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/

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/

June 30 – Ka-Boom!

Today’s factismal: It is World Meteor Day. Go out tonight and look for meteors!

The world of meteors is a confusing one to the uninitiated. We speak of meteors and meteorites and falls and finds and astroblemes and bolides and expect everyone else to know what we mean [1] (and we don’t call it “meteorology” because that was already taken; instead, it is called meteorics). But one part of that world is easily understood – today is World Meteor Day because one of the most famous events ever happened 105 years ago today.

Devastation at Tunguska (Image courtesy the Leonid Kulik Expedition)

Devastation at Tunguska
(Image courtesy the Leonid Kulik Expedition)

Known as the Tunguska event, this was the largest meteorite impact for at least a million years. What happened was that a chunk of rock roughly the twice as big as a house fell into the Earth’s atmosphere over Tunguska, Russia. As it went deeper into the atmosphere, the pressure caused the rock to break into pieces and burst in the air (what meteoricists cleverly call an “air burster”) in a massive explosion that was 1,000 times stronger than the bomb dropped on Hiroshima. The explosion sent a burst of heat so great that a man 40 miles away felt as if his clothing had caught fire, and a clap of pressure so large that it leveled trees over 830 square miles! To put this into scale, the recent meteorite explosion over Russia was only 1/30th as powerful.

But why did the Tunguska event happen? It turns out that we don’t know. Because it was an air burster and because it was nearly two decades before anyone went to investigate the event, there is very little hard data about it. And without hard data, we can’t make and test hypotheses. And that’s where you come in…

The folks at NASA have put together a Meteor Counter app. All you have to do is lie back, watch the sky and tap the app whenever you see a meteor. Your data will automatically be sent to the researchers, who will use it to help us learn more about meteors and any dangers they might present.
http://science.nasa.gov/science-news/science-at-nasa/2011/13dec_meteorcounter/

[1] For those who like to keep their pedantry straight, here are the distinctions: A meteor is the bit of light streaking across the sky caused by the rock passing through the Earth’s atmosphere.Once it hits the ground, the meteor becomes a meteorite. And if the meteor is exceptionally bright, it is a bolide (also called a fireball). A fall is any meteorite that was observed as it fell to Earth; if it wasn’t seen, it is a find. And if it makes a crater, we call the crater an astrobleme or “star wound”. No go and be pedantic, my padawan!

March 26 – Blue Moon

Today’s Factismal: The first sighting of a moon orbiting an asteroid was made in 1994.

If you have ever gone on a long journey, you know that it is often a good idea to stop every once in awhile to look at the local scenery. You can rest your legs and get more out of the trip than you would if you simply raced on to your destination. The folks at NASA know this, too.

Launching the Galileo probe (Image courtesy NASA)

Launching the Galileo probe (Image courtesy NASA)

That’s why they planned the Galileo mission so that it could take an up-close look at an asteroid while the probe headed out to Jupiter. Galileo was one of only three space probes launched by the Space Shuttle (other probe launches were cancelled after the Challenger disaster due to the risk). Using a combination of gravity-assist and chemical rockets, Galileo’s primary mission was to study Jupiter. But on the way, it would pass through the asteroid belt, which provided an excellent opportunity to study these rocks in detail.

243 Ida coming into view  (Image courtesy NASA)

243 Ida coming into view (Image courtesy NASA)

The asteroid that NASA chose to study was 243 Ida. From spectroscopy, we knew that it was a S-type (rocky) asteroid, but didn’t have many details about the composition. Was it uniform or chunky? Was it one big rock or lots of little ones (a “rubble pile”)? This was a rare chance to find out; 243 Ida would be only the second asteroid ever visited by a space probe.

243 Ida and its moon Dactyl  (Image courtesy NASA)

243 Ida and its moon Dactyl (Image courtesy NASA)

As Galileo raced past the asteroid, it took a series of pictures and sent them back to Earth for analysis. And, while looking through those images, we discovered a lot of interesting things. 243 Ida was shaped like a croissant. It was made up of chunks of rock, blanketed over the surface in a loose regolith (“rock blanket”) and covered with impact craters. But, most astonishing of all was the fact that 243 Ida had a tiny moon orbiting it.

Since then, moons have been discovered around other asteroids. Now that we know what to look for, we have seen it elsewhere. But this discovery changed how we think about asteroids and has led to more research into how they form and interact.

If you’d like to be part of that work, then why not join the Lowell Amateur Research Initiative?
http://www.lowell.edu/LARI_welcome.php

Bonus Factismal: Asteroid Fly-by

If you are a fan of asteroids or just like to think about what might have killed the dinosaurs (and who doesn’t?), then tomorrow is your day and tonight is your night. Right now, there is an asteroid that is 1.7 miles across and zooming closer and closer to Earth. Even better, the asteroid has a moon that wasn’t discovered until this fly-by! (Remember that asteroid moons are fairly common but still cool. Like fezzes.)

The asteroid 1998 QE2 and its (as yet un-named) moon (Image courtesy NASA)

The asteroid 1998 QE2 and its (as yet unnamed) moon
(Image courtesy NASA)

Known as 1998 QE2 (after the year and the order in which it was discovered), this beauty is about one-ninth as large as the impactor that created the Chicxulub crater and had a role in changing the dinosaurs from the Earth’s dominant species to stars of Saturday morning kid’s television. But it is still large enough to do serious damage if it landed on Earth; if it hit land, it would make a crater 17 miles across and devastate an area about the size of Virginia (the moon is only large enough to destroy DC). Fortunately, neither it nor its moon will be staying. They’ll buzz by and head back out to deep space, not to be seen again for two hundred years.

If you’d like to see the asteroid for yourself during this close encounter of the lithologic kind, then you have two choices. You can pull out a pair of decent binoculars and scan the skies, but you’ll need patience and a bit of luck to see it. Large as it is, the asteroid will still be fainter than the dimmest stars visible with the naked eye. Or you can watch one of the watch parties. NASA and the White House will host a Google hangout tomorrow from 2-3 PM, and the Slooh SpaceCamera will show the approach live.

Good luck!