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Comparison of Transit Paths (Artist’s Concept)

A red giant star is in the center of the image. An exoplanet passing in front of the star (called a transit) is shown in silhouette in a number of steps from left to right. A similar linear trajectory is shown at the bottom of the image. It is called a grazing transit rather than a full transit because it just clips the bottom of the star. This is considered a less accurate observing geometry in estimating the planet's size. Hubble Space Telescope's accuracy can distinguish between these two scenarios, yielding a precise measurement of the planet's diameter.

This diagram compares two scenarios for how an Earth-sized exoplanet is passing in front of its host star. The bottom path shows the planet just grazing the star. Studying the light from such a transit could lead to an inaccurate estimate of the planet's size, making it seem smaller than it really is. The top path shows the optimum geometry, where the planet transits the full disk of the star. Hubble Space Telescope's accuracy can distinguish between these two scenarios, yielding a precise measurement of the planet's diameter.

  • Release Date
    November 16, 2023
  • Science Release
    NASA’s Hubble Measures the Size of the Nearest Transiting Earth-Sized Planet
    Read the release
  • Credits
    NASA, ESA, Elizabeth Wheatley (STScI)

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Related Images & Videos

Artist's concept of nearby exoplanet LTT 1445Ac, which is the size of Earth. The rocky planet appears as a small black dot against a bright light-red sphere at image center. The star is in a triple system, with two closely orbiting red dwarfs — a pair of red dots — seen at upper right. Another exoplanet in the system, LTT 1445Ab is in the foreground at lower left.

Exoplanet LTT 1445Ac (Artist's Concept)

This is an artist's concept of the nearby exoplanet LTT 1445Ac, which is the size of Earth. The planet orbits a red dwarf star. The star is in a triple system, with two closely orbiting red dwarfs seen at upper right. The black dot in front of the bright light-red sphere at...

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Last Updated
Mar 10, 2025
Contact
Media

Claire Andreoli
NASA’s Goddard Space Flight Center
Greenbelt, Maryland
claire.andreoli@nasa.gov

Artwork Credit

NASA, ESA, Elizabeth Wheatley (STScI)

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