by Ruth Titz-Weider, May 2025
This workhorse of astronomers has been in use for more than 30 years. It was developed by NASA with the support of ESA. Progress has been made in all fields of astronomical research thanks to its data, be it classic celestial bodies such as planets, stars and nebulae or mysterious objects such as black holes, galaxies, dark matter and dark energy. Hubble takes pictures at different wavelengths, not only in the visible range, but also in the ultraviolet spectral range from 100 nm to the near infrared at 2.5 µm. Due to its position in the Earth’s thermosphere, where there is no more interfering water vapor, it is subjected to far less disturbance than a ground-based telescope.
Hubble satellite in its Earth orbit.. Credit: NASA
A rocky start
However, immediately after its arrival in orbit on April 24, 1990, it looked more like a disaster: the surface of the 2.4 m primary mirror did not meet the requirements because a faulty control unit had been used and no independent verification of the test results had been carried out on the ground. As a result, Hubble’s images did not have the expected – and for many scientific applications necessary – sharpness.
Fortunately, the Hubble telescope orbits the Earth and is never more than 520 km from its surface. This made it possible to repair the satellite with the help of NASA’s Space Shuttle. Five missions initially enabled a corrective lens to be fitted in front of the faulty primary mirror, which was later removed again and the individual instruments were each given their own “glasses”.
Photograph of the galaxy Messier 100 before and after the corrective lens’ installation. Credit: ESA/Hubble
A big harvest
The images from the Hubble Space Telescope provide sensational insights into astronomical objects. More than one million observations have been made, which have been reported on in more than 21,000 peer-reviewed articles. Many insights have been gained into galaxies, black holes and star formation. Here are just a few:
- Confirmation that supermassive black holes exist.
- Proof that there is a black hole in the center of almost all galaxies.
- The first image of the surface of a star that is not the sun.
- Confirmation that the Andromeda galaxy will collide with our Milky Way.
The impressive images have also inspired the non-scientific public and have resonated and in some cases become iconic. A picture gallery at ESA offers a large pool of images: https://esahubble.org/images/archive/top100/
Hubble and the planets
Hubble has provided new insights not only in the large dimensions of astronomy, but also in planetary research and made them accessible to the interested public through its impressive images:
Jupiter
Photograph of Jupiter and its moon Europa, done by Hubble 25th August 2020. Credit: NASA, ESA, A. Simon (Goddard Space Flight Center), and M. H. Wong (University of California, Berkeley) and the OPAL team
This image was taken on June 27, 2020 and shows details that have never been seen before. Jupiter was “only” 644 million kilometers away from Earth. It is completely covered by clouds. The large red dot is the eye of a storm that has been raging on the planet for at least 360 years.
Water plumes on Jupiter’s moon Europa
A composite image of Jupiter’s moon Europa with suspected plumes of water. The images of the moon are from the Galileo and Voyager missions, superimposed are the Hubble ultraviolet images showing the plumes at the edge. Credit: NASA, ESA, W. Sparks (STScI), and the USGS Astrogeology Science Center
The plumes at the 7 o’clock position are probably a fountain of water vapor that can be seen in the silhouette of Europa as it passes in front of Jupiter. Hubble’s sensitivity to ultraviolet radiation made it possible to detect these phenomena rising more than 160 kilometers above Europa’s icy surface. It could originate from a subsurface ocean on Europa. The Hubble data was taken on January 26, 2014. The image of Europa superimposed on the Hubble data was compiled from data from the Galileo and Voyager missions.
Polar lights around Jupiter’s moon Ganymede
The picture of Jupiter’s moon Ganymede comes from the Galilei mission, the polar lights in the ultraviolet were photographed by Hubble. Credit: NASA, ESA, and J. Saur (University zu Köln)
An image taken by Hubble in the ultraviolet range showing two rings of auroras around the moon Ganymede. The blue rings are superimposed on an image from the Galileo mission, which shows the moon in visible light. The position of the auroras points to the moon’s magnetic field and provides clues to the internal structure of the celestial body where the magnetic field is generated. The rocking motion of the magnetic field is due to interaction with Jupiter’s vast magnetosphere and is evidence that the moon has a subsurface ocean of salt water.
New moons around Pluto and Neptun
Image of the moons of Pluto. Hubble discovered the fourth moon P4, after Charon, Nix and Hydra. Credit: NASA, ESA, and Z. Levay (STScI) Credit: NASA, ESA, and M. Showalter (SETI institute)
It was only with Hubble that it became possible to show Pluto and its companion Charon separately. Hubble’s keen eye was able to locate four smaller moons. Further companions have also been found on Neptune.
Hubble and exoplanets
Observation time with Hubble is highly sought after and it is easy to see that such an instrument will not be used to search for transit events to find new extrasolar planets. However, the space telescope has enabled important advances in the characterization of already known exoplanets.
The Hubble Space Telescope has achieved great success in the field of exoplanets by observing transits at different wavelengths. In contrast to the JWST, it not only covers parts of the infrared spectrum, but also the visible and UV range. Transmission spectroscopy is used to observe a transit at different wavelengths. Differences in the transit signals provide information about molecules in the ring-shaped atmosphere for the observer, because they absorb the starlight differently.
Spectroscopy: A method where light is split into its different wavelengths. This way, we can learn something about exoplanet atmosphere composition. Credit: ESA, CC BY-SA 3.0 IGO
Some specific exoplanets Hubble took a look at
Depiction of exoplanet HD 209458b’s atmosphere based on Hubble measurements. Credit: NASA, ESA, and A. Feild (STScI)
The first exoplanet whose atmosphere was studied with Hubble was HD 209458b in 2003. This veteran exoplanet is a hot Jupiter that was discovered in 1999 using the radial velocity method and was the first planet to be observed in transit.
Exoplanets of the sub-Neptune type have come into focus in recent years. With radii between one and four Earth radii, these are planets that we are not familiar with in our solar system and that can provide an insight into the formation and development of planets, in particular whether and what type of atmosphere they have. Observations with Hubble were often followed by further investigations with the JWST or with ground-based telescopes. Of particular interest were the strong indications of sub-Neptunes which could have an atmosphere enriched with water vapor. However, it is difficult to describe the atmosphere unambiguously on the basis of the measured spectra, and models sometimes contain ambiguities and different compositions.
Artist’s depiction of exoplanete GJ 9827d. Credit: NASA, ESA, Leah Hustak and Ralf Crawford (STScI)
Ein Beispiel ist GJ 9827d, ein Sub-Neptun mit einer Größe von zwei Erdradien, vermutlich ein Gesteinsplanet. Aus der Kombination von Transitmessungen mit Hubble und dem JWST und hat man einen sehr wahrscheinlichen Aufbau für die Atmosphäre abgeleitet: eine mit Wasserdampf angereicherte Atmosphäre (steam atmosphere) angereichert mit „schwereren“ Elementen (high metallicity).
Some specific exoplanets Hubble took a look at
Depiction of exoplanet HD 209458b’s atmosphere based on Hubble measurements. Credit: NASA, ESA, and A. Feild (STScI)
The first exoplanet whose atmosphere was studied with Hubble was HD 209458b in 2003. This veteran exoplanet is a hot Jupiter that was discovered in 1999 using the radial velocity method and was the first planet to be observed in transit.
Exoplanets of the sub-Neptune type have come into focus in recent years. With radii between one and four Earth radii, these are planets that we are not familiar with in our solar system and that can provide an insight into the formation and development of planets, in particular whether and what type of atmosphere they have. Observations with Hubble were often followed by further investigations with the JWST or with ground-based telescopes. Of particular interest were the strong indications of sub-Neptunes, which could have an atmosphere enriched with water vapor. However, it is difficult to describe the atmosphere unambiguously on the basis of the measured spectra, and models sometimes contain ambiguities and different compositions.
Artist’s depiction of exoplanet GJ 9827d. Credit: NASA, ESA, Leah Hustak and Ralf Crawford (STScI)
One example is GJ 9827d, a sub-Neptune with a size of two Earth radii, probably a rocky planet. From a combination of transit measurements with Hubble and JWS, scientists have concluded a probable atmospheric composition: an atmosphere enriched in water steam (steam atmosphere) and in heavy elements (high metallicity).
The Hubble telescope is still working and continues to deliver data. Even though it has long exceeded its originally planned mission duration of 15 years and no further repair missions can be carried out in the foreseeable future, NASA assumes that the telescope will be operational for several more years and will continue to contribute to great discoveries in astronomy for that long.
To learn more, visit the Hubble webpage at NASA or the Hubble project page at STScI.