by Duncan Lunan

In a month when the heavyweight players in space have been relatively quiet, this is a good moment to take note of two important spacecraft which are no longer with us.

Japan’s Akatsuki Venus probe was launched on May 20^th 2010  (Figs. 1 & 2), and made history as the first interplanetary probe to use solar sail propulsion  (Figs. 3, 4 & 5). 

That was a success but the intended rocket braking into orbit failed  (Figs. 6, 7 & 8)  and the spacecraft, already separated from the sail, went on into circumsolar orbit. 

A prolonged effort by the engineers of the Japanese agency JAXA brought it back five years later, to a much higher orbit than first planned, but from there it made extensive discoveries of previously unknown features in the upper and lower atmosphere  (Figs. 9 & 10).  But in December 2025 it was announced that contact with Akatsuki had been lost a year before, and the mission had finally been declared over, leaving no spacecraft currently monitoring the planet.

NASA’s MAVEN probe  (Mars Atmosphere and Volatile Evolution Orbiter), launched in 2013, has had a much more sudden end after a long and successful career studying the evolution of the Martian atmosphere over time.  Although still working perfectly, it was scheduled to be switched off by the Trump administration, and has pre-empted that by falling silent, on the far side of the planet, during observations of the interstellar object 3I/ATLAS in November.  Conspiracy theorists have made a big deal of that, but the ‘comet’ was over 18 million miles away at the time, and none of the other spacecraft observing it was affected.  Investigation is continuing but all that’s known is that MAVEN may have undergone a sudden increase in spin rate, for which there could be many possible causes including a meteor impact.  For years now MAVEN has been acting as a communications relay for the Curiosity and Perseverance rovers on the Mars surface, but fortunately there are other orbiters to fill the gap  (Fig. 11).

I’ve held back for a month on 3I/ATLAS in case there was a big story following its passage behind the Sun on October 21^st, perihelion  (closest approach to the Sun), at over 125 million miles on November 29^th, and its closest to Earth at 167 million miles on December 19^th.  What has happened instead is a continuing build-up of facts which take 3I/ATLAS still further from the status of ‘a typical comet’, a mantra which continues to be repeated by people who really ought to know better.  Prof. Avi Loeb, the chief originator of alternative ideas, has not unreasonably objected to Britain’s Chris Lintott having dismissed his work as ‘madness on stilts’.  But at the other extreme, by the first week of December he had lost patience with a YouTube site which was broadcasting absurd caricatures of his idea, backing them up with videos which were generated by AI and obviously false, e.g. not showing a facial injury he had sustained shortly beforehand.  YouTube conceded his point after a relatively mild threat of legal action  (by comparison with you-know-who), but within hours another one equally false had appeared in its place.

Picking up where I left off, my last reports on 3I/ATLAS were in ‘The Sky Above You, November 2025’  (ON, 3^rd November 2025)  and ‘Interstellar Comet Updated’  (ON, 23^rd November).  The issues at the time mainly concerned the jets coming off from the nucleus, one very large one going sunwards  (Fig. 13)  and up to seven travelling rearwards  (Fig. 14). 

I saw at least one media story describing the sunward jet as ‘terrifying’ and as a retrofire thrusting 3I/ATLAS towards Earth, which isn’t actually how retrofires work.  Avi Loeb raised the point that the jets had to be travelling with considerable speed to remain straight, when they should have picked up the rotation of the nucleus, which was estimated from variations in brightness to be about 16.6 hours.  I backed him up with illustrations of Comet Swift-Tuttle, the Great Comet of 1862, which also had seven jets, but they could be seen curling around the nucleus as it rotated  (‘Interstellar Comet Updated’.)  The linear nature of the jets this time was clearly shown by images taken in Italy on October 30^th  (Fig. 15), and from Namibia on December 12^th  (Fig. 16). 

As more images came in from spacecraft such as MAVEN, Europa Clipper and the navigational camera on JUICE, from the Hubble Space Telescope, and the ground-based observatories including amateur ones that were now within range, it became apparent that the sunward jet was much larger than the others  (Figs. 17 and 18). 

Avi Loeb also pointed out that the 16.6 hour rotational period, supposedly tracking bright features on the nucleus of 3I/ATLAS, was conjectural and not supported by the evidence, in his view.  He remarked that there might be some other cause, to do with emissions from the surface, and that it resembled ‘breathing’ – at which some journalists rushed to say that he thought the comet was ‘alive’.  Letting that one stick to the wall, as my late father would say… 

This jet had already proved to contain a great deal of dust, some metallic and seemingly a highly refined form of nickel.  The idea that 3I/ATLAS  might be a highly reflective metal object, perhaps with a dense coating of dust accumulated from the interstellar medium over billions of years, was still on the table  (Fig. 19). 

Avi Loeb calculated that ordinary comet dust, driven off by solar heating, should be turned back by sunlight pressure within 5000 km of its origin.  But x-ray images obtained by JAXA’s XRISM telescope on the International Space Station at the end of November (Fig. 20), backed up by more three days later from ESA’s XMM-Newton telescope  (Fig. 21), showed that the sunward jet had to be at least 400,000 km long, more than the distance from the Earth to the Moon.    

The discovery of the x-rays caused more panic headlines, supposedly confirming the change in trajectory because x-rays are generated by the plasma around spacecraft entering the atmosphere.  Indeed they are, and large incoming comets or asteroids would kill people in the line of sight that way, even before they struck the ground.  Sydney Jordan illustrated that in my Lance McLane story ‘The Phoenix at Easter’  (Daily Record, 1982-83, Fig. 22)  But the temperatures and densities around  3I/ATLAS are nothing like those around a re-entry fireball, and x-rays are quite commonly generated when solar wind particles strike the gases of comets.  

New images taken by the Hubble Telescope on November 30^th  (just after perihelion), December 12^th and December 27^th, added a new dimension to the situation.  In those focussed on the region within 24,000 km of the nucleus  (Fig. 23), three prominent jets stand out, 120 degrees apart.

In the November one the lower jet is seen to be structured, and the December one shows that the structure has expanded into three larger, fainter blobs.  In the images looking out to 100,000 km  (Fig. 24), the structure can be seen in the earlier one  (not to be confused with the line of three stars alongside), but it can’t be seen on the later one. 

Images taken in Belgium on 27^th December confirmed the 400,000 km estimate for the sunward jet’s length, with one processed to show it in full  (Figs. 25 & 26).

I shall probably be damned for saying this, but somebody has to.  What these blobs look like are the ones expelled in polar jets by outbursts from neutron stars, stellar black holes and supermassive black holes at the hearts of galaxies – expelled and then illuminated by subsequent bursts of radiation emitted by matter falling into the superdense objects.  The idea that 3I/ATLAS might contain a superdense power source has been mooted in speculative articles, and even Avi Loeb has given thought to the idea that its brightness might at least be due to an artificial light source.  All such ideas have been dismissed with the ‘just a typical comet’ refrain.  But it’s perhaps worth mentioning again  (as in ‘Interstellar Comet Update’)  that the amount of material emitted by  3I/ATLAS before and during perihelion suggests a diameter of 20-30 km, where the latest estimates from the HST centre on 2 km as the most likely value.  As far as I know, that problem and the related mass discrepancy have yet to the resolved.

The new data allow the characteristic of the dust to be calculated, and the particles are between 1 and 100 μm in diameter, at least 10 times the size of ordinary comet dust, possibly dense enough to make the inner region around the nucleus opaque.  It’s possible that the brightness of  3I/ATLAS is coming from a highly reflective cloud rather than the nucleus itself.  That may be confirmed by infrared images of the dust in the spikes  (Figs. 27 & 28). 

And what is very hard to understand is how the jets manage to remain so compact  (‘highly collimated’)  over such large distances, unless they’re constrained by magnetic fields, like the particle streams of solar Coronal Mass Ejections, or the plasma jets from supermassive black holes.  What could be generating such fields in a ‘typical comet’ is a question to which I’d love to hear an answer. 

It’s also noteworthy, and atypical, that the material holds its geometric relationship to its source, despite the supposed rotation – which may instead be 15 hours 50 minutes, which is quite a difference.  Once the material was moving away from 3I/ATLAS sunwards, at high speed, orbital dynamics should have taken it on different orbits, smearing out the spikes and separating it from its source.  It seems that the pattern of material around 3I/ATLAS is being replenished, and that has led Avi Loeb to a new and much more surprising, suggested layout for the process.

In this model, the rotational axis of 3I/ATLAS was originally pointing to the Sun – a remarkable circumstance in itself.  The material of the sunward jet is coming from a source 7 degrees off that axis, responding to sunlight as it turns and generating the supposed ‘breathing’ effect, which is a product of the wobble in the jet as 3I/ATLAS approached perihelion and the Sun tracked across the sky.  But still more remarkably, there’s a corresponding source at the same latitude on the opposite hemisphere – and what seems extraordinary is that the two of them have swapped roles after perihelion, with the source that was previously less powerful having stepped up to precisely the same output, with precisely the same composition, seamlessly taking over the job of maintaining the sunward jet which makes 3I/ATLAS atypical of comets, in so many ways.

The other matter which Avi Loeb has raised, is that the acceleration given to 3I/ATLAS by the matter ejected from it, has had the effect of lining up its path with the edge of the ‘Hill sphere’, where Jupiter’s gravity is balanced by the Sun’s.  Jupiter’s Hill sphere is a large target, which would take up a large area of sky if we could see it.  But to gain any noticeable effect there would require meeting it precisely at a tangent, and although Prof. Loeb says that rocket manoeuvres can very easily be made there, and indeed that’s true – it only happens if you’re moving at very low speed, which 3I/ATLAS very definitely is not.  In his contribution to my Incoming Asteroid!  What Could We Do About It?  (Springer, 2013), Prof. Colin McInnes explained how the well-known Lagrange points, special solutions to the three-body problem  (Fig. 29), are themselves special solutions of ‘3-dimensional periodic orbits that emerge from the first bifurcation of the planar Lyanpunov family’. 

Considering such orbits as examples of ‘flattened spacetime’, as the late Prof. Robert Forward had named the Lagrange points, he and his colleagues had identified 12 small asteroids which might be captured at the Earth-Moon L1 and L2 points with velocity changes of under 500 metres per second.  But the point was that the captures all involved starting with a velocity of that order.  It’s far, far below 3I/ATLAS’s 58 kilometres per second, approximately 130,000 miles per hour, and to take it anywhere meaningful almost all of that velocity would have to be shed.  But if 3I/ATLAS has near-unlimited amounts of power, maybe what it’s going to do is to use the cloud as reaction mass to take it up to a really useful interstellar velocity.  That would silence the critics, at any rate. 

(It would also provide an actual instance of something that repeatedly annoyed me in my childhood, when adults, ignorant of Newon’s Third Law of Motion, would insist that space travel was impossible because ‘rockets have to push on the air behind’.  The New York Times ridiculed Dr Robert Goddard for that supposed mistake in 1926.  They apologised on the day of the Moon landing, which did him little good as he had lived, worked and died as a recluse in response to their abuse.)  

Hill sphere surface are another example of the ‘isogravispheres’ which I mentioned in ‘Let’s Talk about the Neighbours’  (ON, 22^nd June 2025).  For my Man & the Planets  (Ashgrove Press, 1983), the late A.T. Lawton calculated the shape of the Sun’s isogravisphere, and found it to be a lot more convoluted than one might expect, extending to 10 light-years in some directions but deeply penetrated by dents, funnels and bubbles generated by nearer stars.  Back in the 1960s, the late poet David Godwin had suggested that near such boundary regions, the path of an object in space in multiple gravitational fields might cease to be predictable and become a matter of probability – and then he cited the idea, current at the time in the pages of Astounding and later Analog, that ‘psi’ powers such as psychokinesis or teleportation might result from manipulating probability.  He imagined spaceships powered merely by thought, sweeping through the Galaxy from one such gateway to the next.  (Although Tony Lawton liked the imaginative ideas, when they came up in my Man and the Planets, he insisted that they had to be clearly differentiated from his own.)

Quoting David Godwin there put me in touch with a Russian student, Natasha Leonov, who believed that quantum tunnelling might be achieved on a macroscopic scale, by manipulating probability.  Unlike ‘gates’ in regions of high space-time curvature such as black holes, Natasha’s idea could be tested in very low-curvature, ‘flat’ spacetime between the stars;  but once perfected, might be used even within a gravitational field, especially in Bob Forward’s ‘flattened spacetime’ mentioned above.  Frankly, Natasha’s maths were beyond me, and I haven’t heard from her since she returned to Russia;  but as they take us away from the highly speculative subject of ‘psionics’, if there is anything to them, and if 3I/ATLAS is by any chance from a culture maybe 9 billion years ahead of us, maybe when it passes Jupiter on March 14^th, it will do something that will really surprise us.

All of the December posts by Prof. Avi Loeb used here, 14 in all, can be accessed at Medium.com on payment of a subscription.  For discussion of Prof. McInnes’s ideas, Dr. Robert Forward’s and Natasha Leonov’s, see Duncan’s Children from the Sky  (Mutus Liber, 2012), and Incoming Asteroid  (2013).   Those and his other recent books are available from bookshops and through Amazon;  for details see his website, www.duncanlunan.com.