Apophis orbital elements

Apophis orbital elements

obaeyens 12 Feb 2011 17:40

Does anyone have the orbital elements of Apophis?
I originally used the Wikipedia version but these seem to be more accurate.

I found this one in a JPL document from 2008.
http://neo.jpl.nasa.gov/apophis/Apophis_PUBLISHED_PAPER.pdf

Eccentricity (e) 0.1910573105795565 ±0.0000000297
Perihelion distance (q) 0.7460599319224038 ±0.0000000339 AU
Perihelion date (Tp) 2453924.3091729818 ±0.0000076340 d (JD)
Longitude of ascending node (Ω) 204.45996801109067 ±0.0000425720 deg
Argument of perihelion (ω) 126.39643948747843 ±0.0000422150 deg
Inclination (i) 3.33132242244163 ±0.0000007966 deg
Semimajor axis (a) 0.9222654975186300 ±0.0000000096 AU
Orbit period, sidereal (P) 323.5060220661519 ±0.00000504 d
Mean anomaly (M) 61.41677858002747 ±0.0000010854 de

But for my astronomy simulation program I need Peri. Long and True Long.
Anyone knows how to calculate those from these orbital elements?

Re: Apophis orbital elements

obaeyens 14 Feb 2011 03:01

I am still searching for the orbital elements. I had a very good 2029 simulation but the 2036 I still do not get it.
And this makes a very interesting realization that deflecting Apophis would be pretty easy to do.
Just slow down or speed up (delta V) a tiny fraction is enough to miss Earth completely.

The reason why my simulation fails to get the 2036 target is because of a very minute speed change that gets amplified big time of the gravity assist of Earth. Too fast and it gets ahead of Earth slowing the Orbit down. Too slow and it gets behind Earth speeding up its orbit. But in both ways it completely misses its 2036 target.

It actually amazes me that an asteroid could hit Earth after all.

Re: Apophis orbital elements

Daggerstab 14 Feb 2011 08:39

What kind of software do you use to simulate the orbit? Most astronomy applications treat orbits as fixed curves. Indeed, orbital elements describe an orbit as a fixed ellipse. You need some kind of gravity simulator that solves the n-body problem if you want a prediction of the trajectory after its close encounter with the Earth in 2029.

Here's NASA JPL's Small Body Browser on Apophis:
http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=99942
The current orbital elements are listed.

The information is also available through the Minor Planet Center's database:
http://www.minorplanetcenter.org/iau/mpc.html

Here's a page about modeling its trajectory:
http://neo.jpl.nasa.gov/apophis/

Re: Apophis orbital elements

obaeyens 14 Feb 2011 12:25

Astrograv, it simulates using gravity.
But I need a starting position and starting speed vector so the orbital elements should give me such a thing.

Re: Apophis orbital elements

bikenbeer2000 14 Feb 2011 12:01

But for my astronomy simulation program I need Peri. Long and True Long.
Anyone knows how to calculate those from these orbital elements?

Peri. Long = Longitude of ascending node + Argument of perihelion.
True Long = Peri. Long + Mean anomaly.
True long = Peri. Long + True anomaly
To obtain the True anomaly, some mathematical manipulations involving the eccentricity are required, as shown here.

The Minor Planet Center has some orbital elements here.

Last edited on 14 Feb 2011 20:07 by bikenbeer2000 Show more

Re: Apophis orbital elements

obaeyens 14 Feb 2011 12:25

Thanks :-)

Re: Apophis orbital elements

bikenbeer2000 14 Feb 2011 20:09

Sorry. A correction is needed. See above.

Re: Apophis orbital elements

obaeyens 14 Feb 2011 21:07

Thanks, I will continue the simulation when I can find time.

I already invested 4 hour last night in this. And I can tell you that getting a none-powered object close to earth and make it collide with Earth next time is pure witchcraft. A tiny wrong estimate of mass or speed and the asteroid is off by millions of kilometres missing Earth completely. The 1 in 250,000 estimate is not 1 chance that it will hit Earth but 249,999 times it will not hit Earth!

You really need a rocket power to do course corrections. I don't think that any scientist can claim that it will crash and where with the data we have now.