The Sky Above You, March 2025

by Duncan Lunan

On March 14^th there will be a total lunar eclipse in the Americas, Australia and Japan, but setting in the UK before totality begins;  the spring equinox is on March 20^th, and on the 29^th there will be a partial eclipse of the Sun, better seen from northern Scotland and Ireland  (45%)  than from England  (30%).  

With four spacecraft currently heading for the Moon, and one of them already in difficulties, detailed reports on them will be in ‘Space Notes’ on March 9^th, by which time the landings of Blue Ghost and IM-2 Athena will hopefully have taken place.  The Japanese Resilience probe is in a long orbit around the Moon, waiting for a suitable orientation for a landing in the far lunar north, in Mare Frigoris, the Sea of Cold.  An interesting photo from its lunar flyby shows the Mare north of the better-known features of the Man in the Moon  (Fig. 1). 

On March 1^st the planet Mercury lies below Venus and the Moon, near the evening horizon, at the end of the much-promoted visibility of all the planets at once, albeit spread across the sky from horizon to horizon, captured by a fisheye lens in Fig. 2.  

At its furthest from the Sun on the 8^th, Mercury sets at 7.40 p.m., passing Venus on the 12^th.  It then diminishes in brightness as it approaches the Sun, passing inferior conjunction with it on March 24^th.  Do not look for it when the Sun is still up!

Venus is still brilliant in early evening, near the crescent Moon on the 1^st and 2^nd, above Mercury in the first half of March, but passing between us and the Sun on March 23^rd and reappearing in the morning sky at the end of the month.  As should be needless to say, don’t look for it either when the Sun is up at the same time.  

Mars is in Gemini, below Castor and Pollux, setting at 4.30 a.m., very close to the Moon on the night of the 8-9^th, within a degree at 2 a.m..  On Mars the Perseverance rover picked up and stored its 26^th sample, at a site called ‘Silver Mountain’ on the rim of Jezero crater.  The sample dates from the Noachian period, about 4 billion years ago, when Mars was still subject to big impacts as the Solar System settled down after its formation, and is the oldest collected so far.  (Brett Tingley, ‘Perseverance Mars Rover Finds ‘One-of-a-Kind Treasure’ on Red Planet’s Silver Mountain’, Space.com, online, 6^th February 2025.)

Previously in 2014, two years after landing in Gale crater, the Curiosity rover found evidence of a phase 3.7 billion years ago when there were shallow lakes on the crater floor  (Fig. 3), later than the deep lake which filled the crater about 4 billion years ago  (Fig. 4). 

On January 15^th 2025 it was announced that further study of the deposits had identified ripples in rock layers laid down by water 2 metres deep or less, but formed by wind-driven waves  (Fig. 5), indicating that liquid open water had survived on Mars for significantly longer than had been thought, increasing the possibility that life once existed there.   

On Christmas Day 2024, an asteroid named 2024 YR₄ was detected by ATLAS, the Asteroid Terrestrial-Impact Last Alert System, in Chile.  (At least its acronym commands some attention, unlike the International Asteroid Warning System, IAWN, which seems designed to head off public alarm.)  When first seen, its chances of hitting Earth were 1 in 83, but then shortened to 1 in 43, then 1 in 32 on February 18^th, with a ‘redline’ possible impact track crossing South America and Africa on December 22^nd, 2032  (Fig. 6). 

It would be lost to sight in May, with no prospect of checking further until 2028, which was cutting it fine.  Described as ‘the size of a football pitch’, 130 to 300 feet across, and depending on its composition, it had the potential to do a great deal of damage around the impact site, by tsunamis if it hit ocean, and to climate worldwide.  Depending on composition, again, it might be deflected by an impactor, as the 525-foot asteroid Dimorphos was in the DART experiment of 2015.  Dr. Brian Cox suggested that a deflector be prepared in case it’s needed, because if not, it can be used elsewhere, and that made a lot of sense if the odds did not improve.  As observations continued it was expected that they would improve, and sure enough by February 23^rd the chance of an impact had dropped to 1 in 20,000, which rates as a zero on the Torino scale of hazard assessment.

What we’re looking at here is an ellipse within which the asteroid’s pass is expected to happen, which contracts as more observations are made  (Fig. 7).  If the contracting ellipse remained centred on the Earth, or within the Earth’s diameter, then there would be increasing grounds for concern.  Some day it’s bound to happen, and indeed there’s now an increased chance  (1 in 56)  that 2024 YR₄ will hit the Moon, which will be a very spectacular and informative event if it happens.  (Kelly Kizer Whitt, ‘Asteroid 2024 YR4 Now at Level 0:  No Hazard’, February 23^rd, 2025.)

The details show the continuing need for vigilance.  Asteroid designations are allocated in alphabetical order:  after the year of discovery, the next letter indicated the half-month in which it was found, with the letters I and Z unused, and the next letter indicates the day of discovery.  The system has some parallels with the Roman dating system, in which the 17^th of March, for instance, would be ‘two days after the Ides of March’, notorious for the death of Julius Caesar.  In 1971 I wrote a story about an imaginary asteroid 1985 JA, the first to be discovered in the first half of May that year;  of course now there is one, which was discovered by Carolyn Shoemaker at Mount Palomar on May 14^th, 1985, and is now officially asteroid 3553 Mera, after Maera, daughter of Praetus or Proetus, the son of Sisyphus.  It’s an Amor-class asteroid, crossing the orbit of Mars but not the Earth’s, composition apparently unknown.  So 2024 YR₄ was discovered on 24^th December last year – so far so good – but the subscript ‘4’ indicates the number of times that ‘R’ has been used so far in that half-month, so the asteroid was the 117^th to be discovered in that time.  

The listing applies to all asteroids, of course, not just ‘Earth-grazers’, but it gives some idea of how many small ones there are out there, given that they can’t ordinarily be detected at distances greater than 1 Astronomical Unit, the Earth’s distance from the Sun.  In 1998, the US Congress had directed NASA to detect 90% of all asteroids over 1 km in diameter within 10 years;  by 2003 it was estimated that about half of them had been found, and the NEOWISE project using the former WISE infrared space telescope raised that estimate to over 98%  (see ‘A Farewell to the WISE’, ON, November 10^th, 2024).  In 2005 NASA’s objective was extended to finding 90% of all asteroids from 150 m to 1 km in diameter, a much harder task because of the numbers involved and the relatively limited detection range. It was to be completed by 2020, with only an estimated 25% found by 2016.  (Bill Keeter, ‘NASA Office to Coordinate Asteroid Detection, Hazard Mitigation’, NASA, online, January 7^th, 2016.)  As of February this year, the total number found was 11,209, out of an estimated 25,000, but those are only the ones in that size range which pass close to Earth.  (NASA Science Editorial Team, ‘Near-Earth Asteroids as of February 2025’, online, updated from September 29^th, 2023, accessed 28^th February 2025).

A recent exception to the distance limitation was the James Webb Space Telescope’s ‘serendipitous’ discovery of 138 small asteroids, 10-150 metres across, in the Main Belt between Mars and Jupiter, while making other observations  (Fig. 8). 

There appears to be a break in sizes around 100 metres, and in light of the recent discovery that the samples from the asteroid Bennu have come from all over the Solar System, the implication is that Main Belt asteroids have more collisions and exchanges of material than preciously thought.  If so, continuous tracking of them will be that much more difficult, but it’s estimated that the JWST could detect many thousands of them without changing its existing research programme.  (Artem Y. Burtanov et al, ‘JWST sighting of decametre main-belt asteroids and view on meteorite sources’, Nature, 9^th December 2025.)  

But that’s less likely to happen if the Trump administration goes through with its plan to cut JWST funding by 20%, even though requests for observing time on it are running at nine times what can be accomplished.  (Tariq Malik, ”It’s extremely worrisome,’ NASA’s James Webb Space Telescope faces potential 20% budget cut just 4 years after launch’, Space.com, online, February 21^st, 2025.)  The Hubble Space Telescope is in the same situation, and the Chandra X-ray space telescope faces a complete wind-down to termination, though still fully operational  (see ‘The Need to Save Chandra’, ON, 30^th June 2024).  It appears that the President is only concerned with putting Americans back on the Moon on his watch, and Elon Musk has recently stated again that his only concern is the human settlement of Mars.  It recalls Ronald Reagan’s proposal to switch off Voyagers 1 and 2, soon after their Saturn flybys, on the grounds that nobody was interested in Uranus and Neptune, far less the further exploration which is still going on today  (see below).  That proposal was abandoned after the outcry from the international scientific community, but whether the current administration will bow to similar persuasion is very much in doubt, however much it’s to be hoped for.

Jupiter is still bright, between ElNath in Auriga and Aldebaran in Taurus, setting around 1.30 a.m..  The Moon passes it on the 5^th and 6^th.  

Saturn in Aquarius is too close to the Sun to observe, in conjunction with it on the 12^th,  and the rings will be edge-on to us on the 23^rd, when space observatories will be watching in hopes to see objects in the rings projecting out of the ring plane, or by shadows which they cast across them.  Saturn will be near the Moon on the 28^th, but will not be visible, setting at the same time as the Sun.

Uranus moves from Aries into Taurus, setting at 11.30 p.m..  The case for a return mission to Uranus and its moons, which would be the first since Voyager 2’s in 1986, has gained a boost from two recently published papers.  One of the biggest mysteries is the situation on Uranus’s innermost substantial moon, Miranda, whose surface shows evidence of convulsive rearrangement of the crust – so much so that it might even have been torn apart and reassembled.  A point not previously stressed was that the Voyager 2 images show only the southern hemisphere of Miranda  (Fig. 9), due to the axial tilt of Uranus and its moons, through which Voyager flew face-on, as if through the concentric rings of a dartboard.  We simply don’t know what the other hemisphere of Miranda is like.

A new hypothesis attempts to track back the evolution of the surface, on the assumption that the convulsions were caused by tidal forces as Miranda came out of resonance with the planet or with one of the other moons.  Such effects would have to be caused by the sloshing of a large internal ocean, possibly 100 to 500 million years ago.  The ocean of water would have to be no more than 19 miles below the surface, and no less than 62 miles deep.  As the tidal stresses eased the ocean would cool, but if it exists it has not yet frozen, because there’s no sign of the surface cracking that would occur as it contracted.

I’ve previously mentioned ideas that huge grooved features on the other Uranus moons Ariel  (Fig. 10)  and Titania may be due to subsurface water action  (see ‘Uranus, Neptune and Their Moons’, ON, November 14^th, 2021).  Ariel’s surface is now known to have deposits of carbon dioxide and other carbon compounds, which appear to have come from inside, not merely deposited on the surface.  New findings suggest that they come from what are called medial grooves, within the larger ones, which appear to be ‘spreading centres’ like those found on seafloors on Earth  (Fig. 11). 

Part of the evidence is that the canyon walls flanking them fit together, when the intervening floors are removed, the way the edges of continental plates do on Earth;  and parallel ridges on those floors resemble the ones on the mid-Atlantic floor on Earth.  It all suggests upwelling of carbon-bearing fluid from below, and on the available evidence, that fluid is likely to be liquid water.

Though near the Moon on the 1^st, Neptune is not visible in March, at conjunction beyond the Sun on the 19^th.

As it approaches the 10^th anniversary of its Pluto flyby in July, the New Horizons probe has been in partial hibernation to save fuel since October 3^rd last year. 

Alan Sterns, the Principal Investigator  (Fig. 12), says that he is now ‘Fuel hoarder in chief’ in case a new Kuiper Belt object is discovered near its flightpath.  When the new ground-based Vera Rubin Telescope is commissioned, a fresh search will be made.  (Leonard David, ‘Leaving Pluto in the dust: New Horizons probe gearing up for epic crossing of ‘termination shock”, MSN News online, 20^th February 2025).  It will be awakened on April 2^nd for a download of accumulated data, and this will be of particular interest because New Horizons is approaching the ‘termination shock’ where the Solar Wind of outflowing particles meets and is halted by the interstellar medium.  Only Voyager 1 and 2 have previously crossed it, and although the crossing may take only 10 minutes, it may occur several times as the Solar Wind fluctuates due to events on the Sun, billions of miles astern.  This, and how it affects cosmic-ray counts in the inner Solar System, is particularly relevant to the question of how events on the Sun affect the Earth, which I mentioned in ‘The Politics of Survival, Part 1′, (ON, 16^th February, 2025).  The New Horizons event may not occur until 2027, but investigators want to be certain that they’re not caught by surprise.

Duncan’s story ‘How to Blow Up an Asteroid’, about the imagined 1985 JA, is reprinted in his collection The Other Side of the Interface  (Other Side Books, 2021).  His recent books are available through Amazon;  details are on Duncan’s website, http://www.duncanlunan.com.

You can download a copy of the March Sky Map 2025 here: