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Concerned
2014-Oct-31, 10:40 PM
Hi,

I was just reading the wiki regarding asteroid apophis. It stated that the asteroid is not likely to impact earth in 2029 or 2036. Still I see in another article that the asteroid is considered a possible target for the don Quixote mission, as well as several other countries considering methods to deflect it. Is the asteroid a threat to us, and if so, shouldn't we be doing more to deal with it?

Noclevername
2014-Nov-01, 01:44 AM
No, it's not a viable threat, but since it comes near Earth and passes through a known "keyhole" (a tipping point on its orbital path), we can use it as a test case for asteroid deflection.

Jeff Root
2014-Nov-01, 01:07 PM
I'd say it probably is a threat. Someone who knows more
about the details of its orbit than I do might be able to say
that it is definitely a threat. But I know enough to say that
any possible threat is *many* decades in the future, and is
probably very low when considered over the next several
centuries. So there is no reason to rush into preparing for
a possible impact now. We can think about what we might
do if it turns out to be on a collision course with Earth, but
it won't make any real difference if we think about it now
or twenty years from now. Either way there will still be
plenty of time (decades) to act.

-- Jeff, in Minneapolis

Noclevername
2014-Nov-01, 01:56 PM
Per Wikipedia:

http://en.wikipedia.org/wiki/99942_Apophis


As of May 6, 2013 (April 15, 2013 observation arc), the probability of an impact on April 13, 2036 has been eliminated.[3] Preliminary observations by Goldstone radar in January 2013 effectively ruled out the possibility of an Earth impact by Apophis in 2036.[9] As of May 6, 2013, using observations through April 15, 2013, the odds of an impact on April 12, 2068, as calculated by the JPL Sentry risk table is 3.9 in a million (1 in 256,000).[3] Of objects not recently observed, there are about ten asteroids with a more notable Palermo Technical Impact Hazard Scale than Apophis.[

Concerned
2014-Nov-01, 07:00 PM
I'd say it probably is a threat. Someone who knows more
about the details of its orbit than I do might be able to say
that it is definitely a threat. But I know enough to say that
any possible threat is *many* decades in the future, and is
probably very low when considered over the next several
centuries. So there is no reason to rush into preparing for
a possible impact now. We can think about what we might
do if it turns out to be on a collision course with Earth, but
it won't make any real difference if we think about it now
or twenty years from now. Either way there will still be
plenty of time (decades) to act.

-- Jeff, in Minneapolis
Thanks all for responding.

I read about the keyhole, but thought there was some uncertainty as to whether the asteroid would pass through this 800 metre wide zone. If so, there was possibility of an impact, but I read this would not occur until 2036. Reading the wiki, it seems to indicate there is no threat. However, I guess I'm a bit different of thinking, 20 years in the future does not seem that long, and in terms of a deflection mission, untried, I thought it actually takes a couple of years to prepare one?

Noclevername
2014-Nov-01, 08:03 PM
Thanks all for responding.

I read about the keyhole, but thought there was some uncertainty as to whether the asteroid would pass through this 800 metre wide zone. If so, there was possibility of an impact, but I read this would not occur until 2036. Reading the wiki, it seems to indicate there is no threat. However, I guess I'm a bit different of thinking, 20 years in the future does not seem that long, and in terms of a deflection mission, untried, I thought it actually takes a couple of years to prepare one?

Since none have ever been prepared as of yet, and none are currently planned, we aren't sure how far off in the future a deflection mission (even a practice run) could be.

Jeff Root
2014-Nov-01, 08:59 PM
From where we are right now, I'd guess it would take between
ten and 20 years to prepare and begin carrying out a deflection
mission. But we probably have *at least* a few centuries in
which to do it, not just a few decades. So if we start thinking
about it now or twenty years from now wouldn't make any real
difference. I took the 2068 date to be the absolute earliest
possible date for a collision, and as Noclevername points out,
that date is extremely unlikely. 2036 or 2068 might be good
times to give Apophis a tiny nudge to prevent a collision in the
far future, but even if they are (other times might be better),
we don't have to start working on it now. The 2036 encounter
would more likely be a mission to determine Apophis's mass,
composition, and structure for a much later deflection mission.
That kind of mission should be doable in under ten years with
no emergency effort.

-- Jeff, in Minneapolis

Hornblower
2014-Nov-01, 09:45 PM
I would prefer to practice on one that is no threat at all, rather than risk messing up on a first mission and accidentally turning what would have been a miss into a hit.

tony873004
2014-Nov-02, 05:45 PM
An asteroid can only impact Earth if its orbit crosses the 1-AU mark on the ecliptic.

I've tried simulating recently-discovered asteroids that have come within a lunar distance, hoping to find out on average how many orbits it will take them to hit the Earth.

It turns out that due to orbital precession, within a few thousand years, their orbits no longer intersect the 1-AU mark at the ecliptic. They now miss Earth's orbit too high or too low. They don't return to intersecting 1-AU at the ecliptic for 10s to 100s of thousands of years, depending on their inclination.

So any asteroid that is currently making very close (< 1 lunar distance) passes of Earth has only a few shots at actually hitting us before they're tossed from the PHA (potentially hazardous asteroids) bin for at least 10s of thousands of years. Other asteroids will of course take their place. They too will only have a few opportunities to strike Earth.

If Apophis doesen't hit us in the next few thousands of years, its threat level will completely drop to zero for a long time.

publiusr
2014-Nov-03, 08:53 PM
I wonder if there are other objects that come close to Apophis

The best links I've seen here on NEOs
http://arxiv.org/abs/1410.4471
http://arxiv.org/abs/1409.5588
http://arxiv.org/abs/1410.1357

tony873004
2014-Nov-09, 04:49 AM
Here's an Apophis simulation you can try.

IF Apophis were to pass through the keyhole in 2029, the key to deflecting it would be to act before 2029. How much deflection is necessary? It depends on when you apply it.

The following simulation runs in your browser, so there's nothing to install. It sets up the solar system and gives you 3 different versions of Apophis: Apophis, KeyholeA, KeyholeB. The first one is simply Apophis following its nominal trajectory. But a mere 10 km away from Apophis, on parallel trajectories, sits a pair of objects, KeyholeA and KeyholeB. In 2029, these WILL pass through the keyhole. They WILL return to strike Earth in 2036. The simulation is set up so that you can edit the velocity of KeyholeB in the "Vectors" dialog. Just change its velocity. See how small of a change you can make to ensure it misses the keyhole.

This simulation takes some time to run. It depends on the speed of your computer. You'll be tempeted to leave it run and come back to it later. So I made it automatically pause a few days before Apophis' Earth encounters. You have to press the ">" button on the Time Step interface to get it to resume. This simulation also controls the time step for you. If you run it too fast (> 2048, >32 during Earth encounters) you will not get good results. So the simulation controls this for you. Don't adjust the time step. It slows things down and speeds them up as necessary.

How to use:
When you click the link, you'll see the gray Moon orbiting the Earth in 2014. You'll also see a "Vectors" dialog box that allows you to control the position and velocity of any object in the solar system. It's set to control KeyholeB. It show KeyholeB's position and velocity with respect to KeyholeA. Pause the simulation with the || button before editing the numbers. Change its velocity slightly. Unpause the simulation. It will continue to 2029. A few days before the Apophis encounter, it will slow the timestep to 32 seconds and pause the simulation. Unpause and watch the three objects approach Earth. They will probably be too close to discern from each other until after they pass Earth. A few days after the Earth encounter, the simulation will increase the time step to 2048 seconds. It will run until April 2036. A few days before the Earth encounter, it will again slow to a time step of 32 seconds. KeyholeA will strike the Earth. KeyholeB may or may not strike the Earth, depending on how hard you nudged it.

After striking the Earth, the objects will pass through Earth and continue to orbit the Sun. Their trajectories are unrealistic after the collision.
http://orbitsimulator.com/gravitySimulatorCloud/apophis2014.html