🌌 Exoplanet Discovery Calculator
Calculate detectability of exoplanets using transit and radial velocity methods
1.0 = Sun's radius (~696,000 km)
1.0 = Earth's radius (~6,371 km)
How to Use This Calculator
Select Detection Method
Choose between Transit Photometry (detects planets passing in front of stars) or Radial Velocity (detects star wobble due to planets).
Enter Parameters
For Transit method: Enter star radius (in solar radii) and planet radius (in Earth radii). For Radial Velocity: Enter orbital period in days.
Calculate and Interpret
Click "Calculate" to see the transit depth (for transit method) or period detectability (for radial velocity). The calculator indicates if the planet would be detectable with current telescopes.
Formula
Transit Photometry Method
δ = (Rp / R★)² × 100%
Where:
- δ = Transit depth (percentage)
- Rp = Planet radius
- R★ = Star radius
Example: Earth transiting the Sun
Rp = 1 R⊕, R★ = 1 R☉
δ = (1/109)² × 100% ≈ 0.0084%
Very small, but detectable with space telescopes like Kepler/TESS
Radial Velocity Method
K = (2πG / P)1/3 × (Mp sin i) / (M★ + Mp)2/3
Where:
- K = Radial velocity amplitude (m/s)
- P = Orbital period (seconds)
- Mp = Planet mass
- M★ = Star mass
- i = Orbital inclination
Detectable if K > 1 m/s (typical precision limit)
About the Exoplanet Discovery Calculator
The Exoplanet Discovery Calculator helps determine if an exoplanet would be detectable using the two most successful detection methods: Transit Photometry and Radial Velocity. These methods have discovered thousands of exoplanets, revolutionizing our understanding of planetary systems beyond our solar system.
When to Use This Calculator
- Exoplanet Research: Estimate detectability of hypothetical planets
- Telescope Planning: Determine if a planet candidate is observable
- Educational Purposes: Learn about exoplanet detection methods
- Mission Design: Plan space telescope observations
- Astronomy Projects: Understand why some planets are easier to find than others
Why Use Our Calculator?
- ✅ Two Methods: Calculate using both transit and radial velocity techniques
- ✅ Detectability Indicator: Shows if the planet would be detectable
- ✅ Educational Tool: Understand exoplanet detection physics
- ✅ Real-World Values: Based on actual telescope capabilities
- ✅ Free to Use: No registration required
- ✅ Mobile Friendly: Works on all devices
Transit Photometry Method
Transit photometry detects planets by measuring the tiny dimming of a star when a planet passes in front of it:
- How it Works: Measures periodic decreases in stellar brightness
- Transit Depth: The fraction of light blocked = (Rp/R★)²
- Detectability: Typically requires depth > 0.01% (0.0001) for ground telescopes, > 0.001% for space telescopes
- Advantages: Can detect small planets, measures planet radius directly
- Limitations: Requires edge-on orbit, planet must transit the star
- Success Stories: Kepler, TESS, and CHEOPS have found thousands of planets this way
Radial Velocity Method
Radial velocity detects planets by measuring the star's wobble caused by the planet's gravity:
- How it Works: Measures Doppler shift in star's spectrum as it moves toward/away from us
- Velocity Amplitude: Larger planets and closer orbits create larger velocity changes
- Detectability: Typically requires K > 1 m/s for ground telescopes
- Advantages: Can detect planets at any orbital inclination, measures planet mass
- Limitations: Best for massive planets close to star, requires high spectral resolution
- Success Stories: First exoplanet around a main-sequence star (51 Pegasi b) discovered this way
Other Detection Methods
- Direct Imaging: Photographing planets directly (very difficult, only for large, young planets)
- Gravitational Microlensing: Detecting planets by gravitational lensing effects
- Astrometry: Measuring star position changes (future method with very precise telescopes)
- Pulsar Timing: Detecting planets around pulsars by timing variations
Tips for Using This Calculator
- Larger planets are easier to detect with transit method - Jupiter-sized planets are much easier than Earth-sized
- Smaller stars make planets easier to detect - planets around red dwarfs are more detectable
- Shorter orbital periods are easier to confirm - multiple transits can be observed quickly
- For transit method, remember that only edge-on orbits (inclination ≈ 90°) produce transits
- Real detection also depends on stellar activity, brightness, and telescope sensitivity
Frequently Asked Questions
What is transit photometry?
Transit photometry detects exoplanets by measuring the periodic dimming of a star when a planet passes in front of it. The depth of the dimming reveals the planet's size relative to the star. This is the most successful method, having found thousands of planets.
What is radial velocity method?
The radial velocity method detects planets by measuring the star's motion toward and away from Earth caused by the planet's gravitational pull. This creates a Doppler shift in the star's spectrum, revealing the planet's presence and mass.
Why is Earth hard to detect as an exoplanet?
Earth is small (1 Earth radius) and orbits far from the Sun (1 AU), making it challenging. Transit depth would be only 0.0084%, requiring very precise space telescopes. The radial velocity signal would be tiny (~0.1 m/s), below current detection limits for Sun-like stars.
What makes a planet easier to detect?
Larger planets, planets closer to their star, planets around smaller stars, and planets with shorter orbital periods are easier to detect. Hot Jupiters (large planets very close to their stars) are the easiest to find.
How many exoplanets have been discovered?
As of 2024, over 5,000 confirmed exoplanets have been discovered, with thousands more candidates. The majority were found using transit photometry (Kepler, TESS missions) and radial velocity methods.
Can we detect Earth-like planets?
Yes, but it's challenging. Space telescopes like Kepler and TESS have detected Earth-sized planets, and upcoming missions like PLATO and the James Webb Space Telescope will improve our ability to find and characterize potentially habitable worlds.