by Duncan Lunan

On the publication day of ‘The Sky Above You, September 2025’, ON, 2^nd September 2025, both the European Space Agency and the Daniel K. Inouye Solar Observatory published more images and information about two of the stories covered.  Both appeared in the September 2^nd issue of EarthSky, online, headed ‘Two disasters [Afghanistan and Sudan], Sharpest Ever Solar Flare Image’, also including the ESA release. 

The spectacular image of coronal loops  (Figs. 1 & 2) was taken by the solar observatory on August 27^th, and shows a bright X-class solar flare, ‘the nastiest there is’, but at the lower end of the X-class range  (Fig. 3). 

The flare appears bright and the slightly colder coronal loops above it look dark by contrast, though they’re still at very high temperature  (Fig. 4), as is the sunspot below into which they’re seen cascading in the video.  One expert compared the coronal loops to being able to see individual trees, where previously we could only see the forest.  (Paul Scott Anderson, ‘Stunning new solar flare images show unprecedented detail’, EarthSky, as above.)

The Venus flyby on August 31^st by the Jupiter Icy Moons Explorer on its way to Jupiter took no photographs because the sunlight was too intense for the cameras, which are designed to function at the much lower light level of the Jupiter system, though they worked fine at launch  (Fig. 5)  and in the first Earth flyby of August 19^th 2024  (Figs. 6 & 7). 

Passing Venus, the heat from the Sun and the heat reflected from the Venus clouds on the other side would together have been too much, and the spacecraft’s high-gain parabolic antenna was pointed towards Venus at closest approach, to reflect as much heat as possible back towards the planet.  Venus and Jupiter are still fairly close in the sky after their conjunction in August, and a dramatic photograph during the flyby shows them in line with the antenna of ESA’s Deep Space Antenna 2 at Cerebros, 77 km west of Madrid  (Figs. 8 & 9).

  As well as tracking their own spacecraft, ESA’s network often contributes to the missions of other nations, including NASA’s Deep Space Network and China’s lunar missions  (Figs. 10 & 11).  The next two Earth flybys will be in September 2026 and January 2029, finally beginning the outward coast to Jupiter in 2031  (Fig. 12).

Another of my topics was the interstellar mystery object 3I/ATLAS, which is due to pass Mars on September 24^th.  Mars is now on the far side of the Sun, and so will 3I/ATLAS be when at perihelion, when a normal comet would be at its brightest and most active.  Avi Loeb suggested that NASA’s Juno orbiter, which is about to be switched off, could use its remaining fuel to escape from Jupiter and make a close encounter with 3I/ATLAS in March, which isn’t going to happen, partly because Juno is where it is because of a problem with its engine at the last attempt to fire it.  There was a remote chance that NASA’s MAVEN probe could image the object from Mars orbit on September 24^th, as might Mars Express, Mars Reconnaissance Orbiter (MRO), Tianwen-1, and Hope, but there wasn’t much chance because 3I/ATLAS at its closest approach to Mars would still be at a distance of 0.2 AU, 1,860,000 miles.  A detailed assessment by T. Marshall Eubanks, Chief Scientist at Space Initiatives Inc., and University of Luxembourg researcher Andreas M. Hein, now puts the distance at 18 million miles, ten times that  (Robert Lea, “Interstellar invader comet 3I/ATLAS could be investigated by these spacecraft as it races past the sun:  ‘This could be literally a once-in-a-lifetime opportunity’”, Space.com, 2^nd September 2025), and that figure is confirmed in a recent post by Avi Loeb  (‘The Blind Date of Mars with 3I/ATLAS in a Month’, Medium, 2^nd September 2025).

When Comet Siding Spring  (aka Comet McNaught, because it was discovered by Robert McNaught from Prestwick)  passed Mars at 80,000 miles in October 2014, most satellites saw nothing.  Mars Orbiter Mission (MOM) saw it as a faint dot, and the Curiosity rover  (which has just completed 13 years on Mars)  captured it as a streak on a time exposure, but no details were visible.  And if 3I/ATLAS remains a dot with no coma or strong tail, there will be still less to see.  ESA’s JUICE mission to the moons of Jupiter will be at 43 million miles from it, and NASA’s Psyche asteroid mission will be at 28 million miles, so neither has much of a better chance.  3I/ATLAS will also pass through the fields of view of ESA’s Solar and Heliospheric Observatory (SOHO), NASA’s PUNCH solar monitoring spacecraft, and the Parker Solar Probe as the comet passes near the Sun, but the distances involved are still greater.  For the record, from NASA’s Europa Clipper and Psyche missions, and ESA’s HERA spacecraft, 3I/ATLAS will be too close to the Sun which they are not designed to look at.

All that brings us back to Juno, and apart from the problem with the engine, there is a question about how much fuel it has left.  The deceleration planned for 2018 would have used almost all of it, but as Juno fell towards Jupiter it would acquire a speed close to escape velocity, and Avi Loeb and colleagues calculated that in an ‘Oberth manoeuvre’ near Jupiter, an expenditure of 110 kg  (5.4% of Juno’s initial mass)  would impart the extra 2 kps needed for Juno to escape Jupiter and fly past 3I/ATLAS in March.  (‘How Close Can the Juno Spacecraft Get to the Interstellar Object 3I/ATLAS?’, Medium, August 2^nd 2025).  I did wonder if Juno would have that much fuel left at what was intended to be the end of its mission, and when I read in one article a throwaway statement that ‘Juno is very low on fuel’, I wondered even more about that, when the mission has already been extended by seven years due to the cancellation of the 2018 burn.  

Juno is spin-stabilised at 2 rpm, and it must have some active attitude control to keep photographing Jupiter and make the multiple photographic flybys which it has done of the Galilean moons.  Do the attitude control thrusters tap the same tanks as the main propulsion engine, or are they separate?  I have tried long and hard to find out, and this is an example of how you can only find things on the internet if someone else has already found them of interest, to put up.  I have read more descriptions of Juno’s instruments than I could shake the proverbial stick at, but nothing about the propulsion system since the 2016 arrival, when I got the images I used in ‘Little Red Dots, Interstellar Comet’  (ON, 24^th August 2025), and nothing whatever about attitude control.  I found one article which said that Juno could have had a further three-year extension beyond this month, but didn’t get it   (Fig. 13), and exhaustion of fuel would explain why NASA had decided to ‘abandon in place’ rather than make a final attempt to deorbit into Jupiter.

Backed by Congresswoman Anna Paulina Luna, who had made the same suggestion to NASA, Loeb asked NASA whether that was feasible at the beginning of August, and while I haven’t read all the posts he’s sent me since, he’s no longer mentioning the possibility in the recent ones like ‘The Blind Date of Mars…’ above, so presumably it’s been ruled out. 

In the last few days I’ve been seeing headlines and receiving links about a story that Mars has turned out to be internally ‘lumpy’.  As I recall that has been known since the Mariner 9 orbiter of 1971, if not from earlier flybys, so I wondered what the story was.  Recently indications have been found within the Earth’s mantle of large embedded masses, possible remnants of Gaia, the Mars-sized planetoid which collided with Earth about 4.5 billion years ago and gave rise to the Earth-Moon system we know today, but on the whole the Earth, Moon, Mercury and Venus are organised in relatively smooth concentric layers.  It turns out that the news is from ongoing analysis of the results from NASA’s INSIGHT  (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport), which landed in November 2018 and lasted until May 2022, when it succumbed to buildup of dust on its solar panels  (Fig. 14). 

Artwork showing its seismic probe going half-way to the planet’s core was of course exaggerated  (Figs. 15-17), but in the event the drill was barely able to penetrate the ground, perhaps due to a hard boulder like the one which stopped Chang’e-5’s drill 5 metres down, out of the intended 10, on the Moon in 2020. 

Scientists had to be content with surface waves picked up by the Seismic Experiment for Interior Structure  (SEIS)  experiment, and many small quakes were detected  (where the Viking 1 lander in 1976 didn’t register any), (Fig.18) but on 24^th December 2021 a 100-ton impact half-way around Mars  (Figs. 19-20), heard by INSIGHT’s onboard microphone  (Fig. 21), found by Mars Reconnaissance Orbiter in February 2022 to have unearthed ice blocks  (Fig 22), revealed that INSIGHT was sitting on an unusually thin segment of the Martian crust  (Fig. 23), and allowed seismic waves passing through the planet to be detected for the first time. 

A second, larger impact on May 4^th 2022  (Figs. 24-26), before power failed in December, proved still more informative, indicating water-bearing rock deep within the crust  (Fig. 27, James Tuttle Keane, Aaron Rodriquez, Scripps Institution of Oceanography), and now further analysis has produced results from deeper still.  They’ve been published in Bi Huixing, et al, ‘Seismic detection of a 600-km solid inner core in Mars’, Nature, 3^rd September 2025.  To quote the abstract:

“Mars has a solid inner core. We identify two seismic phases, the deep core-transiting phase, PKKP, and the inner core boundary reflecting phase, PKiKP, indicative of the inner core  [Fig. 28]. 

Our inversions constrain the radius of the Martian inner core to about 613 ± 67 km, with a compressional velocity jump of around 30% across the inner core boundary, supported by additional inner-core-related seismic phases.  These properties imply a concentration of distinct light elements in the inner core, segregated from the outer core through core crystallisation.”  

Furthermore, a major factor in the ‘lumpiness’ is that large objects striking Mars in its early history (Fig. 29)  have generated magma oceans into which they sank, becoming embedded in the mantle  (Fig. 30). 

Taken together, the two sets of data show that circulation from the core of Mars up to the mantle must be extremely slow, unlike Earth’s, where the currents take about 2000 years – something I made use of in my first story for Sydney Jordan’s Lance McLane strip in the Daily Record, ‘The Phoenix at Easter’, 1983  (Fig. 31). 

‘The Phoenix at Easter’, Daily Record, 22^nd January – 20^th May 1983, was reprinted in Jeff Hawke’s Cosmos, Vol. 9 No. 3, January 2016.  Duncan Lunan’s recent books are available through Amazon;  details are on Duncan’s website, www.duncanlunan.com.

The Sky Above You, September 2025