Watch a transiting planet's arrival time drift slightly early or late from a perfectly periodic schedule - the gravitational fingerprint of a second, unseen planet tugging on it. Pick a real Kepler system, scrub through transits, and reveal the hidden world the timing wobble points to.
Transit-Timing Variation (TTV) 3D Explorer
Scrub through forty transits of a real Kepler planet and watch its arrival time drift early or late from a perfectly periodic schedule - the same gravitational fingerprint astronomers used to find planets that have never once been seen crossing their own star.
Three preset buttons load three real, published systems; a slider and a "Play transits" button step the timeline forward while a strip graph plots the timing offset transit by transit, and a "Reveal hidden planet" button shows the second, unseen world whose gravity causes the wobble.
- Kepler-19b + 19c preset: Kepler-19b's transits drift up to about 5 minutes early or late on a roughly 300-day repeating cycle - Kepler-19c has never once been seen transiting its own star
- Kepler-9b + 9c preset: the first system ever confirmed by transit-timing variations (2010), with drift rates of about 4 and 39 minutes per orbit
- Kepler-36b + 36c preset: two planets passing within about 0.013 AU of each other, whose TTV signal alone measured both masses despite a striking density contrast
- The bright marker's up-or-down position on the orbit ring is a stylized, exaggerated readout of the timing offset - not an actual spatial displacement of the planet
- Drag to orbit, scroll or pinch to zoom; runs fully in the browser with the vendored three.js engine - no account, no upload; your last preset and reveal choice are remembered on your device
| System | Periods | What the TTV revealed |
|---|---|---|
| Kepler-19b + 19c | 9.287 d / 28.7 d | A second planet that has never been directly observed to transit |
| Kepler-9b + 9c | 19.2 d / 38.9 d | The first system confirmed by mutual transit-timing variations |
| Kepler-36b + 36c | 13.8 d / 16.2 d | Both planets' masses, from timing alone, with no radial-velocity data |
Why a transit can arrive early or late at all
A single planet orbiting a star alone would transit on a perfectly predictable schedule, one orbital period apart every time. A second planet's gravity tugs on the first one as they pass each other, speeding it up or slowing it down slightly depending on where each planet is in its own orbit. Watch closely enough and the transiting planet's arrival time traces out a repeating wobble instead of a straight line - and the size and pace of that wobble tells astronomers how massive the tugging planet is and roughly where it orbits, even though nobody has ever seen it directly.
For a single planet's own direct brightness dip - the light-curve signal a transit produces by itself, with no second planet involved - see the Exoplanet Transit 3D Explorer. This page instead visualizes the second, indirect signal: the timing wobble a hidden sibling planet leaves behind.
Everything renders on your device with WebGL. The 3D engine loads once (about 0.7 MB) and is cached, and nothing about your visit is sent to a server.
This is an educational approximation, not a numerical N-body integrator: the two orbital periods shown for each preset are the real published values, and the Kepler-19 preset's timing-drift amplitude and cycle length are the real published figures, but the exact shape of the wobble curve is a stylized teaching curve, not a fit to any one system's actual measured timings. The marker's up-or-down position on the ring is a deliberately exaggerated readout for visibility, not a real spatial displacement - real transit-timing variations are a difference in arrival time, never a change in the planet's position in space.
Frequently Asked Questions
What is a transit-timing variation (TTV)?
It is a small, repeating drift in when a planet's transit actually arrives compared to a perfectly periodic schedule. The drift is caused by the gravitational pull of another planet in the same system, and its size and pace reveal that second planet's mass and roughly where it orbits.
Has Kepler-19c ever been seen transiting its star?
No. Kepler-19c has never once been directly observed crossing its own star. It is known only from the timing wobble it causes in Kepler-19b's transits - later confirmed independently by radial-velocity measurements.
What was the first system confirmed by transit-timing variations?
Kepler-9, in 2010. Kepler-9b and Kepler-9c sit close to a 2:1 orbital resonance, and their mutual gravitational tugging produces some of the largest TTV drift rates ever measured - about 4 minutes per orbit for Kepler-9b and about 39 minutes per orbit for Kepler-9c.
Can transit-timing variations measure a planet's mass without radial-velocity data?
Yes. Kepler-36b and Kepler-36c orbit within about 0.013 AU of each other at closest approach, and the resulting TTV signal alone was strong enough to pin down both planets' masses (4.1 and 7.5 Earth masses) with no radial-velocity observations at all.
What does the bright marker's up-and-down movement mean?
It is a stylized, exaggerated readout of the timing offset for the currently selected transit - not a real spatial displacement. The real effect is a difference in arrival TIME, measured in minutes; the planet does not actually move up or down in space.
How is this different from the Exoplanet Transit 3D Explorer?
The Exoplanet Transit 3D Explorer shows a single planet's own direct brightness dip as it crosses its star - the light-curve signal that planet produces by itself. This page instead visualizes the second, indirect signal: how an unseen sibling planet's gravity shifts the first planet's transit timing.
How many planets has the TTV method found?
As of February 2020 the NASA Exoplanet Archive credited the transit-timing-variation method with 21 confirmed planet discoveries.
Is this a real orbital-mechanics simulation?
No. It is an educational approximation. The two orbital periods shown for each preset are the real published values, and the Kepler-19 preset's timing-drift amplitude and cycle length are the real published figures, but the exact wobble curve is a stylized teaching shape, not a numerical integration of the real orbits.