Simulation of Asteroid Orbits
- Please note that the new integrator will only work in up-to-date browsers and seems to work best in the new Edge browser (I.E. on Windows 10).
The animation window shows orbits and trails of Solar System objects. The animation is a genuine gravity simulation based on the masses of the objects and their initial positions and velocities (state vectors). Initial state vectors of planets are taken from JPL Horizons. Those for asteroids and comets are obtained using observations (from the MPC) and Find Orb.
The simulator works by calculating the gravitational attraction between all the bodies then using Newton's equations (slightly adjusted for relativity) to work out how they will move during a short time-step. This is done repeatedly so that the positions of the objects can be traced over time. (Just the sort of work a computer likes!)
There is a set of buttons under the animation that zoom, tilt, rotate (etc) the view. The Orbits/Trails button cycles through showing orbits, trails, orbits and trails or no orbits or trails. The Speed+/- buttons make it run faster/slower. Maximum usable speed will vary hugely depending on computer and browser.
Play with these controls to view whatever interests you.
Bodies in the Solar System move according to the laws of physics. Kepler discovered, and Newton proved, that planets move in elliptical orbits round the Sun. However, orbits get disturbed (perturbed) by the gravitational attractions between the bodies. For asteroids and comets, orbits can get changed significantly when they pass close to a planet.
NEO's and PHA's
There are millions of asteroids in the Solar System and some of them come quite close to earth. (Some actually try to land as at the Chelyabinsk Event). There is an ongoing effort to find and track these objects to see if they might be dangerous. Objects that come close to Earth are called Near Earth Objects (NEO). If they are big, and we think there is a chance they may impact Earth, their orbit is analysed into the future. Objects that possibly may become dangerous in the future are call Potentially Hazardous Asteroids (PHS). There are many different types of orbit an asteroid may have and they all have special names - but you don't need to remember them all.
Link to PHA example
Resonance, Horseshoes and Tadpoles
The effects of gravity and perturbation can have some weird effects. Objects can become locked in "Resonant" orbits. In effect their gravitational relationship increases/decreases speeds so that their orbital periods maintain a fixed ratio. For example Pluto and Neptune have a resonance with their orbital periods locked in the ratio 3:2.
A particular relationship exists when the ratio of orbital periods is one-to-one. For example an asteroid with a period very close to one year will be at an average distance from the Sun the same as the Earth. However, it's eccentricity and inclination may be such that it never comes close.
Link to example
Some asteroids with a 1-year period do come close. They can interact with the Earth in such a way that they "horseshoe", alternatively approaching Earth from the east then the west, having wandered all the way round the back of the Sun in between.
Link to example
Lagrange, Trojans and Tadpoles
A Mathematician called Lagrange discovered that there are certain regions in a planet's orbit where asteroids can congregate and stay at a roughly fixed position relative to the planet. These points are called Lagrange(ian) points L1 to L5. Jupiter has lots of objects at it's L3 and L4 Lagrange Points.
Earth does not seem to have objects permanently at it's Lagrange points, probably due to the disturbing effects of Mars and Venus. However, some of our NEOs do spend quite a bit of time near such points.
Clones and Virtual Impactors
It takes many years of careful observations to be able to work out the orbit of an asteroid. Newly discovered objects have very uncertain orbits and projecting them into the future does not tell us much. We can, however, generate a set of "virtual asteroids" in the computer, each having a slightly different orbit, spread across the range of uncertainty in our knowledge of the true orbit. These virtual objects are sometimes called "clones".
In the computer we can simulate the orbits of the clones into the future. If some of the clones impact a planet then we know there is some chance that the real object might hit the planet. These are called virtual impactors.
We can also simulate the clones orbits into the past to get an idea where they have been and how their orbit has evolved.
Link to clone example
On the left are links to a selection of different simulations. The General ones have been set up to demonstrate various orbit types. The specific Asteroid ones take a close look at some asteroids of interest.