Revealing the Complexity of Other Worlds

There are thousands of planets orbiting other stars—extrasolar planets, or “exoplanets,” yet in 1990, when Hubble was launched, the study of planets beyond our solar system was not even a field of research. Astronomers discovered the first so-called exoplanet in 1992. In 2008, a year before NASA's planet-hunting Kepler space telescope was launched to look for Earth-sized worlds around distant stars, Hubble took the first visible-light snapshot of a planet beyond the solar system.

These systems are very different than what astronomers had expected, and show us that star systems are quite unlike our solar system. Huge gas giant planets have been found extremely close to their stars, and many "super-Earths" two to 10 times the mass of our own planet have been discovered. Despite the unexpected discoveries, the question that drives us remains the same: Are there other planets out there that could, or do, support life?

In the last two decades, the Hubble Space Telescope has worked with other telescopes to open a window onto the mystery of planet formation. Hubble's ability to peer into nearby nebulae and to probe the regions around neighboring stars has shown us planetary systems under construction, the conditions planets form in, and numerous diverse exoplanets in unusual systems. Hubble's revelations have sometimes confirmed our ideas and sometimes showed us things we never imagined, all the while helping us better understand how planets form.

Planet Comparison Graphic

From debris disks to exoplanet diversity

Hubble early on unveiled debris disks, the scattering of small dust particles hypothesized to be produced by collisions between small planetary bodies such as asteroids in the regions around forming stars. The disks of material are produced from these grinding collisions. As disks form they flatten, become denser, and may produce planets. Hubble further unveiled planetary systems in formation through observation of stellar nurseries such as those found embedded in the Orion Nebula complex.

Exoplanet characteristics were uncovered in Hubble observations of transits and direct measurements of chemical compositions of planetary atmospheres. Numerous planets with clear skies were found, as well as others with hazy atmospheres, and several with cloudy atmospheres that could be obscuring water.

Through Hubble studies, researchers found that exoplanet characteristics vary widely, from the large “hot Jupiters”-- planets the size of Jupiter – and numerous other large gas planets, to those objects almost as small as the Earth.

Deeper understanding of parent stars

The parent stars in these systems are also diverse, from stars similar in mass to the Sun, to much smaller, active stars that may threaten the longevity of their planets. Hubble studies show that single, double and triple star systems can harbor planets.


The orbital motion of the planet Fomalhaut b observed through repeated observations with Hubble.
The orbital motion of the planet Fomalhaut b observed through repeated observations with Hubble.
Artist’s conception of a planet orbiting a binary star system.
Artist’s conception of a planet orbiting a binary star system.


STScI conducts a variety research programs and offers various tools for analyzing archive data on exoplanets from HST and other missions such as TESS, Kepler, and in the future, JWST.

Exoplanet and Planetary Science at STScI

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