Mercurial Musings

For the first time since 1975, a manmade spacecraft is surveying the innermost planet of our Solar System.

MESSENGER, which stands for "MErcury Surface, Space ENvironment, GEochemistry, and Ranging," left Earth's surface back in 2004 and took the long way round the inner Solar System before reaching its final destination on March 17th, 2011. And when I say "long," I mean 4.9 billion miles long. The full route consists of multiple flybys of Earth, Venus, and Mercury itself, as visualized in this animation. (For a more detailed discussion of gravitational assists, see my previous post on MESSENGER here.)

Now, almost eight years later, MESSENGER has settled into its new home and will begin taking data next week. The spacecraft's primary mission is to look for answers to such questions as: Why is Mercury so dense? What is the nature of Mercury's magnetic field? And what is the structure of Mercury's core?

Of the terrestrial planets in our Solar System, Mercury is by far the smallest and densest. Its surface is extremely old and undergoes daily temperature swings of over 1000 degrees. And its also the least explored. The better we can understand how Mercury formed and evolved, the better we can understand the conditions during the formation of our Solar System -- and our Earth.

Designing, building, and operating MESSENGER is no small feat. Neither is launching a sophisticated chunk of electronics into space and maneuvering it through the solar neighborhood. The scientists and engineers who got it there deserved to be celebrated. As does our desire to explore.

(Image credit: http://www.nasa.gov/mission_pages/messenger/main/index.html)

The Starry Messenger

The universality of the sky was revealed to me last night.

It started simply enough. Dinner in the valley with my godparents, a typical Saturday evening in August. Given the size of the valley and the small social circles, it's common to run into several friends and families at any given event, and this time was no different. The couples at the table outside, the family at the table next to us and the one next to that, and the neighbors at the table in the far corner, all known to my godparents and after tonight known to me as well. But one of these introductions was to mean more than the others.

The house up the hill from my godparents belongs to a couple who open their home to most of the valley each year when they honor their patriarch. I have vague memories of attending these fetes as a young child and sporadic ones as an adolescent, which came flooding back to me as I was walking into the house for this year's celebration. This particular summer I had come to know two of the three now full grown children in the family so I was especially excited to attend. In between the cocktail chaos and the bustling buffet though, I never came across the third and eldest daughter and her husband...until Saturday night.

As I am introduced to the husband I find myself volunteered and volunteering to set up a telescope for the family, which the aforementioned patriarch has just purchased for their mountain house. I worry a little to myself that my academic qualifications may not translate directly into telescopic proficiency, but being an engineer in a former life and a tinkerer by birth, I can't wait to get my hands on the shiny new toy.

Late Sunday afternoon, I head up the hill to report for duty. Within an hour the hardware is assembled, but due to a lack of batteries, we cannot test the AutoStar function which is where all the fun is - once the telescope is calibrated to a location, it can automatically slew to any number of celestial targets. Instead, I am made an offer that I cannot refuse: drinks and dinner on the porch on a future and hopefully clear night in exchange for returning to help with the remaining set-up. I return home and immediately look up the weather forecast; it's my last week in the valley and I pray that there will be at least one clear night. Tuesday jumps out at me. I check multiple weather websites, and they corroborate the first - Tuesday looks perfect.

Tuesday morning I awake to blue skies and bright sunshine, just the kind of day that makes you never want to leave the valley. As I am going about the online portion of my day, a friend tells me to check out Google's home page - it's familiar logo is composed of telescopes in honor of Galileo Galilei. Unbeknownst to me, it is exactly 400 years to the day after Galileo first unveiled his telescope to Venetian lawmakers. His intention at the time may have been to sell the instrument to merchants for use at sea or in trade, but I have no doubt he had already turned his to the sky. Less than six months later, he would publish his first telescopic astronomical observations in a brief treatise he titled Sidereus Nuncius, or Starry Messenger.

Now across time and space, from a stone patio on the side of a mountain, I find myself looking at the very same sky that Galileo first explored, low those many years ago. The telescope has been calibrated and aligned and it is asking us to choose an object. The Milky Way brilliantly spills across the sky directly overhead with the Summer Triangle practically at the zenith. The Big Dipper is hiding behind the pine trees lining the driveway. An occasional shooting star flashes in and out of view. Unanimously, the dinner party demands a closer look at the exceptionally bright object rising in the southeast from behind the house: Jupiter. Upon acquiring its target, the telescope reveals the exact picture that Galileo once set his sights on. His discovery of four small satellites orbiting Jupiter was what prompted him to question to the principles of Aristotelian Cosmology that required the orbits of all heavenly bodies to be centered on the Earth.

The telescope we are using is not terribly more powerful than Galileo's original one. And the sky has only changed imperceptibly since his time. Standing there with my eye glued to the eyepiece and Jupiter and its four Galilean Moons sliding across my field of view, I feel a sense of connection to Galileo, the Earth, and the cosmos stronger than I've ever felt before. Contrary to many people's reaction to the vastness of space and time, I feel all the more special and privileged to be a part of something universal, in all senses of the word.

What You Missed v. What Missed You

Wow, that was close!

Did you see that?!?

There was not one, but two, near misses in the inner solar system last week. Asteroid TU24 buzzed by Earth last Tuesday while Asteroid WD5 just missed Mars on Wednesday. Who knew there was so much traffic amongst the planets?!

The Minor Planet Center (MPC) knew. They know a lot. They operate from the Smithsonian Astrophysical Observatory (SAO) under the auspices of the International Astronomical Union (IAU). They are responsible for naming, compiling, checking, and making available all data related to minor bodies in the solar system. These include all natural satellites (moons), asteroids, centaurs, Trans-Neptunian/Kuiper Belt objects, and comets. Traditionally asteroids are small rocky bodies that collectively occupy and define the asteroid belt, the region between the orbits of Mars and Jupiter. It is thought that there are close to two million asteroids in the solar system above 1 km in diameter. (For reference the smallest moon in the solar system is Mars' second moon, Deimos, which is only seven miles in diameter). This number is only an estimate because due to their small size and composition, asteroids are inherently hard to detect. 

To be visible through a telescope, even a very powerful one, an object must reflect a fairly large amount of sunlight. The larger the object, the more light it reflects. And the more light it reflects, the farther away you can see it. The same is true when you drive on a dark road at night; the larger and more reflective an object on the road is, the better and the earlier you will see it in your headlights. Asteroids typically have an albedo, or reflectivity, of less than 5%, meaning they reflect less than 5% of the sunlight that hits them, much like fresh asphalt. This is what makes them so hard to see.

The term asteroid is Greek for "star-like" and the first asteroid, Ceres, was discovered in 1801. The discovery of their numbers was slow at first until computerized methods were developed late last century. At first, they weren't of much interest to astronomers - some even termed them "vermin of the skies" - but when asteroids with orbits very near to Earth began to be discovered, the potential threat of an Earth impact caused astronomers to take notice. With the 1994 and crash of Comet Shoemaker-Levy into Jupiter and the increasing acceptance of the proposal that an asteroid impact may have caused the Cretaceous-Tertiary extinction, the threat became real. Now everyone is paying attention and each new discovery of a near-Earth object (NEO) brings with it both the hype and the fear that this may be the big one. One day that may be the case (that's a topic for another post), but today NASA's Near-Earth Object Program Office has it all under control.

Asteroids TU24 and WD5 were discovered by the Catalina Sky Survey on October 11th and November 20th, 2007, respectively, but merely seeing an asteroid once means nothing. For astronomers to properly calculate its physical properties such as size, mass, composition, rotation, and orbit, an asteroid must be observed multiple - the more, the better. Of these, size and orbit matter most when a potential collision with Earth is at stake. Multiple observations over consecutive nights enable astronomers to see how the light reflected by the asteroid changes, thereby helping them to estimate its overall shape and size. Tracking its path with respect to background stars gives a measure of its distance from Earth and its orbital path. Taken together, these parameters help astronomers to determine whether or not the asteroid is likely to pose a danger to us or not. Potentially hazardous asteroids whose orbits bring them close to Earth or across our orbital path are put on a watch list and are continually monitored by telescopes and observers all over the world. As a result of detailed follow-up observations of Asteroids TU24 and WD5 we now know much more about them.

Meet Asteroid TU24:


This sequence of images was taken by the Goldstone Solar System Radar Telescope out in the Mojave Desert, over the course of a few hours. Though the resolution isn't great, about 20-meters per pixel, the shift of the brightest spot in each image clearly shows how the asteroid is rotating. These images also allowed astronomers to refine their estimate of the asteroid's size to approximately 800 feet (250 meters) in diameter, or about the length of one and a half cross-town blocks in Manhattan. In the end, TU24 passed us at the safe distance of 0.003 astronomical units - 1.4 times this distance to the moon - roughly 334,000 miles. Twelve hours before this closest approach, the Arecibo and Green Bank radio telescopes were able to get this snazzy image.


And now for Asteroid WD5:

This one is a bit camera shy, and so with fewer observations, less is known about it. But the most important detail - that it would not hit Earth - was thankfully confirmed. Mars was a different story though. It was given 1 in 75 odds to brace for impact, an exceptionally high probability when astronomers primarily deal with one in a million and one in a billion statistics. Still, that's almost a 99% chance of WD5 missing Mars completely. The asteroid's orbit skims close to Earth's orbital path (long after we had been there) and continues on to intersect Mars', as illustrated in this diagram released by NASA in mid-December.


To determine if Mars and WD5 would both reach the same point in space at the same time, astronomers additional observations were required to accurately measure the asteroid's speed. Upper limits estimated WD5 to be traveling 13-and-a-half kilometers per second which still left some uncertainty as to whether or not a collision with Mars was inevitable. This animation (click to play) shows how that uncertainty factors in to where the asteroid is likely to pass across Mars' orbit.


While both Earth and Mars escaped the events of last week unscathed, near Earth objects are an actual concern that might one day pose a true danger. As of today, the inner solar system looks like this...


The Minor Planet Center updates this plot daily and it's hard not to look at it and realize that the statistics may not be in our favor in the long run.

(Photo credits: Credit: Arecibo/Green Bank, NASA/JPL-Caltech, Gareth Williams/Minor Planet Center)

Playing with Mercury

No, not the quicksilver kind. That will make you batty. I'm talking about the planet Mercury. NASA has a playdate with the first rock from the Sun coming up on Monday the 14th, its first in more than 30 years. The spacecraft MESSENGER (an acronym for a mouthful called MErcury Surface, Space ENvironment, Geochemistry, and Ranging) will flyby Mercury on Monday on its way to eventually going into orbit around the planet in 2011. Why isn't it going into orbit now instead of doing a flyby of its supposed target you may ask? Welcome to the world of gravity assists. You may think that gravity always keeps your feet on the ground, but in the case of cruising through the Solar System, it can also give you a swift kick in the pants, metaphorically speaking of course.


Since its launch on August 3. 2004, MESSENGER has rendezvoused with Earth once and Venus twice. After dashing past Mercury on Monday, it will fly by the planet three more times over the next four years before finally dropping in to orbit it once and for all. While this sounds like a long and winding road all over the inner Solar System (and it is), believe it or not, it is also the most efficient and therefore the cheapest route.

In the wonderful world of space flight, human or otherwise, to maneuver in space you need rockets, and rockets need fuel. Naturally, fuel for these rockets has to be stored on board the spacecraft as there are no gas stations after launch. There are warning signs at Cape Canaveral: No Gas - Next Gazillion Bagillion Miles. And just as gravity keeps your feet firmly on the ground, gravity tries its utmost to keep launch vehicles from leaving the Earth, and once in space, gravity is everywhere, despite any rumors of zero-g you may have heard.

At launch, we overcome gravity with fully fueled rocket engines. The majority of fuel on any space bound vehicle is used up during launch and most of the weight of the payload can be attributed to fuel as well; over 55% of MESSENGER's launch weight was due to propellant. This is what keeps long distance space travel just out of reach for us humans: to pack enough sustenance and fuel for the journey, you need to use even more fuel to start the journey - this becomes a runaway process resulting in an overweight space transport system that can't get its butt of the ground. Once in space, we again overcome gravity with rocket engines to keep us on course. Vehicles sent out of Earth's orbit are tugged on by every other object in our Solar System, some more than others. Naturally, the Sun is usually the winner in this case, but the other planets, especially Jupiter, always want a piece of the action. Therefore, traveling in a straight line from Earth to Mercury is a bit of a challenge, from both a mathematical and a fuel standpoint. And we haven't even gotten to the fact that Mercury is a moving target to say the least, orbiting around the Sun roughly once every three months. Unmanned spacecraft don't share human sustenance requirements and aren't restricted to non-stop flights, so to speak. Therefore, they are free to wind their way around the Solar System, however long it takes to get them to their destinations.

For example, check out this animation of MESSENGER's circuitous route from Earth to Mercury:



Each time the spacecraft passes a planet, the path changes color - indicating that its orbit has been altered by the encounter and it has moved into a new orbit around the Sun. These are the gravity assists I spoke of at the beginning of the post. They enable the spacecraft to tweak its trajectory with minimal use of fuel, sometimes none at all. The engineers in mission control only have to ensure that the spacecraft approaches the planet just right (in speed and angle) for the necessary assist, and gravity does the rest. Severe changes require the spacecraft to brake, slow down, and come in close in order to be flung around by the planet's gravity, while high speed, high altitude flybys result in only slight changes of direction. However, as the animation reveals, sometimes only good old fashioned manual steering will do the trick and MESSENGER will do five deep space maneuvers to compliment the gravity assists it gets along the way to ensure it reaches its target.

Planet hopping is not an easy task. So keep your fingers crossed for Monday when MESSENGER comes within 125 miles of Mercury at the breakneck speed of 15,877 mph (that's 4.410 miles per second!). And stay tuned for the sequel next October when MESSENGER catches up with Mercury for the second time!

(Photo credits: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

Rudolph the Red Planet

Mars overload? Never.


The previous Mars posts were in reference the close pass between Earth and Mars which occurred on Monday night. However, orbital mechanics gives us something else to celebrate this holiday season. Earth, Mars, and the Sun will all align on Christmas Eve!

This particular configuration is called "opposition" as Mars will be directly opposite from the Sun with respect to Earth, or more simply Earth is directly between the Sun and Mars. For those of you who are uber keen, "conjunction" is the other time this alignment occurs, but with Mars on the far side of the Sun or the Sun directly between Earth and Mars. The diagram in Wednesday's post is actually more pertinent to this post as it illustrates the oppositions of Earth and Mars rather than their closest encounters. Jump back there for a look and then proceed on.

It's not easy to see in the diagram, but the elliptical orbits of the planets actually allow for their closest encounter and their opposition to occur separately. If all orbits were perfectly circular, the two events would be simultaneous and inseparable.

Let's step back a second, and discuss the geometry of the Solar System.

Each planet in the Solar System orbits the Sun in an elliptical orbit, as discovered by Johannes Kepler back in the day. As opposed to a circle, and ellipse has two 'centers' - termed foci - instead of one. For our Solar System, the elliptical orbits of the planets all have the Sun at one focus. But the orbit of each planet is elliptical in a different way; ellipses come in varying degrees of eccentricity, or distortion from circular. A circle is defined by an eccentricity of 0, while ellipses can have a range of eccentricities greater than 0 and less than 1. The more eccentric the orbit, the farther apart the two foci are. At an eccentricity of 1, the closed path of an ellipse breaks and becomes a parabola instead with the second focus at a distance of infinity. But that's a lesson for another day, back to Earth and Mars.

Earth's orbit is less eccentric than Mars' orbit, so the second focus of our elliptical path is closer to the Sun than the second focus for Mars. In the diagram this exaggerated to the point where Earth's orbit looks almost circular by comparison. This, combined with the oppositions plotted on the diagram, make it harder to see how the Earth can really be closer to Mars when the two aren't directly in line with the Sun, but this can be the case. Only once in much less than a blue moon will the two events occur at the same time. More often they will happen in succession as they do this year, with the closest encounter on Monday, December 18th and opposition on Monday, December 24th.

If you feel you are sinking into a geometrical quagmire, just take my work for it.

Whew, all that academic lead-up for what is hopefully still a worthwhile payoff...

The reason for this point being that in honor of this Christmas Eve spectacular, The New York Times ran an AP piece last week that proposed a cover version of "Rudolph the Red-Nosed Reindeer", with Mars as Santa's new best friend. Check out the lyrics in their entirety below and the full article here. Feel free to sing along!

Mars is a red-tinged planet
With a very shiny glow
And if you look to see it
You will find the moon in tow.

All of the other Yuletides
Santa would have at his side
The shiny nose of Rudolph
Acting as his big sleigh's guide

But this very Christmas Eve
Santa came to say:
''Rudolph, now with Mars so bright,
You can stay at home tonight.''

Then all the reindeer teased him.
And they shouted out with glee:
''Rudolph, the red-nosed reindeer
Outsourced to astronomy.''

Mars Returns

A follow up post to yesterday's, but with a bit more detail about what's happening with Mars and why - for those of you looking to expand your science literacy (and your minds).

The biannual date between Mars and Earth happens because both planets take a different amount of time to orbit the Sun. Earth takes 365+ days and Mars takes approximately 687 days. Therefore, Earth moves faster in it's orbit and gradually "laps" Mars in the race around the Sun. The approach and subsequent passing of Mars is what occurs every two years. However, not every meeting generates such great views of the Red Planet.

As mentioned in the previous post, both planets have elliptical orbits and as such, this complicates the occurrence of these close encounters. The diagram below best illustrates what's going on here. It show how two elliptical orbits have a point where their paths come closest together and where they are farthest apart. Also shown in the diagram, to an exaggerated effect, is that Mars' orbit is more eccentric than Earth's, i.e. it's orbit is more elliptical and in fact over five times more so. If you combine this with the different speeds of each planet in their orbit, they won't always be nearest to each other at the same point in space each time Earth is about to lap Mars.


You may or may not recall a huge fuss about Mars from 2003. This was because Earth lapped Mars that year very close to the point where their orbits are the closest they ever get, approximately 34.6 million miles. This happens roughly every 15-17 years as the lapping point precesses around the Sun over time; it takes 15-17 years to occur back at the same point in space. Each biannual meeting of the planets since a closest encounter like in 2003 will produce less and less spectacular viewing opportunities of the Red Planet until the lapping point comes around again. However, while the planets are still within a certain range of each other, the viewing can still be quite exciting. After this we will have to wait another nine years before the fun begins anew. Compared to 2003, Mars will be 20 million miles farther away this year, at a distance of 55 million miles as Earth overtakes it. But surprisingly, 20 million miles makes less of a difference than you might think. There is still a good show to be had.

(photo credit: Our Dark Skies, http://www.ourdarkskies.com)

Close Encounters of the Mars Kind

At 11:45pm tonight, Mars and Earth will be the closest they've been since October 2005. This planetary rendezvous is due to the elliptical orbits of both planets around the Sun and the point at which these two ellipses are nearest to each other. It happens once every two years for Mars and Earth and it's tonight!

So wrap yourself up in your warmest winter coat(s) and get your bum outside to check it out. No excuses for even you city dwellers as Mars easily outshines any urban light pollution (except for maybe in Times Square) and is well above the horizon. It can be best seen looking south in the middle of the night, moving westward till dawn. And with its red-orange color and steady glow, it is also larger than any star you're used to seeing in the sky - in fact, it is 1/100th the size of the full moon. That may not sound like much, but I assure you it's enough to grab your attention. For reference the full moon takes up half a degree of the sky and a typical star in the night sky is on average less than 1/1000th of the the full moon. So Mars is over 10 times bigger than the stars you are used to seeing! And to put it all in perspective, as many of you may know from seeing Apollo 13, the size of the full moon is comparable to the width of your thumb at arms length. You could say then that Mars is 1/100th the width of your thumb, but that's besides the point.

It's big, it's bright, it's red, and it's awesome.

(photo credits: NASA and the Hubble Space Telescope)

My Fifteen Minutes

In reference to the previous post, I actually first heard about the dent in the solar system on my favorite podcast, The Bryant Park Project. The BPP is a new morning show on NPR with a fresher, hipper vibe, and as such it's hosted by the absolutely awesome duo of Luke Burbank and Alison Stewart. Some of you may remember Alison from MTV Choose or Lose fame. I listen to the BPP podcast every weekday morning over here to keep me entertained, informed, and connected to the homeland. If you are at all inclined to listen to NPR but you still like your radio a little funky, you must check out the BPP.

So on the broadcast for Wednesday morning (which I was listening to on my Thursday morning), one of the newscasters, Korva Coleman, brought up the story of the dent in the solar system. Only problem is, she kept referring to it as the dent in the universe. Being the astute listener and astrophysicist that I am, I immediately took offense to this and was compelled to email the show and say as much! I then went on with my day.

To my surprise, around 2pm, I received an email from Korva Coleman herself with the best. subject. line. ever. - "sorry about the universe". Not only did she get my comment and correct the mistake on air, but best of all, she gave me a shout out during the broadcast for bringing the matter to her attention. I MUST find a way to isolate that segment of the podcast to post later! It is the greatest fifteen seconds of my astrophysics career to date. And for that, the BPP is totally getting an acknowledgment in my thesis.

How Did That Dent Get There?

Second digression of the day, but this time relate to astrophysics, is the news that the two Voyager spacecraft, launched in 1977 mind you, have both now passed through the heliopause. This is the somewhat fluid boundary between the edge of our solar system as defined by the meeting of the solar wind with the interstellar medium in our neighborhood of the Milky Way.

Think of it like this...

The sun generates energy in the form of radiation that blasts out into space in all directions (like an expanding sphere or bubble with the sun, and with it the solar system, at its center). But our solar system is surrounded by other stars and gas and dust in our galaxy. So the outward expansion of the bubble created by our sun burning is balanced at somepoint by the pressure from not only all the other bubbles around stars in our neighborhood, but also from the existence of gas and dust between the stars in our galaxy (the aforementioned interstellar medium). The balancing point between these two forces is termed the heliopause, helio for sun and pause as in break.

The scientific result of this event is that the two Voyager spacecraft left our solar system, crossing the heliopause at two different points of the bubble. They have since reported back to us and it turns out that our bubble is dented! Have a read if you want to know more:

Scientists find the dent in our solar system
http://www.msnbc.msn.com/id/22186054/

(photo credit: Opher et al. 2006, 2006AIPC..858...45O)