NASA Aids in Characterizing Super-Earth Atmosphere

A team of astronomers, including two NASA Sagan Fellows, has made the first characterizations of a super-Earth's atmosphere, by using a ground-based telescope. A super-Earth is a planet up to three times the size of Earth and weighing up to 10 times as much. The findings, reported in the Dec. 2 issue of the journal Nature, are a significant milestone toward eventually being able to probe the atmospheres of Earth-like planets for signs of life.

The team determined the planet, GJ 1214b, is either blanketed with a thin layer of water steam or surrounded by a thick layer of high clouds. If the former, the planet itself would have an icy composition. If the latter, the planet would be rocky or similar to the composition of Neptune, though much smaller.

"This is the first super-Earth known to have an atmosphere," said Jacob Bean, a NASA Sagan Fellow and astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "But even with these new measurements, we can't say yet what that atmosphere is made of. This world is being very shy and veiling its true nature from us."

GJ 1214b, first discovered in December 2009, is 2.7 times the size of Earth and 6.5 times as massive. Previous observations of the planet's size and mass demonstrated it has a low density for its size, leading astronomers to conclude the planet is some kind of solid body with an atmosphere.

The planet orbits close to its dim star, at a distance of 0.014 astronomical units. An astronomical unit is the distance between Earth and the sun, approximately 93 million miles. GJ 1214b circles too close to its star to be habitable by any life forms.

Bean and his team observed infrared light as the planet crossed in front of its star. During such transits, the star's light filters through the atmosphere. Gases absorb the starlight at particular wavelengths, leaving behind chemical fingerprints detectable from Earth. This same type of technique has been used to study the atmospheres of distant "hot Jupiters," or Jupiter-like planets orbiting close to their stars, and found gases like hydrogen, methane and sodium vapor.

In the case of the super-Earth, no chemical fingerprints were detected; however, this doesn't mean there are no chemicals present. Instead, this information ruled out some possibilities for GJ 1214b's atmosphere, and narrowed the scope to either an atmosphere of water steam or high clouds. Astronomers believe it's more likely the atmosphere is too thin around the planet to let enough light filter through and reveal chemical fingerprints.

"A steamy atmosphere would have to be very dense – about one-fifth water vapor by volume -- compared to our Earth, with an atmosphere that's four-fifths nitrogen and one-fifth oxygen with only a touch of water vapor," Bean said. "During the next year, we should have some solid answers about what this planet is truly like."

The team, which included Bean's co-authors -- Eliza Miller-Ricci Kempton, a NASA Sagan Fellow at the University of California in Santa Cruz, and Derek Homeier of the Institute for Astrophysics in Gottingen, Germany -- examined GJ 1214b using the ground-based Very Large Telescope at Paranal Observatory in Chile.

"This is an important step forward, narrowing our understanding of the atmosphere of this planet," said NASA Exoplanet Exploration Program Scientist Douglas Hudgins at NASA Headquarters in Washington. "Bizarre worlds like this make exoplanet science one of the most compelling areas in astrophysics today."

The Sagan Fellowship Program is administered by the NASA Exoplanet Science Institute at the California Institute of Technology in Pasadena. Its purpose is to advance the scientific and technical goals of NASA's Exoplanet Exploration Program. The program is managed for NASA by the Jet Propulsion Laboratory in Pasadena, Calif. Caltech manages JPL for NASA.

More information about NASA's planet-finding missions is online at:http://planetquest.jpl.nasa.gov . More information about NASA's Sagan Fellowship Program is at http://nexsci.caltech.edu/sagan .

Thin Air - Cassini Finds Ethereal Atmosphere at Rhea

NASA's Cassini spacecraft has detected a very tenuous atmosphere known as an exosphere, infused with oxygen and carbon dioxide around Saturn's icy moon Rhea. This is the first time a spacecraft has directly captured molecules of an oxygen atmosphere – albeit a very thin one -- at a world other than Earth.


The oxygen appears to arise when Saturn's magnetic field rotates over Rhea. Energetic particles trapped in the planet's magnetic field pepper the moon’s water-ice surface. They cause chemical reactions that decompose the surface and release oxygen. The source of the carbon dioxide is less certain.

Oxygen at Rhea's surface is estimated to be about 5 trillion times less dense than what we have at Earth. But the new results show that surface decomposition could contribute abundant molecules of oxygen, leading to surface densities roughly 100 times greater than the exospheres of either Earth's moon or Mercury. The formation of oxygen and carbon dioxide could possibly drive complex chemistry on the surfaces of many icy bodies in the universe.

"The new results suggest that active, complex chemistry involving oxygen may be quite common throughout the solar system and even our universe," said lead author Ben Teolis, a Cassini team scientist based at Southwest Research Institute in San Antonio. "Such chemistry could be a prerequisite for life. All evidence from Cassini indicates that Rhea is too cold and devoid of the liquid water necessary for life as we know it."

Releasing oxygen through surface irradiation could help generate conditions favorable for life at an icy body other than Rhea that has liquid water under the surface, Teolis said. If the oxygen and carbon dioxide from the surface could somehow get transported down to a sub-surface ocean, that would provide a much more hospitable environment for more complex compounds and life to form. Scientists are keen to investigate whether life on icy moons with an ocean is possible, though they have not yet detected it.

The tenuous atmosphere with oxygen and carbon dioxide makes Rhea, Saturn's second largest moon, unique in the Saturnian system. Titan has a thick nitrogen-methane atmosphere, but very little carbon dioxide and oxygen.

"Rhea is turning out to be much more interesting than we had imagined," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "The Cassini finding highlights the rich diversity of Saturn’s moons and gives us clues on how they formed and evolved."

Scientists had suspected Rhea could have a thin atmosphere with oxygen and carbon dioxide, based on remote observations of Jupiter's icy moons by NASA's Galileo spacecraft and Hubble Space Telescope. Other Cassini observations detected oxygen escaping from icy Saturn ring particles after ultraviolet bombardment. But Cassini was able to detect oxygen and carbon dioxide in the exosphere directly because of how close it flew to Rhea – 101 kilometers, or 63 miles – and its special suite of instruments.

In the new study, scientists combined data from Cassini's ion and neutral mass spectrometer and the Cassini plasma spectrometer during flybys on Nov. 26, 2005, Aug. 30, 2007, and March 2, 2010. The ion and neutral mass spectrometer "tasted" peak densities of oxygen of around 50 billion molecules per cubic meter (1 billion molecules per cubic foot). It detected peak densities of carbon dioxide of around 20 billion molecules per cubic meter (about 600 million molecules per cubic foot).

The plasma spectrometer saw clear signatures of flowing streams of positive and negative ions, with masses that corresponded to ions of oxygen and carbon dioxide.

"How exactly the carbon dioxide is released is still a puzzle," said co-author Geraint Jones, a Cassini team scientist based at University College London in the U.K. "But with Cassini's diverse suite of instruments observing Rhea from afar, as well as sniffing the gas surrounding it, we hope to solve the puzzle."

The carbon dioxide may be the result of “dry ice” trapped from the primordial solar nebula, as is the case with comets, or it may be due to similar irradiation processes operating on the organic molecules trapped in the water ice of Rhea. The carbon dioxide could also come from carbon-rich materials deposited by tiny meteors that bombarded Rhea's surface.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency, and the Italian Space Agency. NASA's Jet Propulsion Laboratory, Pasadena, Calif., a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The ion and neutral mass spectrometer team and the Cassini plasma spectrometer team are based at Southwest Research Institute, San Antonio.

For more information about the Cassini mission, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov .

Rocks and Stars with Amy: This Asteroid Inspected by #32

Over the course of the nine months we’ve been operating WISE, we’ve observed over 150,000 asteroids and comets of all different types. We had to pick all of these moving objects out of the hundreds of millions of sources observed all over the sky — so you can imagine that sifting through all those stars and galaxies to find the asteroids is not easy!

We use a lot of techniques to figure out how to distinguish an asteroid from a star or galaxy. Even though just about everything in the universe moves, asteroids are a whole lot closer to us than your average star (and certainly your average galaxy), so they appear to move from place to place in the WISE images over a timescale of minutes, unlike the much more distant stars. It’s almost like watching a pack of cyclists go by in the Tour de France. Also, WISE takes infrared images, which means that cooler objects like asteroids look different than the hotter stars. If you look at the picture below, you can see that the stars appear bright blue, whereas the sole asteroid in the frame appears red. That’s because the asteroid is about room temperature and is therefore much colder than the stars, which are thousands of degrees. Cooler objects will give off more of their light at longer, infrared wavelengths that our WISE telescope sees. We can use both of these unique properties of asteroids — their motion and their bright infrared signatures — to tease them out of the bazillions of stars and galaxies in the WISE images.


Thanks to the efforts of some smart scientists and software engineers, we have a very slick program that automatically searches the images for anything that moves at the longer, infrared wavelengths. With WISE, we take about a dozen or so images of each part of the sky over a couple of days. The system works by throwing out everything that appears again and again in each exposure. What’s left are just the so-called transient sources, the things that don’t stay the same between snapshots. Most of these are cosmic rays — charged particles zooming through space that are either spat out by our sun or burped up from other high-energy processes like supernovae or stars falling into black holes. These cosmic rays hit our detectors, leaving a blip that appears for just a single exposure. Also, really bright objects can leave an after-image on the detectors that can persist for many minutes, just like when you stare at a light bulb and then close your eyes. We have to weed the real asteroid detections out from the cosmic rays and after-images.

The data pipeline is smart enough to catch most of these artifacts and figure out what the real moving objects are. However, if it’s a new asteroid that no one has ever seen before, we have to have a human inspect the set of images and make sure that it’s not just a collection of artifacts that happened to show up at the right place and right time. About 20 percent of the asteroids that we observe appear to be new, and we examine those using a program that we call our quality assurance (QA) system, which lets us rapidly sift through hundreds of candidate asteroids to make sure they’re real. The QA system pops up a set of images of the candidate asteroid, along with a bunch of “before” and “after” images of the same part of the sky. This lets us eliminate any stars that might have been confused for the asteroids. Finally, since the WISE camera takes a picture every 11 seconds, we take a look at the exposures taken immediately before the ones with the candidate asteroid — if the source is really just an after-image persisting after we’ve looked at something bright, it will be there in the previous frame. We’ve had many students — three college students and two very talented high school students — work on asteroid QA. They’ve become real pros at inspecting asteroid candidates!

Meanwhile, the hunt continues — we’re still trekking along through the sky with the two shortest-wavelength infrared bands, now that we’ve run out of the super-cold hydrogen that was keeping two of the four detectors operating. Even though our sensitivity is lower, we’re still observing asteroids and looking for interesting things like nearby brown dwarfs (stars too cold to shine in visible light because they can’t sustain nuclear fusion). Our dedicated team of asteroid inspectors keeps plugging away, keeping the quality of the detections very high so that we leave the best possible legacy when our little telescope’s journey is finally done.

In the well known Pleiades star cluster, starlight is slowly destroying this wandering cloud of gas and dust. The star Merope lies just off the upper

In the well known Pleiades star cluster, starlight is slowly destroying this wandering cloud of gas and dust. The star Merope lies just off the upper left edge of this picture from the Hubble Space Telescope. In the past 100,000 years, part of the cloud has by chance moved so close to this star--only 3,500 times the Earth-Sun distance--that the starlight itself is having a very dramatic effect. Pressure of the star's light significantly repels the dust in the reflection nebula, and smaller dust particles are repelled more strongly. As a result, parts of the dust cloud have become stratified, pointing toward Merope. The closest particles are the most massive and the least affected by the radiation pressure. A longer-term result will be the general destruction of the dust by the energetic starlight.

In the well known Pleiades star cluster, starlight is slowly destroying this wandering cloud of gas and dust. The star Merope lies just off the upper

In the well known Pleiades star cluster, starlight is slowly destroying this wandering cloud of gas and dust. The star Merope lies just off the upper left edge of this picture from the Hubble Space Telescope. In the past 100,000 years, part of the cloud has by chance moved so close to this star--only 3,500 times the Earth-Sun distance--that the starlight itself is having a very dramatic effect. Pressure of the star's light significantly repels the dust in the reflection nebula, and smaller dust particles are repelled more strongly. As a result, parts of the dust cloud have become stratified, pointing toward Merope. The closest particles are the most massive and the least affected by the radiation pressure. A longer-term result will be the general destruction of the dust by the energetic starlight.

Spiral Extraordinaire

Scientists have yet to discover what caused the strange spiral structure. Nor do they know why it glows. The glow may be caused by light reflected from nearby stars. As for the spiral itself, current supposition is that this is the result of a star in a binary star system entering the planetary nebula phase, when its outer atmosphere is ejected. Given the expansion rate of the spiral gas, a new layer must appear about every 800 years, a close match to the time it takes for the two stars to orbit each other. The above image was taken in near-infrared light by the Hubble Space Telescope.

first Imager full-disk infrared image of the Earth

Operational Environmental Satellite – GOES-15 – took its first Imager full-disk infrared image of the Earth on April 26 starting at 1730 UTC (1:30 p.m. EDT). Each of the five Imager spectral bands are shown. There is one visible band and four infrared bands (shortwave window, water vapor, longwave window and a CO2 sensitive band)

The Sounder is another instrument on GOES-15 which also took Infrared images of the Earth. The Sounder is designed to provide data from which atmospheric temperature and moisture profiles, surface and cloud-top temperatures, and ozone distribution can be deduced by mathematical analysis.

GOES-15 also provides visible images of Earth. On April 6, GOES-15 captured its first visible image of Earth.

Climate Variability

The ocean is a significant influence on Earth's weather and climate. The ocean covers 70% of the global surface. This great reservoir continuously exchanges heat, moisture, and carbon with the atmosphere, driving our weather patterns and influencing the slow, subtle changes in our climate. The oceans influence climate by absorbing solar radiationand releasing heat needed to drive the atmospheric circulation, by releasing aerosols that influence cloud cover, by emitting most of the water that falls on land as rain, by absorbing carbon dioxide from the atmosphereand storing it for years to millions of years. The oceans absorb much of the solar energy that reaches earth, and thanks to the high heat capacity of water, the oceans can slowly release heat over many months or years. The oceans store more heat in the uppermost 3 meters (10 feet) that the entire atmosphere, the key to understanding global climate change is inextricably linked to the ocean.

Climate is influenced by storage of heat and CARBON DIOXIDE in the ocean, which depends on both physical and biological processes. Let's look at some of these processes. At the end of the last ice age, about 15,000 years ago, and the ice sheets melted away and climate warmed at that time. Ice sheets began to grow, and climate cool about 130,000 years ago at the beginning of the last ice age. About 130,000 years ago, fed by evaporation of ocean waters, the polar ice caps thickened and expanded Earth cooled by almost 12° C and global sea level to drop 130m below its current level. About 15,000 years ago, this process was reversed as more sunlight reached areas near the Arctic Circle, and Earth emerged from the ice age. Earth is about 8° Celsius (14° Fahrenheit) warmer today than it was then. Still recovering from the ice age, global sea level continues to rise. The past century alone has seen global temperature increase by 0.6 degree Celsius (1 degree Fahrenheit), and the average global sea level over the past decade has risen steadily. Is this just part of the natural cycle? How much of this warming is due to the burning of fossil fuels? Is human nature affecting Mother Nature? What should we do? Our response to the challenge of global warming begins by formulating the right set of questions.

The first step in addressing the issue of global warming is to recognize that the warming pattern, if it continues, will probably not be uniform. The term "global warming" only tells part of the story; our attention should be focuses on "global climate change." The real threat may not be the gradual rise in global temperature and sea level, but the redistribution of heat over the Earth's surface. Some spots will warm, while others will cool; these changes, and the accompanying shifts in rainfall patterns, could relocate agricultural regions across the planet. By studying the oceans from space, we can unlock a vast store of information about our changing environment.

Climate is effected by both the biological and physical processes of the oceans. In addition, physical and biological processes affect each other creating a complex system. Both the ocean and the atmosphere transport roughly equal amounts of heat from Earth's equatorial regions - which are intensely heated by the Sun - toward the icy poles, which receive relatively little solar radiation. The atmosphere transports heat through a complex, worldwide pattern of winds; blowing across the sea surface, these winds drive corresponding patterns of ocean currents. But the ocean currents move more slowly than the winds, and have much higher heat storage capacity. The winds drive ocean circulation transporting warm water to the poles along the sea surface. As the water flows poleward, it releases heat into the atmosphere. In the far North Atlantic, some water sinks to the ocean floor. This water is eventually brought to the surface in many regions by mixing in the ocean, completing the oceanic conveyor belt (see below). Changes in the distribution of heat within the belt are measured on time scales from tens to hundreds of years. While variations close to the ocean surface may induce relatively short-term climate changes, long-term changes in the deep ocean may not be detected for many generations. The ocean is the thermal memory of the climate system.

• Physical characteristics of heat transport and ocean circulation impact the Earth's climate system. Like a massive 'flywheel' that stabilizes the speed of an engine, the vast amounts of heat in the oceans stabilizes the temperature of Earth. The heat capacity of the ocean is much greater than that of the atmosphere or the land. As a result, the ocean slowly warms in the summer, keeping air cool, and it slowly cools in winter, keeping the air warm. A coastal city like San Francisco has a small range of temperature throughout the year, but a mid-continental city like Fargo, ND has a very wide range of temperatures. The ocean carries substantial heat only to the sub-tropics. Poleward of the sub-tropics, the atmosphere carries most of the heat.

• Climate is also influenced by the "biological pump," a biological process in the ocean that impacts concentrations of carbon dioxide in the atmosphere. The oceanic biological productivity is both a source and sink of carbon dioxide, one of the greenhouse gases that control climate. The "biological pump" happens when phytoplankton convert carbon dioxide and nutrients into carbohydrates (reduced carbon). A little of this carbon sinks to the sea floor, where it is buried in the sediments. It stays buried for perhaps millions of years. Oil is just reduced carbon trapped in sediments from millions of years ago. Through photosynthesis, microscopic plants (phytoplankton) assimilate carbon dioxide and nutrients (e.g., nitrate, phosphate, and silicate) into organic carbon (carbohydrates and protein) and release oxygen.

• Carbon dioxide is also transferred through the air-sea interface. Deep water of the ocean can store carbon dioxide for centuries. Carbon dioxide dissolves in cold water at high latitudes, and is subducted with the water. It stays in the deeper ocean for years to centuries before the water is mixed back to the surface and warmed by the sun. The warm water releases carbon dioxide back to the atmosphere. Thus the conveyor belt described below carries carbon dioxide into the deep ocean. Some (but not all, or even a large part) of this water comes to the surface in the tropical Pacific perhaps 1000 years later, releasing carbon dioxide stored for that period. The physical temperature of the ocean helps regulate the amount of carbon dioxide is released or absorbed into the water. Cold water can dissolve more carbon dioxide than warm water. Temperature of ocean is also impacted the biological pump. Penetrative solar radiation warms the ocean surface causing more carbon dioxide to be released into the atmosphere. Oceanic processes of air-sea gas fluxes effect biological production and consequentially impacting climate. But as plant growth increases, the water gets cloudy and prevents the solar radiation from penetrating beneath the ocean surface.

NASA Oceanography & Climate

NASA satellite observations of the oceans of the past three decades have improved our understanding of global climate change by making global measurements needed for modeling the ocean-atmosphere climate system. NASA uses several instruments to get sea-surface temperature (AVHRR or other), height

(altimeter), winds (scatterometers), productivity (MODIS), and salinity (future instruments). Global data sets available on time scales of days to years (and, looking ahead, to decades) have been and will be a vital resource for scientists and policy makers in a wide range of fields. Ocean surface topography and currents, vector winds (both speed and direction), sea-surface temperature, and salinity are the critical variables for understanding the ocean-climate connection.

Sea Winds

Scatterometers are used to measure vector winds. The SeaWinds scatterometer has provided scientists with the most detailed, continuous global view of ocean-surface winds to date, including the detailed structure of hurricanes, wide-driven circulation, and changes in the polar sea-ice masses. Scatterometer signals can penetrate through clouds and haze to measure conditions at the ocean surface, making them the only proven satellite instruments capable of measuring vector winds at sea level

day and night, in nearly all weather conditions.

Combined with data from Topex/Poseidon, Jason-1, and weather satellites, moorings and drifters, data from SeaWinds and its follow-on missions will be used to study long-term change. Earth's weather patterns such as El Niño, and the Northern Oscillation, which affect the hydrologic and bio-geochemical balance of the ocean-atmosphere system.

Ocean Surface Topography

Radar altimeters like those on the Topex/Poseidon and Jason missions, are used to measure ocean surface topography. Bouncing radio waves off the ocean surface and timing their return with incredible accuracy, these instruments tell us the distance from the satellite to the sea surface within a few centimeters - the equivalent of sensing the thickness of a dime from a jet flying at 35,000 feet! At the same time, special tracking systems on the satellites give their position relative to the center of mass of Earth also with an accuracy of a few cen timeters. By subtracting the height of the satellite above the sea from the height of the satellite above the center of mass, scientists calculate maps of the sea-surface height and changes in the height due to tides, changing currents, heat stored inthe ocean, and amount of water in the ocean.

By mapping the topography of the ocean we can determine the speed and direction of ocean currents. Just as wind blows around high- and lo w-pressure centers in the atmosphere, water flows around the high and lows of the ocean surface.

Maps of sea-surface height are most useful when they are converted to topographic maps. To determine topography of the sea-surface, height maps are compared with a gravitational reference map that shows the hills and valleys of a motionless ocean due to variations in the pull of gravity. The GRACE (Gravity Recovery and Climate Experiment) mission will provide very accurate maps of gravity that will allow us to greatly improve our knowledge of ocean circulation. GRACE has provided gravity measurements that are up to 100 times more accurate than previous values. This improved accuracy will lead the way to break-throughs in our understanding of ocean circulation and heat transport.
Two animations showing sea surface height (SSH) and sea surface temperature (SST) Anomalies in the Pacific Ocean from October 1992 to August 2002. The increase in temperature and height in the equatorial region west of South America illustrates the 1997-98 El Nino event.

Temperature & Salinity

Water is an enormously efficient heat-sink. Solar heat absorbed by bodies of water during the day, or in the summer, is released at night, or in winter. But the heat in the ocean is also circulating. Temperature & Salinity control the sinking of surface water to the deep ocean, which affects long-term climate change. Such sinking is also a principal mechanism by which the oceans store and transport heat and carbon dioxide. Together, temperature and salinity differences drive a global circulation within the ocean sometimes called the Global Conveyor Belt.

The heat in the water is carried to higher latitudes by ocean currents where it is released into the atmosphere. Water chilled by colder temperatures at high latitudes contracts (thus gets more dense). In some regions where the water is also very salty, such as the far North Atlantic, the water becomes dense enough to sink to the bottom. Mixing in the deep ocean due to winds and tides brings the cold water back to the surface everywhere around the ocean. Some reaches the surface via the global ocean water circulation conveyor belt to complete the cycle.

During this circulation of cold and warm water, carbon dioxide is also transported. Cold water absorbs carbon dioxide from the atmosphere, and some sinks deep into the ocean. When deep water comes to the surface in the tropics, it is warmed, and the carbon dioxide is released back to the atmosphere.

Salinity can be as important as temperature in determining density of seawater in some regions such as the western tropical Pacific and the far North Atlantic. Rain reduces the salinity, especially in regions of very heavy rain. Some tropical areas get 3,000 to 5,000 millimters of rain each year. Evaporation increases salinity because as evaporation occurs, salt is left behind thus making surface water denser. Evaporation in the tropics averages 2,000 millimeters per year. This denser saltier water sinks into the ocean contributing to the global circulation patterns and mixing. Ocean salinity measurements have been few and infrequent, and in many places salinity has remained unmeasured. Remotely sensed salinity measurements hold the promise of greatly improving our ocean models. This is the challenge of project Aquarius, a NASA mission scheduled to launch in 2008, which will enable us to further refine our understanding of the ocean-climate connection.

The Biological Pump

Life in the ocean consumes and releases large quantities of carbon dioxide. Across Earth's oceans, tiny marine plants called phytoplankton use chlorophyll to capture sunlight during photosynthesis and use the energy to produce sugars. Phytoplankton are the basis of the ocean food web, and they play a significant role in Earth's climate, since they draw down carbon dioxide, a greenhouse gas, at the same rate as land plants. About half of the oxygen we breathe arises from photosynthesis in the ocean.

Because of their role in the ocean's biological productivity and their impact on climate, scientists want to know how much phytoplankton the oceans contain, where they are located, how their distribution is changing with time, and how much photosynthesis they perform. They gather this information by using satellites to observe chlorophyll as an indicator of the number, or biomass, of phytoplankton cells.

Probably the most important and predominant pigment in the ocean is chlorophyll-α contained in microscopic marine plants known as phytoplankton. Chlorophyll-α absorbs blue and red light and reflects green light. If the ratio of blue to green is low for an area of the ocean surface, then there is more phytoplankton present. This relationship works over a very wide range of concentrations, from less than 0.01 ton early 50 milligrams of chlorophyll per cubic meter of seawater.