The Slingshot Maneuver

Getting spacecrafts from one planet to another is no easy task. Sure it may sound easy, just fire off a rocket aimed towards the planet of your choice and eventually you will get there. There are many problems with this "point and shoot" method. One is that you would need a lot of fuel to rocket yourself  all the way from Earth to another planet, both to get you there and to keep the ship aimed properly. The more rocket fuel you have though, the harder it is to successfully launch yourself away from Earth, and the more money it costs to fly the space craft. The second major problem comes about once you've reached your destination. Assume you've aimed properly and had enough fuel to make it to the planet in question, now how do you slow down so that you can either safely land on the planet's surface, or orbit it in a stable orbit? More fuel, high tech gadgets, and lot of luck are needed to succeed then. So how do astronomers get spacecrafts from one planet to another? They use the sun! Since the sun is such a massive body, it can be used both to slow spacecrafts down, or speed them up. This is called a gravity assist or slingshot maneuver. When we want to get to Venus or mercury for example, we send spacecrafts around the sun multiple times. The gravitational attraction between the two objects slows the spacecraft down so that it can casually approach the planets. When we want to travel to Jupiter, or the outer edges of our solar system, we use the sun as a slingshot! By sending spacecrafts around the sun at the right distance, the pull of the sun can give the craft angular momentum and increases its speed. As the craft rounds the sun it shot out towards to outer solar system. The key here is to approach the sun with the correct speed, distance and angle, so you get the increase or decrease in speed you desire. Below is the path the Cassini-Huygens mission took around the sun before it was shot out towards Saturn. Carefully planned gravity assists via the sun and inner planets are what got Cassini to Saturn successfully.

 Image Credit: NASA

Jupiter's Ice Moon Europa: Part 2

We discussed Europa's icy surface and possible sub-surface ocean last week. Some images that Galileo sent back showed bumpy features on Europa's surface, almost like blisters. These features (shown below)  look similar to places on Earth where glaciers sit on top of undersea volcanoes. Basically, these underwater vents heat the water above them which melts the overlaying ice. Since these volcanoes are not active all the time, there are periods where the water can re-freeze on the surface. This re-freezing does not leave a smooth sheet, but rather a chaotic frozen pattern, much like the pattern seen on Europa. So what does this all mean? It suggests that there is some sort of internal heating mechanism within the moon, and therefore a subsurface ocean! The depth of this ocean, and the thickness of the ice sheet is still unknown, but further observations and hopefully future missions will enlighten us on Europa's mysterious structure.

 

Thera Macula (false color) is a region of likely active chaos production above a large liquid water lake in the icy shell of Europa. Color indicates topographic heights relative to background terrain. Purples and reds indicate the highest terrain. Image Credit: Paul Schenk/NASA

Jupiter's Ice Moon Europa: Part 1

 Image of Europa taken by the Galileo spacecraft showing surface ice and cracks

The Galileo spacecraft was launched in 1989, and in the 1990's gave astronomers their first up close and personal interview with Jupiter and its moons. One of many big discoveries was that Jupiter's 2nd closest moon, Europa, is a giant ball of ice! And the best part… it's water ice! Astronomers know the surface is water ice because of two main features. One is that albedo (reflectivity) of the planet is what we would expect for a planet covered in ice. Second, spectroscopy of Europa done in the infrared from the earth shows strong water absorption lines. Now that we know what the surface of Europa is made of, the question becomes "is there liquid water underneath that icy surface?" Astronomers speculate that the answer is yes. Based on Galileo images (above), Europa has a mostly smooth surface but exhibits large surface cracks as well (brown lines in the image). This is indicative of something like plate tectonics, where the ice plates sit on top of a liquid ocean and move around due to the motion of the sub-surface ocean. The only way to know for sure if there is a liquid ocean is to send a probe there to drill through the ice. This sort of probe may be in NASA's future, but recent discoveries based on the old Galileo observations suggest that liquid water has already been discovered! Tune in next time to learn more about this amazing discovery!

Image Credit: NASA/JPL

Earth from the ISS

Many pictures have been published on the web of Earth from outer space. Astronauts often take images of Earth from the International Space Station (ISS). The ISS is a satellite in low Earth orbit that houses up to 15 astronauts at one time. It is used to conduct low gravity experiments, monitor Earth's weather and learn how humans and plant life survive in outer space. Using onboard cameras and other instrumentation, astronauts can image every inch of Earth as they fly by. Below is a video compilation of  many images taken from the ISS from August-October of 2011. Note the beautiful aurora which forms at the top of Earth's atmosphere (defined by what looks like a thin yellow shell around Earth). You can also see city lights across all countries, and flashes of lightening within clouds.

Video credits are listed  here: http://vimeo.com/32001208

Earth | Time Lapse View from Space, Fly Over | NASA, ISS from Michael König on Vimeo.

Did the Moon Form From Earth?

Artists impression of the impact which formed our moon

There are many theories out there as to how Earth's moon formed. Some think the moon formed right with the earth out of the circumstellar disk of material around our young sun, others think that it is a captured object that got caught up in Earth's gravity and became our moon. The leading theory is that a Mars sized object crashed into Earth during the Late Heavy Bombardment, and broke off a chunk of earth that formed into the moon. But why do we think this is the case? Well first of all, measurements of  the amount of Tungsten-182 (decay product  of Halfnium-182) in returned moon rocks suggest that the moon appears to be ~100 million years younger than the Earth. I know that sounds like a long time, but it's really fairly short, considering the Earth is 4.6 billion years old. The age of the moon suggests that after the Earth was hit, the moon formed in a short period of time, but it took an extra 100Myrs for Earth to recuperate and reform back into a spherical planet. So this rules out the "same time formation" theory (the moon is younger). So what about the "captured rock" theory? Well, based on analysis of moon rocks and the lunar composition via satellite missions to the moon, we know that the moon is made almost solely of molecules that consist of oxygen (silica, alumina, iron oxide, sodium oxide, etc.). Measurements of the oxygen isotope ratios in rocks tell us that this ratio is almost exactly the same as that on Earth. It's very unlikely that a random captured rock would have exactly the same oxygen isotope ratios as we do on Earth, so the moon probably formed from a piece of the Earth!

Image Credit: Fahad Sulehria

GOES-R

Artists impression of GOES-R

Besides taking awesome pictures with telescopes and studying deep space, astronomers often work with geologists to study the structure of Earth and our weather patterns. One such endeavor is the Geostationary Operational Environmental Satellite (GOES) project, run by the US Environmental, Satellite, Data, and Information Service. Their job is to launch satellites that constantly study weather patterns on different part of the Earth so that the weather man can give us an "accurate" forecast each morning. The GOES satellites are in a geosynchronous orbit around earth. That means they orbit the Earth at the same speed at which the Earth rotates, allowing the satellite to appear stationary in space from a given spot on Earth. Currently there are 5 functional satellites (GOES 11-15), with the next generation (GOES-R, artists impression above) pending launch in 2015. Want to learn more about GOES, GOES-R and their mission pgoals? Have children that are interested in space and weather? Check out the GOES-R page for kids: scijinks.gov, or download the free game app: Satellite Insight.

Image credit: Lockheed Martin

Free Astronomy Apps

If you have an iphone or other smartphone, you've probably discovered that there are quite a few astronomy apps out there. Most of them cost a few bucks,  but there are some pretty cool free ones out there. Here's what I have downloaded to my iphone that you should check out for yourself:

Exoplanet Database: This is an awesome app if you're into exoplanets! It's a database with information about all the different exoplanets that have been discovered, and includes size, period, distance, and other useful information. You can read news about exoplanets, view where any exoplanet is located in the galaxy, make handy graphs of exoplanet properties, and even get links to scientific papers about the exoplanets. The coolest part about this app… it sends a text message to your phone every time a new exoplanet is discovered!

APOD Viewer Lite: An application that lets you view the astronomy picture of the day. It shows you the image, explanation, and lets you look back at previous images. Very nice app to quickly view today's APOD.

NASA: Basically this is NASA.gov in app form. You can find news,  launch schedules, pictures, videos, telescope info, and anything astronomy you can imagine. Excellent educational app.

ArXiv: This app allows you to search the astrophysics arXiv for scientific papers, and download the pdf to your iphone (using a pdf reader app). This is more for the serious astrophysicists, but anyone can peruse through the papers and maybe you'll find something interesting.

Galaxy Collider Lite: A cute app that shows you what would happen if two galaxies collided. I'm not sure how scientifically accurate the simulations are, but it's cool to watch the galaxies interact regardless. You can set the number of stars, mass of the galaxies, speed of collision, etc. and observe how that changes things

If you've discovered any other cool free apps, post them in the comments section below! Also feel free to leave your opinion about different non-free apps as well!