FITS is the file format used for scientific data in the Hubble archive.
FITS stands for Flexible Image Transport System. It was designed for astronomical data and can store not only two-dimensional images but also multidimensional arrays, tables, calibration information, and detailed metadata describing an observation.
Hubble data are archived through institutions including the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute. The scientific files remain in FITS because the format preserves the information astronomers need for analysis, rather than just storing a display-ready picture.
A frequent misunderstanding is to treat Hubble archive data like ordinary photographs. JPEG and TIFF versions are produced for public-facing images, including selected Hubble Heritage releases, but they are not the archive’s primary scientific format. PNG is likewise an image format, not the standard container for Hubble’s calibrated research data.