Venus life mark, is the data processing wrong? Scientists use papers to "hammer" papers

The Surging News reporter Yu Hanqi

470 degrees Celsius, 90 times the Earth's atmospheric pressure, the "rain" is sulfuric acid, such a Venus will have a "sign of life"? Not to mention that many melon-eating masses do not believe it, and many scientists have also questioned it.

Since September 14, the University of Cardiff in the United Kingdom, the University of Cambridge, the University of Manchester, the Massachusetts Institute of Technology and other institutions jointly published an explosive paper entitled "Phosphine gas in the cloud decks of Venus" (hereinafter referred to as the "original paper") in Nature Astronomy, and the neighbor that has been snubbed for a long time has soared, and at the same time, There are also many people who pour cold water.

The most open contest in the scientific community is to use the paper to fight back against the paper. ArXiv, a website where scientists pre-upload drafts before publishing papers, became the main battlefield for "reasoned" exchanges.

On October 19, October 27, and October 28, three articles refuting the original paper appeared on ArXiv, one from a Dutch team, one from the National Aeronautics and Space Administration (NASA) team, and one British professor.

The breaking points of the three opposing articles are basically the same, pointing out that the data processing method of the original paper is inappropriate and easy to cause false results. After re-examining the telescope's original data household using independent analysis tools, let alone whether Venus's "life mark" came from life, the "sign" itself no longer exists.

You know, modern astronomers are no longer directly "looking at the stars", but "looking at data". Instead of taking pictures of the stars directly like a camera, telescopes transmit massive amounts of spectral data. What astronomers have to do is bury their heads in the data to dig through the clues and see if they can tell a story that fits some theoretical model and makes logical sense.

This involves a complex data processing process, and the final match between the data and the story is evaluated by the Statistical Society. To meet certain mathematical standards, it is a reliable story.

So, what kind of "story" is the original paper telling?

The original paper's statement

In simple terms, we can imagine that the spectrum is like a comb, and each comb teeth in turn represent light waves of different frequencies.

When the comb "combs" through The atmosphere of Venus, some of the chemicals inside absorb light waves of a specific frequency, breaking some of the corresponding comb teeth.

So, scientists can look at which comb teeth are broken on the final comb, and how long they are missing, and they can deduce what chemicals are in Venus's atmosphere and how much they are.

The original paper found that it was 267 gigahertz (GHz) that this "comb tooth" was missing a significant part. They believe that the chemical corresponding to this comb tooth is phosphine (PH3).

Also an oxygen group hydride, phosphine is as foul-smelling and toxic as the more famous hydrogen sulfide, so why can it be used as a "sign of life"?

It turns out that human beings currently only find perphosphine in the high temperature and high pressure atmosphere of the large gaseous planets of the solar system, while the highly oxidized surfaces and atmospheres of rocky planets will quickly destroy phosphine.

On our Planet, for example, the production of phosphine is only associated with human industrial production or anaerobic microbial activity.

Estimated from the degree of spectral deletion, the abundance of phosphine in the Venus cloud is 20 ppb, that is, twenty phosphine molecules per billion molecules.

The original paper read: "Exhaustive steady-state chemistry and photochemical path analysis, the presence of phosphine in Venus is difficult to explain." There is no known way of abiotic production in Venus's atmosphere, clouds, ground, underneath, lightning, volcanoes, or meteorites. ”

According to the simulations, at the temperature and concentration of Venus, the photochemical path produces this concentration level of phosphine gas, and the reaction rate is 4 to 6 orders of magnitude different.

That is, the concentration of phosphine on Venus is difficult to explain by the existing chemical knowledge of humans, which not only implies that there is life in the clouds of Venus, but may also be living life, and is also constantly producing phosphine to counteract the rapid decomposition process.

The paper concludes: "Phosphine may come from unknown photochemical or geochemical processes, or life, similar to phosphine, an biological source on Earth." ”

The voice of the opposite

Although the conclusions of the original paper were cautious, it did not directly say that there is life on Venus. But taking a step back, does this phosphine signal really exist?

The data used in the original paper came from two millimeter-wave (30GHz to 300GHz)/submillimeter-wave telescopes, namely the Maxwell Telescope (JCMT) in Hawaii and the Atacama Telescope (ALMA) in Chile.

On October 19, four Dutch scholars, including Ignas Snellen, professor of observational astrophysics at Leiden University in the Netherlands, took the lead in uploading the first "hammer" in ArXiv: "Re-analysis of the 267-GHz ALMA observations of Venus No statistically significant." detection of phosphine），

The "hammer" is the way ALMA data is processed.

The team believes that the 12th-order polynomial used in the original paper to fit the passband portion of the spectrum would lead to spurious results. With this "recipe", you can also create 5 other strong signals.

After the Dutch team reprocessed the ALMA data with its own method, the reliability of the phosphine signal was only 2σ, which did not meet the usual requirements of statistics. In short, after the Dutch team used what they thought was a more reliable data processing method, the 267GHz signal proposed by the ALMA telescope could not be said to be from phosphine.

The paper also notes that the authors of the original paper have notified everyone that the ALMA data processing script has been updated. At the same time, the data from the ALMA scientific archives are being corrected in the same way. The reprocessed data no longer includes the strong ripples of the original paper report, which corroborates the Dutch team's findings.

On October 28, Mark Thompson, a professor at the University of Hertfordshire in the United Kingdom, uploaded an article in ArXiv titled "The statistical reliability of 267 GHz JCMT observations of Venus: No significant evidence." article for phosphine absorption.

The point at which he questioned the result of the JCMT data was exactly the same as the point at which the Dutch team questioned the result of the ALMA data, which is polynomial fitting. Thompson found that the polynomial fitting process also leads to false-positive results in the JCMT spectrum. Therefore, there is no clear evidence of phosphine absorption in the JCMT Venus spectrum.

The title of the long biography of 27 people, including NASA scientist Geronimo Villanueva, is more concise and straightforward: "No phosphine in the atmosphere of Venus."

Due to "serious baseline calibration issues," the NASA team concluded that the phosphine signal in the ALMA data was invalid. They were also independently calibrated and analyzed using different analytical tools, and no trace of phosphine was observed.

The so-called phosphine signatures observed by the JCMT telescope can be explained by medium abundance (about 100 ppbv) of sulfur dioxide, which is more conventional and reasonable.

Moreover, if the signal in the ALMA or JCMT telescope is indeed phosphine, then phosphine must appear at an altitude of more than 70 kilometers, completely inconsistent with their photochemical networks.

Heat PK cold water

It is worth mentioning that the NASA team sent the article to Jane Greaves, the first author of the original paper, and Luca Maltagliati, editor of Nature-Astronomy, on October 21. On October 26, we went to the "Matters Arising" section of Nature-Astronomy.

"Renewal Matters" is a section launched by Nature at the end of 2018, and if there is a particularly interesting and timely peer commentary or interpretation of a paper previously published by Nature, it can be published in the form of "Renewal Matters". At the same time, the author of the original text who was commented on was given a chance to reply. If the editorial board considers the response to "constructively advance the discussion," it will publish the reply article in conjunction with the "Renewal Matters" article.

The Dutch team and Thompson have submitted their papers to Astronomy & Astrophysics (A&A) and monthly Notices of the Royal Astronomical Society (MNRAS), respectively, both top journals in astrophysics.

It seems that the fascinating scientific topic of "Venus Life Mark" will soon officially launch "Season 2".

Editor-in-Charge: Han Shengjiang

Proofreader: Luan Meng