0 comments on “M is for (exo)Moons”

M is for (exo)Moons

By Jonathan Farrow of the Thoughtful Pharaoh

With this post, rising-ape.com is now caught up with my website, thoughfulpharaoh.  From now on, I will be posting articles simultaneously on both sites, on Wednesdays.

Thanks to everyone for following along and as always, if there is a topic you have in mind, don’t hesitate to leave a comment below.

And now for this week’s article: exomoons.

There are 8 planets in our Solar System (sorry Pluto). ¬†Most of these planets have companions that follow them around, like obedient pets and criminal records. ¬†The total count of these moons is 181. ¬†We are all quite familiar with the big shiny one that orbits Earth (that may or may not be made of cheese), but what many people don’t know is the sheer number of¬†other¬†moons that exist in our Solar system.

Just like planets, these moons come in all different shapes and sizes. ¬†S/2009 S1 is only 400m across and orbits in one of Saturn’s rings, making it the very smallest moon. ¬†Ganymede, the solar system’s largest moon, measures in at about 5300km across, almost half the size of earth.

One of the biggest findings to come from¬†the Kepler mission is that most of the stars in the galaxy have planets. ¬†In other words, our solar system isn’t unique. ¬†That means our Solar System probably isn’t the only whose planets have moons. ¬†If our system, with 22 times more moons than planets, is any indication, there are a lot of moons to find.

This presents two immediate problems: firstly, why should we want to find them?  Secondly, how do we go about finding them?

Why find an exomoon?

The same thing that makes seawater rise and fall twice a day, tidal forces, can heat up a moon.  Tides are a result of the fact that the strength of the force of gravity is related to the distance between two objects.  On Earth, the water on the side close to the moon gets pulled out towards the moon stronger than the water on the other side, this creates bulges of water that move around as the earth spins: tides.

Tides stretch.  Image by Krishnavedala
Tides stretch. Image by Krishnavedala

The Earth is too small and our moon is too far away for much more than sea level change to happen, but Io, one of Jupiter’s moons, has over 400 active volcanoes¬†caused by extreme tides from the gravity of its host planet Jupiter. In this case, it’s not just bulges of water that are created, but bulges in the crust of the moon itself. ¬†This creates an immense amount of friction and heat.¬†Europa, another moon of Jupiter, gets enough energy to keep a planet-wide ocean of water liquid¬†under its icy crust. ¬†Some people think Europa might be habitable, even though it is so far away from the Sun.

If there are moons here in our Solar System that can be habitable at Jupiter-like distances,¬†there could be moons in other systems that orbit planets much closer, at Earth- or Mars-like distances. ¬†Some people, like Rene Heller at¬†McMaster University’s Origins Institute (a fine institution, if I do say so mystelf *full disclosure: I did my undergrad¬†there*), think exomoons might be our best shot for finding habitable places in the galaxy simply because of their abundance relative to planets (remember, there are 22 times more moons in our system than planets).

How to find an exomoon

This is the tricky part. ¬†It was hard enough finding exoplanets. Finding a transiting exoplanet is often compared to looking for the effect of a mosquito passing in front of a car’s headlight. ¬†In that analogy, finding an exomoon would be like finding out how many legs it has. ¬†No easy task.

It’s not impossible, though. ¬†Moons do have effects on their planets and if we look carefully enough, we can find them.

One way to find exomoons in transit data takes advantage of the fact that, viewed edge-on, a moon will appear more often at the edges of its orbit.

ExoMoonTransit
Image by Rene Heller

If you capture many transits over time, you can begin to see these wingtips in the transit data.

Image by Rene Heller
Image by Rene Heller

The grayscale bar in the image above represents the average effect of a moon orbiting a planet.  What astronomers can look for in the transit data is a preliminary dip (1) that starts off severe then levels off, followed by the regular planetary transit (2), followed by another characteristic dip (3) as the other wingtip passes in front of the star.

This method only works if you have a lot of data, but luckily Kepler was operational for four years and gathered just the right kind of data.

So now the search will begin. ¬†Who will find the first exomoon? ¬†And what if it turns out to be “no moon” at all?

An artist's impresison of a view from an exomoon with a triple star system.  Far out, dude.  Image by NASA/JPL-Caltech
An artist’s impresison of a view from an exomoon with a triple star system. Far out, dude. Image by NASA/JPL-Caltech
0 comments on “K is for Kepler”

K is for Kepler

“Truth is the daughter of time, and I feel no shame in being her midwife.”¬†Johannes Kepler

These words, written by Johannes Kepler in 1611, are profound.  At the time, Galileo had just discovered the Galilean moons (including Europa) in Florence but was being persecuted for his belief that the Earth orbits the sun.  Kepler, a staunch supporter of heliocentrism, was working as the Imperial Mathematician in Prague.  When word that Galileo had used a telescope to find the moons reached Kepler, he was so fascinated and impressed that he wrote an enthusiastic letter of support and scrawled that pithy aphorism.

While Kepler enjoyed some social status as Imperial Mathematician and was much more free to contradict Aristotle¬†than his Italian counterparts, his life was by no means a charmed one. ¬†The son of “an immoral, rough and quarrelsome soldier” (his own words), Kepler managed to carve himself a place in history¬†based on his skill as a mathematician and astronomer. ¬†He kept on working through many family disasters, including the deaths of his wife and his seven year old son and a witch trial about his mother.

Kepler was a devout Christian and grew up Lutheran but was excommunicated due to his rejection of the Augsburg Confession.  This left him neither a Lutheran nor a Catholic and between sides when the Thirty Years War broke out in 1618.

You've got to love that frilly collar.  Just like Shakespeare!  Actually, come to think of it, Kepler actually lived at the exact same time as Shakespeare.  I wonder if they ever met and what they might say to each other at a dinner party.  Image is public domain.
You’ve got to love that frilly collar. Just like Shakespeare! Actually, come to think of it, Kepler lived at the same time as Shakespeare. I wonder if they ever met and what they might say to each other at a dinner party. Image is public domain.

Despite all of this, Kepler revolutionized astronomy by formulating mathematical laws that accurately describe the motions of the planets. ¬†These are still taught in astronomy today and are called Kepler’s Laws.

The first law is that planets orbit in ellipses with the sun at one focus.  Before Kepler, most Western astronomers modelled the orbits of planets as circles and had to invoke a strange concepts like epicycles and equant points.

1. Planets orbit in ellipses, not circles.
1. Planets orbit in ellipses, not circles.  Image my own

The second law is that a line between a planet and a star will sweep out equal area in equal time. In other words, planets move faster when they are closer to their star and slower when they are further away.  This law is better understood with a diagram:

asd
2. Planets don’t have constant speed ¬†Image by RJHall

The third law, formulated after the first two, is that the time it takes a planet to make an orbit (orbital period) is directly proportional to its distance from the star.  This law allows astronomers to calculate how far a planet is from its star based only on information about the length of its year and the mass of the star.  Remember this one, because it will become important later.

As you can see, Kepler’s Laws are fundamental to our understanding of how planets move, or orbital dynamics. ¬†It will come as no surprise then that every young astronomer is all too familiar with Kepler’s laws. ¬†This isn’t the only reason he’s familiar though. ¬†He is also shares a name with the most successful exoplanet hunter the world has ever produced. ¬†The Kepler Space Telescope.

Kepler: Planet Hunter is kind of Like Abraham Lincoln: Vampire Hunter.  Except more real.  And frankly, a little more impressive.    Image by Wendy Stenzel at NASA
Kepler: Planet Hunter is kind of like Abraham Lincoln: Vampire Hunter. Except more real. And frankly, a little more impressive. Image by Wendy Stenzel at NASA

Launched in 2009, the Kepler Space Telescope used 42 image sensors to continuously observe over 145,000 stars. ¬†Unlike a lot of other telescopes that try to take magnified images, Kepler wasn’t interested in images. ¬†It wanted accurate data on brightness. ¬†It basically had a staring contest with these 145,000+ stars, waiting for them to blink. ¬†I say blink because Kepler was waiting for the brightness to go down and back up. ¬†The brightness of stars can vary for all sorts of reasons, but planets passing in front of their stars make the brightness dip in a particular way. ¬†This dip is called a transit and finding transits¬†was Kepler’s mission.

When a transit occurs, the size of the brightness dip corresponds to the size of the planet and the length of the dip corresponds to the time it takes a planet to orbit (as well as the size of the star). ¬†Remembering Kepler’s third law,¬†¬†if we know the time it takes to orbit, we can figure out the distance to the star. ¬†And if we know the brightness of a star and the distance, we can figure out how much energy¬†the planet receives. ¬†Plug all that in to a¬†simple(ish)¬†equation, and out pops temperature.

Stars, just like planets and people, come in all different shapes and sizes.  That means light curves also vary widely.   Image from Planethunters.org
Stars, just like planets and people, come in all different shapes and sizes. That means light curves also vary widely. Image from Planethunters.org, a great citizen science project that combines people’s natural pattern-finding ability with Kepler data to find planets.

So thanks to the Keplers (both Johannes and the Space Telescope) we can start to look for alien worlds that have temperatures similar to the ones we find here.  The hope is that one day we will find evidence of life on another planet.  And then we can begin our transition into any one of several sci-fi galactic civilizations (my personal favourite is Foundation, but some people prefer Star Wars, Star Trek, or Eve Online).

Unfortunately, in May 2013 one of the components that kept Kepler (the telescope) stable failed, meaning the mission was apparently over.  The mission had been hugely successful, discovering over 1000 confirmed planets, with 4000 other planet candidates waiting to be confirmed.  It turns out that most stars probably have planets and that a lot of planets in the galaxy might be the right temperature to be habitable.

Astronomers are nothing if not persistent though, so an ingenious method was devised to make sure Kepler can continue observing even without its stabilizer.  This new mission, dubbed K2, uses the radiation pressure from the sun itself to balance the telescope.  Instead of continuously observing the same 145 000 stars, K2s targets will change periodically as it orbits the sun.  There will be far less data coming down, but as of this writing four new planets have already been found since K2 began in earnest in June 2014.

There's a lot of information there, but I think the most impressive bit is that K2 is metaphorically balancing a pencil on a fingertip, remotely, from 150 million km away.  Image by NASA
There’s a lot of information there, but I think the most impressive bit is that K2 is metaphorically balancing a pencil on a fingertip, remotely, from 150 million km away. Image by NASA

Currently, while there are all sorts of really interesting exoplanets out there (from hot jupiters like 51 peg b to mirror earths like Kepler-438b), we have yet to find signs of life.  But I think that before too long, we will.  Just as the truth of heliocentrism eventually came out thanks to Kepler, a telescope with his name will be instrumental in uncovering the truth of life elsewhere in the universe.  Just like he said,

“Truth is the daughter of time, and I¬†feel no shame in being her midwife” Johannes Kepler

0 comments on “J is for Jupiter’s Great Red Spot”

J is for Jupiter’s Great Red Spot

By Jonathan Farrow from the Thoughtful Pharaoh

If you look up in the night’s sky and point even a simple pair of binoculars at Jupiter, like Galileo did with a rudimentary telescope 405 years ago, you will see what he did: a reddish-pink planet with swirling masses of clouds. These clouds are beautiful in their own right, but there is one particular feature that has drawn the eyes and the fascination of people for over four centuries. The Great Red Spot.

This swirling, gurgling red super-storm could fit three earths inside of it and has been raging on the gas giant ever since we’ve been keeping records. How it has lasted for so long and why it has such a different colour has long been a mystery.

In 2000, on the way to Saturn, an ESA mission called Cassini aimed to give us some clues when it flew within 9.7 million kilometres of Jupiter and looked more closely at the spot than we had ever done before or since. 9.7 million kilometres sounds like a lot, but consider that is only about 1% of the distance between Jupiter and Saturn. (As a side note, did you know that Jupiter and Saturn are further away from each other than Jupiter and Earth? I didn’t!).

It might have looked kind of like this, but with Jupiter instead of Saturn in the background.  Cassini's main mission was to Saturn and its moons.
It might have looked kind of like this, but with Jupiter instead of Saturn in the background. Cassini’s main mission was to study Saturn and its moons. ¬†Image by NASA

With its flyby, Cassini found out that the clouds that form the spot are up to eight kilometres higher than the surrounding clouds and started to understand the chemical composition of the clouds.

14 years later, in November 2014, NASA scientists released results that combine data from the Cassini flyby with lab experiments on Earth. They showed that the colour must come from the interaction of ultraviolet (UV) light from the sun and the ammonia and acetylene in the top layers of the storm. Once the red particles are produced, they are trapped by the circular winds of the storm. This overturns the previous theory that it was the bottom clouds which provided the colour. The NASA scientists compare the colour of the storm to a sunburn rather than a blush.

So, thanks to NASA and the Cassini mission, we have a better idea about how the spot gets its colour, but last spring the astronomy world was in a tizzy because news came that the spot has been shrinking.

That's some pretty serious shrinkage!
That’s some pretty serious shrinkage! ¬†Image by NASA

Since it is so noticeable, the storm has been recorded as far back as the 1800s, when it was believed to be about 41000 km across (roughly equal to the circumference of Earth).  The most recent image, from 2014, puts the size at only 16500 km (less than the length of the great wall of China).  Not only is it much smaller than it used to be, but the rate of shrinkage is increasing.

Totally, 100% peer-reviewed, recollection of secondary school math to figure out when the spot will disappear.
Totally 100% peer-reviewed recollection of secondary school math to figure out when the spot will disappear.  Image my own

If my calculations are correct, and if the storm keeps shrinking the way it has been, it will disappear entirely in about 35 years, in 2059.  That means we may be among the last people to ever see the spot that Galileo spied on that fateful night in 1610.

Instead of relying on me and my calculations, however, NASA sent a spacecraft to go investigate.  Juno left in 2011 and by now is more than halfway to its destination. When it arrives in July 2016, Juno will study the gas giant in a variety of ways and hopefully get the bottom of this whole shrinking storm mystery.

JUNO
Image by NASA
0 comments on “G is for Gravity Waves”

G is for Gravity Waves

By Jonathan Farrow from the Thoughtful Pharaoh

Deep in Antarctica, right on top of the geographic South Pole, there is a research station that peers back in time to the very beginning of our universe. Named the Amundsen-Scott Station, it is home to instruments such as the creatively named South Pole Telescope (SPT), the Keck Array, and the BICEP experiments.

The temperature is currently sitting at about -30C and it’s the height of summer. ¬†The sun won’t set at the station until March 23rd and once it sets, it won’t rise again until September. ¬†So why the heck (or, one might say…Keck)¬†would we build an observatory there?

Because the temperature is so low and the altitude is so high (2743m) at the South Pole, the air is thin and dry, reducing blurriness normally caused by¬†the atmosphere. ¬†There are no cities nearby to cause light pollution and there are months of nonstop night, allowing for¬†continuous observation. ¬†It’s an astronomer’s dream. ¬†Except the nearly-constant -30C temperatures. ¬†And the remoteness. ¬†But otherwise, dreamlike.

Damn that looks cold! Photo from 2003
The perfect place to set up a top-secret laboratory from which to take over the world!… I mean… uh… from which to observe the beginnings of the universe. ¬†Yeah, that’s what we’re doing. ¬†Definitely that. ¬†Image credit: NASA

So what are astronomers looking for all the way down there at the end of the world? ¬†They are searching for clues as to how the universe started. ¬†Ever heard of the Big Bang Theory? ¬†No, not these clowns, the theory about the beginnings of the universe. Although, come to think of it, the theory is actually pretty well summed up by the first line of the Barenaked Ladies’ theme song to the Big Bang Theory (yes, those clowns):

Our whole universe was in a hot dense state,
Then nearly fourteen billion years ago expansion started. Wait…

That’s really the core of the¬†theory: ¬†everything used to be really hot and dense and now its¬†not. ¬†What happened in between is what the astronomers at the South Pole are trying to figure out.

History of Universe
For a bit of a primer on this diagram, check out A Short History of (The Universe), an essay I wrote which introduces the origins of the universe.  Image by NASA

Astronomy is awesome because when we look up, we are actually looking back in time. ¬†The distances involved are so great that it can take years (or billions of years) for light to reach us. ¬†So, what if we just looked as far as we could, wouldn’t we be able to see the Big Bang happening? ¬†What would that even look like?

Unfortunately, because everything was so hot and dense right at the start of the universe, nothing could stick together so the universe was just a soup of energetic particles.  Any light that was emitted was bounced around like the light from a flashlight in thick fog.  About 380 000 years after the Big Bang , the universe had cooled and expanded enough to let atoms form and collect electrons.  Atoms are mostly empty space, which means that unless they are packed very close together like in a solid or liquid, they are transparent.  What resulted was light spreading pretty evenly throughout the universe, starting 13.7996 billion years ago.  This is what is called the Cosmic Microwave Background Radiation (CMBR).  Cosmic because it comes from space, Microwave because it has lost a lot of energy since the Big Bang and is now only 2.7 degrees above absolute zero, Background because it is there no matter which direction you look, and Radiation because it is light.

WMAP
A map of the Cosmic Microwave Background Radiation. The different colours represent slight anomalies (about 10^-5 degrees C difference). Red is a little bit hotter, dark blue is a little bit colder.  Image by NASA

So, no matter how far you try to look, this map is all that you see.  It is all that can be seen because it is the oldest light that escaped.  Sounds kind of disappointing, but astronomers think that that image (what some refer to as the baby picture of the universe) holds clues to what happened before.

If there was inflation, faster-than-light expansion of space and time (again, check out my essay on the history of the universe¬†if you’re confused), that process should have produced gravitational waves.

“Woah, woah, woah. ¬†Hold up. ¬†I understand gravity, apples falling on heads, etc etc… ¬†How the Keck could there be gravity¬†waves?”

One of Einstein’s key contributions to science was the understanding that space and time are¬†linked and that they are¬†influenced by mass. ¬†He described space-time as a fabric that could be warped by the presence of mass. ¬†All that¬†gravity is, he said, is the curvature of space-time around mass. ¬†A simplified way to understand this is by thinking of¬†space-time as a trampoline. ¬†If you put a mass on the trampoline, it will create a depression. ¬†The heavier the mass, the more extreme the depression. ¬†Now, if you have an extreme depression and move it very quickly back and forth, it will create waves in the same way that a moving hand in a pool will create waves. ¬†Astronomers think that inflation must have created gravity waves with a very specific signature. They also think that very heavy stars moving quickly, like binary neutrino stars, would create these gravitational waves.

Loooook into my gravity waaaaves.  You are not getting sleepy.  You are paying attention, commenting below, and sharing this with your friends.
Loooook into my gravity waaaaves. You are not getting sleepy. You are paying attention, commenting below, and sharing this with your friends.  Image by NASA

If (or, once they are discovered for sure, when) gravity waves pass through you, it is space itself which is expanding and contracting.  You are not moving, but as the wave passes through your arm, your arm will be closer to your body than it was before and time for it will move slower.

The thing about gravity, though, is that it is by far the weakest of the fundamental interactions (Electromagnetic, Weak, Strong being the other, stronger ones).  By a factor of about a nonillion (1 with 30 zeroes after it).  This makes the waves it creates very difficult to detect.  While your arm is probably having a taste of timelordery as you read this, there is no way you could possibly feel it.  Gravity waves are not interesting for how they make us feel, but rather for the challenge they present in detecting, for the possible confirmation of our current physical model, and for what they can tell us about the origin of the universe.

So let’s come back¬†back to the barren, frigid wasteland of Antarctica and the astronomers freezing their buns off for science. ¬†BICEP2, the second iteration of the¬†Background Imaging of Cosmic Extragalactic Polarization experiment, looked at the¬†CMBR and looked for patterns in the light. ¬†These patterns, called b-mode polarization, can be produced by gravity waves, but also by interstellar dust.

In order to cancel out the effect of dust, the BICEP2 team used data from Planck, a European satellite launched in 2009 with a very similar mission: to study the early universe. ¬†Whereas BICEP2 could only look at one particular wavelength with high sensitivity, Planck could look in a few different wavelengths but didn’t have quite as much sensitivity for these b-modes. ¬†Dust doesn’t leave the same polarization patterns in¬†light in¬†different wavelengths, so by comparing the results from different wavelengths from Planck, the BICEP2 team was able to show that the b-modes weren’t from dust and so had to be from gravity waves from the early universe. ¬†Proof of inflation! ¬†Proof of the standard model! A possible Nobel Prize!

./b_over_b_rect.eps
Those swirls are the b-mode polarization that astronomers were looking for. ¬†This diagram, while confusing as Keck (it’s going to catch on!) and quite complicated, was EVERYWHERE when the announcement was made. ¬†Image by BICEP2 team

So, understandably excited and with a positive result in hand, there was a big announcement at the Harvard-Smithsonian in March of last year.  Unfortunately, the data they used was preliminary.  In September, new data was released and the effect of dust seems to have been larger than they thought.  The team reduced the confidence in their findings but still stood by a significant result.  Just last month, in January 2015, another set of data was released that makes the BICEP2 findings inconclusive.

It seems the team jumped the gun a little bit, were blinded by the impact of their apparent discovery, and had too much confidence in preliminary data. The result of all this is that there is still no direct evidence of inflation or of gravitational waves and the teams at Planck and BICEP are going to work together now with the strengths of their instruments.  Within a few years, the effect of dust should be able to be cancelled out and we will be able to see whether we were right about the beginning of the universe.  And all the frostbite will have been worth it.