January 16 – Blowin’ In The (Cosmic) Wind

Today’s Factismal: The Stardust mission returned samples from a comet ten years ago today but the science continues!

There are a lot of things we don’t know in science. But there are a lot of things that we know, too. For example, we know that everything in the Solar System, from the Sun to the Earth to the smallest asteroid, all formed from the same cloud of interstellar dust and gas that collapsed some 4.5 billion years ago. But the Sun is very different from the Earth, which is very different from a comet or an asteroid. So while we know where we came from (as one astronomer used to say “We are all stardust”), how we got here is still something of a mystery. Though we have samples of the rocks on Earth, the Moon, Mars, and several asteroids, all of those have been changed by different geologic processes over the past 4.5 billion years. What we really need to understand how our Solar System formed is a sample of the original material.

The Stardust probe (NASA illustration)

The Stardust probe
(NASA illustration)

And that’s why the NASA Stardust mission happened. In 1999, NASA launched a space probe that was designed to do something that had never been done before: to go to a comet, grab samples of the dust, and return it safely to Earth. The probe looked a little like a five and a half foot long shoe box with a surfboard on either side; the two surfboards were solar panels that supplied the energy to run the instruments. Like other space probes, Stardust included a mass spectrometer to identify the composition of dust and gases it encountered and a camera to provide images. But Stardust’s heart (which was located on the front of the probe) was the sample collector.

Comet dust captured by Stardust (Image courtesy NASA)

Comet dust captured by Stardust
(Image courtesy NASA)

In order to collect samples of comet dust without damaging it or heating it up, NASA used aerogel, a material that is 99.8% empty space. Though aerogel had been invented as a bar bet in 1931, it hadn’t found a practical use until the Stardust mission (since NASA popularized the material, it has become very common in some industrial applications). Because aerogel is so light, it would stop the dust grains gradually with a minimum of breakage. And because aerogel is translucent, the tracks made by dust grains could easily be spotted by scientists.

The Wild 2 comet, as seen by Stardust (Image courtesy NASA)

The Wild 2 comet, as seen by Stardust
(Image courtesy NASA)

Both aerogel and the mission were an unqualified success. Stardust visited the asteroid 5535 Annefrank and discovered that it is larger and more interesting than previously thought. Stardust successfully captured dust both from between the planets and from comet Wild 2 and discovered that comets may not be as pure as we thought. And Stardust took the names of more than a million people (including me!) out between the planets.

During it's twelve year mission, Stardust visited an asteroid and two comets (Image courtesy NASA)

During it’s twelve year mission, Stardust visited an asteroid and two comets
(Image courtesy NASA)

Today, the samples from that mission are being analyzed by people just like you. If you’d like to take a stab at identifying dust grains and helping discover how our Solar System started, then fly on over to:
http://stardustathome.ssl.berkeley.edu/

January 9 – Miss Demeter

Today’s Factismal: Ceres was first thought to be a comet.

Most astronomy fans know Ceres by reputation if not by name. It is the largest body in the asteroid belt, that loose pile of rubble that never quite coalesced into a real planet back when the Solar System was being built. It is small enough that you could it would take 78 chunks of rubble the size of Ceres to build one Moon. But what most astronomy fans (and other folks) don’t know about Ceres is that it has caused trouble for astronomers from the day it was found – and continues to cause trouble today!

When Giuseppe Piazzi first observed Ceres in 1801, he called it a comet. But Johan Bode decided that it was in the right place to be the “missing planet” he was looking for between Mars and Jupiter, and so he called it a planet and gave it an astronomical symbol. Unfortunately for Ceres, astronomers soon discovered over a hundred more “missing planets” in the same neighborhood, and they took to calling it a minor planet (astronomers get upset whenever there are more than ten planets; nobody knows why) when they didn’t call it an asteroid (astronomy speak for “tiny little star-like thingamabob”). And then, when yet more Pluto-sized objects were found in the outer Solar System, Ceres was reclassified yet again as a dwarf planet (see the previous note about astronomers and numbers bigger than ten).

An image of Ceres, taken by the Hubble Space Telescope

An image of Ceres, taken by the Hubble Space Telescope

Even its name is a subject for debate. In America, it is known as Ceres, for the Roman goddess of the harvest. But the Greeks have never consented to that name; they prefer to call it Demeter (which causes all kinds of confusion as there is another asteroid known as 1108 Demeter). And the Germans prefer to call it Hera for reasons that are inscrutable to anyone but a German.

Ceres as seen by the DAWN probe (Image courtesy NASA)

Ceres as seen by the DAWN probe
(Image courtesy NASA)

What is not in doubt is that Ceres is large enough to be shaped into a ball by its gravity, and that it has an interior that is divided into an icy outer part, a rocky middle section, and a metallic core (i.e., meets the definition of planet for everyone but the IAU). It is also possible that Ceres has an inner ocean between the outer icy part and the rocky middle; this is exciting because it makes Ceres one of the few places in the Solar System where life as we know it could exist. Ceres’ size and shape tell us that it is a relic of the early days of the Solar System, when everything was collapsing into small bodies that then collided to form the planets. So we can add planetismal and protoplanet to Ceres’ list of appellations.

The layers of Ceres, as we now know them. We expect to learn a lot more about Ceres once DAWN arrives there in 2015. (Image courtesy NASA)

The layers of Ceres, as we now know them. We expect to learn a lot more about Ceres once DAWN arrives there in 2015. (Image courtesy NASA)

Right now, the DAWN spacecraft is orbiting Ceres. Planetologists (i.e., the folks who still classify Pluto as a planet) are studying the asteroid in order to learn more about how planets form and develop over time, and to see evidence of the early history of the Solar System. They’ll also compare Ceres, which is the largest asteroid, with Vesta, which is the second largest and was visited by DAWN in 2013. As part of the NASA mission, JPL has launched the Asteroid Mappers website, where you can help to identify features on Ceres and Vesta:
http://dawn.jpl.nasa.gov/DawnCommunity/asteroid_mappers.asp

October 10 – Mad, Mad Moon

Today’s factismal: 3753 Cruithne was discovered in 1986 orbiting near the Earth.

Back in 1986, the search for Near Earth Asteroids was just getting started. And one of the first objects that they found was an oddball that they named 3753 Cruithne (pronounced “CREW-eee-nuh”; it is the name of a Pictish king).Why is it so odd? Well, for one thing, it is in a 1:1 resonance with the Earth; what that means it that it takes the same amount of time to go around the Sun that the Earth does. But because it has a highly elliptical orbit, sometimes it is far away from the Earth and sometimes it is very near. (Well, not that near; at its closest, 3753 Cruithne is thirty times farther away than the Moon.)

A plot of the orbits for 1,400 of the Near Earth Asteroids; 37 Cruithne is in there somewhere (Image courtesy NASA)

A plot of the orbits for 1,400 of the Near Earth Asteroids; 3753 Cruithne is in there somewhere
(Image courtesy NASA)

Because 3753 Cruithne has a regular relationship to the Earth, some folks refer to it as a “second moon” even though it isn’t. The confusion happened because astronomers love to think about what things look like, especially orbits. And when you look at 3753 Cruithne’s orbit, something amusing (to the astronomers) orbits. If you flew above the Sun and watched 3753 Cruithne orbit, you would see it moving out toward Mars and back in toward Venus, crossing Earth’s orbit twice on each trip. And, thanks to the odd shape of 3753 Cruithne’s orbit, it actually takes about a year to complete each go-round. It would look something like this:

3753 Cruithne's orbit as seen from above the Sun (Image courtesy Jecowa)

3753 Cruithne’s orbit as seen from above the Sun
(Image courtesy Jecowa)

But if you stand on Earth and watch 3753 Cruithne orbit, it looks much different. Because Earth passes 3753 Cruithne in its orbit, it appears that the asteroid is making a “horseshoe” in space. So the astronomers giggled for a while about some asteroids being close enough for horseshoes and left it there. Which is where the internet found it. Unfortunately, most of the people on the internet aren’t astronomers. (You are shocked, I know.) As a result, they don’t know that the horseshoe “orbit” of 3753 Cruithne only happens when you look at the asteroid from the moving Earth; that it is a geocentric view. Since we know that the heliocentric view is much closer to reality, using a geocentric one to claim that an asteroid is the Earth’s second moon makes about as much sense as claiming that the Sun orbits the Earth. And 3753 Cruithne is hardly the only asteroid to look like it is orbiting Earth when it isn’t; in 2014, 2014 OL339 was shown to also have a horseshoe orbit.

When viewed from Earth, it appears that 3753 Cruithne orbits us (as does everything else) (Image courtesy Jacowa)

When viewed from Earth, it appears that 3753 Cruithne (and everything else) orbits us
(Image courtesy Jecowa)

But that isn’t to say that the Earth doesn’t have a second moon every once in a while. (This is where life gets even more interesting than the internet thinks it is.) Due to the odd orbital interactions of all of the various bits of junk out there, every so often a small asteroid will get trapped in orbit around the Earth for a few days or a few weeks or a few years. When this happens, Earth truly does have a “second moon”; because these asteroids aren’t trapped by Earth’s gravity and are just “passing through”, they are referred to as coorbiting asteroids. In 1999, asteroid 2003 YN107 began a coorbit of Earth that lasted for seven years. And some experts estimate that we have a small, temporary “second moon” almost all the time!

The path of Earth's true

The path of Earth’s true “second moon”
(Image courtesy NASA)

So why aren’t we sure about how often the Earth has a “second moon” (even if it never is 3753 Cruithne)? Simply because asteroids are small and space is vast. As anyone who has ever tried to find a remote control in a room has discovered, it can take a long time to locate something if it is very small compared to the room that you are looking in. But having more people looking can help. And that’s where you can join in on the fun! The Asteroid Survey is looking for folks who are looking to be looking for asteroids! (Here’s looking at you, KD!) You’ll sort through photos, identifying objects as stars, asteroids, or “junk”. And you’ll be helping to identify the millions of bits of junk that fly through our Solar System and give us our second moons. To join in on the fun, orbit over to:
http://www.asteroidzoo.org/

June 6 – Down To The Levee

Today’s Factismal: Tropical Storm Allison did $5,500,000,000 in damage, making it the costliest tropical storm in US history.

It is hurricane season again, and that means that a small disturbance over the Gulf of Mexico or the Atlantic Ocean might grow into larger one. And, if that disturbance is very, very lucky, then it can gain enough energy from the water evaporated by the ocean to grow into a tropical storm. And if it is luckier still, then it will turn into a hurricane. This year, experts believe that we’ll get a typical hurricane season. They expect between 11 and 16 named storms, fewer than eight of which will turn into hurricanes, and fewer than four major hurricanes (think Katrina).

An aerial view of flooded Houston (Image courtesy KHOU)

An aerial view of flooded Houston
(Image courtesy KHOU)

An aerial view of flooded Houston (Image courtesy KHOU)

An aerial view of flooded Houston
(Image courtesy KHOU)

But the storms don’t have to become hurricanes to do a lot of damage, as the people who are living in Texas right now can attest. Wet as it is right now, the current mess pales before Tropical Storm Allison in 2001. Though Allison never grew large enough or strong enough to form an “eye”, it was nevertheless the worst tropical storm ever to hit the continental United States. In some parts of Texas, Allison dropped 40 inches of rain in just two days. The storm caused widespread flooding, displacing some 30,000 people and doing more than $5.5 billion in damage (that’s $7.4 billion in current money). Unfortunately, Allison also killed some 41 people (23 in Texas alone); the total would have been much higher but for the warnings and other information put out by the National Weather Service.

Rafting down the main street in Houston after Allison (Image courtesy KHOU

Rafting down the main street in Houston after Allison
(Image courtesy KHOU)

However, the National Weather Service is only as good as their data. And they need more data and better data. And they’d like you to provide it. They have partnered with the Citizen Weather Observer Program, which is a group of citizen scientists like you who take regular readings of temperature, humidity, rainfall, and other weather-related measurements and then pass them onto the National Weather Service using free software (available on the website). If this sounds like something you’d like to do, then head on over to
http://wxqa.com/cwop_info.htm

March 29 – Where the Home Fire Burns

Today’s factismal: Heinrich Olbers discovered Vesta , the eleventh planet in the Solar System, 209 years ago today.

If there is one thing that is sure to set planetologists and astronomers fighting, it is the question of how to define a planet. Astronomers claim that they get to define what a planet is because they are in the sky; planetologists claim that right because planets are what they study. But no matter how you define a planet, both sides will agree that the definition has changed several times.

For example, when Galileo discovered the four largest moons of Jupiter he called them planets. (Well, first he called them stars before realizing his mistake.)  And astronomers agreed with him until similar planets were found orbiting Saturn and the number of planets around Jupiter reached embarrassing levels – how could a mere planet have more planets than the Sun did? So astronomers decreed that any planet orbiting another planet was actually just a moon.  When Uranus was discovered in 1781, it fit neatly into the system as a new planet. When Titania and Oberon were seen circling Uranus and Enceladus and Mimas were seen orbiting Saturn, those were moons. Problem solved.

But then came Ceres. Astronomers had been searching for a “missing” planet between Mars and Jupiter based on the assumption that planetary orbits followed a spacing pattern that they called the Titus-Bode law. Like Kepler’s laws of orbital mechanics, Titus-Bode was an empirical rule based on observation and not theory. Unlike Kepler’s laws, Titus-Bode wouldn’t work out, though we wouldn’t discover that for more than a century. In the meantime, astronomers used it to tell them where to look for new planets. And, for a while, it seemed to deliver.

In 1801, Guiseppe Piazzi discovered a planet exactly where Titus-Bode predicted and named it Ceres. Less than a year later, Heinrich Olbers discovered another planet in the same area and named it Pallas. Then Karl Harding found Juno in 1804 and Olbers spotted Vesta in 1807. All in all, there were four planets where astronomers had expected to see but one and there were a total of eleven planets in the Solar System. But the new planets were tiny little things, just barely visible in the best telescopes of the day. Because they were so small, they could hardly be discerned from the stars behind them, and so Herschel proposed calling them “asteroids” or “star shaped”.

Despite the new nomenclature, astronomers still considered the asteroids to be planets. And that’s how they were spoken of in the press and in scientific papers for nearly forty years. They were given astronomical symbols to make it easier for astronomers to look them up in their texts and the origin of these planets was hotly debated. One popular suggestion was that they were the remains of a single, larger planet that had somehow broken apart. And other asteroids were eagerly sought to help fill in the gaps. But, despite many efforts, no new planets were found for nearly four decades.

The Universe, as matters stood in 1853. The four planets of Ceres, Pallas, Juno, and Vesta all fit into a gap that had been predicted by Titus and Bode.

But when they did start finding new asteroids, the floodgates opened. By 1860, 62 minor planets had been discovered. By 1890, that number had risen to 300. And in 1891, Max Wolf perfected a means of identifying asteroids using photographic plates that allowed them to be discovered almost automatically; indeed, a variant of that method is now in use and has identified more than 700,000 different asteroids!

Asteroids closer than Mars (Image courtesy JPL)

Asteroids closer than Mars (Image courtesy JPL)

Now here’s the crazy part: even though we’ve found more than 700,000 asteroids there are probably at least another 700,000 out there. And the ones still in hiding are too small or too lumpy or too weird to be found by an automatic program. What they need to find the remaining asteroids is someone who knows how to play hide-and-seek with a lump of rock a million  miles away. They need a human.

And that’s where you come in. Asteroid Zoo needs people to look at images and mark where they think an asteroid is hiding. With enough folks like you, we can find out where the remaining “vermin of the skies” (as the astronomers call them) are so we can know things how the Solar System formed, where the hazardous asteroids are, and if any of them are worth visiting. To learn more, zip on over to:
https://www.asteroidzoo.org/

October 16 – The Gold Bug

Today’s factismal: There is more gold on one asteroid (433 Eros) than has ever been mined on Earth.

Ask any third grader what killed the dinosaurs and odds are she’ll tell you that an asteroid did it. (That’s not quite correct but it is close enough for now.) And if the third grader is especially clever, she may even know the name of the asteroid: Chicxulub (“Chick-sue-loob” or “the well of the great horns”). Like all major impact structures, the name comes from the closest town and not from the actual asteroid; those are usually given names like  433 Eros or 1992 QB1 or 1999 FN53. But what your third grader may not know is that Chicxulub was hardly the only asteroid to every hit the Earth.

Every day, nearly 170 meteorites hit the Earth; that adds up to 42,000 meteorites each year! (For the purposes of this article, we’ll treat asteroids and meteorites and comets as being roughly equivalent simply because they are, planetologically speaking.) Most of these are small pieces of rock and ice about the size of a grain of rice that burn up in the outer atmosphere leaving nothing behind but a little dust and a pretty lightshow. But about 2,800 of those meteorites each year are large enough to actually make it deeper into the atmosphere.

A meteorite as seen from above the atmosphere (Image courtesy NASA/Ron Garan)

A meteorite as seen from above the atmosphere
(Image courtesy NASA/Ron Garan)

Every year, about 500 meteorites survive their fiery plunge through the atmosphere and make it to the ground. Most of those are small and do little damage, but every once in a while we get something a little larger that causes trouble. In 2013, a meteor that was 60 ft across and weighed more than the Eiffel tower fell above Chelyabinsk, Russia. When it exploded in the sky, it created a shockwave that shattered glass for miles around, injuring more than 1,500 people who had gone to the window to see what the pretty bright light was. When it was all over and done, the Chelyabinsk meteor left behind $33 million in damages, more than 1,500 pounds of fragments, and a 20 ft wide hole known as an “astrobleme” (star wound) in the trade or a “meteor crater” to news reporters.

And that isn’t the worst that could happen. Based on what we know right now, scientists expect to see an impact creating a Chelyabinsk style crater roughly every 250 years, an Odessa style 500 ft crater every 540 years, a Wolfe Creeksized half-mile across crater every 13,000 years, a (Barringer) Meteor Crater mile-wide crater every 21,000 years, a Pingualuit two mile across impact every 50,000 years, and a Chicxulub 110 mile across crater every 100,000,000 years. As you might guess from that big gap at the end, there is still a lot that we don’t know for sure about impact craters.

The Pingualuit impact crater (Image courtesy NASA)

The Pingualuit impact crater (Image courtesy NASA)

But we can learn. And surprisingly on of the best places to learn about impact craters is from the things that make them – asteroids! That’s because unlike the Earth, which has wind and water and plate tectonics to erase old impact craters, the asteroids just have impacts to erase other impacts. So by examining impact craters on asteroids, we can learn more about how they happen on Earth which can help us keep another Chicxulub from knocking on our planet one day. If you’d like to learn more about imact craters on asteroids, why not zoom over to Vesta Mappers at Cosmo Quest? They’ll show you how to identify impact craters on the latest images of Vesta and then let you loose on the newest data we’ve got!
https://cosmoquest.org/?application=vesta_mappers

March 3 – Moon Madness

Today’s factismal: 3753 Cruithne does not orbit the Earth.

Of late, there have been a lot of blog posts (even, sadly, on supposedly “science oriented” websites) claiming that Earth has a “second moon” named 3753 Cruithne (pronounced “CREW-eee-nuh”; it is the name of a Pictish king). As is often the case with things found on the internet, the truth is both less and more interesting. First, the less interesting part: 3753 Cruithne is not a moon of the Earth or any other planet; instead, it orbits the Sun all by itself. This may sound like nitpicking, but it is an essential part of the definition of the word “Moon”. Until 1655, everything that we saw in the sky was either a star, or a comet, or a planet with the sole exception of the Moon. Galileo’s discovery of four new things orbiting Jupiter was taken in stride; those things were planets according to the astronomers (even though Galileo called them stars). But in 1655, they started seeing planets orbiting Saturn as well. Before long, Saturn had five planets and a ring orbiting it while Jupiter’s planet count grew to ten. So the astronomers decided that they would redefine the word planet. If it was big enough to see and orbited the Sun, it was a planet. If it was big enough to see and orbited another planet, it was a moon. And so, because the asteroid 3753 Cruithne orbits the Sun and not the Earth, it isn’t a moon. (It isn’t a planet because it isn’t big enough; at just three miles across, it is too small to be round.)

So where did all of this nonsense about 3753 Cruithne being a second moon of the Earth get started? With the astronomers, of course. You see, astronomers love to think about what things look like, especially orbits. And they started looking at the orbits of Near Earth objects (i.e., things that had an orbit similar to Earth’s) and found several that had amusing (to the astronomers) orbits. If you flew abovethe Sun and watched 3753 Cruithne orbit, you would see it moving out toward Mars and back in toward Venus, crossing Earth’s orbit twice on each trip. And, thanks to the odd shape of 3753 Cruithne’s orbit, it actually takes about a year to complete each go-round. It would look something like this:

3753 Cruithne's orbit as seen from above the Sun (Image courtesy Jecowa)

3753 Cruithne’s orbit as seen from above the Sun
(Image courtesy Jecowa)

But if you stand on Earth and watch 3753 Cruithne orbit, it looks much different. Because Earth passes 3753 Cruithne in its orbit, it appears that the asteroid is making a “horseshoe” in space. So the astronomers giggled for a while about some asteroids being close enough for horseshoes and left it there. Which is where the internet found it. Unfortunately, most of the people on the internet aren’t astronomers. (You are shocked, I know.) As a result, they don’t know that the horseshoe “orbit” of 3753 Cruithne only happens when you look at the asteroid from the moving Earth; that it is a geocentric view. Since we know that the heliocentric view is much closer to reality, using a geocentric one to claim that an asteroid is the Earth’s second moon makes about as much sense as claiming that the Sun orbits the Earth. And 3753 Cruithne is hardly the only asteroid to look like it is orbiting Earth when it isn’t; just last year, 2014 OL339 was shown to also have a horseshoe orbit.

When viewed from Earth, it appears that 3753 Cruithne orbits us (as does everything else) (Image courtesy Jacowa)

When viewed from Earth, it appears that 3753 Cruithne (and everything else) orbits us
(Image courtesy Jecowa)

But that isn’t to say that the Earth doesn’t have a second moon every once in a while. (This is where life gets even more interesting than the internet thinks it is.) Due to the odd orbital interactions of all of the various bits of junk out there, every so often a small asteroid will get trapped in orbit around the Earth for a few days or a few weeks or a few years. When this happens, Earth truly does have a “second moon”; because these asteroids aren’t trapped by Earth’s gravity and are just “passing through”, they are referred to as coorbiting asteroids. In 1999, asteroid 2003 YN107 began a coorbit of Earth that lasted for seven years. And some experts estimate that we have a small, temporary “second moon” almost all the time!

The path of Earth's true "second moon" (Image courtesy NASA)

The path of Earth’s true “second moon”
(Image courtesy NASA)

So why aren’t we sure about how often the Earth has a “second moon” (even if it never is 3753 Cruithne)? Simply because asteroids are small and space is vast. As anyone who has ever tried to find a remote control in a room has discovered, it can take a long time to locate something if it is very small compared to the room that you are looking in. But having more people looking can help. And that’s where you can join in on the fun! The Asteroid Survey is looking for folks who are looking to be looking for asteroids! (Here’s looking at you, KD!) You’ll sort through photos, identifying objects as stars, asteroids, or “junk”. And you’ll be helping to identify the millions of bits of junk that fly through our Solar System and give us our second moons. To join in on the fun, orbit over to:
http://www.asteroidzoo.org/