GRAIL

Artists impression of GRAIL

Even though the space shuttle program has ceased, NASA is still alive and active with eyes towards the moon. On Saturday, September 10th around 9am EST, NASA launched the Gravity Recovery and Interior Laboratory (GRAIL) spacecraft from Cape Canaveral, FL. GRAIL is a set of two satellites that will orbit the moon and map its gravitational field. The moon has about 15% the amount of gravity we experience here on Earth, mainly because it is only about a quarter of the size of Earth. Understanding the moons gravitational field will help scientists understand the moons interior structure reconstruct its past. We will be able to answer questions like: Does the moon have a molten core? Why do the craters on the light side of the moon appear to be filled with solid magma, while those on the dark side do not? One interesting thing about the launch of GRAIL is its journey to the moon. A trip to the moon for the space shuttle took about 3 days, but GRAIL is going to take 3.5 months! The rocket was actually aimed in the direction of the sun, and with the help of small thrusters the trajectory will be corrected so that the satellites will reach the moon. This is called a low-energy trajectory and was done intentionally to save fuel, and to leave time for the satellites and equipment to adjust for space conditions. Think about it like this: if we hurtle towards the moon in three days, it will take a lot of fuel and energy to slow the satellites descent so they don't crash into the moon. But if instead we go the "long way around" and leisurely approach the moon, we can just float into orbit using very little fuel only to adjust trajectory. In these hard economic times, NASA is trying to save every penny they can!

Image credit: NASA/JPL/MIT

Solar Spectrum

So how do we know that the sun is made mostly of Hydrogen, Helium and a handful of other elements? Astronomers use a technique called spectroscopy and here is how it works.

White light really consists of all the colors of the rainbow. You can make the colors appear by shining a light through a prism (just like the cover of that Pink Floyd album).  Astronomers use a device called a spectrograph which is mounted on a telescope and has the ability to split light into all the colors of the rainbow. What's the purpose of all this? The sun generates white light in its core as Hydrogen fuses into Helium. Each light particles (called a photon) has a slightly different amount of energy. This is what actually causes the rainbow. Red light has a certain energy, while blue light has a little bit more energy, and we perceive this energy difference as a difference in color.

 The chemical elements within the sun are made of protons, neutrons, and electrons. Thinking back to your chemistry days, the electrons orbit the outside of the atom, while the protons and neutrons make up the core or nucleus. These electrons sit in "energy levels" and light (photons) have the ability to excite these electrons to higher energy levels. When a photon hits an atom, if that light has just the right amount of energy, the electron will absorb the photon and be "excited". Electrons around different elements require different amounts of energy to get excited.

So here's the connection. If the Sun is made of lots of Hydrogen, then colors of light that excited Hydrogen electrons will be absorbed by the Hydrogen atoms in the sun. So when we look at the Sun's spectrum (above) we see black lines where color has been absorbed by different elements. These are called absorption lines. In chemistry labs we can see what absorption lines Hydrogen, Helium and other elements produce. Then when we have a spectrum from the sun, we can look for specific absorption lines from different elements and decipher what the sun is made of! Spectroscopy is used to figure out what stars are made of, along with the atmospheres of planets, and even giant clouds of gas in outer space! The image above is the entire visible spectrum of the sun. We see many absorption lines caused by Hydrogen, Helium, and other heavier elements.

Solar Composition

Most of us know that the sun is a giant ball of gas, but what exactly is it made of? Astronomers have been working on uncovering the sun's exact composition for many years, and this is the current theory...

Composite image of the sun on 9/7/2011 from the Solar Dynamics Observatory

Since different elements have different weights, we can talk about the solar composition in terms of weight. The sun weighs about 4*10^30 pounds (that's a 4 with 30 zeros after it!). About 74% of that mass is Hydrogen atoms, 25% of the mass is helium atoms, and 1% is a variety of other elements including oxygen, carbon, iron and others. Another way to think of the sun's composition is in terms of number of atoms (or volume, essentially). In these terms,  92% of the sun is filled with hydrogen atoms, about 7.8% is made of helium atoms, and that other tiny 0.2% is made of heavier elements. This composition is ever changing, as the sun is continually undergoing fusion of hydrogen into helium in its core. The sun is also shedding mass in solar wind and solar flares, but this amount is so small compared to the size of the sun that it's practically unnoticeable. Over a human lifetime the composition of the sun will stay pretty much constant.

So how did astronomers figure out what the sun is made of? Tune in later this week to find out!

Image courtesy of NASA/SDO and the AIA, EVE, and HMI science teams

Earth's Magnetic Field

It's a good thing Earth has a magnetic field! If it didn't, we'd be showered with solar radiation 24/7 and probably wouldn't survive for very long! But what is this magnetic field and how does it work? Astronomers have some idea…

The Earth's magnetic field is thought to be caused by a molten iron core deep inside Earth. With fancy math and physics one can prove that a molten electrically conductive material  that is spinning will produce a magnetic field. This magnetic field is very similar to the one a bar magnet produces, just on a much larger scale. A bar magnet always has a north and south pole. If you sprinkle some iron filings around a bar magnet, you will see that they align themselves in a curved pattern extending from the north to the south pole. The iron filings are tracing the magnetic field lines, or in other words the force, produced by the magnet. One would naturally think that the north pole on Earth should represent the north end of the "bar magnet" inside Earth, and the south pole the south end, but it's actually the exact opposite! Let's stop and think… opposite ends of a magnet attract, while similar ends repel. So if a compass always points North, it must be attracted to the southern magnetic pole! Another fun fact about our magnetic poles is that they do not coincide with the physical north and south poles on Earth, they actually move quite a bit each year! In 2005, the north pole was measured to be at about 83N 114W, but today it is further west by roughly 10 degrees! Astronomers and geologists don't fully understand the production of Earth's magnetic field, and therefore don't fully understand why it is moving, especially at such a quick pace. There's much more work to be done on this subject.

Apollo Moon Landings

I'm sure many of you remember that glorious day when man first stepped on the moon. The date was July 16, 1969, the mission: Apollo 11. Neil Armstrong, Buzz Aldrin, and Michael Collins left the Earth that day, and five days later made history by putting the mark of a human being on another astronomical body.  This is the day most people think of when someone mentions the moon landing, but we've actually sent man to the moon a total of 7 times. Missions Apollo 11 through Apollo 17 all rocketed towards the moon, and all but Apollo 13 landed successfully on the moon. During each mission astronauts set foot on the moon, and the Apollo 15 mission was the first to drive a vehicle on the moon, called the lunar rover (pictured above). After Apollo 17, manned missions to the moon were canceled due to lack of funding. NASA needed to make some budget cuts, and decided to put money towards Skylab instead. Man has not set foot on the moon since. Many orbiters and robotic landers have studied the moon since then, and the next mission, a set of orbiters called GRAIL, is set to launch from Cape Canaveral on September 8th, 2011.

The movie Apollo 18 comes out this Friday and it looks like it's going to be a great sci-fi thriller! It's based on the idea that NASA actually did send astronauts to the moon again as an Apollo 18 mission, but never told the world because of what they found…. aliens on the moon! Of course these creatures are hostile and live on the dark side of the moon, what sci-fi movie would be complete without killer aliens? I'm surprised it took 40 years to come out with a film like this, and I hope it's a good one!

Image Credit: NASA

A Planet Made of Diamond!

 Artist's impression of the diamond planet

You read that right! Astronomers believe that they have discovered an exoplanet made of diamond! How can this happen? Well here's the scenario. There was once two stars orbiting each other in a binary system in our galaxy. One star was  bigger than other, and began stealing material from the other smaller star. Over time, the large star stripped so much material off the small star that it couldn't withstand the external pressure and exploded as a supernova! This huge explosion cleared away any gas and star material in the area, leaving behind only the core of the large star (now called a neutron star) and a the core of the small star. Because this is a binary system, the leftover cores began to orbit each other extremely quickly. The angular momentum in the system (speed of rotation, essentially) caused the neutron star to spin on its axis in a fraction of a second (once every 0.0057 seconds to be exact)! We call these stars pulsars, as they emit light from their poles which appears as mili-second pulses in radio telescopes. The small star's core now orbits the pulsar so closely that it only takes two hours for the planet to go around the star! Based on orbital speed and distance to the host star, astronomers speculate that it is less than half the size of Jupiter, but weighs about 1.2 times as much! This high density suggests that the star is made of carbon, and its close proximity to the host star would make it crystallized. And you know what crystallized carbon is… Diamond! A planet 5 times the size of Earth made diamond. I Think I agree with other astronomers who suggest that we somehow find a way to travel to this planet and bring some diamond back! (Though it's quite implausible.) Wouldn't it be awesome to have an exoplanet-diamond ring ? And I thought a meteorite necklace was cool!

Our Solar System

After some recent teaching experiences and discussions, I've come to realize that many adults have forgotten the basics about our solar system. So today ADYK presents a Solar System "refresher" to help you recall those astronomy facts you learned back in elementary school.

 

Above is a collection of real telescope images of the planets in our solar system (NOT to scale!). This is what the planets look like when you use very high power telescopes or planet orbiting satellites to observe them.

Our solar system contains 8 planets (Pluto doesn't count anymore),  one star (the Sun) and two large asteroid belts. Mercury, Venus, Earth and Mars and the four closest planets to the sun and are often called the terrestrial or rocky planets. They are basically giant chunks of rock in a roughly spherical shape. Mercury is made mostly of metals and is heavily cratered like the moon. Venus has a thick carbon dioxide atmosphere, and is essentially the poster child for what would happen if global warming got out of hand on earth. Earth is our home and is made of 70% salt water and has a rich Nitrogen atmosphere. Mars is the red planet where all the aliens live, supposedly. (*wink wink*). Beyond Mars sits the first asteroid belt, filled with oddly shaped rocks the size of people to the size of cities. Jupiter, Saturn, Uranus and Neptune sit beyond the asteroid belt and are often called the gaseous or Jovian planets. Jupiter is the largest planet, about 10x the size of Earth, and has that big red spot. Saturn is the one with the prominent ring structure, though all Jovian planets have a slight ring structure around them. Uranus and Neptune are the blue planets, and are about 4x the size of Earth. Uranus is turned on it's side, meaning that its spin axis is tilted 90 degrees from being straight "up and down". Past the Jovian planets is the Kuiper belt, a giant ring of asteroids which defines the edge of the solar system. Pluto, it's moons, and over 70,000 similar objects orbit in this ring. Most everything there is small, cold, and icy.

There you go, elementary school astronomy class in one paragraph!