Ross Lucksinger

Roaming the Cosmos – Vega

Fourteen thousand years ago, the North Star wasn’t the North Star.

The night sky in the northern hemisphere currently turns around Polaris, the brightest star in the Little Dipper. But that changes, ever so slowly, because the Earth is not a perfect sphere. Its spin gives it a slight bulge at the equator. Gravitational forces from both sun and moon apply a gentle torque to this bulge, causing the pole to move in a circle. This movement is called axial precession and it takes 26,000 years to complete one circle.

1024px-precession_nThe North Pole circles a huge swath of the sky over that time, allowing many different stars to be the North Star. But the brightest by far is Vega.

Vega is the second-brightest star in the northern celestial hemisphere and the fifth-brightest star in any sky visible from Earth. That’s because it’s both big and close. At twenty-five light years away, it’s in the stellar neighborhood and it’s a burning hot blue giant more than twice the size of the sun and fifty-eight times brighter.

In summer in the northern hemisphere, Vega is located nearly straight overhead at night. But fourteen thousand years ago the north pole pointed right at it and the night sky spun around Vega all-year long.

Let’s travel to the star itself. If you’re expecting an orderly system with planets at regular intervals, you will be quite surprised.

Excess infrared flux coming from Vega indicates that the star is surrounded by a massive, disc-shaped cloud of debris that’s as big as our solar solar system.

Lots of stars have protoplanetary discs around them right after they form, but Vega is not a newly-formed star. It’s been around for millions of years. For that much debris to be circling Vega, there has to be a continual source of replenishment. The inner-part of the disc, close to Vega, must have an extremely high dust production rate, since stellar wind pressure should have pushed out all small grains long ago. Where does this big cloud come from?

The quickest way to get a cloud of dust in space is by smashing big things together. There must be a tremendous amount of bombardment going on. One possible explanation would be the migration of giant planets in Vega’s outer disc. The cloud is very uneven, indicating the potential presence of large objects.

Either from one big collision between planets or many small collisions from smaller planetoids (or both), Vega is surrounded by chaos. If you stood on a crumbling world near Vega, you could see the dust of the system lacing the sky.

Through this haze, the sun would be visible. Our sun, that is. Twenty-five light years is a great distance, but not so far as to change the stars in the sky too much. Roughly the same constellations could be seen from the Vega system. The sun would be a faint star in the Columba constellation.

We view the Vega system top down. It’s one of the reasons why this disc of debris is so easy to see. Because we are located directly above Vega, the sun might be the North Star of a planet in the Vega system.

Or, if not, we might become the North Star at some point. After all, guiding stars change all the time.

Sources/Additional Reading:

Vega: The Once and Future North

Vega’s StardustCNRS International Magazine

New evidence for Solar-like planetary system around nearby star – Royal Observatory, Edinburgh

The Vega Debris Disk: A Surprise from Spitzer – Cornell University Library

Precession chart created by Wikipedia user Tauʻolunga.

Roaming the Cosmos – Proxima Centauri B

As we move farther away from the sun, our journey gets colder and colder. If we want to find warmth and light again, it will be around distant suns.

Every star has a habitable zone — a range of orbits in which a planet could have liquid water on its surface. Our system has one planet in the habitable zone. But how common is this? How many stars must we pass in order to find one with a planet in the right orbit for liquid water?

None. Because the closest star with a planet in its habitable zone is the next closest star.

At 4.25 light-years from the sun, Proxima Centauri is closer than any other star. It’s small, red, and dim. Its diameter is about 1/7th that of the sun and only one and a half times the size of Jupiter. But orbiting very close to this cool star is a planet: Proxima Centauri B. It’s about 1.3 times the size of Earth, meaning it likely has a similar composition (i.e. rock instead of gas).

Proxima Centauri B’s distance from its host star puts it square in the habitable zone. Of course, that doesn’t automatically mean it’s room temperature on the surface. There are some significant challenges to livability. Its close proximity to the host star means it gets 2,000 times as much stellar wind pressure. In addition, Proxima Centauri is a “flare star” — a star that goes through frequent and unpredictable increases in brightness, showering any surrounding planets in radiation.

Proxima Centauri B is so close to its star that an orbit is just eleven days. Because the planet is so close, it might be tidally locked, just like how the moon always shows the same side toward us. In that case, one side of Proxima Centauri B would be blazing hot, the other side cold and dark.

But even in that situation, liquid water could still exist on the surface. Right at the border between day and night the temperature might be just right. Any atmosphere that did exist would be turbulent. Powerful winds would constantly blow in from the hot side.

Imagine a narrow, windy ocean. A great red star is locked on the horizon in permanent sunset/sunrise. The light is never brighter than twilight on Earth, as the dim star casts two percent of the light that Earth gets. Even with the red sun visible, the night sky would always be there, including the binary pair of nearby Alpha Centauri A and B shining brighter than any stars in our sky.

Or perhaps Proxima Centauri B does spin, albeit slowly. Not all close orbiting planets are tidally locked. It could be in a 3:2 orbit, much like Mercury around the Sun. In this case, a day on Proxima Centauri would last about 7.5 Earth days, but that’s still enough of a spin to have liquid oceans and livable temperatures. Relatively livable, anyway.

Or course, living there is not an immediate concern. Using conventional propulsion, even sending a probe to the system would take 30,000 years. However, Project Starshot seeks to change that. It’s a $100 million program to develop a proof of concept for solar sails that could accelerate a fleet of tiny probes to 20 percent of the speed of light, arriving in the Proxima Centauri system in only 20 years.

In 2010, JAXA (the Japan Aerospace Exploration Agency) deployed the first craft to accelerate itself using a sail to catch solar wind. That was on a much, much smaller scale and Project Starshot plans to use ground-based lasers rather than just solar wind, but though there are plenty of hurdles, the early research is promising.

Regardless, we know Proxima Centauri B is out there. That knowledge matters.

In 1961 Frank Drake, an astrophysicist and one of the founders of the SETI program — the search for extraterrestrial intelligence — created an equation for estimating the number of extraterrestrial civilizations with which we could someday receive communications. This is the Drake Equation:

N = R* · fp · ne · fl · fi · fc · L

“N” is the number of alien civilizations in our galaxy with which communication might be possible. The numbers that are multiplied together are all of the factors (according to Drake) that are necessary to find “N,” such as the average rate of star formation, what fraction of those stars have planets, and how many of those planets could support life, all the way down to the average length of time which civilizations could release signals into space.

We don’t have the answers to all of the factors, but we do have answers to a few. Current estimates put the total number of Earth-sized planets in the habitable zones of sun-like stars and red dwarfs in the Milky Way at about 40 billion.

Perhaps that number would seem staggeringly impossible without the knowledge that one of those planets is around the next closest star. And if we continue to find high numbers for each individual factor within the Drake Equation, it increases the likelihood that “N” is a lot bigger than you or I might think.

Sources/Additional Reading:

One Star Over, a Planet That Might Be Another EarthThe New York Times

A Family Portrait of the Alpha Centauri SystemEuropean Southern Observatory

Stephen Hawking Helps Launch Project ‘Starshot’ for Interstellar Space

Starshot – Breakthrough Initiatives

Alpha Centauri: Nearest Star System to the

Prevalence of Earth-size planets orbiting Sun-like stars – Proceedings of the National Academy of Sciences

Ikaros: First Successful Solar

Solar Sail Demonstrator (‘Sunjammer’) – NASA

Roaming the Cosmos – Haumea

Astrophysicists currently surveying the outer edges of our solar system estimate that there are thousands of dwarf planets, though only five have been researched enough to be recognized officially by the International Astronomical Union: Ceres, Pluto, Haumea, Makemake, and Eris.

Ceres is the only dwarf planet in the inner solar system. It’s a part of the asteroid belt. Indeed, about one-third of the mass in the entire asteroid belt is concentrated in Ceres. The distant Eris is the most massive of all identified dwarf planets. It’s followed closely by Pluto and right behind is Makemake.

But the strangest by far is Haumea.

Located just past Pluto – Pluto’s distance from the sun averages about 3.7 billion miles and Haumea’s average is about 4 billion miles out – Haumea’s most obvious oddity is its shape. Rather than being spherical like most planets and planetoids, Haumea is a super-elongated ellipsoid that’s almost twice as long as it is wide. And this football-shaped dwarf planet is spinning wildly. Haumea has the fastest rotational speed of any large object in the solar system. In fact, it’s spinning as fast as physically possible. If Haumea were spinning any faster, it would tear in half under its own rotational energy.

We’ve previously explored places with high rotational speed. But if you were standing on a small asteroid, it would be apparent that it was the object that you were standing on that was spinning. But on Earth you do not feel as if you are spinning, even though the Earth is rotating at 1040 miles per hour at the equator. The sun and moon appear to move. The stars pass overhead. Yet you feel as if you are stationary while the universe turns above. The feeling would be the same on Haumea, only the universe would be turning much, much faster. Haumea completes a full rotation in just under four hours.

The brightest spots in this ever-moving sky would be the distant, distant sun and Haumea’s two moons. Haumea is named for the Hawai’ian goddess of childbirth and its moons are named for her daughters Namaka and Hi’iaka. According to IAU naming requirements, classical Kuiper Belt objects (the ring of icy planetoids outside of Neptune’s orbit) are named for deities associated with creation, but the usage of Hawai’ian gods is especially appropriate, given how important Hawai’i has been in exploring the universe. The Keck and Gemini telescopes at the Mauna Kea Observatory discovered both of Haumea’s moons and determined the dwarf planet’s surface composition… its strange, strange surface composition.

The bulk of Haumea is rock, but its surface is covered in a crystalline water ice features. Seeing the stars warp as their light passes through the massive ice features would be amazing. It’s also amazing because these features shouldn’t exist.

Haumea is located so far out in the solar system that crystal ice shouldn’t be able to form. Its surface temperature is below negative 370 degrees (F). At such an extremely low temperature water freezes so fast that the molecules don’t have time to arrange into crystals, instead creating amorphous ice. In addition, due to constant bombardment from cosmic rays, any crystal ice that did form should have reverted to amorphous ice over the course of about ten million years. But based on its position in the solar system, Haumea had to have formed over a hundred million years ago.

Crystal ice can be carried from underground to the surface by cryovolcanic processes, but Haumea’s surface doesn’t have any of the compounds that are associated with cryovolcanism, such as ammonia hydrate.

So far, no plausible resurfacing mechanism has been proposed. We just don’t know. How this strange and wonderful place at the edge of our solar system came to be is a story yet to be told.

Sources/Additional Reading:

Haumea –

Haumea: The Strangest Known Object in the Kupier Belt – California Institute of Technology

Dwarf Planet Named After Hawai’ian GoddessHawai’i Magazine

Haumea: Dwarf Planet and Hawai’ian Goddess – Love Big Island

From Hawaii’s Mauna Kea, a Universe of DiscoveriesThe New York Times

The Youthful Appearance of the 2003 EL61 Collisional FamilyThe Astronomical Journal

Strange Dwarf Planet Has Red Spot –

Roaming the Cosmos – Uhlanga Regio, Triton

It’s currently late summer in the southern hemisphere of Triton, and it will be for a while. Seasons on Triton, Neptune’s largest moon, last over 40 years, with each pole spending 80 years in sunlight followed by 80 years of darkness.

So where is the best place to spend a (very, very, very) extended summer vacation on Triton?

We suggest Uhlanga, the southern polar region of Triton, named after the marsh from which humanity was born in Zulu mythology. There you will find marvels worthy of any creation myth.

Bring your sunglasses. The icy surface of Triton reflects over 70 percent of the sunlight that hits it. You’ll walk through jutting uplifts of sparkling crystal scattering the light of a seemingly endless day.

But the true wonder is the geysers. Triton is one of only four bodies in the solar system with volcanic activity and it is by far the coldest. Constantly active geysers eject material that snap-freezes in the cold sky and scatters it as glistening nitrogen snow.

This is not a soft settling of snow either. The winds on Triton nearly reach the speed of sound. Thankfully, it’s unlikely to knock you over, as Earth’s atmosphere is 50,000 times more dense than Triton’s.

All of this outgassing creates a constant haze in the summer, extending up to 30 kilometers from the surface. It’s composed largely of hydrocarbons and nitriles created by a methane reaction with both solar and stellar ultraviolet light. The sky is also patched with clouds in the form of nitrogen ice particles. But even through the haze the great blue planet Neptune dominates the sky. Triton is about the same distance from Neptune as Luna is from Earth, but Neptune is 17 times the mass of Earth.

The icy geysers are not the only thing that makes Triton strange place. Its orbit around Neptune is in reverse.

This is unique. Triton is the only large moon in the solar system (and, thus, the only one we know about) that’s in a retrograde orbit. Some outer, irregular satellites of Jupiter, Saturn, and Uranus travel in retrograde, but they’re mostly oddly-shaped, smaller rocks. The absolute largest of them, Phoebe (a pock-marked asteroid revolving around Saturn), has 0.03 percent of the mass of Triton. The other objects in retrograde also tend to be on highly-irregular orbits, but Triton’s orbit around Neptune is a nearly perfect circle, with an eccentricity of almost zero.

This unusual arrangement suggests that Triton was once a dwarf planet, much like Pluto, that was then pulled from the Kupier belt by Neptune’s gravity and captured as a moon.

Pluto, however, will not join Triton. Because Pluto’s orbit occasionally passes within Neptune’s orbit (from 1979 to 1999 Pluto was closer to the Sun than Neptune), many people have wondered if the former member of the Nine will ever become a moon like Triton. But Pluto’s orbit takes it 17 degrees above and below the plane Neptune orbits on and the two never get within 100 million kilometers of each other.

Triton’s capture must have been a chaotic event, and it’s probably why Neptune has so few moons. Jupiter has 67 moons, Saturn has 62, Uranus 27, and Neptune only has 14… and most of those are small. For example, Uranus has four moons with a diameter of greater than 1000 kilometers (Ariel, Oberon, Titania, and Umbriel). Excluding Triton itself, Neptune has none that are even 500 kilometers in diameter.

It’s likely that Neptune was once like the other giants in our solar system, with its own suite of large moons. Then Triton came swinging around Neptune, knocking other moons out of orbit as its oceans of liquid water sloshed around the dwarf planet. It is likely that Triton at one point had liquid water because its post-capture eccentricity probably resulted in severe tidal heating. It could have remained fluid for billions of years as it slowly refroze and drifted into its quiet, nearly-perfect retrograde orbit.

It’s a reminder that the apparent serenity we see now in the solar system is because we’re only seeing a snapshot, a tiny piece of processes that occur on a cosmic scale.

All of our solar system’s planets, and moons – yes, even us – are survivors of this chaos arranged in strange and beautiful fashion, like a backward-orbiting-former-dwarf-planet-moon blasting sun-glowing nitrogen crystals into speed-of-sound-40-year-summer winds.

Sources/Additional Reading:

Triton: In DepthNASA

Seasons Discovered on Neptune’s Moon

MIT researcher finds evidence of global warming on Neptune’s largest moonMIT News

The Atmosphere of TritonWindows to the Universe

Dynamics of Triton’s AtmosphereNature

Captive worlds: Is Neptune’s moon Triton a kidnapped Pluto?

Will Pluto Ever Hit Neptune?

The coupled orbital and thermal evolution of TritonGeophysical Research Letters

Photograph No. 1: Triton’s southern polar region, Voyager 2 spacecraft, Aug. 25, 1989; Photograph No. 2: Neptune (top) and Triton, Voyager 2 spacecraft, Aug. 28, 1989

Roaming the Cosmos – Verona Rupes, Miranda

[Update: Recent images of Charon, a moon of Pluto, from the New Horizons mission indicate that Charon may be home to the tallest cliff in the solar system. See: A ‘Super Grand Canyon’ on Pluto’s Moon Charon]

In the woods near my childhood home there was a cliff. I suppose it is more accurate to say there is a cliff — cliffs don’t move much on a scale of decades — but ‘was’ seems more appropriate because the actual size of the cliff does not represent the size that existed in my young mind. The fear of standing near the edge prevented any reasonable calculation of height.

But I could count. I could throw a rock and listen for how long it took for the ‘crack‘ sound to echo up from the canyon below. Being able to count out whole numbers before hearing the rock strike was almost as frightening as looking over the edge. Almost.

Despite what I may have imagined as a child, that cliff in the woods near home is not, in fact, the tallest cliff in the world. The greatest purely vertical drop is the 1.25 kilometer cliff on the side of Mount Thor in Canada. The greatest nearly vertical drop is a 1.34 km fall from the Trago Towers, a group of rock towers in the self-governing Pakistani territory of Gilgit-Baltistan. A fall from either would take approximately twenty seconds.

Not only is that an excruciatingly long time to fall, it is more than enough time to reach the human body’s terminal velocity in Earth atmosphere of 200 kph. [This depends, of course, on your preferred method of falling. A speed of 200 kph assumes a horizontal alignment. If you go nose-first, you can probably get it up to about 320 kph, assuming you have a particularly compelling reason to hit the Earth face-first at bullet-train speed.]

Neither Thor nor the Trago Towers come close to being the tallest cliff in the Solar System. The tallest is the Verona Rupes on Miranda, a moon of Uranus. If you were to look down from the sudden, shear edge of the rupes (Latin for “cliff”), you’d see a vertigo-inducing ten-kilometer drop.

Just why there is this giant cliff on Miranda is still studied and debated. It shouldn’t be there, given that Miranda is one of the smallest objects in the Solar System to be spherical under its own gravity. Yet Miranda is covered in mountains and cliffs. Perhaps it’s the result of crust rifting or cryovolcanic eruptions of icy magma. Or perhaps there was a single, massive collision with another moon, tearing Miranda asunder before reassembling into its current shape.

Whatever process created the massive mountain, a jump from the cliff’s edge would take a long, long time to complete. Thanks both to the distance and Miranda’s very, very low gravity, the fall would take a full eight minutes. Partially this is because of how slow the fall would be at the beginning.

Gravitational acceleration on Miranda is 0.079 meters per second squared. If you dove out from the cliff, it would appear momentarily as if you were hovering, floating still with the great cyan orb of Uranus above. The Sun would look like the star that it is – a bright star, certainly, but just a star. If you looked hard enough you could probably pick out Uranus’s other four large moons: Ariel, Umbriel, Titania, and Oberon.

Then the fall would start.

Slow at first. It would take about twelve or thirteen seconds just to get to the lazy pace of one meter per second. But with no air resistance to speak of, you’d just keep getting faster and faster, and ten kilometers is a long way to go. Faster and faster. By the time you’re near the ground, you’d be traveling at over 144 km per hour (90 mph).

Survival is possible. After all, 144 kph is fast, but not as fast as you’d be traveling during the much shorter fall from Mount Thor. All that’s needed is something that could cushion a 90 mph impact. A parachute wouldn’t help, as there’s no atmosphere to catch with it. A large, quick-inflating airbag might suffice. Or some kind of retrorocket boots, like an Iron Man-type thing.

Get creative.

Sources/Additional Reading

Jumping the Tallest Cliff in the Solar System – NASA

Terminal Velocity – NASA

Voyager, Uranus Images – NASA

Photojournal: Miranda High Resolution of Large Fault – NASA

Radii, shapes, and topography of the satellites of Uranus from limb coordinatesIcarus

Photograph No. 1: Miranda from Voyager 2 spacecraft, Jan. 24, 1986; Photograph No. 2: Verona Rupes from above, Voyager 2 spacecraft, Jan. 24, 1986

Roaming the Cosmos – Xanadu, Titan

Titan is appropriately named.

The great ringed gas giant Saturn has sixty-two moons. But ninety-six percent of the mass of those moons is found in one object: Titan.

At 5,150 km across, it’s diameter is greater than the planet Mercury. It is three-quarters the size of Mars and fifty percent larger than Earth’s moon, Luna.

Titan is the only place in the solar system – apart from Earth – where you’ll find liquid on the surface and it is the only known natural satellite with a thick atmosphere. In fact, the atmosphere is so dense and extends so far from the moon’s surface that its opaque clouds caused astronomers for many, many years to mistakenly call Titan the largest moon in the solar system. (Take away Titan’s shroud and Ganymede, a moon of Jupiter, has a diameter that is two percent greater).

The massive moon is unlike any place in the solar system. It’s worth a visit. But before you land on Titan, be sure to spend some time in the clouds.

Hovering above Titan, you may be surprised by the sky that surrounds you. Though it appears a near uniform yellow from above, the scattering of light in the atmosphere makes it appear an Earthly blue while you’re in the clouds themselves.

You’ll also want to spend some time up there before your descent so you can get a good look at Saturn.

Saturn will be huge in the sky above. From Titan you can see at the swirling, golden storms that race around the planet at speeds as high as 1,800 km/hr. It’s famous rings will appear as a wire-thin white line bisecting the great planet because Titan orbits edge-on with Saturn’s rings, as do most of the moons.

Once you’ve had your fill of Saturn, it’s time to descend into the yellow swirling clouds below, cutting through layer after layer of titian sky (titian as in the color, not the moon Titan (no, seriously, titian is a color (it’s a golden-orange-brown (no, it’s not called that because of Titan (it is a complete coincidence that Titan is titian in color (titian comes from the English name of Tiziano Vecelli, a sixteenth-century Italian painter (women in his paintings commonly have bright brownish orange hair))))))).

As the surface becomes visible through the fog, you’ll see dark streaks across the land. Much a Titan is desert, rolling black dunes of windblown ice crystals and ammonia, as well as hydrocarbons carried from the atmosphere to the surface by rain. But the dunes are not our destination. We are headed for Xanadu.

In the Xanadu region, an Australia-sized uplift, you’ll find river networks, hills, valleys, and the occasional large crater caused by an asteroid large enough to penetrate the thick atmosphere. Mountains are relatively small on most of Titan, but in Xanadu they’re as big as the Appalachians, most likely due to tectonism (shifting plates) and cryovolcanic (ice volcano) processes.

When you land, you’ll find the surface beneath your feet to be soft, almost like mud (quite a shift from the hard surfaces we’ve visited so far). But the mud is not created by water…

…or, rather, there is water, but the water isn’t the wet part. As it were. The surface temperature on Titan is 290 degrees below 0 F. That’s cold enough to make ice as hard as rock. And, indeed, the “rock” part of the mud is ice. The “wet” part is methane. CH4, more commonly known as natural gas. On Titan, natural gas is a liquid… and there is a lot of it. Lakes and rivers of it.

As you look about in the orange twilight glow created by the clouds, you’ll see a scattering of rocks and boulders on the muddy ground. These ice rocks are smooth and sit in depressions, like river rocks on Earth. That’s because they are river rocks.

Much like a desert on Earth, Titan has brief and intense wet seasons. Methane falls from the cold sky as rain, creating huge rushing rivers. Due to Titan’s low gravity, waves in the lakes and rivers would be seven times taller than waves on Earth. But they also move three times slower.

This sounds like ideal surfing conditions, but the low surface tension and relative low density of liquid methane might make the attempt… difficult. You can take a shot if you’re up for it, but we recommend instead trying something that you can’t do on Earth: fly.

Not hang-gliding, not a wing suit drop, we mean actual, human flight. The atmosphere on Titan is so thick and the gravity is so low that humans with properly designed wings strapped to their arms could get off the ground just by flapping. It takes some practice. And it carries a lot of risks. So if you’re feeling particularly adventurous, know what you’re getting into and ensure you’re properly equipped.

Speaking of equipment, night vision goggles are a must. Not only will the ability to see in infrared give you a clearer view of surface features, you’ll also be able to see a curious phenomenon only available on Titan.

It rains on Titan and where there’s rain, there are rainbows. Aside from Earth, Titan is the only other known place where rainbows can form. Due to the lack of direct sunlight, visible rainbows are rare, but infrared rainbows are very common. Since the rainbows are caused by methane and not water, the primary radius of each arc would be 49 degrees, as opposed to 42.5 (the index of refraction of liquid methane is 1.29, as opposed to 1.33 for water).

On Titan you get big rainbows. Or, rather, rather, methanebows.

They are quite beautiful. I’m actually composing a song about them.

Somewhere over the methanebow, way up high
There’s a land that I heard of once in a lullaby
Somewhere over the methanebow, skies are yellow
And the dreams that you dare to dream really do come true…o

It’s a work in progress.

Sources/Additional Reading:

Titan: Facts About Saturn’s Largest

Cassini Reveals Titan’s Xanadu Region To Be An Earth-Like LandScience Daily

Rainbows on Titan – NASA

Titan’s Surface Revealed – NASA

Sizes, shapes, and derived properties of the saturnian satellites after the Cassini nominal mission – P.C. Thomas, Cornell University

Photograph No. 1: Cassini spacecraft on May 21, 2011, at a distance of approximately 1.4 million miles (2.3 million kilometers) from Titan – Photograph No. 2: Cassini spacecraft on March 31, 2005, at a distance of approximately 5,900 miles (9,500 kilometers) – Photograph No. 3: Image of Titan’s surface taken by the Huygens probe on January 14, 2005, at a distance of approximately… well, you know… ZERO miles (zero kilometers)

Roaming the Cosmos – The Caves of 87 Sylvia, Asteroid Belt

Hidden among millions of massive objects in the Asteroid Belt is a rare astronomical gem: an asteroid with two moons of its own.

Asteroid 87 Sylvia, named for the Roman mythical mother of twins Remus and Romulus, is an oblong rock averaging 286 kilometers in diameter. It’s twin moons are, of course, named Remus and Romulus.

Sylvia is an exceptionally low density asteroid. At least a quarter and probably more than half of its interior is empty space. At about 385 kilometers from tip to tip, there are plenty of weaving catacombs through 87 Sylvia to explore. Thanks to the light gravity of the asteroid, the caves can be traversed quite easily with huge leaps and bounds.

Though you can jump tremendous distances, you don’t have to worry about accidentally launching yourself into space. With an escape velocity of 138 meters a second, your giant leaps will carry you far, but will always bring you back to the surface. (Though… how gently depends largely on the nature of your leap. Please be cautious and utilize proper safety equipment for any bouncing space spelunking.)

Now that you know where to go, we can address the question of when.

Thanks to its twin moons, you can end your leaping cave exploration by finding a spot on the asteroid’s porous surface to watch a spectacular double (double!) eclipse.

A “double eclipse” sounds like it would be a rarity, but not on 87 Sylvia. Due to the asteroid’s relatively high rotation speed, a double eclipse is a surprisingly frequent occurrence. 87 Sylvia completes a rotation about once every five hours, Remus orbits its parent asteroid about once every day-and-a-half, and Romulus orbits 87 Sylvia about once every three-and-a-half days.

So, about once every three (Earth) years, Remus and Romulus come together in alignment between 87 Sylvia and the Sun. Each moon makes a nearly perfect eclipse of the other, as they each would look like they’re the same size from the surface (the farther one, Romulus, being larger than the inner moon, Remus).

This is not like a terrestrial eclipse. Romulus and Remus are relatively small (about 14 and 7 km in diameter, respectively), but they’re so close that they’ll appear to be huge to you, about twice as big as the Moon appears from Earth. The Sun, meanwhile, looks much, much smaller so far out.

Remus and Romulus totally devour the Sun in an eclipse. And with the light of the Sun converted into a soft halo around apparently massive twin spheres, the full sky is visible.

You won’t see other asteroids. Despite popular imaginings of the Asteroid Belt, most asteroids are so far from each other that no other asteroids are visible from each other’s surfaces. In fact, a third of the mass of the Belt is in one object, the dwarf planet Ceres.

But you’ll see so, so many stars. You have to travel great distances on Earth and wait a very long time to see all the stars above and below the poles. The fast rotation of 87 Sylvia means you only have to wait a few hours to see every star in the sky. With no sun and no atmosphere, the double eclipse on 87 Sylvia gives you the clearest star-filled sky in the inner solar system.

Well, except for one very big object.

87 Sylvia is part of the Cybele Group, on the outer edges of the Belt, which means if it’s nearby in its orbit, Jupiter would dominate the sky. When they’re on the same side of the solar system, Jupiter is almost three times closer to 87 Syliva than it is to Earth. You should even be able to make out Jupiter’s biggest moons with just the naked eye.

While sitting in your viewing spot, if you reached down to pick up a rock or part of asteroid, it would likely crumble away. 87 Sylvia is dark, ancient rubble pile of the primordial pieces of the Solar System’s creation held together by the collective gravity of those rocks.

The Asteroid Belt is a strange place, and a window into its star system’s early days.

As the giant planets moved all about – and Jupiter causing the most damage – over 99 percent of the Asteroid Belt’s original mass was lost in the first 100 million years of the Solar System’s history.

It was a chaotic time. At one point there were two large, rocky planets passing around the Sun at the same distance. (They eventually ran into each other and created the Earth and the Moon.) Other planets fell into the Sun or were ripped free. No doubt there are entire planets from the early days of our Solar System out wandering between the stars, unknown lost worlds flung from the Sun’s gravity.

Eventually it all stabilized. Relatively speaking, of course. Though it appears stable, the Solar System is constantly changing. 87 Sylvia likely got its moons in a collision with another asteroid.

The truth is the chaos never stopped. The Solar System is so old, so massive, so complex, that we are only experiencing a moment of apparent stability. The Asteroid Belt is a reminder of that. Every time Jupiter passes by it stirs up the rocks.

Eventually all of this apparent order will scatter. But for now, as in every moment of a solar system’s evolution, there are perfectly balanced wonders to find.

Like an asteroid with two moons.

Sources/Additional Reading:

Asteroid Diversity Points to a “Snow Globe” Solar System – Harvard-Smithsonian Center for Astrophysics

Asteroid Belt Between Mars And Jupiter Is A ‘Melting Pot’ Of Diverse Celestial ObjectsInternational Business Times

Asteroids, Meteorites, and Comets by Linda T. Elkins-Tanton

Could You Walk on the Surface of a Comet?WIRED

First Asteroid Trio Discovered –