How do you observe that the Universe is expanding? 

In 2011, the Nobel Prize in Physics was awarded to Saul Perlmutter, Brian Schmidt and Adam Riess for discovering that the Universe is expanding at an accelerating rate. We’d known for a while that the Universe has been expanding ever since its birth - but we didn’t know whether the expansion was slowing down, staying the same, or speeding up. 

So, how exactly do you discover something like this? 

Perlmutter, Schmidt, and Riess did it by observing a special type of supernovae: Type Ia supernovae. Supernovae are the explosive deaths of large stars, and they usually occur when a star runs out of fuel and collapses under its own weight, generating a shockwave that blasts its material out into space. However, this only happens when a star is big enough - the initial star has to have a critical, threshold mass, called the Chandrasekhar limit. Our sun, for example, won’t go supernova because the Chandrasekhar limit happens to be around 1.4 solar masses. When it runs out of fuel, our sun will instead gently blow off its outer layers and quietly become a dense core of carbon and oxygen, called a white dwarf. 

But here’s the kicker: not all white dwarfs stay white dwarfs. 

Some white dwarfs exist as one half of a binary system, where two stars orbit each other in a perpetual celestial dance. In some situations, the white dwarfs can actually “steal” matter from their partner star, siphoning it off and guzzling it up to grow more and more massive. Eventually, when their mass hits the Chandrasekhar limit, the white dwarf is ripped apart in a supernova. 

Image Credit

This happens in binary systems all across the Universe, and because these white dwarfs all go supernova at exactly the same mass, this means we know exactly how bright the supernovae are. When they’re observed through telescopes, some look brighter and some look fainter depending on their distance - but because we know their actual intrinsic brightness, we can work out how far away they really are. (You could do this yourself using a more earthly standard candle.) For this reason, Type Ia supernovae are called “standard candles”. 

In their observations, Perlmutter, Schmidt, and Riess realised that far away supernovae were more redshifted than the supernovae close by. “Redshift” is essentially a measure of how much the Universe has expanded since the light left the supernovae, so by comparing the distance and the redshift of the supernovae, they could create an “expansion history” of the Universe. 

This showed pretty clearly that the universe isn’t just expanding, it’s accelerating - i..e, everything’s flying apart more quickly than it was yesterday, or a century, or a billion years ago. Why? Dark energy. 

This week is Earth Science Week! It runs from 9-15 October and is an awesome time to explore and reflect on the natural world around you. Earth science is a diverse field that encompasses geology, oceanography and meteorology - it’s essentially the study of how the forces of our planet intersect.

Celebrate by learning a bunch of interesting stuff:

The above photos are some of the winners of the Geological Society of London’s 2016 Earth Science Week photo competition. Click through to see the rest!

The Universe’s Baby Photo 

The space between stars and galaxies looks completely black, but if you were to point a satellite dish towards any dark point in space, you would actually see a staticky glow a bit like the white noise that sometimes crackles across your TV screen. But this static is coming from all across the universe: no matter where you pointed your satellite dish, you’d record the same signal. But there are no astronomical objects that could create such a uniform signal - so what causes it? 

Let’s quickly review a fundamental idea: everything in the universe emits radiation. You, me, trees, zebras, toasters, tacos, Uranus, stars - they all emit a continuous spectrum of thermal radiation with a peak that depends on their temperatures. Cool things mainly emit radiation with long wavelengths and low energies, while hot things mainly emit radiation with short wavelengths and high energy. 

Image Credit

The uniform signal we observe everywhere in the sky is radiation with a wavelength of about 1 millimetre, which corresponds to a temperature of 2.7 Kelvin - very close to absolute zero. It’s called the cosmic microwave background (CMB) because it’s actually the leftover radiation from the Big Bang. 

When the Universe was born over 14 billion years ago, it was so hot and pressurised that atoms couldn’t form yet - instead, it spent 300,000 years as a soup of photons and hot plasma, which was made up of protons, neutrons, and electrons: the building blocks of atoms. The photons couldn’t get very far because they kept interacting with the pesky electrons floating around everywhere, and so the early Universe was trapped in a perpetual fog. But as the Universe expanded and cooled, atoms could finally form, and the photons escaped. 

The cosmic microwave background is a record of these early photons at the moment of their jailbreak. The Universe has since expanded massively, so these photons don’t appear as hot and energetic as they once were: they’ve been stretched out or red-shifted to much longer wavelengths and lower temperatures, to almost exactly 2.7 Kelvin (-270 degrees Celsius). They’re everywhere in the universe today - 400 of them in every cubic centimetre - and they’re like the Universe’s baby photos. 

By studying them and the tiny fluctuations within them, we can learn about the Universe’s infancy and how stars and galaxies began to form.

Our Galaxy is Being Invaded

If you shake off the bright lights of the city and head out into the country, you’ll see the bright band of the Milky Way stretching across the sky. The Milky Way is the galaxy we live in, our home metropolis populated by more than 100 billion stars, and it’s part of the Local Group: an imaginatively-named, gravitationally-bound group of galaxies, hanging out close to each other in space. We’ve known about most of our galactic neighbours for decades, like the Large and Small Magellanic Clouds and the Andromeda galaxy - but in 1994, astronomers realised that there was another one lurking right next door.

Image Credit: R. Ibata, R. Wyse & R. Sword

They were studying the stars at the centre of the Milky Way, where there’s a large bulge of high concentrations of stars, when they realised that some of these stars weren’t moving as expected. This odd group of stars were all moving together at the same speed, and it was soon realised that they didn’t belong to the Milky Way at all - they’re part of a dwarf galaxy chilling out on the other side of our galaxy’s central bulge. Dubbed the Sagittarius Dwarf Spheroidal Galaxy, it’s just 50,000 light years from the centre of the Milky Way, which isn’t very far when you consider that our galaxy is 100,000 light years in diameter.

But here’s the interesting part: our neighbour doesn’t just keep to itself. It’s a satellite galaxy of the Milky Way, orbiting us every billion years, and it can get pretty friendly, actually plunging through the plane of the Milky Way as it orbits. It’s orbited us at least 10 times in the past, and is going to pass through us again in the next 100 million years. In the first image above, you can see the blue spiral of the Milky Way with the orbit of the dwarf galaxy traced out in red.

Eventually, the tidal forces from the much bigger Milky Way will probably tear the Sagittarius Dwarf Spheroidal Galaxy apart, and we’ll absorb all of its stars into our own galaxy in an act of immensely cool galactic cannibalism.

Extraterrestrial volcanoes 

Everyone remembers making their first bicarb-and-vinegar volcano back in school, because there’s a special kind of happiness that comes from watching froth pour down the sides of your badly-painted volcano and slosh onto your classroom floor. For most people, volcanoes - simulated and real - are an endless source of fascination and sometimes fear...but did you know that Earth isn’t the only place in the solar system with active volcanoes? 

Lighting up Jupiter with Io 

Io, one of Jupiter’s largest moons, is the most volcanically active world in the solar system. It’s caught in a never-ending game of tug of war between Jupiter and two of its neighbouring moons, Europa and Ganymede, which literally stretch and compress Io with with their huge and uneven gravitational forces. The actual solid rock that Io is made of can bulge out by more than 100 metres and then back again, as if Jupiter is using Io as a stress ball. 

All this friction generates a whole lot of energy inside of Io, which creates heat that drives volcanoes on the surface. Voyager 1 and 2 first spotted these volcanoes back when they sped past in 1979, noticing that not only do the volcanoes spew out molten rock like Earth’s volcanoes, but some eruptions also blast out sulfur and sulfur dioxide up to 500km above the surface. 

What’s super interesting is that some of these particles become caught up in Jupiter’s magnetic fields and flow down to the poles, where they interact with the gases there and create brilliant aurorae.

Frozen explosions of Triton 

When Voyager 2 flew past Neptune’s largest moon, Triton, it captured images of geysers erupting from the surface. Plumes of nitrogen gas and fine particles of dust were blasted up to 8 km into the air, before falling back down to the surface like a weird, nitrogen snow - the dark streaks on the image below. 

But Triton’s volcanism isn’t due to immense tidal forces like Io: instead, it’s thought to be caused by solar heating. Triton’s surface is composed of a frozen, transparent layer of nitrogen atop a darker substrate below, and when solar radiation hits the surface, it becomes trapped by the darker layer. It’s kind of like the greenhouse effect, but in a solid object. This heats up subsurface nitrogen and causes it to vaporise, and eventually there’s so much pressure that it erupts out through the crust above. 

Fountains on Enceladus 

In 2005, the Cassini spacecraft flew right through a plume that had erupted from a cryovolcano on Enceladus, a moon of Saturn. Over 100 cryovolcanoes were discovered at Enceladus’s south pole, which blast out jets of ice-water and simple organic molecules. 

Like Io, the volcanic activity on Enceladus is probably caused by the powerful gravity of Saturn and its other moons. Enceladus gets stretched and compressed, heating up the interior and creating a subsurface ocean of liquid water. Sometimes, slushy ice and other materials get shot up through an opening in the surface and out into space. Some of this material falls back to the surface, and the rest is captured by Saturn’s massive E ring and orbits around the planet, so essentially the ring fed by volcanoes. 

Our Explosive Solar System 

Other bodies in the solar system are suspected to have active cryovolcanic activity too, like Ceres, Pluto and its moon Charon, and Saturn’s moon Titan - stay tuned for more explosive updates!

Chasing shooting stars

It’s New Year’s Eve, and after a tense three days of searching in the heart of the South Australian outback, Professor Phil Bland has finally found the impact site. After leaping off his quad bike and running across the salty mud flats, he falls to his knees and thrusts his hand straight into a hole smashed into the landscape. His arm disappears nearly half a metre into the earth - and when it emerges again, there’s a mud-slathered rock clutched in his fist. 

“It’s an iron meteorite, mate!” are Bland’s first, breathless words. He holds it reverently, wiping off the thick, clay-like mud. He’s kneeling on Kati-Thanda, also known as Lake Eyre, and what he holds in his hands is a hunk of rock older than the Earth itself. 

It’s also the first proof that the Desert Fireball Network works. 

Built by Professor Bland’s research team at Curtin University, WA, the Desert Fireball Network is an automated meteor tracking system made up 49 digital cameras dotted across the Australian outback. Over the next few years, it’s projected to watch a third of Australian skies - and it does exactly what its name says. It looks for fireballs. 

As meteors from the wider solar system plough down into the Earth’s atmosphere at hypersonic velocities, they burn up. For fleeting moments, they sear across the sky and light up the darkness. Often, bits of these meteors hurtle all the way down to the surface. The multiple cameras of the Fireball Network can spot a fireball and triangulate its path through the atmosphere, so its trajectory can be reconstructed in 3D. This can give information about the meteorite’s mass, its orbit and origins in the Solar System, and the location where it smashed into the surface. 

On November 27th last year, Professor Bland’s team got the heads up from their network that a fireball had blazed through the atmosphere and fallen to Earth in the middle of South Australia. Its landing site was narrowed down to within a small area in the bed of Lake Eyre, a massive salt lake, and so they knew they had to get to it fast: if too much rain came, any trace of the impact could be washed away. They organised to fly a spotter plane over the area to get eyes on the impact site, then the team flew across states, rented 4WDs and camping gear, got permission from the Arabana people, who are the traditional custodians of Kati-Thanda... Then finally, on December 31st, Bland pulled the meteorite from the mud just hours before heavy rains swept across Lake Eyre. 

It turns out that the meteorite itself is fairly ordinary - if you can call any 4.6 billion year old object ordinary - but the most interesting thing is that the Fireball Network could attach an orbit to it. It was traced it back to the asteroid belt between Mars and Jupiter, where it used to be part of a larger asteroid that broke up in an impact. This gives it incredibly useful context that other meteorite discoveries don’t have. 

If the team can observe and study enough meteorites and their original orbits, they’ll be able to make a geological map of the solar system. This will give invaluable insights into the solar system’s formation, especially the formation of the planets. Hopefully, it will help answer questions like: how did the Earth form? How are planets made? 

If you want to keep updated on the project, you can download their app - which also lets you contribute by reporting fireball sightings of your own, from anywhere in the world!

All images courtesy of Fireballs in the Sky

Commander Chris Hadfield

Can a gamma-ray burst cause a mass extinction? 

440 million years ago in the late Ordovician period, a mass extinction wiped out 85% of marine species. Most research indicates that glaciation was to blame, since it looks like the extinction was associated with a cooling climate and sea level decline, but a handful of scientists have a different idea: What if it was caused by a gamma-ray burst? 

A gamma-ray burst (GRB) is an intense flash of high-energy radiation thought to result from the collapse of a massive star. If one occurred close enough to Earth (within a radius of about 3,000 light years), the radiation could severely damage our biosphere. One study estimates that a GRB could occur within this radius twice every billion years. 

Gamma-ray bursts would be harmful because they would expose the Earth to highly energetic photons. When these photons collide with our atmosphere, they break apart molecules there, including the molecular oxygen that makes up the ozone layer - and destroying ozone allows damaging UV radiation in. The energetic photons would also produce nitrogen dioxide in the atmosphere, blocking out sunlight and causing global cooling, which would be lethal to photosynthesising organisms. 

Image Credit: Wikimedia

The damage a GRB can do is fairly consistent with what we know about the Ordovician extinction, more notably the fact that species who lived in environments more exposed to UV radiation seemed to suffer more severely. The surviving fauna of the extinction seem to have come from deeper water, where UV radiation can’t penetrate effectively or from higher latitudes. 

But currently, we don’t have any evidence that a nearby gamma-ray burst actually happened - so maybe a GRB alone might not be sufficient to completely explain the extinction. 

(By the way, recent studies have shown that gamma-ray bursts just aren’t that common in our galaxy anymore, because most of the massive stars that would collapse and produce GRBs have already done so - so don’t get too worried about GRBs causing a mass extinction in our lifetime!)  

Want to hear more about gamma-ray bursts and their threat to Earth? Have a listen to this UniverseToday podcast. 

What happened to the dinosaurs, anyway?

Long ago, dinosaurs roamed the Earth: sweeping through the skies on great leathery wings, hunting in forests with gnashing teeth, and thundering in herds across the plains. But about 65 million years ago, their world was brought to a sudden, crashing end. Have you ever wondered what caused it?

Fossilised remains tell us endless stories about the creatures they were, the world they lived in, and the world that killed them. They tell us that in the past 570 million years, the Earth has been devastated by five major mass extinction events .

During these events, 99% of all species that have ever existed were wiped out, but it didn’t happen spontaneously: evidence indicates they’re caused by cosmic impacts smashing into our planet.

What are cosmic impacts?

The asteroids and comets orbiting our sun are leftovers from when our solar system formed out of a cloud of dusty gas: bits that didn’t end up forming into planets. Earth is battered with a steady shower of them, and although most just burn up in the atmosphere, once in a while, we get one big enough to devastate our biosphere.

How much damage can an impact cause?

When you think of an asteroid, your mind probably conjures a picture of a burning rock hurtling down through the atmosphere, slamming into the Earth’s surface and creating a massive crater. Earthquakes and tsunamis may also feature in in this vision, since two-thirds of cosmic impacts land in the ocean (because our planet is so covered with them). The impact that killed the dinosaurs struck a shallow sea near Chicxulub, Mexico, and it created tsunamis up to 300m high. We’ve found deposits of marine fossils in Florida, Texas and Haiti that tell us the tsunami rushed 300km inland.

The location of the K-T impact crater, Mexico. Source: Atlasobscura

An impact like this can cause wildfires, which would create huge amounts of smoke, as well as put out chemicals that could case acid rain lasting years.

But surprisingly, the biggest threat to life is plain old dust. When they smash into the surface, impacts can hurl massive amounts of dust into the atmosphere, causing long-lasting dust storms that block the sun and darken the world. Without light and warmth, photosynthesising organisms like plants and algae - which rely on the sun for energy - would suffer, and so would all the organisms that depend on them.

The asteroid that wiped out the dinosaurs was a devastating event, causing the extinction of three-quarters of the animals living on Earth at the time.

But many species survived, including most mammals, birds, turtles, crocodiles, lizards, snakes, and amphibians - and from these lucky creatures, our world today evolved.

More cool stuff:

The new kid on the block has arrived! Just an hour ago, the Juno spacecraft braved intense radiation and successfully slid into orbit around Jupiter, ready to study the mysteries of the biggest planet of our solar system.

Welcome to Jupiter, little guy - and congrats to the HARDCORE NASA TEAM who guided Juno INCREDIBLY PRECISELY into orbit around a world over 800 million kilometres away.

Wanna know more about what Juno’s up to?

JUNO: The lowdown on NASA’s mission to Jupiter 

Ever since Galileo first turned his telescope to Jupiter back in 1610, we’ve been marvelling at the monstrous planet. We’ve been captivated by its sheer size (so big it can fit 1,300 Earths inside), its moons (all 67 of them), its incredible magnetic field (which creates shimmering auroras at the poles) and its swirling storms - including the Great Red Spot, which has been raging for more than 300 years. 

In mythology, Jupiter was the king of the Roman gods, and the goddess Juno was his wife. In one story, Jupiter draws a veil of clouds around himself to hide his mischief - and Juno was the only person who was able to peer through the clouds and see Jupiter’s true nature. Like its namesake, NASA’s Juno spacecraft  will help us unlock the mysteries beneath the giant gas planet’s thick clouds.

After travelling 2.8 billion kilometres over the past five years, Juno will arrive late Monday night and will spend nearly two years orbiting the giant gas planet.  Powered by solar panels each the size of a bus, Juno will study Jupiter’s atmosphere, finding out far the clouds and storms go down - are they just a thin layer, or do they go all the way down to the planet’s core? And what’s the core made of? Is it metallic hydrogen, or rock, or heavy metal, or something we haven’t even thought of? 

Juno will also help us study the formation of Jupiter and indeed the formation of the whole solar system. We know that Jupiter is made up of hydrogen and helium gas, like the Sun, but it also contains a higher proportion of heavier elements and we’re currently not sure why. Learning more about what Jupiter’s composition will help us figure out how it formed, over four billions of years ago when our sun was was newborn. This in turn will help us understand the formation and evolution planetary systems we’re discovering around distant stars. 

Juno will also study the Great Red Spot, measure the water in the atmosphere, and study the enormously strong magnetic fields and how they create Jupiter’s auroras. 

But Jupiter is a dangerous neighbourhood to explore. The intense magnetic field creates a radiation belt around the planet, made up of super energetic particles. Even though Juno is equipped with titanium vault to protect its scientific equipment, eventually the radiation will fry the spacecraft’s electronics. Then, NASA scientists will direct Juno to plunge into the clouds of Jupiter, where it will break apart and melt. 

But two years are a long time to explore the enigmas beneath the swirling clouds of Jupiter - and Juno is sure to answer many of our burning questions.

Keep an eye on the developments over at NASA, or check out Hubble’s view of Jupiter’s spectacular auroras

FUNDING FUNGI 

A while back I compiled a list of super cool citizen science projects that anyone can participate in. One of them was a research group at the University of Oklahoma who send out soil collection kits to anyone in the US. You gather up some dirt from your area, send it back, and they screen the fungi in the sample for bioactivity against a variety of diseases to help in drug development. 

These guys now have a whole NIH-funded research project based on this - but they still need a bit of help. Their funding doesn’t cover the cost of sending the kits back and forth to the people who want to contribute, so they’ve started kickstarter-like campaign through the University of Oklahoma's Thousand Strong Page.

Check it out for more info, and support them if it’s something you’re interested in!

You can’t hack the stars 

You’re probably familiar with GPS as the handy tool to find your way to a new restaurant, or to make sure you don’t end up in the middle of nowhere on a road trip. But its uses are widespread, from farming and mining to banking to weather forecasting, as well as being crucial to security and military operations. Our GPS system is a space-based navigation system made up of 24 satellites in geostationary orbits, sending signals down to GPS enabled devices to help determine precise locations and times. 

But both natural phenomena and deliberate attacks pose real threats to these satellites and the way we use them: massive solar flares could disrupt their signals, jamming devices could block GPS devices on the ground, and electromagnetic pulses could shut off the power of a military vessel or aircraft. If you’re in the middle of the ocean or high over enemy territory, losing your navigation system would be a huge problem. That’s why the US Navy have gone back to basics and decided to train their new personnel in a traditional navigation technique known as celestial navigation. 

Celestial navigation is an ancient skill, used for most of human history by sailors and explorers who guided their ships based on the stars. It’s a bit more time consuming and unwieldy than GPS, but it works - it basically involves finding the positions of the stars in the sky and then comparing them to an almanac of compiled measurements for various locations. A few calculations later, and voila, the position of your ship can be triangulated to within a few kilometres - no computers of satellites required. This is much less accurate to the few metres precision that GPS gives us, but in a back up, it’s pretty damn handy. 

After cutting it out of the curriculum more than a decade ago, the US Naval Academy have now fully reintroduced celestial navigation as a course - and the graduation class of 2017 will be the first in over a decade to graduate with such traditional navigation skills. 

After all, malicious forces could potentially bring down GPS systems, but they can’t change the position of the stars in the sky.

Kickstarting the Universe

Cosmology is honestly a mind-blowing field. It’s basically all about understanding the universe on a huge scale, like where did it come from? How did it evolve, and according to what fundamental laws? Will it come to an end? If so, how and when?

In the 1980s, cosmologists had two major problems to solve: the flatness problem and the horizon problem. The flatness problem is the fact that the universe seems to be geometrically flat. It’s expanding at an accelerating rate, and if it’s flat, it means that the rate of expansion is balanced very precisely with the amount of matter in the universe. Basically, this means that there’s enough stuff to eventually halt the universe’s expansion, but not enough to make it collapse back in on itself again afterwards. 

Image Credit: io9

It also means that the universe was even more perfectly balanced near the time of the Big Bang, because if there were any deviations from the nice, flat, smoothness, then these ‘defects’ would have grown very dramatically and very obviously over the past 14 billion years – and yet, we see nothing of the sort. This is so coincidental that it’s almost unbelievable – there’s no reason for it to be this way. 

Another issue is the horizon problem. Wherever you look in the universe, it seems to be roughly the same. When we measure the temperature of the cosmic microwave background (CMB, pictured above), we see that it’s exactly the same temperature in every single direction. This is weird, because for two regions to have the same conditions (like the exact same temperature), they must be close enough to exchange ‘information’ and come into equilibrium with each other. But since the universe is expanding, the photons from the CMB haven’t actually had time to reach and exchange heat with photons on the other side of the universe. These distant regions of the universe are isolated from each other, so how can they have the exact same temperature?

Image Credit

To answer these questions, astronomers put forth the idea of inflation: a period right after the Big Bang when the universe experienced ultra-fast, exponential expansion. 

Before this massive acceleration, the entire universe would have been in contact – regions that are now hugely separated would have been close enough to come to equilibrium, which explains the horizon problem. The rapidly expanding space also would have flattened the universe by “expanding away” any large curvatures, so now everything looks flat from our local perspective. To understand that, imagine if the Earth were the size of a basketball. We’d easily notice that it’s a sphere, but if we then expanded it to the size it is now, the curvature would be harder to see – and indeed in most places on Earth, the surface appears almost flat. Now imagine if it expanded to the size of the universe – everything would look completely flat in every direction, because it would just be so massive relative to us.

While inflation explains these problems, we have no idea about the mechanisms behind it – what started the ultra-fast expansion? And what stopped it again? Cosmologists generally agree that the idea is correct, but there are still a lot of kinks to be expanded out.

Lord of the Rings

Saturn is one of the most recognisable planets because of the magnificent rings that sweep around it, gleaming bright in the sunlight. The rings are made up of billions of icy particles, ranging in size from dust-size grains to a particles the size of houses. The particles are 99.9% pure water-ice with a tiny rocky component, and this ice is the reason they’re so brilliant - the sun just reflects right off them.

They rings actually highly structured, with a bunch of separate rings orbiting concentrically, with some gaps in between. The main rings are imaginatively but practically called C, B, and A, with fainter rings on the inside and outside of these three. Two of Saturn’s 60 moons actually orbit in the gaps between the rings, keeping the gaps open with their gravity.

The thickness of the rings  ranges from around 10m to 1km, but in total the rings are over 250,000 km across. It’s like if you had a DVD that was about 1mm thick, but 5km across! One cool effect of this is that the rings are so thin that when they’re viewed edge-on, they seem to disappear.

There are a few different ideas for how the rings were formed. One idea is that thy used to be a moon of Saturn, until it was pulled too close to the planet and ripped apart by tidal forces. Its rocky components were drawn in and burned up in the atmosphere, while millions of pieces of icy debris were strewn out into orbit around the planet, settling into rings. Another idea is that this early moon was slammed into by an asteroid of comet, shattering it in a similar way. Astronomers still aren’t united on a theory of formation, but it’s generally agreed that the rings formed very early on in Saturn’s history.

But to be honest, Saturn isn’t all that unique with the ring situation - all of the gas giants in our solar system have rings. But Jupiter, Uranus and Neptune’s rings are more rocky, and so reflect less light and are much less spectacular than Saturn’s ice-dominated rings.

Image Credit: Wikimedia Commons