[X] My Assistant

[Guest_PhilCo126_*]

The Near-Earth Asteroid 99942 Apophis ( former designation 2004 MN4 ) was headline news again this week both in Newspapers & TV news. Observations pointed out that the Asteroid climbed a bit higher on the Torino impact hazard scale ( equivalent cosmic ‘Richter’ scale ) and could hit the Earth ( Southern Hemisphere ) on April 13, 2036 ( a Friday 13th I believe ).

Anyway, Apophis should pass between the Moon & Earth ( distance 250.000 KM ) in April 2029 … an amazing sight visible from Europe!
Interesting to know is the fact that European Space Agency ESA plans a mission to find out if an asteroid could be deflected from its course ( Don Quichote mission: Hidalgo is an impacter & Sancho is the observer probe ). American astronauts LU & LOVE wrote a paper in NATURE about a tug-rocket and NASA is making plans for a mission called ‘ The Son of Deep Impact ‘ … to be continued…



More on the Asteroid at:
http://www.esa.int/gsp/ACT/mission_analysis/asteroid.htm


Philip

[Rob Pinnegar]

I guess these guys must be pretty certain about their calculated orbit for this object. If it is going to make a close pass by Earth in 2029, forecasting a near miss of Earth in 2036 is quite a trick.

Of course, I haven't done the math, but, for example, if you were to change the position of the object by 1 km during the 2029 encounter, how much would this change its forecasted position in 2036?

[ljk4-1]

Paper: astro-ph/0512204

Date: Thu, 8 Dec 2005 05:17:15 GMT (21kb)

Title: How unlikely is a doomsday catastrophe?

Authors: Max Tegmark (MIT), Nick Bostrom (Oxford)

Comments: 3 pages, 1 fig
\\
Numerous Earth-destroying doomsday scenarios have recently been analyzed,
including breakdown of a metastable vacuum state and planetary destruction
triggered by a "strangelet" or microscopic black hole. We point out that many
previous bounds on their frequency give a false sense of security: one cannot
infer that such events are rare from the the fact that Earth has survived for
so long, because observers are by definition in places lucky enough to have
avoided destruction. We derive a new upper bound of one per 10^9 years (99.9%
c.l.) on the exogenous terminal catastrophe rate that is free of such selection
bias, using the relatively late formation time of Earth.

\\ ( http://arXiv.org/abs/astro-ph/0512204 , 21kb)

[Guest_Richard Trigaux_*]

Paper: astro-ph/0512204

Date: Thu, 8 Dec 2005 05:17:15 GMT (21kb)

Title: How unlikely is a doomsday catastrophe?

Authors: Max Tegmark (MIT), Nick Bostrom (Oxford)

Comments: 3 pages, 1 fig
\\
Numerous Earth-destroying doomsday scenarios have recently been ...

I think it would be interesting to have this in the SETI thread. Such possibilities of destruction of an inhabited planet by space events (gamma ray burst, meteorites...) account much in the probability of finding other civilizations.

[Guest_Richard Trigaux_*]

I guess these guys must be pretty certain about their calculated orbit for this object. If it is going to make a close pass by Earth in 2029, forecasting a near miss of Earth in 2036 is quite a trick.

Of course, I haven't done the math, but, for example, if you were to change the position of the object by 1 km during the 2029 encounter, how much would this change its forecasted position in 2036?

The result could be a complete change in trajectory. This situation is similar to a gravitationnal assitance for a probe. It is used to send the probe in the wished direction.

This makes that forecast for asteroid position is very difficult, as a small uncertainty on such an encounter makes a very large uncertainty on the next encounter.

[JRehling]

The  result could be a complete change in trajectory. This situation is similar to a gravitationnal assitance for a probe. It is used to send the probe in the wished direction.

This makes that forecast for asteroid position is very difficult, as a small uncertainty on such an encounter makes a very large uncertainty on the next encounter.

Yes, in principle multibody orbits are chaotic, and in practice no matter how accurately we observe an object through an encounter like this, the small uncertainties will lead to large uncertainties in the future. As a rule of thumb, you can say that we will only know about the next close pass -- it is not possible to see two close passes into the future. Simulations can tell us about probabilities regarding far-future passes, but not certainties.

If a body like this were perceived as a long-term threat, the general solution might be to place a superb navigational device and a modest thruster on it, and try to make very small perturbations that could lead the object to collide, in a subsequent pass, with the Moon.

[RNeuhaus]

I have read a paper about "Gravitation Tractor for Towing Asteroids" It takes many years to deviate the asteroid's path. As an example:

if the asteroid is 200 meters diameter, with a density of 2g/cm^3, provided it can maintain a total thrust T = 1 N. The velocity change imparted to the asteroid per year of hovering is Δv = 4.2×10−3 (m/ 2×104 Kg)(d /100m)−2 (m/ s)( yr)−1. Because Δv is largely independent of the asteroid’s detailed structure and composition, the effect on the
asteroid’s orbit is predictable and controllable, as needed for a practical deflection
scheme.

The mean change in velocity required to deflect an asteroid from an Earth impact
trajectory is ~3.5×10−2 / t m/s where t is the lead time in years. Thus, in the example
above, a 20 ton gravitational tractor can deflect a typical 200m asteroid, given a lead time of about 20 years. The thrust and total fuel requirements of this mission are well
within the capability of proposed 100kW nuclear-electric propulsion systems, using
about 4 tons of fuel to accomplish the typical 15 km/sec rendezvous and about 400 Kg
for the actual deflection.

For a given spacecraft mass, the fuel required for the deflection scales linearly with the asteroid mass. Deflecting a larger asteroid requires a heavier spacecraft, longer time spent hovering, or more lead time. However, in the special case where an asteroid has a close Earth approach followed by a later return and impact, the change in velocity needed to prevent an impact can be many orders of magnitude smaller if applied before the close approach.

For example, the asteroid 99942 Apophis (2004 MN4), a 320m asteroid that will swing by the Earth at a distance of ~30000km in 2029, has a small 10−4 probability of returning to strike the Earth in 2035 or 2036. If it indeed is on a return impact trajectory, a deflection Δv of only ~10−6m/s a few years before the close approach in 2029 would prevent a later impact (Carusi, personal communication). In this case, a 1 ton gravitational tractor with conventional chemical thrusters could accomplish this deflection mission since only about 0.1 Newtons of thrust are required for a duration of about a month. Should such a deflection mission prove necessary, a gravitational tractor spacecraft offers a viable method of controllably steering asteroid 99942 Apophis away from an Earth impact.

We are still on time to catch it up.

Rodolfo

Attached File(s)

 Gravitational_Towing_for_Asteroides_0509595.pdf ( 144.11K ) Number of downloads: 329

 

[RNeuhaus]

Urge to Merge: Here Comes Andromeda

The above article mentions about looking at the last term of the Drake Equation, we see that it relates to the lifetime of technological civilizations – how long they last as technological (meaning interstellar communicating) entities. The three biggest considerations for our civilization at the moment could be characterized as a) getting along with each other, getting along with the environment, and c) staying technologically alert for large-scale concerns from space.

1) The dinosaurs lived more than 200 millions years and they didn't take any care to predict from the external cause of extintion.

2) Magnetic reversal, talks about the strong magnetic field of Jupiter that will be uninhabitable to Galliean moons since the magnetic field of Jupiter causes a 5 million ampere electric current to flow through it. The Earth magnetic field will be revert many times in the future so we must take the prevenitive measure to protect from the Sun radiations.

3) Moon Stabilizes Earth's Rotation. But the Earth rotation will become even slower that in the future its rotation period would not take one day but one month and the Moon will start to approach to Earth and at a certain distance, the Moon will be desintegrated and Earth will have rings like the Saturn. This also tells that in doing some of these kinds of calculations for Mars, it was discovered that the direction of Mars’ rotational axis could flip rather suddenly. Now this is not the normal "precession" (as it is called) of a few degrees that changes, for example, our north star though the millennia. Mars was calculated to have flipped its rotation axis up to 90 degrees in as little as a couple of million years. This was a result of the orbital angular momentum, under certain circumstances, being transferred to the rotational angular momentum and causing a coupling that led to such a flip in rotation axis direction.

4) The future collision between the Milky and Andromeda galaxies, in 6 billions years.

http://www.space.com/searchforlife/seti_do...rge_051208.html
Richard, this article might be good for the topic about Seti.

Rodolfo

[mike]

You mean to say that eventually we'll all die of something?! WHY WASN'T I NOTIFIED!

[dvandorn]

If a body like this were perceived as a long-term threat, the general solution might be to place a superb navigational device and a modest thruster on it, and try to make very small perturbations that could lead the object to collide, in a subsequent pass, with the Moon.

I would think that would be rather harder to do than to just aim it away from a collision course. However, lunar scientists would just about come in their pants if given the opportunity to observe the collision of a fair-sized asteroid with the Moon, I bet.

Of course, then you would have a fair number of people insisting that we were planning to do horrible things to the Moon's natural environment...

-the other Doug

[Guest_Richard Trigaux_*]

Important things in the discutio above, JRehling, RNeuhaus, dvandorn:


To avoid a future collision with an asteroid, it is enough to give it a very small push at the right moment (just before a close encounter with a planet) and this is mostly achievable with today or near future technology.

The chaotic aspect of their trajectory, which makes this trajectory difficult to predict, especially after a close encounter (this is called, I think, sensitive dependency to initial conditions) turns to our advantage: a very small tug just before a close encounter allows to completelly change the future trajectory.

Eventually crashing all the Earth threatening objects on other planets is not a bad idea. This would allow us for a safe future, even in the case in which we abandon any high technology.

By the way, nuking asteroids, as it was proposed by some who have nukes but who rather don't know what to do with, is just sheer deliria: the asteroid would be broken apart, but all the pieces would continue on the same trajectory (this is basic celestial mechanics). So, in place of receiving a huge asteroid, we would receive several small ones, plus the radioactive wastes of the bomb. It is not sure that it would be better.

[Guest_Richard Trigaux_*]

I would think that would be rather harder to do than to just aim it away from a collision course.  However, lunar scientists would just about come in their pants if given the opportunity to observe the collision of a fair-sized asteroid with the Moon, I bet.

Of course, then you would have a fair number of people insisting that we were planning to do horrible things to the Moon's natural environment...

-the other Doug

I don't think there are enough people on the Moon to protest against the idea. The only concern is that I want the thing done when the Moon is visible from my country!!!

[tfisher]

The Near-Earth Asteroid 99942 Apophis ( former designation 2004 MN4 ) was headline news again this week both in Newspapers & TV news. Observations pointed out that the Asteroid climbed a bit higher on the Torino impact hazard scale ( equivalent cosmic ‘Richter’ scale ) and could hit the Earth ( Southern Hemisphere ) on April 13, 2036 ( a Friday 13th I believe ).

I think this is another case of the press misreporting things slightly. The risk assessment has been steady at 1 on the Torino scale, unchanged since recovery and precovery operations last december ruled out the 2029 impact.

The description of Torino level 1 is "A routine discovery in which a pass near the Earth is predicted that poses no unusual level of danger. Current calculations show the chance of collision is extremely unlikely with no cause for public attention or public concern. New telescopic observations very likely will lead to re-assignment to Level 0."

The last quantitative change in the risk assessment was a slight tweak in the estimated probability of impact, from 0.015% to 0.018%, based on radar observations this August. A history of the risk assessment is here.

As has been pointed out above, the close encounter in 2029 makes precise predictions for the following close encounter nearly impossible. There is an uncertainty of about .15 AU, or 14 million miles, as to where along its orbit the asteroid will be at the time of the encounter in 2036. (Source: NEODyS)

The only reason this is showing up in the press again is that someone has adopted it as the poster child for arguing for designing space missions to deflect asteroids. While I agree we absolutely should have plans for such a mission prepared (and even hardware built -- just in case), I'm still annoyed when doomsday scenarios are overplayed by the press...

[tty]

Urge to Merge: Here Comes Andromeda

The above article mentions about looking at the last term of the Drake Equation, we see that it relates to the lifetime of technological civilizations – how long they last as technological (meaning interstellar communicating) entities. The three biggest considerations for our civilization at the moment could be characterized as a) getting along with each other, getting along with the environment, and c) staying technologically alert for large-scale concerns from space.

1) The dinosaurs lived more than 200 millions years and they didn't take any care to predict from the external cause of extintion.

Actually more like 150 million years, though no individual dinosaur species lasted for more than a few million years. We mammals have already outlasted the dinosaurs.

2) Magnetic reversal, talks about the strong magnetic field of Jupiter that will be uninhabitable to Galliean moons since the magnetic field of Jupiter causes a 5 million ampere electric current to flow through it. The Earth magnetic field will be revert many times in the future so we must take the prevenitive measure to protect from the Sun radiations.

The last field reversal happened about 780,000 years ago. There were already humans around then (though not Homo sapiens), and they survived without taking any special precautions (presumably).

3) Moon Stabilizes Earth's Rotation. But the Earth rotation will become even slower that in the future its rotation period would not take one day but one month and the Moon will start to approach to Earth and at a certain distance, the Moon will be desintegrated and Earth will have rings like the Saturn. This also tells that in doing some of these kinds of calculations for Mars, it was discovered that the direction of Mars’ rotational axis could flip rather suddenly. Now this is not the normal "precession" (as it is called) of a few degrees that changes, for example, our north star though the millennia. Mars was calculated to have flipped its rotation axis up to 90 degrees in as little as a couple of million years. This was a result of the orbital angular momentum, under certain circumstances, being transferred to the rotational angular momentum and causing a coupling that led to such a flip in rotation axis direction.

That is a very slow process. I don't have the figures handy, but studies of the number of days in a month and a year (which are detectable in certain types of corals) shows that the day has lengthened about 2 hours since the Devonian (>350,000,000 years)

4) The future collision between the Milky and Andromeda galaxies, in 6 billions years.

Not to worry. Long before that the sun will have left the main sequence, turned into red giant and sterilized the Earth.

tty

[tty]

By the way, nuking asteroids, as it was proposed by some who have nukes but who rather don't know what to do with, is just sheer deliria: the asteroid would be broken apart, but all the pieces would continue on the same trajectory (this is basic celestial mechanics). So, in place of receiving a huge asteroid, we would receive several small ones, plus the radioactive wastes of the bomb.  It is not sure that it would be better.

Actually that idea is not as silly at it sounds. The idea was to blow a nuclear charge some distance from the asteroid. The energy would vaporize a thin surface layer on the exposed side. The vaporized material would blow away at high speed and the recoil would change the asteroid´s trajectory slightly.

Now the biggest problem in changing asteroid trajectories is probably that many (most?) asteroids are just rubble piles, very weakly bound by gravity. Most apparently less violent ways to move an asteroid would probably also break it up.

This is the beauty of the "gravity tug concept". Since it is based on gravity it affects all of the asteroid in the same way and there is no breakup. The downside is that it is quite slow.

In cases where the warning time is short (say a few years or less) the "Nuclear recoil concept" may actually be the best bet. If the charge is exploded at some distance and a directed-energy design is used the "push" will be nearly parallell and approximately the same all over the asteroid so the breakup forces shouldn't be too bad.

It would of course be a good idea to try it out on some non-earth crossing asteroid first.

tty