Like me, you’re probably a little ego-geocentric about the importance of Earth. It’s where you were born, it’s where you keep all your stuff. It’s even where you’re going to die – I know, I know, not you Elon Musk, you’re going to “retire” on Mars, right after you nuke the snot out of it.
For the rest of us, Earth is the place. But in reality, when it comes to planets, this is somebody else’s racket. This is Jupiter’s Solar System, and we all sleep on its couch.
Jupiter accounts for 75% of the mass of the planets of the Solar System, nearly 318 times more massive than Earth, and isn’t just the name of everyone’s favorite secret princess. It’s the 1.9 × 10^27 kilogram gorilla in the room. Whatever Jupiter wants, Jupiter gets. Jupiter hungry? JUPITER HUNGRY.
What Jupiter apparently wants is to throw our stuff around the Solar System. Thanks to its immense gravity, Jupiter yanks material around in the asteroid belt, preventing the poor space rocks from ever forming up into anything larger than Ceres.
Jupiter gobbles up asteroids, comets, and spacecraft, and hurtles others on wayward trajectories. Who knows how much mayhem and destruction Jupiter has gotten into over the course of its 4.5 billion years in the Solar System.
Some scientists think we owe our existence to Jupiter’s protective gravity. It greedily vacuums up dangerous asteroids and comets in the Solar System.
Other scientists totally disagree and think that Jupiter is a bully, perturbing perfectly safe comets and asteroids into dangerous trajectories and flushing earth’s head in the toilet during recess.
Which is it? Is Jupiter our friend and protector, or evil enemy. We’ve already figured out how to dismantle you Jupiter, don’t make us put our plans into action.
Some of the most dangerous objects in the Solar System are long-period comets. These balls of rock and ice come from the deepest depths of the Oort cloud. Some event nudges these death missiles into trajectories that bring them into the inner Solar System, to shoot past the Sun and maybe, just maybe, smash into a planet and kill 99.99999% of the life on it.
The Solar System. Credit: NASA
There’s a pretty good chance some of the biggest extinctions in the history of the Earth were caused by impacts by long period comets.
As these comets make their way through the Solar System, they interact with Jupiter’s massive gravity, and get pushed this way and that. As we saw with Comet Shoemaker-Levy, some just get consumed entirely, like a tasty ice-rock sandwich.
The theory goes that Jupiter pushes these dangerous comets out of their murder orbits so they don’t smash into Earth and kill us all.
But a competing theory says that Jupiter actually diverts comets that would have completely missed our planet into deadly, Earth-killing trajectories.
Will the Sailor Scouts provide us any clues? Who can say?
At top, an image of the comet Shoemaker-Levy 9 (May 1994) after a close approach with Jupiter which tore the comet into numerous fragments. An image taken by Andrew Catsaitis of components B and C of Comet 73P/Schwassmann–Wachmann 3 as seen together on 31 May 2006 (Credit: NASA/HST, Wikipedia, A.Catsaitis)
Here’s friend of the show, Dr. Kevin Grazier, a planetary scientist and scientific advisor for many of your favorite sci-fi TV shows and movies.
… [ see video for Interview with Dr. Grazier about Jupiter]
So which is it? Is Jupiter our friend or enemy? We’ll need to run more simulations and figure this out with more accuracy. And until then, it’s probably best if we just tremble in fear and worship Jupiter as a dark and capricious god until the evidence proves otherwise. It’s what Pascal would wager.
What are some other theories you’ve heard about and you’d like us to dig in further? Make some suggestions in the comments below.
Thanks for watching! Click subscribe, never miss an episode.
If you’re into other facts about our Solar system here’s a link to our Solar system playlist. Thanks to Ben Johnson and Tal Ghengis, and the members of the Guide to Space community who keep these shows rolling. Love space science? Want to see episodes before anyone else? Get extras, contests, and shenanigans with Jay, myself and the rest of the team. Get in on the action. Click here.
In addition to being the birthplace of humanity and the cradle of human civilization, Earth is the only known planet in our Solar System that is capable of sustaining life. As a terrestrial planet, Earth is located within the Inner Solar System between between Venus and Mars (which are also terrestrial planets). This place Earth in a prime location with regards to our Sun’s Habitable Zone.
Earth has a number of nicknames, including the Blue Planet, Gaia, Terra, and “the world” – which reflects its centrality to the creation stories of every single human culture that has ever existed. But the most remarkable thing about our planet is its diversity. Not only are there an endless array of plants, animals, avians, insects and mammals, but they exist in every terrestrial environment. So how exactly did Earth come to be the fertile, life-giving place we all know and love?
Illustration of Jupiter and the Galilean satellites. Credit: NASA
Jupiter was appropriately named by the Romans, who chose to name it after the king of the gods. In addition to being the largest planet in our Solar System – with two and a half times the mass of all the other planets combined – it also has the most moons of any Solar planet. So far, 67 natural satellites have been discovered around the gas giant, and more could be on the way.
The moons of Jupiter are so numerous and so diverse that they are broken down into several groups. First, there are the largest moons known as the Galileans, or Main Group. Together with the smaller Inner Group, they make up Jupiter’s Regular Satellites. Beyond them, there are the many Irregular Satellites that circle the planet, along with its debris rings. Here’s what we know about them…
Discovery and Naming:
Using a telescope of his own design, which allowed for 20 x normal magnification, Galileo Galilei was able to make the first observations of celestial bodies that were not visible to the naked eye. In 1610, he made the first recorded discovery of moons orbiting Jupiter, which later came to be known as the Galilean Moons.
At the time, he observed only three objects, which he believed to be fixed stars. However, between January and March of 1610, he continued to observe them, and noted a fourth body as well. In time, he realized that these four bodies did not behave like fixed stars, and were in fact objects that orbited Jupiter.
Portrait of Galileo Galilei by Giusto Sustermans, 1636 . Credit: Royal Museum Greenwhich
These discoveries proved the importance of using the telescope to view celestial objects that had previously remained unseen. More importantly, by showing that planets other than Earth had their own system of satellites, Galileo dealt a significant blow to the Ptolemaic model of the universe, which was still widely accepted.
Seeking the patronage of the Grand Duke of Tuscany, Cosimo de Medici, Galileo initially sought permission to name the moons the “Cosmica Sidera” (or Cosimo’s Stars). At Cosimo’s suggestion, Galileo changed the name to Medicea Sidera (“the Medician stars”), honouring the Medici family. The discovery was announced in the Sidereus Nuncius (“Starry Messenger”), which was published in Venice in March 1610.
However, German astronomer Simon Marius had independently discovered these moons at the same time as Galileo. At the behest of Johannes Kepler, he named the moons after the lovers of Zues (the Greek equivalent of Jupiter). In his treatise titled Mundus Jovialis (“The World of Jupiter”, published in 1614) he named them Io, Europa, Ganymede, and Callisto.
Galileo steadfastly refused to use Marius’ names and instead invented the numbering scheme that is still used today, alongside proper moon names. In accordance with this scheme, moons are assigned numbers based on their proximity to their parent planet and increase with distance. Hence, the moons of Io, Europa, Ganymede and Callisto were designated as Jupiter I, II, III, and IV, respectively.
Drawing of Jupiter made on Nov. 1, 1880 by French artist and astronomer Etienne Trouvelot showing transiting moon shadows and a much larger Great Red Spot. Credit: E.L. Trouvelot, New York Public Library
After Galileo made the first recorded discovery of the Main Group, no additional satellites were discovered for almost three centuries – not until E. E. Barnard observed Amalthea in 1892. In fact, it was not until the 20th century, and with the aid of telescopic photography and other refinements, that most of the Jovian satellites began to be discovered.
Himalia was discovered in 1904, Elara in 1905, Pasiphaë in 1908, Sinope in 1914, Lysithea and Carme in 1938, Ananke in 1951, and Leda in 1974. By the time Voyager space probes reached Jupiter around 1979, 13 moons had been discovered, while Voyager herself discovered an additional three – Metis, Adrastea, and Thebe.
Between October 1999 and February 2003, researchers using sensitive ground-based detectors found and later named another 34 moons, most of which were discovered by a team led by Scott S. Sheppard and David C. Jewitt. Since 2003, 16 additional moons have been discovered but not yet named, bringing the total number of known moons of Jupiter to 67.
Though the Galilean moons were named shortly after their discovery in 1610, the names of Io, Europa, Ganymede and Callisto fell out of favor until the 20th century. Amalthea (aka. Jupiter V) was not so named until an unofficial convention took place in 1892, a name that was first used by the French astronomer Camille Flammarion.
Jupiter and its largest moons. Image credit: NASA/JPL
The other moons, in the majority of astronomical literature, were simply labeled by their Roman numeral (i.e. Jupiter IX) until the 1970s. This began in 1975 when the International Astronomical Union’s (IAU) Task Group for Outer Solar System Nomenclature granted names to satellites V–XIII, thus creating a formal naming process for any future satellites discovered. The practice was to name newly discovered moons of Jupiter after lovers and favorites of the god Jupiter (Zeus); and since 2004, also after their descendants.
Regular Satellites:
Jupiter’s Regular Satellites are so named because they have prograde orbits – i.e. they orbit in the same direction as the rotation of their planet. These orbits are also nearly circular and have a low inclination, meaning they orbit close to Jupiter’s equator. Of these, the Galilean Moons (aka. the Main Group) are the largest and the most well known.
These are Jupiter’s largest moons, not to mention the Solar System’s fourth, sixth, first and third largest satellites, respectively. They contain almost 99.999% of the total mass in orbit around Jupiter, and orbit between 400,000 and 2,000,000 km from the planet. They are also among the most massive objects in the Solar System with the exception of the Sun and the eight planets, with radii larger than any of the dwarf planets.
They include Io, Europa, Ganymede, and Callisto, and were all discovered by Galileo Galilei and named in his honor. The names of the moons, which are derived from the lovers of Zeus in Greek mythology, were prescribed by Simon Marius soon after Galileo discovered them in 1610. Of these, the innermost is Io, which is named after a priestess of Hera who became Zeus’ lover.
This global view of Jupiter’s moon, Io, was obtained during the tenth orbit of Jupiter by NASA’s Galileo spacecraft. Credit: NASA
With a diameter of 3,642 kilometers, it is the fourth-largest moon in the Solar System. With over 400 active volcanoes, it is also the most geologically active object in the Solar System. Its surface is dotted with over 100 mountains, some of which are taller than Earth’s Mount Everest.
Unlike most satellites in the outer Solar System (which are covered with ice), Io is mainly composed of silicate rock surrounding a molten iron or iron sulfide core. Io has an extremely thin atmosphere made up mostly of sulfur dioxide (SO2).
The second innermost Galilean moon is Europa, which takes its name from the mythical Phoenician noblewoman who was courted by Zeus and became the queen of Crete. At 3121.6 kilometers in diameter, it is the smallest of the Galileans, and slightly smaller than the Moon.
Europa’s surface consists of a layer of water surrounding the mantle which is thought to be 100 kilometers thick. The uppermost section is solid ice while the bottom is believed to be liquid water, which is made warm due to heat energy and tidal flexing. If true, then it is possible that extraterrestrial life could exist within this subsurface ocean, perhaps near a series of deep-ocean hydrothermal vents.
The surface of Europa is also one of the smoothest in the Solar System, a fact which supports the idea of liquid water existing beneath the surface. The lack of craters on the surface is attributed to the surface being young and tectonically active. Europa is primarily made of silicate rock and likely has an iron core, and a tenuous atmosphere composed primarily of oxygen.
Next up is Ganymede. At 5262.4 kilometers in diameter, Ganymede is the largest moon in the Solar System. While it is larger than the planet Mercury, the fact that it is an icy world means that it has only half of Mercury’s mass. It is also the only satellite in the Solar System known to possess a magnetosphere, likely created through convection within the liquid iron core.
Ganymede is composed primarily of silicate rock and water ice, and a salt-water ocean is believed to exist nearly 200 km below Ganymede’s surface – though Europa remains the most likely candidate for this. Ganymede has a high number of craters, most of which are now covered in ice, and boasts a thin oxygen atmosphere that includes O, O2, and possibly O3 (ozone), and some atomic hydrogen.
Callisto is the fourth and farthest Galilean moon. At 4820.6 kilometers in diameter, it is also the second largest of the Galileans and third largest moon in the Solar System. Callisto is named after the daughter of the Arkadian King, Lykaon, and a hunting companion of the goddess Artemis.
Composed of approximately equal amounts of rock and ices, it is the least dense of the Galileans, and investigations have revealed that Callisto may also have an interior ocean at depths greater than 100 kilometers from the surface.
Callisto is also one of the most heavily cratered satellites in the Solar System – the greatest of which is the 3000 km wide basin known as Valhalla. It is surrounded by an extremely thin atmosphere composed of carbon dioxide and probably molecular oxygen. Callisto has long been considered the most suitable place for a human base for future exploration of the Jupiter system since it is furthest from the intense radiation of Jupiter.
This natural color view of Ganymede was taken from the Galileo spacecraft during its first encounter with the Jovian moon. Credit: NASA/JPL
The Inner Group (or Amalthea group) are four small moons that have diameters of less than 200 km, orbit at radii less than 200,000 km, and have orbital inclinations of less than half a degree. This groups includes the moons of Metis, Adrastea, Amalthea, and Thebe.
Along with a number of as-yet-unseen inner moonlets, these moons replenish and maintain Jupiter’s faint ring system – Metis and Adrastea helping Jupiter’s main ring, while Amalthea and Thebe maintain their own faint outer rings.
Metis is the closest moon to Jupiter at a distance of 128,000 km. It is roughly 40 km in diameter, tidally-locked, and highly-asymmetrical in shape (with one of the diameters being almost twice as large as the smallest one). It was not discovered until the 1979 flyby of Jupiter by the Voyager 1 space probe. It was named in 1983 after the first wife of Zeus.
The second closest moon is Adrastea, which is about 129,000 km from Jupiter and 20 km in diameter. Also known as Jupiter XV, Amalthea is the second by distance, and the smallest of the four inner moons of Jupiter. It was discovered in 1979 when the Voyager 2 probe photographed it during a flyby.
A schema of Jupiter’s ring system showing the four main components. For simplicity, Metis and Adrastea are depicted as sharing their orbit. Credit: NASA/JPL/Cornell University
Amalthea, also known as Jupiter V, is the third moon of Jupiter in order of distance from the planet. It was discovered on September 9, 1892, by Edward Emerson Barnard and named after a nymph in Greek mythology. It is thought to consist of porous water ice with unknown amounts of other materials. Its surface features include large craters and ridges.
Thebe (aka. Jupiter XIV) is the fourth and final inner moon of Jupiter. It is irregularly shaped and reddish in colour, and is thought like Amalthea to consist of porous water ice with unknown amounts of other materials. Its surface features also include large craters and high mountains – some of which are comparable to the size of the moon itself.
Irregular Satellites:
The Irregular Satellites are those that are substantially smaller and have more distant and eccentric orbits than the Regular Satellites. These moons are broken down into families that have similarities in orbit and composition. It is believed that these were at least partially formed as a result of collisions, most likely by asteroids that were captured by Jupiter’s gravitational field.
Amalthea, as photographed by the Galileo spacecraft. The left is from August 12, 1999 at a range of 446,000 km, the right from November 26, 1999 at a range of 374,000. Credit: NASA/JPL
Those that are grouped into families are all named after their largest member. For example, the Himalia group is named after Himalia – a satellite with a mean radius of 85 km, making it the fifth largest moon orbiting Jupiter. It is believed that Himalia was once an asteroid that was captured by Jupiter’s gravity, which then experienced a impact that formed the moons of Leda, Lysithea, and Elara. These moons all have prograde orbits, meaning they orbit in the same direction as Jupiter’s rotation.
The Carme group takes its name from the Moon of the same name. With a mean radius of 23 km, Carme is the largest member of a family of Jovian satellites which have similar orbits and appearance (uniformly red), and are therefore thought to have a common origin. The satellites in this family all have retrograde orbits, meaning they orbit Jupiter in the opposite direction of its rotation.
The Ananke group is named after its largest satellite, which has a mean radius of 14 km. It is believed that Ananke was also an asteroid that was captured by Jupiter’s gravity and then suffered a collision which broke off a number of pieces. Those pieces became the other 15 moons in the Ananke group, all of which have retrograde orbits and appear gray in color.
This image shows the Themis Main Belt which sits between Mars and Jupiter. Credit: Josh Emery/University of Tennessee, Knoxville
The Pasiphae group is a very diverse group which ranges in color from red to grey – signifying the possibility of it being the result of multiple collisions. Named after Paisphae, which has a mean radius of 30 km, these satellites are retrograde, and are also believed to be the result of an asteroid that was captured by Jupiter and fragmented due to a series of collisions.
There are also several irregular satellites that are not part of any particular family. These include Themisto and Carpo, the innermost and outermost irregular moons, both of which have prograde orbits. S/2003 J 12 and S/2011 J 1 are the innermost of the retrograde moons, while S/2003 J 2 is the outermost moon of Jupiter.
Structure and Composition:
As a rule, the mean density of Jupiter’s moons decrease with their distance from the planet. Callisto, the least dense of the four, has an intermediate density between ice and rock, whereas Io has a density that indicates its made of rock and iron. Callisto’s surface also has a heavily cratered ice surface, and the way it rotates indicates that its density is equally distributed.
This suggests that Callisto has no rocky or metallic core, but consists of a homogeneous mix of ice and rock. The rotation of the three inner moons, in contrast, indicates differentiation between a core of denser matter (such as silicates, rock and metals) and a mantle of lighter material (water ice).
Surface features of the four members at different levels of zoom in each row. Credit: NASA/JPL
The distance from Jupiter also accords with significant alterations in the surface structure of its moons. Ganymede reveals past tectonic movement of the ice surface, which would mean that the subsurface layers underwent partial melting at once time. Europa reveals more dynamic and recent movement of this nature, suggesting a thinner ice crust. Finally, Io, the innermost moon, has a sulfur surface, active volcanism, and no sign of ice.
All this evidence suggests that the nearer a moon is to Jupiter, the hotter its interior – with models suggesting that the level of tidal heating is in inverse proportion to the square of their distance from the planet. It is believed that all of Jupiter’s moons may have once had an internal composition similar to that of modern-day Callisto, while the rest changed over time as a result of tidal heating caused by Jupiter’s gravitational field.
What this means is that for all of Jupiter’s moons, except Callisto, their interior ice melted, allowing rock and iron to sink to the interior and water to cover the surface. In Ganymede, a thick and solid ice crust then formed while in warmer Europa, a thinner more easily broken crust formed. On Io, the closest planet to Jupiter, the heating was so extreme that all the rock melted and the water boiled out into space.
Jupiter, a gas giant of immense proportions, was appropriately named after the king of the Roman pantheon. It is only befitting that such a planet has many, many moons orbiting it. Given the discovery process, and how long it has taken us, it would not be surprising if there are more satellites around Jupiter just waiting to be discovered. Sixty-seven and counting!
In the list of crazy hypothetical ideas, terraforming the Sun has to be one of the top 10. So just how would someone go about doing terraforming our sun, a star, if they wanted to try?
In our series on terraforming other worlds, we’ve covered Mars, Venus, the Moon and Jupiter. Even though I solved the problem of how to terraform Jupiter (you’re welcome, science), you wanted to take things to the next level and you demanded I sort out how to terraform the Sun. Seriously? The Sun. Fine… here we go.
Let’s see what we’ve got to work with here. It’s a massive ball of plasma, containing 333,000 times more mass than the Earth. It’s about 74% hydrogen and 25% helium with a few other trace elements. There’s no solid surface to stand on it, so we need to fix that.
The average temperature on the surface of the Sun is about 5,500 Celsius, while the average temperature on Earth is about 15 C. Iron boils at only 2,800 degrees, so… that’s probably too hot. We’ll need to cool it down.
The gravity on the surface of the Sun is 28 times the gravity of Earth. If you could stand on the surface of the Sun, which you can’t, you’d be crushed flat. Okay, so we’ll add reduce the gravity… check.
There’s no breathable atmosphere, there’s no solid ground, the Sun generates deadly X-rays. Oh, and don’t forget about the terrible sunburns from the ultraviolet radiation.
So, what’s the list? Hot fire unbreathable pressure cooker goo surface gravity crushing machine. Sounds impossible, or does it?
First, the gas. As we covered in a previous episode, scientists have actually considered ways that you might extract the hydrogen and helium off of a star like the Sun, known as “stellar lifting”. There are a few ways you could work this. You could zap the surface of the Sun with a powerful laser, increasing the speed of solar wind in that area, forcing the Sun to throw its mass off into space.
Another method is to set up powerful magnetic fields around the Sun’s poles, and channel its hydrogen into jets that blast out into space. I’m not sure how you actually set up those magnetic fields, but that’s not my problem.
Once you’re done with the Sun, you’ve stripped away all its hydrogen and helium gas. What are you left with? About 5,600 times the mass of the Earth in heavier elements, like oxygen, silicon, gold, etc. Great!
Except 5,600 sounds like a lot. Jupiter is only 316 times the mass of the Earth. We’re looking to reform a “planet” with more than 10 times the mass of Jupiter. And not only that, but we had to kill the Sun to make this work. You monsters.
This is a terrible idea. What else could we do? If you’re a science fiction fan, you’ve heard of a Dyson Sphere. If not, you’ve got some TNG to catch up on.
First proposed by Freeman Dyson, you cover an entire Sun in a metal ball. Instead of the measly amount of energy that falls on Earth, this would allow you to capture 100% of the energy released by the Sun: 384 yottawatts.
According to Dyson and a variety of matheletes, you could dismantle all planets in the Solar System and build a sphere at a distance of 1 Earth radii at 8 to 20 centimeters thick. That would give you a surface area 550 million times more than the Earth.
Although, building an actual rigid sphere is probably unfeasible because it would be pretty unstable and eventually collapse. It probably makes more sense to build a swarm of satellites surrounding the Sun, capturing its energy.
We did a whole video on Dyson Spheres. Check it out here.
So there you go. I just terraformed the Sun. I’m terrified about your next suggestion: how could you terraform a black hole? I guess that’ll be the next video.
Would you like to live on my imagined terraformed Sun? If not, what about a Dyson Sphere or swarm?
We know that in space, no one can hear you scream. But what would things sound like on another planet?
When humans finally set foot on Mars, they’re going to be curious about everything around them.
What’s under that rock? What does it feel like to jump in the lower Martian gravity. What does Martian regolith taste like? What’s the bitcoin to red rock exchange rate?
As long as they perform their activities in the safety of a pressurized habitation module or exosuit, everything should be fine. But what does Mars sound like?
I urge all future Martian travelers, no matter how badly you want to know the answer to this question: don’t take your helmet off. With only 1% the atmospheric pressure of Earth, you’d empty your lungs with a final scream in a brief and foolish moment, then suffocate horribly with a mouthful of dust on the surface of the Red Planet.
But… actually, even the screaming would sound a little different. How different? Let me show you. First you just need to take your helmet off for a just a little sec, just an itsy bitsy second. Here, I’ll hold it for you. Oh, come on, just take your helmet off. All the cool kids are doing it.
What about Venus? Or Titan? What would everything sound like on an alien world?
We evolved to exist on Earth, and so it’s perfectly safe for us to listen to sounds in the air. No space suit needed. Unless you didn’t evolve on Earth, in which case I offer to serve as emissary to our all new alien overlords.
You know sounds travel when waves of energy propagate through a medium, like air or water. The molecules bump into each other and pass along the energy until they strike something that won’t move, like your ear drum. Then your brain turns bouncing into sounds.
The speed of the waves depends on what the medium is made of and how dense it is. For example, sound travels at about 340 meters/second in dry air, at sea level at room temperature. Sound moves much more quickly through liquid. In water it’s nearly 1,500 m/s. It’s even faster through a solid – iron is up past 5,100 m/s. Our brain perceives a different sound depending on the intensity of the waves and how quickly they bounce off our ears.
Artist’s impression of the surface of Venus. Credit: ESA/AOES
Other worlds have media that sound waves can travel through, and with your eardrum exposed to the atmosphere you should theoretically hear sounds on other worlds. Catastrophic biological failures from using your eardrums outside of documented pressure tolerances notwithstanding.
Professor Tim Leighton and a team of researchers from the University of Southampton have simulated what we would hear standing on the surface of other worlds, like Mars, Venus or even Saturn’s Moon Titan.
On Venus, the pitch of your voice would become deeper, because vocal cords would vibrate much more slowly in the thicker Venusian atmosphere. But sounds would travel more quickly through the soupy atmosphere. According to Dr. Leighton, humans would sound like bass Smurfs. Mars would sound a little bit higher, and Titan would sound totally alien.
Dr. Leighton actually simulated the same sound on different worlds. Here’s the sound of thunder on Earth.
Here’s what it would sound like on Venus.
And here’s what it would sound like on Mars.
Here’s what a probe splashing into water on Earth would sound like.
And here’s what it would sound like splashing into a hydrocarbon lake on Titan.
You might be amazed to learn that we still haven’t actually recorded sounds on another world, right up until someone points out that putting a microphone on another planet hasn’t been that big a priority for any space mission.
A fish-eye view of Titan’s surface from the European Space Agency’s Huygens lander in January 2005. Credit: ESA/NASA/JPL/University of Arizona
Especially when we could analyze soil samples, but hey fart sounds played and then recorded in the Venusian atmosphere could prove incredibly valuable to the future of internet soundboards.
The Planetary Society has been working to get a microphone included on a mission. They actually included a microphone on the Mars Polar Lander mission that failed in 1999. Another French mission was going to have a microphone, but it was cancelled. There are no microphones on either Spirit or Opportunity, and the Curiosity Rover doesn’t have one either despite its totally bumping stereo.
Here’s is the only thing we’ve got. When NASA’s Phoenix Lander reached the Red Planet in 2008, it had a microphone on board to capture sounds. It recorded audio as it entered the atmosphere, but operators turned the instrument off before it reached the surface because they were worried it would interfere with the landing.
Meh. I’m going to need you to do better NASA. I want an actual microphone recording winds on the surface of Mars. I hope it’s something Dethklok puts on their next album, they could afford that kind of expense.
It turns out, that if you travel to an alien world, not only would the sights be different, but the sounds would be alien too. Of course, you’d never know because you’re be too chicken to take your helmet off and take in the sounds through the superheated carbon dioxide or methane atmosphere.
What sounds would you like to hear on an alien world? Tell us in the comments below.
Rogue stars are moving so quickly they’re leaving the Milky Way, and never coming back. How in the Universe could this happen?
Stars are built with the lightest elements in the Universe, hydrogen and helium, but they contain an incomprehensible amount of mass. Our Sun is made of 2 x 10^30 kgs of stuff. That’s a 2 followed by 30 zeros. That’s 330,000 times more stuff than the Earth.
You would think it’d be a bit of challenge to throw around something that massive, but there are events in the Universe which are so catastrophic, they can kick a star so hard in the pills that it hits galactic escape velocity.
Rogue, or hypervelocity stars are moving so quickly they’re leaving the Milky Way, and never coming back. They’ve got a one-way ticket to galactic voidsville. The velocity needed depends on the location, you’d need to be traveling close to 500 kilometers per second. That’s more than twice the speed the Solar System is going as it orbits the centre of the Milky Way.
There are a few ways you can generate enough kick to fire a star right out of the park. They tend to be some of the most extreme events and locations in the Universe. Like Supernovae, and their big brothers, gamma ray bursts.
Supernovae occur when a massive star runs out of hydrogen, keeps fusing up the periodic table of elements until it reaches iron. Because iron doesn’t allow it to generate any energy, the star’s gravity collapses it. In a fraction of a second, the star detonates, and anything nearby is incinerated. But what if you happen to be in a binary orbit with a star that suddenly vaporizes in a supernova explosion?
That companion star is flung outward with tremendous velocity, like it was fired from a sling, clocking up to 1,200 km/s. That’s enough velocity to escape the pull of the Milky Way. Huzzah! Onward, to adventure! Ahh, crap… please do not be pointed at the Earth?
This artist’s impression shows the dust and gas around the double star system GG Tauri-A.
Another way to blast a star out of the Milky Way is by flying it too close to Kevin, the supermassive black hole at the heart of the galaxy.
And for the bonus round, astronomers recently discovered stars rocketing away from the galactic core as fast as 900 km/s. It’s believed that these travelers were actually part of a binary system. Their partner was consumed by the Milky Way’s supermassive black hole, and the other is whipped out of the galaxy in a gravitational jai halai scoop.
Interestingly, the most common way to get flung out of your galaxy occurs in a galactic collision. Check out this animation of two galaxies banging together. See the spray of stars flung out in long tidal tails? Billions of stars will get ejected when the Milky Way hammers noodle first into Andromeda.
A recent study suggests half the stars in the Universe are rogue stars, with no galaxies of their own. Either kicked out of their host galaxy, or possibly formed from a cloud of hydrogen gas, flying out in the void. They are also particularly dangerous to Carol Danvers.
Considering the enormous mass of a star, it’s pretty amazing that there are events so catastrophic they can kick entire stars right out of our own galaxy.
What do you think life would be like orbiting a hypervelocity star? Tell us your thoughts in the comments below.
Need an easy way to remember the order of the planets in our Solar System? The technique used most often to remember such a list is a mnemonic device. This uses the first letter of each planet as the first letter of each word in a sentence. Supposedly, experts say, the sillier the sentence, the easier it is to remember.
So by using the first letters of the planets, (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune), create a silly but memorable sentence.
Here are a few examples:
My Very Excellent Mother Just Served Us Noodles (or Nachos)
Mercury’s Volcanoes Erupt Mulberry Jam Sandwiches Until Noon
Very Elderly Men Just Snooze Under Newspapers
My Very Efficient Memory Just Summed Up Nine
My Very Easy Method Just Speeds Up Names
My Very Expensive Malamute Jumped Ship Up North
The Sun and planets to scale. Credit: Illustration by Judy Schmidt, texture maps by Björn Jónsson
If you want to remember the planets in order of size, (Jupiter, Saturn, Uranus, Neptune, Earth, Venus Mars, Mercury) you can create a different sentence:
Just Sit Up Now Each Monday Morning
Jack Sailed Under Neath Every Metal Mooring
Rhymes are also a popular technique, albeit they require memorizing more words. But if you’re a poet (and don’t know it) try this:
Amazing Mercury is closest to the Sun,
Hot, hot Venus is the second one,
Earth comes third: it’s not too hot,
Freezing Mars awaits an astronaut,
Jupiter is bigger than all the rest,
Sixth comes Saturn, its rings look best,
Uranus sideways falls and along with Neptune, they are big gas balls.
Or songs can work too. Here are a couple of videos that use songs to remember the planets:
If sentences, rhymes or songs don’t work for you, perhaps you are more of a visual learner, as some people remember visual cues better than words. Try drawing a picture of the planets in order. You don’t have to be an accomplished artist to do this; you can simply draw different circles for each planet and label each one. Sometimes color-coding can help aid your memory. For example, use red for Mars and blue for Neptune. Whatever you decide, try to pick colors that are radically different to avoid confusing them.
Or try using Solar System flash cards or just pictures of the planets printed on a page (here are some great pictures of the planets). This works well because not only are you recalling the names of the planets but also what they look like. Memory experts say the more senses you involve in learning or storing something, the better you will be at recalling it.
Planets made from paper lanterns. Credit: TheSweetestOccasion.com
Maybe you are a hands-on learner. If so, try building a three-dimensional model of the Solar System. Kids, ask your parents or guardians to help you with this, or parents/guardians, this is a fun project to do with your children. You can buy inexpensive Styrofoam balls at your local craft store to create your model, or use paper lanterns and decorate them. Here are several ideas from Pinterest on building a 3-D Solar System Model.
If you are looking for a group project to help a class of children learn the planets, have a contest to see who comes up with the silliest sentence to remember the planets. Additionally, you can have eight children act as the planets while the rest of the class tries to line them up in order. You can find more ideas on NASA’s resources for Educators. You can use these tricks as a starting point and find more ways of remembering the planets that work for you.
How long would it take for the gravitational well created by the Sun to disappear, and the Earth and the rest of the planets fly off into space?
In the very first episode of the Guide to Space, a clean shaven version of me, hunched over in my basement explained how long it takes for light to get from the Sun to the Earth. To answer that question, it takes light about 8 minutes and 20 seconds to make the trip.
In other words, if the Sun suddenly disappeared from space itself, we’d still see it shining in the sky for over 8 minutes before the everything went dark. Martians would take about 12 minutes to notice the Sun was gone, and New Horizons which is nearly at Pluto wouldn’t see a change for over 4 hours.
Although this idea is a little mind-bending, I’m sure you’ve got your head wrapped around it. We’ve sure gone on about it here on this show. The further you look into space, the further you’re looking back in time because of the speed of light, but have you ever considered the speed of gravity?
Let’s go back to that original example and remove the Sun again. How long would it take for the gravitational well created by the Sun to disappear.
When would the Earth and the rest of the planets fly off into space without the Sun holding the whole Solar System together with its gravity? Would it happen instantly, or would it take time for the information to reach Earth?
It sounds like a simple question, but it’s actually really tough to tell. The force of gravity, compared to other forces in the Universe, is actually pretty weak. It’s practically impossible to test in the laboratory.
According to Einstein’s Theory of Relativity, distortions in spacetime caused by mass – also known as gravity – will propagate out at the speed of light. In other words, the light from the Sun and the gravity of the Sun should disappear at exactly the same time from the Earth’s perspective.
But that’s just a theory and a bunch of fancy math. Is there any way to test this out in reality? Astronomers have figured a way to deduce this indirectly by watching the interactions with massive objects in space.
In the binary system PSR 1913+16, there’s a pair of pulsars orbiting each other within just a few times bigger than the width of the Sun. As they spin around each other, the pulsars warp the spacetime themselves by releasing gravitational waves. And this release of gravitational waves causes the pulsars to slow down.
It’s amazing that astronomers can even measure this orbital decay, but the even more amazing part is that they use this process to measure the speed of gravity. When they did the calculations, astronomers determined the speed of gravity to be within 1% of the speed of light – that’s close enough.
Scientists have also used careful observations of Jupiter to get at this number. By watching how Jupiter’s gravity warps the light from a background quasar as it passes in front, they were able to determine that the speed of gravity is between 80% and 120% of the speed of light. Again, that’s close enough.
So there you go. The speed of gravity equals the speed of light. And should the Sun suddenly disappear, we’ll be glad to get all the bad news at the same time.
Gravity is a harsh mistress. Tell us a story about a time gravity was too fast for you. Put it in the comments below.
We’ve found hundreds of exoplanets in the galaxy. But only a few of them have just the right combination of factors to hold life like Earth’s.
The weather in your hometown is downright uninhabitable. There’s scorching heatwaves, annual tyhpoonic deluges, and snow deep enough to bury a corn silo.
The bad news is planet Earth is the only habitable place we know of in the entire Universe. Also, are the Niburians suffering from Niburian made climate change? Only Niburian Al Gore can answer that question.
We as a species are interested in habitability for an assortment of reasons, political, financial, humanitarian and scientific. We want to understand how our own climate is changing. How we’ll live in the climate of the future and what we can do to stem the tide of what our carbon consumption causes.
There could be agendas to push for cleaner energy sources, or driving politicians towards climate change denial to maintain nefarious financial gain.
We also might need a new lilypad to jump to, assuming we can sort out the travel obstacles. The thing that interests me personally the most is, when can I see an alien?
The habitable zone, also known as the “Goldilocks Zone”, is the region around a star where the average temperature on a planet allows for liquid water with which to make porridge. It’s that liquid water that we hunt for not only for our future uses, but as an indicator of where alien life could be in the Universe.
Problems outside this range are pretty obvious. Too hot, it’s a perpetual steam bath, or it produces separate piles of hydrogen and oxygen. Then your oxygen combines with carbon to form carbon dioxide, and then hydrogen just buggers off into space.
This is what happened with Venus. If the planet’s too cold, then bodies of water are solid skating rinks. There could be pockets of liquid water deep beneath the icy surface, but overall, they’re bad places to live.
We’ve got this on Mars and the moons of Jupiter and Saturn. The habitable zone is a rough measurement. It’s a place where liquid water might exist.
“The Chemistry of the Solar System” by Compound Interest’s Andy Brunning
Unfortunately, it’s not just a simple equation of the distance to the star versus the amount of energy output. The atmosphere of the planet matters a lot. In fact, both Venus and Mars are considered to be within the Solar System’s habitable zone.
Venusian atmosphere is so thick with carbon dioxide that it traps energy from the Sun and creates an inhospitable oven of heat that would quickboil any life faster than you can say “pass the garlic butter”.
It’s the opposite on Mars. The thin atmosphere won’t trap any heat at all, so the planet is bun-chillingly cold. Upgrade the atmospheres of either planet and you could get worlds which would be perfectly reasonable to live on. Maybe if we could bash them together and we could spill the atmosphere of one onto the other? Tell Blackbolt to ring up Franklin Richards, I have an idea!
When we look at other worlds in the Milky Way and wonder if they have life, it’s not enough to just check to see if they’re in the habitable zone. We need to know what shape their atmosphere is in.
Astronomers have actually discovered planets located in the habitable zones around other stars, but from what we can tell, they’re probably not places you’d want to live. They’re all orbiting red dwarf stars.
Artists impression of Gliese 581g. Credit: Lynette Cook/NSF
It doesn’t sound too bad to live in a red tinted landscape, provided it came with an Angelo Badalamenti soundtrack, red dwarf stars are extremely violent in their youth. They blast out enormous solar flares and coronal mass ejections. These would scour the surface of any planets caught orbiting them close enough for liquid water to be present.
There is some hope. After a few hundred million years of high activity, these red dwarf stars settle down and sip away at their fuel reserves of hydrogen for potentially trillions of years. If life can hold on long enough to get through the early stages, it might have a long existence ahead of it.
When you’re thinking about a new home among the stars, or trying to seek out new life in the Universe, look for planets in the habitable zone.
As we’ve seen, it’s only a rough guideline. You probably want to check out the place first and make sure it’s truly liveable before you commit to a timeshare condo around Gliese 581.
Do you think habitable planets are common in the Milky Way? Tell us what your perfect planet environment might be in the comments below.
Seasonal flows spotted by HiRISE on northwestern slopes in Hale Crater. (NASA/JPL/University of Arizona)
As the midsummer Sun beats down on the southern mountains of Mars, bringing daytime temperatures soaring up to a balmy 25ºC (77ºF), some of their slopes become darkened with long, rusty stains that may be the result of water seeping out from just below the surface.
The image above, captured by the HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter on Feb. 20, shows mountain peaks within the 150-km (93-mile) -wide Hale Crater. Made from data acquired in visible and near infrared wavelengths the long stains are very evident, running down steep slopes below the rocky cliffs.
These dark lines, called recurring slope lineae (RSL) by planetary scientists, are some of the best visual evidence we have of liquid water existing on Mars today – although if RSL are the result of water it’s nothing you’d want to fill your astro-canteen with; based on the first appearances of these features in early Martian spring any water responsible for them would have to be extremely high in salt content.
According to HiRISE Principal Investigator Alfred McEwen “[t]he RSL in Hale have an unusually “reddish” color compared to most RSL, perhaps due to oxidized iron compounds, like rust.”
See a full image scan of the region here, and watch an animation of RSL evolution (in another location) over the course of a Martian season here.
Perspective view of Hale crater made from data acquired by ESA’s Mars Express. Credit: ESA/DLR/FU Berlin (G. Neukum)
THEMIS image of channels in the southeastern ejecta of Hale crater. Credit: NASA/JPL-Caltech/Arizona State University. (Source.)
Hale Crater itself is likely no stranger to liquid water. Its geology strongly suggests the presence of water at the time of its formation at least 3.5 billion years ago in the form of subsurface ice (with more potentially supplied by its cosmic progenitor) that was melted en masse at the time of impact. Today carved channels and gullies branch within and around the Hale region, evidence of enormous amounts of water that must have flowed from the site after the crater was created. (Source.)
The crater is named after George Ellery Hale, an astronomer from Chicago who determined in 1908 that sunspots are the result of magnetic activity.
UPDATE April 13: Conditions for subsurface salt water (i.e., brine) have also been found to exist in Gale Crater based on data acquired by the Curiosity rover. Gale was not thought to be in a location conducive to brine formation, but if it is then it would further strengthen the case for such salt water deposits in places where RSL have been observed. Read more here.
