TOI-700 d is one of the most important planets on Lisa Kaltenegger’s list because it was the first Earth-sized planet discovered in the habitable zone by NASA’s TESS mission. It is located about 101.4 light-years away in the constellation Dorado.

Key Physical Characteristics

• Planet Type: Terrestrial (rocky) world.
• Size: It is nearly the same size as our home, at about 1.1 times the radius of Earth.
• Mass: Estimated to be roughly 1.7 times the mass of Earth.
• Orbit: It completes one orbit every 37.4 Earth days.
• The Star: TOI-700 is a red dwarf star that is exceptionally quiet. Unlike many others, it does not release violent solar flares, which is a major advantage for the survival of an atmosphere.

Habitability & Environment

In Kaltenegger’s research, TOI-700 d is a “clean” model for an Earth-like world:

• Energy Intake: It receives about 86% of the energy that Earth gets from the Sun. This puts it firmly in the middle of the habitable zone.
• Climate Potential: Because the star is so stable, climate models suggest the planet could maintain an atmosphere for billions of years without it being stripped away by radiation.
• Tidal Locking: It is likely tidally locked, but with such a calm sun, the transition zone between the day and night sides could be very stable and life-friendly.

Scientific Significance

• Double Habitable System: It is part of a system with four planets. In early 2023, a second planet, TOI-700 e, was also found in the habitable zone, making this a rare “double” target for study.
• Atmospheric Testing: Because the star is bright and quiet, TOI-700 d is a primary target for telescopes to search for water vapor and clouds without stellar activity interfering with the data.
• Earth-Size Benchmark: Since it is almost exactly Earth’s size, it helps scientists understand how atmospheres behave on planets that aren’t larger “Super-Earths.”

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Published @ March 24, 2026 9:26 am