NASA Confirms Evidence That Liquid Water Flows on Today’s Mars

These dark, narrow, 100 meter-long streaks called recurring slope lineae flowing downhill on Mars are inferred to have been formed by contemporary flowing water. Recently, planetary scientists detected hydrated salts on these slopes at Hale crater, corroborating their original hypothesis that the streaks are indeed formed by liquid water. The blue color seen upslope of the dark streaks are thought not to be related to their formation, but instead are from the presence of the mineral pyroxene. The image is produced by draping an orthorectified (Infrared-Red-Blue/Green(IRB)) false color image (ESP_030570_1440) on a Digital Terrain Model (DTM) of the same site produced by High Resolution Imaging Science Experiment (University of Arizona). Vertical exaggeration is 1.5.

Credits: NASA/JPL/University of Arizona

New findings from NASA's Mars Reconnaissance Orbiter (MRO) provide the strongest evidence yet that liquid water flows intermittently on present-day Mars.

Using an imaging spectrometer on MRO, researchers detected signatures of hydrated minerals on slopes where mysterious streaks are seen on the Red Planet. These darkish streaks appear to ebb and flow over time. They darken and appear to flow down steep slopes during warm seasons, and then fade in cooler seasons. They appear in several locations on Mars when temperatures are above minus 10 degrees Fahrenheit (minus 23 Celsius), and disappear at colder times.

“Our quest on Mars has been to ‘follow the water,’ in our search for life in the universe, and now we have convincing science that validates what we’ve long suspected,” said John Grunsfeld, astronaut and associate administrator of NASA’s Science Mission Directorate in Washington. “This is a significant development, as it appears to confirm that water -- albeit briny -- is flowing today on the surface of Mars.”

These downhill flows, known as recurring slope lineae (RSL), often have been described as possibly related to liquid water. The new findings of hydrated salts on the slopes point to what that relationship may be to these dark features. The hydrated salts would lower the freezing point of a liquid brine, just as salt on roads here on Earth causes ice and snow to melt more rapidly. Scientists say it’s likely a shallow subsurface flow, with enough water wicking to the surface to explain the darkening.

Dark narrow streaks called recurring slope lineae emanating out of the walls of Garni crater on Mars. The dark streaks here are up to few hundred meters in length. They are hypothesized to be formed by flow of briny liquid water on Mars. The image is produced by draping an orthorectified (RED) image (ESP_031059_1685) on a Digital Terrain Model (DTM) of the same site produced by High Resolution Imaging Science Experiment (University of Arizona). Vertical exaggeration is 1.5.

Credits: NASA/JPL/University of Arizona

"We found the hydrated salts only when the seasonal features were widest, which suggests that either the dark streaks themselves or a process that forms them is the source of the hydration. In either case, the detection of hydrated salts on these slopes means that water plays a vital role in the formation of these streaks," said Lujendra Ojha of the Georgia Institute of Technology (Georgia Tech) in Atlanta, lead author of a report on these findings published Sept. 28 by Nature Geoscience.

Ojha first noticed these puzzling features as a University of Arizona undergraduate student in 2010, using images from the MRO's High Resolution Imaging Science Experiment (HiRISE). HiRISE observations now have documented RSL at dozens of sites on Mars. The new study pairs HiRISE observations with mineral mapping by MRO’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM).

The spectrometer observations show signatures of hydrated salts at multiple RSL locations, but only when the dark features were relatively wide. When the researchers looked at the same locations and RSL weren't as extensive, they detected no hydrated salt.  

Ojha and his co-authors interpret the spectral signatures as caused by hydrated minerals called perchlorates. The hydrated salts most consistent with the chemical signatures are likely a mixture of magnesium perchlorate, magnesium chlorate and sodium perchlorate. Some perchlorates have been shown to keep liquids from freezing even when conditions are as cold as minus 94 degrees Fahrenheit (minus 70 Celsius). On Earth, naturally produced perchlorates are concentrated in deserts, and some types of perchlorates can be used as rocket propellant.

Perchlorates have previously been seen on Mars. NASA's Phoenix lander and Curiosity rover both found them in the planet's soil, and some scientists believe that the Viking missions in the 1970s measured signatures of these salts. However, this study of RSL detected perchlorates, now in hydrated form, in different areas than those explored by the landers. This also is the first time perchlorates have been identified from orbit.

MRO has been examining Mars since 2006 with its six science instruments.

"The ability of MRO to observe for multiple Mars years with a payload able to see the fine detail of these features has enabled findings such as these: first identifying the puzzling seasonal streaks and now making a big step towards explaining what they are," said Rich Zurek, MRO project scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.

For Ojha, the new findings are more proof that the mysterious lines he first saw darkening Martian slopes five years ago are, indeed, present-day water.

"When most people talk about water on Mars, they're usually talking about ancient water or frozen water," he said. "Now we know there’s more to the story. This is the first spectral detection that unambiguously supports our liquid water-formation hypotheses for RSL."

The discovery is the latest of many breakthroughs by NASA’s Mars missions.

“It took multiple spacecraft over several years to solve this mystery, and now we know there is liquid water on the surface of this cold, desert planet,” said Michael Meyer, lead scientist for NASA’s Mars Exploration Program at the agency’s headquarters in Washington. “It seems that the more we study Mars, the more we learn how life could be supported and where there are resources to support life in the future.” 

There are eight co-authors of the Nature Geoscience paper, including Mary Beth Wilhelm at NASA’s Ames Research Center in Moffett Field, California and Georgia Tech; CRISM Principal Investigator Scott Murchie of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland; and HiRISE Principal Investigator Alfred McEwen of the University of Arizona Lunar and Planetary Laboratory in Tucson, Arizona. Others are at Georgia Tech, the Southwest Research Institute in Boulder, Colorado, and Laboratoire de Planétologie et Géodynamique in Nantes, France.The agency’s Jet Propulsion Laboratory (JPL) in Pasadena, California manages the Mars Reconnaissance Orbiter Project for NASA's Science Mission Directorate, Washington. Lockheed Martin built the orbiter and collaborates with JPL to operate it.

Tracking A Mysterious Group of Asteroid Outcasts

High above the plane of our solar system, near the asteroid-rich abyss between Mars and Jupiter, scientists have found a unique family of space rocks. These interplanetary oddballs are the Euphrosyne (pronounced you-FROH-seh-nee) asteroids, and by any measure they have been distant, dark and mysterious -- until now.

Distributed at the outer edge of the asteroid belt, the Euphrosynes have an unusual orbital path that juts well above the ecliptic, the equator of the solar system. The asteroid after which they are named, Euphrosyne -- for an ancient Greek goddess of mirth -- is about 156 miles (260 kilometers) across and is one of the 10 largest asteroids in the main belt. Current-day Euphrosyne is thought to be a remnant of a massive collision about 700 million years ago that formed the family of smaller asteroids bearing its name. Scientists think this event was one of the last great collisions in the solar system.

A new study conducted by scientists at NASA's Jet Propulsion Laboratory in Pasadena, California, used the agency's orbiting Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) telescope to look at these unusual asteroids to learn more about Near Earth Objects, or NEOs, and their potential threat to Earth.

NEOs are bodies whose orbits around the sun approach the orbit of Earth; this population is short-lived on astronomical timescales and is fed by other reservoirs of bodies in our solar system. As they orbit the sun, NEOs can occasionally have close approaches to Earth. For this reason alone -- the safety of our home planet -- the study of such objects is important.

As a result of their study, the JPL researchers believe the Euphrosynes may be the source of some of the dark NEOs found to be on long, highly inclined orbits. They found that, through gravitational interactions with Saturn, Euphrosyne asteroids can evolve into NEOs over timescales of millions of years.

NEOs can originate in either the asteroid belt or the more distant outer reaches of the solar system. Those from the asteroid belt are thought to evolve toward Earth's orbit through collisions and the gravitational influence of the planets. Originating well above the ecliptic and near the far edge of the asteroid belt, the forces that shape their trajectories toward Earth are far more moderate.

"The Euphrosynes have a gentle resonance with the orbit of Saturn that slowly moves these objects, eventually turning some of them into NEOs," said Joseph Masiero, JPL's lead scientist on the Euphrosynes study. "This particular gravitational resonance tends to push some of the larger fragments of the Euphrosyne family into near-Earth space."

By studying the Euphrosyne family asteroids with NEOWISE, JPL scientists have been able to measure their sizes and the amount of solar energy they reflect. Since NEOWISE operates in the infrared portion of the spectrum, it detects heat. Therefore, it can see dark objects far better than telescopes operating at visible wavelengths, which sense reflected sunlight. Its heat-sensing capability also allows it to measure sizes more accurately.

The 1,400 Euphrosyne asteroids studied by Masiero and his colleagues turned out to be large and dark, with highly inclined and elliptical orbits. These traits make them good candidates for the source of some of the dark NEOs the NEOWISE telescope detects and discovers, particularly those that also have highly inclined orbits.     

NEOWISE was originally launched as an astrophysics mission in 2009 as the Wide-field Infrared Survey Explorer, or WISE. It operated until 2011 and was then shut down. But the spacecraft, now dubbed NEOWISE, would get a second life. "NEOWISE is a great tool for searching for near-Earth asteroids, particularly high-inclination, dark objects," Masiero said.

There are over 700,000 asteroidal bodies currently known in the main belt that range in size from large boulders to about 60 percent of the diameter of Earth's moon, with many yet to be discovered. This makes finding the specific point of origin of most NEOs extremely difficult.

With the Euphrosynes it's different. "Most near-Earth objects come from a number of sources in the inner region of the main belt, and they are quickly mixed around," Masiero said. "But with objects coming from this family, in such a unique region, we are able to draw a likely path for some of the unusual, dark NEOs we find back to the collision in which they were born."

A better understanding of the origins and behaviors of these mysterious objects will give researchers a clearer picture of asteroids in general, and in particular the NEOs that skirt our home planet's neighborhood. Such studies are important, and potentially critical, to the future of humanity, which is a primary reason JPL and its partners continue to relentlessly track these wanderers within our solar system. To date, U.S. assets have discovered more than 98 percent of the known NEOs.

NASA's Jet Propulsion Laboratory in Pasadena, California, manages the NEOWISE mission for NASA's Science Mission Directorate in Washington. The Space Dynamics Laboratory in Logan, Utah, built the science instrument. Ball Aerospace & Technologies Corp. of Boulder, Colorado, built the spacecraft. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

NASA's Near-Earth Object Program at NASA Headquarters, Washington, manages and funds the search, study and monitoring of asteroids and comets whose orbits periodically bring them close to Earth. JPL manages the Near-Earth Object Office for NASA's Science Mission Directorate in Washington.

Tracking A Mysterious Group of Asteroid Outcasts

High above the plane of our solar system, near the asteroid-rich abyss between Mars and Jupiter, scientists have found a unique family of space rocks. These interplanetary oddballs are the Euphrosyne (pronounced you-FROH-seh-nee) asteroids, and by any measure they have been distant, dark and mysterious -- until now.

Distributed at the outer edge of the asteroid belt, the Euphrosynes have an unusual orbital path that juts well above the ecliptic, the equator of the solar system. The asteroid after which they are named, Euphrosyne -- for an ancient Greek goddess of mirth -- is about 156 miles (260 kilometers) across and is one of the 10 largest asteroids in the main belt. Current-day Euphrosyne is thought to be a remnant of a massive collision about 700 million years ago that formed the family of smaller asteroids bearing its name. Scientists think this event was one of the last great collisions in the solar system.

A new study conducted by scientists at NASA's Jet Propulsion Laboratory in Pasadena, California, used the agency's orbiting Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) telescope to look at these unusual asteroids to learn more about Near Earth Objects, or NEOs, and their potential threat to Earth.

NEOs are bodies whose orbits around the sun approach the orbit of Earth; this population is short-lived on astronomical timescales and is fed by other reservoirs of bodies in our solar system. As they orbit the sun, NEOs can occasionally have close approaches to Earth. For this reason alone -- the safety of our home planet -- the study of such objects is important.

As a result of their study, the JPL researchers believe the Euphrosynes may be the source of some of the dark NEOs found to be on long, highly inclined orbits. They found that, through gravitational interactions with Saturn, Euphrosyne asteroids can evolve into NEOs over timescales of millions of years.

NEOs can originate in either the asteroid belt or the more distant outer reaches of the solar system. Those from the asteroid belt are thought to evolve toward Earth's orbit through collisions and the gravitational influence of the planets. Originating well above the ecliptic and near the far edge of the asteroid belt, the forces that shape their trajectories toward Earth are far more moderate.

"The Euphrosynes have a gentle resonance with the orbit of Saturn that slowly moves these objects, eventually turning some of them into NEOs," said Joseph Masiero, JPL's lead scientist on the Euphrosynes study. "This particular gravitational resonance tends to push some of the larger fragments of the Euphrosyne family into near-Earth space."

By studying the Euphrosyne family asteroids with NEOWISE, JPL scientists have been able to measure their sizes and the amount of solar energy they reflect. Since NEOWISE operates in the infrared portion of the spectrum, it detects heat. Therefore, it can see dark objects far better than telescopes operating at visible wavelengths, which sense reflected sunlight. Its heat-sensing capability also allows it to measure sizes more accurately.

The 1,400 Euphrosyne asteroids studied by Masiero and his colleagues turned out to be large and dark, with highly inclined and elliptical orbits. These traits make them good candidates for the source of some of the dark NEOs the NEOWISE telescope detects and discovers, particularly those that also have highly inclined orbits.     

NEOWISE was originally launched as an astrophysics mission in 2009 as the Wide-field Infrared Survey Explorer, or WISE. It operated until 2011 and was then shut down. But the spacecraft, now dubbed NEOWISE, would get a second life. "NEOWISE is a great tool for searching for near-Earth asteroids, particularly high-inclination, dark objects," Masiero said.

There are over 700,000 asteroidal bodies currently known in the main belt that range in size from large boulders to about 60 percent of the diameter of Earth's moon, with many yet to be discovered. This makes finding the specific point of origin of most NEOs extremely difficult.

With the Euphrosynes it's different. "Most near-Earth objects come from a number of sources in the inner region of the main belt, and they are quickly mixed around," Masiero said. "But with objects coming from this family, in such a unique region, we are able to draw a likely path for some of the unusual, dark NEOs we find back to the collision in which they were born."

A better understanding of the origins and behaviors of these mysterious objects will give researchers a clearer picture of asteroids in general, and in particular the NEOs that skirt our home planet's neighborhood. Such studies are important, and potentially critical, to the future of humanity, which is a primary reason JPL and its partners continue to relentlessly track these wanderers within our solar system. To date, U.S. assets have discovered more than 98 percent of the known NEOs.

NASA's Jet Propulsion Laboratory in Pasadena, California, manages the NEOWISE mission for NASA's Science Mission Directorate in Washington. The Space Dynamics Laboratory in Logan, Utah, built the science instrument. Ball Aerospace & Technologies Corp. of Boulder, Colorado, built the spacecraft. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

NASA's Near-Earth Object Program at NASA Headquarters, Washington, manages and funds the search, study and monitoring of asteroids and comets whose orbits periodically bring them close to Earth. JPL manages the Near-Earth Object Office for NASA's Science Mission Directorate in Washington.

NASA: There is No Asteroid Threatening Earth

Numerous recent blogs and web postings are erroneously claiming that an asteroid will impact Earth, sometime between Sept. 15 and 28, 2015. On one of those dates, as rumors go, there will be an impact -- "evidently" near Puerto Rico -- causing wanton destruction to the Atlantic and Gulf coasts of the United States and Mexico, as well as Central and South America.

That's the rumor that has gone viral -- now here are the facts.

"There is no scientific basis -- not one shred of evidence -- that an asteroid or any other celestial object will impact Earth on those dates," said Paul Chodas, manager of NASA's Near-Earth Object office at the Jet Propulsion Laboratory in Pasadena, California.

In fact, NASA's Near-Earth Object Observations Program says there have been no asteroids or comets observed that would impact Earth anytime in the foreseeable future.  All known Potentially Hazardous Asteroids have less than a 0.01% chance of impacting Earth in the next 100 years.

The Near-Earth Object office at JPL is a key group involved with the international collaboration of astronomers and scientists who keep watch on the sky with their telescopes, looking for asteroids that could do harm to our planet and predicting their paths through space for the foreseeable future. If there were any observations on anything headed our way, Chodas and his colleagues would know about it.

"If there were any object large enough to do that type of destruction in September, we would have seen something of it by now," he stated.

Another thing Chodas and his team do know -- this isn't the first time a wild, unsubstantiated claim of a celestial object about to impact Earth has been made, and unfortunately, it probably won’t be the last.  It seems to be a perennial favorite of the World Wide Web. 

In 2011 there were rumors about the so-called “doomsday” comet Elenin, which never posed any danger of harming Earth and broke up into a stream of small debris out in space. Then there were Internet assertions surrounding the end of the Mayan calendar on Dec. 21, 2012, insisting the world would end with a large asteroid impact. And just this year, asteroids 2004 BL86 and 2014 YB35 were said to be on dangerous near-Earth trajectories, but their flybys of our planet in January and March went without incident -- just as NASA said they would.

"Again, there is no existing evidence that an asteroid or any other celestial object is on a trajectory that will impact Earth," said Chodas. "In fact, not a single one of the known objects has any credible chance of hitting our planet over the next century."

NASA detects, tracks and characterizes asteroids and comets passing 30 million miles of Earth using both ground- and space-based telescopes. The Near-Earth Object Observations Program, commonly called "Spaceguard," discovers these objects, characterizes the physical nature of a subset of them, and predicts their paths to determine if any could be potentially hazardous to our planet. There are no known credible impact threats to date -- only the continuous and harmless infall of meteoroids, tiny asteroids that burn up in the atmosphere.

JPL hosts the office for Near-Earth Object orbit analysis for NASA's Near Earth Object Observations Program of the Science Mission Directorate in Washington. JPL is a division of the California Institute of Technology in Pasadena.

International Space Station Flyover of Australia

From the International Space Station, NASA astronaut Scott Kelly (stationcdrkelly on Instagram) took this photograph and posted it to social media on April 6, 2015. Kelly wrote, "Australia. You are very beautiful. Thank you for being there to brighten our day. #YearInSpace"

Kelly and Russian Federal Space Agency (Roscosmos) cosmonaut Mikhail Kornienko began their one-year mission aboard the space station on March 27. Most expeditions to the space station last four to six months. By doubling the length of this mission, researchers hope to better understand how the human body reacts and adapts to long-duration spaceflight.

Flying Over An Aurora

NASA astronaut Scott Kelly (@StationCDRKelly) captured photographs and video of auroras from the International Space Station on June 22, 2015. Kelly wrote, "Yesterday's aurora was an impressive show from 250 miles up. Good morning from the International Space Station! ‪#‎YearInSpace‬"

Clear Skies Over the United States

On Sept. 17, 2015, NASA astronaut Scott Kelly captured images and video from the International Space Station during an early morning flyover of the United States. Sharing with his social media followers, Kelly wrote, "Clear skies over much of the USA today. #GoodMorning from @Space_Station! #YearInSpace."

Tuesday, Sept. 15 marked the midpoint of the one-year mission to the space station for Kelly and Russian cosmonaut Mikhail Kornienko. The average International Space Station expedition lasts four to six months. Research enabled by the one-year mission will help scientists better understand how the human body reacts and adapts to long-duration spaceflight. This knowledge is critical as NASA looks toward human missions deeper into the solar system, including to and from Mars, which could last 500 days or longer.

The Nile at Night

NASA astronaut Scott Kelly, recently past the halfway mark of his one-year mission to the International Space Station, photographed the Nile River during a nighttime flyover on Sept. 22, 2015. Kelly (@StationCDRKelly) wrote, "Day 179. The #Nile at night is a beautiful sight for these sore eyes. Good night from @space_station! #YearInSpace."

Why NASA Studies the Ultraviolet Sun

Spacecraft record solar activity as a binary code, 1s and 0s, which computer programs can translate into black and white. Scientists colorize the images for realism, and then zoom in on areas of interest.

Credits: NASA/Karen Fox

Four of the telescopes on the Solar Dynamics Observatory observe extreme ultraviolet light activity on the sun that is invisible to the naked eye.

Credits: NASA/SDO

The Solar Dynamics Observatory observed a solar flare (upper left) and a coronal mass ejection (right) erupting from the sun’s limb in extreme ultraviolet light on August 6, 2010.

Credits: NASA/SDO

You cannot look at the sun without special filters, and the naked eye cannot perceive certain wavelengths of sunlight. Solar physicists must consequently rely on spacecraft that can observe this invisible light before the atmosphere absorbs it.

“Certain wavelengths either do not make it through Earth’s atmosphere or cannot be seen by our eyes, so we cannot use normal optical telescopes to look at the spectrum,” said Dean Pesnell, the project scientist for the Solar Dynamics Observatory, or SDO, at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

Several spacecraft can observe these invisible light wavelengths. SDO for example has four telescopes that image the sun in the ultraviolet spectrum. As beams of ultraviolet light pass into the telescope, a mirror with special coatings filters and amplifies the ultraviolet light’s otherwise poor reflection. The incoming photons are then recorded as pixels and converted into electrical signals, similar to how your cell phone camera sees visible light.

“It’s exactly the same process, whether it’s ultraviolet light, infrared light, visible light, or radio,” said Joseph Gurman, project scientist for both the Solar and Heliospheric Observatory and the Solar Terrestrial Relations Observatory at Goddard. “In this case we’re trying to understand how the sun changes and how those changes affect life here on Earth.”

Ultraviolet light causes molecular radiation damage to our skin, seen as sunburns that can lead to cancer. Its cousin, extreme ultraviolet radiation, and the associated solar storms have the potential to disrupt communications and spacecraft navigation. “These are very damaging, energetic photons, and we want to understand what chain of events produces these photons,” Pesnell said.

Thankfully our planet’s atmosphere absorbs much of this solar radiation, making life on Earth possible. However, this means that to study extreme ultraviolet light, instruments must do it from the vacuum of space.

“Ultraviolet light from the sun can show us the origins of solar storms that can lead to power outages, cell phone disruptions, and delays in shipping packages due to the rerouting of planes from over the pole,” Gurman said.

By understanding what occurs in the sun’s atmosphere, scientists hope to predict when powerful solar events such as coronal mass ejections and solar flares may occur.

“You really want to know what’s happening on the sun as soon as you can,” said Jack Ireland, a solar visualization specialist at Goddard. “We can then use computer models to estimate how solar events will affect Earth’s space environment.”

The information can then be used by NOAA’s Space Weather Prediction Center, in Boulder, Co. to alert power companies and airlines to take the necessary precautions, thus avoiding power outages and keeping airplane passengers safe.

Sun Unleashes Mid-level Flare

SDO captured this image of the mid-level flare, an M6.6-class, on June 22, 2015.

Credits: NASA/SDO

View full disk image

The sun emitted a mid-level solar flare, peaking at 2:23 p.m. EDT on June 22, 2015. NASA’s Solar Dynamics Observatory, which watches the sun constantly, captured an image of the event. Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground, however -- when intense enough -- they can disturb the atmosphere in the layer where GPS and communications signals travel.

To see how this event may affect Earth, please visit NOAA's Space Weather Prediction Center athttp://spaceweather.gov, the U.S. government's official source for space weather forecasts, alerts, watches and warnings.

This flare is classified as a M6.6 flare. M-class flares are a tenth the size of the most intense flares, the X-class flares. The number provides more information about its strength. An M2 is twice as intense as an M1, an M3 is three times as intense, etc.

Scientists Study Atmosphere of Venus through Transit Images

Image of Venus taken by Hinode’s Solar Optical Telescope. In this image, Venus is just beginning its journey across the face of the sun. Its atmosphere is visible as a thin, glowing border on the upper left of the planet.

Credits: JAXA/NASA/Hinode

Two of NASA’s heliophysics missions can now claim planetary science on their list of scientific findings. A group of scientists used the Venus transit - a very rare event where a planet passes between Earth and the sun, appearing to us as a dark dot steadily making its way across the sun’s bright face - to make measurements of how the Venusian atmosphere absorbs different kinds of light. This, in turn, gives scientists clues to exactly what elements are layered above Venus’s surface. Gathering such information not only teaches us more about this planet so close to our own, but it also paves the way for techniques to better understand planets outside our solar system.

Composite of images of the Venus transit taken by NASA’s Solar Dynamics Observatory on June 5, 2012. The image, taken in 171 angstroms, shows a timelapse of Venus’s path across the sun in 2012.

Credits: NASA/Goddard/SDO

Transits of Venus are so rare that they only happen twice in a lifetime. About every 115 years, Venus will appear to cross over the face of our home star twice, with eight years passing between the pair of transits. This stunning phenomenon is not only incredible to watch, but it provides a unique opportunity for scientific observations of one of our nearest neighboring planets.

NASA’S Solar Dynamics Observatory, or SDO, and the joint Japanese Aerospace Exploration Agency and NASA’s Hinode mission took pictures of the entire event in several wavelengths of light. A team of scientists led by Fabio Reale of the University of Palermo used these pictures to watch the backlit planet as it crossed in front of the sun. By observing the planet's atmosphere in different wavelengths of light during its journey, they learned more about what kinds of atoms and molecules are actually in its atmosphere. This work was published in NatureCOMMUNICATIONS on June 23, 2015.

Just as on Earth, each of the layers of Venus’ atmosphere absorb light differently from one another. Some layers may completely absorb a certain wavelength of light, while that same wavelength can pass right through another layer. As Venus passes across the face of the sun -- which emits light in almost every wavelength of the electromagnetic spectrum -- scientists get a rare chance to see how all different types of light filter through Venus’s atmosphere.

A layer in the upper atmosphere around Venus--called the thermosphere--absorbs certain high-energy wavelengths of light. When looking at the planet against the sun in one of these high-energy wavelengths, the thermosphere will appear opaque, rather than transparent as it does in visible light.

“Radiation goes into the atmosphere and is absorbed, creating ions and a layer of the atmosphere called the ionosphere,” said Dean Pesnell, SDO project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. Because the energy in this light is captured by the ions, it is not re-emitted on the other side. In certain wavelengths, Venus’s atmosphere is as solid as a wall, blocking light from traveling to our eyes. To our telescopes, the atmosphere is as dark as the planet itself -- so, Venus will appear to have a different size, depending on the wavelength of the telescope’s pictures.

Reale and his team chose images of the Venus transit taken in several X-ray and ultraviolet wavelengths and measured the apparent size of the planet to within several miles. For each set of pictures, the team calculated just how large the atmospheric blocking was--a measure of how high in Venus’ atmosphere that particular wavelength of light is completely absorbed.

Because the various types of atoms absorb light slightly differently, the height of this light absorption lets scientists know how many and what types of molecules make up Venus’s atmosphere. This information is important for planning missions to Venus, as those ions and molecules can change the amount of course-altering drag a spacecraft feels.

“Learning more about the composition of the atmosphere is very important for understanding the braking process for spacecraft when they enter the upper atmosphere of the planet, a process called aerobraking,” said Reale.

The shape of Venus’ atmosphere also gave scientists important clues to how the sun impacts the atmosphere. “If the atmosphere observed were asymmetric, that could tell us more about how the star is impacting the planet,” said Sabrina Savage, NASA project scientist for Hinode.

During the transit, only the sides of the atmosphere could be seen, but they were particularly interesting areas. From the perspective of Venus, these were the areas where day turns into night and night turns into day--on Earth, these transition areas can host interesting effects in the ionosphere. The data from the Venus transit showed that these two transition areas are virtually the same.

“The planet appeared very round in all wavelengths,” said Pesnell. “If the transition from day to night were different from the transition from night to day, you would expect a bulge in the atmosphere on one side of the planet.”

Studying the Venus transit can also help improve studies of planets around other stars.  Such exoplanets are often discovered by transits just like this, as we can detect the very small amount of light the planets block as they pass across their home star. The more we can observe transiting planets close to home the more it will teach us about how to study distant exoplanets that we can't currently see in as much detail. When instrument technology advances, we may be able to gather better information about the atmospheres of such exoplanets as well.

“In the future, there might be missions that have enough sensitivity to detect the difference in radius in different wavelengths,” said Reale. “In particular, if there are exoplanets with an extremely thick thermosphere, the size difference in different wavelengths will be larger and there will be a better chance of detecting the change.”

NASA's SDO Catches a Double Photobomb

This animation shows the relative movement of Earth and the moon as they both crossed SDO’s field of view on Sept. 13, 2015. Just as the moon came into SDO’s field of view on a path to cross the sun, Earth entered the picture, blocking SDO’s view completely. When SDO's orbit finally emerged from behind Earth, the moon was just completing its journey across the sun’s face.

Credits: NASA/SDO

On Sept. 13, 2015, as NASA’s Solar Dynamics Observatory, or SDO, kept up its constant watch on the sun, its view was photobombed not once, but twice. Just as the moon came into SDO’s field of view on a path to cross the sun, Earth entered the picture, blocking SDO’s view completely. When SDO's view of the sun emerged from Earth’s shadow, the moon was just completing its journey across the sun’s face.

Though SDO sees dozens of Earth eclipses and several lunar transits each year, this is the first time ever that the two have coincided. This alignment of the sun, moon and Earth also resulted in a partial solar eclipse on Sept. 13, visible only from parts of Africa and Antarctica.

SDO’s orbit usually gives us unobstructed views of the sun, but Earth’s revolution around the sun means that SDO’s orbit passes behind Earth twice each year, for two to three weeks at a time. During these phases, Earth blocks SDO’s view of the sun for anywhere from a few minutes to over an hour once each day. 

NASA’s Solar Dynamics Observatory captured this image of Earth and the moon transiting the sun together on Sept. 13, 2015. The edge of Earth, visible near the top of the frame, appears fuzzy because Earth’s atmosphere blocks different amounts of light at different altitudes. On the left, the moon’s edge is perfectly crisp, because it has no atmosphere. This image was taken in extreme ultraviolet wavelengths of 171 angstroms. Though this light is invisible to our eyes, it is typically colorized in gold.

Credits: NASA/SDO

You may notice that Earth’s outline looks fuzzy, while the moon’s is crystal-clear. This is because—while the planet itself completely blocks the sun's light—Earth’s atmosphere is an incomplete barrier, blocking different amounts of light at different altitudes. On the other hand, the moon has no atmosphere, so during the transit we can clearly see the crisp edges of the moon's horizon.

NASA Mars Rover Moves Onward After 'Marias Pass' Studies

This low-angle self-portrait of NASA's Curiosity Mars rover shows the vehicle at the site from which it reached down to drill into a rock target called "Buckskin." The MAHLI camera on Curiosity's robotic arm took multiple images on Aug. 5, 2015, that were stitched together into this selfie.

Credits: NASA/JPL-Caltech/MSSS

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This version of a self-portrait of NASA's Curiosity Mars rover at a drilling site called "Buckskin" is presented as a stereographic projection, which shows the horizon as a circle. The MAHLI camera on Curiosity's robotic arm took dozens of component images for this selfie on Aug. 5, 2015.

Credits: NASA/JPL-Caltech/MSSS

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This low-angle self-portrait of NASA's Curiosity Mars rover from Aug. 5, 2015, shows the vehicle above the "Buckskin" rock target in the "Marias Pass" area of lower Mount Sharp. The MAHLI camera on Curiosity's robotic arm took dozens of images that were stitched together into this sweeping panorama.

Credits: NASA/JPL-Caltech/MSSS

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This view of a test rover at NASA's Jet Propulsion Laboratory in California results from advance testing of arm positions and camera pointings for taking a low-angle selfie of NASA's Curiosity Mars rover.

Credits: NASA/JPL-Caltech/MSSS

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Curiosity's DAN instrument for checking hydration levels in the ground beneath the rover detected an unusually high amount at a site near "Marias Pass," prompting repeated passes over the area to map the hydrogen amounts. This map shows color-coded results from multiple traverses over the area.

Credits: NASA/JPL-Caltech/Russian Space Research Institute

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NASA's Curiosity Mars rover is driving toward the southwest after departing a region where for several weeks it investigated a geological contact zone and rocks that are unexpectedly high in silica and hydrogen content. The hydrogen indicates water bound to minerals in the ground.

In this "Marias Pass" region, Curiosity successfully used its drill to sample a rock target called "Buckskin" and then used the camera on its robotic arm for multiple images to be stitched into a self-portrait at the drilling site. The new Curiosity selfie from a dramatically low angle is online at:

http://www.jpl.nasa.gov/spaceimages/details.php?id=pia19808

The rover finished activities in Marias Pass on Aug. 12 and headed onward up Mount Sharp, the layered mountain it reached in September 2014. In drives on Aug. 12, 13, 14 and 18, it progressed 433 feet (132 meters), bringing Curiosity's total odometry since its August 2012 landing to 6.9 miles (11.1 kilometers).

Curiosity is carrying with it some of the sample powder drilled from Buckskin. The rover's internal laboratories are analyzing the material. The mission's science team members seek to understand why this area bears rocks with significantly higher levels of silica and hydrogen than other areas the rover has traversed.

Silica, monitored with Curiosity's laser-firing Chemistry and Camera (ChemCam) instrument, is a rock-forming chemical containing silicon and oxygen, commonly found on Earth as quartz. Hydrogen in the ground beneath the rover is monitored by the rover's Dynamic Albedo of Neutrons (DAN) instrument. It has been detected at low levels everywhere Curiosity has driven and is interpreted as the hydrogen in water molecules or hydroxyl ions bound within or absorbed onto minerals in the rocks and soil.

"The ground about 1 meter beneath the rover in this area holds three or four times as much water as the ground anywhere else Curiosity has driven during its three years on Mars," said DAN Principal Investigator Igor Mitrofanov of Space Research Institute, Moscow. DAN first detected the unexpectedly high level of hydrogen using its passive mode. Later, the rover drove back over the area using DAN in active mode, in which the instrument shoots neutrons into the ground and detects those that bounce off the subsurface, but preferentially interacting with hydrogen. The measurements confirmed hydrated material covered by a thin layer of drier material.

Curiosity initially noted the area with high silica and hydrogen on May 21 while climbing to a site where two types of sedimentary bedrock lie in contact with each other. Such contact zones can hold clues about ancient changes in environment, from conditions that produced the older rock type to conditions that produced the younger one. This contact is the lure that led the rover team to choose Marias Pass as a route toward higher layers of Mount Sharp. Pale mudstone, like bedrock the mission examined for the first several months after reaching Mount Sharp at an area called "Pahrump Hills," forms one side of the contact. The overlying side is darker, finely bedded sandstone.

Curiosity examined the Marias Pass contact zone closely with instruments mounted on its mast and arm. The unusual levels of silica and hydrogen in rocks passed during the climb prompted a choice to backtrack to examine that area and acquire a drilled sample.

Buckskin was the first rock drilled by Curiosity since an electrical circuit in the drill's percussion mechanism exhibited a small, transient short circuit in February during transfer of sample powder from the third target drilled in the Pahrump Hills area.

"We were pleased to see no repeat of the short circuit during the Buckskin drilling and  sample transfer," said Steven Lee, deputyPROJECT MANAGER for Curiosity at NASA's Jet Propulsion Laboratory, Pasadena, California. "It could come back, but we have made changes in fault protection to continue safely drilling even in the presence of small shorts. We also improved drill percuss circuit telemetry to gain more diagnostic information from any future occurrences."

Curiosity reached the base of Mount Sharp after two years of fruitfully investigating outcrops closer to its landing site and trekking to the mountain. The main mission objective now is to examine layers of lower Mount Sharp for ancient habitable environments and evidence about how early Mars environments evolved from wetter to drier conditions.

JPL, a division of the California Institute of Technology in Pasadena, built the rover and manages the project for NASA's Science Mission Directorate in Washington. For more information about Curiosity, visit: