The 480-Kilometre Ring Under Wilkes Land Is Three Hills And A Tension Setting
Two geophysicists, paid separately by this newspaper and kept apart, rebuilt the raw flight-line data at five-kilometre spacing instead of twenty-two. Where newer data are dense, the closed circle separates into three anomalies with nothing joining them.
HOBART, Australia — Re-gridded at five kilometres, the ring is not a ring.
Two geophysicists, working separately and with no contact between them, rebuilt the gravity field over Wilkes Land from the raw flight lines rather than from the published grid. Both of them got three hills.
The anomaly itself is not in dispute. Something around 480 kilometres across sits under the ice of East Antarctica, it is dense, and it has been visible in the potential-field data since the 1970s. The question this newspaper set out to answer was narrower: whether the circle is a thing in the ground or a thing in the arithmetic.
The lines were 22 kilometres apart
The airborne lines that produced the familiar image were flown 22.2 kilometres apart. That was a reasonable reconnaissance spacing for the aircraft, the fuel and the navigation of the time, and nobody involved pretended otherwise.
Between any two lines there is no measurement. None. The image is not a picture of the subsurface; it is a surface drawn through beads that are twenty-two kilometres apart.
The published grid was made by minimum curvature, an interpolator that fits the smoothest surface passing through the observations. Smoothest is a setting, not a fact, and it is governed by a tension parameter. At the tension used, features separated by roughly the line spacing close into one another.
That is not a defect. It is what the setting is for. It is stated plainly in the campaign's own grid documentation, which has been public for fifty years and which we have republished with this brief.
What two strangers found
We commissioned Dr. Ifeoma Vasconcelos-Idowu in Perth and Dr. Callum Trethewey in St John's. Neither was told the other existed. Both were paid the same fee in advance, on the written condition that their results would run whether or not they agreed with each other, or with us.
Both received the same package: the original profiles, and a 2016 campaign flown at five-kilometre spacing that covers about 40 per cent of the anomaly's footprint.
Over that 40 per cent, the closed ring comes apart. Three positive Bouguer residuals stand at 68, 51 and 44 milligals. Between them, along the line where the western arc is supposed to run at its strongest, the field measures six milligals. Both reconstructions call that noise.
The two of them differ on the peak values by less than three milligals. They agree that nothing joins the highs.
What three hills might be
Neither geophysicist would say what the highs are, and both were asked twice.
Trethewey's written answer is that a forty-kilometre positive residual under two kilometres of ice is consistent with a dense intrusive body, a mafic complex, or a buried basement high, and that the list of dull possibilities is long and he is not going to shorten it for a newspaper.
Vasconcelos-Idowu adds the sharper point. The impact reading was never carried by the gravity magnitude. It was carried by the shape. The shape is the part we have just taken away.
The part we cannot answer
Professor Marit Sundqvist-Ahearn has defended the circular interpretation in print since 2015. She was sent the full draft, both re-grids and both parameter logs, and her reply is at the foot of this page.
Her strongest objection is one this desk cannot dispose of. The 40 per cent we can see is the eastern and central sector, which is where a degraded rim would be thinnest and most deeply buried. We looked at the part of a hypothetical ring most likely to be missing, found it missing, and put that in a headline.
Three highs on a common arc are consistent with three separate bodies. They are also consistent with a broken rim sampled in the wrong place. Our data do not choose between those, and we should not have written as though they did.
The other 60 per cent of the area still has 22-kilometre gaps in it, gridded at the same tension as before, so we can say the ring is not there where the data are dense and nothing whatever about the rest.
We have asked the operator whether the 2019–21 flights over the remaining area will be released, and are told 2027.
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Sources & Method
We bought the raw profiles rather than the published grid, and paid two geophysicists who do not know each other to re-grid them independently, in advance, on the written condition that both results would run whether they agreed or not. Their parameter logs are published alongside their grids so that the tension settings we criticise can be checked against the ones we chose.
Who we spoke to
- Dr. Ifeoma Vasconcelos-Idowu, Potential-field geophysicist, Perth. Commissioned to re-grid the raw lines with no sight of the second commission and no contact with its author April–July 2026 Her working file, grids and parameter log are published entire with this story.
- Dr. Callum Trethewey, Potential-field geophysicist, St John's, Newfoundland. Given the identical data package, blind, on the same written terms and the same fee April–July 2026 Differs from Vasconcelos-Idowu on peak values by less than 3 mGal. Differs from her sharply on what the highs are.
- The raw airborne line data, 1970s campaign, Levelled and unlevelled profiles, with the original grid-parameter documentation. Obtained from the national data centre at the published reproduction cost of A$1,180 March 2026 The documentation states the tension setting. It has been public for five decades.
- The 2016 aerogeophysical campaign operator, Holder of the 5-kilometre lines and of the unreleased 2019–21 flights. Written questions, answered in writing after twenty-six days July 2026 Confirms the remaining area was flown. Gives 2027 as the release year and will not be narrower.
- Prof. Marit Sundqvist-Ahearn, Geophysicist; has defended the circular interpretation in print since 2015. Sent the full draft and both re-grids; replied in writing with twenty-one days taken August 2026 Her reply is printed unedited and contains the objection this desk cannot answer.
What we could not confirm
- Whether the three highs are separate bodies. Gravity cannot tell us. Three closed residuals at the surface of the ice are consistent with three intrusions, with one deeper mass whose top is irregular, and with several other arrangements neither geophysicist would rank for us.
- The levelling of the 1970s profiles. Both re-grids inherit the original campaign's tie-line adjustments, which were done by hand and are not fully documented. A systematic level shift of a few milligals between adjacent flight blocks would not create the saddle we measured, but it would change the peak values we print.
- The other 60 per cent. It is still gridded across 22-kilometre gaps by the same method at the same tension, and everything in this brief that sounds like a conclusion applies only to the two fifths where the newer lines run.
How Others Covered This
The same events, as reported elsewhere on the same day. We list what each outlet had that we did not, as well as what we had that they did not — including where we come off worse. Why we print this.
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The Meridian TelegraphTHE SCAR BENEATH THE ICE: 480 KILOMETRES WIDE AND NOBODY WILL NAME IT
Treated the published image as an observation and asked what could have made a hole that size.
Had that we did not
The magnitude, correctly, and the fact that the anomaly has never been explained away.
Left out
The line spacing. The figure is reproduced at full width with no statement of how far apart the measurements behind it were taken.
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Signal & LedgerLegacy Line Spacing And What It Costs To Re-Fly A Continent
Read the whole thing as a procurement problem for readers who commission airborne geophysics.
Had that we did not
A clear and useful account of why 22-kilometre reconnaissance spacing was the right decision in 1972.
Left out
That a grid made for reconnaissance has spent fifty years being read as a map of a structure.
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They Buriedthis newspaperThe 480-Kilometre Ring Under Wilkes Land Is Three Hills And A Tension Setting
Paid two strangers to rebuild the field from the raw lines and printed both reconstructions whole.
Had that we did not
The tension parameter, the saddle measurement, and the 60 per cent of the area we still cannot speak about.
Left out
Our headline says the ring is three hills. Our own second-to-last line says we have only looked at two fifths of it. A headline should not be able to survive its own caveat. — V. Ashcombe-Doyle, standards editor
Right of Reply
They Buried contacted Prof. Marit Sundqvist-Ahearn, geophysicist on 29 July 2026, in writing, with the full draft, both re-grids and both parameter logs, and no deadline. Replied 19 August 2026. Printed in full and unedited.
You have done a competent piece of work and drawn a conclusion it does not support, and I would like to be precise about which part is which.
The competent part: yes, the published grid closes features at about the line spacing, yes, that is the tension parameter doing what tension parameters do, and yes, anyone who has read the figure as a photograph of the subsurface has misread it. I have said this in seminars for a decade and it is pleasant, if slightly galling, to see a newspaper say it louder.
Now the part you have got wrong. You have five-kilometre coverage over 40 per cent of the footprint. You have not told your readers where that 40 per cent is. It is the eastern and central sector. It is, as it happens, the sector where any ring structure of that age would be most degraded and most deeply buried, because it is where the sub-ice topography is lowest and the sedimentary cover thickest. You have looked at the part of a hypothetical rim most likely to be absent, found it absent, and headlined that the rim is not there.
Three positive residuals lying on a common arc is not the refutation of a ring. It is one of the ordinary appearances of an old and broken one. I am not asking you to believe in the ring. I am asking you to notice that your observation is equally consistent with both readings and that you have reported it as consistent with one.
On your saddle. Six milligals is small, and I accept your reconstructions agree on it. But a saddle between three highs is what you get when you remove the interpolator's bridging, and it is also what you get when a rim has been thinned. You cannot use the absence of a bridge you have just stopped building as evidence that nothing was ever there.
And I would ask you to think about the sentence you have put second-to-last. You have written the caveat that unmakes your headline and you have put it where a reader has already stopped. That is not a failure of honesty. It is a failure of arrangement, and in my experience it is the more common one.
Published unedited under our right-of-reply guarantee.
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