When I was in the field of astronomy, I studied both comets and some of the most distant objects in the universe, high redshift radio galaxies or HZRGs. The two object types are at opposite ends of the distance scale, but can be said to be connected in this weird way.

A term that was perhaps tossed around was “Galactic Ecology”. The audacity of those astronomers! It has since become a bit of a pet peeve to see professional astronomers going out of their lanes, like when Neil de Grasse Tyson stated that bats are blind. What’s happening is that, like his hero Carl Sagan, he wants to be a spokesperson for science. Props to NDGT. He’s been an excellent spokesperson for science. And here I go, outside of my lane.

In any case, Galactic Ecology is a subject that Carl Sagan would have approved of.

In graduate school for astronomy, certain tenured professors would sometimes toss out the term jokingly, but they were secretly thinking that it was possible. These were offhand remarks, because this was all unseen, a question left for future generations to ponder and perhaps solve.

Ecology, of course, is the description of communities of populations of organisms. Organisms do many different things, functionally, but they all do two specific things. First, they extract energy somehow, from their habitat, by feeding. Second, they carry around genetic information and try to transmit that information to the future. They procreate.

So how could there be a Galactic Ecology?

Let’s back up a bit and talk some astronomy. If you know, you know, and I don’t want to bore you, so skip past this bit about Population II stars.

In the early universe there was hydrogen, helium and a little bit of lithium. Nothing else. Nothing to make planets from, rocks, oceans, plants and animals. None of those heavier elements. So the first stars had only hydrogen, helium, and a little bit of lithium. And we don’t really know what kind of environments they formed in, in the early universe.  Those stars died and the larger ones went supernova and distributed heavier elements.

There are still some of these Population II stars around. One, Kapetyn’s Star is only 12.84 light years away in the constellation of Pictor, in the southern summer (northern hemi) sky. How is it still around? Well, it turns out that low mass stars last a long time. It is thought that this particular star was formed in a dwarf galaxy that long ago merged into the Milky Way Galaxy.

The thing is, we don’t know how these Population II stars formed. These weird objects called globular clusters are made of them, little island galaxies of millions of stars, sometimes, like the largest one, Omega Centauri, visible to the naked eye. I recall the first time I saw it, hovering mere degrees over the desert horizon in California’s Owen’s Valley from its location somewhat outside of our Galaxy. In a small telescope the millions of stars are revealed, an amazing sight.

So we don’t know how they formed. Perhaps in the violent collapse of hydrogen gas around a super massive black hole. We see these objects in the distant universe undergoing what is termed “violent relaxation”. A great term, to be sure, meaning the collapse of vast quantities of hydrogen gas under gravitational attraction. What’s thought to be left over after all of the matter has fallen onto the central object forming an accretion disk that is heated to millions of degrees is a giant elliptical galaxy. These we see, and many, perhaps all, still have supermassive black holes at their core. The stars formed in these environments later seeding their host galaxies with star stuff, the stuff of planets and oceans and ultimately, life. This is what astronomers call enrichment.

“We are all star stuff.” Carl Sagan

This is parallel to what happens in terrestrial ecology, with soil development. Enrichment of nutrients, but on a galactic scale.

But this is not life, and ecology concerns life.

Those audacious astronomers, speculating about things they don’t know but suspect to be true.

Another aspect of ecology, terrestrial ecology, are the concepts of colonization and succession, in which species take root in new habitats and change the environment around them.

This is where the leap to galactic ecology becomes speculative. How could genetic information travel through interstellar space. Well, we know that some objects travel through interstellar space, we have found three such objects, like 2/I Borisov, 1/Oumuamua, and 3I/Atlas in 2025. These objects are thought to have been ejected from the stellar systems by interactions with giant planets like Jupiter. This happens. Gravitational models show these ejections happen. Also, you can have the rare, odd-angle collision that ejects objects. Or, you can have an interloper, perhaps a brown dwarf, transit a stellar system and perturb loosely bound objects, like comets in the Oort cloud, enough to unseat them from their long, lonely orbits far from their parent stars.

Of these Oumuamua and Borison were very dark, implying that their surfaces, at least, are rich in carbon. Could they have contained other compounds necessary for life? Could they have contained life? Could they have carried viruses?

This we don’t know, as they all sped through the solar system at speeds that meant they were gone forever.

However, we are starting to get an understanding that astrobiology is real, and many cometary objects contain organic molecules.

In 2023 NASA analyzed samples collected from Comet Bennu by the OSIRIS-Rex mission, identifying, 14 of the 20 amino acids necessary to make proteins, and all five nucleobases that life on Earth uses to store and transmit genetic instructions in DNA and RNA. This is an amazing result. This confirms that the early Earth was likely seeded with organic compounds from the inter-planetary space. Given that we can’t really assume that our stellar system is unique, this may well indeed be the case elsewhere.

But, again, this isn’t life. Viruses aren’t considered life either, and they do not feed and only replicate, but they do transmit genetic information. And they might be able to survive in space in spaces protecting them from cosmic rays, X-rays, and UV radiation, perhaps under the surface of an interstellar interloper. We just don’t know.

As an aside, did you know that we have viral DNA in our bodies? The way this happens is through infection of sex cells prior to reproduction, a very unlikely process that has happened and injected Herpes virus DNA into the human genome, producing a mutation that enhances placental development. Fully 8% of the human genome contains genetic material from ancient viruses, called human endogenous retroviruses or HERVs. Pretty weird.

I mention this because if viruses can be transmitted through interstellar space the certainly can be incorporated into the gene pool of organisms, an example of galactic ecology.

One thing we know from Earth’s history is that if you give nature enough time, things are going to happen. It can take a long time, and complex life on Earth really started four billion years after the Earth’s formation.

All we can say at this point is that it is very unlikely, but certainly possible, that some organism survived interstellar space and after billions of years, perhaps, found its way to our solar system.

But since so many people want to believe, actual travel and colonization of stellar systems would be a solid way of establishing a galactic ecology.

There’s a book called, “Ecological Imperialism” by Alfred W. Crosby that details the transmission of non-native organisms to the New World. Vast quantities of microbes, plants, and animals were assisted in colonization of new lands, forever altering the landscape. Even the soils were not safe, and 70 species of earthworms were introduced to North America, altering soil chemistry. This largely happened during the 18^th century, but one species was introduced to Alaska for fishing bait. The Colombian exchange, which distributed tomatoes, potatoes, peanuts, cacao, coffee, chili peppers, and a long list of other food plants and animals around the planet.

The idea being that interstellar travelers would bring organisms with them. Galactic Ecology. Now, of course, this needs to be qualified with a mention of the Drake Equation, which tries to estimate that number of technological civilizations in the Galaxy. This is an exercise I recommend everyone try with an online Drake Equation calculator, as you’ll find that the least certain constraint is the lifetime of civilizations.

And the opposite to biological colonization of Eart has likely already happened, with our visits to Mars and the Moon introducing viruses and perhaps a few tough bacteria that may wait billions of years for a more suitable host and habitat to come along. It’s likely that a few lie dormant inside a lander vehicle.  

In my personal view, interstellar travelers would probably be tourists, after the first few introductory handshakes and gift giving. (The whole alien invasion thing being silly as an alien species wanting to get rid of us would probably just engineer a virus.) Would they be interested in our beaches? Probably not, they’ve probably seen better. But maybe they would be most interested in our tasty fruits. Perhaps they come from a planet without tree fruits and have never tasted a perfectly sweet mango so succulent and juicy that it should properly be eaten in the bathtub, an essential human experience. Perhaps they have never tasted cold watermelon on a hot day. Yes, I think space tourists would come for the fruit, as they are one of the most amazing things about our planet.

One can pick tasty food right from the tree. What a planet!