“Well you run and you run to catch up with the Sun but it’s sinking,
racing around to come up behind you again.
The Sun is the same in a relative way but you’re older,
shorter of breath and one day closer to death.” -Pink Floyd
For the last four-and-a-half billion years, the Earth has spun on its axis, orbiting its parent star: our Sun. Today, our home planet looks something like this.
Looking at our world, even from outer space, you see some very familiar features that we think of as essential parts of our world. The vast, watery oceans. Our substantial (but not too thick) cloud-filled atmosphere. And the great land masses: our continents. These continents are, perhaps, the most striking feature to a traveler looking down on our rock from space, as the land on our world is not merely the color of the rock that composes it or the ice frozen upon it.
No; huge swaths of our Earth’s land is transformed by the color of the life that dwells upon it.
The way we got here is a remarkable story in its own right. What we commonly think of as complex life — the plants and animals visible to our naked eyes — has existed on Earth for only around 600 million years.
Prior to that, life was mostly colonies of single-celled organisms, engaging in relatively simple life processes, like turning sunlight into energy, or somewhat more complex lifeforms feeding off of that abundant biomass. It makes you wonder what took so long; what took the Earth around four billion years to bring about the large plants and animals that have dominated the planet?
We’ve gone from fish to insects to reptiles and dinosaurs to (eventually) birds and mammals. We’ve gone from the seas up onto the land and into nearly every possible location on the planet. And yet, what science tells us is that for nearly 90% of the Earth’s history, we didn’t have anything like what we have today. It turns out we’ve actually been incredibly fortunate to go down the path that we did.
The atmosphere that we take for granted is a relatively recent thing. In particular, it took billions of years of organisms turning sunlight, carbon dioxide and water into carbohydrates — an energy source that could be used even in the absence of sunlight — which produced oxygen as a by-product. At first, this trace amount of oxygen was absorbed by the oceans or by the seabed rock. Once the oxygen began to make its way out of the oceans, it was absorbed by the land surface. Finally, the oxygen accumulated in the atmosphere, paving the way for life as we know it.
It took more than four billion years for life to make it onto land on our planet, and we’ve got maybe another 500 million to one billion years left.
What, that’s it?
Yes, that’s it. Why such a short time?
Because the Sun, like all stars, burns more luminously as it gets further and further along in its life cycle. By the time its energy output increases by another 10-20%, the oceans will boil, and terrestrial life as we know it will cease to exist.
If we had a cooler, lower-mass star, it would burn its fuel more slowly, and increases in such a star’s energy output would give us more than this narrow, 1-1.5 billion year window for land-based life.
That’s not so hard; while our Sun certainly isn’t the biggest, hottest, or brightest star out there, being a G-type star, only 5% of the stars in existence are brighter and hotter than our Sun! Most stars — meaning around 90% — are either K or M-type stars, which not only live longer than our Sun, but burn cooler and in a more stable fashion than our Sun does.
So while our Sun and Earth have been around for 4.5 billion years, the Universe has been around for 13.7 billion, or more than three times as long. If you were to condense the entire history of the Universe into one calendar year, the gas cloud that collapsed, forming the Sun and Earth, wouldn’t have done so until early September of that year.
That’s good, because back on January 1st, there was no carbon for our sugars, nitrogen for our DNA, oxygen for our lungs, calcium for our bones, iron (or copper) for our blood, or phosphorous for our body’s (ATP) energy system. There was no silicon for the “rocky” part of our rocky planets.
It took generations of stars to live and die, fusing their primordial hydrogen and helium into the heavier elements that make us up, spitting that spent fuel out into the Universe once those earlier stars reached the end of their life cycles.
But did we really need 9+ billion years of previous generations of stars to have the type of planet we have today? What if these generations came and went quickly in some places in the Universe, and gave rise to rocky planets many billions of years before Earth was a twinkle in its grandfather-star’s belly?
What if, instead of in September of the Universe’s history, there were rocky planets in the Universe’s early days, some of which might still be around today?
If this possibility sounds exciting, have I got news for you.
375 light-years away, here in our own galaxy, lies an old, non-descript star, just a little less massive than our own Sun. If our Sun formed in the Universe’s “early September”, this star, HIP 11952, was formed in late January/early February, an estimated 12.8 billion years ago.
What’s remarkable about this star? It’s the oldest, most ancient star ever confirmed to have planets orbiting it!
So far, they have confirmed two gas giants planets orbiting it, with the smaller one just a bit less massive than Jupiter, while the more massive one nearly is three times as heavy as our Jovian giant. The star itself has fewer heavy elements than any other star ever found with planets around it, but, compared to most other stars its age, is extremely enriched with these elements essential to all we hold dear.
We’ve long known that there are regions of space that burn through generations of stars much more quickly than, say, our corner of the Milky Way does. A prime example is any actively star-forming region, such as the center of our own galaxy.
With the oldest confirmed gas giant planets around it (according to this research, published last month), could this star also have rocky planets around it, too? With a longer lifetime than the Sun, if there are rocky planets here, could they have harbored complex, macroscopic life for not just half-a-billion years, but for many billions of years?
If so, what would that look like? And if they were technologically savvy, what could they accomplish?
And if not, we’ve got literally billions of old, cool stars — stars that may be rich enough in heavy elements to have rocky planets — to sift through and search. We’ve found solar systems with Earth-sized (or smaller) planets, we’ve found solar systems with rocky planets in their star’s habitable zones, we’ve found cool stars, sun-like stars and hotter stars with rocky planets, and now we’ve found very old stars with planets around them, too.
We normally think of Earth — and the complex life on it — as the epitome of what the Universe can create with its building blocks. But there’s a whole Universe out there just waiting to be discovered, and what’s out there may be more fantastic than anyone has ever imagined.
(My apologies for the unusually long time between posts. I thought a few times about cranking out something short and light, but you’ve grown accustomed to things being of a certain quality here, and I wouldn’t dare disappoint you. Hope it was worth the wait!)