This SciShow Space video is supported by you enjoying our amazing Complexly calendars all throughout the year 2023. Whether you're into bizarre beasts of the modern day or ancient times, you can find the calendar to match your interests at complexlycalendars.com for a limited time.

I'm not here to accuse astronomers of hyperbole, but they sure do love a catchy name. In space, we can find ghosts, vampires, and even dragons. Metaphorical ones, but still!

It's clear that the only thing that captures our imagination more than space is something in space with a cool name. So, in honor of the spookiest time of year, we picked a few of the spookiest-named stuff in the cosmos.

First up is the red ghost of a planet next door. Mars's dead sand dunes can tell us a lot about what happened on the planet when it was a bit more... lively. Here's Caitlin to tell us more.

Today, Mars is like the ghost of a planet, a desert world full of canyons and sand dunes. Once, it was more like Earth, with a thicker atmosphere and liquid water, but those days are billions of years in the past.

Now, looking at Mars, it's hard not to wonder, "What happened here?" And while there are many ways to try to answer that question, one place that scientists are looking for clues is in the planet's ancient sand dunes.

Sand dunes build up over time as strong winds pick up individual grains and then drop when some obstacle breaks up the air flow. We see them on a few different planets and moons in the solar system, and the different forms they take can tell us a lot about the environments that created them.

On Mars, scientists are especially interested in what are called fossil dunes. Satellite images show that these dunes seem to be frozen in place, and they have been that way for billions of years, possibly because the wind in Mars's thin atmosphere no longer has the oomph to move them. As a result, these dunes are relics of a different time, and just like ordinary fossils, which preserve clues about ancient organisms, fossil dunes record clues about ancient wind patterns.

For example, in the Arkhangelsky crater in Mars's southern hemisphere,

there are ancient dunes in the shapes of crescents. And dunes like this, also known as barchan dunes, are common on Earth and Mars. They form in places where the wind blows in one direction, and the tips of the crescents point in the direction of the wind.

But in the Arkhangelsky crater, there seem to be multiple layers of dunes, and they don't all point in the same direction. The tips of the older crescents point toward the southwest, which tells us they were formed by a southwesterly wind. But newer, larger dunes that seem to have grown over them at a later time point in a different direction, indicating a northeasterly wind. So together the layers of dunes in this field appear to preserve the record of some ancient climate change. 

And these aren't the only dune features that hold clues to the planet's past. Mars also has what are called ghost dunes. These are kind of like the opposite of dunes, actually: large pits that formed in places where lava or sediment once collected around a dune and hardened. Then, after the dune itself eroded away, their shapes remained.

Ghost dunes can be especially valuable because by looking at that sediment or lava that formed that hardened cast, scientists can figure out the age of the dunes. That lets them estimate what the climate was like at a fairly specific point in time, which isn't always easy with a fossil dune.

For example, ghost dunes in a region called Noctis Labyrinthus show that around 3 billion years ago, the wind was northerly, unlike today, when it's largely out of the northeast. That might seem like a small detail, but these subtle clues about things like wind direction, air pressure, and timing can help us reconstruct past climates. And that in turn can help us understand things like whether or not Mars was ever hospitable to life, and how and when that changed.

But not all of Mars's dunes are relics of the past, even though astronomers assumed they were when they first saw dunes on Mars in the 1970s. Since the late '90s, satellite imagery has revealed that some are still active. Most seem to move pretty slowly, maybe only a few centimeters every thousand years, so compared to dunes on Earth, movement that takes only a few months here may take a hundred thousand years on Mars.

But astronomers have noticed a few quicker movements, too: places where the wind was strong enough to move dunes around at Earth-like speeds.

These active dunes may not reveal Mars's past, but they can help us see how it's evolving in the present, and how this ghost of a planet is actually continuing to change through processes like erosion.

For instance, some of the biggest shakeups happen near boundaries in the landscape, like the edge of craters where dramatic changes in elevation and temperature whip up super strong winds, which not only tells us something specific about Mars, it also highlights the fact that Mars and Earth have important geological differences.

So while a lot of the factors drive Earth's geology, like rain, underground water, and plant life don't really affect Mars, the red planet still is shaped by certain things, like craters. And those are things we might not have thought to consider if we hadn't looked at sand dunes.

All this goes to show that a s much as dunes seem to be a relatively common phenomenon in our solar system, that doesn't mean they're not totally awesome! By looking at the dunes, we can better understand how Mars is similar to the Earth, how it's not, and what factors make the difference.

So, even living dunes can tell us a bit about how a planet became a ghost. That's pretty cool!

What's scarier than a ghost planet? A black hole.

But what happens when astronomers can't agree about whether a black whole even exists? If we're lucky, they put their heads together and find a vampire. A vampire star, that is.

When is a black hole not a black hole? This isn't a riddle; it's an example of scientific cameraderie: astronomers from around the world with different hypotheses working together to solve an interstellar mystery. And instead of a dead star, they may have found one sucking the life out of its companion.

Black holes can't be observed directly. We can only observe the effects they have on other things. So when astronomers study these celestial objects, they're usually looking at something we can see and inferring the presence of a black hole based on the gravitational effects it has on one or more visible objects.

So, back in 2020, astronomers used one of the telescopes at the European Southern Observatory in Chile to look at a star system with the very creative name of HR 6819.

Its light looked a bit wonky, possibly influenced by an object they couldn't see.

But, because there's only so much time a telescope can dedicate to studying a particular part of space, and when stars are so far away they can look like single pixels, astronomers can only capture so much data. And that means they use computer models to help fill in the gaps and draw educated conclusions about what's going on, based on equations that describe how we believe the universe works.

In this case, the team felt the model which best fit their data was that of a trinary system: two stars more massive than our sun and something with a similar mass, but invisible: a black whole, created after a massive star went supernova.

The setup they described requires the black hole to tightly co-orbit one of the stars, like once every 40 days, with the other star much further away. That central star, called a B-type star, is known for living fast and dying young. It weighs in at a mass of about 6 times the mass of our sun.

The more distant one is a Be star, which is a B-type star that is just about to run out of hydrogen fuel. It also spins way faster than normal and has a disk of debris around its equator.

After their results were published in the journal Astronomy & Astrophysics, various news outlets picked it up, because this black hole would be a record setter. At a mere 1000 light years from Earth, HR 6819's black hole was the closest one ever detected! But, because the data could only provide a partial picture, other teams could run their own models on HR 6819 and reach different conclusions.

And they did. Like one team who argued there could actually be four bodies in the system. And others argued there didn't need to be a black hole at all, just two stars with a very special relationship.

Instead of a B star closely orbiting a black hole and the Be star further away, the two would be so close to one another

that the Be star was acting like a cosmic vampire, using the power of gravity to siphon matter off of its companion. In fact, it was that process which could explain why it's spinning so fast.

Now, it's not like the first team wasn't aware of this phenomenon, but it's such a blink-and-you'll-miss-it process, at least on the scale of a star's lifetime, that it would've been extremely unlikely for them to have captured it.

Rather than getting into a big academic fight about which conclusion was right, a group of these astronomers teamed up to collect and analyze new data from more powerful instruments at the same observatory: the ESO.

Like, instead of a 2.2-meter wide telescope to collect data, this time, they got to use an 8.2-meter wide telescope. That allowed them to actually take what was one tiny blob of light and detect two tiny blobs of light. The question was, was that enough to show that one of them was orbiting a black hole?

Based on this new data, the team was able to confirm that both stars were orbiting one another more tightly than Earth goes around the Sun, with no sign of a black hole's influence in sight.

While there's still some amount of uncertainty, like how much mass each star has, and how far away the system actually is from Earth, it's pretty clear there's no record-breaking black hole next door. Which you might think is disappointing, but a vampire star is still pretty cool.

It means the B star isn't as normal as astronomers thought it was. It's been stripped of most of its hydrogen, so it's way less massive, bloated, and mostly made helium.

These observations have managed to capture an event which actually doesn't last that long, astronomically speaking, like having front row seats to unique moments in a massive star's life cycle without having to leave our cosmic couch.

And the team is keeping up with the collab. They're going to continue to monitor HR 6819 as the system evolves. And all this extra close data

will help other astronomers figure out all the nuances of other binary systems out there.

But, as far as black holes in the neighborhood, the search continues. There could be as many as a hundred million of them, peppered throughout the galaxy. And the nearest, at least that we know of, is only about 3000 light years away.

It's studies like these which do a great job at revealing a side of science we don't always get to see: that the first answers we arrive at shouldn't be carved in stone, and you never know what cool update is around the corner.

You really do never know what scientists will come up with next. And in the Space Age heyday of the 1960s, some of the ideas were pretty out there. For example, they proposed a rocket so big, it would've had to launch from the ocean, like a dragon rising out of the sea.

The early 1960s was an optimistic time for space engineering. With the space race between the US and the Soviet Union in full swing, cameras, animals, and humans were being launched into orbit, and the world seemed headed for a spacefaring future, where hundreds or even thousands of people would be living and working off Earth.

Getting that civilization into orbit, though, would require a lot of power, and in 1963, a team led by the engineer Bob Truax proposed a solution: a supersized rocket capable of launching an entire space station in one go. They called it the Sea Dragon, and while it never launched it was well ahead of its time, and it continues to inspire engineers today.

When the Sea Dragon was proposed, the Soviets were leading the charge with rockets that were about 50 meters long and 3 meters wide. They would carry maximum payloads of about 5 metric tons.

The Sea Dragon would've been an absolute monster by comparison. It would've been more than 150 meters tall and more than 22 meters wide, and it was designed to carry more than 500 metric tons into space. And it would have been nearly 400 times more powerful than rockets of the time, and 10 times more powerful than the future Saturn V, the rocket that eventually took humans to the Moon.

And, as the name suggests, it was also intended to launch from the sea.

And not on a floating platform or anything. Like, directly out of the water. As impractical as that might sound, there are actually a few good reasons why a water launch was the best option.

For one, it would have made transporting and assembling the rocket's huge components a lot easier, since a buoyant environment would support the rocket safely as it was being constructed.

Then, there was all that thrust. At ignition, the Sea Dragon's powerful engines would have caused major damage to launch pads of the time, tearing apart concrete and melting metal. Water, on the other hand, just boils off or flows away.

Finally, after launch, the Sea Dragon's huge and scalding exhaust plume would be kept far away from populated areas.

Of course, while a water launch offered a ton of benefits, it did create a few potential engineering challenges, too. For example, salt water is really good at corroding metal and messing up delicate electronic components.

To get around that, though, engineers hoped to borrow techniques from submarines, which spend months at a time completely submerged in salt water.Their idea was to build the rocket with thick steel plates, insulation, or special paint to resist corrosion, and to place access panels to waterproofed electrical components above the waterline.

But besides some water protection, the rocket's design was really simple: a style that would become known as a big dumb booster. Each of the Sea Dragon's two stages would store fuel and liquid oxygen in pressurized tanks. At liftoff, simple valves would open, and the chemicals would mix, igniting on contact to produce a bunch of thrust that would carry the payload into space.

This design is less efficient than those found on the sophisticated Saturn V, but the Sea Dragon's huge size would have made up for that, making it considerably cheaper per kilogram of payload.

The simple design would've also helped ease its assembly and launch. The main components would be built in dry docks and on-shore facilities, then would be floated and assembled in a specially made lagoon in Cape Canaveral, Florida. The rocket would then be filled with fuel and pressurized before being towed out to the launch point about 60 kilometers from the shore.

When it was time to launch, ballast sacks attached to the bottom would be filled with a heavy fluid like mud and clay. Then they would sink, and that would pull the Sea Dragon upright.

Once the engines were lit, water would be expelled from the first stage, and everything would work pretty much like any other rocket. Its massive payload would be in low Earth orbit in a few minutes.

All of this is really cool, but the Sea Dragon had one more innovation up its gigantic sleeves, one that would put it way ahead of its time. The rocket was designed to be almost entirely reusable.

After launch, bags on the ballast tanks would be inflated with air to float the tank back to the surface. And both the rocket's first and second stages would be fitted with inflatable drag skirts to point them in the right direction and slow them down enough to survive a water landing with no damage. Each Sea Dragon would have been able to make more than a hundred flights, and that reuse would have massively reduced the cost of getting to space. 

It really was a time of infectious optimism. Although the Sea Dragon was many times bigger than anything that had come before it, none of the engineering challenges seemed insurmountable. The team even got as far as a couple of prototypes to prove that a sea launch was possible.

Unfortunately, though, the whole program just kind of... fizzled out after a while. And while Truax was asked to develop other versions of his designs over the next few decades, nothing ever really got of the ground. Or out of the water, I guess.

What left the Sea Dragon adrift wasn't the engineering challenges or even the cost, but the motivation. Although some of the public may have looked forward to a spacefaring future, NASA was more tightly focused on a single goal: getting a man to the moon.

The Sea Dragon was an incredible tool, but not one that the space agency really needed at the time. It was a workhorse for a large scale settlement of space at a time when pioneers were still making tentative steps to explore space. Even today, we're not launching anything that needs the Sea Dragon's massive lifting power.

Still, the idea of a sea launch certainly isn't dead in the water. Among the many private companies clamoring for space, several are proposing sending their rockets from the sea. One of the many benefits is that you don't need a designated launch pad, which could become really useful as we start to launch more rockets and set our sights on a spacefaring future once again.

And, if the day ever comes where we do want to launch a city into space, well, we have a design we're dusting off.

At least this entry wasn't so spooky,

since it never flew... yet, anyway.

Thanks for spending some spooky time with us today in this particularly spooky time of year.

If you're the kind of person who could use a calendar to tell you when the spooky season approaches, you're in luck. We have Complexly calendars available for you! You can buy them online and have them shipped anywhere in the world, but only for a little while longer until they're gone.

Do you like pi? We've got a calendar for you. If you're into moons, we've got a calendar about them too. And if you like animals that don't even exist anymore, we made a calendar all about them.

So forget about those kittens in a basket. You could have microscopic organisms on your wall in an awesome 2023 calendar. Just go to complexlycalendars.com or click the link in the description to get whichever one speaks to you.

Thanks for watching this video, and thanks for supporting SciShow Space.