On June 10, 2009 a Space.com article titled "Military Hush-Up" reported: "Scientists have benefited from data gleaned by U.S. satellites of natural fireball events [meteors] in Earth's atmosphere - but no longer. A recent U.S. military policy decision now explicitly states that observations by government spacecraft of incoming bodies and fireballs are classified secret and are not to be released. Scientists say not only will research into the threat from space be hampered, but public understanding…will be diminished…Where the space-based surveillance truly shines is over remote stretches of ocean…But all that ended within the last few months, leaving scientists blind-sided and miffed by the shift in policy. scientists want to know about these events so they can better predict the risk here on Earth. 'Fireball data together with astronomical observations of larger near-Earth asteroids define the nature of the impact hazard and allow rational planning to deal with this issue,' said David Morrison a Near Earth Object (NEO) scientist at NASA's Ames Research Center, 'so it's ironic that the availability of these fireball data should be curtailed just at the time the NEO program is moving toward surveying the smaller impactors that are most likely to be picked up in the monitoring program. These data have been available to the scientific community. It's unfortunate this information is now shut off just when it's becoming more valuable to the community interested in characterizing near Earth asteroids and protecting our planet from asteroid impacts.'" - Space.com, June 2009
EDIT Aug 2009
NASA cannot keep up with killer asteroids
Congress assigned mission four years ago, but never gave NASA money
WASHINGTON - NASA is charged with spotting most of the asteroids that pose a threat to Earth but does not have the money to complete the job, a U.S. government report says. See last post for details
How many comets do you think there are in and around our solar system ?
1000 ?
10,000 ?
A million ?
well i have been doing some more research for my mars project ( yes i know i have been "researching" this for years !! it's just that it would be such an epic project and to do it justice the renders would have to be top notch..i am a bit doubtful if i am really capable of doing it justice..so i research !!)
Firstly there is of course the confusion as to what is the difference between an asteroid and a comet, the standard differences are these :
A comet gives off gas ( this gives the tail) though many comets can become inert and many asteroids have been known to "wake up" and out-gas. So it may well be that many asteroids are "dead" or dormant comets
Comets tend to have a very eccentric orbit coming close to the sun and then moving very far away from it, however many show more regular orbits.
In general we can say that a Comet is a large rocky/icy body that tends to vent gasses when near the sun, it can become inert and resemble an asteroid, which is a non venting rock or iron bollide. A meteor is the debris from a comet or asteroid that has fragmented and a meteorite is a meteor that has made it through the earhs atmosphere
That said if we take the classical view of what a comet is then how many are there ? Well we can only approximate since 1. we don't have the time or equipment to study them all and 2. Many are just too far away
The biggest concentration of comets is believed to be in the Oort cloud, a theoretical shell of comets some 50,000 AU ( AU = distance from the earth to the sun) from the sun. The Oort cloud may contain a TRILLION COMETS..depending on your definition of a trillion... that is 1x 10e12. It is estimated that many of these could be planet killers..over 300 KM in diameter
The other main collection of comets is in the Kuiper belt, a disc shaped region some 30-50 Au's from the sun, there is no real definitive calculation of how many comets are here but it is estimated that there are around 35,000 comets in the kuiper belt that are over 100 Km in diameter and maybe 100 million 20 KM objects. the comet that wiped out the dinosaurs was about 10 KM in diameter
Mars was killed by the sustained bombardment of thousands of large impactors ( asteroids or fragment of a comet that passed within it's Roche limit)
The Roche limit is an area around a planet whos size is dictated by the mass of the planet, rather like a black hole's event horizon. It acts as a sort of protection zone for the planet. Anything really massive like a comet which trangresses this zone will get pulled apart but the planets gravitational field. this fragmentation means that altough there may well be several extinction level impacts the planet as a whole should be able to survive the impacts
A classic example of the roche limit in action was the shoemaker-levy comet impacts on jupiter, during earlier passes the comet was torn apart into many smaller ( 2Km or so) fragments
Where do these comets come from ? It has been argued that they are made from matter that never made it into the main planets, others argue that the comets are the remamnets of an exploded planet or planets that collided.
A more interesting origin involves understanding how dynamic our solar system actual is. You see the sun orbits our galactic center ( and the galaxy orbits around within a cluster of galaxies)
Now differnet stars move at different speeds around the center of the galaxy, and stars pass through the spiral arms as they rotate ( the spiral arms are themselves dynamic) It takes about 250 million years for the sun to complete one orbit of the galactic center
At the same time the sun moves up and below the galactic plane in a cyclical fashion taking 120 million years to comple a single cycle
No one really knows what spiral arms are made of, it is thought that they are very dynamic and that the galactic core is constantly generating new ones and it is now thought that comets coalesce in the spiral arms, it takes about 50-100 million years for the sun to pass through a spiral arm and cou[led with the "up and down" cycles we think that the sun enters spiral arms every 30 milliom years or so
The sun also encounters Giant molecular clouds which can be inside spiral arms or outside them. these are star nurseries and also may contain many newly formed comets. In the suns lifetime it may have come close to a GMC on 50 occasions and possibly emtered some on 12 occasions
Whem the sun enters any of these comet rich areas it "grabs hold" of some comets which enter the oort cloud, others are knocked out of their orbits and spiral into the kuiper belt and there is a knock on effect which sends others into the inner solar system
This is a regular cycle of events with a 30 million year cycle modulated by another 250 million year cycle which can be directly linked to extinction events occuring on earth 94.5 million years ago, 65 million years ago and 36.9 million years ago. These can all be linked to massive earth impacts. We are due another extinction level event..now ..Unless of course it has occured..on mars
The K/T impactor which hit earth ( the one that "did for" the dinosaurs and around 90 % of all other living species, was as i said only 10 KM in diameter, but it impacted with a force equivalent to 1000 times all the nuclear weapons that exists on earth
But the three killer objects that hit mars were hellas ( about 100 KM diameter) Isidis ( 50Km diameter) and Argyre (36 Km Diameter). Most scientists do not connect these 3 but i am one of those who believe that these three, as well as many more smaller objects, impacted about the same time and were all part of one unimaginable catastrophe that decimated Mars in a few hours.
imagine what the 100 KM hellas impact on mars would do !! then imagine it's 50 and 36 KM companions and the countless other 1 KM impactors that hit around the same time..now perhaps you know why i am so nervous about starting the project... but wow what a movie it would make !!!
here is a topographical map of mars showing the blue hellas impact crater, the entire state of Alaska could be dropped into it
marstopo.jpg (37.78K)
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