Exoplanet Calculator
Estimate exoplanet mass, radius, density, and orbital velocity from star mass, orbital period, and semi-major axis using Kepler's laws.
What Is an Exoplanet Calculator?
An exoplanet calculator estimates physical and orbital properties of planets orbiting stars other than the Sun. Given a star mass, orbital period, and semi-major axis, Kepler's third law links the orbit to the total system mass. With planet mass and radius, you can also find bulk density and surface gravity.
Kepler's Third Law
In solar units (period in years, semi-major axis in AU, mass in solar masses):
$$P^2 = \frac{a^3}{M_{\text{total}}}$$Orbital velocity follows from:
$$v = \frac{2\pi a}{P}$$Bulk density and surface gravity use:
$$\rho = \frac{M}{\frac{4}{3}\pi R^3}, \quad g = \frac{GM}{R^2}$$Related tools: Kepler's Third Law Calculator, Exoplanet Travel Planner, and Cube Density Calculator.
Frequently Asked Questions
What inputs do I need?
Enter star mass, orbital period, and semi-major axis for orbital calculations. Add planet mass and radius to compute density and surface gravity.
What units does the calculator use?
Star mass is in solar masses, period in days, semi-major axis in AU, planet mass in Earth masses, and planet radius in Earth radii.
How is system mass estimated?
Kepler's third law gives total system mass from period and semi-major axis. Subtracting the known star mass estimates the planet's gravitational contribution.
What is a typical exoplanet density?
Rocky planets like Earth are around 5.5 g/cm³. Gas giants are closer to 1 g/cm³. Super-Earths often fall between 3 and 8 g/cm³ depending on composition.
Can I verify a known exoplanet?
Yes. Use published values for 51 Pegasi b or Proxima Centauri b and compare the computed orbital velocity and density with catalog data.
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