Tuesday, September 11, 2012

Pluto: Planet?

Is it or isn't it?  Many people, comfortable and familiar with Pluto's status as the 9th rock from the Sun, have expressed dismay at the International Astronomical Union (IAU)'s ruling that Pluto would be demoted. The 2006 vote that determined what exactly constitutes a planet banished Pluto to the role of dwarf planet.

But what do we really know about our poor friend Pluto, other than that it's really far away?
(By the way, it is really far away: Pluto orbits between 30 and 49 astronomical units (AU), which is 30-49 times the distance between the Earth and the Sun!)

Quick Facts about Pluto

  • Orbital period: 248 years
    • Apehelion (farthest from the Sun): 48.871AU
    • Perhelion (closest to the Sun): 29.657AU
  • Size: 
    • Radius: 1153 +/- 10km (0.18 Earths)
    • Mass: 1.305x10^22 kg (0.00218 Earths, 0.178 Moons)
  • Temperature in Kelvin:
    • Minimum: 33K (-400F)
    • Maximum: 55K (-360F)
  • Moons:
    • Charon
    • Nix
    • Hydra
    • P4
    • P5

Pluto was discovered in 1929 by Clyde Tombaugh, an astronomer at the Lowell Observatory.  He was actually looking for the mysterious "Planet X", which was supposedly to blame for discrepancies in the orbits of Uranus and Neptune.  To do so, he would compare photographs of the night sky taken two weeks apart. To his surprise, after a year of comparisons he found movement in one of these pairs!  The discovery was big news, and the planet was named Pluto, after the Roman god of the underworld.

Over the next decades, further observations made it less and less likely that Pluto was Planet X.  For starters, they couldn't see a disk and the planet was faint, meaning it was probably small. Its albedo (or brightness) was calculated in 1976 and the researchers determined that with an albedo matching methane ice, Pluto could not be more than 1% the mass of Earth, When Pluto's moon Charon was discovered, they were able to calculate its mass and found that it was only 0.2% of the Earth's, which made it way too small to cause the gravitational disturbances of two gas giants.  When Voyager 2 passed by Neptune in 1989, scientists were able to revise the mass of the planet, which eliminated the discrepancies and nixed Planet X forever.

What makes Pluto different?

Pluto is slightly out of place compared to the 8 other planets. The biggest inconsistency is its orbit. While the other planets orbit on the same plane, Pluto's orbit is tilted so that it crosses the plane and orbits above and below it.
It also has an exaggerated elliptical orbit, compared to the almost-circular orbits of the dominant 8 planets.  

Pluto seems to be made up of methane and water ice, with a possible rocky core, much like a comet.

However, it does have quite a bit in common with the other objects in its neighborhood, such as the highly inclined orbit, size and orbital period.

Why can't it be a planet?

The IAU has 3 criteria that a body must meet to be considered a planet.
1. It must orbit the sun
2. It must be pulled into a spherical shape by gravity
3. It must clear the neighborhood around its orbit

Pluto meets the first two, as it does orbit the sun (however strangely) and is roughly spherical. However, the other planets have relatively clear orbits. Most of them have some small asteroids like Trojans or Centaurs that are scattered through their orbits, but the planet itself takes up the majority of the mass of its orbit.  Pluto, however, orbits through this cloud of rocky bodies called the Kuiper Belt  (pronounced like Piper).  You can see in the diagram below that Pluto (the outermost red ring) most definitely doesn't clear its orbit.  (Forgive the non-perfect orbits, paint can only do so much).

What happens to Pluto now?

Never fear, our dwarf planet hasn't been forgotten. It actually holds the honor of being the first of the Plutoids, or Trans-Neptunian bodies (meaning they orbit beyond Neptune) that orbit the sun in a similar fashion to Pluto and are large enough to be rounded. This family has expanded in recent years to include not only Pluto, but Eris, Haumea, Makemake, Quaoar, Orcus and Sedna

It's estimated that hundreds of objects like Pluto are orbiting in the Kuiper Belt and beyond; however, their distance and size make them difficult to even find, let alone observe.  

As for Pluto, I have exciting news! In 2015, the New Horizons mission will arrive at Pluto and perform a flyby, giving us our first actual images of that cold, dark world.  It will perform a number of experiments, such as determining the makeup of Pluto's surface, discovering if it has a thin atmosphere as theorized, and perhaps even finding that it has much in common with Triton, Neptune's largest moon and a possible capture from the Kuiper Belt.   It will then continue on through the debris that rings our Solar System to see if there are more bodies like the Plutoids out there, silently swinging through space around our Sun.

If you have any other questions about Pluto, please ask in the comment section below!

Thursday, September 6, 2012

Dawn and Vesta

On Wednesday (5 September 2012), the probe Dawn left the asteroid Vesta, a 525km (236 miles, for those who dislike metric) wide hunk of rock orbiting the sun between Mars and Jupiter in our main asteroid belt.  Vesta happens to be a very special asteroid, however. Besides being the 2nd most massive asteroid, it is a fossil of sorts, a link to how rocky planets like Earth may have formed.

Vesta is the last protoplanet with a differentiated interior. This means that if we were to take a chunk out of the asteroid, we'd see that it has a crust, mantle and core, just like Earth.

Earth's interior
Vesta's interior

This is very exciting and very important, because the Earth was most likely formed from a protoplanet similar to Vesta.  There are estimated to have been a few hundred bodies like Vesta, which eventually (over the course of 100 million years) collided due to perturbations in their orbits and formed the dominant 8 planets we know today. (Before you say "what about Pluto?!", hang on! I'll address our lonely little friend in my next post.)  

The Dawn mission objective is to visit Vesta (done!) and Ceres, a dwarf planet in the asteroid belt.  These two bodies are useful because of some specific characteristics.
  1. Vesta has highly magnetized rocks. These, along with a differentiated interior, could help explain what starts a planetary dynamo. This is the process that creates a magnetic field, which in turn helps shield a planet from solar winds.  (Earth has a very strong magnetic field, while Mars has a very weak one.)
  2. Ceres is believed to have a layer of surface or sub surface water ice, as well as a thin but permanent atmosphere.
These two bodies present incredible insights into the formation of worlds like Earth. It could help us understand our own origins, and possibly predict what we'll encounter around stars similar to our own.

Wikipedia, "Protoplanet"

Wednesday, September 5, 2012

Why are the sciences important?

I'd like to start with a little inspiration.

E.O. Wilson is a pioneer in the study of ants, and a distinguished scientist and mentor who has counselled and taught many good people how important their study of the sciences are to humanity.  In this video, he reads some excerpts from his upcoming book, "Letters to a Young Scientist".  He implores young scientists (and in my opinion, anyone with interest in it) to explore, to dream, to be creative and to innovate.

Science is fun!

Welcome all! I'll try my best to bring you science news in a digestible form (for your brain, anyway).  My main interests lie in all things space-related, so expect quite a bit of that. I will, however, take requests for other areas of science and do my best to explain it like you're five.

My goal for this blog is to make current science accessible for my friends, family and whoever else might read this.  I feel that it's extremely important for everyone to be at least semi-science literate, and unfortunately modern journalism tends to exceptionalize and editorialize even scientific papers.  

I hope to bring you all a daily (or more) dose of science news that you can easily understand and share, and thus create a scientific society.