Talk:99942 Apophis/Archive 2

This is an archive of past discussions about 99942 Apophis. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.

Archive 1

Archive 2

Risk of hitting other objects

Excluding the satellite theory, what is the risk of a collision with other asteroids that may alter its path to the detriment of earth?

Impact Zone Estimation

Which source supports that image where Mexico is the most probable country to be impacted by Apophis? kardrak 05:48, 5 January 2008 (UTC)

I agree with you, that path seems to be wrong. I found a couple of sources with the estimated/simulated trajectory. I will write a couple of lines and provide the sources for anybody to go deeper on this subject of the impact trajectory, or even redo the image.Mariordo (talk) 13:45, 18 February 2008 (UTC)

The two sites with papers presenting the risk paths are (they are almost identical): http://www.b612foundation.org/papers/wpdynamics.pdf and http://www.aero.org/conferences/planetarydefense/2007papers/S3-4--Gennery-Paper.pdf. So Mexico is not in the risk path, the image in the article is definitively wrong. This weekend I will try to edit a short section with a brief description (images are not in the public domain) with these two and some other sources talking about the 2036 risk path. Or, any one is welcome to work the proposed section. Mariordo (talk) 03:29, 22 February 2008 (UTC)

Mass range

That 10¹¹ was correct? Then the numbers are in the wrong order I think. --fvw * 15:25, 2004 Dec 28 (UTC)

JPL's page is currently saying mass 1.3e+11 kg. (I haven't found a reference for the 8.3e+10 figure.) —Korath ^会話 15:40, 28 Dec 2004 (UTC)

As to the order, it makes sense to me: diameter decreases from 440m to 390m, and mass decreases from 1.2×10¹¹kg to 8.3×10¹⁰kg (a decrease of not quite one third). —Korath ^会話 15:58, 28 Dec 2004 (UTC)

Yeah, I just thought it was common to list the lower figure first for ranges. I hadn't noticed that the diameter/mass figure ranges were supposed to be linked by the way. --fvw * 16:37, 2004 Dec 28 (UTC)

The estimated diameter (300 m) and mass (5×10¹⁰ kg) yield a density of about 4 t/m³. That seems awfully high. Refs? --Urhixidur 12:33, 18 July 2006 (UTC)

The diameter and mass estimates are both uncertain by factors of several, so we can't say anything about the density. Michaelbusch 22:36, 18 July 2006 (UTC)

Risk of human intervention

Asteroids such as Mr. Apophis have a risk of affecting the Earth via human intervention. A fellow Wikipedian has insisted that "we most likely couldn't make the thing hit the Earth even if we tried". Nonetheless, the trajectory looks to be well within range of lunar orbit at closest approach, raising the concern of:

a) fighting over the asteroid

b) Said asteroid wreaking havoc on /crashing into spacecraft/satellites

c) A nudge of said asteroid being used by a rogue country in attempt to cause trouble elsewhere on Earth or in space

d) Rocks being blown off said asteroid into satellites/spacecraft.

Of course, said asteroid could also have benefits due to its location: using it as a staging ground for spacecraft/ space station/ communications satellite/ fueling depot for space exploration (the idea being that it would head well into space and thus be useful as a "stepping stone" to elsewhere, likely some other relatively small minor planet. — Rickyrab | Talk 02:32, 20 June 2006 (UTC)

I was the one reverting your addition. Sorry for just giving the short explanation in the edit summary. But I think the addition implied a possibility of something so remote that we shouldn't mention it.

First: It's highly improbable that anyone will attempt making the asteroid impact earth. I assume you're thinking along some terrorist plot or something, but anyone attempting to hit the asteroid with a space probe will of course be notised by space agancies (or even amateur astronomers) all over the world. Someone with resources to hit the asteroid in space have much better alternative methods for creating havoc, like, say, just starting a nuclear war.

Second: Deflecting an asteroid like this the amount of distance it would take to make it hit earth is probably impossible in the short timespan from now to 2029. If the asteroid had been on impact course with earth in 2029 (as was seen as a remote risk a year and a half ago) it would be hard enough to deflect it in time the necessary 1 earth radii to make it miss. This asteroid has an estimated closest encounter in 2029 of more than 5 earth radii. I don't think it's possible to push the asteroid that much out of course in just 20 years. At the very least the terrorists (or whoever) should start sending up rockets pretty soon and start pushing it to make it happen. I really don't think anyone will. But it makes for a good SciFi plot. Shanes 03:13, 20 June 2006 (UTC)

Said sci-fi plot type has already been exploited by Stephen Baxter, although I believe his book Titan was written before we discovered Apophis. His book had a powerful nation-state (the People's Republic of China), capable of nuclear warfare, do the asteroid-nudging - and the asteroid was bigger than our Apophis, seeing as it causes an Extinction level event in the novel. As for Apophis itself, it still has the potential to be used as a base (for good or for evil: for example, if someone sets foot on it, what's to keep him/her from putting other stuff on it for various purposes, ranging from exploration to usage as a staging ground for missiles). Furthermore, the fact that Apophis is to come within the orbits of some of our satellites means someone's going to have to move them out of the way if they don't want them to become asteroid dressing. Another source for extraterrestial worry: space junk. If the asteroid whacks into far-floating space junk, it could send space junk crashing into other objects, including working spacecraft. I wonder if there are contingency plans for that. — Rickyrab | Talk 03:47, 21 June 2006 (UTC)

Ok, I only explained why I reverted your edit that read like some reservation to the fact that the asteroid will not impact earth in 2029, that the no impact claim assumed no human intervention. As to whether any satellites stand a risk of being hit by the asteroid, I don't know. If we can find authorative sources that discusses it, we could/should include a section on it. I suspect myself that the risk is very minute, but I don't know enough about the most probable asteroid trajectory and wether there will be any satelites in its vicinity to comment any further. About landing on the asteroid, maybe we will. That's not really anything new. NEAR Shoemaker collected probes from asteroid Eros in 2001, for instance, and recently Hayabusa collected probes from another asteroid. I've never heard or read any serious discussions about using asteroids for evil. Shanes 13:22, 21 June 2006 (UTC)

VELOCITY!

Someone asked what the velocity estimate is for 99942 Apophis. The answer was that it is difficult to establish accuracy to within hundreds of kilometers per second. If the accuracy cannot be established to within hundreds of kilometers per second, it takes some nerve to say that 99942 Apophis has any meaning to Earth at all in terms of impact 30 years from now.

Let's take this thing down to its most basic element. I'd like to see a professional citation that says what the estimated velocity of Apophis is, right now, or at any point in time anybody wants to declare, within what range, to 90% confidence. In other words, I'd like to see a citation that says:

"99942 Apophis has a velocity of (x) km/s, within +/- (y) km/s, with 90% confidence."

If nobody can make this declaration, this page is fear-mongering. This page should then be rewritten to contain the barest known facts, which seem to boil down to: "99942 Apophis is an asteroid called 99942 Apophis". And people can list whatever data is known or believed, but nobody can reasonably say 99942 Apophis is any threat to Earth at all. Uh-uh. Press releases can go somewhere else, like, "Asteroid Fear-Mongering in Media". 99942 Apophis has no more meaning in relation to impact with Earth than any other object, because if an expert can't measure the asteroid's velocity and declare a reasonable confidence level, much less vector, density, mass, composition, or without velocity where this smudge will be next week much less 30 years from now, nobody can reasonably say it has any meaning in terms of impact with Earth. You don't know velocity, you don't know nothin'.

So get somebody at NEO to stand by a declaration. Get a published quote from a named professional. —The preceding unsigned comment was added by Roukan (talk • contribs) .

I don't know where you read that the orbit velocity is uncertain within hundreds of kilometers pr sekond, but I can assure you that such a number is absurd. If an object passing the earth has a velocity of several hundred km/s it isn't in a solar orbit. This article lists its mean solar orbit velocity as 30.73 km/s, and that sounds about right to me (The earth has a mean orbit velocity of a little less than 30km/s). Se this link listed under references here for more orbit data. Calculating the orbit velocity when the orbit is known (as this one is) is a trivial excersise in Newtonian mechanics that even a high school physics student should be able to do. Shanes 06:37, 4 July 2006 (UTC)

Ç:Thank you Shanes. I'm glad you came along, so soon, so I can begin to discuss this with somebody. I heard it in the convo with Chris on this page, above, and you are right to pick at it, but I'm not after that claim, it is an example of what I'm after. Frankly I've been following the asteroid thing since it first came to prominence the month the Berlin wall fell. That month is when the concern first hit the press. I've reviewed the data you refer me to, and though I see the number of Doppler observations, I don't see a velocity estimate for those obversations. My understanding is that these readings are said to be very accurate, however, I am still gathering information on confidence levels. What is odd to me is that nearly every piece of information is available in terms of what the numbers are said to be, however, there is no declaration I can find in relation to the accuracy of these declarations. And accuracy is everything. If the accuracy is off by 1 cm/s, over 30 years we're talking 315 kilometers, which is pretty bad when somebody's declaring Apophis can go through a 400 meter "keyhole". So we want to know the range of the estimate for velocity at least, +/-, and the confidence level for that. I mean, we could take it at face value. We're looking at your number of 30.73 km/s, which seems right to you. I don't doubt that, in fact I'm certain you've got more on the ball on this than I do, to have formed such a mental pattern. But if we said it was good to its last decimal place, lets call the 30.73 right to the .01, we're talking up to .3073 km/s error by multiplying .01 x 30.73. Let's drop the last two decimals due to the extra ones arriving in the calculation, it also gives the estimate a little edge. After a day .30 x 86400 seconds can mean an error of 25,920 kilometers displacement in terms of where the asteroid is expected to be. And I'm aware of Chi Square analysis of these estimates, and they're not very encouraging either, if we make it 5% we're still talking 1296 kilometers displacement in one day.

Now we can say, gee, we can continually make observations and hone our accuracy, until we know more. No problem, let's watch it, and have fun. But let's talk about a threat to Earth when there's real evidence of a threat, I say. If the best accuracy is what's in front of us, it fails on the 30 year declaration. If we say the number comes from things far more accurate, well, that's what I'm after. If I could find it easily, I wouldn't be here, I wouldn't bug you. But accuracy + confidence ain't coming up. And that's suspicious, when you're talking about threats to Earth. You'd think there'd be no problem flooding the sciences with everything possible, all the data possible, in order to deal with the threat. But no accuracy declarations. I'm saying it takes a lot of nerve to say there's a problem with Apophis in the beginning, if the tools are anywhere near accurate, and have the numbers jerk around like this over months, and then claim there's a threat 30 years from now. Nope, I'm not buying this, not just yet. The range of adjustment of the estimate over months is a serious indicator that the accuracy required isn't there to begin with, it is prima facie evidence the science isn't there. And it was worse at the beginning, when the least was known about it, and this is also suspicious. Properly, the thing to declare is that very little is known about Apophis, because, in fact, very little was known, instead we got the claim there's a lot to worry about, and the name Apophis to amplify that fear. Responsible scientists don't do this. Scientists who need a certain regular dose of funding and don't care how they get it might. Scientists like that might want a certain level of alarm from time to time, but not enough to really draw the kind of scientific scrutiny that knocks them out of the water, which likely happens when money is taken from other science programs. So I want the science, not the declarations of science. Not that you're doing that, I'm just explaining what I'm after in the hopes someone like you can straighten me out.Roukan 16:57, 4 July 2006 (UTC)

Since you already deleted my first response, I don't know why I try, but the accuracy in the determination of these orbital elements is typically 1 part in 10⁷ at 65% confidence, which suggests an uncertainty of less than 1 cm/s in velocity, but I'm not inclined to actually do the full conversion for you. As of the last update, NASA declares the chance of impact is about 1 in 38000. Also, NASA says they know where Apophis will be 30 years from now with an 1 sigma uncertainty of ~8 km, so talking about a 400 m keyhole certainly does make sense. Now, would you kindly stop assumming that NASA is fear mongering? Dragons flight 00:11, 5 July 2006 (UTC)

I didn't delete any response here. I deleted one on an admin query page because my remark there was deleted. I don't remember if that was you or not. The discussion should take place here. I'm glad you responded. Let me go over what you've provided and I'll get back. This is exactly the sort of thing I am looking for, thanks. However, I don't make assumptions, assumptions are being made in relation to the claims. It was and still is an assumption that Apophis is any more threat than any other asteroid, or that any asteroid is a threat. Roukan 23:37, 5 July 2006 (UTC) Roukan

Well, gee, there's some data here, but nothing meaningful in relation to velocity. There's an estimate of velocity entering the atmosphere, and velocity of impact, to two decimal places. How fast is it going right now, and what is the degree of uncertainty in that calculation? Are we stuck with two decimal places in relation to 30 km/s? That's not very encouraging.

Look, I'm not interested in editing this page, and be wrong. That's why I'm talking here. That's what this page is for. I'd even bet if we talk enough one of you guys will do it if you guys can't prove it. NASA needs to come across with some confidence numbers for an estimate of velocity for Apophis. What's the big deal? Don't you find this interesting, that it seems exceedingly difficult to get basic information relating to a velocity estimate along with a statement of confidence in that basic thing? Weren't you thinking something like that when you gathered what you did? I'd be thinking, "There's something here, but not really. Wow." Why are there some things there that appear accurate, and not this basic thing? I'm sure some calculation of "these orbital elements" applies in the way you describe, but how fast is Apophis going? See what I mean? Roukan 00:11, 6 July 2006 (UTC)

We know the velocity of Apophis in 2006 to ~30 cm/sec (99.7% probability). Asking for an absolute value of "How fast is Apophis going" is a meaningless question. If you are asking, "what is the velocity relative to Earth during the 2029 approach", we know that to within 100 m/s (99.7% probability), as compared to the ~20 km/s total relative velocity. If you are asking "what is the average velocity of Apophis relative to the Sun over one orbital period?", we know that to better than 1 m/s. Michaelbusch 16:47, 19 July 2006 (UTC)

Aw jeez...

Look what I noticed.

Apophis's number is 99942.
999 upside down is 666, the number of the beast, according to the Bible.
42 is the meaning of life, the universe, and everything, according to Douglas Adams.
It makes its "keyhole" approach to earth on Friday the 13th, 2029. Friday the 13th is considered unlucky in some places.

Now, this doesn't have any significance whatsoever, but judging from other such things (9/11 attack "mysteries"), people will behave rashly. Just get ready for a lot of edits to this article in the next few decades, by people who think that this is somehow significant. (Very) pre-emptive strike. :)--Planetary 02:13, 9 September 2006 (UTC)

I think something similar happened a few months ago.Michaelbusch 02:18, 9 September 2006 (UTC)

What was it?--Planetary 03:29, 12 September 2006 (UTC)

2006 QV89. Had a probability of 1/500 of impacting on September 11, 2019. We (the asteroid radar group at JPL and Arecibo Observatory observed it and obtained radar astrometry. There is no significant probability of impact, of course.Michaelbusch 03:42, 12 September 2006 (UTC)

I'm glad to hear the the end times aren't upon us just yet. (: --Planetary 05:55, 7 October 2006 (UTC)

Well all theories aside, I just hope Apophis doesn't hit us. :) -- Riffsyphon1024 22:37, 6 October 2006 (UTC)

I may not live to be 50... man i'm freaked out.... i need to calm down now... omfg..

As the late Douglas Adams wrote, this is all just another meaningless coincidence. ☢ Ҡi∊ff⌇↯ 12:35, 16 December 2006 (UTC)

Never truer words spoken.--Planetary 08:39, 17 December 2006 (UTC)

Haha, great insight. Hi-larious indeed. And if it does strike the earth, kudos to you!

-G —Preceding unsigned comment added by 134.117.158.83 (talk) 19:07, 27 October 2007 (UTC)

Are the numbers right?

In the section History of estimates, it says that 176 observations were used on December 27, while 157 were used on December 30. Why would the number of observation used have gone down? -- kenb215 talk 05:38, 28 December 2006 (UTC)

I'm not sure. Perhaps because the first set was to pin-point its location, and after that fewer were needed to track it? --Planetary 06:43, 28 December 2006 (UTC)

Because with the radar data and more optical measurements, some of the earlier optical data were found to be biased and unreliable. They were therefore not included in the later solutions. Michaelbusch 16:30, 28 December 2006 (UTC)

Of course. :) That sounds more correct. --Planetary 20:46, 28 December 2006 (UTC)

2029 Flyby

Given the proximity of the asteroid, could it affect the tides while it passes by the Earth?Mustang6172 08:36, 13 February 2007 (UTC)

I doubt it. It's a very small body, relatively speaking.--Planetary 15:40, 13 February 2007 (UTC)

Tidal force proportional to mass and inversely proportional to the cube of distance. Apophis is about 1/2.5E12 the mass of the Moon, and will come within about 1/20 the distance. So the maximum tide on the Earth from Apophis will be ~3E-9 that of the Moon, or something measured in atomic radii in deformation. The tide of the Earth on Apophis is another matter: Dan Scheeres has determined that Apophis's rotation state will change drastically during the encounter. Michaelbusch 18:46, 13 February 2007 (UTC)

Alright. Thanks for the information.Mustang6172 06:13, 14 February 2007 (UTC)

Minor correction but one which does not alter the conclusions here: Tidal force is proportional to mass and inversely proportional to the square of the distance. 155.91.45.231 16:51, 19 February 2007 (UTC)

No. Gravity goes as one over distance squared. Tide = gradient of gravity and goes as one over distance cubed. Michaelbusch 18:10, 19 February 2007 (UTC)

Given its current path, does Apophis present a serious threat to our satellites? —The preceding unsigned comment was added by 71.237.236.45 (talk • contribs).

No. Michaelbusch 03:24, 26 February 2007 (UTC)

Gravity Tractor

There is a article in Reuters Alert (http://www.alertnet.org/thenews/newsdesk/N17363374.htm) on a group of astronauts, engineers, and scientists preparing a report about what procedure the UN should take in dealing with objects like Apophis that have a significant chance of damaging earth impact. There is mention of a "gravity tractor" to tug on the asteroid well before it gets near earth in order to change its orbit and reduce the risk. To me this sounds somewhat like science fiction. "Gravity tractor"? The only thing I can think of involving known physics is to use the mass of a probe sent to intercept the asteroid in order to alter the trajectory.But to me it seems surprising that the tiny gravitation of a human-made probe can alter the orbit significantly. I mean the Apophis weighs around 10 power 10 kgs! Can this proposal be taken seriously? Is it energetically less costly than using kinetic impact or an explosion? It seems this group is using the Apophis asteroids notoreity in the media in order to garner media attention for their report. Should this group and their proposal get mention here?

Domandologo 14:15, 18 February 2007 (UTC)

A gravity tractor has been proposed (Science last year, forget the date), and would work. I'd have thought it already had a Wikipedia page. But here is the math: get a spacecraft that would be pulled towards Apophis with a force of 1 N while you are a few Apophis radii away from the object. Hover, probably using an ion engine, directing your exhaust so that it doesn't hit the object (that negates the tug). You are now exerting a constant 1 N tug on the asteroid-spacecraft system. Do this for six years (1E8 s), and you've changed Apophis' velocity by 2 cm/s. 2 cm/s moves you an Earth radius (the minimum distance for certain deflection) in 5 years, so we can deal with impacts provided we know about them more than about a decade ahead of time. A spacecraft that would weigh 1 N 250 m out from Apophis' center would have a mass of ~100 tonnes, which can be whatever you want. The tug works, but it is slow and gentle. This is a good thing: it gives you fine control and you don't knock off pieces of the object. Obviously the spacecraft mass you need for a particular acceleration at a given distance from an object will be proportional to the mass of the object and inversely proportional to the time you are willig to take. Michaelbusch 17:18, 18 February 2007 (UTC)

Reconcile Please

Can someone reconcile the data in the info box with the info in the article? 70.177.68.179 15:46, 20 February 2007 (UTC)

Which data in particular do you find inconsistent? Please remember that the uncertainties in several of Apophis' physical properties are very large. Michaelbusch 16:29, 20 February 2007 (UTC)

I noticed this also, the mass indicated in the body of the article is 4.6e+10 kg. In the info box it's listed at 2e+10 kg. On the NEO website it's estimated at 2.1e+10 kg. Further, the article states that "A more refined later NASA [impact] estimate was 880 megatons." The NEO website lists the kinetic energy at impact at 4.0e+02 MT. Is there some question over NASA's numbers or is the article just out of date? (NASA NEO website: http://neo.jpl.nasa.gov/risk/a99942.html#summary) Infohack 04:54, 21 February 2007 (UTC)

To the level of uncertainty, all of those numbers are the same. We only know the mass, and hence the energy of any possible impact, to a factor of ten. This has come up before. How should I convey order-of-magnitude uncertainties in the article? Michaelbusch 04:56, 21 February 2007 (UTC)

If the value can be as much as an order of magnitude higher or lower, would something like 4.6⁺⁴¹
_−4.1 ×10¹⁰ kg be acceptable? It's fairly ugly. —RP88 05:14, 21 February 2007 (UTC)

I'd like to put the uncertainty in the exponent, if possible, but you're right. No matter how we right it, it is going to be messy. Michaelbusch 05:21, 21 February 2007 (UTC)

Perhaps something like 4.6×10^10±1, or 4.6x10^{10^+0.7
_−0.3}? —RP88 06:26, 21 February 2007 (UTC)

I would do 4.6×10^10±0.5. Michaelbusch 07:06, 21 February 2007 (UTC)

Sounds good to me. I wasn't recommending any particular values, just suggesting formatting style. I'd be perfectly happy with 4.6×10^10±0.5 kg if that reflects the range of current scientific consensus. —RP88 07:36, 21 February 2007 (UTC)

Uses Buy Man =

Has anyone considered the possible uses FOR Apophis? This thing is a huge, huge, huge amount of minerals and resources RIGHT HERE!!! CLOSER THAN ALSTRAILIA. By God! How much money is locked up in this thing? Trillions? Hundreds of trillions? Carbon, iron, ice, gold, silicon!!! Not to mention the fantastic addition to our knowledge of the solar system! The questions should not be "will it hit us?", But instead, "How can we get all this?"

Well, the windows of opportunity is kinda small isn't it? It's not gonna stop next to Earth and wait for people to get on it and start mining, then ask "are you finished?" and continue merrily on its way. :P 85.19.140.9 18:31, 5 March 2007 (UTC)

This is like a golden train passing thrugh town, and everybody says, "get off the tracks!"

No, more like a big rocky armed nuclear bomb, if it hits, we are DEAD.

Let's get us some golden train pieces!

Not this one. Delta-v is too high, and there is no gold in this one. Just rock. Michaelbusch 03:27, 29 November 2006 (UTC)

Okay, so maybe the next one. I love the optimism! Instead of near-Earth objects being a nuisance, if we use them and the asteroids as a resource, then keeping track of them will be like the accounting in a successful business. It won’t be the funnest part but we won’t mind so much because the rest of it is so good.

And then, like so many things, it becomes a question of ‘how,’ not ‘if.’ We human beings are eventually going to mine the asteroids. The question is, ‘How?’ I don’t want it to be like when we developed oil resources and we burned off natural gas to get to the more valuable oil. We need an environmental ethic backed by effective regulation. How much of the asteroid can be wasted to get to the really good stuff? That needs to be publicly discussed and decided on by an informed citizenry. And the regulation I hope will be a combination of both baseline and incentive, like power plant regulation should have been: ‘Your technology needs to be at least within ten years of being up-to-date. That part is hard-wired in. Now, if you exceed that, there are various positive incentives.’ And with a faster growing technology like mining asteroids, that mandatory might be only five years, or even three years. And there also needs to be an archaeological ethic as it were. Yes, you can build on a historic site (or in this case, tear one down), but you first need to have archaeologists there to map, record, and save artifacts from the site (in this case, to record each layer of the asteroid).

So, bottom line, you can form your own company and mine an asteroid as long as you do it right and have independent observers. At first, this will involve a team of environmental scientists and a team of planetary scientists. Later on, when we get pretty good at it, you’ll probably be able to get by with a single environmental scientist and a single planetary archaeologist. FriendlyRiverOtter 06:14, 13 March 2007 (UTC)

It's a matter of cost, and not a matter of how far Australia is. Besides, doesn't this well informed discussion belong, if anywhere, in the talk page of the asteroid mining article? Jim.henderson 20:12, 13 March 2007 (UTC)

Stepping stone?

Shouldnt we attempt to slow this down as it approches earths orbit so that we can use it as a stepping stone to get at the moon?

We don't really have technology on this scale to "slow it down". The best we can do is probably nuclear bombs, but the most these will do will possibly slightly misdirect the asteroid (we wouldn't have much control over where it would go) or it would blow parts of it up, resulting in thousands of meteors raining down on the Earth and causing havoc. Your stepping stone to the moon idea is interesting, but even if we could control the orbit somehow, it's really not necessary as a "stepping stone" to the moon, since the moon is relatively close, and we were able to successfully reach the Moon on multiple Apollo missions. FranksValli 00:47, 28 October 2007 (UTC)

"A stepping stone to the moon" implies another body in between here and the moon upon which a base can be constructed, and resources dumped on. The asteroid itself is likelty to be far too small and have far too little gravity (as in "do a star jump and you won't come back") to be of much use at all. Like a tiny rock jutting out of the mid Atlantic being a "Stepping stone" between Europe and America Felneymike (talk) 16:26, 19 February 2008 (UTC)

April 13

There are references in this article to 13 April 2029 (originally thought to be a possible impact event, now a close flyby), and also a reference to 13 April 2036, another possible impact event. Are both of these dates correct? If they are, then the selective use of a phrase such as "in 2036, also on April 13, ..." should be considered to ensure that readers are not left confused as to which year(s) the date April 13 is significant. --D P J 15:08, 4 July 2007 (UTC)

Yeah it seems they are.See here. And the internet archive version here.All are on 13 April. It doesn't give the 2029 date but I reckon its for 13 April as all the other dates are for 13 April. --Trounce 11:46, 11 July 2007 (UTC)

Check out the JPL Small-Body Database Browser. On my system it shows Aphphis/Earth close approaches on 14 April 2029 and 22 Dec 2035. That's a bit off the dates I vaguely remember from past uses of this tool, and I see that some features of the tool are now not working for me. I've updated Java since I last used the tool, and may now have a problem. Anyhow, those dates are close. An item which interests me and which I haven't seen mentioned is the Apophis/Venus close approach around 16 April 2016. I'm wondering if the effect of that has been factored into the orbit calculations about the 2029 Apophis/Earth close approach. -- Boracay Bill 01:46, 12 July 2007 (UTC)

Let's look on those dates from view of numerology - 13 April 2029 and 22 Dec 2035. What we get - 1+3=4, April is the 4.month, 2+0+2+9=13=1+3=4. Three 4s, that's really bad! And the second date - 2+2=4, December is the 12.month, 1+2 + 2+0+3+5 = 3+10 = 13 = 1+3 = 4. Two 4s, again bad combination. 78.84.201.227 (talk) 22:34, 16 April 2008 (UTC)

Internet forums

I'm sorry,but this is a very stupid thing to include. No one cares what John Q. Nobody says on some forum about this asteroid unless they're qualified in this field. —Preceding unsigned comment added by Ashmole (talk • contribs) 16:08, 16 July 2007 (UTC)

chaotic aspects of tumbling?

The Big Splat, or How Our Moon Came to Be, Dana Mackenzie, John Wiley & Sons, Inc., Hoboken, New Jersey, 2003, pages 169-170:

“As early as 1981, an astronomer named Jack Wisdom brought the idea of chaos back into planetary science where it started, by showing that the tumbling motions of an irregularly shaped asteroid were chaotic.”

Accurate dates?

The introduction to this article mentions a close approach date of April 13th, 2036. Later in the the section titled Close Approach, the date of close approach for 2029 is also said to be April 13th. Is there a mistake? —Preceding unsigned comment added by Kimholder (talk • contribs) 19:05, 1 January 2008 (UTC) Oh... sorry, didn't see the previous comment on the same topic. —Preceding unsigned comment added by Kimholder (talk • contribs) 19:10, 1 January 2008 (UTC)

2016 Venus encounter

I've noticed that current Apophis path estimates are based on data gleaned from more and more observations of its current path. I presume that this data is projected as if there will be no post-current-data alterations in the path. I also observe that a pretty close Apophis-Venus encounter is forecast in 2016 (March, as I recall, but don't have the info handy just now and too rushed to check). I'm wondering whether and how much error this forecast encounter might contribute to currentl path forecasts. If this is significant, it should be mentioned in the article. If it is not significant, perhaps that should be mentioned. -- Boracay Bill (talk) 11:55, 17 April 2008 (UTC)

Perturbations by Venus (and other planets and the Moon) are part of the model. Not accounting for it would make a significant difference. I just used SOLEX9.1 with and without Venus. (beginning with the actual position and trajectory for April 2007). The dates of the 2029 passes are close, but the distances are different. With no Venus, the distance came to 6.86 Gm, as opposed to .038 Gm predicted. Saros136 (talk) 20:05, 17 April 2008 (UTC)

Looking at NEODys (not listed since it would have to pass closer than 0.05AU for a planet other than Earth) and Horizons (Observer Location:@Venus): On 2016-Apr-24, Apophis will come within 0.0782 AU (11.7 million km) of Venus. At that distance it is really a non-issue. The Earth passes on 2013/01/09 (0.09666AU = 14.4 million km) and 2021/03/06 (0.1126AU = 16.8 million km) will be more critical for refining future trajectories since it will be observable with Earth based telescopes. -- Kheider (talk) 18:23, 17 April 2008 (UTC)

Crikey! Let's stick with the 'no original research' policy, and keep the emotives out too.

This will not just stay written, will it?

Am editing the 'back of envelope calculations' (whatever that means) et al out, as it patently contradicts the 'original research' policy, moreover, I don't believe an anonymous 'back of envelope' calculation really can stand as fact. I would love to have something in there debunking if there is a real quote from a real, recognised person or organisation who can attest to the impossibility or not. If whomever put that in reads this, please read the policy before putting it back. Speculation et al belongs in a blog or editorial, which this encyclopaedia is not.PeterSmithee (talk) 07:19, 19 April 2008 (UTC)

Yeah, you're right about that bit. But here's an official source claiming the effects are meaningless. Like I've stated before, well within all the noise the asteroid has to deal with. — Kieff | Talk 07:30, 19 April 2008 (UTC)

Maybe you or someone else can help me with a format question, where I've added this : "Predicting Apophis' Earth Encounters in 2029 and 2036" (Giorgini, Benner, Ostro et al I'm just wondering what the format/policy is for credits, do we credit authors or not, and how do we decide where to cut the names off? Those first three were all from the JPL and I put them in order as per the url credits ( the original person who put them in the article had a huge screed of credits etc that did not show in the article (do we paste them up and mark as invisible?) but linked to the wrong article (the one linked to I listed under space missions, interesting proposed methods for dealing with Apophis; so I thought 3 names all from the first agency (JPL) and the subsequent contributors become 'et al' - fair enough? PeterSmithee (talk) 08:48, 19 April 2008 (UTC)

We usually avoid in-line external links in favor to the use of the reference tag <ref>. There's the {{cite-web}} template as well to be used within it, and that's how we had that page referenced with details before you changed it back. The information was not "invisible", just below the article on the reference block. Your frequent claims that the link was "incorrect" are ridiculous too, because the link was correct and you never really changed anything about it, except for making a inline link to the page. I'm not sure of what's going on here. — Kieff | Talk 19:56, 19 April 2008 (UTC)

Thanks for the clarification but I take exception to your wording of 'ridiculous' - let's keep things on a professional level, shall we? My description of changes regarding links might not have been accurate in all of the edits where I was just making inline links etc, however, I did fix a few of my broken links when they didn't test correctly (I began saving rather than testing the page a little more often when I lost a bunch of stuff whilst someone else was editing too) but at least one link purporting to link to the updated apophis JPL page ""Predicting Apophis' Earth Encounters in 2029 and 2036" actually linked to the rather fascinating pdf "SCENARIOS FOR DEALING WITH APOPHIS , a paper presented by Donald B. Gennery (which did not discuss Marchand's erroneous project); I moved it to the "proposed space missions" section. I apologise if I offended you somehow by doing this, but the link went to the wrong paper. It all seems to work ok now.PeterSmithee (talk) 15:51, 21 April 2008 (UTC)

Is someone going to reinstate the stuff that was anonymously removed?? (vis a vis the schoolboy story)

Like it or not the schoolboy story WAS/is news whether proved or not, I really don't understand the penchant for messing with it but I may be preaching to the choir. At all stages the added stories were referenced and sourced correctly, nobody said he was right, and like it or not it's part of the story and therefore ought to be part of the article but for some odd reason it seems impossible to revert the article. In case the person who removed the references reads this, don't be blinded by your belief the kid was wrong (and according to nasa and the news, he is) this is a REFERENCE place so the articles have to include all the facts available, and the fact is, some kid was reported to have redone the math, papers reported it was correct, then it was disproved, etc. Should wikipedia leave out articles about Hitler or Pol Pot or psoriasis because we don't like it or disapprove?

We're dealing in facts and information, not opinions (at least, in the articles we are) PeterSmithee (talk) 07:23, 21 May 2008 (UTC)

OK, I've restored a single section which I think is concise enough, let's just leave it be, ok?PeterSmithee (talk) 09:07, 21 May 2008 (UTC)

It was probably vandalism; the reflist was removed also. --Harald Khan Ճ 10:52, 21 May 2008 (UTC)

For the record books (in case someone wants to re-instert a section): Edits on 16 May 2008 by 79.193.86.86. I say it was vandalism since they have not been back to downsize more articles. -- Kheider (talk) 15:03, 21 May 2008 (UTC)

I figured as much, people are somewhat stubborn (re the vandalism) and perhaps fail to understand the difference between reference pieces (report all the facts and salient articles) and opinion pieces....Thanks for cleaning that up, at one point I'd managed to mess up the ref list too; I stopped when I kind of had it sort of ok and hoped someone would clean it up again, thanks for the link :"> PeterSmithee (talk) 18:03, 21 May 2008 (UTC)

Next time you might want to call an Admin or a Rollbacker. :-) AFAIK, they should be able to revert a row of undesired edits from a certain user in one go; at least my adminship on the nn wiki allows me. --Harald Khan Ճ 18:29, 21 May 2008 (UTC)

Hmm yeah that would be a great idea, it was a struggle getting it all together again especially since I didn't really know how to do it - I wondered if there was a way of flagging it, I'll do that next time. On the upside, I learned the interface a bit better, and spotted a few things on the way that could be improved.PeterSmithee (talk) 07:14, 22 May 2008 (UTC)

Apophis will hit us

The asteroid Apohpis will be .0023 AU from the Earth on April 14 2029. JPL denies this but I got this information from thier own orbit diagram page you can see what the diagramis if you go to <http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=99942;orb=1> The earths gravity feild is biger than .0023 AU on each side and strong enough to hold the moon in it's place.

Nothing is secret. JPL's Horizons site (telent version) gives close approach data. April 13 at .000255 AU-about 6.0 Earth radii-with some uncertainty. (That's about a tenth of the distance you cited) Saros136 (talk) 08:50, 5 August 2008 (UTC)

In fact, the article cites NASA/JPL sources backing this up. The future for Apophis on Friday, April 13 of 2029 includes an approach to Earth no closer than 29,470 km (18,300 miles, or 5.6 Earth radii from the center, or 4.6 Earth-radii from the surface) [1] (.00024 AU) This is about the same as the others. Saros136 (talk) 09:04, 5 August 2008 (UTC)

Umm, according to google... radius of Earth = 4.26349283 × 10-5 Astronomical Units, so it won't hit. 72.29.167.236 (talk) 15:33, 28 July 2008 (UTC) The only thing you have to worry about is the gravity feild of the earth.

Damn right it'll hit. They lied about the syphilis experiments conducted during World War II, lied about Roswell, are lying about Mars, UFOs, aliens, now Apophis.65.173.105.133 (talk) 06:21, 5 August 2008 (UTC)

As for worrying about the gravity field. The perturbations due to the gravity of the Earth are included in the calculations. Saros136 (talk) 09:05, 5 August 2008 (UTC)

sorry for the miss take but according to JPLs orbit diagram appophis will be 7.0E-4 AU from the earth on april 14 2029.  —Preceding unsigned comment added by 71.179.13.34 (talk) 20:36, 17 September 2008 (UTC)

Math

>"Albedo and size determination of potentially hazardous asteroids: (99942) Apophis" Icarus, Volume 188, Issue 1, May 2007, Pages 266-269 M. Delbò, A. Cellino and E.F. Tedesco

This article gives Apophis size at 270m +or- 60m, smaller than previously thought(or than listed here).

That is the same number AND reference as in the article. JPL just does not list the +- figure. (kilo = 1,000.) -- Kheider (talk) 00:19, 8 September 2008 (UTC)

The Harvard Catalog of PHA's, continuously revised, I believe, lists:

Object: (99942) Apophis Date of encounter: 2029 Apr. 13.91 Distance(AU): 0.0002318

That's 2000 miles. Klasovsky (talk) 23:39, 7 September 2008 (UTC)

0.0002318 * Astronomical unit = 34676km on my calculator. Horizons shows Apophis @ 0.0002551AU (2029-Apr-13 21:45) = 38162km
-- Kheider (talk) 00:19, 8 September 2008 (UTC)

yeah- slipped a zero: 20,000 miles- 21,299 more precisely @ 0.0002318AU Klasovsky (talk) 05:31, 8 September 2008 (UTC)