Not a hazard, not a shattered planet — a place where a planet was never allowed to finish. Where it sits, why it has clean lanes through it, and why the gaps are really a portrait of Jupiter.
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Distances from the sun are in AU — one AU is the Earth’s average distance, 149,597,870 km — and the angle is where the body sits around its orbit, measured from the March equinox direction.
The main belt runs from about 2.06 AU to 3.28 AU — between Mars and Jupiter — and it is not evenly filled. Every edge and every clean lane in it is a resonance with Jupiter: an asteroid whose orbital period is a simple fraction of Jupiter’s year gets the same gravitational tug at the same point over and over, and is eventually pushed somewhere else.
That means the whole structure can be calculated rather than remembered. A body in a p:q resonance orbits at Jupiter’s distance times (q/p)2/3, and the table below is that formula applied to Jupiter’s own semi-major axis — the same number the simulator draws Jupiter with. Change one and the other moves.
| Resonance | Distance | What is there |
|---|---|---|
| 4:1 | 2.065 AU | The inner edge |
| 3:1 | 2.501 AU | Kirkwood gap |
| 5:2 | 2.825 AU | Kirkwood gap |
| 7:3 | 2.958 AU | Kirkwood gap |
| 2:1 | 3.278 AU | The outer edge |
| 3:2 | 3.971 AU | The Hilda group sits here |
| 1:1 | 5.203 AU | The Trojans, 60° ahead of and behind Jupiter |
Switch on Asteroid belt above and jump to the belt or Jupiter view to see it drawn, gaps and all. The Trojan clouds move with Jupiter, so they are wherever Jupiter is on the date you have chosen.
Between them these hold about half the mass of the entire belt, and Ceres alone is roughly a third of it.
| Object | Distance | Width | |
|---|---|---|---|
| Ceres | 2.766 AU | 939 km | A dwarf planet, a quarter of all the mass in the belt, with water ice under its crust |
| Vesta | 2.362 AU | 525 km | The brightest asteroid, bright enough to see without a telescope, and a differentiated protoplanet |
| Pallas | 2.771 AU | 511 km | On a 35-degree tilt, so it crosses the belt rather than lying in it |
| Hygiea | 3.142 AU | 433 km | Round enough that it may count as a dwarf planet too |
The simulator draws the belt as a band and never as individual dots. The orbit of an asteroid is a fact that needs no date; where it sits on that orbit today is something this site does not solve for, and a dot in an invented place would be exactly the kind of confident wrongness these pages are built to avoid.
Every one of these is genuinely unsettled — not simplified for the page, not waiting on a textbook update.
Models in which the giant planets migrate depopulate the belt by a factor of a hundred or more and mix in bodies from elsewhere — which would explain why the belt contains both dry inner-system rock and water-rich outer-system material. How much migration, and when, is not settled.
It has ammoniated clays on its surface, and ammonia is not stable that close to the Sun. Either Ceres formed much further out and was moved in, or the ammonia was delivered. It is a dwarf planet with water ice and possible brines, sitting in a region we thought we understood.
The largest metal-rich asteroid has been described for years as the exposed core of a shattered protoplanet, which would make it the only place we could look at a planetary core directly. Density measurements since have muddied that: it may be far more porous and less purely metallic than the story requires. The Psyche spacecraft arrives in 2029.
Findings reviewed August 2026. Space science moves; a date on a finding is part of the finding.
The date, the zoom, the span, the speed, the layers and any flight path are all in the address bar, so copying the URL shares exactly what is on screen. Set it up above, then take the link — it is the quickest way to hand a class one specific thing to look at.
This one is about the whole system. If the question is where the sun and the moon are from where you are standing — what time the sun comes up, why tonight's moon is the shape it is — that is the Sun, Earth & Moon movement simulator, which has a page for every city and a slider over a day, a week or a month.
Comets · Jupiter, which made the belt what it is · Also: the classroom guide · sunrise & sunset by city · moon phase & moonrise · lunar eclipses · how the positions are worked out
How much of the belt did Jupiter throw away? Models in which the giant planets migrate depopulate the belt by a factor of a hundred or more and mix in bodies from elsewhere — which would explain why the belt contains both dry inner-system rock and water-rich outer-system material. How much migration, and when, is not settled.
Where did Ceres form? It has ammoniated clays on its surface, and ammonia is not stable that close to the Sun. Either Ceres formed much further out and was moved in, or the ammonia was delivered. It is a dwarf planet with water ice and possible brines, sitting in a region we thought we understood.
What is Psyche? The largest metal-rich asteroid has been described for years as the exposed core of a shattered protoplanet, which would make it the only place we could look at a planetary core directly. Density measurements since have muddied that: it may be far more porous and less purely metallic than the story requires. The Psyche spacecraft arrives in 2029.