Posted on by Nancy Atkinson

Arctic Ozone Levels Reach All-Time Low

This set of images by the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite shows March 19, 2010 on the left, and the right shows the same date in 2011. March 2010 had relatively high ozone, while March 2011 has low levels. NASA image by Rob Simmon, with data courtesy of Ozone Hole Watch.

In the past, massive ozone loss over Antarctica has grabbed the headlines. But this year, measurements by several different sources show record levels of stratospheric ozone loss over the Arctic. Scientists say the main reason for the record ozone loss this year is that unusually cold stratospheric temperatures, which have endured later into the season than usual. Scientists say the unusual loss is not catastrophic, but something that needs to be monitored.

The World Meteorological Organization cautioned that people who live in northerly latitudes could get sunburned easier, noting that ozone-depleted air masses extended from the north pole to southern Scandinavia.

The record low temperatures were caused by unusually strong winds, known as the polar vortex, which isolated the atmospheric mass over the North Pole and prevented it from mixing with air in the mid-latitudes.

This has allowed for the formation of polar stratospheric clouds, and the catalytic chemical destruction of ozone molecules occurs on the surface of these clouds which form at 18-25 kilometers height when temperatures drop below -78 C.

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This created conditions similar to those that occur every southern hemisphere winter over the Antarctic.
Measurements by ESA’s Envisat satellite, the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite, and France’s MetOp satellite, as well as observations made since January from the ground and from balloons show all show that 40% of ozone molecules have been destroyed over the Arctic.

Ozone is a protective atmospheric layer found at around 25 km altitude that acts as a sunlight filter shielding life on Earth from harmful ultraviolet rays, which can increase the risk of skin cancer and cataracts in humans and harm marine life.

Stratospheric temperatures in the Arctic usually do vary widely from winter to winter. Last year, temperatures and ozone above the Arctic were very high. The last unusually low stratospheric temperatures over the North Pole were recorded in 1997.

See this link from ESA that shows a animation comparison between 2010 and 2011.

“This depletion is not necessarily a big surprise,” said Paul Newman, an atmospheric scientist and ozone expert at NASA’s Goddard Space Flight Center. “The ozone layer remains vulnerable to large depletions because total stratospheric chlorine levels are still high, in spite of the regulation of ozone-depleting substances by the Montreal Protocol. Chlorine levels are declining slowly because ozone-depleting substances have extremely long lifetimes.”

Ozone “holes” do not form consistently over the North Pole like they do in Antarctica. “Last winter, we had very high lower stratospheric temperatures and ozone levels were very high; this year is just the opposite,” Newman said. “The real question is: Why is this year so dynamically quiet and cold in the stratosphere? That’s a big question with no good answer.”

Scientists will be watching in coming months for possible increases in the intensity of ultraviolet radiation (UV) in the Arctic and mid-latitudes, since ozone is Earth’s natural sunscreen. “We need to wait and see if this will actually happen,” Newman said. “It’s something to look at but it is not catastrophic.”

Scientists are also investigating why the 2011 and 1997 Arctic winters were so cold and whether these random events are statistically linked to global climate change. “In a changing climate, it is expected that on average stratospheric temperatures cool, which means more chemical ozone depletion will occur,” said Mark Weber from the University of Bremen.

Experts say that on a global scale, the ozone layer is still on a long-term course for recovery. But for decades to come, there remains a risk of major ozone losses on yearly or regional scales.

Sources: Nature, ESA, NASA, The Independant Science Daily Earth/Sky Blog

Posted on by Nancy Atkinson

From the Earth and Moon (and Russia) With Love

Russia's Elektro-L spacecraft captured this view of the Moon over the Red Sea region of the Earth. Credit: NPO Lavochkin

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This stunning picture of the Moon and Earth was taken by Russia’s new Elektro-L spacecraft, a weather-forecasting satellite that launched in January 2011. This is the first major spacecraft developed in post-Soviet Russia, and it is designed to give Russian meteorologists the ability to watch the entire disk of the planet, thanks to the satellite’s position in the geostationary orbit 36,000 kilometers above the equator. The clarity of the images is fantastic, as you can see in another image of just the Earth, below. The Elektro-L is designed to last at least a decade, and will enable local and global weather forecasting, analysis of oceanic conditions, as well as space weather monitoring, such as measurements of solar radiation, properties of Earth’s ionosphere and magnetic field.

On Feb. 26, 2011, at 14:30 Moscow Time, the Elektro-L satellite produced its first breathtaking image of the home planet. Credit: NPO Lavochkin

Learn more about the Elektro-L mission at their website.

h/t: SDO Facebook page.

Posted on by Nancy Atkinson

Study: Thawing Permafrost Could Accelerate Global Warming

From a press release from the University of Colorado Boulder:

Up to two-thirds of Earth’s permafrost likely will disappear by 2200 as a result of warming temperatures, unleashing vast quantities of carbon into the atmosphere, says a new study by the University of Colorado Boulder’s Cooperative Institute for Research in Environmental Sciences (CIRES).

The carbon resides in permanently frozen ground that is beginning to thaw in high latitudes from warming temperatures, which will impact not only the climate but also international strategies to reduce fossil fuel emissions, said CU-Boulder’s Kevin Schaefer, lead study author. “If we want to hit a target carbon dioxide concentration, then we have to reduce fossil fuel emissions that much lower than previously thought to account for this additional carbon from the permafrost,” he said. “Otherwise we will end up with a warmer Earth than we want.”
Continue reading “Study: Thawing Permafrost Could Accelerate Global Warming”

Posted on by Nancy Atkinson

More Asteroids Could Have Made Life’s Ingredients

This artist's concept uses hands to illustrate the left and right-handed versions of the amino acid isovaline. Credit: NASA/Mary Pat Hrybyk-Keith

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From a NASA press release:

A wider range of asteroids were capable of creating the kind of amino acids used by life on Earth, according to new NASA research. Amino acids are used to build proteins, which are used by life to make structures like hair and nails, and to speed up or regulate chemical reactions. Amino acids come in two varieties that are mirror images of each other, like your hands. Life on Earth uses the left-handed kind exclusively. Since life based on right-handed amino acids would presumably work fine, scientists are trying to find out why Earth-based life favored left-handed amino acids.

In March, 2009, researchers at NASA’s Goddard Space Flight Center in Greenbelt, Md., reported the discovery of an excess of the left-handed form of the amino acid isovaline in samples of meteorites that came from carbon-rich asteroids. This suggests that perhaps left-handed life got its start in space, where conditions in asteroids favored the creation of left-handed amino acids. Meteorite impacts could have supplied this material, enriched in left-handed molecules, to Earth. The bias toward left-handedness would have been perpetuated as this material was incorporated into emerging life.

In the new research, the team reports finding excess left-handed isovaline (L-isovaline) in a much wider variety of carbon-rich meteorites. “This tells us our initial discovery wasn’t a fluke; that there really was something going on in the asteroids where these meteorites came from that favors the creation of left-handed amino acids,” says Dr. Daniel Glavin of NASA Goddard. Glavin is lead author of a paper about this research published online in Meteoritics and Planetary Science January 17.

This is a photo of a carbon-rich meteorite analyzed in the study. Credit: Antarctic Meteorite Laboratory/NASA Johnson Space Center

“This research builds on over a decade of work on excesses of left-handed isovaline in carbon-rich meteorites,” said Dr. Jason Dworkin of NASA Goddard, a co-author on the paper.

“Initially, John Cronin and Sandra Pizzarello of Arizona State University showed a small but significant excess of L-isovaline in two CM2 meteorites. Last year we showed that L-isovaline excesses appear to track with the history of hot water on the asteroid from which the meteorites came. In this work we have studied some exceptionally rare meteorites which witnessed large amounts of water on the asteroid. We were gratified that the meteorites in this study corroborate our hypothesis,” explained Dworkin.

L-isovaline excesses in these additional water-altered type 1 meteorites (i.e. CM1 and CR1) suggest that extra left-handed amino acids in water-altered meteorites are much more common than previously thought, according to Glavin. Now the question is what process creates extra left-handed amino acids. There are several options, and it will take more research to identify the specific reaction, according to the team.

However, “liquid water seems to be the key,” notes Glavin. “We can tell how much these asteroids were altered by liquid water by analyzing the minerals their meteorites contain. The more these asteroids were altered, the greater the excess L-isovaline we found. This indicates some process involving liquid water favors the creation of left-handed amino acids.”

Another clue comes from the total amount of isovaline found in each meteorite. “In the meteorites with the largest left-handed excess, we find about 1,000 times less isovaline than in meteorites with a small or non-detectable left-handed excess. This tells us that to get the excess, you need to use up or destroy the amino acid, so the process is a double-edged sword,” says Glavin.

Whatever it may be, the water-alteration process only amplifies a small existing left-handed excess, it does not create the bias, according to Glavin. Something in the pre-solar nebula (a vast cloud of gas and dust from which our solar system, and probably many others, were born) created a small initial bias toward L-isovaline and presumably many other left-handed amino acids as well.

One possibility is radiation. Space is filled with objects like massive stars, neutron stars, and black holes, just to name a few, that produce many kinds of radiation. It’s possible that the radiation encountered by our solar system in its youth made left-handed amino acids slightly more likely to be created, or right-handed amino acids a bit more likely to be destroyed, according to Glavin.

It’s also possible that other young solar systems encountered different radiation that favored right-handed amino acids. If life emerged in one of these solar systems, perhaps the bias toward right-handed amino acids would be built in just as it may have been for left-handed amino acids here, according to Glavin.

The research was funded by the NASA Astrobiology Institute (NAI), which is administered by NASA’s Ames Research Center in Moffett Field, Calif.; the NASA Cosmochemistry program, the Goddard Center for Astrobiology, and the NASA Post Doctoral Fellowship program. The team includes Glavin, Dworkin, Dr. Michael Callahan, and Dr. Jamie Elsila of NASA Goddard.

Posted on by Ken Kremer

2010 Tied for Warmest Year on Record say NOAA and NASA

World map with global temperature changes from 1880 to 2010. Credit: NASA GISS

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Newly released scientific data shows that 2010 equals 2005 as the Earths warmest year on record over the last 131 years, say researchers from NOAA and NASA. Temperature measurements from instrumented monitoring stations date back to 1880.

The past decade from 2001 to 2010 was the warmest on record and includes 9 of the 10 hottest years. A NOAA ranking of the 15 hottest years globally shows they all occurred in the last 15 years since 1995.

2010 was the 34th consecutive year with global temperatures above the 20th century average of 57.0 F (13.9°C), according to NOAA data. 1976 was the last year with a below average global temperature. Updated.

Global surface temperature anomalies for 2010. Credit: NOAA

Overall, the combined global land and ocean surface temperatures for 2010 and 2005 has risen 1.12 F (0.62 C) compared with the 20th century average, according to NOAA. The average global temperature in 2010 was 58.12 degrees compared to 57.0 F (13.9°C) as the average for all of 20th century. 2010 was also the wettest year on record.

The rise in Earths’ global temperature has been accompanied by a decline in arctic sea ice. Specifically, surface air temperatures in the arctic were warmer than normal during the summer of 2010. The sea ice extent measured in September 2010, was the 3rd lowest on record since accurate monitoring began in 1979, states NOAA in the annual Arctic report card. See Video below.

Scientists from NOAA’s National Climatic Data Center (NCDC) in Asheville, N.C. and NASA’s Goddard Institute for Space Studies (GISS) in New York City announced the findings on Jan 12. The temperature data are collected by weather stations that span across the globe.

Global measurements by independent researchers in the UK at the Met Office Hadley Centre and at the Japanese Meteorological Agency closely match the trend of warming temperatures gathered by NOAA NCDC and NASA GISS.

The graphic below combines the actual temperature data collected independently by the four research agencies. The temperature trend lines are remarkably consistent.

Multiple institutions monitor global surface temperatures. Despite subtle differences in the ways the scientists perform their analyses, these four widely referenced records show remarkable agreement. Credit: NASA Earth Observatory/Robert Simmon

Much of the rise in global temperatures has taken place since the late 1970’s, says NASA. The rate of increase has been about 0.36 F per decade. The NASA GISS weather data were collected using over 1000 meteorological stations around the world, satellite observations of sea surface temperature and Antarctic research station measurements.

2010 average annual temperature ranks by state in the US. Credit: NOAA

The data are fed into a computer program which then calculates temperature anomalies — the difference between surface temperature in a given month and the average temperature for the same period during 1951 to 1980. NASA GISS uses that three-decade period as the baseline for analysis against which climate change can be tracked. NOAA uses the entire 20th century.

For the contiguous United States, NOAA analysis shows that “2010 was the 14th consecutive year with an annual temperature above the long-term average. Since 1895, the temperature across the US has increased at an average rate of approximately 0.12 F per decade.”

More at these press releases from NOAA and NASA

There are large areas in the Arctic without weather stations. NASA GISS approaches the problem by filling in gaps with data from the nearest land stations. The Climatic Research Unit at the University of East Anglia, which works jointly with the Met Office Hadley Centre, leaves much of the region out of its global temperature analysis. Credit: NASA Earth Observatory/Robert Simmon
2010 Global Significant Weather and Climate Events. Credit: NOAA
Global Temperatures.
The year 2010 tied with 2005 as the warmest year since records began in 1880. The annual global combined land and ocean surface temperature was 0.62°C (1.12°F) above the 20th century average. The range associated with this value is plus or minus 0.07°C (0.13°F). The 2010 combined land and ocean surface temperature in the Northern Hemisphere was also the warmest on record, while the combined land and ocean surface temperature in the Southern Hemisphere was the sixth warmest such period on record. Credit: NOAA

NOAA Arctic Report Card 2010

Posted on by Nancy Atkinson

“Aflockalypse” — Mass Animal Deaths Now Mapped on Google

Screenshot of the Google Maps Aflockalypse maps of mass bird deaths.

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You have to admit, the news is a little weird: 5,000 blackbirds falling dead from the sky in Arkansas; tens of thousands of dead fish in Chesapeake Bay; 50-100 dead birds found strewn in lawns in Sweden; 40,000 dead crabs washed up on England’s shores; 530 penguins, numerous other seabirds, five dolphins, and three giant sea turtles dead in Brazil; 200 American Coots dead on a Texas bridge; hundreds of snapper fish dead in New Zealand. And the list keeps growing.

Eerie coincidence? Or just a symptom of the digital age where news travels faster than you can say “The End is Nigh?”

You can now keep track of what is being called “Aflockalypse” on Google Maps.

Google Maps links reports of animal deaths, as well as reports of birds that have succumbed to the bird flu. By clicking on the blue balloons on the map you will be given a link that will provide the original news report. You can also click the links in the left side panel of the map.

The map provides a quick look at where the mass, unexplained deaths are taking place. But some say the map could help solve the mystery, as there has been suggestions the map could be overlaid on a current global oil exploration map to test the hypothesis that the deaths could have been caused by ground penetrating tomography.

This isn’t the first time that unexplained mass animal deaths have occurred — see this article on Time for the “Top 10 Strange Mass Animal Deaths” — but it seems unprecedented to have them happen all over the world within a few days.

Or is it? Others have suggested that the internet age allows us to connect the dots where there are none to be connected. The dead birds in Arkansas on New Years Eve — seemingly the first report of mass animal deaths — have been attributed to them flying through a fireworks display, and there could be logical reasons for the others, too.

Find out more by interacting with the Google Map.

Posted on by Matt Williams

North American Plate

All About Plate Tectonics

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Oftentimes when we think of the Earth, we tend to think of stable landmasses that are surrounded by vast oceans. It’s easy for us to forget that the Earth is still very much a work in a progress, that its foundations are mobile slabs of rock, known as plates, which are constantly on the move and shuffling back and forth. In our next of the woods, aka. North American, we inhabit what is appropriately named the North American Plate, the tectonic boundary that covers most of North America, Greenland, Cuba, Bahamas, and parts of Siberia and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. It is composed of two types of lithosphere: the upper crust (where the continental land masses reside) and the thinner oceanic crust.

As one of the Earth’s original continents, the North American Plate started forming some three billion years ago when the planet was much hotter and mantle convection much more vigorous. Roughly two billions years ago, the Earth cooled and these old floating pieces of the lithosphere, called cratons, stopped growing. Since that time, the plates have been moving back and forth across the globe, their cratons colliding to form the continents that we know and recognize today. Beginning in the Cambrian period, over five hundred million years ago, the cratons of Laurentia and Siberia broke off from the main landmass of Pangaea, which thereafter would be known as Gondwana. By the late Mezosoic era (circa two hundred million years ago) the Laurentian and Eurasian cratons combined to form the supercontinent of Laurasia. Since that time, the separation of the North American and Eurasian plates has led to the separation of the North America from Asia. As the North American plate drifted west, the landmasses of Iceland and Greenland broke off in the east while in the west, it collided with the Eurasian plate again, adding the landmass of Siberia to East Asia.

In terms of what makes the plates move across the Earth, a number of theories coexist. One theory is what is known as the “conveyor belt” principle, where the Earth’s lithosphere has a higher strength and lower density than the underlying asthenosphere and lateral density variations in the mantle result in the slow drifting motion of the plates, resulting in collisions and subduction zones. One of the main points of the theory is that the amount of surface of the plates that disappear through subduction along the boundaries where they collide is more or less equal to the new crust that is formed along the margins where they are drifting apart. In this way, the total surface of the Globe remains the same. A different explanation lies in different forces generated by the rotation of the Globe and tidal forces of the Sun and the Moon. A final theory which predates the Plate Tectonics “paradigm”, has it that a gradual shrinking (contraction) or gradual expansion of the Globe is responsible.

We have written many articles about the North American Plate for Universe Today. Here’s an article about the continental plate, and here’s an article about the plate tectonics theory.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded related episodes of Astronomy Cast about Plate Tectonics. Listen here, Episode 142: Plate Tectonics.

Sources:
http://en.wikipedia.org/wiki/North_American_Plate
http://en.wikipedia.org/wiki/Plate_tectonics
http://www.platetectonics.com/book/page_5.asp
http://www.uwgb.edu/dutchs/GeolColBk/NAmerPlate.HTM
http://en.wikipedia.org/wiki/Mantle_convection
http://en.wikipedia.org/wiki/Craton
http://en.wikipedia.org/wiki/Laurasia

Posted on by Matt Williams

How Much Does the Earth Weigh?

Winter Solstice
Earth as viewed from the cabin of the Apollo 11 spacecraft. Credit: NASA

Earth is, by any reckoning, a pretty big place. Ever since humanity first began the process of exploring, philosophers and scholars have sought to understand its exact dimensions. In addition to wanting to quantify its diameter, circumference, and surface area, they have also sought to understand just how much weight it packs on.

In terms of mass, Earth is also a pretty big customer. Compared to the other bodies of the Solar System, it is the largest and densest of the rocky planets. And over the course of the past few centuries, our methods for determining its mass have improved – leading to the current estimate of 5.9736×1024kg (1.31668×1025 lbs).

Size and Composition:

With a mean radius of 6,371.0 km (3,958.8 mi), Earth is the largest terrestrial planet in our Solar System. This means that it is composed primarily of silicate rock and metals, which are differentiated between a solid inner core, an outer core of molten metal, and a silicate mantle and crust made of silicate material.

This cutaway of planet Earth shows the familiar exterior of air, water and land as well as the interior: from the mantle down to the outer and inner cores. Currents in hot, liquid iron-nickel in the outer core create our planet's protective but fluctuating magnetic field. Credit: Kelvinsong / Wikipedia
This cutaway of planet Earth shows the familiar exterior of air, water and land as well as the interior: from the mantle down to the outer and inner cores. Credit: Kelvinsong / Wikipedia

Earth is composed approximately of 32% iron, 30% oxygen, 15% silicon, 14% magnesium, 3% sulfur, 2% nickel, 1.5% calcium, and 1.4% aluminum, with the remaining made up of trace elements. Meanwhile, the core region is primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements.

Mass and Density:

Earth is also the densest planet in the Solar System, with a mean density of 5.514 g/cm3 (0.1992 lbs/cu in). Between its size, composition, and the distribution of its matter, the Earth has a mass of 5.9736×1024 kg (~5.97 billion trillion metric tons) or 1.31668×1025 lbs (6.585 billion trillion tons).

But since the Earth’s density is not even throughout – i.e. it is denser towards the core than it is at its outer layers – its mass is also not evenly distributed. In fact, the density of the inner core (at 12.8 to 13.1 g/cm³; 0.4624293 lbs/cu in), while the density of the crust is just 2.2–2.9 g/cm³ (0.079 – 0.1 lbs/cu in).

The layers of the Earth, a differentiated planetary body. Credit: Wikipedia Commons/Surachit
The layers of the Earth, a differentiated planetary body. Credit: Wikipedia Commons/Surachit

This overall mass and density are also what causes Earth to have a gravitational pull equivalent to 9.8 m/s² (32.18 ft/s2), which is defined as 1 g.

History of Study:

Modern scientists discerned what the mass of the Earth was by studying how things fall towards it. Gravity is created by mass, so the more mass an object has, the more gravity it will pull with. If you can calculate how an object is being accelerated by the gravity of an object, like Earth, you can determine its mass.

In fact, astronomers didn’t accurately know the mass of Mercury or Venus until they finally put spacecraft into orbit around them. They had rough estimates, but once there were orbiting spacecraft, they could make the final mass calculations. We know the mass of Pluto because we can calculate the orbit of its moon Charon.

The Geoid 2005 model, which was based on data of two satellites (CHAMP and GRACE) plus surface data. Credit: GFZ
The Geoid 2005 model, which was based on data of two satellites (CHAMP and GRACE) plus surface data. Credit: GFZ

And by studying other planets in our Solar System, scientists have had a chance to improve the methods and instruments used to study Earth. From all of this comparative analysis, we have learned that Earth outstrips Mars, Venus, and Mercury in terms of size, and all other planets in the Solar System in terms of density.

In short, the saying “it’s a small world” is complete rubbish!

We have written many articles about Earth for Universe Today. Here’s Ten Interesting Facts About Earth, What is the Diameter of the Earth?, How Strong is the Force of Gravity on Earth?, What is the Rotation of the Earth?

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Sources:

Posted on by Matt Williams

Solar Day

Winter Solstice
Earth as viewed from the cabin of the Apollo 11 spacecraft. Credit: NASA

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Since the dawn of time, human beings have relied on the cycles of the sun, the moon, and the constellations through the zodiac in order to measure time. The most basic of these was the motion of the Sun as it traced an apparent path through the sky, beginning in the East and ending in the West. This procession, by definition, is what is known as a Solar Day. Originally, it was thought that this motion was the result of the Sun moving around the Earth, much like the Moon, celestial objects and stars seemed to do. However, beginning with Copernicus’ heliocentric model, it has since been known that this motion is due to the daily rotation of the earth around the Sun’s polar axis.

Up until the 1950’s, two types of Solar time were used by astronomers to measure the days of the year. The first, known as Apparent Solar Time, is measured in accordance with the observable motion of the Sun as it moves through the sky (hence the term apparent). The length of a solar day varies throughout the year, a result of the Earth’s elliptical orbit and axial tilt. In this model, the length of the day varies and the accumulated effect is a seasonal deviation of up to 16 minutes from the mean. The second type, Solar Mean Time, was devised as a way of resolving this conflict. Conceptually, Mean solar time is based on a fictional Sun that is considered to move at a constant rate of 360° in 24 hours along the celestial meridian. One mean day is 24 hours in length, each hour consisting of 60 minutes, and each minute consisting of 60 seconds. Though the amount of daylight varies significantly throughout the year, the length of a mean solar day is kept constant, unlike that of an apparent solar day.

The measure of time in both of these models depends on the rotation of the Earth. In both models, the time of day is not plotted based on the position of the Sun in the sky, but on the hour angle that it produces – i.e. the angle through which the earth would have to turn to bring the meridian of the point directly under the sun. Nowadays both kinds of solar time stand in contrast to newer kinds of time measurement, introduced from the 1950s and onwards which were designed to be independent of earth rotation.

We have written many articles about Solar Day for Universe Today. Here’s an article about how long a day is on Earth, and here’s an article about the rotation of the Earth.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Sources:
http://en.wikipedia.org/wiki/Solar_time
http://www.tpub.com/content/administration/14220/css/14220_149.htm
http://scienceworld.wolfram.com/astronomy/SolarDay.html
http://www.britannica.com/EBchecked/topic/553052/solar-time?anchor=ref144523
http://en.wikipedia.org/wiki/Hour_angle

Posted on by Nancy Atkinson

Simple Colors Could Provide First Details of Alien Worlds

At best, the few extrasolar planets we have imaged directly are just points of light. But what can that light tell us about the planet? Maybe more than we thought. As you probably know the, Deep Impact spacecraft flew by comet Hartley 2 today, taking images from only 700 km away. But maneuvering to meet up with the comet is not the only job this spacecraft has been doing. The EPOXI mission also looked for ways to characterize extrasolar planets and the team made a discovery that should help identify distinctive information about extrasolar planets. How did they do it? By using the Deep Impact spacecraft to look at the planets in our very own solar system.

The spacecraft imaged the planetary bodies in our solar system — in particular the Earth, Mars and our Moon — (see here for movies of the Moon transiting Earth) and astronomer Lucy McFadden and UCLA graduate Carolyn Crow compared the reflected red, blue, and green light and grouped the planets according to the similarities they saw. The planets fall into very distinct regions on this plot, where the vertical direction indicates the relative amount of blue light, and the horizontal direction the relative amount of red light.

This suggests that when we do have the technology to gather light from individual exoplanets, astronomers could use color information to identify Earth-like worlds. “Eventually, as telescopes get bigger, there will be the light-gathering power to look at the colors of planets around other stars,” McFadden says. “Their colors will tell us which ones to study in more detail.”

On the plot, the planets cluster into groups based on similarities in the wavelengths of sunlight that their surfaces and atmospheres reflect. The gas giants Jupiter and Saturn huddle in one corner, Uranus and Neptune in a different one. The rocky inner planets Mars, Venus, and Mercury cluster off in their own corner of “color space.”

But Earth really stands out, and its uniqueness comes from two factors. One is the scattering of blue light by the atmosphere, called Rayleigh scattering, after the English scientist who discovered it. The second reason Earth stands out in color is because it does not absorb a lot of infrared light. That’s because our atmosphere is low in infrared-absorbing gases like methane and ammonia, compared to the gas giant planets Jupiter and Saturn.

“It is Earth’s atmosphere that dominates the colors of Earth,” Crow says. “It’s the scattering of light in the ultraviolet and the absence of absorption in the infrared.”

So, this filtering approach could provide a preliminary look at exoplanet surfaces and atmospheres, giving us an inkling of whether the planet is rocky or a gas planet, or what kind of atmosphere it has.

EPOXI is a combination of the names for the two extended mission components for the Deep Impact spacecraft: the first part of the acronym comes from EPOCh, (Extrasolar Planet Observations and Characterization) and the flyby of comet Hartley 2 is called the Deep Impact eXtended Investigation (DIXI).