This week, my son Zack has been shadowing me at work. This is an official internship that all 9th graders in France do. He talked to some other researchers in my department (the Laboratoire d’Astrophysique de Bordeaux) and visited the labs where they build cool stuff (like electronics for radiotelescopes and pieces used in space…
A group of planets can share the same, stretched-out orbit around a star. And it’s pretty extreme.
The landscape of exoplanet systems is a wasteland: from an orbital point of view, the majority of systems look like the beat-up survivors of giant dynamical battles. The reason for this is simply that their original configurations were not “Lindy” — that is, not built to last indefinitely.
If it exists, Planet Nine should be found in the next few years by the Vera Rubin telescope. The problem is: no one know how a planet could have got there — until now.
While we humans get massive health benefits from social interactions, the same cannot be said for planetary systems. Passing stars are like darts being thrown at the Solar System.
The classic sci-fi series Firefly takes place in a 5-star system called the Verse. Unfortunately, the Verse as it was originally envisioned is unstable. Let’s re-imagine the Verse — or actually, four different “Better Verses” that are stable and include all of the elements that made Firefly such a great show.
Life on Earth has about a billion years left. There’s a 1% chance of a star zooming within 100 astronomical units of the Sun in that time. Could a flyby rescue life on our planet?
This is a re-post of an article written by Jason Wright, Steve Desch and myself, and published on medium on July 18th. It’s a more nicely laid out, somewhat more clearheaded, and less snarky version of my blog post ‘Oumuamua: was it aliens? (spoiler: no).You can find the original version here. Discovery of the first…
Could a protoplanet, or even a full-sized planet, be lurking in the icy darkness of the Oort cloud?
It’s time to revisit one of my favorite topics: co-orbital planetary systems, in which more than one planet share the same orbit around a star. (Side note: co-orbital systems can exist on different size scales — many stars can share an orbit around a black hole, or many moons share an orbit around a planet,…
It’s time for an astronomy poem throw-down: me against Chat-GPT. It’s on like Donkey Kong!
To celebrate the opening of Avatar 2, I made a series of slides to give a little more astrophysical context to Pandora. And, like the movies, it’s all about the visuals…
Earth will lose its oceans. Chaos may destabilize the rocky planets. The Sun will go red giant and swallow the inner planets. The outer planets’ orbits will widen as the Sun becomes a white dwarf. Passing stars will destabilize the planets’ orbits and, in about 100 billion years, finally strip away the last planet.
The list of factors needed for life to originate on Earth remains uncertain, although water was essential. Earth’s water was likely delivered by planetesimals scattered inward by Jupiter. Yet, ironically, Earth would probably be much wetter with no Jupiter.
TL;DR: The planets’ orbital shapes, tilts and spins oscillate due to the gravity of the other planets — this has a strong effect on Earth’s climate. On billion-year timescales the terrestrial planets’ orbits are chaotic and cannot be predicted precisely.
Asteroids and comets are the leftovers from the planets’ formation. They’re like the potato peels that end up on the floor instead of in the mashed potatoes. So, what have those leftovers been up to the past few billion years?
TL;DR: The Moon is thought to have formed in Earth’s last giant impact with a planetary embryo about 100 million years after the start of planet formation. Highly-siderophile elements indicate that ~0.5% of Earth’s mass was accreted after that point.
TL;DR: The giant planets underwent a dynamical instability that shook up the entire Solar System and likely ejected an extra ice giant. The instability happened early, perhaps triggered by the dispersal of the gaseous planet-forming disk.
This is chapter 6 in the Solar System’s story. This is an action-packed, epic chapter in which a lot of pieces of the puzzle are put together in different ways. (It’s my favorite part.)
TL;DR: Most giant planets form in a bottom-up way, by first growing large cores and then piling gas on top. They migrate throughout their formation. Jupiter may have protected Earth from migrating ice giants.
TL;DR: Earth- to Neptune-mass planets migrate through the disk — usually inward, and fast. Giant planets carve gaps in the disk (“anti-donuts”) and migrate slowly, usually inward. Things can get crazy when lots of planets migrate together.
This is chapter 3 in the Solar System’s story. We’re chugging along, growing bigger and bigger things… Planetesimal accretion After mountain-sized (~100 km-scale) planetesimals form from concentrations of drifting pebbles, they continue to grow in two ways. The simplest growth route for planetesimals is simply to crash into other planetesimals; this is called planetesimal accretion….
TL;DR: planetesimals are mountain-sized rocks (sometimes with ice) that grow from clumps of drifting dust (“pebbles”). The two types of meteorites come from planetesimals that formed in different parts of the Solar System and remained separate.
The TL;DR version of this post: the Sun formed in a cluster of about 1000 stars. The Sun’s gas-dominated disk disappeared in a few million years, about the same timescale as the cluster’s dispersal.
This blog series will discuss what we know (and don’t know) about the formation and evolution of our Solar System.
Just like a doofus with the remote control bouncing between two TV shows, planets can bounce between stars in a binary system…
Time for an astro-thought experiment. You belong to a super-advanced civilization with the ability to shape the cosmos as you wish. You can move around black holes, stars, planets, comets and moons (like the builders of the ultimate planetary systems). What would your civilization plan for big celebrations? What are their ‘fireworks’? What astronomical phenomena…
Here’s something brand new – we made a big splash!
A pile of free-floaters just dropped with a crash!
A hundred new rogue planets! Yup, we just found ‘em
They orbit among stars instead of around ‘em.
If too many rocks hit a planet by chance
It breaks up the system’s whole resonant dance!
The time capsule must serve as a beacon. Any other civilization that detects it should immediately suspect that it is of artificial origin. And it needs to survive for countless billions of years.
This post starts off with some world-building, jumps into eclipses and moons’ orbits, and finishes with a brand new Kalgash system that Isaac Asimov would be proud of (dropped into darkness every 2000 years!). More than one planet can share the same orbit around a star. This is not big news: the concept of Trojan…
Just one stretched-out orbit takes up lots of space
Can’t add any planets, there just isn’t space
Now, circles are best. And trust me, I’ve tried
Eight or ten orbits fit nicely inside.
The Sun will puff up to gargantuan size
As big as Earth’s orbit. And fill up our skies
The red giant Sun will eat Venus alive
But Mercury’s first. It will not survive.
Where are those Trojans? Just where are they hiding?
Are they at the store, or maybe hang-gliding?
We think they exist — just what have we missed?
Well, every good story should end with a twist…
Some people like to call Jupiter and Saturn the "architects" of the Solar system, as though they had a clear plan for how our system should turn out. Not us. We think of the gas giants as bullies that pushed Earth around and made a lot of decisions for us.
This post is an adventure in world-building. I use N-body simulations to find orbital configurations of planetary systems that (I think) are completely new, pretty awesome and unexpected. It involves cohorts of co-orbital planets…
These poems were written for every age
There’s rhymes and astronomy on every page
There’s science galore, and plenty of jokes
It’s perfect for kids or for any old folks.
Ceres is Queen of the belt. She’s the best-a.
Her husband is Pallas. Court jester is Vesta.
She makes up a third of the belt on her own
She’s cratered and icy and sits on her throne.
Have you ever been lost in the desert?
Stumbling along the sand dunes, the Sun beating down on you, your mouth sticky and dry. All you can think about is water…
Sometimes removing the outer atmosphere from a Neptune-like planet can reveal an ocean paradise!
To start things off, a limerick: My dear old friend ‘Oumuamua I asked her — What’s up? What is new-ah? “I’ve been thinking of That guy Borisov The interstellar number Two-ah!” Figuring out what’s up with a new population of astronomical objects is like going to a party without knowing the dress code. Here’s what’s…
A while back I wrote a series of posts called How planets die. It was about all the ways planets can be sterilized or destroyed. I even made a “planetary death scale”. Gruesome stuff. Let’s liven things up with a new mini-series on Second-Chance Planets. These are planets that get a second chance at life. …
Planets and bread may have something in common. The starter. Some of the best breads use a yeast starter. A starter is just a small piece of dough from an older batch of bread. The starter provides the yeast for the next batch. Each batch builds on the last one. An essential ingredient for today’s…
Imagine this. You’re drinking your morning coffee. A small blob zooms at top speed through the kitchen, into the hall and out an open window. You only catch a quick fuzzy glimpse before it’s gone. What was that thing? What’s your first guess? A neighborhood cat? A squirrel? Maybe something more exotic like a raccoon…
A space mission to intercept an Oort cloud comet — or, if we’re lucky, an interstellar object like ‘Oumuamua.
Where would we be without the occasional asteroid crashing into the Earth?
Just like people, stars age. Their planets go along for the ride and are often killed or maimed in the process….
If trees could scream, would we be so cavalier about cutting them down? We might, if they screamed all the time, for no good reason. — Deep Thoughts by Jack Handey This series is about how planets die — it is introduced here. Earth is a cosmic freaking paradise. Just look at our neighboring planets:…
If you ever drop your keys into a river of molten lava, just let them go because, man, they’re gone. — Deep thoughts by Jack Handey This series is about how planets die — it is introduced here. What do you think of when you hear the word tides? Ocean waves? The Moon? Maybe sitting…
Gas giants have murdered rocky planets (or their building blocks) around ~5 billion stars in our galaxy! (Usually by dropping them onto their Suns!).
Just like people, planets are born and they die. We know how people die. But google “how planets die” and you’ll get the wrong answer.
Can moons orbit moons? wondered Juna and I.
Some planets have moons, you know, up in the sky
But none of those moons has its own moon around it.
When Juna’s son learned this he just was astounded!
Planets orbit stars. Moons orbit planets. But no moons have their own moons (let’s call them submoons). Why is that?
One star. Two planets share an orbit, with one following a horseshoe-shaped path around the other. Boom!
Welcome to what might very well be the culmination of the Building the Ultimate Solar System series. Teaser: the system built in this post could also be called the Ultimate Engineered Black Hole Eyeball Ringworld Solar System (if you’re really not into the whole brevity thing). Our Solar System has one habitable planet. A few…
Short answer: Well sort of, but it’s more useful to think of it as being built from the same stuff as comets. Like an Uncle of the comets. Read on for an explanation. Earlier this week my wife mentioned a headline she saw. “Pluto is a giant comet? Whoa!” It was all over the place:…
What happens when the central body in a planetary system is replaced with a million-Sun black hole?
One fine week in May, well, I needed some peace
I packed up my bags and I headed to Nice…
Mars is a weirdo. (Well, as far as planets go). Why is it so small (just 11% as massive as Earth)?
Planets are kind of my thing. But black holes are awesome too. I mean, they can just suck you right in… (I will never apologize for my bad jokes!) I want to bring black holes and planets together. In this post, I’ll first introduce black holes. Then we’ll build the Black Hole Solar System. In…
Let’s find out what it takes to build a system in which a planet remains in perpetual daylight, except for once every few thousand years….
Isaac Asimov‘s sci-fi stories are one reason I wanted to become an astronomer (I talked about this in a recent interview). So I’m a little sad to shoot down a classic…. Nightfall is a classic Asimov story (and later, novel). The residents of a planet called Kalgash live in system of six stars that leaves…
I once ordered a beer then straight away spilled it all over the bar. There was just a tiny sip left in the glass. Frowny face.
Remember ‘Oumuamua, the weird-shaped rock flying through the Solar System? Just like my sip of beer, it might only be a small piece of what it once was.
Gas giants are the bullies of planetary systems. They are hundreds of times more massive than small rocky or icy worlds, so when gas giants throw a tantrum, their whole planetary system feels it. Giant planet moons are among the innocent bystanders swept up in the chaos. Giant planets around other stars have different orbits…
In Rendezvous with Rama (by Arthur C. Clarke), a mysterious object is discovered passing through the Solar System. The object has a strange shape — it’s a giant cylinder. It was discovered by the Spaceguard survey, designed to find objects that might impact Earth (so-called near-Earth objects). Spoiler alert: the cylinder is a spaceship sent…
The asteroids may be cosmic refugees, ejected from their homes to wander the Solar System, eventually settling in the asteroid belt.
Imagine a dry Earth. No waterfalls. No oceans. No beer (or people to drink it). A sad place. Water is pretty important stuff. In this post we will go deep into how Earth got its water (much deeper than in this post from a while back). And since it’s connected with how Earth formed, our…
I always thought that only 2 or 3 planets could share the same orbit. I was wrong. And it changes everything (for a super-advanced civilization, anyway).
I stumbled upon a simple way to tighten up the Ultimate Solar System. And by stumbled upon, I mean I discovered that someone else had figured it out. And I took it.
Systems of super-Earths may form as long resonant chains, most of which go unstable.
Wake up now people, I’ve got some big news! You won’t want to miss this. You don’t want to snooze. We just found some planets while we were stargazing Gather ’round, listen up. These ones are amazing! And it’s not just one new planet. There are seven! All orbiting one star up there in the…
Trojan planets are the best! I am a big fan. I love the idea of two planets sharing the same orbit around a star. To me, it’s where physics meets magic. (Remember, we’re talking planets not condoms! See here for a little refresher, and here for another article about Trojans). As a planet orbits a…
At a Solar System party, in a room full of planets, the asteroid belt is full of angst. And it should be. It’s out of place. It’s wearing a clown outfit but it’s not a costume party. What makes the asteroid belt so different? Well, for one, it’s not just one object like each individual…
This planet and star, now, you really should know ‘em.
And that’s why I’m bothering writing this poem.
There is only one Superman. One Wonder Woman, one Captain America, one Ironman. All told, a few dozen superheroes. And billions of superhero fans. What about our Solar System? Are we one-in-a-million like Batman? Or a dime-a-dozen like Batman’s fans? How unique, how special is our Solar System? For the first time in human history,…
What happens when good planetary systems go bad….
Let’s keep building the ultimate Solar System. In Part 1 we chose our star. In Part 2 we chose our planets. In Part 3 we chose our planets’ orbit. In Part 4 we learned two ninja moves about orbits. In Part 5 we put the pieces together. In this post we will take the Ultimate…
Life is caught in a chicken-and-egg situation. For life to exist on a planet, the planet must of course have the right conditions for life. The planet must be habitable. But a planet’s habitability depends in large part on whether it already has life. It’s a lot easier for a planet with life to be habitable. So a planet needs life to be able to host life....
This post could also be titled: How blogging and social media help make science happen. Here is the story. Planet Nine was conjectured in late January 2016. In February 2016 I started to think about where Planet Nine may have come from. This led to 3 blog posts, each exploring a different origins story for…
Two days ago we built a planetary system with an Earth that has five Suns in the sky. It looks like this: Yesterday we explored the motions of the heavens on this 5-Sun Earth: how the Suns move across the sky and when night falls (not too often, it turns out). Today we are going…
In yesterday’s post we built a planetary system with an Earth that has five Suns in the sky. Here is what it looks like: Today we are going to pretend that we are inhabitants of this five-Sun Earth and look up at the sky. How do the Suns move across the sky? And, with all…
We Earthlings have just one Sun. Tatooine has two. Wouldn’t it be even cooler with three Suns in the sky? Or four or five or twenty? Several extra-solar planets have been found in triple- and even quadruple-star systems (for example, GJ 667C and PH1b). But none of these planets has more than two Suns because…
It is hard to know where things come from. If I drink a Belgian-style beer brewed in Colorado using hops from Washington state and I live in France, where did the beer actually come from? And what does that mean anyway? The cosmic situation is just as confusing. We know where the planets are right…
We are discussing the origins of Planet Nine. In part 1 we explored whether it could have been produced during an orbital instability in the early Solar System. In part 2 we showed that Planet Nine could have been captured from another star. Here we will explore another plausible idea that is a little less…
We are discussing the origins of Planet Nine. In part 1 we explored whether it could have been produced during an orbital instability in the early Solar System. Here we will explore a much more exotic origin. Scenario 2. Planet Nine is a planet that formed around another star and was captured by the Sun…
It’s official: there might be an extra planet in the Solar System. It’s called Planet Nine. Like Hansel, it’s so hot right now. To find it you must trek past Uranus and Neptune into the dark reaches of the Solar System. It’s on an orbit hundreds of times larger than Earth’s, that takes 20,000 years…
Carl Sagan famously called Earth the "pale blue dot". Viewed from a large distance, that is what our complex, vibrant, living planet looks like. In the search for life around other stars, we should be looking for other pale blue dots, right? Maybe not. There is some reason to think that not all habitable planets…
Welcome to Real-life Sci-fi worlds. I use science to explore life-bearing worlds that are the settings for science fiction stories. This post is a pared-down summary of an article I wrote for Aeon in April 2015 — see the original article here. The Sun is pretty key for us here on Earth. The number one…
There are at least three aspects of the Solar System that are weird or at least unusual: No hot super-Earths. About half of stars contain a planet larger than Earth interior to Venus’ orbit. We don’t have one. That puts us in the minority. Jupiter. Only about 15% of Sun-lilke stars appear to have gas…
Welcome to Real-life Sci-fi worlds. I use science to explore life-bearing worlds that are the settings for science fiction stories. We have already taken a look at hot Eyeball planets. Today, I have a post on Nautilus’ blog about Eyeball worlds, both icy and hot. Check it out here. The article is a bit shorter…
Welcome to Real-life Sci-fi worlds. I use science to explore life-bearing worlds that are the settings for science fiction stories. Up today: can the moon of a gas giant planet — like Pandora from the movie Avatar — really be habitable? Pandora is one of the coolest-ever settings for a science fiction story. The life-bearing…
Welcome to Real-life Sci-fi worlds. I use science to explore life-bearing worlds that are the settings for science fiction stories. Up today: a desert planet like Arrakis from the classic Dune books (and the movie and miniseries). A tribute for author Frank Herbert‘s birthday (a couple days late). Dune is one of the all-time classic…
Welcome to Real-life Sci-fi worlds. We are using science to explore life-bearing worlds that are the settings for science fiction stories. Up today: an Earth-like planet orbiting a brown dwarf. Setting Planets have been found orbiting all kinds of stars. Stars like the Sun. Stars brighter and fainter than the Sun. Giant stars. Planets have…
Welcome to Real-life Sci-fi worlds. We are using science to explore life-bearing worlds that are the settings for science fiction stories. Up today: the oscillating Earth. Setting Earth’s orbit is not fixed. Gravitational kicks from the other planets change the shape of Earth’s orbit. Earth’s orbit oscillates between being perfectly circular (having an "eccentricity" of…
Welcome to Real-life Sci-fi worlds. We use science to explore life-bearing worlds that are good settings for science fiction. Up today: the hot Eyeball planet. Planets very close to their stars are too hot for life, right? Well, not always! Take the Earth and move it closer and closer to the Sun. It gets hotter…
Welcome to Real-life Sci-fi worlds. We are using science to explore life-bearing worlds that are good settings for science fiction. Let’s take the Earth and change just one small characteristic: the shape of its orbit. Setting. Earth’s orbit is nearly a perfect circle. Earth is always the same distance from the Sun (to within a…
A desert world with two suns in the sky. The jungle-covered moon of a gas giant planet. A planet completely enveloped in ice. A stormy ocean-covered world. A planet infested with bubbling lava fields. These are the settings for science fiction stories. They paint pictures of other worlds. Where life can exist but things are…
Giraffes are covered in patches. The patches are brown and the space in between the patches is white. Everyone knows this. Here is something you probably didn’t know: you can see those patches in infrared light. In simple terms, infrared light measures heat (at least at the temperatures we are used to in everyday life). …
I discovered something spectacular completely by accident. I was getting ready for the announcement of the discovery of the extra-solar planet Kepler-186 f. You remember, the Earth-sized planet in the habitable zone? It was all over the news (even in French) just a couple months ago. I made an animation of the Kepler-186 system. The…
We are building the ultimate Solar System. In Part 1 we chose the right star. In Part 2 we chose the right planets. In Part 3 we chose the right orbits for the planets. In Part 4 we learned two ninja moves about how more than one planet/moon can share the same orbit. Today’s…
We are building the ultimate Solar System. In Part 1 we chose the right star. In Part 2 we chose the right planets. In Part 3 we chose the right orbits for the planets. Today’s job: Discovering two ninja moves that will allow us to pack way more worlds in the habitable zone. The…
We are building the ultimate Solar System. In Part 1 we chose the right star. In Part 2 we chose the right planets. Today’s job: choosing the right orbits for the planets. Let’s get started. Our goal is simple. We want to pack as many planets into our star’s habitable zone as possible. We…
We are building the ultimate Solar System. In Part 1 we chose the right star. Today’s job: choosing the right planets to put in our ultimate Solar System. Let’s stick to two defining characteristics: a planet’s size (or mass) and its composition. We want Goldilocks-ish planets. They shouldn’t be too small, too big, too…
We are building the ultimate Solar System. Here is an introduction to the game. What kind of star will anchor our ultimate Solar System? It comes down to two choices: stars like the Sun or cooler, redder stars sometimes called “cool stars” or “red dwarfs”. Why not stars bigger than the Sun? Because they…
A while back I performed an experiment called build a better Solar System. The game was to make better use of the Solar System’s habitable real estate. In the game I was required to keep all of the Solar System’s planets (and large moons) and their orbital configurations. Just by switching the orbits of different…
That spanking new planet’s already a star. K-186 f, you know who you are. You’re making us wonder if we’re all alone. The planet out there in the habitable zone. I’ve been on the radio. Been on TV. Talking ‘bout the planet. Just what can we see? Just what do we know about this special…
In the spirit of last week’s poetic post, here are two more stanzas for your reading pleasure…. There is a new exoplanet in town. This planet has only just now been found. Why should you care? It’s only one more. Well this is one planet we’d love to explore. This planet’s orbit is really just…
Here is a tale ’bout a bright star named Vega. For years, astronomers have combed through their data and discovered that Vega is more than a star. It’s surrounded by dust clouds: one near and one far. Next to the star is some dust that’s quite hot. We’ve only just found it. There isn’t…
Carnival mirrors. They make you look…. different. Here’s what my son Zack looks like with one carnival-mirror effect on my computer. If every planet we saw was reflected in carnival mirrors, how would we figure out what the planets really look like? It turns out this is how it actually works! Every time we detect…
We’ve discussed some classes of planet that are pretty strange: hot super-Earths, hot Jupiters and eccentric gas giants. But that was just the warm-up. In this post we’ll check out three more extra-weird ones. First up: Tatoine planets. In case you are less nerdy than you should be, Tatooine is where Luke came from in…
Hot Jupiters: check. Super-Earths and mini-Neptunes: check. Up next is another unusual class of planet. But what is different is not these planets’ physical properties but the shapes of their orbits. Time to get technical. An orbit is the path a planet follows around its star. The simplest orbit is a circle with the star…
It’s official: you are weird. It’s nothing personal, you can’t help it. You live in a weird Solar System. It’s just not like other planetary systems. It’s just not SUPER enough…. Most Sun-like stars have a planet orbiting close-by. Not a hot Jupiter — those are rare. Planets just a little bigger than Earth are…
Let’s meet a planet called WASP-12b. [Before you ask, extra-solar planets are named based on how they were discovered or their catalog number. Wasp-12b is the twelfth found by the WASP (“Wide Angle Search for Planets”) survey. The “b” indicates that the object is a companion; Wasp-12 itself is the planet-hosting star.] WASP-12b is a…
We have a lot of weird neighbors. By neighbors I mean planets orbiting other stars. And by weird I mean that most of the extra-solar planets that we know look a lot different than the planets in the Solar System. To start with, let’s take a look at our neighbors’ houses. By houses I mean…
Oceans cover 71% of our planet. About 60% of the human body is water (more for kids, less for adults). Beer is 90-97% water. But, on a global scale, Earth is actually very dry. Earth is only about 0.1% water by weight. If all of Earth’s water were smushed into a ball it wouldn’t even…
[This post is co-written by Franck Selsis] Where should we look for extra-solar life? In a star’s habitable zone of course! Any planet in that magical Goldilocks zone must host life, right? Well, not exactly. The habitable zone should really be called the liquid water zone. A planet with the right characteristics that orbits its…
One of the most exciting recent things that I’ve worked on recently — with colleagues in France and the US — is a new model for how the Solar System formed that we call the Grand Tack. “Why do we need a new model for how the Solar System formed?”, you might ask. “What was…
[UPDATE: a new series on building the ultimate Solar System starts here] The Solar System is a disappointment. It does contain an inhabited planet with forests and oceans and frisbees and beer (Earth). But it only has one. There are a couple worlds with some potential, but they are pretty disappointing too. Jupiter’s moons Europa…
A primary theme of this blog is to explore the different processes that affect the existence and evolution of planets that could harbor life. Today’s question: Are binary stars good or bad? Short answer: BAD, but not in all cases or for the reasons you might expect. (Jump to the end for a quick summary…