with Ethan Siegel • May 16, 2026
Greetings readers,
I always have a new slate of stories for you each week, but they don’t always have a consistent theme to them. This week, though, all six stories, including an all-new podcast about Neptune’s giant moon, Triton, focus on one of the most exciting concepts in science: discovery. We discovered more about the inner structure of the giant, nearby active galaxy, Messier 77, just by looking at it with JWST. Combined with the fact that it’s one of the only known neutrino-emitting galaxies in all the Universe, something profound is surely afoot. We have a history of discovery when it comes to identifying the most distant cosmic objects, and wow, have we come a long way since the development of the first telescope! We found an unexpected atmosphere on a tiny world, just 500 km across, in the distant Kuiper belt. And that’s just the start.
We also took a deep dive into the notion of “fundamental,” revealing precisely why including only the fundamental ingredients of the Universe and the laws that govern them isn’t enough to reproduce everything we observe. To get there, extra pieces of information — such as initial conditions and/or boundary conditions — are required. For Ask Ethan, we took on the question of the age of the Universe: whether it can differ for different observers in different regions of space or whether it depends on one’s motion through space. And if you’ve kept up with our stories over the last two weeks, you’ll recall that we gave the science case for keeping Pluto out of the class of “planet,” and then a counterpoint with arguments for why its planethood should be reinstated. Well, from our podcast, Triton originated from the Kuiper belt and is both more massive and larger than Pluto; should it be a planet, too? Have a listen for yourself, and let us know what you think!
There’s always more to wonder about and more to ponder in our quest to understand the Universe. As long as we remain curious, there will always be more to explore. Science may only ever be able to give us our best approximation to a picture of reality thus far, but when you consider how far we’ve come, it’s arguably the most remarkable achievement of all.
All the best,
Ethan
THE PODCAST
Starts With A Bang podcast #129 – Triton and the outer solar system
Neptune was discovered in 1846, and its large moon, Triton, was discovered just 17 days later. Little did we know, we had just found our first body that originated from the Kuiper belt. As we look at the geology, interior processes, and for hints of life on planetary bodies all across the solar system, it’s worth remembering how important outer solar system bodies can be. In this episode, we take an in-depth look at all that’s going on around Uranus, Neptune, and beyond, and take a look at the cooler side of things: the icy worlds in the far reaches of our cosmic backyard.
COSMIC BLINDSPOT
What physics gets wrong about the idea of “fundamental”
Our quest for the most fundamental thing in the Universe has led us to the elementary quanta that compose everything we know and interact with. But this bottom-up approach ignores two enormously important aspects of reality: boundary conditions and top-down conditions that govern the cosmos. In searching for answers only at the smallest scales, we may be overlooking truths that emerge from the largest ones.
ASK ETHAN
Ask Ethan: Is the Universe the same age everywhere?
From our perspective today, 13.8 billion years have elapsed since the start of the hot Big Bang: the current age of the Universe. But relativity tells us there’s no universal standard for time, meaning different observers could measure different cosmic ages. Even so, almost everyone, everywhere, would still arrive at nearly the same value: 13.8 billion years. Here’s why.
If you have a burning question about the Universe,
email startswithabang@gmail.com!
JAMES WEBB SPACE TELESCOPE
Cosmic beacon unveiled inside nearby active galaxy by JWST
Just 45 million light-years away, the giant face-on spiral galaxy Messier 77 shines with a brilliant, active nucleus. Discovered in 1780, it has been imaged many times, including by Hubble, and is one of only four objects linked to neutrinos detected on Earth. But new JWST images, especially in mid-infrared light, reveal its central region like never before. Here’s what we found inside, and what it shows about JWST’s unique capabilities.
A LOOK TO THE STARS
A brief history of the cosmic distance record
When we gaze out into the depths of space, the glittering points of light that we see represent objects at a wide variety of distances: in our solar system, in our galaxy, and from far beyond. With the naked eye, the most distant objects we can observe are typically just a few million light-years away: galaxies in our own cosmic backyard. But with telescopes, we can see much farther. From galaxies to quasars to the Hubble era all the way to the modern JWST era, we’ve broken the old cosmic distance record many times over. Here’s how far we’ve seen in space and time.
ICY WORLD SECRET
The discovery of an atmosphere on a tiny Kuiper belt world
Back in the late 1990s and early 2000s, planetary astronomers began finding many solar system bodies out beyond the orbit of Neptune: trans-Neptunian objects, primarily located in the Kuiper belt. One of them, 2002 XV93, was initially thought to be unremarkable: small, about 500 km in diameter, and in a 3:2 orbital resonance with Neptune. But a stellar occultation in 2024 revealed a surprise: an atmosphere. This object is suddenly a whole lot more interesting, being only the second known Kuiper belt object, behind Pluto, to have an atmosphere. Here’s how that discovery happened, and what it might imply.
Ethan Siegel, Ph.D., is an award-winning theoretical astrophysicist who's been writing Starts With a Bang since 2008. You can follow him on Twitter @StartsWithABang.
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Outstanding topic. In fact the act of "Discovery" merits a more lengthy essay, almost as if the act itself is one of the many items on a "Periodic Table of Human Events of Consequence".