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New Horizons for Solar System Exploration: To Pluto and Beyond

To quote the late sci-fi author Douglas Adams, “Space is big, really big.  You just wouldn’t believe how hugely, vastly, mindbogglingly big space is.  You might think it’s a long way down the road to the chemist but that’s just peanuts to space.”  It takes a really long time to traverse the vast distance of even interplanetary space from Earth to Mars.  The recently deceased comet ISON spent the better part of a year travelling between Jupiter to the Sun before its demise in the Sun’s inferno.  Jupiter is roughly 778,000 kilometers from the Sun and Saturn is nearly twice that far away at 1.4 billion kilometers away.  Twice the distance from the Sun to Saturn is Uranus sitting a whopping 2.8 billion kilometers from the Sun.  Even further still is icy Neptune, so far away it’s existence was predicted before it was directly observed sits an incredible 4.8 billion kilometers from the Sun.  At this point in the solar system the Sun is nothing more than a small point of light almost appearing as just another background star in the Milky Way.  But the orbit of Neptune is just the seashore of the cosmic ocean that is our solar system.  Far beyond the orbit of Neptune lies a huge area known as the Kuiper Belt which is home to an unknown number of tiny icy worlds.  The most well-known of the Kuiper Belt objects (KBO) is the dwarf planet Pluto.  Until 2006 Pluto was recognized as the ninth planet in the solar system but was downgraded to dwarf planet when astronomers began discovering objects in its neighborhood that were both larger and smaller.  Pluto lies a mindbogglingly 5.8 billion kilometers from the Sun.  Together with its large moon Charon, Pluto marks the beginning of unexplored territory in our solar system.  No human spacecraft has ever visited Pluto.  Much of Pluto’s characteristics are unknown to us.  The same goes for all of the KBO’s in Pluto’s neighborhood.

Artists conception of New Horizons probe at Pluto

Artists conception of New Horizons probe at Pluto

NASA is on the verge of changing that.  The New Horizons spacecraft which was launched in January 2006 is just a year away from the beginning of its mission at Pluto.  New Horizons is travelling at about 1 million miles per day as it speeds into uncharted waters so to speak.  Currently approaching the orbit of Neptune, New Horizons is approximately 4 billion kilometers from the Sun.  The probe will arrive at its closest approach of Pluto on July 14, 2015 but the science will begin well before that in January 2015.  New Horizons is equipped with many instruments to help scientists analyze Pluto.  One such instrument is the Long Range Reconnaissance Imager (LORRI) which is essentially a long focal length telescope with a CCD imager to take high resolution images of the Plutonian surface beginning in January 2015.

An Historic Mission

Pluto is part of a vast unexplored trans-Neptune region of the solar system called the Kuiper Belt.  The inhabitants of the Kuiper Belt are thought to be the leftovers of planetary formation when rocky and icy bodies were being flung around the solar system.  These icy worlds didn’t quite form into full-fledged planets but they are worlds nonetheless.  Only five human spacecraft have ever traveled in this cold void before.  New Horizons is the first spacecraft to be sent to directly study a new body since the Voyager probes thirty years ago.  For my generation (milllennials) this is akin to the Apollo 11 moon landing in its scientific value.  I can’t think of any mission that is more important to the understanding of our solar system than New Horizons.

The unknown face of Pluto taken by Hubble.

The unknown face of Pluto taken by Hubble.

The Science

New Horizons will provide scientists with a smorgasbord of priceless data about Pluto and the KBO’s nearby.  Besides LORRI New Horizons is equipped with an ultraviolet spectrometer (ALICE) which will be used to analyze Pluto’s atmosphere, an optical/infrared instrument (RALPH) that will be used to create maps of the surfaces of Pluto and Charon, a particle detection instrument (PEPSSI) used to detect molecules escaping from the atmosphere, a particle instrument (SWAP) to measure the solar wind at Pluto, a radio instrument (REX) to observe the atmosphere and a student created instrument to collect dust particles that have traveled from the inner solar system.  The only thing we know about the surface of Pluto is from Hubble which provide a low resolution map that can only resolve surface features that are hundreds of kilometers in size.

One of the more interesting observations New Horizons will make is the study of Pluto’s atmosphere.  Pluto’s orbit is highly inclined to the ecliptic, the plane all the planets orbit in, and is highly eccentric (oval shaped).  This means that Pluto’s distance from the Sun varies greatly depending on where it is in its orbit.  The vast distance change is thought to cause molecules in Pluto’s atmosphere to condensate and sublimate and be lost to space.  The ALICE, PEPSSI, and REX instruments on New Horizons will measure the constitution of Pluto’s atmosphere and the rate at which it is being lost to space.

Beyond Pluto

Once New Horizons has completed its mission objectives for Pluto and Charon it will move on to studying some nearby KBO’s if any are in the vicinity.  So little is known about the Kuiper Belt and its citizens so any information on these icy worlds is practically invaluable.  The mission is slated to end in 2026 but if the spacecraft is still operational NASA has targeted the edge of the solar system just like with the Voyagers 1 and 2 missions.  Hopefully New Horizons will be able to reach the heliopause (the region where the solar wind from the Sun begins to interact with interstellar particles) and map this boundary point.  With the data from Voyager still inconclusive it is necessary to continue to explore this strange region of space.  The spacecraft is predicted to be inoperable by 2038 signally the end of its lifetime.  By then New Horizons will have contributed a massive volume of science and radically changed the way we view our solar system’s outer reaches.  Who knows what we’ll see when it finally reached Pluto next July?  Besides the data New Horizons provides, the probe is fulfilling our human curiosity and our desire to explore.  Space is the last frontier and there sure is a lot out there!

Comets: Why the Solar System Rocks!

When we look back, 2013 may be remembered as the Year of the Comets.  As I’m sure you may have heard already we have two potentially immensely wonderful comets heading our direction this year; the first of which will be its closest to the Sun on March 10th.  The more you learn about comets the more you appreciate how amazing the solar system is!  When you consider what comets are, how they get here, and what on Earth makes them shine so beautifully then fade into oblivion for thousands of years you are left with a sense of awe because the answer to all of these questions is…the Sun.

Thanks to Nicolas Copernicus we know that the Sun is the center of our solar system and that everything in the solar system orbits the Sun on regular and predictable paths.  You have the 8 major planets, the asteroids in the asteroid belt, the minor, or dwarf, planets of a region called the Kuiper belt, of which Pluto is a member, then far, far away from the Sun at a distance of almost one light year you is the region known as the Oort Cloud.  The Oort cloud is a massive region of space mostly by tiny chunks of ice and rock left over from the formation of the solar system.  These chunks of ice and rock are so far away from the Sun that they are approximately one-quarter the distance to the nearest star, Proxima Centauri.  The Sun is barely more than a pin point of light out here and its gravity is just strong enough to keep these tiny chunks of ice loosely in orbit.  However, the gravity is so weak that objects in the Oort Cloud are influenced by passing stars and the Milky Way itself.  All it takes is the slightest gravitational nudge from another star to dislodge an ice chunk from its happy orbit and send it drifting slowly towards the inner solar system.

Cutaway drawing of Oort Cloud  Image credit: NASA/JPL

Cutaway drawing of Oort Cloud Image credit: NASA/JPL

This is how we believe most long period comets are born.  Long period comets are comets with highly eccentric (or lopsided) orbits that span between 200 and thousands, or even millions of years.  Comet McNaught that passed through the solar system back in 2007 is a long period comet with an orbit of about 92,600 years.  It’s safe to say that we won’t see that bad boy again in our lifetimes!

Once the ice chunk is dislodged from its orbit in the Oort Cloud it begins its long, slow journey towards the Sun.  The Sun’s gravity begins to pull it in towards itself on an epic tour of the solar system that spans almost an entire light year (one light year is 6 trillion miles).  Comets are typically no bigger than a hundred or so meters across but the Sun causes something to happen on their surface that makes them spectacular sights in the night sky.  Out in the Oort Cloud it is mind-bogglingly cold.  Before they turn into comets the chunks rocks and dust mixed with chunks of frozen water, ammonia, carbon dioxide or methane that are so cold they’re as hard as steel.  But once they get close enough to the Sun they begin to heat up.

Once the comet arrives in the inner solar system the Sun’s heat begins to melt the ice and it begins to evaporate and glow brightly which is caused by solar ionization.  The glowing cloud of evaporating gas is called the coma.  Once the coma is formed the tell-tale…well, tail of the comet begins to form as the solar wind from the Sun blows against the comet.  The comet, tail, and coma steadily brighten as the comet gets closer and closer to the Sun.  They also begin to pick up more speed the closer they get.  By the time a comet is visible on Earth it already has a dazzling coma and tail that can be as bright as the stars and perhaps even the planets!

It is once the comet is within the orbit of Mercury that the fate of the comet is determined.  Most comets slingshot around the Sun at a safe distance that they make it around without a problem and begin their lonely journey back out of the solar system into oblivion.  Other comets called sun grazers get so close to the Sun that they actually pass through the Sun’s upper atmosphere, the photosphere, or even the solar corona where the temperature is millions of degrees Fahrenheit.  Some sun grazers make it out intact while others break apart and disintegrate, much like a frozen coffee mug when boiling water is poured in it.  Others still are known as sun divers which literally plunge right into the Sun and are never heard from again.

Comet Hale Bopp in 1997

Comet Hale Bopp in 1997

Once the point of perihelion, or the comets closest approach to the Sun is reached the comet begins it’s journey back to where it came from.  Depending upon the positioning of the planets on its return journey, some comets stay in orbit around the Sun and will eventually return.  If a planet’s gravity nudges the comet on the way out it could end up being ejected from the solar system entirely and be doomed to roam the void of interstellar space forever.  Whatever the fate of the comet we get to observe the magnificent effects of the Sun on them from the Earth, both visually and scientifically.

This year we have two potentially dazzling and memorable comets heading our way!  The first of which is named comet C/2011 L4 PANSTARRS, or PANSTARRS for short.  With a perihelion of March 10, 2013 it promises to put on a nice show throughout the months of March and April.  Observers in the northern hemisphere won’t be able to see the comet until after its perihelion though.  So be sure to get outside during clear nights in March and April to see this orbiting rocky ice clump.  Currently, PANSTARRS is projected to get as bright as the planet Venus if everything goes according to plan with its passage around the Sun.  PANSTARRS will be bright and low in the sky about 30 minutes after sunset in mid-March.

If you miss PANSTARRS or couldn’t get enough comet viewing action for one year you’re in luck!  Even brighter and more spectacular than PANSTARRS will be comet ISON in the fall months.  ISON is currently close to Jupiter on its voyage towards the Sun but will begin to be visible in binoculars in the beginning of October.  By November 1st ISON will be within the orbit of Earth and should be a spectacular -6 magnitude!  Astronomers measure brightness by magnitude with the lower the number being a brighter object.  The planet Saturn is +1 magnitude and the brightest star in the sky, Sirius, is -1.46.  By the time it reaches its perihelion on November 28th it is expected to reach a -12.6 magnitude which is as bright as the full moon!  That means that as it passes next to the Sun it will be visible during the daytime if you use your hand to cover the Sun!  ISON should put on a show of a lifetime during November and December and will truly be something to tell your kids and grandchildren about because ISON will likely never return.  If you own a telescope or a pair of binoculars make time to get out with your friends and observe this marvelous comet.  This one has the potential to be the brightest comet in recent history, brighter even than the famous Halley’s comet.

Comet McNaught from 2007

Comet McNaught from 2007

It never ceases to amaze me that all the wonderful things we love about comets, their beautiful tails and diamond-like sparkle is all due to the power of the Sun.  We live in an active solar system that is constantly moving and it is all thanks to the Sun’s influence.

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