After years of work, a team of NASA scientists and engineers is poised to realize a lifetime goal: building an instrument powerful and accurate enough to gather around-the-clock global atmospheric carbon-dioxide (CO2) measurements from space.

The instrument, called the CO2 Sounder Lidar, is a strong contender for a potential next-generation carbon-monitoring mission, the Active Sensing of CO2 Emissions over Nights, Days and Seasons, or ASCENDS. Although the scientific community supports such a mission, scientists say its development depends on whether the National Research Council endorses the mission in its next Earth Science Decadal Survey, which represents a consensus of the most important research areas and the order in which they should be built.

Furthermore, the technology must be mature enough to measure the greenhouse gas with needed and unprecedented precision and resolution, regardless of the season or time of day, scientists say.

{LINKKI POISTETTU}Mark Stephen (left) and Tony Yu are part of the team, including Jeffrey Chen (not pictured), who developed the advanced laser system used on the CO2 Sounder Lidar.

Engineers and scientists at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, believe they can make the case for the technology — especially now that they’ve analyzed data gathered during the instrument’s most recent aircraft campaign over California and Nevada earlier this year. The team, led by Goddard scientist Jim Abshire, presented these results at the International Workshop on Greenhouse Gas Measurements from Space in Kyoto, Japan, in early June.

{LINKKI POISTETTU}Developers of the CO2 Sounder Lidar snapped this photo during a field campaign over California and Nevada earlier this year.

Proven Aircraft Demonstrations

The team’s work began about a decade ago with funding from Goddard’s Internal Research and Development program and later with support from NASA’s Earth Science Technology Office. The lidar operates by bouncing an infrared laser light off the Earth’s surface. Like all atmospheric gases, carbon dioxide absorbs light in narrow wavelength bands — in this case, the infrared. By tuning the laser to the infrared, scientists can detect and then analyze the level of carbon dioxide in that vertical path. The more gas along the light’s path, the deeper the absorption lines.

Recent data analyses indicated that the CO2 Sounder can execute its job faster and with greater accuracy than earlier incarnations of the instrument. Team members attribute their success to several key technologies.

For one, the lidar is equipped with the world’s first solid-state detector that is highly sensitive to the near and mid-infrared wavelengths — a spectral sweet spot for detecting greenhouse gases in Earth’s atmosphere. Made of a special alloy called mercury-cadmium-telluride, this breakthrough detector can effectively count each returning infrared photon, and as a result, enjoys unparalleled sensitivity.

Faster, More Efficient Retrieval

“During the CO2 Sounder’s 2016 (aircraft) campaign, we realized the detector’s high sensitivity,” said Anand Ramanathan, an instrument-development team member. “It took 10 seconds to accumulate enough light to make a measurement in our 2013 campaign. In 2016, it took just one second. This is like improving the photographic film speed so that camera exposure can get shorter and one can get a higher frames-per-second rate. Besides the high sensitivity, the detector also demonstrated a highly linear dynamic range, which was of great help flying over snow, which is surprisingly dark in the infrared,” he added.

Equally important, Abshire said, is the instrument’s laser system, a capability not enjoyed by current spaceborne carbon-monitoring missions. Unlike existing instruments, which rely on passive or reflected sunlight to gather measurements, the CO2 Sounder’s laser system provides the light source, giving it the ability to measure carbon dioxide day and night, regardless of the season — an essential capability for ASCENDS.

Laser Demonstrates Pluck

“The laser team deserves many kudos,” Abshire said, referring to Goddard laser engineers Mark Stephen, Jeffrey Chen and Tony Yu, who are advancing the instrument’s tunable laser system. “The laser keeps getting better all the time.”

To measure trace gases like carbon dioxide and methane, the laser should produce many different wavelengths of light, particularly those around the wavelength known to absorb the gas of interest. While other lidar groups use one laser per wavelength, the Goddard approach uses a single laser that rapidly and accurately tunes to up to 30 different wavelengths. Called a “step-lock” system, the laser can rapidly switch between the 16 wavelengths used by the CO2 Sounder. “It’s so fast you can precisely step through the wavelengths a hundred times, all within the blink of an eye,” Ramanathan said.

For scientists interested in knowing the atmosphere’s chemical makeup, the laser offers another important benefit: the ability to measure water vapor whose absorption lines lie next to CO2’s absorption lines. “The step-locked system enabled us to make simultaneous water-vapor measurements along with the CO2 measurement,” he added.

Between its highly sensitive detector and rapidly improving laser system, the team believes it’s on the cusp of maturing a flight-ready ASCENDS-type instrument. The one remaining hurdle, Abshire said, is assuring that the laser is powerful enough to deliver a beam of light and accurately measure the returning signals for spectroscopic analysis. But even there, Abshire is confident.

“We need to increase the power so we can take our instrument into space. These guys have figured a way to that,” Abshire said, referring to the special type of fiber amplifier the team has advanced to literally increase the laser’s power by a factor of 100. The sounder’s final design will include six of these laser amplifiers used in parallel, Stephen said, adding that testing of the laboratory breadboard will occur over the next year.

“The advancement of technology has been amazing. I wouldn’t have thought this was possible just a few years ago,” Ramanathan said.

Three billion miles from Earth, NASA’s New Horizons spacecraft, moving at speeds that would get it from New York to Los Angeles in about four minutes, was pointing cameras, spectrometers, and other sensors at Pluto and its moons – distant worlds that humankind had never seen up close – recording hundreds of pictures and other data that would forever change our view of the outer solar system.

“New Horizons not only completed the era of first reconnaissance of the planets, the mission has intrigued and inspired. Who knew that Pluto would have a heart?” said NASA’s Director of Planetary Science Jim Green. “Even today, New Horizons captures our imagination, rekindles our curiosity, and reminds us of what’s possible.”

To say that New Horizons shook the foundation of planetary science is an understatement—discoveries already culled from the pictures and compositional and space environment readings have not only introduced us to the Pluto system, but hint at what awaits as scientists examine other worlds in the Kuiper Belt. New Horizons Principal Investigator Alan Stern of the Southwest Research Institute, Boulder, Colorado, lists the mission’s most surprising and amazing findings from Pluto (so far):

- The complexity of Pluto and its satellites is far beyond what we expected.

- The degree of current activity on Pluto’s surface and the youth of some surfaces on Pluto are simply astounding.

- Pluto’s atmospheric hazes and lower-than-predicted atmospheric escape rate upended all of the pre-flyby models.

- Charon’s enormous equatorial extensional tectonic belt hints at the freezing of a former water ice ocean inside Charon in the distant past. Other evidence found by New Horizons indicates Pluto could well have an internal water-ice ocean today.

- All of Pluto’s moons that can be age-dated by surface craters have the same, ancient age—adding weight to the theory that they were formed together in a single collision between Pluto and another planet in the Kuiper Belt long ago.

- Charon’s dark, red polar cap is unprecedented in the solar system and may be the result of atmospheric gases that escaped Pluto and then accreted on Charon’s surface.

- Pluto’s vast 1,000-kilometer-wide heart-shaped nitrogen glacier (informally called Sputnik Planum) that New Horizons discovered is the largest known glacier in the solar system.

- Pluto shows evidence of vast changes in atmospheric pressure and, possibly, past presence of running or standing liquid volatiles on its surface
something only seen elsewhere on Earth, Mars and Saturn’s moon Titan in our solar system.

- The lack of additional Pluto satellites beyond what was discovered before New Horizons was unexpected.

- Pluto’s atmosphere is blue. Who knew?

“It’s strange to think that only a year ago, we still had no real idea of what the Pluto system was like,” said Hal Weaver, New Horizons project scientist from the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. “But it didn’t take long for us to realize Pluto was something special, and like nothing we ever could have expected. We’ve been astounded by the beauty and complexity of Pluto and its moons and we’re excited about the discoveries still to come.”

New Horizons is now nearly 300 million miles beyond Pluto, speeding to its next destination deeper into the Kuiper Belt, following NASA approval of an extended mission. About 80 percent of the data stored on the spacecraft’s recorders has been sent to Earth; transmission of the remainder will be complete by October.

“Our entire team is proud to have accomplished the first exploration of Pluto and the Kuiper Belt—something many of us had worked to achieve since the 1990s,” said Stern. “The data that New Horizons sent back about Pluto and its system of moons has revolutionized planetary science and inspired people of all ages across the world about space exploration. It’s been a real privilege to be able to do that, for which I’ll be forever indebted to our team and our nation.”

Secrets lie deep within Jupiter, shrouded in the solar system's strongest magnetic field and most lethal radiation belts. On July 4, 2016, NASA's Juno spacecraft will plunge into uncharted territory, entering orbit around the gas giant and passing closer than any spacecraft before. Juno will see Jupiter for what it really is, but first it must pass the trial of orbit insertion.

https://www.youtube.com/watch?v=A2fknqVk2yk

{LINKKI POISTETTU}Scientists from NASA’s New Horizons mission used state-of-the-art computer simulations to show that the surface of Pluto’s informally named Sputnik Planum is covered with churning ice "cells" that are geologically young and turning over due to a process called convection. The scene above, which is about 250 miles (400 kilometers) across, uses data from the New Horizons Ralph/Multispectral Visible Imaging Camera (MVIC), gathered July 14, 2015.
Credits: NASA/JHUAPL/SwRI

Combining computer models with topographic and compositional data gathered by NASA’s New Horizons spacecraft last summer, New Horizons team members have determined the depth of this layer of solid nitrogen ice within Pluto's distinctive "heart" feature – a large plain informally known as Sputnik Planum – and how fast that ice is flowing. The study is published in the June 2 issue of the journal Nature.

Mission scientists used state-of-the-art computer simulations to show that the surface of Sputnik Planum is covered with icy, churning, convective "cells" 10 to 30 miles (16 to 48 kilometers) across, and less than one million years old. The findings offer additional insight into the unusual and highly active geology on Pluto and, perhaps, other bodies like it on the outskirts of the solar system.

“For the first time, we can determine what these strange welts on the icy surface of Pluto really are,” said William B. McKinnon, from Washington University in St. Louis, who led the study and is a co-investigator on the New Horizons science team. “We found evidence that even on a distant cold planet billions of miles from Earth, there is sufficient energy for vigorous geological activity, as long as you have ‘the right stuff,’ meaning something as soft and pliable as solid nitrogen.”

McKinnon and colleagues believe the pattern of these cells stems from the slow thermal convection of the nitrogen-dominated ices that fill Sputnik Planum. A reservoir that’s likely several miles deep in some places, the solid nitrogen is warmed by Pluto’s modest internal heat, becomes buoyant and rises up in great blobs – like a lava lamp – before cooling off and sinking again to renew the cycle.

The computer models show that ice need only be a few miles deep for this process to occur, and that the convection cells are very broad. The models also show that these blobs of overturning solid nitrogen can slowly evolve and merge over millions of years. Ridges that mark where cooled nitrogen ice sinks back down can be pinched off and abandoned, resulting in Y- or X-shaped features in junctions where three or four convection cells once met.

“Sputnik Planum is one of the most amazing geological discoveries in 50-plus years of planetary exploration, and the finding by McKinnon and others on our science team that this vast area—bigger than Texas and Oklahoma combined – is created by current day ice convection is among the most spectacular of the New Horizons mission,” said New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute, Boulder, Colorado.

These convective surface motions average only a few centimeters a year – about as fast as your fingernails grow – which means cells recycle their surfaces every 500,000 years or so. While slow on human clocks, it’s a fast clip on geological timescales.

“This activity probably helps support Pluto’s atmosphere by continually refreshing the surface of ‘the heart,’” McKinnon said. “It wouldn’t surprise us to see this process on other dwarf planets in the Kuiper Belt. Hopefully, we’ll get a chance to find out someday with future exploration missions there.”

New Horizons could also potentially take a close-up look at a smaller, more ancient object much farther out in the Kuiper Belt – the disk-shaped region beyond the orbit of Neptune believed to contain comets, asteroids and other small, icy bodies. New Horizons flew through the Pluto system on July 14, 2015, making the first close observations of Pluto and its family of five moons.

{LINKKI POISTETTU}Location of the southern Antarctic Circumpolar Current front (white contour), with -1 degree Celsius sea surface temperature lines (black contours) on Sept. 22 each year from 2002-2009, plotted against a chart of the depth of the Southern Ocean around Antarctica.

Why has the sea ice cover surrounding Antarctica been increasing slightly, in sharp contrast to the drastic loss of sea ice occurring in the Arctic Ocean? A new NASA-led study finds the geology of Antarctica and the Southern Ocean are responsible.

A NASA/NOAA/university team led by Son Nghiem of NASA's Jet Propulsion Laboratory, Pasadena, California, used satellite radar, sea surface temperature, land form and bathymetry (ocean depth) data to study the physical processes and properties affecting Antarctic sea ice. They found that two persistent geological factors -- the topography of Antarctica and the depth of the ocean surrounding it -- are influencing winds and ocean currents, respectively, to drive the formation and evolution of Antarctica's sea ice cover and help sustain it.

"Our study provides strong evidence that the behavior of Antarctic sea ice is entirely consistent with the geophysical characteristics found in the southern polar region, which differ sharply from those present in the Arctic," said Nghiem.

Antarctic sea ice cover is dominated by first-year (seasonal) sea ice. Each year, the sea ice reaches its maximum extent around the frozen continent in September and retreats to about 17 percent of that extent in February. Since the late 1970s, its extent has been relatively stable, increasing just slightly; however, regional differences are observed.

Over the years, scientists have floated various hypotheses to explain the behavior of Antarctic sea ice, particularly in light of observed global temperature increases. Are changes in the ozone hole involved? Could fresh meltwater from Antarctic ice shelves be making the ocean surface less salty and more conducive to ice formation, since salt inhibits freezing? Are increases in the strength of Antarctic winds causing the ice to thicken? Something is protecting Antarctic sea ice, but a definitive answer has remained elusive.

To tackle this cryospheric conundrum, Nghiem and his team adopted a novel approach. They analyzed radar data from NASA's QuikScat satellite from 1999 to 2009 to trace the paths of Antarctic sea ice movements and map its different types. They focused on the 2008 growth season, a year of exceptional seasonal variability in Antarctic sea ice coverage.

Their analyses revealed that as sea ice forms and builds up early in the sea ice growth season, it gets pushed offshore and northward by winds, forming a protective shield of older, thicker ice that circulates around the continent. The persistent winds, which flow downslope off the continent and are shaped by Antarctica's topography, pile ice up against the massive ice shield, enhancing its thickness. This band of ice, which varies in width from roughly 62 to 620 miles (100 to 1,000 kilometers), encapsulates and protects younger, thinner ice in the ice pack behind it from being reduced by winds and waves.

The team also used QuikScat radar data to classify the different types of Antarctic sea ice. Older, thicker sea ice returns a stronger radar signal than younger, thinner ice does. They found the sea ice within the protective shield was older and rougher (due to longer exposure to wind and waves), and thicker (due to more ice growth and snow accumulation). As the sea ice cover expands and ice drifts away from the continent, areas of open water form behind it on the sea surface, creating "ice factories" conducive to rapid sea ice growth.

To address the question of how the Southern Ocean maintains this great sea ice shield, the team combined sea surface temperature data from multiple satellites with a recently available bathymetric chart of the depth of the world's oceans. Sea surface temperature data reveal that at the peak of ice growth season, the boundary of the ice shield remains behind a 30-degree Fahrenheit (-1 degree Celsius) temperature line surrounding Antarctica. This temperature line corresponds with the southern Antarctic Circumpolar Current front, a boundary that separates the circulation of cold and warm waters around Antarctica. The team theorized that the location of this front follows the underwater bathymetry.

When they plotted the bathymetric data against the ocean temperatures, the pieces fit together like a jigsaw puzzle. Pronounced seafloor features strongly guide the ocean current and correspond closely with observed regional Antarctic sea ice patterns. For example, the current stays near Bouvet Island, located 1,000 miles (1,600 kilometers) from the nearest land, where three tectonic plates join to form seafloor ridges. Off the coast of East Antarctica, the -1 degree Celsius sea surface temperature lines closely bundle together as they cross the Kerguelen Plateau (a submerged microcontinent that broke out of the ancient Gondwana supercontinent), through a deep channel called the Fawn Trough. But those lines spread apart over adjacent deep ocean basins, where seafloor features are not pronounced. Off the West Antarctica coast, the deep, smooth seafloor loses its grip over the current, allowing sea ice extent to decrease and resulting in large year-to-year variations.

Study results are published in the journal Remote Sensing of Environment. Other participating institutions include the Joint Institute for Regional Earth System Science and Engineering at UCLA; the Applied Physics Laboratory at the University of Washington in Seattle; and the U.S. National/Naval Ice Center, NOAA Satellite Operations Facility in Suitland, Maryland. Additional funding was provided by the National Science Foundation.

NASA uses the vantage point of space to increase our understanding of our home planet, improve lives and safeguard our future. NASA develops new ways to observe and study Earth's interconnected natural systems with long-term data records. The agency freely shares this unique knowledge and works with institutions around the world to gain new insights into how our planet is changing.