‘Lucky’ MESSENGER data upends long-held idea about Venus’ atmosphere

Posted: April 22, 2020 by oldbrew in atmosphere, modelling, research
Tags: ,


The atmosphere of Venus has surprised and puzzled scientists before.

Philosopher Nicholas Rescher once wrote, “Scientific discoveries are often made not on the basis of some well-contrived plan of investigation, but through some stroke of sheer luck,” quotes Phys.org.

For a team of researchers at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, that statement couldn’t be more true.

What started as a dry run to ensure instruments on NASA’s Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) spacecraft worked properly later turned into a 10-year saga that resulted in a chance discovery unrelated to the mission’s target planet, Mercury. It’s about Venus and its atmosphere.

The team reports April 20 in Nature Astronomy that data fortuitously collected by MESSENGER reveals a sudden rise in nitrogen concentrations at about 30 miles above Venus’ surface, demonstrating the planet’s atmosphere isn’t uniformly mixed, as expected. That finding upends an understanding about Venus’ atmosphere that has prevailed for decades.

The story started in June 2007 as MESSENGER sailed above Venus for its second flyby before veering toward Mercury. Mission instrument teams took the opportunity to test their devices and collect data before the real show was set to begin some six months later.

Among the team members was David Lawrence, a nuclear physicist at APL. He was the instrument scientist for MESSENGER’s neutron spectrometer, which detects neutrons set loose into space from cosmic rays colliding with molecules in a planet’s atmosphere or surface. It aimed to find the telltale signs of neutrons coming from hydrogen atoms in water molecules that were suspected (and later confirmed) to be frozen in the crater shadows at Mercury’s poles.

Over Venus, however, Lawrence just wanted to collect some data to verify the instrument was operating correctly. An initial check showed it worked, and the data was tabled.

But in 2010, Lawrence revisited those measurements, this time with Patrick Peplowski, another nuclear physicist at APL. Despite 50 years of sending robotic missions to Venus, including 13 atmospheric probes or landers, a lot of uncertainty about the nitrogen concentration in Venus’ atmosphere, especially between 30 and 60 miles above the surface, remained.

That puzzled Peplowski and Lawrence because nitrogen is the second most abundant molecule floating in Venus’ atmosphere, after carbon dioxide.

“The uncertainty wasn’t necessarily just in the MESSENGER instrument—it could be in the entire planet,” Lawrence said.

Lawrence knew of a 1962 paper, however, that suggested neutron spectroscopy could help determine Venus’ atmospheric nitrogen concentration. Nitrogen is fairly good at scavenging loose neutrons, unlike carbon and oxygen, which are some of the worst. So on Venus, the number of neutrons an instrument detects should depend on the amount of atmospheric nitrogen.

MESSENGER just happened to collect that information.

The pair ran a computer simulation that divvied the planet’s 60-mile-thick atmosphere into bands in which they could manipulate the nitrogen concentration and realistically model how many neutrons would come streaming out to the spacecraft above.

When they compared their models with the MESSENGER data, they found the best match was when atmospheric nitrogen made up 5% of the volume, about 1.5 times that measured lower in the atmosphere. And all of the neutrons came from a region between roughly 35 and 60 miles above the surface—exactly where there had been the greatest uncertainty.

That was very much a stroke of luck,” Peplowski said.

Why nitrogen increases at higher altitude remains unknown. Their discovery raised more than a few eyebrows, Peplowski said, but not because people were blown away.

“Many scientists seemed surprised that this was even something worth investigating,” Peplowski said. “The notion that there’s a higher nitrogen concentration in the upper atmosphere than in the lower was outside people’s range of thought.”

Full article here.
– – –
See also: The deep atmosphere of Venus and the possible role of density-driven separation of CO2 and N2 – Published: 26 June 2017

Comments
  1. oldbrew says:

    Nitrogen concentration through Venus’ atmosphere; the red line is a trend line fitted to data from multiple missions, including the MESSENGER data, which was collected between 60 and 100 km high. Image credit: Johns Hopkins University Applied Physics Laboratory.

  2. Paul Vaughan says:

    “outside people’s range of thought.”

    Same as sensible handling of corona.

  3. tallbloke says:

  4. tallbloke says:

  5. oldbrew says:

    Ackerman’s ‘An Alternative View of Venus’ has some interesting ideas. Whether any or all of them are on the right lines I don’t know, but here are a couple of quotes re. the data [bolds added]:

    Thus independent measurements on five vehicles, one measuring the energy emitted into space from the cloud tops, and four measuring some component of the up-welling or net (upwelling minus down-welling) energy flux in the atmosphere at completely different geographic locations, are consistent and indicate that Venus is radiating an enormously larger amount of energy than it receives from the Sun. In spite of this data, the authors of every one of these papers deferred to the theoretical model of Pollack, suggesting that all five of the radiation instruments on which their analyses are based, might be in error – even though there was no indication of problems in the calibration data.

    Click to access fvenuspaper.pdf

    Also from the paper:
    The High Atmospheric Pressure

    Because of the great number of active vents and the high velocities at which large volumes of sulfur are being expelled every second, an enormous mass of sulfur is suspended in the atmosphere up to 48 kilometers. It is these heavy molecules and crystals which load down the atmosphere, causing the high surface pressure (some 92 atmospheres). This implies that the large mass of CO2 assumed to be the cause of the high pressure is not present, and therefore neither is the primary source of the hypothesized runaway greenhouse effect.
    – – –
    In the graphic I posted earlier, the ‘sulfuric acid cloud layer’ is supposed to be about 95% CO2?

    From our blog post: Why nitrogen increases at higher altitude remains unknown.

    Possibly because the sulphur that crystallises at 48 km acts as a kind of boundary? (again, see earlier graphic)

    Another one from the paper:
    the CO2 channel counts from the Pioneer Venus mass spectrometer dropped dramatically as the large probe descended through an altitude of about 50 kilometers. This unexpected drop in what was assumed to be the dominant constituent of a well mixed atmosphere, was interpreted by the Pioneer Venus scientists as being caused by a blockage of the inlet leak.

    But we now know from the blog post above that it’s NOT a well mixed atmosphere.

  6. oldbrew says:

    Wikipedia’s current atmospheric profile of Venus.


    Temp. at 1 bar on Venus similar to Earth at 1 bar (= surface)?
    – – –
    Clive Best: Venus calling
    Posted on September 10, 2012

    Just a tiny 2.5% of incident sunlight (just 17 watts/m2 !) reaches the surface [2]. That is equivalent to one light bulb heating a small room. So the narrative of a runaway CO2 greenhouse effect on Venus caused by CO2 absorbing IR emitted from the surface thereby causing warming through “back radiation” (IMHO) simply cannot be true. Instead I think Venus is “heated” from the top of the atmosphere downwards via the adiabatic lapse rate.

    http://clivebest.com/blog/?p=4048

    The emission from the surface could be geothermal, hence all the sulphur in the lower atmosphere.

  7. oldbrew says:

    Published: 02 December 2012
    Variations of sulphur dioxide at the cloud top of Venus’s dynamic atmosphere

    Here we report that the sulphur dioxide column density above Venus’s clouds decreased by an order of magnitude between 2007 and 2012 using ultraviolet spectrometer data from the SPICAV instrument onboard the Venus Express spacecraft. This decline is similar to observations during the 1980s.

    https://www.nature.com/articles/ngeo1650
    – – –
    Ackerman: Our scenario predicts that Venus is not in a steady state condition. Indeed, a continuous decrease in the amount of sulfur dioxide in the highest clouds of Venus has already been measured remotely since the Pioneer Venus mission in 1979. Advocates of a steady state Venus are forced to explain this as being due to the eruption of a large volcano just before that mission, since they absolutely cannot believe the planet is cooling continuously at a significant rate.
    . . .
    For instance, it would be of interest to determine if any significant change has occurred in the extent of the ‘Hadesphere’ as defined by the altitude of the lower cloud layer. We predict that this will continuously decrease with time, and that the next atmospheric probe will find a measurable decrease in its altitude compared to that found by Pioneer Venus.

    [all bolds added]

    Click to access fvenuspaper.pdf

  8. pochas94 says:

    Just as a helium (mw=4) balloon will rise in the earth’s atmosphere (mw=29), a nitrogen balloon (mw=28) will rise in a CO2 atmosphere (mw=46). There is a buoyancy effect even with individual atoms.

  9. oldbrew says:

    Scientists baffled to discover that Venus’ spin is slowing down
    Posted: September 2, 2013 by tallbloke

    https://tallbloke.wordpress.com/2013/09/02/scientists-baffled-to-discover-that-venus-spin-is-slowing-down/
    – – –
    Has it had a long time to resolve its spin rate, or not?

  10. oldbrew says:

    Sulfur dioxide in the Venus atmosphere: I. Vertical distribution and variability
    2017

    Abstract
    Recent observations of sulfur containing species (SO2, SO, OCS, and H2SO4) in Venus’ mesosphere have generated controversy and great interest in the scientific community. These observations revealed unexpected spatial patterns and spatial/temporal variability that have not been satisfactorily explained by models. Sulfur oxide chemistry on Venus is closely linked to the global-scale cloud and haze layers, which are composed primarily of concentrated sulfuric acid. Sulfur oxide observations provide therefore important insight into the on-going chemical evolution of Venus’ atmosphere, atmospheric dynamics, and possible volcanism. [bold added]

    https://www.sciencedirect.com/science/article/abs/pii/S0019103516303281
    – – –
    Open Access
    Published: 13 August 2018
    Venus Atmospheric Thermal Structure and Radiative Balance

    The question of the absorbers of sunlight in the Venus cloud layer is still very much unsettled.
    . . .
    Surprisingly, almost no absorption of sunlight occurs between 57 and 48 km where the bulk of the cloud layer is located.
    . . .
    Due to its high albedo the planet absorbs only 157.6 6 W m−2 on average, less than that deposited on Earth (∼240 W m−2), despite the fact that Venus is 30% closer to the Sun. Both models and observations show that less than 10% of the total solar energy incident on Venus reaches the surface. The largest portion of solar energy is absorbed above 57 km by the unknown UV absorber at the cloud tops. This is in contrast with the Earth, where 74% of the solar energy is absorbed directly at the ground level (Arking 1996).
    [bold added]

    https://link.springer.com/article/10.1007/s11214-018-0525-2

    But 100% of the atmospheric pressure reaches the surface. How is carbon dioxide supposed to ‘trap’ radiation that never reaches the surface in the first place?

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