“A rose by any other name…”

In my last post, “It seems the sky is falling…”, I talked about the Russian meteor event and flyby of asteroid 2012 DA14, both of which occurred on Friday, February 15, 2013. In that post I talked a lot about the various terms of things in space that can enter the Earth’s atmosphere and ultimately cause an “impact”. But there are a lot of terms and some of them have very minute differences, so I figured I’d devote a post just to explaining these terms. Specifically, I’d like to look at a few differences.

“Meteoroid” vs. “Meteor” vs. “Meteorite”

These words all share the same root, the Greek word meteōros, meaning “suspended in the air”, and look very similar, but they do mean different things. To start off, let’s think of a small piece of rock in space. We don’t care what kind of rock it is or where it comes from, let’s just call it a small rock. Now, let’s say that small rock is happily zipping around the solar system, obeying the law of gravity as it orbits the Sun, when suddenly it gets too close to Earth and the gravitational pull of the planet sends tugs it out of its original orbit and towards our planet. Now, that small piece of rock that’s on it’s way into the Earth’s atmosphere, that’s a “meteoroid”. Once that “meteoroid” hits the Earth’s atmosphere travelling at high speed it’s going to heat up and leave a trail in the sky. That heating up and the resulting streak in the sky is a “meteor”- commonly referred as a “shooting star”. If you get a whole bunch of associated “meteoroids”, say a whole bunch of little pieces of rock left over from an asteroid or comet that passed by, that enter the atmosphere at the same time, creating meteors, that’s called a “meteor shower”. So, the “meteoroid” is the small rock that causes streak of light and the “meteor” is the actual visible streak we see. Now as that “meteoroid” is hurtling through the atmosphere and heating up, it can literally blow up. That huge flash that’s caused by the disintegration of the “meteoroid” is known as a “fireball” and really bright “fireballs” are known as “bolides”. That huge flash of light is usually associated with a large deposit of energy into the atmosphere that causes a pressure wave like to ones seen in Tunguska and Chelyabinsk.

A meteor or “shooting star” streaking across the sky is really a piece of debris burning up in the atmosphere. Credit: Wikipedia

The solar system is full of little pieces of debris moving really fast and without the atmosphere that debris would constantly be pummeling the surface of the planet…and us. So the atmosphere protects us. Things are constantly entering the atmosphere and burning up, creating “meteors”. Most of these “meteoroids” are about the size of a pebble- much to small to reach the Earth’s surface. But it does happen occasionally. When large objects enter the atmosphere and make it down to Earth, that remaining piece of rock that reaches the ground is known as a “meteorite”. So yeah, if you’re one your way to work in the morning and see that there’s a huge piece of rock sitting on your car, that’s probably a “meteorite”…or there’s someone who really doesn’t like you. Don’t worry though, as Bad Astronomer Phil Plait writes, only one person has ever been hit by a meteorite and that occurred in Alabama in 1954.

This Canyon Diablo meteorite was part of the 50-meter asteroid that formed the mile-wide Meteor Crater in Arizona. Credit: Wikipedia

Now, not all “meteors” and “meteorites” are caused by natural objects in space. Think about all of the satellites and “space junk” orbiting the Earth. If any of that space junk were to re-enter the atmosphere it would burn up, just like a space rock, and cause a meteor. And another, less appealing example is astronaut waste. On the now-retired Space Shuttles, the urine was expelled out into the upper atmosphere to burn up/evaporate– this actually created a visible glow. Solid waste on the Space Shuttles was collected and removed once the Shuttle returned to the ground, unfortunately that’s not really an option on the International Space Station (ISS), where astronaut waste is stored, then loaded into a disposable space probe and ejected out to burn up in the atmosphere. So yeah, next time you wish on a shooting star, just think that it might actually be astronaut poop.

“Comet” vs. “Asteroid”

Okay so now we’ve talked about the differences between the things that enter the atmosphere. But beyond man-made sources, where do those “meteoroids” come from? Many of them are from rocky, metallic objects in the solar system known as “asteroids”. What are asteroids? According to NASA:

“Most asteroids are made of rock, but some are composed of metal, mostly nickel and iron. They range in size from small boulders to objects that are hundreds of miles in diameter. A small portion of the asteroid population may be burned-out comets whose ices have evaporated away and been blown off into space. Almost all asteroids are part of the Main Asteroid Belt, with orbits in the vast region of space between Mars and Jupiter.”

Most asteroids are actually leftover bits and pieces of planets that weren’t able to coalesce under gravity. As the NASA page describes, most asteroids live in the Asteroid Belt that orbits between Mars and Jupiter. However, as those asteroids travel around the Sun, they can bump into each other, causing a rogue asteroid to leave the Asteroid Belt and traverse the solar system. Sometimes those asteroids fall into the Sun, sometimes they collide with Earth or other planets.

Vesta, one of the largest asteroids in the solar system, was recently studied by NASA’s Dawn mission. Dawn was the first spacecraft ever to go into orbit around an asteroid. Credit: Wikipedia

So what’s the difference between an asteroid and a comet? A “comet” is an icy body that lives out in the farthest regions of the solar system. There is belief by scientists that many comets primarily live in a region at the edge of the solar system known as the Oort Cloud. As these icy bodies come into the inner solar system and approach the Sun, they increase in brightness as the heat from the Sun causes the ice to melt and reflect sunlight. Comets are generally much easier to view than asteroids due to the high reflectivity of the water vapor it releases as they travel through the inner solar system. Generally comets that pass by the orbit of the Earth leave a debris trail in their wake. When the Earth’s orbit takes it through one of those debris trails, it causes a meteor shower.

Comet West made a spectacular show for skywatchers in March 1976. This image shows a great example of the two types of tails that comets often have. One tail is caused by water vapor coming off from sunlight and the other is ionization caused by the solar wind of particles streaming off of the Sun. Credit: APOD/NASA

So comets are mostly icy bodies that live out at the very edge of the solar system and asteroids are rocky, metallic bodies that generally live in the Asteroid Belt in the region between Mars and Jupiter.

So what did we learn?

So let’s review in this handy table made by the great folks at NASA’s Near-Earth Object Program:

Asteroid A relatively small, inactive, rocky body orbiting the Sun.
Comet A relatively small, at times active, object whose ices can vaporize in sunlight forming an atmosphere (coma) of dust and gas and, sometimes, a tail of dust and/or gas.
Meteoroid A small particle from a comet or asteroid orbiting the Sun.
Meteor The light phenomena which results when a meteoroid enters the Earth’s atmosphere and vaporizes; a shooting star.
Meteorite A meteoroid that survives its passage through the Earth’s atmosphere and lands upon the Earth’s surface.

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It seems the sky is falling…

Imagine driving in your car on a lovely Friday morning and seeing a flaming ball of death streaking across the sky and coming, as best you can tell, right at you.

This view from a Russian dashboard camera shows a terrifying view of the fireball as the meteoroid entered the atmosphere and hurtled over the city of Chelyabinsk. Credit: Discovery News

That’s what terrified citizens in the lovely Russian city of Chelyabinsk experienced on the morning of Friday, February 15. The multitude of videos and photos of this meteor are simply horrifying since many of them give the impression that this huge chunk of flaming interplanetary death is about to smash right into the camera. Not only did this fireball make a scary visual impression, but it packed a very literal punch as well. As the meteoroid hurtled through the atmosphere at 40,000 mph, the heat and pressure it felt caused it to break apart with a huge amount of energy, the equivalent of 470 kilotons of TNT (or 30-40 times the power of the atomic bomb dropped on Hiroshima). The deposition of that huge amount of energy into the sky caused a pressure wave that blasted the city. Over 1,000 people were injured by the blast, mostly due to cuts and scrapes from glass as windows shattered. Scientists have now come to the conclusion that the initial object was only 17 meters wide– that’s about the size of a tractor trailer. That’s pretty small cosmically speaking. Imagine the damage that could have been inflicted if something larger had hit the atmosphere. The last time a meteor had significant large-scale impact was in 1908, again in Russia. This impact, known as the “Tunguska event“, is the largest impact ever recorded- 20-30 times larger than the one that happened this month. This meteoroid, which is estimated to have been about 100 meters wide (the size of a football field), blew up in the air and released 10-15 megatons of energy, leveling 830 square miles of trees. Witnesses to the event said that the heat and pressure from the explosion made their skin feel like it was on fire.

The 1908 Tunguska event, the largest impact near or on Earth ever recorded, leveled trees over 830 square miles. Credit: nightsky.org

Luckily the 2013 Russian meteor was much smaller, so windows got knocked out but buildings weren’t leveled. The object was actually so small that astronomers didn’t even see it coming. NASA has a whole division of people who track objects that could potentially come close to Earth, it’s known as the Near-Earth Object Program. Unfortunately, for scientists to be able to see an object it needs to be large enough to reflect an observable amount of light. That didn’t happen here.

The meteor also came as a bit of a shock since scientists were so focused on another Near-Earth Object called 2012 DA14. This 45-meter wide asteroid was scheduled for a flyby of Earth on the same day, February 15. This relatively small piece of space rock flew closer to the Earth than any other celestial body. It was 17,200 miles away at its closest approach, that’s closer than satellites in geosynchronous orbit and much, much closer than the Moon. Although scientists were certain that DA14 wouldn’t impact the Earth, they were very excited to use the close flyby as an opportunity to study the asteroid.

This collage of 72 individual radar-generated images of asteroid 2012 DA14 was created using data from NASA’s 230-foot Deep Space Network antenna at Goldstone, CA. Credit: NASA

Of course it was ironic that after weeks of assuring the public that there was no threat of an impact from DA14 another huge impact happened in Russia the same day. Scientists from NASA’s Meteoroid Environment Office concluded that the Russian meteor and DA14 were totally unrelated, having come from two very distinct trajectories/orbits. This means it was a huge cosmic coincidence that they just happened to occur on the same day…weird.

This plot of the orbits of the Russian meteor and asteroid 2012 DA14 show that the two bodies came from very different parts of the solar system and were unrelated. The Russian meteoroid most likely originated from the Asteroid Belt out past Mars. Credit: NASA/Space.com

The Cosmic Distance Ladder, part 1…

For the past few months, I’ve been spending a lot of time in my position as Manager of the UNH Observatory, in helping to prepare for the 2012 New England Fall Astronomy Festival. The event, lovingly known as NEFAF, is a family-friendly astronomy-related event that will be hosted by the UNH Physics Department in partnership with the New Hampshire Astronomical Society. As you can imagine, this is quite an undertaking, but in an incredibly exciting turn of events, we just found out that Dr. Alex Filippenko, noted astronomer from UC-Berkeley and member of the research team that won the 2011 Nobel Prize in Physics, will be giving the keynote talk at NEFAF 2012! In addition to being a highly acclaimed professor, Filippenko is also the co-author of an extremely popular astronomy textbook and a frequent contributor to the documentary series The Universe on The History Channel.

Dr. Alex Filippenko, the newly announced keynote speaker for the 2012 New England Fall Astronomy Festival to be held at the UNH Observatory.

That extremely exciting news has inspired me to do a couple of posts about the expansion of the universe, the area of research that Dr. Filippenko works on. But before we can really get into talking about that, we need to cover a very basic aspect of astronomy, but something that most non-astronomers don’t really know about. I was at a public session at the Observatory this weekend when a guest who had never studied astronomy before asked me what she thought might be an “ignorant” question: she wanted to know how exactly astronomers knew the distances to objects in space. This is by no means an ignorant question, in fact it’s a very fundamental and very involved question that really gets at the very nature of astronomy.

Astronomy by definition is an observational science. Unlike many other scientific disciplines, astronomers can’t really do experiments in a laboratory (although some do). But the stereotypical astronomer can’t throw his subject (a star or galaxy) on a lab bench and dissect it or set up an experiment to test it, so astronomers need to observe and record data. Okay, so we observe light, that tells us what something looks like, where it is, and how bright it is. Big deal, is that really that helpful scientifically. Well, not really. So we have to come up with ways to get more information from observing the light. The main way we do that is by breaking the light up in a spectrometer, an instrument that breaks light down into a spectrum of colors. This breakdown of light can reveal an abundance of new information including what the object is made up of, how hot it is, how fast and in what direction it’s moving, how old it is, and more.

The question of how astronomers calculate the distance to an astronomical object varies depending on how far away the object is. Because most of these techniques only work up to a certain distance, there is actually a progression of different approaches that astronomers use to measure distance to celestial objects. This list of methods of measuring astronomical distances is known as the Cosmic Distance Ladder (or less poetically, the extragalactic distance scale).

A graphical representation of the distance-measuring techniques that make up the Cosmic Distance Ladder. “1 A.U.” is 1 astronomical unit or approximately 93 million miles, the distance from the Earth to the Sun. A “pc” is a parsec, equal to 3.2 lightyears (206,265 A.U.) or about 20 trillion miles. “Mpc” stands for “Megaparsec” or millions of parsecs. Credit: University of Rochester

In our solar system

The first step in our exploration of the universe was to our own celestial neighborhood. The first step was precise measurement of the size scale of the solar system, which started with the determination of the distance between the Earth and the Sun. As I’ve explained before, this measurement was originally calculated via observations of transits of the planet Venus across the disk of the Sun. Early on in the 20th century, observations of asteroids also played an important role in this measurement. But today the distance from the Earth to the Sun, defined as 1 Astronomical Unit or “AU”, is measured with high precision using radar ranging. By bouncing a radar beam off another planet, usually Venus, and measuring the time that beam takes to return to Earth, scientists can very accurately determine the difference in the size of the two planets’ orbits. Using that difference and the ratio of the two orbital sizes, we can very easily calculate the distance the Earth must be from the Sun. We use a similar process even closer to home. During the Apollo missions of the late 1960s-early 1970s, astronauts deployed the lunar laser ranging experiments, arrays of mirrors that allowed scientists to measure the distance to Earth’s only natural satellite with extreme precision using lasers. This radar ranging is how we’ve calculated the distance to most of the objects in our solar system. More recently, we can also use spacecraft in orbit around other planets as a tape measure by measuring the time it takes for a signal to travel from the spacecraft to its controllers on Earth.

Another  way we can get measure the distance to the planets and to nearby stars is a phenomenon known as stellar parallax. This method is less accurate than radar ranging for planets, but is very good for stars in our local stellar neighborhood. Parallax is something you experience almost every day. Hold your thumb up at arm’s length. Close one eye, then open that one and close the other. Notice how your thumb appears to shift with respect to the objects far off in the distance? That’s parallax! Astronomers take measurements of a planet or star a two points in Earth’s orbit (6 months apart) and measure the angular shift of an object with respect to the background stars between those two measurements. Then, because we know the distance the Earth is from the Sun, we can use some basic geometry to calculate the distance to that star or planet in the foreground.

This diagram shows how parallax is used to find the distance to planets in our solar system and nearby stars. Scientists make two observations 6 months apart, measuring the angle that an object (the red dot) makes with regard to the background stars between the two observations. Then using the distance from the Earth to the Sun (1 A.U.) and some simple geometry, the distance to the object (d) can be calculated. Credit: Hyperphysics

It was using parallax, that Italian astronomer Giovanni Domenico Cassini was able to roughly calculate the distance to Mars in 1672. His calculation was a little bit off though, because instead of taking two measurements 6 months apart, he sent his colleague to Cayenne, French Guiana (on the northern coast of South America) to make observations while he stayed in Paris. Then Cassini could make the same parallax calculation using the known distance between the two observation points (~4400 miles) instead of the distance from the Sun to the Earth. This single direct measurement of the distance to Mars, which is now easily calculated and heavily used by missions such as Curiosity, actually allowed for the calculation of the distances to all the planets. Since geometry and Kepler’s Laws governed the basic ratios the Sun-planet distances, you only needed to measure one Earth-planet distance to be able to easily calculate them all. This major contribution and several others in planetary science (including the discovery of four of Saturn’s moons and joint discovery of Jupiter’s Great Red Spot) prompted NASA to name the Saturn-bound spacecraft mission after the him.

Giovanni Domenico Cassini

[To be continued…]

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Curiosity did not kill the cat…

So as I’m sure you’ve all heard, NASA’s Curiosity rover successfully landed on the surface of Mars in the early hours of yesterday morning (east coast time). In an earlier post, I relayed the video by NASA of the harrowing entry that Curiosity needed to go through to reach the Martian surface safely and highlighted that the entire elaborate landing procedure was 100% automated since it takes double the time the landing would take to occur for information to be relayed back to Earth. And all the taxings of a mission so complicated, despite all the finesse and delicacy needed to execute such a bold attempt, and despite all the things that could go wrong, the scientists and engineers at NASA succeeded. Honestly, if you watch the 7 Minutes of Terror video, realize that scientists built and programmed a machine that could do that all automatically, millions of miles away from Earth (352 million to be exact) while moving at thousands of miles per hour and have it work flawlessly, and aren’t awed and impressed, then well you should probably check your pulse.

The Mars Science Laboratory’s mission is to investigate the interior of the Gale Crater for signs of microbial life. Top left: A profile of Curiosity’s landing site, Gale Crater. Top Right: A simulation of Curiosity’s proposed mission. Bottom: A map showing the distribution of NASA’s missions to the Martian surface. Credit: BBC News

In addition to being the largest rover we’ve ever sent to another world, twice as long (about 10 feet)  and five times as heavy as NASA’s twin Mars Exploration RoversSpirit and Opportunity, launched in 2003, Curiosity also has new equipment that allows it to gather samples of rocks and soil, process them, and then distribute them to various scientific instruments it carries for analysis; that internal instrument suite includes a gas chromatograph, a mass spectrometer, and a tunable laser spectrometer with combined capabilities to identify a wide range of organic (carbon-containing) compounds and determine the ratios of different isotopes of key elements. There’s clearly a reason why the mission is called the Mars Science Laboratory.

This illustration from NASA shows the size and instrumentation of Curiosity that will help it to investigate the possibility of microbial life on Mars. (A) Six independent wheels allowing the rover to travel over the rocky Martian surface. (B) Equipped with 17 cameras, Curiosity will identify particular targets and then zap them with a  laser to probe their chemistry. (C) If the signal is significant, Curiosity will swing over instruments on its arm for close-up investigation. (D) Samples drilled from rock, or scooped from the soil, can be delivered to two hi-tech analysis labs inside the rover body. (E) The results are sent to Earth through antennas on the rover deck. Return commands tell the rover where it should drive next. Credit: BBC News

According to NASA, Curiosity carries with it “the most advanced payload of scientific gear ever used on Mars’ surface, a payload more than 10 times as massive as those of earlier Mars rovers.” All that gear will be important as Curiosity investigates its main science objective: whether or not there is evidence of microbial life (past or present) in Martian rocks. Although both Spirit and Opportunity listed the search for life as among their scientific goals, neither rover was really equipped to search for microbial life; the twin early generation rovers were more specifically looking for water or the evidence of past water on the Martian surface and then whether that water could sustain life. Curiosity, on the other hand, is specifically equipped to look for microbial life (or evidence of it) in the rocks and soil of the Red Planet. More than just the roving explorer that its forebears were, Curiosity is for all intents and purposes a laboratory on wheels.

This image of Curiosity descending to the Martian surface with its parachute was taken by the High-Resolution Imaging Science Experiment (HiRISE) camera on the Mars Reconnaissance Orbiter. The rover is descending toward the etched plains just north of the sand dunes that fringe Aeolis Mons. Credit: NASA

And it’s not just the instrumentation that Curiosity is equipped with that make NASA rover 2.0 better than previous generations, but the technology it used to get to the Martian surface is leaps and bounds ahead of how Spirit and Opportunity landed. If you watch this NASA movie that highlights the landing process for the Mars Exploration Rovers (which only had six minutes of terror), you’ll notice that most of the landing procedure seems similar to Curiosity’s. Extremely high-speed entry into the Martian atmosphere, heat shield, parachute, rocket thrusters, etc. Until you get to the last step, when Spirit and Opportunity wer basically dropped onto the Martian surface at nearly 60 mph, surrounded by huge air bags, and allowed to bounce three or four times until they settled. Compared to the fine precision placement of the Curiosity rover earlier this week, the previous rovers’ landings were downright barbaric, like trying to hunt a deer by throwing rocks.

This image, one of the first returned by Curiosity, shows the rover’s shadow on the Martian surface and one of the main targets of its mission, Aeolis Mons, on the distant horizon. Credit: CNN

Rather than violently smashing the $2.6 billion rover into the surface and hoping for the best, this descent involved a sky crane and the world’s largest supersonic parachute, which allowed the spacecraft carrying Curiosity to target the specific landing area that NASA scientists had meticulously chosen. That landing area is roughly 12 km (7.5 miles) from the foot of the Martian peak previously known as Mount Sharp. Aeolis Mons, as it’s now known, is the 18,000-foot (5,500-meter) peak at the center of Gale Crater, previously known as Mount Sharp. The stratified composition of the mountain could give scientists a layer-by-layer look at the history of the planet as Curiosity attempts its two-year mission to determine whether Mars ever had an environment capable of supporting life.

Possibly the biggest piece of the NASA Curiosity puzzle has been the enormous PR campaign that NASA has thrown behind the rover. Not only has the rover and it’s 7 Minute of Terror video been all over the internet, TV news, newspapers, and other media outlets, but NASA has even gone out of its way to get high-level stars in the fold. Last week they released this video (above) of William Shatner, most famously known as Capt. James Tiberius Kirk of Star Trek, narrating a preview of Curiosity’s “Grand Entrance” to Mars. There was also another video featuring narration by Wil Wheaton (Wesley Crusher from Star Trek: The Next Generation).

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Venus: Earth’s Evil Twin…

I have to say, I learn something new about space pretty much every day. A couple of weeks ago I was covering a lecture for an introductory level astronomy class here at UNH. The lecture topic was the formation of the solar system with a highlight on the details of the inner terrestrial planets. So, in preparation for the lecture (the night before), I looked through the textbook: The Cosmic Perspective. And while reading in there about Venus, my mind was blown. What exactly blew my mind? That Venus’s fate could easily have been Earth’s.

Venus, the second planet from the Sun, is the hottest place in the solar system. This radar image from the Magellan spacecraft shows the planet’s surface. Credit: JPL/NASA

Venus is almost the same size as Earth (95% in radius and 81.5% in mass) and made up of pretty much the same stuff. The similarity in size and density between Venus and Earth leads scientists to believe that they share a similar internal structure: a core, mantle, and crust. Both have significant volcanic activity, although Earth has active plate tectonics and we don’t see evidence of that on Venus. The big difference between the two planets comes in the stuff above the planet’s surface: the atmosphere. Earth’s atmosphere is made up primarily of nitrogen (78%) and oxygen (21%), with trace amounts  (~1% or less) of argon, carbon dioxide, water vapor, and other things. On Venus it’s an entirely different story. The Venusian atmosphere is almost entirely made up of carbon dioxide (97%), a very efficient greenhouse gas.

Now you’ve probably heard of greenhouse gases and their role in the greenhouse effect which is playing a role in concerns about global warming. A quick review of how the greenhouse effect works: a greenhouse gas, is a gas (most commonly a hydrocarbon) that allows visible light to pass through it but traps heat from infrared radiation. Okay, so who cares? Well the atmosphere is full of small amounts of naturally occurring greenhouse gases (such as carbon dioxide, methane, and water vapor) which allow the visible light from the Sun to pass through our atmosphere and reach the surface. That’s awesome, because if those gases were opaque to visible light– meaning they did not allow them to pass through– then all the plants on Earth would die and we’d all be sickly pale. It’s this next part that makes greenhouse gases significant. The Earth is warm, astronomically speaking compared to the cold vacuum of space, and emits its own radiation (or light) in the infrared. Back in the mid-19th century, scientists realized that anything that’s warm emits radiation– called blackbody radiation— most of it at wavelengths that we can’t see. The relation between the spectrum of light that an object radiates and its temperature is governed by Planck’s Law. A practical example are night-vision goggles which pick up on the thermal infrared radiation that’s given off by the warmth of a human’s body. Our Sun (10,340º F) is much, much hotter than Earth (~40º F) or a human (~98º F), so it emits a blackbody spectrum which peaks in the visible, whereas humans and the Earth emit mostly in the infrared. It’s the shifting of this peak which gives stars their different colors.

Here’s an example of how an objects blackbody radiation spectrum changes based on its temperature. The object actually emits light at every wavelength along the curve, but its peak wavelength is directly related to its temperature. Credit: University of Twente

So Earth (and Venus because of its similar size) radiates most of its light in the infrared, which greenhouse gases do not allow to pass through the atmosphere. So instead of that newly radiated heat (IR light) being transmitted out through the atmosphere and into space, it gets trapped and increases the temperature for us on the surface. Now, normally for us on Earth that’s fine because our planet does a great job of regulating the surface temperature through a process known as the carbon dioxide (CO2) cycle. The CO2 cycle helps Earth to self-regulate its temperature. If it’s too hot, the excess carbon dioxide in the atmosphere dissolves in the water in the ocean, then settles and is stored in rocks of the ocean floor. If it’s too cold, then the carbon dioxide which returns to the interior of the planet (via subduction caused by plate tectonics) is released back into the atmosphere by volcanoes. So Earth can do a really good job at keeping track of its own thermostat, which has helped Earth maintain a stable surface temperature even though the temperature of the Sun has changed significantly over time. The problem with the greenhouse effect on Earth is that if we add too many new greenhouse gases (specifically carbon dioxide) that Earth can’t/isn’t ready to handle, then we can mess up the delicate balance that Earth is working so hard to maintain for us.

This diagram shows how the greenhouse effect on Venus allows visible sunlight through, but traps the infrared radiation being released by the planet. Credit: weirdwarp.com

So what, Venus has more carbon dioxide in its atmosphere, why does that matter to Earth? Well, because it could very easily have happened to us. The only reason that Venus is a horrible, deadly world, the hottest in the solar system, with temperatures over 700º F is because it’s closer to the Sun than Earth is. The average distance of Venus’s from the Sun (called the semi-major axis) is ~72% of that of Earth’s; that means it’s roughly 66,928,200 miles away from the Sun (that’s a mere 26,027,600 miles– or 109 times the distance to the Moon– closer than Earth is). Astronomically speaking, that’s a very small distance. If primordial Earth’s orbit was altered enough to move it that roughly 26 million miles closer to the Sun– by, say an asteroid impact similar to the one that we believe created the Moon— then Earth could have ended up the same as Venus. If Earth were to move that mere 30% closer to the Sun, then the liquid water oceans which we have on Earth that dissolve the excess carbon dioxide, removing it from our atmosphere, would have evaporated. Water vapor is actually one of the best greenhouse gases, so the evaporation of the water vapor into the air combined with the failure to remove carbon dioxide from the atmosphere, would result in a runaway heating effect that the planet would have no way to stop.

So it’s by a very small distance, a distance that’s only 30 times larger than the diameter of the Sun, that Earth escaped being a hellish, fiery deathtrap and became the one oasis of life that we know of in the universe.

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7 Minutes of Terror…

Hello all! So I made it successfully back to NASA Goddard from Snowmass Village, Colorado. The conference went well, but as with all scientific conferences, it was quite daunting. However to help me recover, this weekend I visited the Smithsonian National Air and Space Museum’s Steven F. Udvar-Hazy Center to see the recently retired Space Shuttle Discovery. As I’ve chronicled in the past, Discovery is by far the most accomplished of the five Shuttles that have flown (of which only three survive)– an impressive resume that puts it in the upper echelon of American vessels right alongside the USS Enterprise (that’s the Navy aircraft carrier, not the fictional starship…). Seeing Discovery in person was extremely impressive. Being able to see the scorch marks from reentry on the underbelly of the nose and then realizing that each individual tile is labeled was very cool. Up close, the Shuttle looked much more like a patchwork of different components than the sleek space-faring plane that I’m used to seeing in photos. The size also caught me off guard. I’m not sure why, but I’ve always assumed that the Space Shuttle must comparable in size to a commercial airplane that most of us are used to, like a Boeing 747, but it’s not, it’s much smaller. I guess in a way it was both bigger and smaller than I expected…if that makes any sense. Below are some pictures of Discovery.

Moving on to other cool space things. Have you ever wondered what it would be like travelling to Mars? Well a new short video from the great folks at NASA Jet Propulsion Laboratory (JPL) out in Pasadena, CA shows how harrowing the journey might actually be. The team working on the new Mars rover, Curiosity (part of the Mars Science Laboratory mission) have released a new video, entitled 7 Minutes of Terror, detailing the rover’s planned 7-minute descent through the Martian atmosphere and onto the surface of the Red Planet. If you’ve ever doubted the ingenuity or ability of NASA scientists and engineers then you should definitely watch this short video (it’s much less than seven minutes long). The sheer magnitude of the problem that they are attempting to tackle is impressive enough (aka landing something the size of a couch on an object millions of miles away), let alone the fact that they are doing it without any communication with the spacecraft (the entire landing process will have been completed in the time it takes communication to reach Earth from Mars) and dealing with insanely sensitive and delicate instrumentation. It’s just a great look at how insanely talented and inspiring the folks at NASA are. Kudos to them.

Curiosity will be the third functioning NASA rover on Mars, joining its Mars Exploration Rover brethren Spirit and Opportunity who landed in 2004 (Opportunity is still functioning), and will specifically be investigating the habitability of Mars. Curiosity was specifically designed to study layers in Martian mountains that hold evidence about wet environments of the planet’s early existence and assess whether Mars ever had an environment able to support microbial life forms. The rover, launched on November 26, 2011, is scheduled to land on the Martian surface, near the base of a mountain inside Gale Crater, close to the Martian equator, early on August 6, 2012 (EDT) to begin its two-year prime mission.

NASA’s next Mars rover, Curiosity, on a test drive. Credit: NASA/JPL

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Voting for 3QD Science blogging competition closes tonight at midnight!…

For those of you who have already voted, thanks so much!

Shame on the rest of you! But’s it’s okay, go to the 3 Quarks’s Daily voting site and look for my blog post: The Sky’s the Limit: Saturn’s rings explained…, all votes are much appreciated! I’m very close to getting in the top 20 to move on to the next round and voting ends tonight at midnight. Thanks for your support!

And just as a special treat, here’s a galactic birthday cake from Astronomy Picture of the Day. Looks delicious!

The bet the best part is the dark energy filling! Credit: APOD

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