Recently, Gilbert Levin, one of the experimenters behind the Viking labeled release experiment, wrote this letter to the editors of Science. He makes this claim of particular interest

Chlorophyll was reported by spectral analysis of the Martian surface and on newly-appearing material on the lander deck [Levin does not say, but he likely means the Pathfinder lander]. Although the respected scientist who made this claim withdrew the published peer-reviewed publication, inducement is suspected.

Some further digging reveals this interview, in which Levin claims

He [Levin] told me [interviewer] of Carol Stoker, who, in 2002 thought she had detected traces of chlorophyll on Mars, strongly suggesting current life. [...] Levin believes that "NASA made her withdraw the paper."

Around the same time, in 2002, The Guardian reported on the discovery of chlorophyll also:

The Nasa team analysed data obtained by the Pathfinder mission to the red planet which suggests there could be chlorophyll

So. If we believe Levin, there is a peer-reviewed, published, and then retracted paper reporting on the discovery of chlorophyll on Mars. It was likely published some time around 2002, and the author list likely included Carol Stoker. I would very much like to find this paper.

  • 2
    $\begingroup$ Your excerpted quote from the interview with Gilbert Levin implies that Levin claimed NASA made Stoker withdraw a paper related to chlorophyll in 2002, however, the linked article associates the statement "NASA made her withdraw the paper" with a separate claim in 2005 that there may be life on Mars in caves based on methane signatures. $\endgroup$
    – kgutwin
    Nov 2, 2020 at 17:47
  • 3
    $\begingroup$ The full quote from the interview with Levin continues: "When he asked her about it last year at a talk he gave for the Mars Society: "She said, 'Oh, I never said that!'" But he has little doubt: "They had her terrified for her job!" he said. "It's Galileo all over again."" Note that Levin, who has much to gain from the positive discovery of life on Mars, is the one implying suppression by NASA, not Stoker. $\endgroup$
    – kgutwin
    Nov 2, 2020 at 17:52

1 Answer 1


Google searching for "carol stoker chlorophyll" found this Slashdot comment from April 2002 commenting on the controversy, particularly around a BBC article that described the situation in slightly overhyped detail. The comment included a verbatim quote of a poster abstract that was to be presented at the second Astrobiology Science Conference later that month.

Search for spectral signatures of life at the Pathfinder landing site
Carol Stoker NASA Ames Research Center, Pascal Ashwanden NASA Ames Research Center
The Superpan, an image product from the Pathfinder lander camera, is a multispectral panorama of the Pathfinder landing site acquired in 15 wavelengths in the spectral range 440 - 1100 nm. We have performed an automated search of the Superpan image cubes for the spectral signature associated with chlorophyll. First, images were calibrated to radiance values and then the multispectral images were co-registered to subpixel accuracy. An automated pixel-to-pixel search was performed on a 3-filter set of images (530 nm, 670 nm, 980 nm) to identify pixels where the following condition was met: 530 nm > 670 nm, and 980nm > 670 nm. Thus, we searched for the spectral signature associated with red light absorption by chlorophyll. When this case was met by the search routine, we plotted a full spectrum for the involved pixels and carefully examined the images. The condition was met for small areas in six image cases. All of these cases occur in near field images, where resolution is highest. Four of the cases occur on the spacecraft and appear to be associated with spacecraft structure. Two intriguing cases occur in small areas on the ground near the spacecraft.

This abstract is published in the International Journal of Astrobiology, 1 (2) : 87–176 (2002) [DOI: 10.1017\S147355040200112X] and can be found in this PDF at page 162.

It is quite plausible that the claims of a "withdrawn paper" originate with this published poster abstract and the controversy that followed. I could not find any references online to a "retracted" paper by Carol Stoker.

  • $\begingroup$ So in this case the "spectral signatures of life" is only (a > b) x (c < b)? and the take home would be "Life on Mars!" Yikes! As an entry in a school science competition it would be fine, but at an Astrobiology Science Conference I think any good friend would recommend against this particular language. $\endgroup$
    – uhoh
    Nov 2, 2020 at 23:41

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