🌍 Exoplanet Habitability Checker

Search for Life Beyond Earth

Astronomers have discovered over 5,500 confirmed exoplanets orbiting distant stars, with thousands more awaiting verification. Among these alien worlds, scientists search for planets in the “Goldilocks zone”—not too hot, not too cold—where liquid water could exist on the surface, a crucial ingredient for life as we know it.

Our Exoplanet Habitability Checker uses criteria developed by NASA’s Kepler mission and the Planetary Habitability Laboratory to evaluate whether discovered worlds could support life. Input an exoplanet’s mass, radius, orbital distance, stellar type, and atmospheric composition to calculate its Earth Similarity Index (ESI) and habitability score.

From nearby Proxima Centauri b to the intriguing TRAPPIST-1 system with seven Earth-sized worlds, discover which exoplanets are the best candidates for harboring alien life. Could we find biosignatures in their atmospheres using the James Webb Space Telescope? Start your search here!

💧 Liquid Water Requirement

The habitable zone (HZ) is the orbital distance range where a planet receives enough stellar energy for liquid water on its surface—not too close (water boils) or too far (water freezes). For Sun-like stars, this is roughly 0.95-1.37 AU. Smaller, cooler red dwarfs have HZ much closer (0.1-0.2 AU), while hot stars push it further out.

🪨 Rocky Composition

Earth-like life requires solid surfaces. Gas giants like Jupiter (~300 M⊕) won’t work. We look for planets with 0.5-10 Earth masses and densities suggesting rocky or ocean worlds. Super-Earths (2-10 M⊕) might be habitable if they have solid surfaces beneath thick atmospheres. Mini-Neptunes with massive H₂-He envelopes are less promising.

🌫️ Atmosphere Requirements

A suitable atmosphere retains heat (greenhouse effect) while not being too thick (runaway greenhouse like Venus). N₂-O₂ atmospheres like Earth’s are ideal. CO₂ can provide warming for distant planets. Water vapor indicates active water cycle. Biosignatures like O₂ + CH₄ combinations suggest life. JWST is now analyzing exoplanet atmospheres for these markers!

Which exoplanet is most Earth-like?

Proxima Centauri b (ESI ~0.87) orbits our nearest star at 4.2 light-years away in its habitable zone. TRAPPIST-1e also scores highly (ESI ~0.85). Kepler-442b (ESI ~0.84) is another strong candidate. However, “Earth-like” doesn’t guarantee habitability—factors like stellar flares, tidal locking, and atmospheric loss can make otherwise promising worlds inhospitable.

Could life exist on tidally locked planets?

Yes, possibly! Many exoplanets around red dwarfs are tidally locked (one side always faces the star, like our Moon to Earth). While this creates extreme temperature differences, thick atmospheres could redistribute heat. Life might thrive in the “terminator zone” between permanent day and night, or even under ice on the dark side with subsurface oceans.

How do we detect exoplanet atmospheres?

Through transit spectroscopy! When a planet passes in front of its star, starlight filters through its atmosphere. Different molecules absorb specific wavelengths, creating a unique “fingerprint.” JWST’s infrared capabilities can detect water, methane, carbon dioxide, and potentially biosignatures like oxygen or ozone—key indicators that life might exist on these distant worlds!

Are super-Earths better for life than Earth-sized planets?

It depends! Super-Earths (1.5-2.5 R⊕) might retain atmospheres better due to stronger gravity, have more active plate tectonics (recycling nutrients), and maintain magnetic fields longer (protecting from radiation). However, their higher gravity could make rocket launches impossible for any civilization there. Too massive (>2.5 R⊕) and they become mini-Neptunes with thick H₂ atmospheres unsuitable for surface life.