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Exoplanet TOI-421 b and Its Star (Illustration)

Illustration of a bright yellow star and a blue gas giant planet with no obvious patterns or structure

Illustration of what exoplanet TOI-421 b might look like. TOI-421 b is a hot sub-Neptune-sized exoplanet orbiting a Sun-like star roughly 244 light-years from Earth. TOI-421 b is thought to have a clear atmosphere free of haze and clouds. 

This illustration is based on our knowledge of the planet and its host star, and predictions about the likely properties of the planet’s atmosphere. Spectroscopic data from Webb will help us better understand the composition of the planet’s atmosphere. 

TOI-421 b is in between Earth and Neptune in terms of size (radius 2.68 times Earth), mass (7.2 times Earth), and density (2 times water). It orbits its star at a distance of only 0.056 astronomical unit (5.6% of the distance between Earth and the Sun), completing one orbit in 5.2 Earth-days. The star, TOI-421, has a radius 0.87 times that of the Sun, a mass 0.85 times the Sun, and a temperature of 5325 kelvins (around 5050 degrees Celsius), slightly cooler than the Sun.

About the Object

  • R.A. Position
    R.A. PositionRight ascension – analogous to longitude – is one component of an object's position.
    05:27:24.79
  • Dec. Position
    Dec. PositionDeclination – analogous to latitude – is one component of an object's position.
    -14:16:36.27
  • Constellation
    ConstellationOne of 88 recognized regions of the celestial sphere in which the object appears.
    Lepus
  • Distance
    DistanceThe physical distance from Earth to the astronomical object. Distances within our solar system are usually measured in Astronomical Units (AU). Distances between stars are usually measured in light-years. Interstellar distances can also be measured in parsecs.
    244 light-years from Earth
  • Dimensions
    DimensionsThe physical size of the object or the apparent angle it subtends on the sky.
    Radius: 2.68 times Earth; Mass: 7.2 times Earth; Density: 2.05 times water; Distance from star: 0.056 AU; Orbital period: 5.2 Earth-days

About the Data

  • Data Description
    Data DescriptionProposal: A description of the observations, their scientific justification, and the links to the data available in the science archive.
    Science Team: The astronomers who planned the observations and analyzed the data. "PI" refers to the Principal Investigator.

    Illustration based on data from the Transiting Exoplanet Survey Satellite (TESS)

  • Object Name
    Object NameA name or catalog number that astronomers use to identify an astronomical object.
    TOI-421 b
  • Object Description
    Object DescriptionThe type of astronomical object.
    Hot sub-Neptune exoplanet orbiting a G-type (Sun-like) star
  • Release Date
    November 17, 2021
  • Science Release
    NASA’s James Webb Space Telescope Primed to Lift the Haze Surrounding Sub-Neptunes
    Read the release
  • Credit
    Artwork: NASA, ESA, CSA, Dani Player (STScI)

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Simulated Transmission Spectrum of Exoplanet TOI-421 b

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Details

Last Updated
Aug 28, 2025
Contact
Media

Laura Betz
NASA’s Goddard Space Flight Center
Greenbelt, Maryland
laura.e.betz@nasa.gov

Artwork Credit

NASA, ESA, CSA, Dani Player (STScI)

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