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Paul Byrne @theplanetaryguy.com · 7h

This is a cool photo of Venus! Photographed through the rings of Saturn.

A complex, curving pattern of lines that make up Saturn's vast ring system, in various gold and grey hues. The white arc at right is the limb of the planet itself. A tiny point of light is just upper right of centre.

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Paul Byrne @theplanetaryguy.com · 16h

Oh my. The aurora borealis, seen in ultraviolet light from space. Our planet, putting on a show ✨

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Paul Byrne @theplanetaryguy.com · 30/09/2026

This is a photograph of the edge of one of Saturn's rings, looking down from above. Those spiky dark shapes are shadows. Shadows of giant towers of ice and dust grains clumped together that rise up to three *kilometres* above the 10-m thick rings.

A series of bands cross the image from left to right, brighter at the bottom and darkening towards the top. A band of empty space is at the top of the image. About a quarter down from the top is a complex pattern of jagged, spiky shadows cast onto the rings. The icy towers casting the shadows are seen here at a highly oblique angle.

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Paul Byrne @theplanetaryguy.com · 29/09/2026

This is gravitational lensing. Where the a bunch of galaxies are so, so massive they distort the fabric of spacetime itself, and bend the light from background galaxies billions of lightyears more distant.

From the source: "A massive galaxy cluster, made of many golden elliptical galaxies with the largest, brightest one in the centre. Heavily distorted orange galaxies appear all around the cluster, the largest concentrated in a large arc around the cluster's centre; these are images of very distant galaxies, created by gravitational lensing. A few galaxies are large and bluish-white in colour; bright, nearby stars are the same colour."

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Paul Byrne @theplanetaryguy.com · 28/09/2026

This is a photo of our home planet taken only a few hours ago! So what? We have photos of Earth taken from space every day. Ah, but *this* photo was taken by a spacecraft ON ITS WAY TO JUPITER.

From the source: "Mostly black space, most of Earth visible at the top right of the image. Part of a spacecraft visible on the left."

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Paul Byrne @theplanetaryguy.com · 28/09/2026

These are what the clouds on Jupiter look up close. The small patches of white are cloud tops, soaring above the main, colourful cloud layer. Image from NASA's Juno spacecraft during its 38th close approach to Jupiter on 29 November 2021, processed by Kevin Gill (@kevinmgill.bsky.social)

A complex, swirling pattern of lighter and darker clouds. One large system, angled to the upper left in this scene, is a tawny brown colour and is elongate. Another, more circular storm system is at lower centre, and is a grey–greenish colour. The background swirls are various shades of grey to blue; small, white features dot the scene.

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Paul Byrne @theplanetaryguy.com · 25/09/2026

This is a quick workup of what the night sky might look like on a world close to the galactic core. The planet is a rendering by Martin Kornmesser, to which I added the JWST image. So this scene is suggestive more than scientifically accurate. But still... imagine growing up under a sky like this.

The fore- and middle ground shows a rendering of a rocky exoplanet surface. The JWST Sagittarius scene from the first post occupies the upper half of the image.

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Paul Byrne @theplanetaryguy.com · 25/09/2026

The @stsci.edu posted this JWST image from 2023 earlier today—and I had to do the same. This is only a portion (about 50 lightyears across) of the Milky Way's centre. In this view, there's an estimated half-million stars. In our night sky, at a dark site, humans can see ~2,000 stars unaided.

From the source: "In a field crowded with stars, a funnel-shaped region of space appears darker than its surroundings with fewer stars. It is wider at the top edge of the image, narrowing towards the bottom. Toward the narrow end of this dark region a small clump of red and white appears to shoot out streamers upward and left. A large, bright cyan-colored area surrounds the lower portion of the funnel-shaped dark area, forming a rough U shape. The cyan-coloured area has needle-like, linear structures and becomes more diffuse in the center of the image. The right side of the image is dominated by clouds of orange and red, with a purple haze."

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Paul Byrne @theplanetaryguy.com · 24/09/2026

Like, this is an area about TWO PERCENT of the total scene. By my count, there's around 10 stars local to the Milky Way in this view. EVERYTHING ELSE IS A GALAXY

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Paul Byrne @theplanetaryguy.com · 24/09/2026

This is a SMALL version of the largest JWST image released so far—of IC 348, a star-forming region about 1,000 lightyears away. Open up the image and marvel in the incredible beauty even in our galactic neighbourhood. This is what it looks like when stars are born.

From the source: "A star-forming region. It is blanketed in thick clouds of gas and dust, millions of kilometres across, that form swirling patterns. Bright stars are scattered throughout the clouds, with the densest cluster situated in the centre of the scene. Each is crowned with six long points created by the optics of the telescope’s mirrors. In the upper right, a couple of hidden stars blast out long, glowing jets of material."

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Paul Byrne @theplanetaryguy.com · 23/09/2026

I've made an attempt to provide scale in this photo by adding a banana.

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Paul Byrne @theplanetaryguy.com · 23/09/2026

This is the Dragonfly spacecraft, ultimately destined for Titan, photographed in July during early construction at Johns Hopkins University Applied Physics Laboratory. The mission PI, Zibi Turtle, shared this image at the OPAG meeting today. Credit: NASA/JHU APL/Zibi Turtle

The Dragonfly spacecraft structure, showing the main chassis, the four struts to which the propellers will be attached, and various electrical and avionics boxes.

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Paul Byrne @theplanetaryguy.com · 23/09/2026

Another stunner from JWST—this time part of a *much* larger scene I'll post later. This portion is made up of stars and protostars in a cluster about 1,000 lightyears from Earth. The bright, multi-point features are nearby stars. The smaller features in the background are other galaxies.

From the source: "A star-forming nebula that contains young stars called protostars. Two of these protostars are shooting out long jets that are colliding with the nebula, creating glowing, colourful outflows. A few other protostars create orange and red areas in the nebula. Most of the image is covered by blue gas, with brighter areas, denser clouds and dark gaps; the bottom-left corner contains greenish-yellow gas."

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Paul Byrne @theplanetaryguy.com · 23/09/2026

Anyway, this paper is (sequentially) the first of a ten-paper collection at Space Science Reviews. The paper is free to access, read, and download: link.springer.com/article/10.1... And you can find the entire collection (so far) here: link.springer.com/collections/...

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Paul Byrne @theplanetaryguy.com · 23/09/2026

And, we posit, we should expect that underlying theme to be familiar, even if the particular notes and rhythms are different, even markedly so. The Solar System's rocky worlds tell us this, graphically shown in this figure. And we should heed this lesson!

A schematic timeline of major volcanic activity, the generation of an internal magnetic field, and the presence of surface liquid water for the inner Solar System worlds.

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Paul Byrne @theplanetaryguy.com · 23/09/2026

Finally, we turn to Io, Jupiter's crazy volcanic moon. Left to its own devices, Io would be inert. But it's subject to terrific tidal heating around Jupiter, and so serves as a useful template for understanding tidally heated rocky exoplanets. Io is so active, it has no impact craters! Map:

A global map of major geological features on Jupiter’s volcanic moon Io.

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Paul Byrne @theplanetaryguy.com · 23/09/2026

We treat Mercury and the Moon together, not so much because they're all that alike but because they're both *small* rocky planets. Lots of volcanism—for a while. But all major geological activity stopped a loooonnnnng time ago on these worlds, because they're small. Anyway, here are their maps.

A global map of major geological features on Mercury.

A global map of major geological features on the Moon.

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Paul Byrne @theplanetaryguy.com · 23/09/2026

Next is Mars*, a substantially smaller world than either Earth or Venus. Mars still has giant volcanoes, rifts, ice caps, and huge impact basins (especially in the southern uplands), but again no sign of plate tectonics. It was too small to replenish the atmosphere lost to space. *spits on floor

A global map of major geological features on Mars.

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Paul Byrne @theplanetaryguy.com · 23/09/2026

Next is Venus; we talk about its geological history and phenomena as we understand them (which isn't all that well). Here's a global map of Venus' geology; it's important to note that these are schematic maps, designed to be compared with each other. tl;dr: lots of volcanoes, no tectonic plates

A global map of major geological features on Venus.

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Paul Byrne @theplanetaryguy.com · 23/09/2026

A big part of the paper is the distribution and formational history of the major geological elements of Solar System worlds. So we included these maps, which show things like volcanoes, tectonic systems, etc. As our baseline case, this is modern Earth.

A global map of major geological features on Earth.

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Paul Byrne @theplanetaryguy.com · 23/09/2026

We take a deep dive into Earth in particular—since it's the world we understand best (even if there's LOTS about Earth we still *don't* understand). Here's a plot showing how we think Earth's bimodal crust grew through time; continental crust wasn't always there, but oceanic crust probably was.

A conceptual model for how Earth’s hypsometric curve has grown, with schematic curves for the early, mid-, and late Archean, and the late Paleoproterozoic to early Neoproterozoic, all highlighting the
progressive development of its bimodal hypsometry. The horizontal
axis represents proportional area, and the horizontal dashed line marks modern sea level. In the Hadean and early Archean, Earth likely had little exposed land.

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Paul Byrne @theplanetaryguy.com · 23/09/2026

A big part of the paper (and my career) is comparative planetology, the comparing of one world with another. So in this paper, we talk about how and when the crusts of these worlds developed. Those of Mars, Mercury, and the Moon are ancient; some of Earth is very recent. And Venus?? who tf knows

Crustal growth rates of the inner Solar System bodies plotted as cumulative crustal mass as a function of time. Since Earth has two types of crust, it has two curves. Mars, Mercury, and the Moon had the bulk of their crusts in place very early on. Some of Earth's continental crust is very old, but much of it isn't. The Venus crust might be very young, on average, maybe, somehow.

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Paul Byrne @theplanetaryguy.com · 23/09/2026

So, until/if we start imaging the surfaces of these worlds, what might we learn about them? Well, we argue that the Solar System's rocky worlds provide a useful template to start from. And that's the gist of the paper! So we start with Earth, Venus, Mars, Mercury, and the Moon.

Hypsometric curves for the inner Solar System worlds, normalized to their radius. These curves are essentially histograms that describe how much land surface is at a given elevation. Crucially, the hypsometric curve for Earth has two peaks (is bimodal); Mars is bimodal, but Venus, Mercury, and the Moon are unimodal.

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Paul Byrne @theplanetaryguy.com · 23/09/2026

The basic idea is that we're finding more and more exoplanets, including ones that—on the basis of radius and mass—are surely rocky. But that's usually all we have, even though it's tempting to call them "super-Earths" or to otherwise attribute (intentionally or not) certain properties to them.

A plot of planetary mass versus radius (relative to Earth) for known, confirmed exoplanets as of 4 December 2024. Venus, Earth, Uranus, and Neptune are labelled (not to scale). The red line denotes the threshold below which a world is usually taken to be rocky.

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Paul Byrne @theplanetaryguy.com · 23/09/2026

I said I'd do a thread about my new Space Science Reviews paper, so here it is! This is part of a collection of papers arising from a meeting at the International Space Science Institute in Bern in 2024: a workshop to better understand rocky extrasolar planets. A 🧵:

Interior structure models of Earth, Venus, Mercury, Mars, the Moon, and Io, all shown to scale and key elements labelled.

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Paul Byrne @theplanetaryguy.com · 22/09/2026

Interesting tidbit from today's briefing at the Outer Planets Assessment Group (OPAG) meeting by NASA planetary leadership: NASA is considering *two* flagships for flight—one to Uranus, the other to orbit and land on Enceladus. Both were Decadal priorities—but in series, not one over the other.

How does one do alt text for a graphic with loads of text?

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Paul Byrne @theplanetaryguy.com · 21/09/2026

This isn't the diseased skin of some alien—this is Mars! Taken by ESA's Mars Express spacecraft, this colour scene shows a portion of the planet's high southern latitudes where frost, dust, and sunlight combine to produce these pink and purple tones.

From the source: "A purple–pink–coloured patch of Mars, which is lighter on the left and darker on the right. A dark line runs from the top centre towards the bottom right, dividing the light and dark areas. At the centre of the image is a sharp light-coloured crater. Less sharp craters are scattered over the rest of the image. At the bottom left is a bright white-blue triangular patch; it looks icy."

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Paul Byrne @theplanetaryguy.com · 17/09/2026

HOLY SHIT NEW IMPACT CRATER ON THE MOON This crater is 222 m (728 ft) across, and formed in spring 2024. Statistical modelling tells us this is a 1-in-132 year event. So the last time a crater this big formed on the Moon was 1894.

A large crater with bright rays is situated in the centre of this image. The dark, pockmarked lunar surface makes up the background.

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Paul Byrne @theplanetaryguy.com · 15/09/2026

For your Tuesday, here's a shot of deep, deep, deep space from JWST. Every bright, six-pointed feature is a star in the Milky Way. Everything else—even the smallest, faintest dots—are whole galaxies millions to *billions* of lightyears away.

A spiral galaxy sits in the centre of the image; smaller galaxies dot the scene, some resolved only a small, colourful smudges. The six-pointed features are stars in the Milky Way.

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Paul Byrne @theplanetaryguy.com · 13/09/2026

Here, I added Voyager to this shot, now it's better

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Paul Byrne @theplanetaryguy.com · 13/09/2026

See that small bright object in the middle right of this image? That's the small icy moon Mimas. Floating in space against a backdrop of giant Saturn, the planet crossed by shadows from its rings.

A black swath of shadow crosses the scene from top left to bottom right. The background is various shades of blue and grey. A small, illuminated crescent is at upper right. The lower portion of the image is lighter grey/brown.

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Paul Byrne @theplanetaryguy.com · 12/09/2026

I have a new paper out! Over the weekend I'll do a thread on what the Solar System can tell us about rocky exoplanets— but for now, enjoy this to-scale set of cross sections I made of the rocky worlds in *this* system! (They're all different, but still all variations on a theme...)

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Paul Byrne @theplanetaryguy.com · 09/09/2026

This is what our home looks like from 6 billion kilometres away.

A set of colourful streaks of stray light across a dark, noisy background. At centre right is a small, pale, blue dot.

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Paul Byrne @theplanetaryguy.com · 09/09/2026

Modern film version (also you can't hear the dialogue):

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Paul Byrne @theplanetaryguy.com · 09/09/2026

In honour of the day that's in it—the 60th anniversary of Star Trek.

A Constitution-class heavy cruiser on a shakedown test past the Moon. Crescent Earth is in the background.

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Paul Byrne @theplanetaryguy.com · 09/09/2026

Astrophotographer Adam (AJ) Smadi caught this image a few hours ago from Washington state. A thin crescent Moon, sunlight illuminating the rugged lunar surface. And 2,400 times farther away—and on the other side of the Sun—mighty Jupiter, and its moons Io (left) and Ganymede (right).

A crescent Moon seen during the day, arcing from upper left to lower right of the frame. At lower centre is the full disk of Jupiter; the small dots to its upper left and lower right and Io and Ganymede, respectively.

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Paul Byrne @theplanetaryguy.com · 07/09/2026

Weird rock on Mars. Photographed yesterday.

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Paul Byrne @theplanetaryguy.com · 07/09/2026

Ground- and space-based telescopes have revealed something new at Saturn: a giant, ten-sided structure in the clouds near the planet's south pole. This decagon is almost stationary, extends deep below the cloud tops, and is similar (though not quite the same) as the famous north pole hexagon.

Left: A Hubble Space Telescope view of Saturn; the decagon at high southern latitudes is barely visible as a dark band. Right: A polar projection of those same data, where the dark decagon is clearly visible.

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Paul Byrne @theplanetaryguy.com · 06/09/2026

You can read the entire paper for free here! agupubs.onlinelibrary.wiley.com/doi/10.1029/...

Tessera on Venus, seen with radar backscatter imagery and a colour stretch that goes from rough (yellow) to smooth (purple).

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Paul Byrne @theplanetaryguy.com · 06/09/2026

I was invited to write up a short blogpost for the Planetary Geomorphology Image of the Month based on our recent JGR Planets paper! We make the case that some of the highlands on Venus have borders that form in the same way mountain belts on Earth do: planetarygeomorphology.wordpress.com

An oblique view from Google Earth looking approximately east, from around the location of Bourg-en-Bresse towards Geneva, which is situated at the eastern end of the crescent Lac Leman at center left. The Jura foothills in the foreground correspond to folds in volcanic plains that run parallel to larger folds in tesserae, which in this analogy are the Alps proper.

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Paul Byrne @theplanetaryguy.com · 04/09/2026

That small black circle is the planet Mercury, seen crossing the face of the Sun by NASA's Solar Dynamics Observatory on 9 May 2016.

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