Re-analysis of Phosphine in Venus’ Clouds. (arXiv:2011.08176v1 [astro-ph.EP])

Re-analysis of Phosphine in Venus’ Clouds. (arXiv:2011.08176v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Greaves_J/0/1/0/all/0/1">Jane S. Greaves</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Richards_A/0/1/0/all/0/1">Anita M. S. Richards</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bains_W/0/1/0/all/0/1">William Bains</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rimmer_P/0/1/0/all/0/1">Paul B. Rimmer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Clements_D/0/1/0/all/0/1">David L. Clements</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Seager_S/0/1/0/all/0/1">Sara Seager</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Petkowski_J/0/1/0/all/0/1">Janusz J. Petkowski</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sousa_Silva_C/0/1/0/all/0/1">Clara Sousa-Silva</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ranjan_S/0/1/0/all/0/1">Sukrit Ranjan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fraser_H/0/1/0/all/0/1">Helen J. Fraser</a>

We first respond to two points raised by Villanueva et al. We show the JCMT
discovery spectrum of PH3 can not be re-attributed to SO2, as the line width is
larger than observed for SO2 features, and the required abundance would be an
extreme outlier. The JCMT spectrum is also consistent with our simple model,
constant PH3-abundance with altitude, with no discrepancy in line profile
(within data limits); reconciliation with a full photochemical model is the
subject of future work. Section 2 presents initial results from re-processed
ALMA data. Villanueva et al. noted an issue with bandpass calibration. They
have worked on a partially re-processed subset of the ALMA data, so we note
where their conclusions, and those of Greaves et al., are now superseded. To
summarise: we tentatively recover PH3 in Venus’ atmosphere with ALMA
(~5{sigma} confidence). Localised abundance appears to peak at ~5
parts-per-billion, with suggestions of spatial variation. Advanced
data-products suggest a planet-averaged PH3 abundance ~1 ppb, ~7 times lower
than from the earlier ALMA processing. The ALMA data are reconcilable with the
JCMT detection (~20 ppb) if there is order-of-magnitude temporal variation;
more advanced processing of the JCMT data is underway to check methods.
Independent PH3 measurements suggest possible altitude dependence (under ~5 ppb
at 60+ km, up to ~100 ppb at 50+ km; see Section 2: Conclusions.) Given that
both ALMA and JCMT were working at the limit of observatory capabilities, new
spectra should be obtained. The ALMA data in-hand are no longer limited by
calibration, but spectral ripples still exist, probably due to size and
brightness of Venus in relation to the primary beam. Further, spatial ripples
are present, potentially reducing significance of real narrow spectral
features.

We first respond to two points raised by Villanueva et al. We show the JCMT
discovery spectrum of PH3 can not be re-attributed to SO2, as the line width is
larger than observed for SO2 features, and the required abundance would be an
extreme outlier. The JCMT spectrum is also consistent with our simple model,
constant PH3-abundance with altitude, with no discrepancy in line profile
(within data limits); reconciliation with a full photochemical model is the
subject of future work. Section 2 presents initial results from re-processed
ALMA data. Villanueva et al. noted an issue with bandpass calibration. They
have worked on a partially re-processed subset of the ALMA data, so we note
where their conclusions, and those of Greaves et al., are now superseded. To
summarise: we tentatively recover PH3 in Venus’ atmosphere with ALMA
(~5{sigma} confidence). Localised abundance appears to peak at ~5
parts-per-billion, with suggestions of spatial variation. Advanced
data-products suggest a planet-averaged PH3 abundance ~1 ppb, ~7 times lower
than from the earlier ALMA processing. The ALMA data are reconcilable with the
JCMT detection (~20 ppb) if there is order-of-magnitude temporal variation;
more advanced processing of the JCMT data is underway to check methods.
Independent PH3 measurements suggest possible altitude dependence (under ~5 ppb
at 60+ km, up to ~100 ppb at 50+ km; see Section 2: Conclusions.) Given that
both ALMA and JCMT were working at the limit of observatory capabilities, new
spectra should be obtained. The ALMA data in-hand are no longer limited by
calibration, but spectral ripples still exist, probably due to size and
brightness of Venus in relation to the primary beam. Further, spatial ripples
are present, potentially reducing significance of real narrow spectral
features.

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