The twin stars of Zeta 2 Reticuli can be seen to the right. (image credit: Google Sky)

The twin stars of Zeta Reticuli can be seen at the far right. (image credit: Google Sky)

Reticulum (literally “the net” but used in the sense of an archaic form of eyepiece reticule) is a constellation of the southern hemisphere’s sky (we cannot see it from Northern Ireland). Diamond-shaped, the constellation lacks bright stars and is apparently an unimpressive sight. Only just visible to the unaided eye, Zeta Reticuli was first referred to as such in 1756. Can I just repeat that Zeta Reticuli has been seen in the sky without a telescope for centuries. Anyone who tells you it was not discovered until after the Hill’s story became famous is utterly wrong.  The whole identification of this system as a homeworld to ufonauts is based on the thorough and painstaking work of Marjorie Fish, which is now believed to be incorrect being based on out-dated data on star positions.   Through a telescope Zeta Reticuli can be clearly seen to be two stars (you can do this without a telescope if the sky is dark enough). The two stars are both very similar in mass, diameter, temperature and brightness to our own Sun (Zeta 1, a G3 class star, is slightly smaller, cooler and more orange than the Sun, while Zeta 2 is G2 class, almost identical to the Sun). They orbit a common centre of mass approximately midway between them and are separated by at least 3750 AU (about 0.06 light years). By the standards set by objects in our own Solar System, this is a huge distance; about a hundred times as far as Pluto is on average from the Sun. A beam of light from one of the stars would take three weeks to reach its companion.  

This is great enough a separation for each star in the duo to have its own planetary system.  Unlike some other  binary systems where the stars are closer, the skies of any Reticulan planet would not feature two suns. From the planets of one star, the other star would be a brilliantly bright star about 30 times as bright as Venus looks in Earth’s sky and would be visible even in the daytime sky. Each star could have its own habitable zone (or Goldilocks zone, a region where there is enough warmth from a star to allow water to persist as a liquid on the surface of a planet). Another myth about the Zeta Reticuli system I have encountered states that emissions from the two stars contribute to a dangerous level of background radiation in their vicinity. The two stars are too far apart for this and this idea seems to have been dreamed up by the perpetrators of the staggeringly inept Project SERPO hoax.


What are the prospects for life in this star system? Both stars are similar to the Sun and if they have suitable planets it is not impossible that life has arisen there. Older sources claim these stars to be relatively old (6-8 billion years old is often quoted) but more recent evidence acquired by analysing the stars’ light with spectroscopes suggests these are young stars, possibly only two billion years old (compared to our own Sun’s 4.5 billion year age). Their youth may count against the possibly of higher forms of life having evolved on Zeta Reticulan worlds. After all there has been life on Earth for most of the planet’s existence, for most of this time terrestrial life has been single-celled micro-organisms, whereas multicellular life, plants and animals and so on, appeared only in the last 600 million years. If the story of life on Earth is typical (and who knows for sure), I would not bet on there being any little grey men, or indeed ladies, on any Zeta Reticulan planets unless they were colonised from elswhere. I should note that there is some controversy over these stars’ ages, see the comments section if you want to know more.

  The stars’ similarity to our own has prompted astronomers to search for planets there, but no planets have yet been discovered around either star. There has been a false alarm though. In 1996 astronomers at the European Southern Observatory announced that they had observed evidence of a giant planet around Zeta 2. The planet appeared to be tugging on the star causing it to make slight rhythmic movements, suggesting the planet had a mass about a quarter that of Jupiter and was moving in a close orbit (0.14 AU) with a period of 18.9 days. This would have been an example of what astronomers call a ‘hot Jupiter’ and would be a hopeless prospect for any kind of life. Within days, however, this discovery announcement was retracted as it was recognised that the wobbles in the star’s motion could also be just the star’s slight but regular pulsations. Of course UFO true believers still tell the story of “the scientists who reported a planet at Zeta Reticulum but the government made them cover it up”. To the best of my knowledge, the Hubble Space Telescope (HST) has never observed this system. Why? Well, its not a conspiracy, rather there is no point as the HST could not resolve any planets at this distance, this is something it was not designed to do.  

In 2010, another team of astronomers announced that far-infrared wavelength observations with ESA’s Herschel space telescope showed a ring of cold dust and ice about 100 AU across around Zeta 2 Reticuli. Almost certainly there are comet nuclei and dwarf planets, analogues of our Pluto, Eris, Makemake and Haumea, in this ring. This debris disc is not symmetrical, a possible indication that the material is being gravitationally effected by an unseen planetary companion. To be honest, based on the distribution of exoplanets in the Milky Way it would be very surprising if in fact there were no planets in the Zeta Reticulum system. However as our methods for finding exoplanets are still pretty limited it may be a long time before we know for sure.


Until we actually discover any Zeta Reticulan planets the best we can do is watch out for them in science fiction. “Reticulans” were name-checked in the X-Files and appeared on screen as “Chigs” in Space: Above and Beyond. By far and away the best-known fictional world in the vicinity of the Zeta 2 Reticuli system is LV-426 (also called Acheron) from the Alien movies and related works. On this world humans first encountered the awful acid-blooded, drooling horrors sometimes called Xenomorphs (yes, I am deliberately ignoring the Aliens vs Predator movies and I advise you to do the same). LV-426, which went unnamed in the first film, is a tiny rocky world, apparently one of several satellites of a gas giant planet. Originally, its tortured landscape was overlaid by a cold but violently stormy atmosphere of nitrogen with methane, carbon dioxide and ammonia but by its second appearance in Aliens it had been terraformed to give it an atmosphere and climate compatible with human life. The moon was apparently devoid of native life; Xenomorph eggs were found there in a derelict starship belonging to some other enigmatic alien civilisation (I also prefer to pretend Prometheus never happened).


LV-426 is completely fictitious and not based on any speculation by scientists, nor is the “LV-” numbering scheme used for planets (also in Prometheus)  a real piece of scientific methodology. Dan O’Bannon (1946-2009), who wrote the original story for Alien probably used the name Zeta Reticuli after seeing it in an article about the Hill UFO account.

  Zeta Reticuli is an interesting nearby binary star system, but there is no evidence to suggests it is the home of extraterrestrial visitors to our world.  

(Article by Colin Johnston, Science Communicator. This article was inspired by a conversation I had with a caller to the Planetarium last week, I hope he is reading this.)