Rumour is we recently passed a threshold where we have now found as many celestial objects as there are people who were ever born. Sounds weirdly true. But is it a myth or fact? I decided to investigate.
Top image: Hubble has found a whole lot of galaxies while looking at nothing in particular.
At first, I was thrilled: what a bit of poetic triumph, that we if we named every comet asteroid, planet, dwarf planet, and star for each person that ever lived, we'd have objects left over! Then I started fact-checking, and as so often happens with delightful things that I really want to be true, reality intruded.
The number of people who have ever been born are pretty straightforward to estimate. the number hovers somewhere just under 110,000,000,000 (depending on your naming system, that could be
1.1 trillion or 1.1 billion 0.11 trillion or 110 billion (thanks, darth & CL!)).
A celestial object is any physical, naturally-occurring object in space. That includes things like stars, moons, planets, comets, asteroids, but not space junk. It could also include entire systems of things, like galaxies, planetary systems, galactic clusters, and nebula. Actually counting all the objects is a non-trivial task.
Huh, we have a whole lot of moons floating around in space... Image credit: NASA
The first problem is, are we comparing to the number of objects we think exist, or the number of ones we've actually directly observed? The estimate for how many stars are in the universe is a number so big we don't have a name for it. Forget all the rocks and ice: we could give every person not just a star, but an entire galaxy!
It can't be estimates, so what about celestial objects we've actually observed?
Our solar system has a lot of stuff in it. Image credit: NASA
The solar system has 8 planets, and a handful of confirmed dwarf planets with another 353 potential candidates wandering around the Kuper Belt. From Earth on out, there are 146 moons, plus another 27 provisional moons for 173 moons overall. Hand-wave in its favour to 550 moons, dwarf planets, and planets.
Moving on out, we have at least a million main belt asteroids, and we've found 11,139 near-earth objects as of this week. ESA estimates that there might be a trillion comets in the Oort cloud, but we've only observed about 4,000 of them.
Going beyond our solar system, if we're generous with our rounding and declare all candidates are planets, we've found 5,000 planets and exoplanets. As for stars, the catalogue includes 2.5 million stars of magnitude 10 or brighter in 1.2 million catalogued galaxies.
If we stick to just observed objects, that's 3,720,750 objects. Even if we round even more generously, 4,000,000 is a far cry short of the 110,000,000,000 people ever born.
The observable universe is limited by the distance light could have traveled since the dawn of time. Image credit: Unmismoobjetivo
That's where I'm stuck: the estimated number of celestial objects is far, far greater than the human population can claim, while the actual observed number of objects is way too low. Admittedly, I couldn't find a modern, updated catalogue of nebula or galaxy clusters to add to the total, but I'm fairly certain that's not going to make up the missing 109,996,000,000 objects.
What thresholds have we recently passed that would bump the observed numbers up? Am I missing an entire class of celestial bodies in my Comic-Con induced stupor? What caveats could we hang off the estimates to bring the estimated-objects number down to our relatively puny every-human-ever? Can we find a way to rephrase this trivia into something that is both poetic and true?
Until then, I have to relinquish this bit of trivia, chucking it to the bin of myths and misunderstandings along with "10% of your brain is useful," "chupacabra don't exist," and "suicides fund the space program."
Tip via neuroscience graduate student Teagan Wall, who wants to know if this trivia is true.