Why is it Tough to Land on a Comet?

Why is it Tough to Land on a Comet?

Why is landing on a comet so difficult and what does this tell us about future missions to comets and asteroids?

Us nerds were riveted by the coverage of the ESA’s Rosetta mission and its arrival at Comet 67/P in 2014. One such nerd is Paco Juarez, friend of the show and patron. He wanted to know why is it so darned hard to land on a comet?

In 2014, the tiny Philae Lander detached from the spacecraft and slowly descended down to the surface of the comet. If everything went well, it would have gracefully touched down and then sent back a pile of information about this filthy roving snowball.
As you know, the landing didn’t go according to plan. Instead of gently touching down on 67/P, Philae bounced off the surface of the comet like a tennis ball dropped from a tower, and rose a kilometer off the surface. Then more descending, and more bouncing, finally settling down on rugged terrain, surrounded by crevices and large boulders. At that point, engineers lost contact with the lander, and so much science went undone.

If I recorded this video a few months ago, that would have been the end of the story. You know how this goes, space exploration is hard and dangerous, don’t be surprised when your missions fail and space unfeelingly smashes up your pretty little robot probes with their little gold foil 27 pieces of flair.

Rosetta
Rosetta

Fortunately, I’m able to report that ESA regained contact with the Philae lander on June 13, 2015, resuming its mission, and scientific operations.

But why is landing on a comet so difficult and what does this tell us about future robotic and human missions to smaller comets and asteroids? When ESA engineers designed Philae, they knew it was going to be very difficult to land on a comet like 67/P because they have a such a low gravity. And they have low gravity because they’re little.

Illustration of the Rosetta Missions Philae lander on final approach to a comet surface. (Photo: ESA)
Illustration of the Rosetta Missions Philae lander on final approach to a comet surface. (Photo: ESA)

On Earth, 6 septillion tonnes of rock and metal give you an escape velocity of 11.2 km/s. That’s how fast you need to be able to jump in order to leave the planet entirely. But the escape velocity of 67/P is only 1 m/s. You could trip off the comet and never return. Whilst small children threw rocks at you from the surface as you drifted away.

Philae was built with harpoon drills in its landing struts. The moment the lander touched the surface of the comet, those harpoons were supposed to fire, securing the lander. The surface of the comet was softer than scientists had anticipated, and the harpoons didn’t fire. Or possibly they were broken and couldn’t fire. Space is hard. Whatever the case, without being able to grab onto the surface, it used the comet as a bouncy castle.

We’re learning what it takes to land on lower mass objects like comets and asteroids. NASA’s OSIRIS-REx mission will visit Comet Bennu, and send a lander down to the surface of the asteroid. From there it’ll pick up a few samples, and return them back to Earth. It’ll be Philae, all over again.

An artist concept of the Philae lander on comet 67P/Churyumov-Gerasimenko.  Credit: Astrium - E. Viktor/ESA
An artist concept of the Philae lander on comet 67P/Churyumov-Gerasimenko. Credit: Astrium – E. Viktor/ESA

In the future, we’re told, humans will be visiting asteroids to study them for science and their potential for ice and minerals. You can imagine it’ll be a harrowing descent, but even just walking around on the surface will be dangerous when every step could throw an astronaut into an escape trajectory. They’ll need to learn lessons from rock climbers and Rorschach.

As we learned with Philae, landings on low mass objects is really tough. We’re going to need to get more practice and develop new techniques and technologies before we’re ready to add asteroid mining to our list of “stuff we just do, NBD”.

What are some unusual worlds you’d like humanity to visit? Put your suggestions in the comments below.

How Massive Can Black Holes Get?

How Massive Can Black Holes Get?

We talk about stellar mass and supermassive black holes. What are the limits? How massive can these things get?

Without the light pressure from nuclear fusion to hold back the mass of the star, the outer layers compress inward in an instant. The star dies, exploding violently as a supernova.

All that’s left behind is a black hole. They start around three times the mass of the Sun, and go up from there. The more a black hole feeds, the bigger it gets.

Terrifyingly, there’s no limit to much material a black hole can consume, if it’s given enough time. The most massive are ones found at the hearts of galaxies. These are the supermassive black holes, such as the 4.1 million mass nugget at the center of the Milky Way. Astronomers figured its mass by watching the movements of stars zipping around the center of the Milky Way, like comets going around the Sun.

There seems to be supermassive black holes at the heart of every galaxy we can find, and our Milky Way’s black hole is actually puny in comparison. Interstellar depicted a black hole with 100 million times the mass of the Sun. And we’re just getting started.

The giant elliptical galaxy M87 has a black hole with 6.2 billion times the mass of the Sun. How can astronomers possibly know that? They’ve spotted a jet of material 4,300 light-years long, blasting out of the center of M87 at relativistic speeds, and only black holes that massive generate jets like that.

Most recently, astronomers announced in the Journal Nature that they have found a black hole with about 12 billion times the mass of the Sun. The accretion disk here generates 429 trillion times more light than the Sun, and it shines clear across the Universe. We see the light from this region from when the Universe was only 6% into its current age.

Somehow this black hole went from zero to 12 billion times the mass of the Sun in about 875 million years. Which poses a tiny concern. Such as how in the dickens is it possible that a black hole could build up so much mass so quickly? Also, we’re seeing it 13 billion years ago. How big is it now? Currently, astronomers have no idea. I’m sure it’s fine. It’s fine right?

We’ve talked about how massive black holes can get, but what about the opposite question? How teeny tiny can a black hole be?

An illustration that shows the powerful winds driven by a supermassive black hole at the centre of a galaxy. The schematic figure in the inset depicts the innermost regions of the galaxy where a black hole accretes, that is, consumes, at a very high rate the surrounding matter (light grey) in the form of a disc (darker grey). At the same time, part of that matter is cast away through powerful winds. (Credits: XMM-Newton and NuSTAR Missions; NASA/JPL-Caltech;Insert:ESA)
An illustration that shows the powerful winds driven by a supermassive black hole at the centre of a galaxy. The schematic figure in the inset depicts the innermost regions of the galaxy where a black hole accretes, that is, consumes, at a very high rate the surrounding matter (light grey) in the form of a disc (darker grey). At the same time, part of that matter is cast away through powerful winds. (Credits: XMM-Newton and NuSTAR Missions; NASA/JPL-Caltech;Insert:ESA)

Astronomers figure there could be primordial black holes, black holes with the mass of a planet, or maybe an asteroid, or maybe a car… or maybe even less. There’s no method that could form them today, but it’s possible that uneven levels of density in the early Universe might have compressed matter into black holes.

Those black holes might still be out there, zipping around the Universe, occasionally running into stars, planets, and spacecraft and interstellar picnics. I’m sure it’s the stellar equivalent of smashing your shin on the edge of the coffee table.

Astronomers have never seen any evidence that they actually exist, so we’ll shrug this off and choose to pretend we shouldn’t be worrying too much. And so it turns out, black holes can get really, really, really massive. 12 billion times the mass of the Sun massive.

What part about black holes still make you confused? Suggest some topics for future episodes of the Guide to Space in the comments below.

Could We Terraform Jupiter?

Could We Terraform Jupiter?

So just what would it take to terraform Jupiter, the largest planet in our solar system?

Just a few videos ago, I blew minds with a “How to” on terraforming the Moon. Once we’ve developed a Solar System spanning civilization and have claimed mastery over the laws of physics, and have common-place technology which staggers and dwarf our current comprehension of what’s possible it should be easy enough.

In fact, it might even be easier than terraforming Mars or Venus, as long as you keep a steady flow of gas to the Moon replenishing the constantly escaping atmosphere.

And in the comments on that video, ABitOfTheUniverse threw down, he wants to know what it would take to terraform Jupiter. All right “ABitOfTheUniverse”, if that is your real name… I’m up for it.

On the surface, this is madness. We already explained how Jupiter is completely and totally inhospitable to life. An alien started a “Build a star kit” and stopped a ? of the way through, because he got bored and wandered away. Just like his Mom said he would.

Jupiter is a ball of hydrogen and helium, which compresses these gasses to almost starlike temperatures and pressures. Fine, Jupiter is the absolute worst. It makes traveling to Venus look like a spa visit.

Jupiter does have something we can work with. Astronomers think below the septillions tons of hydrogen and gas, there’s actually a rocky core. The mass of the core is still a mystery, but recent computer simulations put it at somewhere between 7 and 45 times the mass of the Earth, complete with plenty of water ices and other chemicals you might require on an Earthlike planet.

Furthermore, this core may contain similar constituents as the internal structure of Earth. This means a central core of iron and nickel, surrounded by liquid metal, surrounded by rock.

The problem is you need to strip away 95% of the planet’s mass. It’s all that hydrogen and helium, and that’s pretty much impossible. And almost completely impossible, is still very slightly completely possible.

Cutaway of Jupiter. Credit: Kevinsong
Cutaway of Jupiter. Credit: Kevinsong

Jupiter is made of fuel. It’s like looking at a pool of gasoline and wondering if there was some way to get rid of it all. What good Solar System-spanning civilization hasn’t worked out hydrogen fusion? It’s a technology that’s probably only 30 years away from us now.

You could fly a spacecraft down into Jupiter’s gravity well and scoop up hydrogen fuel from the clouds. Or you could create fusion-powered dirigibles filled with hot hydrogen, which float around the cloud tops of Jupiter, using their fusion reactors to spew hydrogen off into space.

Over untold lengths of time, you could get at that rocky juicy center, once you stripped it of its hydrogen. Then you’ll need to do all that other stuff I mentioned in previous videos, to turn it into a habitable world.

Sure, it’s a world with much higher gravity than Earth, but that’s not my problem. You said “Earthlike”. That’ll teach you to make wishes with a monkey’s paw!

What if you need to move Jupiter first, perhaps a little closer to the Sun. There’s an awesome idea cooked up by Larry Niven in his book, “A World Out of Time”. It’s a fusion candle, and it lets you shift gas giants around.

A Star Trek-inspired space station.
A Star Trek-inspired space station.

You take a long space station, and light up fusion thrusters on both ends. You dip one end down into the upper clouds, where it siphons hydrogen fuel. Both ends of the space station start blasting. One end keeps it from dropping down into the planet, and the other end pushes on the entire planet, pushing it around the Solar System.

Instead of trying to terraform Jupiter, we could just push the planet closer to the Sun, where its icy moons warm up and become habitable themselves.

Well, ABitOfTheUniverse, that sounds a little easier. What do you think? I’ll admit, trying to figure out how to terraform Jupiter was a good exercise in tomfoolery. Fortunately, my imagination is a limitless and renewable source of energy. We’ve done Mars, Venus, the Moon and now Jupiter. What should we terraform next? Tell us in the comments below.

Could We Make Artificial Gravity?

Could We Make Artificial Gravity?

It’s a staple of scifi, and a requirement if we’re going to travel long-term in space. Will we ever develop artificial gravity?

It’s safe to say we’ve spent a significant amount of our lives consuming science fiction.

Berks, videos, movies and games.

Science fiction is great for the imagination, it’s rich in iron and calcium, and takes us to places we could never visit. It also helps us understand and predict what might happen in the future: tablet computers, cloning, telecommunication satellites, Skype, magic slidey doors, and razors with 5 blades.

These are just some of the predictions science fiction has made which have come true.

Then there are a whole bunch of predictions that have yet to happen, but still might, Fun things like the climate change apocalypse, regular robot apocalypse, the giant robot apocalypse, the alien invasion apocalypse, the apocalypse apocalypse, comet apocalypse, and the great Brawndo famine of 2506.
Continue reading “Could We Make Artificial Gravity?”

What About a Mission to Europa?

What About a Mission to Europa?

Europa’s water exists in a layer around the planet, encased in a layer of ice. Could there be life down there?

Hooray! Welcome to the 200th official episode of the Guide To Space!

First off, thank you. Thank you for watching, liking, sharing, subscribing and being a patron of our show. Yes, you. Thank you.

So to celebrate, a few weeks ago we invited the members of the Weekly Space Hangout Crew Google+ Community to suggest topics for episodes, and the winner would receive a precious iron-nickel meteorite. Congratulations Andres Munoz, this meteorite is for you.

This episode, chosen by Andres, is for everyone.

The search for life in the Solar System is about the hunt for water. Wherever we find liquid water on Earth, we find life. I’m talking everywhere. In the most briny, salty pools in Antarctica, in the hottest hot springs in Yellowstone, under glaciers, and kilometers deep underground.

So we go searching for liquid water in the Solar System.

You might be surprised to learn that Jupiter’s moon Europa has the most water in the entire Solar System. If you took all the water on Earth, collected it into a big sphere, it would measure almost 1,400 kilometers across.

Europa’s water would measure nearly 1,800 kilometers.All that water exists in a layer around Europa, encased in a layer of ice. How thick? We don’t know.

Is there life down there? We don’t know.You can say there might be, and it wouldn’t be untrue. However, if you say there isn’t, that’s way less interesting for clickbait purposes. Whenever we don’t know the answers to fundamental and intriguing questions like that, it’s time to send a mission.

Good news! An actual mission to Europa is in the works right now. In 2015, NASA approved the development of an orbiter mission to Europa. If all goes well, and nothing gets cancelled…

And nothing will get cancelled, right? Right? I heard Firefly. Which one of you said Firefly?!?

According to the plan, a spacecraft will launch in the 2020s, carrying 9 instruments to Europa. Most will be familiar cameras, mass spectrometers, and the like, to study the surface of Europa to a high level of resolution. Over the course of 45 flybys, the spacecraft will get down as close as 25 kilometers and capture it with incredible resolution.

A "colorized" image of Europa from NASA's Galileo spacecraft, whose mission ended in 2003. The whiteish areas are believed to be pure water ice. Credit: NASA/JPL-Caltech/SETI Institute
A “colorized” image of Europa from NASA’s Galileo spacecraft, whose mission ended in 2003. The whiteish areas are believed to be pure water ice. Credit: NASA/JPL-Caltech/SETI Institute

Perhaps the most exciting, and controversial instrument on board the new Europa Orbiter mission will be its ice-penetrating radar. Mission planners battled over installing a radar this sophisticated, as it will be an enormous drain on the orbiter’s power.

This for us is incredibly exciting. It will allow the spacecraft to map out the depth and thickness of Europa’s icy exterior. Is it thick or thin? Are there pockets of water trapped just below the surface, or is it tough shell that goes on for dozens of kilometers?

The worst case scenario is that the shell goes thicker than the radar can reach, and we won’t even know how far it goes.

Whatever happens, the Europa orbiter will be a boon to science, answer outstanding questions about the moon and the chances of finding life there.

We’re just getting started. What we really want to send is a lander. Because of the intense radiation from Jupiter, the Sun, and space itself, the surface of the ice on Europa would be sterilized. But dig down a few centimeters and you might find life that’s protected from the radiation.

A future Europa lander might be equipped with a heated drill attached to a tether. The lander would be have with a heat-generated radioisotope thermoelectric generator, like most of NASA’s big, outer Solar System spacecraft.

Artist illustration of a Europa probe. Image credit: NASA/JPL
Artist illustration of a Europa probe. Image credit: NASA/JPL

But in addition to using it for electricity, it’ll use the raw heat to help a tethered drill to grind through the ice a few meters and sample what’s down there.

Drilling more than a few meters is probably the stuff of science fiction. Russian scientists in Antarctica drilled for almost two decades to get through 4,000 meters of ice above Lake Vostok. Imagine trying to get through 100 kilometers of the stuff, on a distant world, with a robot.

But, since I’ve talked about moving the Sun, and terraforming the Moon, maybe I shouldn’t put any bounds on my imagination. Nuclear-powered Europa submarines will get us swimming with the singing Europan space whales in no time.

Europa is the best place to search the Solar System for life, and I’m excited to see what the upcoming Europa Orbiter mission turns up. And I’m even more excited about the possibility of any future lander missions.

It was a lot of fun wrapping my brain around a topic chosen by the fans. What topic would you like us to cover next? I’ve got a whole pocket of meteorites here. Put it in the comments below.

First, I want to thank everyone. It’s been a crazy race getting up to 200 episodes, but it’s been a blast all the way through. Thanks again for all your support and here’s to 200 more!

What’s This Ridge on Iapetus?

What’s This Ridge on Iapetus?

The strangest feature on Iapetus is the equatorial ridge. What could possibly create a feature like this?

To paraphrase the British geneticist J.B.S Haldane, “in my suspicion, the Universe is not only stranger than we suppose, it’s stranger than we can suppose.” The context was life and evolution, but he might as well been talking about Saturn’s moons. Those teeny worlds are some of the strangest places we’ve ever seen.

Titan is a massive moon with an atmosphere thicker than Earth’s. If it wasn’t for the bone crippling cold and unbreathable atmosphere, you could wear a pair of wings and fly around in the Titanic skies.

There’s Enceladus, an icy moon that blasts water out into space through geysers at its southern pole. But the Saturnian moon that fascinates me the most has got to be Iapetus, also known as Saturn’s yin-yang moon.

Here’s a photo captured by Cassini. Check out the bizarre surface features, where half of the moon is icy white and the other is brownish red. Astronomers believe this strange coloration comes from the ice on the warmer side sublimating away, leaving this darker material beneath.

Sure that’s a bit odd, but the strangest feature on Iapetus is the equatorial ridge. This feature measures 1,300 km long and it makes the moon look like a space walnut. Because of the heavy cratering on the ridge, astronomers know that it’s ancient, nearly as old as the moon itself. At 13 kms high, it’s tall enough to keep out the most persnickety white walker or wildling mammoth & giant battalion.

What could possibly create a feature like this?

Astronomers are of a few camps. The first think it formed through convective activity early on in the moon’s history. Saturn pulls Iapetus with its tremendous gravity, and the moon undergoes massive tidal forces. This generates heat in the moon’s interior, and it might have caused it to blob out at the equator.

A ridge that follows the equator of Saturn's moon Iapetus gives it the appearance of a giant walnut. This image was taken by the Cassini spacecraft. Credit: NASA/JPL/SSI
A ridge that follows the equator of Saturn’s moon Iapetus gives it the appearance of a giant walnut. This image was taken by the Cassini spacecraft. Credit: NASA/JPL/SSI

A second idea is that Iapetus consumed one of Saturn’s rings, billions of years ago. The moon might have slowly wandered through the ring plane, and accreted all the ring material, like snow piling up in front of a plow.

A third is that Iapetus was smashed into by a massive asteroid billions of years ago. This impact caused the moon to fly apart, but then mutual gravity pulled it back together. The force of this recombination squeezed out material at the equator, which then solidified in place.

Alternately, it might be a walnut from a Galactus family Christmas stocking. So which is it?

It turns out that Saturn has two more moons in its system with similar equatorial ridges. Its moon Atlas is just 15 km across, but it’s dominated by an equatorial ridge. It looks like a UFO, and Pan has a similar feature.

Saturn's relatively thin main rings are about 250,000 km (156,000 miles) in diameter. (Image: NASA/JPL-Caltech/SSI/J. Major)
Saturn’s relatively thin main rings are about 250,000 km (156,000 miles) in diameter. (Image: NASA/JPL-Caltech/SSI/J. Major)

Astronomers know that both of these created their ridges by pulling material out of the rings and piling it up on their surface. This is the mechanism that seems to match what’s going on with Iapetus.

One mystery, is how distantly Iapetus orbits Saturn. There’s no ring that far out, so where did it get the material to consume? Is it possible that Iapetus drifted outward, or had a ring system of its own?

You want puzzles? Iapetus is one of the strangest places in the Solar System, and it would be my candidate for a future orbiter or lander. Let’s explore it closer.

What’s your favorite bizarre object in the Solar System? Tell us in the comments below.

How Could We Destroy the Moon?

How Could We Destroy the Moon?

What would it take to destroy our moon, and eliminate the enemy of stellar astronomy for all time?

In the immortal words of Mr. Burns, “ever since the beginning of time, man has wished to destroy the Sun.” Your days are numbered, Sun.

But supervillains, being the practical folks they are, know that a more worthy goal would be to destroy the Moon, or at least deface it horribly. Nothing wrecks a beautiful night sky like that hideous pockmarked spotlight. What would it take to destroy it and eliminate the enemy of stellar astronomy for all time?

Crack out your Acme brand blueprint paper and white pencils, it’s Wile E. Coyote time.

The energy it takes to dismantle a gravitationally held object is known as its binding energy, we talked about it in a Death Star episode and inventive ways to overcome it.

For example, the binding energy of the Earth is 2.2 x 10^32 joules. It’s a lot. The binding energy of a smaller object, like our Moon is a tidy little 1.2 x 10^29 joules. It takes about 1800 times more energy to destroy the Earth than it takes to destroy the Moon.

It’s 1800 times easier. That’s downright doable, isn’t it? That’s almost 2000 times easier. Which, on the scale of easy to less easy, is definitely closer to easy.

Take the event that created the Caloris Basin on Mercury. It’s a crater, 1,500 km across. Astronomers think that a big fat asteroid, a fatsteroid(?) around 100 km in diameter crashed into Mercury billions of years ago. This event released 1.3 x 10^26 joules of energy, carving out this giant pit. It’s a thousandth of the binding energy of the Moon. We’ll need something more.

Our Sun produces 3.8 x 10^26 joules of energy every second, the equivalent of about a billion hydrogen bombs. If you directed the full power of the Sun at the Moon for 15 minutes, it’d tear apart.

That’s quite a superweapon you’ve got there, perhaps you’ll want to mount that on a space station and take it for a cruise through a galaxy far far away?

If that scene took that long, we’d have fallen asleep. It’s as if millions of voices gradually became a little hoarse from crying out for a quarter of an hour. There’s another way you could tear the Moon apart that doesn’t require an astral gate accident: gravity.

Astronomers use the Roche Limit to calculate how close an object – like a moon – can orbit another object – like a planet.

This is the point where the difference between the tidal forces on the “front” and “backside” are large enough that the object is torn apart, and if this sounds familiar you might want to look up “spaghettification”.

Spaghettification. Credit: Streeter
Spaghettification. Credit: Streeter

This is all based on the radius of the planet and the density of the planet and moon. If the Moon got close enough to the Earth, around 18,000 km, it would pull apart and be shredded into a beautiful ring.

And then the objects in the ring would enter the Earth’s atmosphere and rain down beautiful destruction for thousands of years.

Fortunately or unfortunately, depending your position in this “Die Moon, Die” discussion, the Moon is drifting away from the Earth. It’ll never be closer than it is right now, at almost 400,000 km, without a little nudge.

Phobos, the largest moon orbiting Mars is slowly approaching the planet, and astronomers think it’ll reach the Roche Limit in the next few million years.

It turns out that if we really want to destroy the Moon, we’ll need to destroy all life on Earth as well.

Now we know your new supervillain project, what’s your supervillain name? Tell us your handle in the comments below.

How Fast is Gravity?

How Fast is Gravity?

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.

Twin pulsars.  Credit: Michael Kramer, University of Manchester

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.

Why Don’t We Send Probes “Up” In The Solar System?

Why Don't We Send Probes "Up" In The Solar System?

Wouldn’t it be easier to see what’s outside the solar system if we just send out probes straight up?

Dammit, science people! Why are you always firing probes “outwards”? Then they have to go past all this stuff, like planets and asteroids and crap to escape the solar system. Don’t you realize that if we want to see what’s outside the solar system we just need to shoot them straight up?

Then we don’t have to go past all that junk, and we can finally see what’s between us and the next star system over! Is it thick goo? Is it thin goo? Is it the aether?!

What the heck is wrong with you! It’s so easy. Just go up! Why are we always going out?

Whenever we talk Solar System, we’re always using flat objects for reference. Plates, flying disks, pancakes and pizzas, as it’s arranged in a flat disk known as the plane of the ecliptic.

Formed from a blob of hydrogen gas and dust in the solar nebula. Gravity pulled everything together, and the conservation of angular momentum set the whole thing spinning, faster and faster. The spinning pulled the whole Solar System into the disk we see today, with our star at the center and the planets embedded in the surrounding disk. As a result, the Sun, Moon, planets and their moons all move through a relatively small region in the sky.

This definitely makes things easier to send spacecraft from world to world. NASA’s Voyager 2 was able to visit Jupiter, Saturn, Uranus and Neptune because they were all lined up like dominoes.

When Willie Sutton was asked why he robbed banks, he answered, “that’s where the money is,” and we explore along the plane of the ecliptic because that’s where the science is. Everything in our Solar System is arranged along this flat area, so it makes sense to look along this region.

But wait! As you know, the Solar System isn’t actually flat. Some objects rise a little above or below the plane of the ecliptic. This is known as a planet’s orbital inclination.

Orbit of Mercury
Orbit of Mercury

Of all the planets, Mercury has the greatest with 7-percent. It’s even crazier for the the dwarf planets, Pluto is 17-percent off the plane of the ecliptic, and Eris is 44-percent.

One of the reasons Eris went undiscovered for so long is because it orbits so far outside the planet of the ecliptic. It wasn’t until Mike Brown and his team from Caltech looked far enough outside the usual hiding spaces that they found these additional dwarf planets.

There really isn’t much outside the flat plane of the ecliptic, it’s also much more difficult to get spacecraft to travel above or below. When spacecraft launch, they already have tremendous velocity just from the rotation of the Earth and the speed of the Earth orbiting the Sun.

I realize this is just more “outwardist” propaganda for you. So why no “up”? If you did want to go that way, you need a powerful rocket capable of creating velocity in this direction, or that direction.

If you wanted to escape the Earth’s gravity and explore the Solar System in the regular old way, you’d need to add about 10 km/s in velocity to your spacecraft. But for straight up, you’d need about 30 km/s, meaning more fuel, and compromises to your payload.

It still sounds like I’m making excuses. Here’s the deal, you might be amazed to learn that spacecraft actually have been sent “up”.

Artist impression of the Ulysses spacecraft. Credit: NASA/ESA
Artist impression of the Ulysses spacecraft. Credit: NASA/ESA

The European Space Agency’s Ulysses spacecraft, launched in 1990 had the goal of looking down on the Sun from above. It wasn’t possible to do this just with a rocket, but engineers were able to use a gravitational assist from Jupiter to kick Ulysses into an orbital inclination of 80-degrees, and for the first time, we were able to see the Sun from above and below.

A new European mission is in the works called the Solar Orbiter, and it’ll get into an orbital inclination of 90-degrees to be able to see the Sun’s poles directly for the first time. If all goes well, it’ll launch in 2018.

So, why don’t we go up? Actually, we do. We’re going “up” again very soon. It’s good to go up. It’s always good to get outside of our regular stomping grounds and see our Solar System from new angles and perspectives.

If you could send a probe anywhere in our Solar System, where would you choose?