As Terragen civilization has spread into the galaxy, it has encountered both living aliens and the remains of extinct aliens. Some of them once built vast empires but have since vanished but for a few enigmatic traces, and indeed had been gone for millions of years before life even crawled up on dry land on Earth.
Telescopic examination of the Milky Way Galaxy in the Interplanetary Age revealed several locations where artificial emissions seemed to indicate the existence of advanced civilisations; but these locations were all many tens of thousands of light years away. These civilisations (if real) were so far away they might disappear before any signals reached them. But would there be any closer civilisations that telescopes might not reveal?
Those early Terragens who were expecting a galactic community of civilizations in the region near Sol were disappointed. Space turned out to be empty and desolate, and aliens few and far between. The first remnant of alien technology, the fragmentary hull of a robotic satellite, was found orbiting Epsilon Sculptoris A in 1460 AT. This artifact was 196 million yaers old, a relic of the unnamed species HIE636MZE.
Although a few of the alien sophont races that have been discovered so far have willingly joined the body of Galactic society, others are aloof or reclusive, lack interest or are unable to understand such concepts. Some, lile the Meistersingers and the Wayfarers, appear to have some measure of contact with the more distant galactic civilisations, but so far they decline to share any significant information concerning these topics.
The most extensive alien empire that has so far been contacted is that of the Muuh; at first believed to be merely a faded remnant of an ancient empre, these slow, low-temperature creatures in fact have a large and widely dispersed network of colonies which are protected by utterly alien AI weapons systems.
Not one single alien race has been found to be similar in physiology to any metazoan life form that originated on Earth, and the process of panspermia has been shown to have had only a minor effect on the emergence of life in the Terragen Sphere. This is not to say that former races did not engage in terraforming and provolve both their own local and other species, for some of them clearly did.
Recent exploration has shown that some xenosophont empires, such as the Black Acropolis Builders and the "Auld Limners", were much more extensive than had previously been believed. This invites even more the question of how such mighty empires could remain for tens or hundreds of thousands of years, and then suddenly disappear. Speculation ranges from mass transcension to doomsday weapons and mysterious robot warships, and consensus regarding the answer remains elusive.
Daharrans, The - Text by Anders Sandberg A tragic victim of cross-species congress, the Daharrans are a quite humanoid species - at least they breathe a human-breathable oxygen atmosphere and are land-living omnivores from a terrestrial world.
Drake Equation - Text by M. Alan Kazlev An early (pre-interstellar age) attempt to estimate the number of civilizations in the galaxy, according to the statement that the fraction of stars harboring intelligent life equals the number of all stars times a sequence of fractions, such as the fraction of all stars having planets, the fraction of planets that are habitable, and so on.
Epsilon Sculptoris - Text by Steve Bowers Binary system 89.5 light years from Sol. The first alien artifact, a fragmentary hull of a autonomous vessel, was discovered here in 1460 AT. This artifact was 196 million years old, a relic of the unnamed species HIE636MZE.
First Contact - Text by Steve Bowers Strategies and policies for contact with alien life forms (xenobiota) and Xenosophonts (intelligent alien life).
Hollerith Anomaly Object - Text by Håkan Andersson A nebula in the Chronos Cluster that contains a nanecology, some semi-sentient entities, and a number of odd phenomena. It is believed to have been left behind by a xenosophont civilization, now no longer evident and assumed by some to have transcended.
Inhibitor - Text by M. Alan Kazlev Hypothetic super-powerful alien race or races proposed to explain why most advanced civilizations fail after only a few tens of thousands to a few millions of years. The Dawn Hunters are the most popular example of inhibitors, although it is not known if they even exist, or if they do, if they really are inhibitors.
Jacks, The - Text by Anders Sandberg; expanded by Stephen Inniss The Jacks (officially known as HIE233MPE) are a xenosophont species, or possibly a cluster of related species, named for a toy of ancient human baseline origin called a "Jack-in-a-box". Their name springs from the fact that they are apparently neither extinct nor extant; instead they have "popped up" several times in the past and may or may not return at some point in the future.
Mysterian - Text by M. Alan Kazlev The name used by the local populace to describe the long vanished terraformers of alien origin who terraformed Ararat II. The mysterian jungle is made of the numerous plant/jellyfish creatures that have taken residence on the planet and, through accident or not, and outlived the mysterians themselves.
Porrima - Text by M. Alan Kazlev Twin star, where the first high technology non-terragen artifact - a derelict alien starship - was discovered in 3752 by the Virginis Combine ship Fra Angelico. The system is currently Solar Dominion protectorate inhabited by a number of bioid and cyborg clades. There is a small but well-equipped Exoarcheology Institute, and a nanoaccurate reconstruction of the Fra Angelico, along with a superficial reconstruction of the artifact, is a popular tourist attraction.
Postalien - Text by M. Alan Kazlev A non-terragen (alien) who has attained the status of an S1 or greater. Sometimes called a postxeonosophont. Almost all of the currently recognized postaliens in the Terragen sphere are ascended To'u'lhs.
Sextans Swarmers - Text by M. Alan Kazlev Nanecology / nanoswarm detected across much of Sextans A (Irregular galaxy - Local Group). It's origin and toposophic nature is unknown. What seem to be a smaller number of similar nanecologies have been detected in Sextans B, showing they were able to make the journey of some million light years separating the two small galaxies.
Steelcliff - Text by Tony Jones The first alien BGC system, discovered in 7852. Steelcliff is an isolated world towards galactic anti-spinward in what is now the Negentropy Alliance Outer Volumes. It appears to be running some kind of virch world, and certainly has sufficient computing resources to run at least millions of entities. It seems to have been put into place some forty million years ago, but as yet no attempt has been made to contact who or whatever may exist inside it.
Sundrivers, The - Text by Todd Drashner Alien civilization discovered in the Virgo cluster approximately 60 million ly from the Milky Way. The seem to be involved in a megascale project that involves the movement of entire stars.
Tau Felis Minoris II - Text by M. Alan Kazlev A cold planet altered by the unnamed species HIE236PPE (an extinct xenosophont race) so that it supports an ecology of cold-adapted lifeforms. These lifeforms share a common ancestry with those found on 12 other worlds.
Terraforming Remnants - Text by Anders Sandberg Natural and artificial ecospheres left by any of several long-vanished terraformer species known only for the biospheres they left behind long ago. Currently terragenkind is busy terraforming suitable planets in the galaxy, and even if they disappear there are going to be lots of human- and ai- derived biospheres left behind. In a few hundreds of millions of years intelligent life might evolve independently there. This life would find a few other habitable worlds with suspiciously similar biochemistries.
Thiogens, The - Text by Matthew C. Johnson Extinct xenosophonts presumed to be responsible for a number of sulphurogenic biospheres on Vitriolic type worlds.
Unnamed Species: HIE236PPE - Text by Aaron Hamilton Xenosophont species that was capable of interstellar travel, extinct for at least 2 billion years, deduced from the common ethane-based biochemistry of fourteen worlds that are now within the Terragen Sphere.
Unnamed Species: HIE565MZE - Text by Aaron Hamilton Xenosophont species known from 125 million year old ruins on a single planet; apparently this species became extinct without developing interstellar travel.
Xenobiont - Text by M. Alan Kazlev Generic term for alien (non-terragen) lifeform. May be animal-like, plant-like, protistan, exotic chemistry, or any other possibility. Does not have to be sophont. In fact just as on Earth, very few alien species ever evolve any measure of cognitive intelligence.
Xenomorph - Text by Steve Bowers Any Terragen entity using an artificial alien (xenosophont) body for the purposes of cultural contact, exploration or colonisation.
Xenosophont Gallery - Text by Various Artists Images of the various Xenosophonts (Alien Species) in the Orion's Arm Volume