This is how science works

Last time, there was a bit of excitement about the possibility of phosphine in the Venusian atmosphere. This time, I’d like to update the current status of this result and explain how science progresses in practise.

Reproducibility

For any measurement or experimental finding to be considered true and reliable, the results must be reproducible. Independent teams must be able to reach the same conclusion with independent methods or an independent analysis. So upon the news of this exciting finding about phosphine in the Venusian atmosphere and its potential implications for life in our solar system, this is exactly what the scientific community attempted to do – to check and verify the results.

No phosphine? Mis-interpretation?

  1. 15/10/2020 Encrenaz et al. “A stringent upper limit of the PH3 abundance at the cloud top of Venus
    This team attempted to search for the same spectral feature using data from a different instrument – and did not detect phosphine, instead only placing a limit on the abundance.
  2. 19/10/2020 Snellen et al. “Re-analysis of the 267-GHz ALMA observations of Venus: No statistically significant detection of phosphine
    This team reanalysed the data used in the original study (from ALMA), and criticised the method used, suggesting that it could create spurious signals that seem to be significant, but are false. They conclude the original results are unreliable.
  3. 28/10/2020 Thompson “The statistical reliability of 267 GHz JCMT observations of Venus: No significant evidence for phosphine absorption
    This person reanalysed the other dataset used in the original study (from ALMA) and also has the same criticism of the original method used – finding that it can create falsely significant features and that in their reanalysis no indication for phosphine is found.
  4. 27/10/2020 Villanueva et al. “No phosphine in the atmosphere of Venus”
    Possibly the most robust refutal of phosphine detection came from the 26 member strong team claiming no detection of phosphine. The original dataset was, apparently, subject to severe calibration issues. Following their independent calibration and analysis (with different methods), they also did not find any evidence for phosphine. This team also considers that the most significant spectral feature indicating phosphine (PH3) could actually be explained by sulphur dioxide (SO2) — a far less controversial molecule to find in that environment.

Response of the original team

With criticism like that, the original team had to respond and defend their findings. On 16/11/2020, Greaves et al. did just that: “Re-analysis of Phosphine in Venus’ Clouds” in which they re-calibrate and re-analyse the data (removing the aforementioned issues). The detection of phosphine is “tentatively” recovered – at a level 7 times lower than that of their first paper. They also dispute the SO2 interpretation.
(At this point, it is worth noting that at least one independent group supported the detection of phosphine.)

Conclusions:
reliable, reproducible, repeatable.

Scientists don’t always agree, especially when results are new. Findings must be considered reliable enough for others to trust; reproducible by independent groups and methods; and repeatable with different experiments and new data.

So far, it seems the detection of phosphine is neither reproducible, nor reliable – failing two of these tests. Repeatable with new data? Let’s wait and see.
Progress in science is made by trial and error; consensus reached by scientific debate; it’s not always black and white.

Life on Venus?

Last week there was a bit of fuss in the news about whether scientists have found evidence of life on Venus. The short answer is: they haven’t. But they have found something very interesting.

Evidence of a molecule called phosphine (PH3) has been detected in the Venusian atmosphere. This came as such a surprise, that the researchers confirmed it with two different telescopes – the JCMT and ALMA – before publishing their result.
Full article here

Why is Phosphine interesting?

On Earth, the molecule Phosphine is produced primarily by microbial life. Although it can be made by other means, the amount detected is so large (20 parts per billion) that its production is difficult to explain. In their study, the researchers calculated and ruled out the origin of phosphine on Venus from:

— chemical reactions from molecules known to exist in the Venusian atmosphere
— chemical reactions from sub-surface material (i.e. volcanoes etc.)
— UV radiation causing reactions producing phosphine
— lightning causing reactions producing phosphine
— meteorites delivering phosphine to Venus
— large scale comet / asteroid impact delivering phosphine
— solar wind / charged particles interacting in the atmosphere…

None of these explanations could match the data. So the message is:
We have detected the presence of a molecule in the atmosphere of Venus. We can’t explain by non-microbial means, but on Earth it is produced by microbial life. Can someone explain this?
Which, with true scientific caution, is not quite the same as “We have found life!”

As Isaac Asimov once famously said:
The most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka!’ but rather ‘That’s funny…’

Venus in false colour from the Mariner 10, 1974
Credit

How was the presence of phosphine confirmed?

Slightly technical here, so feel free to skip this part.
All molecules have specific configurations of electrons occupying energy states around their atoms. When these molecules receive energy, such as from photons of light or radiation, the electrons change energy state in discrete transitions. The amount of energy corresponds to a wavelength of electromagnetic radiation. In a spectrum of light from the atmosphere, this wavelength is reduced, causing an “Absorption line” to appear.
Side note: the opposite effect of releasing energy leads to an increase in a particular wavelength, causing “Emission lines”.
Each molecule has a unique combination of possible transitions, creating a fingerprint in the electromagnetic spectrum.

The fingerprint of phosphine in the atmosphere of Venus was detected via an absorption line at 1.123 mm wavelength (i.e. infrared to radio radiation), first with the JCMT (James Clark Maxwell Telescope) and then confirmed with ALMA (the Atacama Large Millimetre / sub-millimetre Array).

The height of phosphine in the atmosphere could be determined from the width of the absorption line. As the planet is rotating, and different layers of atmosphere move at different speeds, an effect similar to the Doppler effect (why sirens change tone when they go past) causes absorption lines to broaden.

What does this mean for alien life?

We’re still looking. Venus, is a hostile place – if you were to dive through the atmosphere and had enough oxygen with you to avoid breathing in sulphuric acid, you’d still be burnt to a crisp before reaching the surface.

Nevertheless, the part of the atmosphere where Phosphine was found is the most hospitable region, with conditions most similar to those found on Earth. If life was found and confirmed on Venus, it would mean that life can survive in far more widespread conditions than previously thought. A large number of exoplanets are currently known – instead of looking for “Earth-like” exoplanets, the door would be thrown wide open for finding life in all kinds of environments.

Ultimately, we are very far from finding another home for ourselves. So in the meantime, we need to take better care of this one planet Earth that we still have.

Stay tuned, let’s see what happens next.

#BlackLivesMatter – June 10th 2020

Today, 10th June 2020, physicists have called for a Strike for Black Lives. Why? This is not only to add support to the fight against racism and violent discrimination, but also a chance for us to have some uncomfortable conversations. Black people have been and continue to be severely under-represented in academia. We can’t rewrite history, but we can change its course – so why does the percentage of black people in academia remain so low?

Why are there so few black physicists?

Recently I read this article which identified five main influences, that can be roughly categorised as representation (a sense of belonging / self-perception) and support (both academic and personal). In other words, we are discouraged if there are no examples of “people like me”. The absence of coloured physicists is striking, and something I’ve mused upon to colleagues on a few occasions. The ratio is much more biased than in wider society. At several meetings, conferences and work places there is almost always only one black academic. Professionally, I’ve encountered perhaps ~7 people; no more than 10. If you are a black person in academia – you are not alone.

How can we help?

What can we do to improve the situation, without showing favouritism or reducing people to the “token black employee”? Here are a few thoughts.
(Please note – opinions expressed are entirely my own. If I’ve unintentionally offended anyone, or if you have other ideas đŸ™‚ , do not hesitate to let me know)

  • Ensure that we visibly include historical examples of black scientists in outreach and education.
    There is a list of African American scientists on Wikipedia and we would do well to remember and advertise the achievements of Edward Bouchet , George Carruthers , James Harris , Katherine Johnson , Willie Moore , Arthur Walker and others. (and I’m ashamed to learn some of those names for the first time today)
  • Encourage black students and colleagues to join organisations such as https://www.nsbp.org/ not to form “cliques” or promote division, but as a source of support.
  • Advertise opportunities, such as the Bell-Burnell graduate fund that can support people from under-represented backgrounds.
  • Encourage black colleagues to give talks and visibly share their work, collaborate with them and cite them! (Should go without saying.)
  • Give students examples of active black researchers – this could be you too. (Famous examples include Maggie Aderin-Pocock and Neil de Grasse Tyson)

This next one is a bit astronomy specific, but we can give more thought to the cultures we refer to in historical astronomy. We can do more to include not only Asian and Middle-Eastern, but also African, Native American and Aboriginal Australian alongside historical European Astronomy.
(A few minutes on google today led me to the work of Thebe Medupe on traditional African Astronomy and of Duane Hamacher on Aboriginal Australian Astronomy. )

Finally, whilst not being true for all, black people and under-represented groups are facing an uphill battle and may be more reluctant to ask for help – which means we should be all the more willing to offer it.

We are all guilty of unconscious bias; yes, even under-represented groups will also have their own internalised biases. The first step to improvement is becoming more aware of our biases and ways to combat it.

Solar Orbiter

Yesterday, 10th February 2020, saw the successful launch of the Solar Orbiter satellite. This mission will, all being well, provide us with an unprecedented view of our sun, giving us a much better understanding of solar activity, the causes of solar flares and eruptions, as well as in-situ measurements of the solar wind. Let’s break that down a bit.

The sun’s atmosphere, is huge, yet most easily observed from Earth (without extra technology) during a solar eclipse. The uppermost part of the atmosphere is termed the Corona. The solar wind, a stream of charged particles released from the sun, reaches far beyond Earth out through the solar system, yet also has a protective effect against cosmic radiation. For some idea of the scale, the Voyager 2 satellite, launched in 1977, passed Neptune in 1989 yet left the heliosphere in 2018.

Occasionally, the sun releases a significant amount of material (plasma) in a Coronal Mass Ejection (CME). These CME events have the potential to damage and disrupt satellites in orbit around Earth, which could quickly bring down communication and navigation services on which we increasingly rely.

Part of the scientific goals of Solar Orbiter are to better understand these transient events, how and where they form, whether they can be predicted. Solar Orbiter will also give us our first close views of the suns surface near its poles. Just a couple of weeks ago, the most detailed images of the sun’s surface yet were made public, from the Daniel Inouye telescope in Hawaii, resolving for the first time details on the sun’s surface as small as…18 miles.

Despite being continuously seen from Earth, there is a lot we still do not understand about our sun. However, we will have to wait a while for Solar Orbiter to reach it’s final destination, science performance to be verified and the first results made public. Just a few more years should do it.
(see also https://www.mps.mpg.de/solar-physics/solar-orbiter )