WISPR 3I/ATLAS Observations
Between 18-OCT-2025 and 05-NOV-2025, the WISPR instrument on Parker Solar Probe (PSP) was able to successfully capture a sequence of images of comet 3I/ATLAS. This coincided with a period of time at which the comet was unobservable from Earth due to it being in daylight skies. The WISPR cameras are specifically designed to be able to observe very close to the Sun, and thus were able to successfully detect the comet.
We are releasing the raw science data from this observing sequence, as well as our initial cursory processed version of the images. However, there are some critical factors that any users of this data must consider. Standard operating procedure for WISPR data is to release data three months after downlink from the spacecraft. This allows the instrument team to perform the necessary calibrations to make the data useful for scientific investigation. These images have been prepared for release ahead of the typical schedule, and may still be subject to slight changes in the calibration upon further examination. Therefore, use of this data for science investigations, in its current form, is strongly discouraged. We urge anyone seeking to analyze this data to reach out to a member of the WISPR team for guidance.
The data can be obtained in one the following zip files:
- As a complete ~99MB zip file, containing both L1 and L2 FITS data, available at this link [right-click and save-as]
- As a complete ~34MB zip file, containing only L1 FITS data, available at this link [right-click and save-as]
- As a complete ~66MB zip file, containing only L2 FITS data, available at this link [right-click and save-as]
About the Observing Plan
The scheduling of observations for WISPR is such that observing plans must be prepared and uploaded to the spacecraft well in advance of the observations being obtained. An observing plan fundamentally consists of a list of dates, times, exposure times, and (when needed) field of view limits for each planned observation, as well as, in this instance, a spacecraft roll to be able to capture 3I/ATLAS in the field of view. The 3I/ATLAS image sequence was planned to occur as PSP was moving away from the Sun following its most recent encounter, but prior to downlinking the data recorded during that encounter. Thus, there were strict limits on the amount of available storage space left for recording 3I/ATLAS images.
An observing plan was formulated that would extract sub-regions of the full-field of view (to reduce the size of the data obtained and increase the total number of images), and would track the comet as it crossed the field of view of the WISPR Inner detector. While the comet would technically have also crossed the field of view of the WISPR Outer detector, no images from that camera were recorded during this period, because of operational and telemetry limitations. The observing plan was separated into daily sequences of approximately 10 images per day within a fixed subfield each day. The subfield would move on each subsequent day to account for the motion of the comet and spacecraft, and attempt to keep the comet approximately centered in the field of view.
At time of preparation, the predicted brightness of 3I/ATLAS was much fainter than it ultimately ended up as. Therefore, the observing plan sought to use the maximum exposure time possible for each subfield while attempting to minimize the saturation of the sunward side of the images. Typically, exposure times are optimized by using the longest exposure time possible that will not saturate the inner edge of the detector. Because this sequence was at larger distances from the Sun than typical WISPR observations, and because the exact location of the subfield window was changing, these exposure times were estimates of the longest allowable time to make the comet detectable, without saturating the background. Specific exposure times are recorded in the FITS headers of the provided data, following the standard FITS header keyword convention.
The observations approximately span the period surrounding the comet's perihelion (1.36au on October 29, 2025). The spacecraft was moving away from the comet during this period, starting at approximately 1.85au from it, and moving to ~2.1au by the end of the sequence.
As can be seen in the data we provide below, the images obtained on the last few days of the sequence were still somewhat saturated. Regardless, the net result is that the apparent brightness of the comet changes in each day of observations simply due to the decreasing exposure times used on each day. Therefore, any attempt to perform scientific analyses of the Level-1 images should, at an absolute minimum, normalize the data by exposure time (this, along with many other calibration steps, has already been applied to Level-2 images).
Processed Images
As widely described in peer-reviewed publications, WISPR data requires complex processing algorithms in order to remove the excess stray light from the solar "F-corona". In particular, a large span of data (several days) is required to develop accurate models that remove this excess stray light and enable clearer observation of features of interest. Give the newness of this data, and the relative small set of observations recorded during this time period, this additional processing step has not yet been performed.
However, to provide a qualitative 'quicklook' at the WISPR Observations of 3I/ATLAS we have prepared two short image sequences based upon the FITS data made available above, and using image/data processing algorithms employed locally by the WISPR science team. These images are not intended for any kind of scientific study or scrutiny, and were processed simply to enable scientists to quickly validate that the comet was detected in the observations.
Important note: By default, WISPR images are rectified relative to the top side of the spacecraft (spacecraft North). For this set of images, the spacecraft was rolled ~180 degrees to capture the comet. Thus for each movie, the Sun is toward the left of the image, and Solar North is toward the bottom of the image.
This animation shows the raw, unprocessed observations recorded by PSP/WISPR for observing interstellar comet 3I/ATLAS. You can download this movie directly as a 441kB mp4 file.
[Credit: NRL/NASA/JHUAPL. Movie processed/compiled by Phillip Hess (NRL).]
The above image sequence shows byte-scaled Level-2 images from the 3I/ATLAS observing plan. Comet 3I/ATLAS can be seen crossing the field, right to left, a little above center. The only correction made in these files is a scaling factor to try to minimize the overwhelming brightness of the solar F-corona. As described above, the comet appears to 'jump' between frames because a slightly different sub-field image was recorded each day in order to simplify the observing sequence, and optimize telemetry (storage) use.
This animation shows the WISPR observations of 3I/ATLAS in images projected to the celestial sphere, and processed to remove the bright solar corona. You can download this movie directly as a 1.2Mb mp4 file.
[Credit: NRL/NASA/JHUAPL. Movie processed/compiled by Guillermo Stenborg (JHUAPL).]
The above image sequence is also based upon the L2 FITS images from the 3I/ATLAS observing plan. Processing was applied to minimize the effect of the star field and bright solar f-corona, and project the images into an inertial reference system to showcase the comet’s evolution, which in the image frame of the FITS files is difficult to grasp because of the changing pointing of the spacecraft and data gaps during the observing time window.
Work is ongoing to process and analyze this data, and updates will be provided here when available. Again, given the complexity of the WISPR calibration process, we urge anyone wishing to perform scientific studies with these data to contact a member of the WISPR Team for assistance.