Whole New Worlds

What happens when you mix the music of Aladdin with astronomy? Something pretty wonderful:

Going to Mars...in Pixels

David Paliwoda is a Motion and Interaction Designer based out of East London. He has put together a website featuring a fantastic, animated, interactive infographic (what he terms a motion-infographic) that shows you the scale of the distance to the Moon and to Mars as measured in pixels.

Click the image to see the animated site. Or go to How Far is it to Mars?

The Halting of the Hot Jupiter

We haven’t talked about exoplanets for a while, and we should ‘cause they are pretty badass. Through various podcasts and the like, I've been hearing some really cool things about NASA’s Kepler Mission and all of neat astronomical bodies it’s been finding. So I decided to browse around the NASA and JPL websites to see what new coolness has been discovered recently.

NASA’s Kepler Mission was launched in 2009. It was built to detect potentially life-supporting planets around other stars. This satellite has a 0.95-meter diameter telescope that continuously and simultaneously monitors the brightness of 100,000 stars brighter than 14th magnitude in the constellations Cygnus and Lyrae. Kepler uses the transit method of planet finding, looking for the drop in the brightness of a star as a planet crosses in front of it at repeated, regular intervals. This dip in brightness not only tells us of the existence of a planet but also its size and orbit, from which we can calculate temperature. So far, the discovered extrasolar planets (or exoplanets) have been giant, mostly the size of Jupiter and bigger. A “hot Jupiter” is one of these large planets that orbits very close to its star. We’re talking less than 1 astronomical unit (AU), with orbital times of only 1-3 days! As such, they are really really hot. A new paper published in The Astrophysical Journal takes a look at one of the biggest questions in exoplanet research: how did these really big planets get so close to their stars? Or, perhaps more importantly, since they are so close, why weren't they pulled into their stars?

It is currently accepted that hot Jupiters formed further out from their host stars, likely beyond the snow line (or frost line), and then migrated in to their current, closer orbits. By observing how an exoplanet moves and how its parent star rotates (the “Rossiter–McLaughlin effect” for you space nerds), we also know that some exoplanets are misaligned and others are not. The misaligned exoplanets are likely directed inward due to interactions with other bodies in the system (gravitational scattering, the “Kozai mechanism”). Essentially, big things that have lots of gravity affect other big things that have lots of graving and they all push each other around. Aligned planets probably ended up where they are through migration in their primordial disk. As the conditions (density, temperature, magnetic fields, etc.) within this disk and the forming planet’s mass and density change over time the planet moves its orbit. Type-I migration assumes the density structure of the disk is affected by turbulence rather than by planets, and as such, is applicable to small mass planets. With Type-II migration, a gap between the planet and disk forms as the result of tidal torques from the planet becoming stronger than the viscous torques of the disk, and as such, is applicable to larger mass planets. The Type-II migration model is good at telling us how gas giants form beyond the snow line and move inwards but not so good at telling us how this migration stops once it is started.

The new study looks at the large ensemble of close-in exoplanets covering a wide range of host star (or stellar) masses in order to discern which mechanism halts exoplanet migration. First, the researchers collected exoplanet data and subdivided by mass the confirmed exoplanets located less than 1 AU from their star. Then they further subdivided Kepler candidates by estimated planet radius into three groups that approximated the terrestrial, super Earth/Neptune, and Jovian planet masses. Next, they attached stellar masses to the system, constraining their study to masses between 0.1 and 1.5 mass of the Sun.

The researchers then took this exoplanet data and put it into several “migration halting mechanism models” to see which model best explained the observations. Their goal was to “generate a reasonably simple prediction for the density of exoplanets as a function of stellar mass and semi-major axis within 0.1 AU.” Now, I’m not a modeler. I’m not even going to pretend I know how to put one together or even really describe it to you without confusing myself and you. Suffice it to say that the authors ran a bunch of models and did a bunch of Bayesian evaluations (my brain rebels at all things Bayesian too).

The astronomers found their tidal circularization model to provide the best mechanism for halting planet migration. Planet-planet scattering, secular chaos, and the Kozai cycle are all mechanisms that migrate planets inward and invoke tidal (or gravitational) forces on it. These forces lower the semi-major axis (the longest radii of an elliptical orbit) and eccentricity until the orbit of the planet becomes more circular. Put simply, when the gas giant gets close to its star, tidal forces cause the exoplanet’s elliptical orbit to become more circular. This circularization stabilizes the planet’s orbit, halting the inward migration and preventing the planet from getting eaten by its star. This result does not rule out the Type-II migration model, but instead, it says that it isn't the role of the primordial disk (or getting to the edge of it) to halt the migration.

If you will remember, they also took a look at stellar mass. They wanted to see if the mass of the star had an effect on the planets’ distance from it. Their models showed that halting distance depends on the stellar mass. This result actually provides further support to the favored tidal forces model. The tidal forces model predicts that hot Jupiters of more massive stars should, on average, orbit further out. Their results also show a halting distance-stellar mass dependence that was stronger than predicted, suggesting that future theoretical work may be needed to reproduce the observed exoplanet distributions.

This begs the question of why did our own Jupiter not migrate inwards? Or if it did, why did it stop so far away? We should definitely be glad that it did (or didn’t?) or our puny little Earth would have been eaten up or thrown out. Thank you Jupiter for ending up where you are.


Plavchan, P., & Bilinski, C. (2013). Stars Do Not Eat Their Young Migrating Planets: Empirical Constraints on Planet Migration Halting Mechanisms The Astrophysical Journal, 769 (2) DOI: 10.1088/0004-637X/769/2/86


Read JPL's story about this study: "Stars Don't Obliterate Their Planets (Very Often)"

Learn more about NASA's Kepler Mission: http://kepler.nasa.gov/
And I always find good stuff on the NASA and JPL websites!


(image via Cosmos, credit: ESA)

Superman, Please Call Me Neil

I think that introducing a little science into a fictional story is never a bad thing. Science is so cool on its own that it can only make your story that much cooler. In the upcoming issue of Action Comics #14, astrophysicist and science rock star Neil deGrasse Tyson show up to help Superman find his home planet Krypton. We all know how good Neil is at calling the media on their science screw-ups, and so what a wonderful idea it is to get him involved before said screw-ups ever happen. Neil determines that Krypton is located 27.1 light-years from earth in the constellation Corvus. It orbits the red dwarf star LHS 2520 at Right Ascension 12 hours 10 minutes 5.77 seconds, Declination -15 degrees 4 minutes 17.9 seconds, and Proper Motion 0.76 arcseconds per year, along 172.94 degrees from due north (see Celestial Sphere).

“As a native of Metropolis, I was delighted to help Superman, who has done so much for my city over all these years,” Tyson said in a statement. “And it’s clear that if he weren’t a superhero he would have made quite an astrophysicist.”

Also of note is an episode of webseries Fact or Fictional that discusses the plausibility of the  S.H.I.E.L.D. Helicarrier from The Avengers with scientist Phil Plait (of Bad Astronomy). Can that thing actually fly? How much power would it take? What about the cloaking technology?



(via /Film)

The 2012 Transit of Venus

Mark your calendars. On June 5-6, 2012, Venus will pass across the face of the Sun. This is likely the last time you will see Venus transit in your lifetime. Transits of the planet are very rare, coming in pairs separated by more than 100 years. The first of this pair came in 2004, and after this year's transit there will not be another one until 2117. I've listed below some information you should know about where, when, and how to view the transit.

I'll admit that I went a little crazy with the links, there are a lot of them. The idea was to make a sort of one-stop-shop where you could find all of the transit information you could want or links to where you can find it. Because I've included so many links, I tried to break them up by topic, and hopefully that will help you navigate. First, let's start with some general information type links about the up-coming transit of Venus:

• Transit of Venus is a blog style website with all kinds of information on various topics about the transit
•  2012 Transit of Venus Sun-Earth Day Shadows of the Sun is NASA's page and includes maps, galleries, and information
•  Royal Museums Greenwich's 2012 Transit of Venus site 
•  British Astronomical Association's Transit of Venus 2012 site 
•  Sydney Observatory's Transit of Venus site
•  NASA News article that includes information and a great video 
•  Society for Popular Astronomy's Introducing Solar Observing
•  A Science Daily article "The Transit of Venus: June 5-6, 2012" 
•  Royal Astronomical Society's Transits of Venus page including a map of planned public observations and events in the UK
•  A Factsheet put together by The Astronomical Society of Australia 
•  A video of the talk by Tony Sizer, lecturer at the Royal Observatory, on the subject of transits of Venus
•  Sky and Telescope's "Transit of Venus Explained" 
•  History of the Transits of Venus 
•  The Transit of Venus Facebook Group

Location, Location, Location

People from all over the world will be looking up on June 5th and 6th, but where you live determines what time you should be looking for the transit. If you are in Europe, the Middle East, eastern Africa, western Australia, India, and western Asia you should be looking for Venus at sunrise on June 6th. If you are in North America, Central America, and the northwestern parts of South America you should look for Venus around sunset on June 5th.  If you live in central and eastern Australia then lucky you! You will be able to see the entire transit. For specific times of the transit at your location, see the Local Transit Times website.

Links about the where's and the whens:

•  Local Transit Times website to find out about viewing times in your specific location
•  Transit Computer: Locations Worldwide from the US Naval Observatory
•  NASA's guide to the 2012 Transit of Venus
•  A PDF version of the map showing the visibility of the transit (same map as above)
•  A large jpg color map showing the visibility of the transit
•  A diagram that shows the path of Venus across the Sun and the contact times from an earth-centered prospective
•  HM Nautical Almanac Office guide (includes UK predictions)
•  Event locations worldwide. Find an event near you and join in the fun!

How to Observe

First, and most importantly, NEVER look directly at the Sun without proper safety devices unless you prefer permanent blindness. Regular sunglasses do NOT qualify as a proper safety device. Venus covers too little of the solar disk to block the blinding glare of the Sun. Solar filters are widely available for safe solar viewing.

•  A video featuring Ralph Chou about viewing the transit safely and effectively
• NASA's page on Eye Safety During Solar Eclipses (information that applies to transits as well)
• Some really great and very detailed information about viewing the transit and eye safety
• A PDF overview on viewing methods (compiled for the classroom)

Here are some options for safe solar viewing:

Protective Eyewear: If you have access to a welding hood that houses a #14 or darker filter then you can use that. Or you purchase inexpensive Eclipse Shades.

•  Rainbow Symphony is an Australian company that sells several types of Eclipse Shades and hand-held solar viewers
• Amazon sells inexpensive packs of eclipse glasses, hand-held eclipse viewers, and even pricier solar eclipse glasses
• Astronomers Without Borders is selling eclipse glasses for only $2 a pair, and that includes shipping

Telescopes with Solar Filters: Not only do telescopes magnify Venus, but if they are properly filtered they can also give you a better view then you will have with most other viewing options. If you own an inexpensive, small, and/or older model telescope be careful to make sure you are using the correct type of solar filter. If you don't have these then look below in the links for Projection Methods to find out how to turn your telescope into a projector. Don't own a telescope? No problem, me neither. You can do what I'm doing and find your local astronomy club. They will have telescopes set up (probably nice, big ones) and amateur and expert astronomers on hand to answer questions.

• Mr. Sunspot's guide to viewing the Sun with a telescope. He explains how to build solar filters, make a simple telescope, correct ways to look at the sun through a telescope
• AAS Press Officer Richard Tresch Fienberg provides simple instructions and a supplies list for building a Sun Funnel (a closed-loop device that fits in your telescope and projects a magnified image on a screen)
• A Sun Gun device, devised by Bruce Hergerberg, that allows a crowd of spectators to view a large projection of the Sun
• Find solar filters for your telescope at Astro-Physics Inc., Meade Instruments Corp., Orion Telescopes & Binoculars, and Kendrick Astro Instruments
• Front and rear mounted Hydrogen-Alpha (Ha) solar filters

Pinhole Projectors/Camera: These devices are a safe, indirect way to view the Sun. They are popular devices, especially with kids, because they are easy to make and use yourself. Unfortunately they suffer from the problems associated with indirect viewing, namely unmagnified images and lack of detail.

•  How to use a mirror as a reflected pinhole device
• The Exploratorium Museum's instructions on how to build a pinhole projector
• The Solarscope is pinhole camera that is available from Light Tech Optical Instruments
• Bob Miller's Light Walk which includes activities and directions on pinhole viewers

Projection Methods: There are a few types of projection methods, besides pinhole projectors, that you can use to indirectly view the transit. You can project the image of the Sun onto a white surface with a projecting telescope or binoculars (do NOT use the binoculars or telescope to directly look at the Sun!). Another option, especially for children, is to use a Sunspotter telescope viewer.

•  Dr. Doug Duncan, from the University of Colorado, explains how to use projection and even has video
• Projecting the Sun, using binocualrs, adapted from the Society for Popular Astronomy
• The Exploratorium demonstrates how to project using binoculars (the page was set up to see Mercury's transit, but the same techniques apply)
• Hubert van Hecke (Mr. Science) provides design instructions for making a sunspotter as well as how to take sunspot data and analyze it (or in this case, transit data)
• Science First makes The Sunspotter that provides a surface on which you can trace the Sun's outline onto a piece of paper
• Another type of Sunspotter is available from StarLab
• How to use and make a projector for your telescope

Use the Internet: You don't have to go outside to see the transit of Venus. You can go online and look for webcasts from around the world.

•  User-adjustable Applets about the transit of Venus
• Videos that relate specifically to the transit of Venus and similar phenomena
• Astronomers Without Borders has a web app where you can find information and share your experiences
• NASA will have a live webcast from Mauna Kea Observatories in Hawaii that will bring you real-time images of the transit even for the duration
• Live broadcasts is viewable from several locations on Sky-Live
• A live webcast from Mount Wilson Observatory (where Edwin Hubble did his work on the expanding Universe and the nature of galaxies)
• Use a remote solar telescope like Mike Rushford's robotic solar observatory in Livermore, California. You can actually control your realtime view of the Sun from your web browser!

Experiments, Experiments, Experiments

Space agencies and astronomers around the world will be taking this time to study Venus and test some planetary hypotheses. Planetary transits are powerful methods for discovering exoplanets. It is not only one of the ways that astronomers find exoplanets, but it is also a way to learn more about the characteristics of those far away bodies. By measuring the refraction and scattering of light, lots of information can be gathered about the atmospheres of planets. To refine these techniques and to learn more about our own solar system, astronomers can observe planets close to home. Venus is not only one of the most intriguing bodies in our solar system, it also has a thick atmosphere and passes between Earth and the Sun. This combination of factors allows for the observation and measurement of its atmosphere. Techniques that are directly applicable to exoplanet study.

You can even contribute through citizen science. There is an IOS version and an Android version phone apps that will allow you to send your observations to a global experiment to measure the size of the solar system. Prior to the transit, you can use the app to practice your timing and see predicted times for your location. During the transit, you can use the app to assist you in measuring the time of the interior contacts. After the transit, you can use the app to access your data on a map. I recommend thouroughly reading the instructions so that you both recieve and send good information.

Links to some big experiments during the transit of Venus:

•  The Hubble Space Telescope will be observing the transit by watching and measuring the reflection of the Sun on the Moon
•  The Venus Twilight Experiment will be measuring the refraction and scattering phenomena during the transit
•  Some overall information on the phone apps and how the information will be used and an experimental archeology project

And finally, just a few fun links:

• Transit of Venus Music Project where you can download the free Morning Star soundtrack to the transit of Venus trailer
•  Music and literature, with an emphasis on John Philip Sousa, from the Library of Congress
•  Original music from the 2004 Sun-Earth Day
•  Penn High School Orchestra preforms John Philip Sousa's Transit of Venus March in 2004
•  Collection of 18th and 19th century music related to the transit of Venus 
•  A free download of the 2008 album from Transit Venus
•  Song by New Zealand folk singer Willow Mackey composed for the bicentennial of James Cook's voyage
•  Matt Rumley's song Ballad of James Cook
•  Art Gorman and Jeff Tuholski's song Young James Cook

A Habitable Exo-Earth?

The search for terrestrial, Earth-like planets has really been heating up over the last decade or so, since we've been able to find planets orbiting other stars. So far we have identified three types of exoplanets: gas giants, hot-super-Earths in close orbits, and ice giants. The discovery of smaller, terrestrial planets has been a challenge. NASA has been using it's Kepler mission to discover planets and planet candidates. This mission is "specifically designed to survey a portion of our region of the Milky Way galaxy to discover dozens of Earth-size planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets." The "habitable zone," or "Goldilocks zone," is the not-too-hot, not-too-cold region around a star where water is able to stay in a liquid form (see above picture). Kepler identifies these planets using the transit method, measuring dips in the brightness of stars when a planet crosses in front of them (see the post Exoplanet Extravaganza for more on the methods of planet finding).

There has been a lot of buzz this week about NASA's report that the Kepler mission has found it's first planet in the habitable zone. The newly confirmed planet is called Kepler-22b and it orbits in the habitable zone of a star that is similar to our sun, a G-type star. Kepler-22b is 600 light years away from us, has an orbit of 290 days around it's star, and measures about 2.4 times the radius of Earth. This makes it the smallest planet yet found in the habitable zone of such a star. Previous research has suggested that such a planet is out there, but we had yet to find and confirm that one actually exists. We have found planets that orbit on the edges of the habitable zones, similar to Venus and Mars, around smaller, cooler stars. But Kepler-22b orbits right smack in the middle of it's star's habitable zone.

What's the climate like on Kepler-22b?  It hasn't been determined if the planet has a predominately rocky, gaseous or liquid composition. The planet's temperature is probably around 72 degrees Fahrenheit, but it is unknown if the planet has an atmosphere and what it is composed of. To say whether or not it is truly Earth-like this is information we need to know. At the moment, speculations are running a bit wild, from it might not even have a surface to ideas about how civilizations have evolved there. I suppose that type of thing goes along with the discovery of the first anything.

The Kepler Mission has also discovered 1,094 other new planet candidates, bringing Kepler's total planet number up to 2,326. Of these, there are 207 that are approxiamtely Earth-size, 680 that are super Earth-size, 1,181 that are Neptune-size, 203 that are Jupiter-size, and 55 that are larger than Jupiter. These planets are just waiting for follow-up observations to verify that they are actual planets. Kepler-22b is the first to receive this confirmation. In addition to Kepler-22b, there are 48 other planet candidates in their star's habitable zone. It should be exciting to find out more details about these planets too!

I don't have a paper to cite for you on this one, but one is expected to be published soon in The Astrophysical Journal. Results will also be presented at the first Kepler Science Conference this week at NASA's Ames Research Center.

Until then here are some sources to get you started...
Find out more about the NASA's Kepler Mission.
Read NASA's News Release on Kepler-22b: "NASA's Kepler Confirms Its First Planet in Habitable Zone"
McDonald Observatory Release: "NASA Mission, Texas Astronomers Collaborate to find Goldilocks Planet, Others"
Washington Post: "NASA finds new planet Kepler 22b outside solar system with temperature right for life"
ABC News: "New Planet: An Earth-Like World, 600 Light-Years Away?"
The Telegraph: "Kepler 22b: probably not home to interesting aliens"

(image c/o NASA)

Rapid-Rise Mars

I think I've stated before on this blog that I love reading studies about planets. However, when looking back through the blog archive I was surprised to find that I hadn't written any posts about Mars. All that changes today.

The current theory of planetary formation holds that planets form out of the protoplanetary disk of material left over from the formation of a star. The dust and gas in this disk are rotating around the star, and through accretion (coagulation of particles) larger and larger bodies form. When enough particles have come together they form planetesimals (100m to 10km across). The larger ones, which have more gravity, may even perturb the motions of nearby planetesimals, attracting them towards themselves in a process called gravitational focusing. Eventually one planetesimal will outpace all of the others in its orbit and become a larger body known as a planetary embryo. The terrestrial planets are thought to have formed through the collisions between large planetary embryos of diameters between 1,000 and 5,000 km. For Earth, the last collision was the one that formed the Moon approximately 50-150 million years after the birth of the Solar System.

Mars is the fourth planet from the Sun, at a distance of 1.5 astronomical units (AU). Its radius is about half that of the Earth with a mass about 10% that of the Earth. It has highly cratered highlands in the southern hemisphere with relatively smooth lowlands in the northern hemisphere. The structure of the craters in conjunction with areas that appear to have experienced erosions and degradations suggest a combination of aeolian (dust storms, wind streaks, etc.), fluvial (water), and volcanic processes in the planet's history. The crust of the planet has been estimated to be about 25-70 km thick. Below that is a silicate mantle about 1300-1800 km thick. The iron-rich metallic core has a radius of 1500-2000 km.

You add all of this information together an an interesting question comes up: Why is Mars so small?

Model simulations can explain the mass and dynamical parameters of Earth and Venus, but they fall short in explaining the size of Mars. A new(ish) paper in the journal Nature explores one explanation for the planet's diminutive size, that the planetary embryo did not collide and merge with that many other planetary embryos. A "stranded planetary embryo" origin. Now how in the world do you go about figuring that one out? I mean, you don't exactly have the planet's baby pictures.

To assess the formation of Mars the researchers had to know the planet's accretion timescale. How and how fast did it come together. So they used the 182Hf–182W decay system in shergottite-nakhlite-chassignite (SNC) meteorites.

I'm going to try to make a complex subject sound simple in a short amount of space. Chemically and mineralogically, chondrites (stony meteorites) are a good resource for testing the early composition of a planet. The timescales, mechanisms, and chemical differentiation of planets can be figured out by quantifying the radioactive decay of short-lived isotopes. Hafnium (Hf) 182 decays into tungsten (W) 182 in a half-life of nine million years. It doesn't sound like it but this is actually a relatively rapid decay process, and it means that almost all of 182Hf will disappear in 50 million years. Both elements are refractory or non-volatile, and so remain relatively constant in meteorites. They are also lithophile elements which are known to stay in the mantle when the core of Mars formed. All this makes the 182Hf–182W decay system is ideal for dating a planet's core formation.

By chemically testing 30 chondrites and another 20 Martian meteorites, the scientists are able to measure the excess abundance of 182W relative to other non-radiogenic isotopes of W (the tungsten isotopic composition) as well as the Hf/W ratio in the Martian mantle. They also measured the relationships between hafnium (Hf), thorium (Th), and tungsten (W) and generated a hafnium-thorium ratio (Th/Hf). Because Th and W have very similar chemical behaviors the researchers were able to calculate how long it took Mars to develop into a planet. They found that Mars accreted very rapidly and reached about half of its present size in about 1.8 million years or less. This is very rapid formation and consistent with their stranded planetary embryo hypothesis.

There are some other implications for these results. 26Al is known from meteorites and has a half-life of 700,000 years. Thermal modelling shows that planets accreting in under 2.5 million years incorporate enough 26Al for radioactive decay to induce silicate melting. If the time estimates of this study are correct then that would mean "Mars would have reached [about 69%] of its present size by that time and the heat generated from 26Al decay alone would have been sufficient to establish a magma ocean." Whoa! Additionally, this evidence of a quickly forming Mars could help to explain the similarities between the xenon (Xe) content of the Martian atmosphere and Earth's atmosphere, what is referred to as the "missing xenon problem." On both planets, Xe is not very abundant compared to the concentrations of other noble gases or to Xe concentrations in space. The authors suggest that part of the atmosphere of Earth was inherited from an earlier generation of planetary embryos that had their own atmospheres. "Earth may have inherited its missing Xe problem from the atmosphere of a Mars-like planetary embryo, possibly the impactor that also formed the Moon. This idea is consistent with the time when Earth became retentive for Xe, which is estimated to be, 100Myr after the birth of the Solar System and may correspond to the time of the Moon-forming giant impact."

This is the type of paper that reminds me of how cool I think planetary science is while also reminding me why I became an ecologist rather than a chemist. Overall, very interesting results!

You can read the paper for yourself here:
N. Dauphas, and A. Pourmand. (2011) Hf–W–Th evidence for rapid growth of Mars and its status as a planetary embryo. Nature, 2011; 473 (7348): 489. (DOI: 10.1038/nature10077)

Also, check out these stories:
http://news.uchicago.edu/article/2011/05/25/mars-rapid-formation-stunted-growth
http://www.universetoday.com/85998/rapid-formation-may-have-stunted-mars-growth/
http://www.marstoday.com/news/viewpr.rss.html?pid=33647
http://www.sciencedaily.com/releases/2011/05/110525131705.htm

(image via nasa.gov)

Messenger to Mercury

The Messenger has arrived! As of 9:10 p.m. EDT on Thursday March 17th, NASA's Messenger spacecraft entered orbit around the planet Mercury and as of 9:45 p.m. rotated towards Earth and started transmitting data. MESSENGER stands for MErcury Surface, Space ENvironment, GEochemistry and Ranging. The spacecraft was launched August 3, 2004 from Cape Canaveral, Florida with the mission to "unravel the mysteries of planet Mercury." Messenger has spent the last years circling through the inner solar system, performing flybys and gravity assists of Earth, Venus, and even Mercury itself until finally settling into orbit around the innermost planet. The spacecraft carries several instruments that will take images and measurements of the planet:

The Mercury Duel Imaging System (MDIS) consists of wide-angle and narrow-angle imagers that will map landforms and topographic features. The Gamma-Ray and Neutron Spectrometer (GRNS) will detect gamma rays and neutrons that are emitted by radioactive elements on the surface and use that to map relative abundances of different elements. The Magnetometer (MAG) will map Mercury's magnetic field and magnetized rocks in the crust. The Mercury Laser Altimeter (MLA) will beam light to the planet's surface and a sensor will collect any reflected light in order to gather further information about topography. The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) is an instrument that is sensitive to light in the infrared to ultraviolet range in the spectrum and so can measure the abundances of various atmospheric gases and minerals on the surface. The Energetic Particle and Plasma Spectrometer (EPPS) will measure the composition, distribution, and energy of charged particles in the magnetosphere. And finally, the Radio Science (RS) instrument will use the Doppler effect to measure changes in spacecraft's velocity and use that to study Mercury's mass distribution, including variations in the thickness of the crust.

Mercury is the planet closest to the Sun. It is small and extremely dense with a lot of metals, a thin crust, and a thin atmosphere. It is thought to have formed out of the solar nebula, the disk of gas and dust around the newly formed Sun, but it is not known whether or not the planet formed in the location that it is today. It is odd that one of the densest objects in the solar system formed so close to the Sun. There are several ideas out there to explain why. Because Mercury resembles a planet core rather than a whole planet some think it was originally a larger object that suffered an impact that knocked part of the surface off and/or required the planet to reform. Others think that the very active early Sun blasted off the crust early in Mercury's history. Despite this possibly violent possible history, the planet has formed a thin atmosphere. Now we're not talking rain, clouds, wind etc. like we are used to thinking of on Earth. Mercury's atmosphere is more like scattered particles that only occasionally come in to contact with one another, it is more like a gas layer close to the surface, or an "exosphere." That surface has a cracked, scorched look to it. It is thought that the planet's iron core froze (or solidified) and contracted. To visualize this think about a balloon tightly covered by a piece of cellophane, if you let air out of the balloon it creates space between itself and the cellophane, but the cellophane still wants to cling to the surface of the balloon and so develops cracks or folds in order to stay in place. This theory says that Mercury's crust did something similar when the core solidified (note: the presence of a magnetic field suggests that at least part of the core may be liquid). Add to that the impact craters similar to the ones you see on our Moon and you start to get a picture of the planet. Oh yeah, and did I mention the possibility of ice? Uh-huh, the planet closest to the Sun may have ice at its poles. The rotational axis is straight, not tilted like Earth's, and so the poles never see sunlight. Barring other factors, no sunlight equals very cold and that means there could be ice. Neat.

As you can tell, there's a lot of ideas and theories out there about Mercury. Our lack of information mainly comes from the fact that Mercury is very difficult to observe. Think about it. It is really close to the Sun, and the massive amount of light coming from the Sun tends to obscure a lot of the planet's features. If you try to observe it when the Sun is below the horizon, at night, you will find that the planet never gets more than 28 degrees above the horizon. Then add the fact that the planet is tidally locked to the Sun. Tidal locking is when an object takes as long to rotate around its axis as it takes to complete its orbit, just like our Moon to us (a 1:1 resonance). In the case of Mercury, the planet does not have an exactly circular orbit and actually rotates three times for every two orbits around the Sun, in a 2:3 resonance (a year is only one and a half days long!). That tidal locking means that Mercury is always presenting the same side to us. From the two high-speed flyby's by Mariner 10 spacecraft in 1974 and 1975 we have some images, but only of one side of the planet.

It is likely that Mercury is the key to us unlocking the mechanism of terrestrial planet evolution. Messenger will gather data that will help answer the questions of why is the planet so dense, what is its geologic history, what is the nature of the magnetic field, what is the structure of the core, what volatiles (gases etc.) are present and important, and if there is ice at the poles.

But Messenger will not be the last spacecraft to visit Mercury. The European Space Agency (ESA) in a joint mission with the Japanese Aerospace Exploration Agency (JAXA) will be launching the BepiColombo in 2014 that will arrive at Mercury in 2020. This mission will further study the planet's evolution, form, interior, structure, geology, composition, atmosphere, magnetosphere, and polar regions. Find out more about this mission at their website: http://sci.esa.int/science-e/www/area/index.cfm?fareaid=30

Visit these Messenger websites to learn more about the spacecraft, the mission, and up to the minute information and images:
http://messenger.jhuapl.edu/
http://www.nasa.gov/messenger


A few news stories about the newly attained orbit:
http://www.universetoday.com/84195/success-messenger-first-spacecraft-to-orbit-mercury/
http://www.sciencedaily.com/releases/2011/03/110317232139.htm
http://www.iop.org/news/11/feb/page_48432.html
http://www.usatoday.com/tech/science/columnist/vergano/2011-03-18-Mercury-MESSENGER-gravity_N.htm
http://www.nytimes.com/2011/03/19/opinion/19sat4.html
http://www.timeslive.co.za/world/article976680.ece/Nasa-Messenger-makes-it-to-Mercury

Learn more about Mercury:
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Mercury
http://www.universetoday.com/13943/mercury/
http://www.astronomycast.com/astronomy/episode-49-mercury/
http://science.nationalgeographic.com/science/space/solar-system/mercury-article.html
and the Mariner Program:
http://history.nasa.gov/mariner.html
http://www.jpl.nasa.gov/missions/missiondetails.cfm?mission=mariner10

(image from nasa.gov)

Southern Saturnian Aurora

Image credit: NASA/JPL/University of Arizona/University of Leicester

I am absolutely fascinated by the planets. In fact, if I had to choose another field of science to go into it might just be planetary science. As such, when I see new data, particularly images, of planets I just jump on the story. I mean, just look at the above picture...its pretty incredible. What you are looking at is a picture of the planet Saturn (in case the rings didn't give it away). Its what's called a false-color composite image. These types of images show colors that differ from what you would see in a true color image, which are how an object appears to the human eye. Usually they either turn up a color aspect, change one color to another to make a feature more visible, or assign colors to particular aspects or features. When NASA's Cassini space craft took some 65 pictures with its visual and infrared mapping spectrometer (VIMS) one of these features to stand out were the glow of auroras in the south polar region. These auroras were seen streaking out about 600 miles from the cloud tops and were clearly visible in the near-infrared wavelengths of light.

In the false-color images scientists usually designate blue to indicate sunlight reflected at a wavelength of 2 microns, green to indicate sunlight reflected at 3 microns, and red to indicate thermal emission at 5 microns. Since the auroral emission appears to be green, this suggests emissions from hydrogen ions of light between 3 and 4 microns in wavelength. You can clearly see the contrast with the rings which appear blue and have a wavelength of 2 microns. The red, 5 micron, wavelengths you see in the southern hemisphere are due to the heat emission from the interior of Saturn.

Image credit: NASA/JPL/University of Arizona/University of Leicester

The auroras were seen to vary over the course of the Saturnian day. This gas giant rotates extremely fast and so a day only lasts 10 hours and 47 minutes. On what is the Saturn's day equivalent to noon and midnight the aurora can be seen to brighten significantly for several hours. This brightening is likely due to the planets angle to the Sun. The auroras are thought to occur in processes similar to those on Earth, where particles from the solar wind are channeled by the magnetic field toward the planet poles. On Saturn you also add in the effects of the electromagnetic waves generated by the moons moving through Saturn's plasma-filled magnetosphere.

And ok, these are not the first pictures of Saturn's aurora. Cassini has returned a number of detailed snapshots in the past. These images are more data scientists can use to understand this phenomena. Not to mention they look pretty bitchin'.

First, I highly recommend watching this short video by NASA/JPL:
http://saturn.jpl.nasa.gov/multimedia/videos/movies/aurora20091123-480.mov

And here are some story links:
http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=4142
http://www.jpl.nasa.gov/news/news.cfm?release=2010-313
http://www1.nasa.gov/mission_pages/cassini/whycassini/cassini20100923.html
http://www2.le.ac.uk/ebulletin/news/press-releases/2010-2019/2010/09/nparticle.2010-09-24.0238525751

Big Bright Jupiter

Jupiter is the largest planet in our solar system, and it is located at 3.95 Astronomical Units (AU) or 368 million miles from the Earth. In our night sky the planet is always bright, but this month it is even brighter than usual as it makes its closes pass by Earth for the year, and closest since 1963 and until 2022. Jupiter's orbit varies in distance about 10-11 million miles over a period of about 60 years, but in terms of brightness to use you have to look at this relatively small variation in terms of magnitude factors. Normally, the brightness varies between -1.6 and -2.94, with the latter being the brightest. But a change as small as 1% can mean a brightness change in either direction of up to 4%. In the current case, we're talking 4% brighter than normal. Tomorrow, Monday, September 20 will be the nearest point to Earth in this near pass. And on Tuesday, September 21, the Earth will pass between Jupiter and the Sun. So grab your telescope and head outside to take a look!

On the topic of looking at the planets through a telescope, Jupiter is one of the largest planets in terms of how much of the telescope's eyepiece it fills up at about 31 arc seconds across. If you have a standard amateur or backyard telescope then that's about a 12th of your field of view, and with this simple of an instrument you can see some good banding around the planet and some moons. Don't have a telescope? Try some binoculars, the view will still be good and you might even see some of Jupiter's moons (hint: keep your arms nice and steady).

If you are in the mid-northern latitudes then look for Jupiter to the lower right of the Great Square of Pegasus. The "celestial trio," Mars, Venus, and the star Spica, will rise at or just after dusk, and as this trio sets you will see Jupiter rise in the east. Or, just look for a bright "star" near the moon. In these, mid-northern latitudes, you'll see it in the early evening and you should be able to see the planet all night long. As you go further north the earlier and longer you'll see Jupiter, and as you go south the later and less you'll see it.

Also, while you are gazing at Jupiter on September 21st move your telescope or binoculars less than a degree to catch sight of the planet Uranus. Its possible that both of the planets will be visible in the same field of view. The planets line up, or are in opposition, on the same night making finding and viewing them easy.

Learn lots more about this event here:

http://earthsky.org/astronomy-essentials/bright-star-might-be-planet-jupiter-nearly-closest-since-1963

http://science.nasa.gov/science-news/science-at-nasa/2010/15sep_jupiter/

http://www.astronomycast.com/astronomy/episode-56-jupiter/

http://astronomy.fm/skylogs/jovian-chronicles/652/Jupiter-At-Opposition-In-September-2010..html

(image from astronomy.ie)

Taking One for the Team

Volcanic Venus

Venus is the brightest object in the night sky (not including the moon) and the hottest object in our solar system (not including the sun). This planet is super-weird and really intriguing. It is a little bit smaller than Earth, has no moon, has a smaller than expected magnetic field, and rotates very slowly and in the wrong direction. Its year is 244.6 days long and its day is 243 days long. The planet is covered in a thick layer of clouds that are very good at reflecting light (= has a high albedo). The atmosphere is 96.5% carbon dioxide, which traps an extrodinary amount of heat on the planet (a runaway greenhouse effect). It is thought that, at one point in history, Venus may have had oceans, but as the temperature increased they evaporated, UV light broke up the water molecules, and all this increased the greenhouse effect. Radar imaging of the surface, particularly by the Magellan probe in the early 1990's, has given detailed maps of the planet. This imaging has shown a distinct lack of craters, expected when the thick sulfuric atmosphere burns up all but the largest asteroids/meteors. But even these big craters are only about 500 million years old, suggesting that the planet has entirely resurfaced itself (likely caused by a lack of plate tectonics).

In a new online Science paper, evidence is presented that suggests that Venus is still reshaping its surface and cooling its interior via volcanic outpourings. As I said above, it is thought that a dramatic planetary resurfacing event may have occurred 500 million years ago, and this paper suggests that Venus also steadily resurfaces itself through smaller volcanic events. In addition to young craters, the Magellan probe also found nine "hot spots", low rises each a couple of thousand kilometers across, from which lava has more recently flowed. Gravity measurements taken by the probe also revealed plumes of hot rock slowly rising beneath these hot spots that may feed the eruptions. However, the age of the lava flows was unknown.

Planetary scientists from NASA's Jet Propulsion Laboratory (JPL) have taken a look at three of these hot spots using the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on the European Space Agency's Venus Express, still in orbit. Using VIRTIS, the scientists found that the hot spots radiate more heat than the rest of the planet, and were able to infer that the hot spot flows are still pretty fresh an unweathered. Calculations of the flow ages range from a few million years down to 2500 years (young when we are talking planetary history), and the researchers suggest that they are slow, steady outpourings.

Here's the story: http://www.sciencemag.org/cgi/content/full/328/5975/157-a
and www.sciencemag.org/cgi/content/abstract/science.1186785
and a NYT article including video: http://www.nytimes.com/2010/04/10/science/space/10venus.html?ref=science