.FTS file extension

To open .FTS files on Windows, install a FITS viewer listed by NASA (for example, SAOImage DS9) and then open the .FTS file from within the viewer (File → Open).

To open a .FTS file, use a FITS-compatible image/data viewer (commonly used in astronomy), such as SAOImage DS9. Avoid renaming the extension; .fts is a common extension for FITS, and the file needs software that understands the FITS standard.

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Last updated: April 30, 2026 · Reviewed by Julian Stricker

Open on your device

Choose your operating system for a dedicated step-by-step opening guide.

How to open .FTS files

Use these platform-specific instructions to open .FTS files safely.

Windows

Install a FITS viewer listed by NASA (for example, SAOImage DS9) and then open the .FTS file from within the viewer (File → Open).
If double-clicking does not work, right-click the file → Open with → choose your FITS viewer and optionally set it as the default for .fts.

Full Windows guide

Mac

Install a FITS-capable viewer listed by NASA (for example, SAOImage DS9) and open the file using File → Open inside the app.
If Finder does not know how to open it, Control-click the file → Open With → select the FITS viewer.

Full Mac guide

Linux

Install a FITS viewer (NASA lists common options such as SAOImage DS9) and open the .FTS file from the application (File → Open).
If your desktop environment misidentifies the file type, use Open With and select your FITS viewer explicitly.

Full Linux guide

iOS

iOS may not preview FITS/FTS files in Quick Look; transfer the .FTS file to a desktop computer and open it with a FITS viewer (for example, one of the viewers listed on NASA’s FITS viewer page).

Full iOS guide

Android

Android typically does not include built-in FITS viewing; transfer the .FTS file to a desktop computer and open it with a FITS-capable viewer (for example, one of the viewers listed by NASA).

Full Android guide

Security notes

FITS/FTS files are data files (not executable), but they should still be treated as untrusted input: malformed files can trigger bugs in complex image/data parsers. Prefer opening unknown .FTS files with well-maintained FITS tools.
Be cautious with unusually large .FTS files: FITS datasets can be very large and may cause high memory/CPU usage or application instability when opened.
If a file claims to be .FTS but comes from an untrusted source and behaves unexpectedly (e.g., prompts to run code or install software), stop—FITS files should not require executing content to view.

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Can't open this file?

These are the most common causes and fixes when .FTS files fail to open.

Common reasons

The .FTS file won’t open or shows as an unknown format
The image looks blank, very dark, or has strange contrast
The file opens but metadata/headers look confusing
A program reports the FITS file is corrupted or non-compliant

Fix steps

Open the file in a FITS-capable viewer (NASA’s FITS viewer page lists common FITS software, e.g., SAOImage DS9).
If it still fails, confirm the file is actually a FITS file (FTS is commonly used for FITS, but the extension alone is not a guarantee).

OS-specific troubleshooting

What is a .FTS file?

.FTS is typically a FITS file (Flexible Image Transport System), a standardized format for transporting and archiving scientific images and associated metadata. FITS files can store multi-dimensional image data and headers (metadata) defined by the FITS standard. On many systems, .fts is treated similarly to .fits, and the official Internet media type for FITS is image/fits.

Background

FITS (Flexible Image Transport System) is a widely used standard in astronomy and related sciences for storing image data (and more generally, scientific data) together with richly structured metadata. The format is defined by the FITS Standard, which specifies how headers and data blocks are organized so that files can be exchanged reliably across platforms and tools.

In practice, .fts files often appear in workflows involving telescopes, observatories, image processing pipelines, and scientific archives. They may contain a single 2D image, multiple images, or higher-dimensional data; the header typically includes information such as coordinate systems, instrument settings, and observation details.

If you received an .fts file, it is usually best opened on a desktop OS using established FITS software. Mobile platforms often lack robust FITS viewing support, so transferring the file to a computer is commonly the most practical approach.

Common MIME types: image/fits

Common .FTS issues

The .FTS file won’t open or shows as an unknown format

Many default photo viewers do not support FITS/FTS, so the OS may not know which app to use.

Open the file in a FITS-capable viewer (NASA’s FITS viewer page lists common FITS software, e.g., SAOImage DS9).
If it still fails, confirm the file is actually a FITS file (FTS is commonly used for FITS, but the extension alone is not a guarantee).

The image looks blank, very dark, or has strange contrast

FITS pixel data often requires scientific scaling/stretching; it may not display well with default settings.

In your FITS viewer, adjust display scaling/stretch (e.g., different autoscale options) to reveal faint detail.
Check the header metadata and data type handling; some files contain high dynamic range or non-visual data arrays.

The file opens but metadata/headers look confusing

FITS headers use standardized keyword/value cards and can be extensive and technical.

Use your FITS tool’s header viewer to inspect keywords and comments; this is the canonical metadata for the dataset.
Refer to the FITS standard documentation for header structure and keyword conventions.

A program reports the FITS file is corrupted or non-compliant

Incomplete downloads, transfer issues, or non-standard writers can produce files that strict readers reject.

Re-download or re-copy the file using a reliable method and verify it was fully transferred.
Try opening with another FITS-capable tool/library (many software stacks use CFITSIO, which is widely used for FITS reading/writing).

FAQ

Is .FTS the same as .FITS?

Often, yes: .fts is a common filename extension used for FITS (Flexible Image Transport System) files. The most reliable way to confirm is to open it with a FITS-capable viewer and/or inspect the FITS header according to the standard.

What is the official MIME type for .fts (FITS) files?

The registered media type for FITS is image/fits (defined in RFC 4047 and listed in the IANA Media Types Registry). Some desktop systems may also recognize non-standard aliases such as image/x-fits.

Can I open .FTS files in normal photo apps?

Usually not. FITS is a scientific format and typically requires astronomy/scientific imaging software (for example, tools listed on NASA’s FITS viewer page).

Can I convert an .FTS file to PNG/JPEG?

Many FITS viewers and analysis tools can export the displayed image to common formats, but the export may lose scientific metadata and dynamic range. If you need the data for analysis, keep the original FITS/FTS file.

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