Solar System: 10 Things to Know This Week
Whether it's crops, forests or phytoplankton blooms in the ocean, our scientists are tracking life on Earth. Just as satellites help researchers study the atmosphere, rainfall and other physical characteristics of the planet, the ever-improving view from above allows them to study Earth's interconnected life.
1. Life on Earth, From Space
While we (NASA) began monitoring life on land in the 1970s with the Landsat satellites, this fall marks 20 years since we've continuously observed all the plant life at the surface of both the land and ocean. The above animation captures the entirety of two decades of observations.
2. Watching the World Breathe
With the right tools, we can see Earth breathe. With early weather satellite data in the 1970s and '80s, NASA Goddard scientist Compton Tucker was able to see plants' greening and die-back from space. He developed a way of comparing satellite data in two wavelengths.
When healthy plants are stocked with chlorophyll and ready to photosynthesize to make food (and absorb carbon dioxide), leaves absorb red light but reflect infrared light back into space. By comparing the ratio of red to infrared light, Tucker and his colleagues could quantify vegetation covering the land.
Expanding the study to the rest of the globe, the scientists could track rainy and dry seasons in Africa, see the springtime blooms in North America, and wildfires scorching forests worldwide.
3. Like Breathing? Thank Earth's Ocean
But land is only part of the story. The ocean is home to 95 percent of Earth's living space, covering 70 percent of the planet and stretching miles deep. At the base of the ocean's food web is phytoplankton - tiny plants that also undergo photosynthesis to turn nutrients and carbon dioxide into sugar and oxygen. Phytoplankton not only feed the rest of ocean life, they absorb carbon dioxide - and produce about half the oxygen we breathe.
In the Arctic Ocean, an explosion of phytoplankton indicates change. As seasonal sea ice melts, warming waters and more sunlight will trigger a sudden, massive phytoplankton bloom that feeds birds, sea lions and newly-hatched fish. But with warming atmospheric temperatures, that bloom is now happening several weeks earlier - before the animals are in place to take advantage of it.
4. Keeping an Eye on Crops
The "greenness" measurement that scientists use to measure forests and grasslands can also be used to monitor the health of agricultural fields. By the 1980s, food security analysts were approaching NASA to see how satellite images could help with the Famine Early Warning System to identify regions at risk - a partnership that continues today.
With rainfall estimates, vegetation measurements, as well as the recent addition of soil moisture information, our scientists can help organizations like USAID direct emergency help.
The view from space can also help improve agricultural practices. A winery in California, for example, uses individual pixels of Landsat data to determine when to irrigate and how much water to use.
5. Coming Soon to the International Space Station
A laser-based instrument being developed for the International Space Station will provide a unique 3-D view of Earth's forests. The instrument, called GEDI, will be the first to systematically probe the depths of the forests from space.
Another ISS instrument in development, ECOSTRESS, will study how effectively plants use water. That knowledge provided on a global scale from space will tell us "which plants are going to live or die in a future world of greater droughts," said Josh Fisher, a research scientist at NASA's Jet Propulsion Laboratory and science lead for ECOSTRESS.
6. Seeing Life, From the Microscopic to Multicellular
Scientists have used our vantage from space to study changes in animal habitats, track disease outbreaks, monitor forests and even help discover a new species. Bacteria, plants, land animals, sea creatures and birds reveal a changing world.
Our Black Marble image provides a unique view of human activity. Looking at trends in our lights at night, scientists can study how cities develop over time, how lighting and activity changes during certain seasons and holidays, and even aid emergency responders during power outages caused by natural disasters.
7. Earth as Analog and Proving Ground
Just as our Mars rovers were tested in Earth's deserts, the search for life on ocean moons in our solar system is being refined by experiments here. JPL research scientist Morgan Cable looks for life on the moons of Jupiter and Saturn. She cites satellite observations of Arctic and Antarctic ice fields that are informing the planning for a future mission to Europa, an icy moon of Jupiter.
The Earth observations help researchers find ways to date the origin of jumbled, chaotic ice. "When we visit Europa, we want to go to very young places, where material from that ocean is being expressed on the surface," she explained. "Anywhere like that, the chances of finding biomarkers goes up - if they're there."
8. Only One Living Planet
Today, we know of only one living planet: our own. The knowledge and tools NASA developed to study life here are among our greatest assets as we begin the search for life beyond Earth.
There are two main questions: With so many places to look, how can we home in on the places most likely to harbor life? What are the unmistakable signs of life - even if it comes in a form we don't fully understand? In this early phase of the search, "We have to go with the only kind of life we know," said Tony del Genio, co-lead of a new NASA interdisciplinary initiative to search for life on other worlds.
So, the focus is on liquid water. Even bacteria around deep-sea vents that don't need sunlight to live need water. That one necessity rules out many planets that are too close or too far from their stars for water to exist, or too far from us to tell. Our Galileo and Cassini missions revealed that some moons of Jupiter and Saturn are not the dead rocks astronomers had assumed, but appear to have some conditions needed for life beneath icy surfaces.
9. Looking for Life Beyond Our Solar System
In the exoplanet (planets outside our solar system that orbit another star) world, it's possible to calculate the range of distances for any star where orbiting planets could have liquid water. This is called the star's habitable zone. Astronomers have already located some habitable-zone planets, and research scientist Andrew Rushby of NASA Ames Research Center is researching ways to refine the search. "An alien would spot three planets in our solar system in the habitable zone [Earth, Mars and Venus]," Rushby said, "but we know that 67 percent of those planets are not inhabited."
He recently developed a model of Earth's carbon cycle and combined it with other tools to study which planets in habitable zones would be the best targets to look for life, considering probable tectonic activity and water cycles. He found that larger planets are more likely than smaller ones to have surface temperatures conducive to liquid water. Other exoplanet researchers are looking for rocky worlds, and biosignatures, the chemical signs of life.
10. You Can Learn a Lot from a Dot
When humans start collecting direct images of exoplanets, even the closest ones will appear as only a handful of pixels in the detector - something like the famous "blue dot" image of Earth from Saturn. What can we learn about life on these planets from a single dot?
Stephen Kane of the University of California, Riverside, has come up with a way to answer that question by using our EPIC camera on NOAA's DSCOVR satellite. "I'm taking these glorious pictures and collapsing them down to a single pixel or handful of pixels," Kane explained. He runs the light through a noise filter that attempts to simulate the interference expected from an exoplanet mission. By observing how the brightness of Earth changes when mostly land is in view compared with mostly water, Kane reverse-engineers Earth's rotation rate - something that has yet to be measured directly for exoplanets.
The most universal, most profound question about any unknown world is whether it harbors life. The quest to find life beyond Earth is just beginning, but it will be informed by the study of our own living planet.
