Children ice skating in Khakassia, Russia react to the fall of a bright fireball two nights ago on Dec.6
In 1908 it was Tunguska event, a meteorite exploded in mid-air, flattening 770 square miles of forest. 39 years later in 1947, 70 tons of iron meteorites pummeled the Sikhote-Alin Mountains, leaving more than 30 craters. Then a day before Valentine’s Day in 2013, hundreds of dashcams recorded the fiery and explosive entry of the Chelyabinsk meteoroid, which created a shock wave strong enough to blow out thousands of glass windows and litter the snowy fields and lakes with countless fusion-crusted space rocks.
Documentary footage from 1947 of the Sikhote-Alin fall and how a team of scientists trekked into the wilderness to find the craters and meteorite fragments
Now on Dec. 6, another fireball blazed across Siberian skies, briefly illuminated the land like a sunny day before breaking apart with a boom over the town of Sayanogorsk. Given its brilliance and the explosions heard, there’s a fair chance that meteorites may have landed on the ground. Hopefully, a team will attempt a search soon. As long as it doesn’t snow too soon after a fall, black stones and the holes they make in snow are relatively easy to spot.
This photo shows trees felled from a powerful aerial meteorite explosion. It was taken during Leonid Kulik’s 1929 expedition to the Tunguska impact event in Siberia in 1908. Credit: Kulik Expedition
OK, maybe Siberia doesn’t get ALL the cool fireballs and meteorites, but it’s done well in the past century or so. Given the dimensions of the region — it covers 10% of the Earth’s surface and 57% of Russia — I suppose it’s inevitable that over so vast an area, regular fireball sightings and occasional monster meteorite falls would be the norm. For comparison, the United States covers only 1.9% of the Earth. So there’s at least a partial answer. Siberia’s just big.
A naturally sculpted iron-nickel meteorite recovered from the Sikhote-Alin meteorite fall in February 1947. The dimpling or “thumb-printing” occurs when softer minerals are melted and sloughed away as the meteorite is heated by the atmosphere while plunging to Earth. Credit: Svend Buhl
Every day about 100 tons of meteoroids, which are fragments of dust and gravel from comets and asteroids, enter the Earth’s atmosphere. Much of it gets singed into fine dust, but the tougher stuff — mostly rocky, asteroid material — occasionally makes it to the ground as meteorites. Every day then our planet gains about a blue whale’s weight in cosmic debris. We’re practically swimming in the stuff!
Meteors are pieces of comet and asteroid debris that strike the atmosphere and burn up in a flash. Here, a brilliant Perseid meteor streaks along the Summer Milky Way this past August. Credit: Jeremy Perez
Most of this mass is in the form of dust but a study done in 1996 and published in the Monthly Notices of the Royal Astronomical Society further broke down that number. In the 10 gram (weight of a paperclip or stick of gum) to 1 kilogram (2.2 lbs) size range, 6,400 to 16,000 lbs. (2900-7300 kilograms) of meteorites strike the Earth each year. Yet because the Earth is so vast and largely uninhabited, appearances to the contrary, only about 10 are witnessed falls later recovered by enterprising hunters.
A couple more videos of the Dec. 6, 2016 fireball over Khakassia and Sayanogorsk, Russia
Meteorites fall in a pattern from smallest first to biggest last to form what astronomers call a strewnfield, an elongated stretch of ground several miles long shaped something like an almond. If you can identify the meteor’s ground track, the land over which it streaked, that’s where to start your search for potential meteorites.
Meteorites indeed fall everywhere and have for as long as Earth’s been rolling around the sun. So why couldn’t just one fall in my neighborhood or on the way to work? Maybe if I moved to Siberia …
Science fiction has told us again and again, we belong out there, among the stars. But before we can build that vast galactic empire, we’ve got to learn how to just survive in space. Fortunately, we happen to live in a Solar System with many worlds, large and small that we can use to become a spacefaring civilization.
This is half of an epic two-part article that I’m doing with Isaac Arthur, who runs an amazing YouTube channel all about futurism, often about the exploration and colonization of space. Make sure you subscribe to his channel.
This article is about colonizing the inner Solar System, from tiny Mercury, the smallest planet, out to Mars, the focus of so much attention by Elon Musk and SpaceX. In the other article, Isaac will talk about what it’ll take to colonize the outer Solar System, and harness its icy riches. You can read these articles in either order, just read them both.
At the time I’m writing this, humanity’s colonization efforts of the Solar System are purely on Earth. We’ve exploited every part of the planet, from the South Pole to the North, from huge continents to the smallest islands. There are few places we haven’t fully colonized yet, and we’ll get to that.
But when it comes to space, we’ve only taken the shortest, most tentative steps. There have been a few temporarily inhabited space stations, like Mir, Skylab and the Chinese Tiangong Stations.
Our first and only true colonization of space is the International Space Station, built in collaboration with NASA, ESA, the Russian Space Agency and other countries. It has been permanently inhabited since November 2nd, 2000. Needless to say, we’ve got our work cut out for us.
NASA astronaut Tracy Caldwell Dyson, an Expedition 24 flight engineer in 2010, took a moment during her space station mission to enjoy an unmatched view of home through a window in the Cupola of the International Space Station, the brilliant blue and white part of Earth glowing against the blackness of space. Credits: NASA
Before we talk about the places and ways humans could colonize the rest of the Solar System, it’s important to talk about what it takes to get from place to place.
Just to get from the surface of Earth into orbit around our planet, you need to be going about 10 km/s sideways. This is orbit, and the only way we can do it today is with rockets. Once you’ve gotten into Low Earth Orbit, or LEO, you can use more propellant to get to other worlds.
If you want to travel to Mars, you’ll need an additional 3.6 km/s in velocity to escape Earth gravity and travel to the Red Planet. If you want to go to Mercury, you’ll need another 5.5 km/s.
And if you wanted to escape the Solar System entirely, you’d need another 8.8 km/s. We’re always going to want a bigger rocket.
The most efficient way to transfer from world to world is via the Hohmann Transfer. This is where you raise your orbit and drift out until you cross paths with your destination. Then you need to slow down, somehow, to go into orbit.
One of our primary goals of exploring and colonizing the Solar System will be to gather together the resources that will make future colonization and travel easier. We need water for drinking, and to split it apart for oxygen to breathe. We can also turn this water into rocket fuel. Unfortunately, in the inner Solar System, water is a tough resource to get and will be highly valued.
We need solid ground. To build our bases, to mine our resources, to grow our food, and to protect us from the dangers of space radiation. The more gravity we can get the better, since low gravity softens our bones, weakens our muscles, and harms us in ways we don’t fully understand.
Each world and place we colonize will have advantages and disadvantages. Let’s be honest, Earth is the best place in the Solar System, it’s got everything we could ever want and need. Everywhere else is going to be brutally difficult to colonize and make self-sustaining.
We do have one huge advantage, though. Earth is still here, we can return whenever we like. The discoveries made on our home planet will continue to be useful to humanity in space through communications, and even 3D printing. Once manufacturing is sophisticated enough, a discovery made on one world could be mass produced half a solar system away with the right raw ingredients.
We will learn how to make what we need, wherever we are, and how to transport it from place to place, just like we’ve always done.
Mercury, as imaged by the MESSENGER spacecraft, revealing parts of the never seen by human eyes. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Mercury is the closest planet from the Sun, and one of the most difficult places that we might attempt the colonize. Because it’s so close to the Sun, it receives an enormous amount of energy. During the day, temperatures can reach 427 C, but without an atmosphere to trap the heat, night time temperatures dip down to -173 C. There’s essentially no atmosphere, 38% the gravity of Earth, and a single solar day on Mercury lasts 176 Earth days.
Mercury does have some advantages, though. It has an average density almost as high as Earth, but because of its smaller size, it actually means it has a higher percentage of metal than Earth. Mercury will be incredibly rich in metals and minerals that future colonists will need across the Solar System.
With the lower gravity and no atmosphere, it’ll be far easier to get that material up into orbit and into transfer trajectories to other worlds.
But with the punishing conditions on the planet, how can we live there? Although the surface of Mercury is either scorching or freezing, NASA’s MESSENGER spacecraft turned up regions of the planet which are in eternal shadow near the poles. In fact, these areas seem to have water ice, which is amazing for anywhere this close to the Sun.
Images of Mercury’s northern polar region, provided by MESSENGER. Credit: NASA/JPL
You could imagine future habitats huddled into those craters, pulling in solar power from just over the crater rim, using the reservoirs of water ice for air, fuel and water.
High powered solar robots could scour the surface of Mercury, gathering rare metals and other minerals to be sent off world. Because it’s bathed in the solar winds, Mercury will have large deposits of Helium-3, useful for future fusion reactors.
Over time, more and more of the raw materials of Mercury will find their way to the resource hungry colonies spread across the Solar System.
It also appears there are lava tubes scattered across Mercury, hollows carved out by lava flows millions of years ago. With work, these could be turned into safe, underground habitats, protected from the radiation, high temperatures and hard vacuum on the surface.
With enough engineering ability, future colonists will be able to create habitats on the surface, wherever they like, using a mushroom-shaped heat shield to protect a colony built on stilts to keep it off the sun-baked surface.
Mercury is smaller than Mars, but is a good deal denser, so it has about the same gravity, 38% of Earth’s. Now that might turn out to be just fine, but if we need more, we have the option of using centrifugal force to increase it. Space Stations can generate artificial gravity by spinning, but you can combine normal gravity with spin-gravity to create a stronger field than either would have.
So our mushroom habitat’s stalk could have an interior spinning section with higher gravity for those living inside it. You get a big mirror over it, shielding you from solar radiation and heat, you have stilts holding it off the ground, like roots, that minimize heat transfer from the warmer areas of ground outside the shield, and if you need it you have got a spinning section inside the stalk. A mushroom habitat.
Venus as photographed by the Pioneer spacecraft in 1978. Credit: NASA/JPL/Caltech
Venus is the second planet in the Solar System, and it’s the evil twin of Earth. Even though it has roughly the same size, mass and surface gravity of our planet, it’s way too close to the Sun. The thick atmosphere acts like a blanket, trapping the intense heat, pushing temperatures at the surface to 462 C.
Everywhere on the planet is 462 C, so there’s no place to go that’s cooler. The pure carbon dioxide atmosphere is 90 times thicker than Earth, which is equivalent to being a kilometer beneath the ocean on Earth.
In the beginning, colonizing the surface of Venus defies our ability. How do you survive and stay cool in a thick poisonous atmosphere, hot enough to melt lead? You get above it.
One of the most amazing qualities of Venus is that if you get into the high atmosphere, about 52.5 kilometers up, the air pressure and temperature are similar to Earth. Assuming you can get above the poisonous clouds of sulphuric acid, you could walk outside a floating colony in regular clothes, without a pressure suit. You’d need a source of breathable air, though.
Even better, breathable air is a lifting gas in the cloud tops of Venus. You could imagine a future colony, filled with breathable air, floating around Venus. Because the gravity on Venus is roughly the same as Earth, humans wouldn’t suffer any of the side effects of microgravity. In fact, it might be the only place in the entire Solar System other than Earth where we don’t need to account for low gravity.
Artist’s concept of a Venus cloud city — a possible future outcome of the High Altitude Venus Operational Concept (HAVOC) plan. Credit: Advanced Concepts Lab at NASA Langley Research Center
Now the day on Venus is incredibly long, 243 earth days, so if you stay over the same place the whole time it would be light for four months then dark for four months. Not ideal for solar power on a first glance, but Venus turns so slowly that even at the equator you could stay ahead of the sunset at a fast walk.
So if you have floating colonies it would take very little effort to stay constantly on the light side or dark side or near the twilight zone of the terminator. You are essentially living inside a blimp, so it may as well be mobile. And on the day side it would only take a few solar panels and some propellers to stay ahead. And since it is so close to the Sun, there’s plenty of solar power. What could you do with it?
The atmosphere itself would probably serve as a source of raw materials. Carbon is the basis for all life on Earth. We’ll need it for food and building materials in space. Floating factories could process the thick atmosphere of Venus, to extract carbon, oxygen, and other elements.
Heat resistant robots could be lowered down to the surface to gather minerals and then retrieved before they’re cooked to death.
Venus does have a high gravity, so launching rockets up into space back out of Venus’ gravity well will be expensive.
Over longer periods of time, future colonists might construct large solar shades to shield themselves from the scorching heat, and eventually, even start cooling the planet itself.
Earth as seen on July 6, 2015 from a distance of one million miles by a NASA scientific camera aboard the Deep Space Climate Observatory spacecraft. Credits: NASA
The next planet from the Sun is Earth, the best planet in the Solar System. One of the biggest advantages of our colonization efforts will be to get heavy industry off our planet and into space. Why pollute our atmosphere and rivers when there’s so much more space… in space.
Over time, more and more of the resource gathering will happen off world, with orbital power generation, asteroid mining, and zero gravity manufacturing. Earth’s huge gravity well means that it’s best to bring materials down to Earth, not carry them up to space.
However, the normal gravity, atmosphere and established industry of Earth will allow us to manufacture the lighter high tech goods that the rest of the Solar System will need for their own colonization efforts.
But we haven’t completely colonized Earth itself. Although we’ve spread across the land, we know very little about the deep ocean. Future colonies under the oceans will help us learn more about self-sufficient colonies, in extreme environments. The oceans on Earth will be similar to the oceans on Europa or Enceladus, and the lessons we learn here will teach us to live out there.
As we return to space, we’ll colonize the region around our planet. We’ll construct bigger orbital colonies in Low Earth Orbit, building on our lessons from the International Space Station.
One of the biggest steps we need to take, is understanding how to overcome the debilitating effects of microgravity: the softened bones, weakened muscles and more. We need to perfect techniques for generating artificial gravity where there is none.
A 1969 station concept. The station was to rotate on its central axis to produce artificial gravity. The majority of early space station concepts created artificial gravity one way or another in order to simulate a more natural or familiar environment for the health of the astronauts. Credit: NASA
The best technique we have is rotating spacecraft to generate artificial gravity. Just like we saw in 2001, and The Martian, by rotating all or a portion of a spacecraft, you can generated an outward centrifugal force that mimics the acceleration of gravity. The larger the radius of the space station, the more comfortable and natural the rotation feels.
Low Earth Orbit also keeps a space station within the Earth’s protective magnetosphere, limiting the amount of harmful radiation that future space colonists will experience.
Other orbits are useful too, including geostationary orbit, which is about 36,000 kilometers above the surface of the Earth. Here spacecraft orbit the Earth at exactly the same rate as the rotation of Earth, which means that stations appear in fixed positions above our planet, useful for communication.
Geostationary orbit is higher up in Earth’s gravity well, which means these stations will serve a low-velocity jumping off points to reach other places in the Solar System. They’re also outside the Earth’s atmospheric drag, and don’t require any orbital boosting to keep them in place.
By perfecting orbital colonies around Earth, we’ll develop technologies for surviving in deep space, anywhere in the Solar System. The same general technology will work anywhere, whether we’re in orbit around the Moon, or out past Pluto.
When the technology is advanced enough, we might learn to build space elevators to carry material and up down from Earth’s gravity well. We could also build launch loops, electromagnetic railguns that launch material into space. These launch systems would also be able to loft supplies into transfer trajectories from world to world throughout the Solar System.
Earth orbit, close to the homeworld gives us the perfect place to develop and perfect the technologies we need to become a true spacefaring civilization. Not only that, but we’ve got the Moon.
Sample collection on the surface of the Moon. Apollo 16 astronaut Charles M. Duke Jr. is shown collecting samples with the Lunar Roving Vehicle in the left background. Image: NASA
The Moon, of course, is the Earth’s only natural satellite, which orbits us at an average distance of about 400,000 kilometers. Almost ten times further than geostationary orbit.
The Moon takes a surprising amount of velocity to reach from Low Earth Orbit. It’s close, but expensive to reach, thrust speaking.
But that fact that it’s close makes the Moon an ideal place to colonize. It’s close to Earth, but it’s not Earth. It’s airless, bathed in harmful radiation and has very low gravity. It’s the place that humanity will learn to survive in the harsh environment of space.
But it still does have some resources we can exploit. The lunar regolith, the pulverized rocky surface of the Moon, can be used as concrete to make structures. Spacecraft have identified large deposits of water at the Moon’s poles, in its permanently shadowed craters. As with Mercury, these would make ideal locations for colonies.
Here, a surface exploration crew begins its investigation of a typical, small lava tunnel, to determine if it could serve as a natural shelter for the habitation modules of a Lunar Base. Credit: NASA’s Johnson Space Center
Our spacecraft have also captured images of openings to underground lava tubes on the surface of the Moon. Some of these could be gigantic, even kilometers high. You could fit massive cities inside some of these lava tubes, with room to spare.
Helium-3 from the Sun rains down on the surface of the Moon, deposited by the Sun’s solar wind, which could be mined from the surface and provide a source of fuel for lunar fusion reactors. This abundance of helium could be exported to other places in the Solar System.
The far side of the Moon is permanently shadowed from Earth-based radio signals, and would make an ideal location for a giant radio observatory. Telescopes of massive size could be built in the much lower lunar gravity.
We talked briefly about an Earth-based space elevator, but an elevator on the Moon makes even more sense. With the lower gravity, you can lift material off the surface and into lunar orbit using cables made of materials we can manufacture today, such as Zylon or Kevlar.
One of the greatest threats on the Moon is the dusty regolith itself. Without any kind of weathering on the surface, these dust particles are razor sharp, and they get into everything. Lunar colonists will need very strict protocols to keep the lunar dust out of their machinery, and especially out of their lungs and eyes, otherwise it could cause permanent damage.
Artist’s impression of a Near-Earth Asteroid passing by Earth. Credit: ESA
Although the vast majority of asteroids in the Solar System are located in the main asteroid belt, there are still many asteroids orbiting closer to Earth. These are known as the Near Earth Asteroids, and they’ve been the cause of many of Earth’s great extinction events.
These asteroids are dangerous to our planet, but they’re also an incredible resource, located close to our homeworld.
The amount of velocity it takes to get to some of these asteroids is very low, which means travel to and from these asteroids takes little energy. Their low gravity means that extracting resources from their surface won’t take a tremendous amount of energy.
And once the orbits of these asteroids are fully understood, future colonists will be able to change the orbits using thrusters. In fact, the same system they use to launch minerals off the surface would also push the asteroids into safer orbits.
These asteroids could be hollowed out, and set rotating to provide artificial gravity. Then they could be slowly moved into safe, useful orbits, to act as space stations, resupply points, and permanent colonies.
There are also gravitationally stable points at the Sun-Earth L4 and L5 Lagrange Points. These asteroid colonies could be parked there, giving us more locations to live in the Solar System.
Mosaic of the Valles Marineris hemisphere of Mars, similar to what one would see from orbital distance of 2500 km. Credit: NASA/JPL-Caltech
The future of humanity will include the colonization of Mars, the fourth planet from the Sun. On the surface, Mars has a lot going for it. A day on Mars is only a little longer than a day on Earth. It receives sunlight, unfiltered through the thin Martian atmosphere. There are deposits of water ice at the poles, and under the surface across the planet.
Martian ice will be precious, harvested from the planet and used for breathable air, rocket fuel and water for the colonists to drink and grow their food. The Martian regolith can be used to grow food. It does have have toxic perchlorates in it, but that can just be washed out.
The lower gravity on Mars makes it another ideal place for a space elevator, ferrying goods up and down from the surface of the planet.
The area depicted is Noctis Labyrinthus in the Valles Marineris system of enormous canyons. The scene is just after sunrise, and on the canyon floor four miles below, early morning clouds can be seen. The frost on the surface will melt very quickly as the Sun climbs higher in the Martian sky. Credit: NASA
Unlike the Moon, Mars has a weathered surface. Although the planet’s red dust will get everywhere, it won’t be toxic and dangerous as it is on the Moon.
Like the Moon, Mars has lava tubes, and these could be used as pre-dug colony sites, where human Martians can live underground, protected from the hostile environment.
Mars has two big problems that must be overcome. First, the gravity on Mars is only a third that of Earth’s, and we don’t know the long term impact of this on the human body. It might be that humans just can’t mature properly in the womb in low gravity.
Researchers have proposed that Mars colonists might need to spend large parts of their day on rotating centrifuges, to simulate Earth gravity. Or maybe humans will only be allowed to spend a few years on the surface of Mars before they have to return to a high gravity environment.
The second big challenge is the radiation from the Sun and interstellar cosmic rays. Without a protective magnetosphere, Martian colonists will be vulnerable to a much higher dose of radiation. But then, this is the same challenge that colonists will face anywhere in the entire Solar System.
That radiation will cause an increased risk of cancer, and could cause mental health issues, with dementia-like symptoms. The best solution for dealing with radiation is to block it with rock, soil or water. And Martian colonists, like all Solar System colonists will need to spend much of their lives underground or in tunnels carved out of rock.
Two astronauts explore the rugged surface of Phobos. Mars, as it would appear to the human eye from Phobos, looms on the horizon. The mother ship, powered by solar energy, orbits Mars while two crew members inside remotely operate rovers on the Martian surface. Credit: NASA/Pat Rawlings (SAIC)
In addition to Mars itself, the Red Planet has two small moons, Phobos and Deimos. These will serve as ideal places for small colonies. They’ll have the same low gravity as asteroid colonies, but they’ll be just above the gravity well of Mars. Ferries will travel to and from the Martian moons, delivering fresh supplies and sending Martian goods out to the rest of the Solar System.
We’re not certain yet, but there are good indicators these moons might have ice inside them, if so that is an excellent source of fuel and could make initial trips to Mars much easier by allowing us to send a first expedition to those moons, who then begin producing fuel to be used to land on Mars and to leave Mars and return home.
According to Elon Musk, if a Martian colony can reach a million inhabitants, it’ll be self-sufficient from Earth or any other world. At that point, we would have a true, Solar System civilization.
Now, continue on to the other half of this article, written by Isaac Arthur, where he talks about what it will take to colonize the outer Solar System. Where water ice is plentiful but solar power is feeble. Where travel times and energy require new technologies and techniques to survive and thrive.
In the distant past, the orbit of 67P/Churyumov-Gerasimenko extended far beyond Neptune into the refrigerated Kuiper Belt. Interactions with the gravitational giant Jupiter altered the comet's orbit over time, dragging it into the inner Solar System. Credit: Western University, Canada
In the distant past, the orbit of 67P/Churyumov-Gerasimenko extended far beyond Neptune into the refrigerated Kuiper Belt. Interactions with the gravitational giant Jupiter altered the comet’s orbit over time, dragging it into the inner Solar System. Credit: Western University, Canada
Rosetta’s Comet hails from a cold, dark place. Using statistical analysis and scientific computing, astronomers at Western University in Canada have charted a path that most likely pinpoints comet 67P/Churyumov-Gerasimenko’s long-ago home in the far reaches of the Kuiper Belt, a vast region beyond Neptune home to icy asteroids and comets.
According to the new research, Rosetta’s Comet is relative newcomer to the inner parts of our Solar System, having only arrived about 10,000 years ago. Prior to that, it spent the last 4.5 billion years in cold storage in a rough-and-tumble region of the Kuiper Belt called the scattered disk.
The Kuiper Belt was named in honor of Dutch-American astronomer Gerard Kuiper, who postulated a reservoir of icy bodies beyond Neptune. The first Kuiper Belt object was discovered in 1992. We now know of more than a thousand objects there, and it’s estimated it’s home to more than 100,000 asteroids and comets there over 62 miles (100 km) across. Credit: JHUAPL
In the Solar System’s youth, asteroids that strayed too close to Neptune were scattered by the encounter into the wild blue yonder of the disk. Their orbits still bear the scars of those long-ago encounters: they’re often highly-elongated (shaped like a cigar) and tilted willy-nilly from the ecliptic plane up to 40°. Because their orbits can take them hundreds of Earth-Sun distances into the deeps of space, scattered disk objects are among the coldest places in the Solar System with surface temperatures around 50° above absolute zero. Ices that glommed together to form 67P at its birth are little changed today. Primordial stuff.
Watch how Rosetta’s Comet’s orbit has evolved since the comet’s formation
There are two basic comet groups. Most comets reside in the cavernous Oort Cloud, a roughly spherical-shaped region of space between 10,000 and 100,000 AU (astronomical unit = one Earth-Sun distance) from the Sun. The other major group, the Jupiter-family comets, owes its allegiance to the powerful gravity of the giant planet Jupiter. These comets race around the Sun with periods of less than 20 years. It’s thought they originate from collisions betwixt rocky-icy asteroids in the Kuiper Belt.
Fragments flung from the collisions are perturbed by Neptune into long, cigar-shaped orbits that bring them near Jupiter, which ropes them like calves with its insatiable gravity and re-settles them into short-period orbits.
Comet 67P/Churyumov-Gerasimenko is a Jupiter-family comet. Its 6.5 year journey around the Sun takes it from just beyond the orbit of Jupiter at its most distant to between the orbits of Earth and Mars at its closest. Credit: ESA with labels by the author
Mattia Galiazzo and solar system expert Paul Wiegert, both at Western University, showed that in transit, Rosetta’s Comet likely spent millions of years in the scattered disk at about twice the distance of Neptune. The fact that it’s now a Jupiter family comet hints of a possible long-ago collision followed by gravitational interactions with Neptune and Jupiter before finally becoming an inner Solar System homebody going around the Sun every 6.45 years.
By such long paths do we arrive at our present circumstances.
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Bright reflective material in Ceres' Occator crater, imaged by NASA's Dawn spacecraft in Sept .2015. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.
All right, maybe not blinking like a flashlight (or a beacon on the tippity-top of a communication tower—don’t even start that speculation up) but the now-famous “bright spots” on the dwarf planet Ceres have been observed to detectably increase and decrease in brightness, if ever-so-slightly.
And what’s particularly interesting is that these observations were made not by NASA’s Dawn spacecraft, currently in orbit around Ceres, but from a telescope right here on Earth.
Researchers using the High Accuracy Radial velocity Planet Searcher (HARPS) instrument on ESO’s 3.6-meter telescope at La Silla detected “unexpected” changes in the brightness of Ceres during observations in July and August of 2015. Variations in line with Ceres’ 9-hour rotational period—specifically a Doppler effect in spectral wavelength created by the motion of the bright spots toward or away from Earth—were expected, but other fluctuations in brightness were also detected.
“The result was a surprise,” said Antonino Lanza from the INAF–Catania Astrophysical Observatory, co-author of the study. “We did find the expected changes to the spectrum from the rotation of Ceres, but with considerable other variations from night to night.”
Watch a video below illustrating the rotation of Ceres and how reflected light from the bright spots within Occator crater are alternately blue- and red-shifted according to the motion relative to Earth.
First observed with Hubble in December 2003, Ceres’ curious bright spots were resolved by Dawn’s cameras to be a cluster of separate regions clustered inside the 60-mile (90-km) -wide Occator crater. Based on Dawn data they are composed of some type of highly-reflective materials like salt and ice, although the exact composition or method of formation isn’t yet known.
Since they are made of such volatile materials though, interaction with solar radiation is likely the cause of the observed daily brightening. As the deposits heat up during the course of the 4.5-hour Ceres daytime they may create hazes and plumes of reflective particles.
“It has been noted that the spots appear bright at dawn on Ceres while they seem to fade by dusk,” noted study lead author Paolo Molaro in the team’s paper. “That could mean that sunlight plays an important role, for instance by heating up ice just beneath the surface and causing it to blast off some kind of plume or other feature.”
Once day turns to night these hazes will re-freeze, depositing the particles back down to the surface—although never in exactly the same way. These slight differences in evaporation and condensation could explain the random variation in daily brightening observed with HARPS.
These findings have been published the journal Monthly Notices of the Royal Astronomical Society (full text on arXiv here.)
This representation of Ceres' Occator Crater in false colors shows differences in the surface composition. Red corresponds to a wavelength range around 0.97 micrometers (near infrared), green to a wavelength range around 0.75 micrometers (red, visible light) and blue to a wavelength range of around 0.44 micrometers (blue, visible light). Occator measures about 60 miles (90 kilometers) wide. Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
This representation of Ceres’ Occator Crater in false colors shows differences in the surface composition. Red corresponds to a wavelength range around 0.97 micrometers (near infrared), green to a wavelength range around 0.75 micrometers (red, visible light) and blue to a wavelength range of around 0.44 micrometers (blue, visible light). Occator measures about 60 miles (90 kilometers) wide. Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
With NASA’s Dawn spacecraft set to enter its final and lowest orbit around the dwarf planet Ceres, spectral measurements are enabling researchers to gradually unravel the nature of the numerous mysterious and intriguing bright spots recently discovered, and now they conclude that briny mixtures of ice and salts apparently reside just beneath certain patches of the pockmarked surface and that “water is sublimating” from the surface of an “active crater”.
a short animation (spanning about 10 minutes) made out of my follow-up images. The first frame was obtained at 08:17UT while the second frame was obtained at 08:27UT of Nov, 12, 2015. (WT1190F is the star-like object at the centre while stars are trailed because the images were stacked on WT1190F motion). Credit: Ernesto Guido
No one’s 100% certain what WT1190F is — asteroid or rocket stage — but we are certain it will light up like a Roman candle when it re-enters Earth’s atmosphere around 6:20 Universal Time (12:20 a.m. CST) tomorrow morning Nov. 13.
Animation by Jost Jahn of WT1190F’s final hours as it races across the sky coming down off the coast of Sri Lanka
As described in an earlier story at Universe Today, an object discovered by the Catalina Sky Survey on Oct 3rd and temporarily designated WT1190F is expected to burn up about 60 miles (100 km) off the southern coast of Sri Lanka overnight. The same team observed it twice in 2013. Based upon the evolution of its orbit, astronomers determined that the object is only about six feet (2-meters) across with a very low density, making it a good fit for a defunct rocket booster, possibly one used to launch either one of the Apollo spacecraft or the Chinese Chang’e 3 lander to the Moon.
Below a plot of the last three orbits of WT1190F. The small red circle is the Earth. For scale, the large green circle is the orbit of the Moon. Notice that its final orbit takes straight into Earth. Credit: Bill Gray / Project Pluto
Additional observations of WT1190F have been made in the past few days confirming its re-entry later tonight. Checking the latest predictions on Bill Gray of Project Pluto’s page, the object will likely be visible from Europe about an hour before “touchdown”. To say it will be moving quickly across the sky is an understatement. Try about 3 arc minutes per second or 3° a minute! Very tricky to find and track something moving that fast.
Three 90-second exposures showing WT1190F zipping across the Rosette Nebula taken on Nov. 11, 2015 at the Konkoly Observatory in Hungary. Credit: Krisztián Sárneczky
58 minutes later, in the minute of time from 6:18 to 6:19 UT, WT1190F will move one full hour of right ascension and plummet 34° in declination while brightening from magnitude +8 to +4.5. If you’d like to attempt to find and follow the object, head over to JPL’s Horizons site for the latest ephemerides and orbital elements. At the site, make sure that WT1190F is in the Target Body line. If not, click Change and search for WT1190F in the Target Body field at the bottom of the window.
WT1190F re-Entry Trajectory. The object is expected to break up and fall harmlessly into the ocean. Credit: Bill Gray, Project Pluto
You’ll find updates at Bill Gray’s site. According to the most recent positions, the object will pass almost exactly in front of the Sun shortly before plunging into the ocean. Sri Lanka’s capital, Colombo, is expected to get the best views.
Because the mystery object’s arrival has been fairly well publicized, I hope to update you with a full report and photos first thing tomorrow morning. Like many of you, I wish I could see the show.
WT1190F observed on 9 October 2015 with the University of Hawaii 2.2 meter telescope on Mauna Kea, Hawaii. [Credits: B. Bolin, R. Jedicke, M. Micheli]
Get ready for a man-made fireball. A object discovered by the Catalina Sky Survey on Oct 3rd temporarily designated WT1190F is predicted to impact the Earth about 60 miles (100 km) off the southern coast of Sri Lanka around 6:20 Universal Time (12:20 a.m CST) on November 13.
The object orbits Earth with a period of about three weeks. Because it was also observed twice in 2013 by the same survey team, astronomers have the data they need to model its orbit and trajectory, and as far anyone can tell, it’s likely man-made.
The first two stages of the Saturn V rockets used to send the seven Apollo missions to the Moon fell back to Earth, but the third stage (S-IVB), pictured here, propelled the spacecraft into a lunar trajectory. Could this be WT1190F? Credit: NASA
Solar radiation pressure, the physical “push” exerted by photons of sunlight, is proportional to a space object’s area-to-mass ratio. Small, lightweight objects get pushed around more easily than heavier, denser ones. Taking that factor into account in examining WT1190F’s motion over two years, the survey team has indirectly measured WT1190F’s density at about 10% that of water. This is too low to be a typical asteroid made of rock, but a good fit with a hollow shell, possibly the upper stage of a rocket.
Spectacular re-entry of the Jules Verne ATV-1 cargo ship over the Pacific Ocean on September 29, 2008. Still image from a TV camera operated by Jessie Carpenter and Bill Moede of NASA Ames Research Center. A similar spectacle is expected on November 13 south of Sri Lanka.
It’s also quite small, at most only about six feet or a couple of meters in diameter. Most or all of it is likely to burn up upon re-entry, creating a spectacular show for anyone near the scene. During the next week and a half, the European Space Agency’s NEO (Near-Earth Object) Coordination Centeris organizing observing campaigns to collect as much data as possible on the object, according to a posting on their website. The agency has two goals: to better understand satellite re-entries from high orbits and to use the opportunity to test our readiness for a possible future event involving a real asteroid. The latter happened once before when 2008 TC3(a real asteroid) was spotted on October 6, 2008 and predicted to strike Earth the very next day. Incredibly, it did and peppered the Sudan with meteorites that were later recovered.
Assuming WT1190F is artificial, its trans-lunar orbit (orbit that carries it beyond the Moon) hints at several possibilities. Third stages from the Saturn-V rockets that launched the Apollo missions to the Moon are still out there. It could also be a stage from one of the old Russian or more recent Chinese lunar missions. Even rockets used to give interplanetary probes a final push are game.
Near-Earth object J002E3 discovery images taken by Bill Yeung on September 3, 2002. The 16th magnitude object was tentatively identified as the Apollo 12 third stage rocket. Animation created by Bob Denny.
Case in point. What was thought initially to be a new asteroid discovered by amateur astronomer Bill Yeung on September 3, 2002 proved a much better fit with an Apollo 12 S-IVB (third) stage after University of Arizona astronomers found that spectra taken of the object strongly correlated with absorption features seen in a combination of man-made materials including white paint, black paint, and aluminum, all consistent with Saturn V rockets.
On April 14th 1970, the Apollo 13 Saturn IVB upper stage impacted the moon north of Mare Cognitum. The impact crater, which is roughly 30 meters in diameter, is clearly visible in this photo taken by the Lunar Reconnaissance Orbiter. Credit: NASA/Goddard/Arizona State University
Apollo 13’s booster was the first deliberately crashed into the Moon, where it blew out it a crisp, 98-foot-wide (30-meter) crater. Why do such a crazy thing? What better way to test the seismometers left by the Apollo 12 crew? All subsequent boosters ended their lives similarly in the name of seismography. Third stages from earlier missions — Apollos 8, 10 and 11 — entered orbit around the Sun, while Apollo 12, which is orbiting Earth, briefly masqueraded as asteroid J002E3.
The nominal impact point is located about 60 miles south of the island nation Sri Lanka. Given the object’s small size and mass, it will likely be completely incinerated during re-entry. Credit: Bill Gray at Project Pluto
Bill Gray at Project Pluto has a page up about the November 13 impact of WT1190F with more information. Satellite and asteroid watchers are hoping to track the object before and right up until it burns up in the atmosphere. Currently, it’s extremely faint and moving eastward in Orion. You can click HERE for an ephemeris giving its position at the JPL Horizons site. How exciting if we could see whatever’s coming down before its demise on Friday the 13th!
Map showing TB145's position for an observer in the north central U.S. at 15-minute intervals starting at 5:00 UT. Subtract 4 hours from UT for EDT, 5 hours for CDT, 6 for MDT and 7 for PDT. Stars are shown to magnitude +12 and north is up. Credit: Chris Marriott's SkyMap
This simulation by Tom Ruen shows the trajectory of 2015 TB145 across the sky, showing tracer spheres spaced at one hour intervals along its path.
Halloween fireballs, a Supermoon and now a near-Earth asteroid flyby. What a week! While 2015 TB145 won’t be visible in binoculars because of its relative faintness and glare from a nearby waning gibbous Moon, you should be able to see it in an 8-inch telescope or larger telescope without too much difficulty.
Determined amateurs might even catch it in instruments as small as 4.5 inches especially tomorrow morning when the fleeing space mountain will brighten to around magnitude +10.
For western hemisphere observers, TB145 begins the evening in Orion’s Shield not far below the Hyades Cluster looking like a magnitude +11.5 star crawling northeast through the star field. By dawn on Halloween, it will top out around magnitude +10.2 as it zips through Taurus and Auriga traveling around 3-5° per hour depending on the time you look. For most of the night, TB145 will move swiftly enough to notice its motion in real time, resembling an Earth-orbiting satellite. Closest approach occurs around 17:00 UT (noon CDT) when it pass along bottom of the Big Dipper Bowl at around 10° hour. Amazing!
Map showing the asteroid’s progress across the horns of Taurus from 9-10:45 UT (4 – 5:45 a.m.) October 31st. It passes about 1° northwest of the Crab Nebula around 10:30 UT. Credit: Chris Marriott’s SkyMap
My hope is that these maps will help you spot and follow this zippy, aircraft carrier-sized boulder. Three of the four maps cover most of the time between 5:00 and 11:45 UT, equivalent to midnight CDT tonight to 6:45 a.m. tomorrow morning. I used the very latest orbital elements and hand plotted the positions (a tedious exercise but worth it!) at 15-minute intervals. For convenience, when you print them out, I’d suggest using a straight edge to draw a line connecting the position dots.
As we discussed in the previous Universe Today story, parallax comes into play when viewing any nearby Solar System object. Three of the maps show the asteroid’s position from the North Central U.S. One depicts the view from the South Central U.S. from 11-11:45 UT. Parallax is minor early on from midnight to 2 or 3 a.m. but becomes more significant near closest approach. This is based on comparisons I made between latitudes 47°-32° North.
By this time, TB145 will be around magnitude +10.4 and easier to see than at the start our run. The map covers the time from 11-11:45 UT (6 – 6:45 a.m. CDT). Credit: Chris Marriott’s SkyMap
I apologize for the limited number of maps in this article but hope these and the do-it-yourself approach described in the earlier article will be enough to set you on TB145’s trail.
The view from the southern U.S. (about 32° latitude) from 11-11:45 UT. Compared to the northern U.S., the asteroid’s path lies about 5 arc minutes further to the north. Credit: Chris Marriott’s SkyMap
As always when trying to spot asteroids on the move, pick a time and camp out at that spot with your telescope five minutes before the expected arrival time. Take the time to casually memorize the star patterns, so when the interloper arrives, you’ll pick it out straightaway. Again, depending on your location both east-west and north-south of the paths charted, TB145 may arrive a couple minutes earlier or later, but once you spot it, hold on tight. You’ll be going on a most exciting ride!
Map showing TB145’s approximate path starting at 4 hours UT on Oct. 31 (11 p.m. CDT Oct. 30). This view faces east. Tick marks show its hourly position. This map provides context for the detailed maps above. Credit: Chris Marriott’s SkyMap
We’d love to hear from you whether or not you were successful seeing it. If the weather’s uncooperative or you don’t have a telescope, Gianluca Masi’s got your back. He’ll webcast the flyby live on his Virtual Telescope site starting at 7 p.m. CDT (0:00 UT) tonight Oct. 30-31.
Now let’s see the flyby of Earth from the asteroid’s point of view, also by Tom Ruen. Enjoy!
Map showing TB145's approximate path starting at 4 hours UT on Oct. 31 (11 p.m. CDT Oct. 30). This view faces east. Tick marks show its hourly position. This map provides context for the detailed maps above. Credit: Chris Marriott's SkyMap
Trick or treat! I think we’re definitely in for a treat. 2015 TB145 will fly past Earth at a safe distance slightly farther than the moon’s orbit on Oct. 31 at 12:05 p.m. CDT (17:05 UT). Estimated at 1,300 feet (400-meters) across, this Great Pumpkin of an asteroid will be big enough and close enough to show in small telescopes.
Do I hear the doorbell ringing already?
Shining faintly at 18th magnitude on October 22, 2015 TB145 is already under study by amateur and professional astronomers. Its close approach will make for an excellent opportunity to learn a great deal about its surface properties and orbit. Watch for it to brighten up to magnitude +10.1 at peak, bright enough to see in a 4.5-inch telescope. Credit: Gianluca Masi
The close approach of such of TB145 will make for great science opportunities, too. Several optical observatories and the radar capabilities of the agency’s Deep Space Network at Goldstone, California will be tracking this flying mountain as will many amateur astronomers. The 110-foot (34-meter) Goldstone antenna will ping the asteroid with radio waves; the returning echoes will be collected by dishes in West Virginia and Puerto Rico and used to construct images showing the object’s surface features, shape and dimensions. NASA scientists hope to obtain radar images of the asteroid as fine as about 7 feet (2 meters) per pixel.
“The close approach of 2015 TB145 at about 1.3 times the distance of the moon’s orbit, coupled with its size, suggests it will be one of the best asteroids for radar imaging we’ll see for several years,” said Lance Benner, of JPL, who leads NASA’s asteroid radar research program. “We plan to test a new capability to obtain radar images with two-meter resolution for the first time and hope to see unprecedented levels of detail.”
View of the orbit of asteroid 2015 TB145. Its orbit is inclined about 39° to the plane of the Solar System. Credit: P. Chodas (NASA/JPL – Caltech)
Astronomers first nabbed asteroid 2015 TB145 on Oct. 10, 2015, using the University of Hawaii’s Pan-STARRS-1 (Panoramic Survey Telescope and Rapid Response System) telescope atop Mt. Haleakala in Maui. According to the catalog of near-Earth objectskept by the Minor Planet Center, this is the closest currently known approach by an object this large until asteroid 1999 AN10 (about 2,600 feet or 800-m in size) zips by at about 1 lunar distance in August 2027.
The gravitational influence of the asteroid is so small it will have no detectable effect on the Moon or anything here on Earth, including our planet’s tides or tectonic plates. But the planet will certainly have an effect on the asteroid. Earth’s gravity will deflect TB145’s path during the close approach, making it tricky this far out to create an accurate map of its flight across the sky. That’s why the two maps I’ve included with this article are only approximate. As we get closer to Halloween, further refinements in the asteroid’s orbit will allow for more accurate path-making.
TB145’s path starting at 4 hours UT on Oct. 31 (11 p.m. CDT Oct. 30). This view faces east. Tick marks show its hourly position. At the start of the path, the asteroid will shine around magnitude 11.4 but will gradually brighten through the night. To convert from UT, subtract 4 hours for EDT, 5 for CDT, 6 for MDT and 7 for PDT. Click for a large version. Credit: Chris Marriott’s SkyMap
Because the asteroid passes so near Earth, parallax will shift its path north or south up to 1/2°. Parallax is the apparent shift in an object’s position against the more distant background stars depending on the observer’s location on Earth. You can see how parallax works using your eyes and a finger. Stick your arm straight out in front of you and hold up your index finger. Open and close your right and then your left eye in a back and forth blinking pattern and watch your finger jump back and forth across the more distant background. Each eye sees the thumb from a slightly different perspective, causing it to shift position against the distant scene.
Graphic depicting the orbit of asteroid 2015 TB145. The asteroid will safely fly past Earth slightly farther out than the moon’s orbit on Halloween. Credit: P. Chodas (NASA/JPL – Caltech)
This happens all the time with the Moon. You might see it conjunct with a bright planet where skywatchers on the opposite side of the planet see an occultation. That’s why it’s best to make your own map of TB145’s wild ride across the sky. When closest to Earth, the asteroid will cover a Full Moon diameter about every 3 minutes as it tears by us at 22 miles per second (35 km/sec). Without a good map, it’ll get away from you.
Method #1: Using Stellarium
Download the free sky-plotting program Stellarium. Once you’ve set your location, either hit F2 or click on the Configuration icon in the lower left corner of your screen. Now select the Plugins tab then Solar System Editor. Click on Configure at the bottom of the tab, choose Solar System and click Import orbital elements in MPC format.
Next, select the Asteroids option and then from the bookmarks list, choose MPCORB: near-Earth asteroids (NEAs) and then Get orbital elements. Allow the list — a very large one — to load then scroll through it until you find 2015 TD145 and put a check mark in the box. Then click Add objects.
Stellarium view of the sky and featured asteroid seen from northern, Minnesota at 11:55 p.m. October 30, 2015. Notice that a bright, waning gibbous Moon will be nearby during the best viewing opportunities for the Americas, which will make 2015 TB145 a little harder to spot.
Still with me? OK, close the Solar System editor and press F3 or select the magnifying glass icon in the lower left corner of your screen, then type in the asteroid’s name exactly as 2015 TD145. Hit enter and you’ll see a set of rotating red crosshairs. Bingo! This where the asteroid will be at the time you chose. You can adjust your magnitude range, field of view and even download additional files of fainter stars and deep sky objects. Unfortunately, Stellarium can’t draw an arc showing TB145’s changing position with time. Cross your fingers that appears in the next iteration.
Method #2: Download up-to-date orbital elements into your sky-charting program
2015 TB145 belongs to the Apollo family of asteroids, whose orbits cross that of Earth. Amor asteroids approach but don’t cross, while Atens also cross Earth’s path but spend most of their time inside our orbit. Credit: ESA
Let’s say you already have a sky-charting program like Guide, Dance of the Planets, MegaStar or Starry Night. Go to the Minor Planet &Comet Ephemeris Serviceand type in 2015 TB145 in the big, blank box. Next, scroll down and select your program from the list and click on Get Ephemerides/HTML page. Save the file of orbital elements that pops up and place into the appropriate folder in your program. Open your program, select 2015 TB145 and make a chart!
Method #3: Manually input orbital elements into your program
You can also go to JPL’s Horizons site for the very latest orbital elements you can manually input in your program. 2015 TB145 is expected to be as bright as magnitude +10.1 (no problem in a 4.5-inch scope) but that occurs during the afternoon for the Americas. The Middle East and Asia are the place to be for closest approach. Peak brightness over the U.S. will occur before dawn on Halloween, so you can begin observation around 11 p.m. local time Friday evening October 30 when Orion comes up in the east. The asteroid starts shines at around magnitude +11-11.5 that evening and brightens overnight to around +10.3-10.5 before dawn for the Americas.
A word about tracking fast-moving asteroids. I’ve found that the best way to catch sight of one is to “camp” at the place they’ll pass at a certain time. Say you want to see TB145 at 1:15 a.m. October 31. Make a chart that shows its position every 15 minutes. Five minutes before it arrives at the 1:15 a.m. spot, point your telescope there and wait for a “moving star” to enter the field of view. If you don’t see it right way, wait a few minutes and pan around to the north and south of the location. By the way, the asteroid will pass less than a degree northwest of the Crab Nebula (M1) in Taurus around 10:30 UT (5:30 a.m. CDT).
Be aware that the bright, waning gibbous Moon will be within 10° of the asteroid when it’s best visible in the Americas. While this will make observing the asteroid more challenging, don’t let it stop you from trying. If bad weather gets in the way, Gianluca Masi has you covered. He’ll live-stream the flyby on his Virtual Telescope sitebeginning at 0:00 UT (7 p.m CDT) on October 31st.
One way or another, we’ll all have a shot at seeing the Great Pumpkin asteroid this Halloween.
2015 TB145 looks stellar in this photo taken on October 24th when it glowed at only 16th magnitude. Credit: Peter Lake
UPDATE Oct. 27, 2015: There’s been some discussion about TB145’s orbit resembling that of a comet along with speculation it might be a dead or dormant comet. Amateur and professional astronomers have been watching it closely, looking for hints of activity such as a fuzzy coma. So far, photos show the asteroid as completely stellar.
I also wanted to update you on its visibility. Those with 10-inch or larger telescopes can begin looking for the object Thursday night Oct. 29th when it reaches magnitude +13.5. The following night it leaps to +11.5 with a peak brightness of +10.0 occurring around 14:00 UT (9 a.m. CDT) on Halloween. TB145 fades rapidly thereafter – down to 15th magnitude just 8 hours later.
