After Yuri Milner, Mark Zuckerberg and Stephen Hawking launched the Breakthrough Starshot project in 2016, with the intention of sending fleets of laser-propelled probes to the nearer stars, one obvious next step was the search for targets. As Carl Sagan had christened the Earth ‘Pale Blue Dot’, after Voyager 1 imaged the Solar System from the outside, there was a proposal for a dedicated space telescope called ‘Project Blue’, to search for planets of the nearer stars, particularly earth like ones. There had already been a false alarm when an earth-sized planet was thought to have been detected orbiting Alpha Centauri B, but wasn’t confirmed.
But by June 2019 a special instrument called NEAR (Near Earths in the Alpha Cen Region, Fig. 1) had been installed on the European Southern Observatory’s Very Large Telescope, as part of the Breakthrough Watch, and as the Alpha Centauri search drew a blank, initially at least, the remit was extended to Pale Red Dot, for Proxima Centauri (Fig. 2), and then to Red Dots, taking in Barnard’s Star and other more distant ones (Fig. 3).
As reported last week, both of those nearby red dwarf stars are now known to have planets.
At 7.2 light-years, not much further than Barnard’s Star, Figs. 4 & 5 show two more objects, recent discoveries by the WISE infrared space telescope, which came to the end of its run in November last year (see ‘A Farewell to the WISE’, ON, November 10th 2024.) Their colour indicates why they were found so late: both are brown dwarfs, technically not stars at all because they’re not massive enough to sustain fusion reactions, and shine only by the heat of continuing contraction, like the night side of Jupiter.
WISE 0855 (full designation J0855.10.83-71442) has a mottled surface (Fig. 6), slightly warmer than Jupiter’s, and indeed some brown dwarfs have broad bands like Jupiter’s, though the temperatures at their visible surfaces are generally below zero (Fig. 7). They’re not much larger than Jupiter (Fig. 8), but a lot more massive, and there’s a mysterious gap between them and the largest known planets, highlighted some years back by Dr. Duncan Forgan of the University of St. Andrews (Figs. 9 & 10).
At 7.9 light-years there’s another red dwarf, Wolf 359 (Fig. 11), which is best known for the battle in which Star Fleet defeated the Borg (Fig. 12), which gets it a lot of SF references – see Florian Freistetter, The History of the Universe in 100 Stars, ON, January 1st, 2023.
Next beyond it is the red dwarf Lalande 21185, at 8.3 light-years. The star used to be well-known because it was one of the ones which Peter Van de Kamp believed to have a superjovian planet (see ‘Pale Red Dots’ last week), and it does have a super-earth size planet, orbiting close enough for temperatures there to be very high (Fig. 13).
Lalande 21185 is also known as Gliese 411. In Tom Toner’s novels The Promise of the Child and The Weight of the World, (Gollancz, 2015, 2017), set in 14,647 AD, 12,000 years after humans reached the stars, part of the fun is plotting the territory from ancient star designations (ours) such as Kapteyn’s Star (see below), Barnard’s Star and Epsilon Indi (corrupted to Epsilon India), and from those with cryptic, incomplete names like ‘Virginis’ (possibly 61 Virginis at 27.9 light-years). ‘Aquarii’ is harder to identify – possibly EZ Aquarii at 11.1 light-years, or TRAPPIST-1 with its three earthlike planets at 40 l.y., though it’s supposed to be the nearest to Virginis, and that’s a big angular and radial separation. The Weight of the World adds more to identify (‘Proximo’ and ‘Epsilon Iridiani’, sic) or puzzle over. There’s an inner realm known as the Firmament, roughly coinciding with the first wave of interstellar colonisation, in my own Man and the Stars (1974), with a boundary at Tau Ceti, 12 l.y. out, known here as The Last Harbour. The capital is ‘Gliese’, possibly Gliese 876 at 15.2 light-years, more probably Gliese 15AB at 10.7 l.y. but most probably Gliese 411, Lalande 21185.
At 8.6 light-years is Sirius, the Dog Star (Fig. 14), the brightest star in the sky because it’s a type A giant, the most massive star in the Sun’s vicinity. Sirius is the brightest star in Canis Major; it and Procyon in Canis Minor represent Orion’s dogs in the Winter Triangle or the larger Hexagon (Fig. 15). Its name comes from the Greek seirios, scorching, because in classical times the hottest part of the year was the ‘Dog Days’ when Sirius was invisible behind the Sun. It was the first star to be found to have a white dwarf companion. Innes, the Scottish astronomer who discovered Proxima Centauri, worked out its density, couldn’t believe his result and sadly died in a traffic accident before it was realised that Sirius B, ‘the Pup’, was made of condensed matter, formed when a larger star blew off its outer layers and compressed the remaining matter down to the size of the Earth (Figs. 16 & 17).
Some ancient writers describe Sirius as ‘red’, and it’s been suggested that Sirius B was then in its giant phase, but it’s almost inconceivable that the subsequent planetary nebula could have disappeared so completely in only 2000 years: recent estimates put the event at 120 million years in the past. Even today Sirius is so bright that it flashes blue, green and red due to atmospheric refraction, and that probably explains the ancient descriptions.
In his book The Sirius Mystery (Sidgwick & Jackson, 1966), Robert Temple claimed that the rituals of the Dogon tribe in West Africa preserved the memory of visitors from Sirius to the Middle East, more than four thousand years before. These were the Annedoti, the patrons of learning in ancient Mesopotamia, also found as seven sages in Egypt and as seven rishis, holy spirits, in ancient India. In all accounts they are amphibious or aquatic, but also associated with the sky – in India, with the stars of the Plough, and in Egypt with the Moon and with Ursa Minor or Boötes. Robert explained that by saying that intelligent life on a planet of Sirius had to be amphibious, nocturnal or both, because of the star’s intense output of ultra-violet radiation and x-rays; and because Sirius A will have a stable life of only 1 billion years, those beings must have come from elsewhere.
One big problem is that the Dogon are at the crossroads of western Africa and while they do have long-standing links with other parts of the continent, they were also subject to modern influences long before their Sirius beliefs were first recorded in the late 1920s. Not only were there trading posts and schools, but there was a Dogon regiment in the First World War! Perhaps crucially, the Dogon were recorded as believing that Sirius had a third, unseen component. That’s not believed to be the case now, but it was when the Jesuit schools in the area were first set up. In the second edition of his book in 1998, Robert cited a 1995 report that there might be another companion star, but subsequent studies by the Hubble Space Telescope have narrowed the possibilities to a large exoplanet, at most.
No planets have been detected orbiting Sirius B, but intriguingly the possibility can’t be ruled out. In recent years debris has been found around white dwarfs, from planets broken up in the destruction of an original system, and it’s possible that smaller earthlike planets might form from it, even within the very narrow zone of habitable temperatures. Very recent studies have shown that the ultraviolet and x-ray radiation from the white dwarf wouldn’t prevent the origin of life, and conditions would remain tolerable for 7 billion years – more than the present age of the Earth. So although 120 million years isn’t long enough for life to have appeared there yet, it’s not to say that it never will. (Will Triggs, ‘White Dwarfs: the New Hotspots for Alien Life?’, EarthSky, online, March 23rd 2025.)
Another red dwarf, Ross 248, is 10.3 light-years away at present and it will be the closest star to us in about 36,000 years’ time (Fig. 18). Meanwhile, in 29,000 years the interstellar object ’Oumuamua will pass Ross 248 at 0.459 parsecs (1.5 light-years) with a velocity of 104 km/s. (See ‘’Oumuamua’ Parts 1 & 2, ON, 17th and 24th December 2023.) I think that flight-path needs to be looked at much more closely.
At 10.8 light-years, epsilon Eridani is one of the most promising targets for future interstellar missions. It’s a young, sunlike orange star, and in the late 1950s it was believed to be a candidate for supporting intelligent life, monitored for radio signals in Project Ozma, the first attempt to find any. It has asteroid belts, comets and gas giant planets (Figs. 19-21), which are the resources future interstellar voyagers will be looking for (more on that next time).
Part 1 of my first book Man and the Stars (1974) was titled ‘The first phase of interstellar colonisation, out to 12 light-years’. Previous books like Beyond the Solar System, by Willy Ley and Chesley Bonestell (1964), Journey to Alpha Centauri, by the late John W. MacVey of Saltcoats (1965), and Flight to the Stars by James Strong (1965), had looked at the first interstellar mission but not beyond it. Like those earlier books, the discussion group which I formed in 1967 assumed that we were talking about ‘conventional’ spaceships, even if they might be very large ones, and we assumed that their targets were earthlike planets. The likelihood of finding those had been assessed in Habitable Planets for Man, by Stephen H. Dole (Blaisdell, New York, 1964), which Prof. Archie Roy described as “the textbook which you read like a novel”. Dole had assessed all of the hundred or so stars which were known to exist within 22 light-years, almost all of them red dwarfs, and he assumed only sunlike stars were eligible, and would have to have earthlike planets (Fig. 22).
As we now know, there are many more red dwarfs within that radius; and their chances for habitability are much better than previously thought, particularly for those which are past the unstable flare stage. But the only candidates he ended up with were Alpha and Beta Centauri, which he considered most promising, Epsilon Eridani, 61 Cygni A and B, Epsilon Indi and Tau Ceti – all of them grouped within the 10-12 light-year radius, with a big gap before there were any more.
For the record, I should mention Gliese 887, a red dwarf with two super-Earth planets at 10.7 light-years (Figs. 23 & 24), and Procyon, the left-hand star in the Winter Triangle, an ageing Class-F star with a white dwarf companion (Figs. 25 & 26).
At the same distance, 61 Cygni (Fig. 27) has an interesting history, as the first star to have its distance measured, and one of De Kamp’s candidates for a superjovian planet.
It’s a double star. both components of type K, smaller than the Sun (Fig. 28), which is presumably why Dole gave it a low probability for habitable planets. He did the same for Epsilon Indi, at 11.9 light-years, but as stable K-type stars, both would be considered promising nowadays, and the Copernicus satellite examined Epsilon Indi for intelligent laser signals, with no result. It has two distant brown dwarf companions (Fig. 29) and a superjovian planet, which has been imaged by the James Webb Space Telescope (Fig. 30).
Tau Ceti, at just under 12 light-years, has five planets of 2-5 times Earth’s mass, one in the habitable zone (Fig. 31), but all wrapped in a huge envelope of comets which must keep them under constant bombardment (Figs. 32 & 33).
Tau Ceti was the other star studied for extraterrestrial signals in Project Ozma, and in The Cosmic Connection (1973), Carl Sagan published a map looking towards the Sun from there, with a constellation called The Centaur, with the Sun as an extra star in Boötes (as we call it), which he delicately described as ‘the spot below the horse’s tail’, or as most Americans would call it, ‘the horse’s ass’. I spent a lot of time with star maps trying to verify that, and I have to say, appropriate as it seemed to him, it seemed to me that he’d picked out the wrong star.
Tau Ceti is considered to be the limit for Breakthrough Starshot missions, taking 75 years to reach. It’s not clear whether that’s to stay within the confines of a human lifetime, or an actual limit to the technology. Nor is it clear why Fig. 3 includes Ross 154, shown at 15 light-years, unless that’s the limit of the Breakthrough Watch technology rather than Starshot’s. Wikipedia has Ross 154 at only 9.71 light-years, within Starshot range, a red dwarf with no planets detected as yet.
Most of the stars on Dole’s list, between there and 22 light-years, are red dwarfs. Almost the only exception is Delta Pavonis, at 19.89 light-years, a G8 star more massive than the Sun and nearing the end of its stable life. Dole didn’t consider it even remotely likely to have a habitable planet, but it has at least one of Jupiter mass. In The Space-Gods Revealed, a close look at the theories of Erich von Däniken (Harper & Row, 1976), Ronald D. Story discusses the possibility that the figures on the plain of Nazca in Peru, and on pottery found in the region, may represent constellations. His example is the bird figure, identified as a condor (Fig. 34), which looks remarkably convincing when superimposed on the constellation Pavo, the Peacock (Fig. 35).
Without suggesting that it’s evidence of extraterrestrial visitors, it is very interesting that it’s centred on the comparatively faint Delta Pavonis.
One of the many red dwarfs within Dole’s list is Kapteyn’s Star, at 13 light-years, which has a super-Earth companion (Fig. 36).
Like other red dwarfs it’s not much larger than Jupiter (Fig. 37), and is located within a stream of stars which may be a remnant of a Milky Way collision with a dwarf galaxy (Fig. 38), or (by its composition) may have escaped from the fringe of the Omega Centauri globular cluster, 16,000 light-years away (Figs. 39 & 40), near in the sky to the Southern Cross.
Also worth mentioning is Scholz’s Star, 22 light-years away, discovered only in 2013, which was the most recent star to pass close to the Sun, within the Oort Cloud, 70,000 year ago, when its deep red colour must have impressed Neanderthals and Homo Sapiens (Fig. 41).
No doubt many of the other red dwarfs would prove equally interesting, if they were close enough to learn more. Brown dwarfs are still more numerous: going out to 26 light-years, more than twice the distance of Tau Ceti and enclosing more than four times the volume, they are all over the sky (Fig. 42).
As we’re now into summer, it’s fitting to end with two of the stars of the Summer Triangle, now dominant in the morning sky (Fig. 43). Vega (Figs. 44 & 45), an A0 star like Sirius, is 25 light-years away and has a circumstellar disc of material discovered by the IRAS satellite in 1973, though no planets have been found yet.
Altair, much closer at 16.7 l.y., is another A-type star, but at A7 it’s intrinsically fainter than Vega. It has no known planets, but the imagined Altair 4 (Altair-e, as we’d call it now) is the setting for Metro-Goldwyn-Mayer’s Forbidden Planet (1956), with a plot based on The Tempest, though few critics notice that the roles of Caliban and Ariel have been reversed. Characters enthuse about the beauty of the green sky (Fig. 46), but had the film-makers known it, they could also have shown a very different sun.
Like Vega, Altair rotates so rapidly that it has an elliptical shape (Fig. 47), with areas of different temperature in which some people claim to see a face. I’m usually quite good at those things, but I must admit that one escapes me.
Forbidden Planet is set in the 23rd century, by which time we’ve supposedly had faster-than-light travel for a generation or more. We’ll need it, if we’re going to get so far, so soon – but more on that next time.
Duncan Lunan’s recent books are available from Amazon, and full details are on his website, http://www.duncanlunan.com.
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