Sciency Words is a special series here on Planet Pailly celebrating the rich and colorful world of science and science-related terminology. Today, we’re looking at the term:
KIRKWOOD GAPS
Some of the asteroids in the asteroid belt have gone missing.
The asteroid belt begins at a distance of 2.1 AU (astronomical units) from the Sun and stretches all the way out to 3.5 AU from the Sun. But there are empty regions at approximately 2.5 AU, 2.8 AU, 3 AU, and 3.3 AU. These empty regions are called Kirkwood gaps.
Kirkwood gaps are named after Daniel Kirkwood, the astronomer who first discovered them and correctly deduced what caused them.
Any asteroid orbiting the Sun at a distance of 2.5 AU would happen to be in a 3:1 orbital resonance with the planet Jupiter. This means Jupiter would complete exactly one orbit for every three orbits the asteroid completed. The 2.8, 3, and 3.3 AU distances happen to correspond to other orbital resonances with Jupiter.
Asteroids in these resonant orbits would experience nagging, persistent gravitational tugs by the Solar System’s largest planet. This would slowly drag them away from their original circular paths around the Sun and throw them into new, highly eccentric orbits.
Many of the asteroids that cross Earth’s orbital path are probably former residents of the Kirkwood gaps. So the next time an asteroid comes along and wipes out the dinosaurs, don’t get mad at the asteroid. It might not be the asteroid’s fault.
Exact figures for the number of asteroids in the asteroid belt vary widely, but astronomers generally agree there are millions of objects of at least one kilometer in diameter. That sounds like a lot, but it turns out the asteroid belt is a fairly empty and lonely place.
The average distance between main belt asteroids is just shy of 1,000,000 kilometers (600,000 miles). For comparison, the distance between the Earth and Moon is a little less than 400,000 kilometers (240,000 miles).
But for hotshot space pilots like myself, there are still some opportunities to zigzag between and around dangerously close asteroids, perhaps while being pursued by hordes of Imperial TIE Fighters.
Over a hundred asteroids are known to have at least one tiny moon. Binary and trinary asteroids have also been discovered. Those are pairs or trios, respectively, of asteroids of roughly equal mass that are locked into orbit around their common center of gravity.
And of course when asteroids collide, they often form debris fields. This debris can linger for weeks before recombining as a rubble pile asteroid. Maybe these chaotic post-collision debris fields are just the perfect place to try evading the forces of the Evil Empire. Assuming you can find one.
Sciency Words is a special series here on Planet Pailly celebrating the rich and colorful world of science and science-related terminology. Today, we’re looking at the term:
RUBBLE PILE
“Rubble pile” is not a formal part of any asteroid classification system, but it appears so often in scientific literature about asteroids that it deserves special attention. A rubble pile asteroid is really multiple asteroids tenuously held together by their own gravity.
Rubble piles probably form in the aftermath of asteroid collisions. When two asteroids smash into each other, gravity starts pulling the resulting debris back together again. A rubble pile can then form in as little as a few hours.
Since they’re not single, solid objects but conglomerations of multiple objects, rubble piles tend to have empty spaces inside them. This lowers the overall density of the asteroid, which helps astronomers distinguish rubble piles from regular “monolithic” asteroids.
Rubble piles have a minimum rotation period of approximately two hours. If they start spinning faster than that, they’re liable to fling themselves apart. However, astronomers have observed some rubble piles rotating faster than they should be able to, suggesting that additional forces besides gravity may help hold them together.
Exerting even a tiny force on a rubble pile could cause the thing to break apart. You can’t easily land on a rubble pile’s surface for mining purposes, and deflecting a rubble pile from a collision course with Earth would be tricky. As a result, rubble piles could pose many challenges to humanity in the future.
Let’s talk about a certain dwarf planet. No, not Pluto. We’ll save that for Pluto month. Right now, we’re talking about Ceres.
Totally legit Hubble image of Ceres with Pluto visible in the background.
Someday, perhaps someday soon, humanity will start spreading across the Solar System. When we do, the dwarf planet Ceres could become an important part of our interplanetary infrastructure.
Ceres has been in the news a lot lately (almost as much as Pluto). During a recent visit by the Dawn spacecraft, we discovered some surprising features:
A single, lonely mountain in the midst of an otherwise flat landscape.
An unidentified white substance (water ice?) in the basins of several craters.
Plumes of water vapor escaping into space, hinting at possible subsurface oceans.
Even if Ceres doesn’t have vast oceans of liquid water beneath its surface, evidence suggests it at least has plenty of water ice. Water in any form is an incredibly valuable resource for space travelers, and not only for the obvious reasons.
Water can be used for:
Drinking (obviously).
Washing (obviously).
Oxygen: through electrolysis, water can be separated into oxygen and hydrogen, providing a spaceship’s crew with breathable air.
Rocket fuel: hydrogen and oxygen, cryogenically stored in liquid forms, make excellent rocket fuel.
Radiation shielding: water is surprisingly good at blocking solar and cosmic radiation. Well positioned water tanks on a spaceship’s exterior could do a lot to protect the crew.
A colony (or at least an outpost) on Ceres could serve as a convenient refueling depot for spacecraft heading out beyond the asteroid belt or for valiant explorers returning to the inner Solar System. A watering hole in space, if you will.
At the very least, it could make a fun setting for a Sci-Fi story.
Welcome to Molecular Mondays! Every other Monday, we examine the atoms and molecules that serve as the building blocks of our universe, both in reality and in science fiction.
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Humans need water. Our spaceships, however, may need it more than we do.
Human space exploration will never succeed if we have to carry everything we need from Earth. Instead, we have to learn to exploit the material resources space provides.
The Electrolysis of Water
Electrolysis is the process of using electricity to trigger a chemical reaction. Stick a pair of electrodes in water and turn on the power. This will break the chemical bonds holding water molecules (H2O) together.
Hydrogen will then accumulate around the negatively charged electrode. Oxygen will gather around the positive electrode.
Hydrogen, the Ultimate Rocket Fuel
Hydrogen makes the best rocket fuel (in more technical lingo, hydrogen has the highest specific impulse of any known substance). All you need is an oxidizer for the hydrogen to react with… and oh look, you’ve got plenty of oxygen! Just put the two back together in a reaction chamber, and you’re good to go.
Ideally, you’ll want to store your hydrogen and oxygen fuel in liquid form, which means you’ll need a lot of refrigeration equipment to keep them both below their boiling temperatures (roughly 20 Kelvin for hydrogen and 90 Kelvin for oxygen).
Asteroid Hopping
Of course, you’ll have some trouble finding water in space. If you’re planning an extended voyage through the Solar System, plot a course that will take you near some asteroids, specifically carbonaceous asteroids. They tend to contain relatively large amounts of water in the form of ice.
So long as you can find a few places to refuel your spacecraft, and so long as you bring the appropriate equipment along with you, you should be free to travel wherever you like.
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Today’s post is part of asteroid belt month for the 2015 Mission to the Solar System. Click here for more about this series.
Sciency Words is a special series here on Planet Pailly celebrating the rich and colorful world of science and science-related terminology. Today, we’re looking at the term:
M-TYPE ASTEROIDS
Previously on Sciency Words, we examined carbonaceous (C-type) and siliceous (S-type) asteroids, the most common and second most common asteroid types, respectively. We now come to the third most common type. Unfortunately, this is where nomenclature gets complicated.
Astronomers currently use at least two different systems to identify and categorize asteroids: the Tholen classification system and the SMASS classification system. The two systems overlap in some ways and diverge in others. What Tholen calls an M-type asteroid is, in SMASS, mixed into a broader category called the X-group.
I’d guess that eventually one of these classification systems will “win.” Either that or a new system will replace them both, simplifying matters. In the meantime, an M-type asteroid by any other name would smell as sweet.
Characteristics of M-Type Asteroids
The M in M-type stands for metallic. It’s unlikely that an asteroid of pure (or nearly pure) metal could form by itself. Therefore, M-type asteroids are assumed to be the metal cores of larger asteroids or maybe even dwarf planets that, for one reason or another, broke apart.
Most M-types seem to be composites of iron and nickel with traces of other metals—including precious metals like rare earths and platinum group metals. You can expect to find these valuable metals in much higher quantities than you would on Earth.
A typical M-type asteroid could be worth billions upon billions of dollars.
If someone were to capture one of these asteroids and safely bring it back to Earth, that someone would become extremely rich.
Or maybe not…
The Problems with Asteroid Mining
Before you hop into your personal spacecraft and fly out to the asteroid belt hunting for M-types, a few notes of caution:
There’s no way to know the exact composition of an M-type asteroid based solely on observations from Earth. There’s no guarantee that you’ll find substantial amounts of valuable metals.
M-type asteroids can have wildly different orbits from each other, making some much harder to reach than others. Fuel costs will stack up rapidly, seriously cutting into your profits.
M-types are basically solid lumps of metal. You’ll need more than a pickaxe or jackhammer to crack them open. The difficulties associated with mining operations will also seriously cut into your profits.
And yet it’s hard to resist the lure of M-type asteroids. Businesses in existence today (not some far-off Sci-Fi tomorrow) are greedily eyeing M-types, trying to figure out how to go get one. That may soon become a driving force in human space exploration. Or the hunt for M-type asteroids could turn into a huge economic bust.
Just something science fiction writers might want to think about.
Book Recommendation
Asteroid Mining 101: Wealth for the New Space Economy by John S. Lewis. There are plenty of books and articles out there about asteroid mining, but this one takes a serious look at both the pros and cons of the idea. If this is a subject that interests you, Asteroid Mining 101 offers a well-balanced view of the future of the asteroid mining industry.
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Today’s post is part of asteroid belt month for the 2015 Mission to the Solar System. Click here for more about this series.
In 2006, the I.A.U. officially demoted Pluto from planet to dwarf planet. At this point, pretty much everyone knows that, and most people seem to have strong opinions on the matter (especially right now, as New Horizons sends back the first ever detailed images of Pluto). However, Pluto was not the first planet to be demoted. That particular dishonor goes to Ceres.
Discovered on New Year’s Day, 1801, Ceres was initially identified as the long sought missing planet between the orbits of Jupiter and Mars, making it the second planet discovered in modern times (Uranus was discovered about twenty years prior).
A few months later, however, astronomers discovered another object (named Pallas) sharing Ceres’s orbit. Within a few years, they found another (Juno) and another (Vesta). This started getting awkward. How could we have so many planets in the same (or nearly the same) orbit?
And so Ceres went from being the fifth planet to the first known asteroid.
What happened to Pluto is almost the exact same story. When Pluto was discovered, we had no way to know that it was one of a great many trans-Neptunian objects. Once we realized our mistake, Pluto had to be reclassified.
On the upside, the creation of a new category of celestial object allowed us to promote Ceres from asteroid to dwarf planet. So Pluto’s loss was Ceres’s gain.
But what do you think? Do you agree with the I.A.U.’s decision, or do you think Pluto and Ceres should have retained their planethood?
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Today’s post is part of asteroid belt month for the 2015 Mission to the Solar System. Click here for more about this series.
Sciency Words is a special series here on Planet Pailly celebrating the rich and colorful world of science and science-related terminology. Today, we’re looking at the term:
SILICEOUS ASTEROIDS
It’s a tale of two asteroids, one in the inner asteroid belt, the other in the outer region.
Both asteroids started off much the same but wound up quite different. The inner belt asteroid, being closer to the Sun, got blasted by the solar wind, losing many of its lighter materials: water, organic compounds, other volatiles…
The outer belt asteroid, being farther away from the Sun, still feels the solar wind’s effects, but less so.
And so one asteroid becomes a carbonaceous asteroid, retaining many of the lightweight materials that are so appealing to life and perhaps some day asteroid mining corporations. The other became a siliceous asteroid.
Siliceous asteroids, also known as S-type asteroids or sometimes stony asteroids, are basically great big rocks. They’re composed of a mixture of silicon with additional metals and/or minerals. Astronomers estimate 15-20% of asteroids in the Solar System are siliceous, and most reside (not surprisingly) in the inner asteroid belt.
If you’ve seen Star Wars: The Empire Strikes Back, you should have some idea what siliceous asteroids look like. They’re a lighter color than their carbonaceous cousins, making them a bit easier to spot against the dark backdrop of space. They also tend to be reddish brown or sometimes greenish brown, depending on which combinations of metals and minerals they contain.
However, since they’re depleted of water, carbon, and such, it’s unlikely siliceous asteroids could host large populations of mynocks, as seen in Star Wars. They’re also not the most exciting prospects for future asteroid mining operations. Not when there are far more valuable M-type asteroids out there, which will be the subject of next week’s edition of Sciency Words.
Welcome to Molecular Mondays! Every other Monday, we examine the atoms and molecules that serve as the building blocks of our universe, both in reality and in science fiction. Today, we turn our attention to:
THE PLATINUM GROUP METALS
Not all atoms are created equal. Some have super powers.
Pictured above are the platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and of course platinum. All six can be found clustered together on the periodic table of the elements.
Why are the platinum group metals (or P.G.M.s) so special? Here are some of the reasons:
P.G.M.s have excellent catalytic properties, making them an important component in catalytic converters.
P.G.M.s also have excellent electrical properties, which we take advantage of in nearly all modern electronics.
Most of the P.G.M.s are highly resistant to oxidation, even at high temperatures, making them useful for all sorts of industrial applications.
P.G.M.s and P.G.M. alloys make great jewelry because they don’t tarnish easily.
Inconveniently, most of the platinum group metals on Earth sank into the planet’s core while the planet was still forming. The small quantities we have access to, which were for the most part seeded by meteor impacts after Earth’s crust had solidified, can be hard to find and difficult to extract.
How difficult? So difficult that some business people say it would be easier to go into space and try to mine this stuff from asteroids.
No seriously, there are actual businesses that want to do that. Some are already taking the first preliminary steps to figure out how. It’s one of the reasons the American space program became suddenly interested in asteroid capture missions a few years back.
On today’s market, one troy ounce of a platinum group metal (take your pick; this is true for all of them) can cost hundreds or even thousands of dollars. Our increasingly high-tech society depends upon this stuff, and sooner or later we will run out of places to find it here on Earth.
Maybe… just maybe… the search for platinum group metals will be enough to motivate investing serious money in space exploration. Just something futurists and Sci-Fi writers may want to think about.
Sciency Words is a special series here on Planet Pailly celebrating the rich and colorful world of science and science-related terminology. Today, we’re looking at the term:
CARBONACEOUS ASTEROIDS
As the name implies, carbonaceous asteroids (or C-type asteroids) have lots of carbon and carbon-containing compounds. Around 75% of the asteroids in the Solar System are believed to be carbonaceous, with most located in the outer asteroid belt. They’re dark in color, sort of like giant lumps of coal, which makes them difficult to find against the inky blackness of space.
But perhaps the most interesting thing about carbonaceous asteroids is that they can support life.
Bear with me a moment. Some scientists think life in our Solar System may not have originated on Earth or Mars or any planet. Instead, life may have begun on carbonaceous asteroids.
These asteroids contain many of the carbon-based molecules (including amino acids) necessary for life. They also generally have water ice, and at least when the Solar System was young, they would have retained plenty of heat.
And yet, the idea of life evolving and thriving on an asteroid is a bit of a stretch. Carbonaceous chondrite meteorites (fragments of carbonaceous asteroids that fell to Earth) show no signs of past or present biological activity. As a point of comparison, some meteorites originating from Mars offer at least circumstantial evidence of Martian life.
However, carbonaceous asteroids could become useful to life in the future. Space faring civilizations may want to harvest these asteroids for their resources, especially water, which could be used either for drinking or, if separated into hydrogen and oxygen, as rocket fuel. One large carbonaceous asteroid could keep a spaceship and its crew going for a long, long time.
At the very least, carbonaceous asteroids could provide valuable fuel for the imagination of a science fiction writer. What might happen if, while mining carbonaceous asteroids for their resources, we discovered that they do support life after all?
The asteroid belt begins at a distance of 2.1 AU (astronomical units) from the Sun and stretches all the way out to 3.5 AU from the Sun. But there are empty regions at approximately 2.5 AU, 2.8 AU, 3 AU, and 3.3 AU. These empty regions are called Kirkwood gaps.
