation ice turning directly into a gas due to the sun's heat or it might indicate cryo volcanoes Dawn also visited Vesta which is the third largest but second most massive asteroid node Vesta is roundish what's called an oblate spheroid flattened a bit like a ball someone's sitting on the southern hemisphere got hammered by impacts long ago leaving a huge Basin there several other main belt asteroids have been visited by spacecraft mostly via flybys luticia gaspa Steines Matilda Ida is another and was discovered to have a small Moon orbiting it in fact a lot of asteroids have moons or are actually binary with two similar sized bodies and orbit around each other clayopatra a weird dog bone-shaped Rock has two moons you might think asteroids are just giant versions of rocks you might find in your garden tough solid singular bodies but it turns out that's not the case a few years ago scientists realized that asteroids have spent billions of years whacking into one another sometimes in high-speed collisions sometimes more slowly slower hits can disrupt the asteroid crack it but not necessarily be strong enough to actually disrupt it so that it breaks apart over time enough hits like that can leave behind what's called a reubel pile individual rocks held together by their own gravity like a bag of gravel or a car window that's been cracked and still holds its overall shape this became more clear when the Japanese Hayabusa spacecraft visited the asteroid iawa and saw what can only be described as a jumbled mess the asteroid had no craters on it and was littered with rubble and debris it was also very low density just what you'd expect for a Loosely bound rock pile it's weird to think of some asteroids as being not much more than free floating bags of gravel but the universe is under no obligation to adhere to our expectations it's full of surprises and we need to keep our minds flexible so here's a question why is there even a main asteroid belt at all the solar system formed from a disc of material and over time that material started to Clump into bigger and bigger pieces as planets formed they swept up and pulled in lots more stuff and grew large Jupiter consumed a lot of the material around it but not all and left a lot of debris inside its orbit some of this Clump together to form middling sized objects probably smaller than the planets we have now but big enough to undergo differentiation heavy stuff like Metals sank to the middle and lighter stuff formed a mantle in crust collisions broke almost all of them apart though and that's why we see asteroids with different compositions some are from the denser core others from the lighter crust there was probably a lot more material between Mars and Jupiter billions of years ago but it either got eaten by Jupiter or the planet's immense gravity altered the asteroids orbits flinging them away this may be why Mars is so small too Jupiter robbed it of all of its food is it formed While most asteroids live in the main belt not all of them do some have orbits that cross that of Mars taking them closer to the sun we call those wait for it Mars Crossing asteroids some have orbits that take them even closer to the Sun Crossing Earth's orbit we call those Apollo asteroids ah gotcha they're named after the asteroid Apollo the first of its kind to be found some have orbits that are almost entirely inside Earth's orbit called attin asteroids attin and Apollo asteroids can get pretty close to Earth so we call them near Earth asteroids now while they get close to us that doesn't mean they'll hit us because for example their orbits may be tilted so their orbits and the orbit of the earth don't actually ever physically cross but some do have paths that literally intersect Earth's that doesn't mean they'll hit us every pass either after all you can walk across the street without getting hit by a car the problem comes when you try to occupy the same volume of space as a car at the same time astronomers unsurprisingly are very concerned about oids that can hit us that's why we have surveys observatories scanning the skies looking for it this is a pretty important topic and I'll go into it in more depth in a future episode there's another category of asteroid that exists due to a quirk of gravity when a planet orbits a star there are points along the planet's orbit and near it in space where the gravitational forces are in Balance if you place an object there it tends to stay there like an egg in a cup these are called lrange points one of them is along the same orbit as the planet but 60° ahead another is 60° behind behind the first such asteroid found was orbiting 60° ahead of Jupiter and was named Achilles after the Greek hero in the Trojan War as more were found the naming convention stuck asteroids ahead of Jupiter were named after Greek figures in the Trojan War and those behind Jupiter were named for Trojans and now we just call them all Trojan asteroids Trojan asteroids have been spotted for Jupiter Mars Uranus Neptune and even Earth Earths was found in 2010 using observations by an orbiting Observatory called wise which scans the sky as an infrared light where asteroids glow due to their own heat 2010 tk7 as it's called is about 300 M across and 800 million kilometers away orbiting the Sun ahead of Earth there are also asteroids that have orbits that are very similar to Earth's but are slightly elliptical and tilted with respect to RS because of this they can stay relatively near the Earth in space but don't really orbit us instead they sometimes get closer and sometimes recede it's pretty weird but a natural outcome of orbital mechanics some people say these asteroids are moons of Earth but it's better to say they're co-orbital with us only a few are known the most famous being crinia which can get as close as 12 or so million kilometers from us oh one more thing originally asteroids were named after female goddesses siries Vesta Juno and so on but as hundreds more were found and then thousands we ran out of names eventually astronomers who discovered asteroids were allowed to name them through a lengthy proposal and acceptance process governed by the international astronomical Union they also get a number of assigned to them as well a lot of astronomers have asteroids named after them including astronomers who study asteroids like my friend Amy Miner who works on the wise Mission hers is 23475 Amy Miner and Elanor Helen who discovered quite a few asteroids and comets hers is 3267 glow for her nickname and this one it's a 1 km Wide Rock in the main belt and goes by the name 165 347 Phil plate must be coincidence today you learn that asteroids are chunks of rock metal or both that were once of I love astronomy you may have noticed but there's one really frustrating aspect of it everything we study is really far away nearly everything we understand about the universe comes from light emitted or reflected by objects it'd be nice if we could get actual samples from them physical specimens we could examine in the lab well sometimes the universe can be accommodating and allows us to hold it in our hands cot can we get this up on still [Music] store if you go outside on a clear dark moonless night and you really should chances are pretty good that within a few minutes you'll see a shooting star it'll zip across the sky a fiery dot leaving a long glowing trail behind it they're one of the most exciting and fun things you'll see when you look up and they always get a gasp and a squeal of delight from someone who's stargazing what you're actually seeing is a tiny bit of interplanetary debris Rock ice or metal ramming through the Earth's atmosphere heated to incandescence most are faint but some can be astonishingly bright I saw one once that left an afterimage on my eye obviously shooting stars aren't really STS so what do we call them sometimes it seems like astronomers use different names for objects to keep things as confusing as possible but really we do that to separate out different things in this case the actual bit of solid stuff coming from space is called a meteoroid the phenomenon of the meteoroid getting hot and blazing across the sky is called a meteor and finally that hits the ground we call it a meteorite I think the second best way to tick off an astronomer is to mix up meteor and meteorite sometimes astronomers can be pretty pedantic about such things oh the best way to tick off an astronomer ask him hey what's your sign amazingly a typical meteor that you'll see is due to a meteoroid that's tiny probably smaller than a grain of sand how can that be it's because they're hauling Mass you heard me the meteoroid is orbiting the Sun probably at speeds of a few dozen kilometers per second as it approaches the Earth our planet's gravity accelerates an additional 11 km/s Earth's escape velocity and when it enters our atmosphere it's moving incredibly fast up to 70 km/s or more the energy of motion is called kinetic energy if you want to get something moving you have to give it energy and if you want it to stop you have to take that energy away this kinetic energy depends on the mass of the object and how fast it's moving in fact it depends on the square of the Velocity double its speed and it'll have four times the kinetic energy meteoroids May usually be small but they're screaming fast and have a huge amount of kinetic energy as they hit our atmosphere they slow from their ridiculous orbital speed to nearly a standstill and all that energy has to go somewhere it gets converted into light and heat and that's what we see as a meteor a big misconception about meteors is that they get hot due to friction with air actually a far bigger contributor to their heat is compression one of the most basic laws of physics is that when you compress a gas it heats up and a meteoroid coming in at Hypersonic speeds compresses the air in front of it a lot heating it hugely the gas can reach temperatures of thousands of degrees C for a few seconds the air radiates away this heat in turn heating up the meteoroid the material on the surface vaporizes and blows away a process called ablation that ablated material leaves a glowing trail behind the meteor which we call a train sometimes it can glow for several minutes getting twisted up in high altitude winds leaving behind an eerie ghostlike persistent train this all happens high above your head about 90 to 100 kilm above the ground typically from any one location you can see a few meteors per hour it may not seem like much but when you add them up all over the planet you find the Earth is getting pelted to the tune of about 100 tons of material a day but again most of these meteoroids are teeny tiny those random meteors are called sporadic meteors they tend to be Rocky in composition and generally come from asteroids if two asteroids smack into each other the Collision can eject little bits of material that then orbit the sun on their own if their orbit crosses the Earth then you have a potential meteor it may take a few million years but at some point the earth and the meteoroid are at the same place at the same time and boom but sometimes meteoroids travel in packs when that happens we can get meteor showers many dozens or even hundreds of meteors per hour with one exception those don't come from asteroids they come from comets when a comet orbits the Sun the ice on it turns to gas dislodging dust and gravel mixed in this material leaves the comet and tends to stay more or less in the same orbit as the comet itself over time that material gets scattered all along the orbit creating a puffy ribbon of tiny pieces of space debris around the sun when the earth plows through that cloud of debris we get a meteor shower from our viewpoint on Earth we see meteors shooting across the sky apparently radiating away from a single point that's a perspective effect it's like driving through a tunnel and seeing the tiles on the wall and ceiling flying past you all apparently coming from a point ahead of you the point on the sky where the meteors come from is called the radiant and the shower is named after the constellation the radiance in so we have the perced meteor shower the leonids the camelopardalids or the camelopardalids and since the Earth hits a specific Comet stream around the same time every year the showers are annual the perseids are in August and the leonids in November watching a meteor shower is easy just go outside and look up generally they're better after local midnight the Earth plows into the meteoroids so facing the direction of Earth's orbital motion means more meteors just like you get more raindrops on the front windshield of your car than on the back when you're driving through a storm after local midnight you're on the part of the earth facing into the orbit so you see more meteors by the way if you happen to be on the International Space Station you have to look down to see a meteor in 2011 astronaut Ron Garen photographed a Percy had burning up below him but don't worry the odds of the space station getting hit are extremely low space is big oh and that one exception I mentioned before that's the annual Geminid shower which occurs in December that comes from the asteroid 3200 faithon which is on an orbit that takes it very close to the sun it's possible it gets so hot that The Rock vaporizes making it act like a comet the vast majority of meteoroids are small and tend to burn up in our atmosphere but they can be bigger a bolide or Fireball is an extremely bright meteor and those can be about the size of a grapefruit those happen pretty often Somewhere over the Earth I've seen a few myself very rarely an incoming meteoroid will survive all the way to the ground and become a meteorite sometimes the immense pressure of ramming earth's air causes the incoming meteoroid to crumble or even explode raining down dozens or hundreds of smaller pieces typically they slow rapidly after their blaze of glory and simply fall the rest of the way to the ground the air up there is cold and their Interiors are cold from being in space so long so despite what you might think meteorites don't cause fires when they hit the ground in fact they can be quite chilly meteorites are classified into three broad categories Stony which are mostly Rock iron which are mostly metal and Stony Iron which are a mixture of the two the majority of meteorites we find are Stony the Stony meteorites are themselves subdivided into two kinds condres and achondrites condres contain condres small grains of minerals these are very primitive and are thought to have condensed out of the original disc of material that formed the solar system their ages can be found by looking at ratios of elements in them formed from radioactive decay the oldest known meteorite formed 4568 billion years ago before the Earth itself formed AC condres don't have conds in them most likely they came from a bigger asteroid one that was once Molen all the way through mixing the minerals a big Collision disrupted the parent body creating the acond rtic meteoroids iron meteorites most likely come from the center of a large asteroid one big enough that Metals fell to the center via gravity again a big impact blew the asteroid up scattering its material around the asteroid belt and with some on orbits that eventually intersect Ed Earth Stony irons are the rarest some have green or orange crystals of a mineral called Olivine embedded in a web of metal called paloc sites they may be the most beautiful of all meteorites I actually collect meteorites it's fun but can be a somewhat pricey hobby if you're interested make sure you get them from a licensed dealer we have links to some in the dublo of course on occasion the meteoroid coming in can be a tad bigger and when that happens well all hell can break loose on February 15 2013 residents of the Russian city of cheliabinsk got a rude awakening at 9:20 a.m. local time a rock about 19 M across came in at a low angle it got nearly as bright as the sun as it slammed into the atmosphere and the pressure of its passage broke it up into several chunks which broke up again in a moment's time the sudden energy released was equivalent to the detonation of a half million tons of TNT as much as a small atomic bomb while no one was killed over a thousand people were injured by flying glass shattered by the explosion no doubt they were at their Windows gawking at the huge vapor trail in the sky when the shock wave hit there was no warning for this event the asteroid was essentially too small to detect while it was out in space Well for now at least telescopes are coming online soon that should be able to find smaller asteroids and give us some warning astronomers are more worried about ones roughly 100 meters across or bigger these can do serious damage on a Citywide scale or larger but at the moment aren't easy to spot much in advance and what do we do if we do see one headed our way as of right now there's not much we can do Studies have been done to determine the best course of action maybe lobbing a nuke added or simply ramming it with a space probe to change the orbit and make sure it misses Earth these ideas look good on paper but they haven't been tested yet we're still a few years from that the good news is that objects that size hitting the Earth are rare maybe once every Century or three but if we do nothing it will happen eventually as science fiction writer Larry nen points out the dinosaurs went extinct because they didn't have a space program hopefully we're smarter than they were today you learn that meteors are small bits of interplanetary debris sloughed off by asteroids and comets hey Phil plate here and this is Crash Course astronomy since humans have been human we've looked to the skies for portance of the future the Sun the moon the planets the Stars they've all been used for prognostication and so have comets a fuzzy blob moving slowly across the Stars how could soothsayers resist but now we know a lot more about comets they're beautiful fascinating and can bring both life and death Upon Our Little [Music] World comets have been seen in the sky since Antiquity comet Halle for example is shown in the beay tapestry which depicts the Norman invasion of the British Isles in the year 1066 it was seen by ancient Chinese and Greeks too in general and like everything else in the sky comets were considered Omens or harbingers of human events sometimes they were good omen William the Conqueror liked his chances in 1066 after seeing one and sometimes bad that same Comet didn't do so well for King haral II a comet bright enough to see with the naked eye shows up in the heavens every few years or so and some can get spec spectacularly bright in 2007 I saw Comet MCN very near the sun in broad daylight when you think of a comet you probably picture a fuzzy blob and a long tail stretching away from it fair enough but there's a bit more to them than that comets are in many ways similar to asteroids they're roughly heed chunks of stuff left over from the formation of the solar system unlike asteroids which are mostly rock with a dash of ice and maybe metal comets are a more balanced mixture of ice and rock and by ice I mean Frozen water but also Frozen carbon dioxide carbon monoxide methane ammonia things we normally think of as gases on Earth and by Rock I do mean rocks but also gravel and dust in fact astronomers sometimes Call Comets dirty snowballs which is an a half bad term it's that ice that makes comets well comets when they're way out in deep space they're so cold that they're basically inert lumps of ice and rock but many are on elliptical orbits that take them from those subfreezing depths deps into our neck of the woods where the sun can warm them as they heat up the ice turns directly into a gas a process called sublimation the gas then flows away from the comet creating a cloud around it this makes the comet look fuzzy and actually in the past they've been called hairy Stars I like that term too and in a sense we still use it the solid part of the comet is called the nucleus and the gaseous Cloud around it is called the coma Latin for hair in fact that's why we call them comets as the ice sublimates the bits of rock and gravel and dust embedded in it can be freed and leave the nucleus as well this material is what forms the comet's tail but how that happens depends on which material you're talking about the gas and the dust from comets form two different Tails gas molecules emitted by the comet get ionized by the sun's ultraviolet light that means they lose electrons becoming charged and charge particles are highly susceptible to magnetic fields the solar wind is a stream of charged particles blown out by the Sun and carries a magnetic field with it as the wind hits the ionized gas from the comet it picks up those particles and carries them Downstream away from the Sun the solar wind is usually moving far far faster than the comet so this ion tail winds up pointing directly away from the Sun the dust on the other hand is influenced more by sunlight light from the sun exerts a small but inexorable pressure and this pushes on the dust particles the dust streams away but because the pressure isn't as intense as the solar wind is on the gas tail the dust tail blows away more lazily and tends to lag behind the comet in its orbit that means the two tails usually point in two different directions in some comets like 1997's incredibly bright and gorgeous Comet hail Bop this is pretty obvious the dust tails look white or a teeny bit yellowish due to reflected sunlight while the ion tail glows blue or green depending on the primary constituents of the gas carbon monoxide tends to emit blue light while carbon molecules glow a ghostly green a comet's tail can stretch for tens of millions of kilometers but despite the length tails are incredibly low density as low as a few hundred atoms per cubic cimeter the air you breathe is a million billion times denser in 1910 Earth passed through the tail of Comet Halley this caused some public fear because Cyanogen a deadly gas had been detected in the tail but of course nothing happened it turns out getting a gazillionth of the toxic dose isn't that big of a problem broadly speaking comets are classified by their orbits if they have orbital periods less than 200 years they're called short Peri comets these tend to orbit the Sun in the same plane as the planets and go around the Sun in the same direction as well from Earth we see them sticking near the ecliptic the line across the sky that marks the annual path of the sun comets that take longer than two centuries to go around the Sun are called long-term comets and have orbits that are tilted Every Which Way that means they can appear anywhere in the sky but this raises an interesting point comets go away every time they get near the Sun and start outgassing they lose Mass over time they get smaller eventually they should evaporate some do this all at once because they dive into the sun skimming Our Stars surface we call those Sun divers or sun grazers many of those may actually be pieces from a bigger Comet that broke up in space nearly a thousand years ago but besides those we know of some comets with orbits that can be short some with periods of just a few years even a century is like a single flap of a mosquito's Wing compared to the lifetime of the solar system how can comets be billions of years old if their orbits bring them close to the Sun all the time ah astronomers wondered about this very thing over the years they came up with an idea maybe out past Neptune there's a repository of comets chunks of dirty ice millions of them billions orbiting the Sun where it's perpetually cold they could have orbits that last for Millennia or more but then something tweaks them makes them fall toward the sun in fact there may be two such regions since we have both short period and long-term comets turns out this is correct we now know enough about Those Distant regions of the solar system that they deserve their own episode so we'll dive into that topic later so what do comets look like up close like really close studying them from Earth is hard the coma obscures the nucleus making it nearly impossible to see it directly ah from Earth if you instead send your telescope to a comet things change we first did that in the 1980s the last time Comet Halley came around several Nations sent spacecraft to fly past the comet and the Soviet Mission Vega 1 was the first to successfully get pictures of the nucleus the low resolution images revealed a dark lump highlighted with two bright spots later determined to be jets of gas streaming away these images were used to better determine the position of the nucleus and a few days later the European probe giato zip past the nucleus at an incredibly close distance of just 600 km those pictures were more detailed and showed us a flying mountain in a regular chunk 15x 8 km in size and it was dark reflecting only 4% of the light that hit it that makes the nucleus as black as asphalt you might think that all that ice would be shiny but it's not that simple most of Hal's nucleus is covered in thick dust laced with darker molecules with only a few spots emitting gas most likely there are deposits of ice under the surface and only some of them receive enough heat from the Sun to sublimate and blow out gas this has been seen with other comets as well the gas is emitted from specific spots on the comet venting out from cracks in the Crusty surface the surfaces of comets must be in homogeneous different in different places that was brought home magnificently in 2014 by another European Mission Rosetta it went into orbit around the comet 67p Chum off Gasco and found it to be a bizarre little object measuring about 4 kilm end to end 67p has two loes connected by a narrow neck looking very much like a cosmic rubber ducky the surface is completely devoid of craters clearly the surface is very young images show jets of gas emitted from very specific places on the surface and there are wide circular pits here and there which may be gas vents growing wider over time as the ice below is depleted surprisingly the surface is fairly tough and hard when some scientists expected it to be fluffier the comet has a very low density similar to Rubble pile asteroids so it was expected that the surface would be soft Rosetta sent down a Lander named Fel to set down on the surface using harpoons to Anchor itself but instead the Lander bounced unable to penetrate the tougher than expected material one idea to explain this is that the ice is porous and fluffier inside the comet but as it nears the Sun the ice at the surface warms and changes its structure forming that harder crust as for the double lobe thing well that's a bit baffling we see some asteroids shaped that way as well it's possible 67p used to be two separate comets that had a low speed collision and stuck together or maybe it used to be one big lump but over the eons the ice in the middle sublimated more leaving behind the two loes Rosetta is the first time in human history we've had a probe orbiting a comet studying it up close and long term we're still learning still figuring this stuff out incidentally I mentioned earlier that a comets have lots of ice in them and two they also get really close to Earth sometimes in fact they can hit us now not to get all Technical and scientifically but that is what we would call bad as we'll discuss in an upcoming episode but billions of years ago lots of comets hit the earth not long after our planet form together with asteroids many of which are also rich in water ice they may have brought a significant amount of water water to earth scientists are still wrestling over the details of this and it may be a while before the actual numbers are nailed down but it's an intriguing thought even more interesting in 2004 NASA's Stardust space probe physically passed through the coma of comet vilt 2 collecting samples that were returned to Earth careful analysis of the material found the presence of organic carbon-based molecules in them and not just any random molecules but complex ones including amino acids these are the building blocks of all life on Earth amino acids are what our bodies use to create proteins it's possible that the ingredients of life on Earth didn't start here but instead were brought to our planet from Comet impacts or at least there was a mix of the two if that's the case then in a sense all life on Earth is part alien how about that but what gets me are the philosophical ramifications of this when we look into space when we examine our Celestial Neighbors when we send probes to comets and Survey what we find we're looking at our own Origins comets are like time machines allowing us to investigate our past 4 billion years back hinting at the secrets of the origin of life itself and you thought astronomy was just lying out in a field and looking up well it is but if you let it it's also a whole lot more today you learn that comets are chunks of ice and rock that orbit the sun when they get near the so hopefully that will provide a quick overview of what we will be discussing today do you guys have any questions so far Okay cool so for this lecture as seen in the video we're going to discuss meteoroids meteors meteorites uh are you guys still familiar with what is the difference between them so this is a hint a question I like to ask in the test and exams we' discussed it last week as well so it's a meteoroid uh before I discuss it let's see what do you guys think is a meteoroid so it's called a a rock in space before entering the atmosphere that is correct and a meteor right yes so remember the chunk that survived its journey through the atmosphere is called a meteorite if it travels through the aster through the atmosphere it's a meteoroid with a d and if it's in space then there a meteor you guys happy with those definitions awesome so this is how a asteroid containing iron will look like if it land on Earth and you can can see the iron content is melted in this image so here we can see a few of the biggest asteroids in the asteroid belt so the videos explained to work quite nicely so I'm going to give a overview of the slides for this lecture this is how a comet will look like in space so who if you've actually seen the comet before so there's actually a comet now visible that you guys can see with the uned eye um I will provide information on it and post it on the um announcements but yes you can actually see a comment right now so for the this lecture we need to answer four important questions firstly where do meteors and meteorites comes from secondly what are asteroids thirdly what are comets and lastly what happens when asteroids and comets hits Earth and other planets so something interesting there's only one person in recorded history that has been hit by an asteroid and that was in 1954 while Mrs E ulet Hodes of Alabama laid napping on a living room couch an explosion in sharp pain jolted her awake analysis of the brick sized rock that smashed through the ceiling and bruised the left leg showed it was a metor r Mrs Hodes is the only person to have been injured by meteorite coincidentally she lived right across the street from the comet drive-thru theater which is quite ironic but do you guys actually believe it's that one person in history has been hit by a rock so when we look at some of these be right in Earth's atmosphere uh some of them travels at about a speed of 10 to 70 km/s which is quite fast and the streak you see is actually due to friction with Earth's atmosphere that's causing them to heat up and burn some of them vaporize and that is what people commonly refer to as shooting stars the streak and light some of them makes it to the ground others burns up in the Earth's atmosphere so surprisingly one of the best places to look for asteroids is in Antarctica do you guys know perhaps why no nothing to do with Earth's salt also nothing to do with everything is white it's because the environment doesn't really change say for example where we are in Petoria if a meteorite hits the ground how difficult will it be to find it on the ground quite difficult because remember you have buildings you have natural Parks you have Woodlands you have mountains so even if you track the trajectory quite easily it's very hard to find but in Antarctica because the environment is basically desolate it's quite easy to find asteroids and meteoroids so roughly 40,000 neides has been collected from Antarctica does everybody understand the statement I made awesome so in this image you can see some larger meteorites that has been collected from anarctica so something interesting is do you guys know you can actually go work in an Arctica for year so every year there's a crew change in Antarctica so there's a international research base or research facility a better word is research page that you can work for through a four year it is very well paid and they provide you with food they provide you with housing and clothing for that duration the only thing is to be able to qualify for it you need to at least have a honors degree and um you have to be physically and mentally strong enough for it so you go through physical and um psychological tests and if you pass then you add usually round about December the SAS gullas comes and pick you up you guys know what the SAS gas is so South Africa actually has two ships the SAS ug Galas 1 and the SAS ug Galas 2 and they are resar vessels so the whole ship is basically one giant lab and they are usually months on end at Sea conducting research so the SAS gas one or the SAS Galas 2 will pick you up from Cape Town then from Cape Town it's about a month's journey to Antarctica then they drop you off in Antarctica you stay there and conduct research for a year and work on the base and then the following December the SAS ug Galas comes and pick you up again and brings you back to South Africa and then you have a crew change so if you are interested in something Google it they're usually looking for new crew each year to man The Station you can also work on the SAS GIS as well so it's important this is also a question I like to ask for the exam is what are the three broad composition categories of mides the first is Ion mides the second is Stony ion meteorites the third the Stony meteorites and then there's a fourth one called carbonaceous condres so in this image we can see how these differ so here we can see in the top left this is a iron so here we can see is a Stony Iron right here is a Stony meteorite and here we can see is a uh condite uh all four of [Music] them so ion meteorites make up only 6% of the meteorites with witnessed falling from the sky so you can estimated only 6% of meteoroids traveling through space near Earth have an iron composition you you might wonder why do ion mides make up 66% of mides found on the ground and that is because ion mides don't look like ordinary rocks they are easy to recognize because they are heavy dense lumps of metal so if you trip over one on a hike you are more likely to recognize it as something odd carry it home and show it to the local Museum also some Stony meteorites detate rapidly when exposed to weather ions are made of stronger material and generally survive longer the recognizability and durability of iron meteorites means there is a selection effects that makes it more likely they'll be found than other types of mides do you guys understand that awesome so when we take iron meteorites and we cut them open and polish them we would see interesting bands on them called vidman bands and that is caused by Alloys and iron and nickel that formed crystals in a mol and metal and cooled and solidified and the size and shape of the Bands indicator molten metal cooled very slowly indicating a location inside bodies at least 30 kilm in diameter and on the other hand these iron meteorites do not show effects of very high pressures that would exist deep inside a planet evidently iron meteorite material formed in a cooling series of planetesimal sized objects smaller than planets and this is one important clue to meteorites in contrast to irons and Stony Iron and Stony meteorites are common among meteorites seen falling to Earth although there are many different types of Stony meteorites you can classify them into two main categories depending on the physical properties and chemical content condres and a condres condres dark gray granular rocks and in Geral condres contain some volatiles including water and organic compounds a few condres evidently formed in a presence of liquid water and most type of condres also contain conds small round bits of glassy Rock only a few millimeters across to be glassy Rock in crystalline and condr must have cooled from Molton State quickly within a few hours one hypothesis is that conds or bits of matter from the inner part of the solar nebula near that were blown outward by winds or jets to cooler parts of the nebula where they condensed and were later incorporated into larger rocks another hypothesis is that the condil were once solid bits of matter that were melted by shock waves spreading through the solar nebula and then resolidified among the condres the carbonation condres are rare but quite important subtype these dark gray Rocky meteorites are especially rich in water other other volatiles an aonic compounds and those substances all would have been lost if the meteoroid had been heated and to a room temperature a medic carbonous condres also contain small irregular inclusions reaching calcium aluminium and titanium called c a i for calcium aluminium reach inclusions these bits of matter are highly refractory that is they vaporize or condens only at very high temperatures if you could scoop out a portion of the sun's Photosphere and cool it the first particles to solidify would have the chemical composition of CI CIS as the temperature fail other material will become solid in accord with the condensation sequence described in Chapter 15 Section 3 so when we talk about the orbits and origins of meteoroids a typical meteoroid has roughly the mass of a paper clip and vaporizes at an altitude of about 80 km above Earth's surface and a meteor Trail points back along the path of the meteoroid so if you study direction and speed of metus you can get close to the orbits in the solar system before they encountered Earth so at auk Observatory we we have a camera system that continuously track the night sky to look for meteorites and there two reasons for that is then we have software that calculates the trajectory so if it doesn't burn up we can go and collect them and we also use the trajectory to see where it came from to see if it perhaps contract the origin of that specific meteorite that has heat the ground and then also who of you have seen meteor showers so medeia showers are usually called after the constellation from which they seem to radiate from and there's actually two meteor showers we can see every year so how it happens is we have Earth in the sun orbit and here is the orbit of a comet and each time Earth moves through the this band that a comet loses so in image a is a meteor meteor in a meteor shower into Earth's atmosphere it's long as parallel paths but perspective marks appear to driverge from a single point in a sky then image b a similar parallel railroad tracks appear to divert from a point on the horizon and in C meteors in showers are the breeze left behind by the Comets IC nucleus vaporizes and Rocky metallic bits of matter spread along the comet's orbit even if Earth passes through such metal radiate you can see a media shower so usually there's one you can see around about April and another one you can see 6 months later in about October if you are in residential areas you could see between 4 and 6 per hour if you are in Darker Skies you could see upwards to 30 metors per hour which is actually very cool so when we look at this image it shows the origin of meteoroids so some of the planet decimals that formed early in the solar systems history may have differentiated that is melted and separated into layers of different density and composition as did terrestrial planets so you're all familiar with differentiation process that we talked about last in last week's class correct awesome so in some cases some of those planetesimals could be fragmented and that can produce different types of mides so asteroids are bit different than meteorites so asteroids are distant objects too small to study in detail with earth based telescopes an astronomist neveress has learned a surprising amount about those little worlds using spacecraft and space telescopes so evidence from meteorite show that asteroids are the L remains of the rocky planetesimals that build the terrestrial planets 4.6 billion years ago so notice four important points and three new terms most asteroids are irregular in shape and batted by impact cratering and many asteroids seem to be Rubble piles of broken frag ments secondly some asteroids are double objects or have small moons in orbit around them this is further evidence that asteroids have suffered collisions thirdly a few asteroids show signs of geological activity that probably happened on their surfaces when those asteroids were young and then lastly asteroids can be classified by the albos colors and Spectra to reveal Clues to the compositions so what is meant about the albos of an object in space so the alido is the amount of light reflected from its surface so if the Sun Shines on it how much light is reflected so this also allows them to be compared to meteoroids in Labs on Earth and we get ctype S type and mtype asteroids those are the main classes discovered by this method so the first ever asteroid was discovered in 1801 by Sicilian Monk guazi and later named Cirrus and astronomers were excited by Pi's discovery because Cirus orbits 2.8 AU from the Sun in a wide gap between Mars and Jupiter where it was for a planet ought to be but Sirus has less than one quarter the amid of Earth's moon much smaller than any of the planets three even smaller object fellas Juno and Vesta were discovered within a few years all orbiting between Mars and Jupiter so astronomist decided Cirus and the other asteroid should not be considered true planets you learn in chapter 18 section six that Cirus the largest object in the asteroid belt has now been reclassified as a dwarf planet because it has enough gravitational strength to squeeze itself into spherical shape but not enough to have swept up or cleared away the rest of the asteroids today more than 400,000 asteroids have well charted orbits other dwarf planet Cirus only three are larger than 400 kilometers in the Hamer and most are much smaller there are probably a million or more that are larger than one ker in the Hamer as astronomists are sure that all the large asteroids in the asteroid belt have been discovered but are also sure that many small asteroids remain undiscovered movies and TV have created a common misconception that flying fing through an asteroid Bel is an hair raising plunge requiring constant dodging left and right the asteroid Bel between Mars and Jupiter is actually mostly empty space in fact if he was standing on an asteroid it would be many months or years between sightings of other asteroids so something that we do with these asteroids so some of them that's near Earth and could be potentially dangerous to Earth we call them NE Earth objects or NEOS and the most dangerous type of these NEOS um those of them that crosses Earth's orbit are called Apollo objects after the first such asteroid discovered and the combined searches estimated to have found at least 93% of the Apollos and other NEOS larger than one kilometer in hammer and I now focused on finding a similar percentage of objects down to the SI of 150 m in March 2009 Neo Searchers spotted a small asteroid 2 to 3 m in diameter about the size of a small truck on a collision course with Earth astronomers were able to observe it in space before impact and discovered that its color and albo match a type of asteroid found mostly in the out belt the asteroid entered Earth's atmosphere over the desert's of southern Sudan exploded scientists from United States of Sudan search for pieces of the object so in this image we can see the diagram plots the position of known asteroids between the Sun and the orbit of Jupiter on a specific day and most asteroids are in the main belt squares filled or empty show location of known comets although asteroids and comets are are small bodies and lie far apart there are great many of them in the inner solar system so the ones in the green are main Bel asteroids that lie between the orbits of Mars and Jupiter the ones in red are asteroids that could approach Earth and are shown in red and then these on the outside of the main asteroid belt are called troan asteroids and they orbit in two areas 60° ahead of Jupiter and 60 degrees behind Jupiter so this is the team that found one of the of the for the fragments in Sudan so what I found was a 4 kg piece of fragments corresponding to a rare type of Stony meteorite and for the first time a definite connection could could be made between an asteroid observed in space and meteorites with properties measured in Earth's Laboratories in 2010 a Japanese probe bashua returned a Capal to Earth containing few tiny grains from the surface of a stype asteroid itava which were found to be chemically identical to one of the most types of ordinary condite materials AIDS there are other non- belt asteroids beond the main belt and gravitation effects of Jupiter and the sun combined to trap the two asteroids into the Grange points that are 60° ahead of and 60° behind the planet's orbit and these are called Trojan asteroids because individual objects have been named after Heroes of the Trojan War astronomists have also found a few objects in the branch point of the orbits of Mars and Neptune the object sherion found in 197 7 is about 170 km in the Hamer its orbit carries it from the orbit of Uranus to just inside the orbit of Saturn objects like Shuan with orbits between or crossing orbit of the Jovian planets are called cental although it was first classified as an asteroid sharan later surprised astronomer by suddenly releasing Jets of water vapor and dust and you will learn in the next section that this is more resembles characteristics of comets than asteroids so sensors show that a distinction between asteroids and comets is not clearcut as technology allows astronomers to detect smaller and more distant objects they are learning that outer solar system contains large numbers of these small bodies the challenge is to explain their origin so an old hypothesis proposed that asteroids are the remains of a planet that exploded Planet shattering death Rays May make for exciting science fiction movies but in reality planets do not explode the gravitational field of a planet holds the mass together so tily that completely disturbing the planet would take tremendous energy in addition the present day total mass of asteroids is located only about 120 of the mass of Earth's moon so hardly enough to be the remains of a planet so look back at a figure that opens chapter 15 to see an extras solar planetary system with an asteroid Bel interior to the orbit of the jovian planet and that Arrangement have the same cause in our solar system astronomers have evidence that the asteroids are the remains of material line 2 to 4 AU from the Sun that was unable to form a planet because of the gravitational influence of Jupiter the next Planet outward over the 4.6 billion year history of the system most of the object originally in the asteroid Bel have collided fragmented and been covered with craters some asteroids were pbed by the gravity of Jupiter and other planets into orbits collided with planets or the sun caused them to be captured as planetary satellites or ejected them from the solar system and these present day asteroids understood to be very minor remnant of the original Mass in that zone so in this image we can see in image a this is image of the asteroid Vesta made from a distance of 2,000 km per the NASA Dawn spacecraft and it shows Vesta South polar region we is dominated by the Rea impact Basin and then image B dwarf planet Z is the largest object in Asteroid Belt between Mars and Jupiter and a prominent white spots made the soult deposits left by evaporating water so one thing also before we start the discussion with comets is do you guys actually know that Jupiter protects Earth from the majority of asteroid strikes so that is because Jupiter is such a gravitational pull if an asteroid comes loose an asteroid belt or a troan comes loose or something new enters the solar system Jupiter's gravitational field will catch them so Jupiter is a big big protector of Earth it wasn't for Jupiter we might have had a few catastrophic Extinction events such as the dinosaurs extinction level event with asteroids and Jupiter Shields us from them so the next object we need to talk about is comets so few sites in astronomy are more beautiful than a bright Comet hanging in a night sky it is a common misconception that comets whis rapidly across the sky like meteors actually a comet's most is hardly apparent Night by Night its position shifts slightly against the background Stars it may REM visible for months while everyone can enjoy the beauty of comets astronomers study them because they are messengers from the past carrying caros of information about the origin of the solar system always as you begin with your study of a new kind of object by summarizing its observational properties What do comets look like and how do they behave so notice three important properties of comets plus three new terms the first one is comets have two kinds of Tails shaped by the solar wind and solar radiation gas and dust released by comet's icy nucleus produce a head or a coma and are blown outward away from the sun and the gas produce the gas produces a tail and dust produces a separate dust tail secondly comma dust produces not only one of the two types of comma Tails but also spreads throughout the solar system and some of those Comm dust particles later encounter the Earth and are seen as meals and thirdly evidence shows that some Comet nuclea are fragile and can break into pieces so the nuclear of comets are quite small and cannot be studied in detail using earth-based telescopes nevertheless when a comet nucleus approaches the sun it emits material that form into a coma or head and a tail that can be millions of kilometers in size and is easily observed the Spectra of a com plural of coma and Tails indicate nuclear must contain Isis of water and other volatile compounds such as carbon dioxide carbon monoxide oide methane ammonia and so on these are the kinds of compounds that would have condensed in cold regions in the solar nebula this convinces astronomers that comets are ancient samples of the gases and dust from which the outer planets formed as the Isis absorb energy from sunlight they Sublime change from solid into a gas the gases break down and also combined chemically produce other substances found in Comet Spectra for example vast clouds of hydrogen gas observed around the heads of comets understood to derive from the breakup of ice molecules five spacecraft flew past the nucleus of comet Haley when it was visited in a solar system in 1985 and 1986 other spacecraft through plast the comet ble in 2001 Comet wood 2 in 2004 and Comet temp 1 in 2005 and Comet heartley 2 and 2010 images show that all these comets nuclear are 1 to 10 kilm across similar to the size of many asteroids and also irregular in shape in general these nuclea are darker than a lump of coal which suggest composition similar to the carbon which carbonous condite meteorites described earlier in this chapter so the mass and density of of commet nuclear can be calculated from the gravitational influences on passing spacecraft and commet nuclear appear to have densi between 0.1 and 0.25 G per cubic cimer much less dense than a density of ice also you will learn later in this chapter comets subjected to Tidal stresses from Jupiter and Sun or the Sun come apart very easily Comet nucle have been described as dirty snowall or icing mud blls but it seems to be incorrect their shapes low densities and lack of material strength suggest that comets are not solid objects the evidence leads astronomist to conclude that most Comet nuclea must be fluffy mixtures of Isis and dust with significant amounts of empty space on the other hand images of the nuclear nucleus of Comm world to reveals Cliffs sprinkles and other features that show the material has enough strength to stand against the weak gravity of a comet so here we can see different images of comets in now they compare so here we can see the nucleus of comet hardly the hstd uh image of comat Hell Bop and so on so in this image we can actually see some of the structures on asteroid so one of the most famous Landing was the landing of the Rosetta spacecraft on a portion of the com of the Comet so here we can see the ready lips that shown on this image is 16 by 150 M and marks the likely location of the F Lander determined by Rosetta's concert radar experiment and then image B it shows the view of the Comet surface from filet showing a small Cliff or large bould approximately 4 M tall directly in front of the probe the end of the Landers free landing legs can be seen in the foreground so here we can see one of the legs family relationships among the commons can give you clues that the origin most comets have long elliptical orbits with periods greater than 200 years and are known as long period comets the long period comets orbits are randomly inclined to the plane of the solar system so those comets approach the inner solar system from all directions long period comets revolve around the Sun in about equal number of prograde orbits meaning the same direction which the planets move and retrograde orbits in contrast about 100 or so to 600 well study comets have orbit with periods less than 200 years the short period comets usually follow orbits that lie within 30° of the plane of the solar system and most revolve around the sun prograde Comet Haley with a period of 76 years is unusual short period Comet with a retrograde orbit a comet cannot survive long in an orbit that brings it into the inner solar system The Heat Of The Sun vaporizes millions of tons of Isis during each passage and reduces comets to inactive bodies of rock and dust such comets can last at most 100 to a thousand orbits around the Sun astronomist calculated even before a comet completely vaporizes from solar heating he can't survive more than about half a million years crossing the orbits of the planets especially Jupiter without having its path rerooted into the Sun or out of the solar system or colliding with one of the planets therefore comets visible in our skies now can't have survived in their present Orbits for 4.6 billion years since the formation of the solar system and that means there must be a continuous supply of new comets so where do they come from in the 1950s a strong Yan proposed that a long period comets are objects fall inward from what is known as the UR Cloud a spherical cloud of iy bodies that extend from about 10,000 to 100,000 AU from the Sun astronomers are prophesized that a earth Cloud object objects were originally Planet decimals formed in the outer solar system that were tossed to the current distant locations by the gravitational influence of the growing Jovian Planets the Ood cloud is estimated to contain seven trillion icy bodies far from the Sun now very C lacom cells and are invisible from Earth astronomists calculate that some OT Cloud objects can be pbed by the gravitational influence of passing Stars so they fall into the inner solar system there the heat from the Sun BS their Isis and transforms them into comets the fact that long period comets are observed to fall inward from all directions is explained by the ud Cloud Reservoir being spherically distributed around the Sun and inner solar system a few short period comets including Comet Haley also seems to have originated as long period comets from the U cloud and then had their orbits altered by a close encounter with Jupiter however that process can't explain all the short period comets the Kyper Bel which you first encountered in Chapter 15 Section 2 when you initially survey the Sol system is another source for Icy bodies passing through the inner solar system Kyer objects orbit in the same directions as the planets and in the plane of the solar system mathematical models showed that it is likely for Caper objects be tubed inward by the influence of the giant planets to move into an orbit resembling those of the short short period comets comets vary in brightness and orbit nevertheless there are two basic types of comets in our solar system some originate in the ud Cloud for from the Sun others come from the Kyper belt just behind Neptune they all share one characteristic they are ancient icy bodies that were born when a solar system was young so the last thing we need to talk about is asteroid and Comet impacts so most meteor meteors are small particles ranging from few centimeters down to microscopic dust an astronomers estimated Earth gains about 40,000 tons of mass per year from meteoroids of all sizes so that is actually quite amazing 40,000 tons are added to each to added to Earth's mass each year due to impacts from space so that is actually very cool don't know if you guys has actually realized this so we have actually detected a few of these impact craters so the first one is perhaps the baringer crates near Flagstaff Arizona and that is 1.2 kilm diameter and 170 m deep and Eugene shoe marker proved in his 1963 doctoral fees is that a crater must be result of an impact rather than volcanic eruption because quarts crystals in and around it had been subjected to pressures much higher that can be produced by a volcano and further study shows that a Binger crater was created approximately 50,000 years ago by a Metroid estimated to have been 50 m in diameter as large as a good size building and that heat at a speed of 11 km/ second releasing as much energy as a large firman nuclear bomb and an asteroid of that size could be called either a large meteoroid or a small asteroid thebr at a side shows that the impactor was composed of iron so here we can see it you guys actually know there are two big impact craters in South Africa that you can visit so can you name the two so the one is um on the border of king and a free state you know the town called pares uh there is called the fre for Dome on Africans the fre for Kole that is the biggest asteroid impact crater in South Africa you can actually see on Google Maps the crater and the ring fringes and then just north of Petoria there's also a impact crater uh no I can't can't remember what's name let me quickly search um that's the twang crater it's north of Petoria um it's also formed part of the twain natural reserve just one thing is you can go okay so let [Music] me provide you with in [Music] one so ah come on so this is the one and the other one is the the fre fourth crator so one thing that I can justn if you try to visit the twang crater do it in a group unfortunately the hiking trails there has become quite a hot spot for muggings but the one in frea for is much uh safer so you can read up about it and perhaps get some friends together and visit it so they have been inlaw 100 years a quite recent hits so on the summer morning in 1908 reindeer herders and homesteaders in central Siberia was startled to see a brilliant blue white Fireball brighter than Sun streak across the sky still descending it exploded with a blinding Flash and an intense pulse of heat the blast Was Heard up to 1,000 kilometers away and resulting air pressure circled the Earth twice with when when members of the scientific Expedition arrived at a site in 1927 they found that a blast occurred above the Stony tusta River Valley and a knockdown trees pointing away from the sent of region about 30 kilm in radius so this what happens that was one of the most dangerous impacts in the in recent years so no crater has been found and angusta side so it seems that the explosion estimated to have equal 12 megatons of TNT and occurred at least a few kilometers above ground a detailed analysis of all the available evidence suggests that an impact of speed and direction resembles the orbits of Apollo objects astronomist produced computer models of orbit objects entering Earth's atmosphere concluded that the most likely candidate for the tusta object is a Stony asteroid about 30 m in diameter perhaps one the mass of the baringer impact an object of this size and material strength would have fragmented and exploded at just about the right height to produce The observed blast this concussion and consistent with the modern studies of the gusta area shown that thousands of tons of powdered material with composition presently carbonous condres are scattered in the SLL so to think that is what happens with an object 30 m in the Hamer so that is why it's important that we track these objects and that is also important why we need to find a way to the fend Earth uh from these objects and the two years ago NASA did their first impact test so the easiest way to protect Earth is to change the orbit of these asteroids or meteors a little bit and one thing you do it you either slow down the orbit of an asteroid or you speed it up and they send a spacecraft into the asteroid field to test this hypothesis and it crashed into the surface and with the scratch was calculated to speed the orbit a little bit up so we have proved that we can change the orbit of asteroid so that is why it is important for us to track these near Earth objects so also we can see other hits as well of asteroids so one recently was in 2009 when a there was an impact on Jupiter and we could pick it up with our telescopes and afterwards it left these marks on Jupiter we can see which is quite amazing and that brings us to discussion of Planet shaking events that we need to protect ourselves so one of these major events of major strikes on Earth was 65 million years ago when the dinosaurs were wiped out and that changed the extinction event so this is a hint for the test and exams what I usually ask every exam what caused the dinosaurs to to become extinct and the reasons for that is listen carefully the asteroid Heats Earth it knocked up a lot of dust the dust circulated up in Earth's atmosphere blocking out the sunlight which caused Earth to cool down so when Earth cooled down it Formed it caused that plants di because they cannot make use of the photosynthesis method when a plants died the herbivores died when a herbivores died it's nothing to eat for the carnivores and the dinosaurs uh became extinct that's one of the reasons the other reasons is because of the cooled climate it created a cosmic winter so the actual impact didn't kill the dinosaurs it's the secondary impact and that is lack of food and it cooled down the um climate do you guys understand that awesome so the impact crater that killed the dinosaurs is called the chi shal Loop impact crater and it happened in the northern yukatan region of Mexico and the crater is a 180 Cub met in diameter and the object that heit that area is estimated to be between 10 and 15 kilm in diameter so quite a very large object so if you look the Gulf of Mexico yeah we've done it SES Mexico Gulf of Mexico you cut in so right there in the sea and that is where the object hits so one thing is we like I said in class we are overdue for [Music] a planet Extinction event so if you look at statistics every 250,000 years there should be a or there used to be a exension level event on Earth so we are overdue for one and that is why we do this research to see how we can protect ourselves so that ladies and gentlemen is this lecture do you have any questions okay so like we discussed we did a poll in yesterday's class so next week Monday is our last class that class will be online then I'll see you for our last class next week otherwise have a wonderful week I hope hope you're all voting tomorrow so please go vote and good luck with your last week of classes yes I see there is a hand raised not anymore it seems so have a wonderful day everyone