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NASA/JPL/University of Arizona

There's Liquid Water on Mars

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NASA/JPL/University of Arizona

In the image above, do you see those dark, narrow streaks flowing downhill on the steep slopes at Mars's Horowitz crater? Scientists say they provide definitive evidence of water flowing on the red planet. The findings were published today in the journal Nature Geoscience. NASA also held a press conference today to discuss the discovery.

That they might represent water flow has been suspected for several years. In 2011, a team of researchers working on the University of Arizona's HiRISE (High Resolution Imaging Science Experiment), an imaging system aboard the Mars Reconnaissance Orbiter (MRO), hypothesized that these streaks, known as recurring slope lineae, or RSLs, might be evidence of intermittent salty water flows that change with the seasons: 

The current research team (which includes planetary scientists from HiRISE, a few U.S. universities, NASA, and a French research center) combined the HiRISE documentation of RSLs—which were subsequently found at dozens of sites—with spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), an instrument also onboard the MRO.

RSLs have low reflectance compared to the surrounding terrain, and they appear to get larger during warm seasons. The team analyzed at what wavelengths these RSLs absorb light, and then compared their abilities to absorb different wavelengths to those of minerals on Earth. The closest matches were magnesium perchlorate, magnesium chlorate, and sodium perchlorate—hydrated salts, which were detected at four locations during the seasons when RSLs are most extensive.

"Our findings strongly support the hypothesis that recurring slope lineae form as a result of contemporary water activity on Mars," the researchers write. They don't know where the water originates, or how it formed; the favored theory is that it's the result of deliquescence, in which salts absorb moisture from the atmosphere to create liquid water. This water is likely much saltier than our oceans.

Here are two views of slopes where hydrated salts were detected.

Dark narrow streaks known as 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. Image credit: NASA/JPL/University of Arizona

Planetary scientists have detected hydrated salts on these slopes at Hale crater. 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. This is a false-color image. Image credit: NASA/JPL/University of Arizona

What are the implications of this discovery? Potential life on Mars, of course; either native life—which if it does exist is likely microbial and subsurface—or human life, in the future, as part of a manned Mars mission. 

As for Martian life, "I think it’s likely there’s life in the crust of Mars—microbes," said University of Arizona planetary geologist and study co-author Alfred McEwen, speaking at the press conference from Nantes, France. "To me, the chances of life being in the subsurface of Mars has always been very high."

But as Mars Exploration Program lead scientist Michael Meyer noted, “We have only one example of life, and that is us. We don’t know how it started, and so one of the things we found at Mars is that it could have supported life. But we don’t know how life started here, so we don’t know if it’s possible for life to start on Mars.”

As for the possibility of human life on Mars, "these observations are giving us a much better view that Mars has resources that are useful to future travels," said John Grunsfeld, astronaut and associate administrator of NASA’s Science Mission Directorate. For one thing, he noted, there's the potential to make rocket fuel (which is commonly made from liquid hydrogen and liquid oxygen). "The exciting thing is that we'll send humans to Mars in the near future," Grunsfeld said.

Before humans ever set foot on the red planet, there are several unmanned missions to Mars on the horizon. Next year, NASA will send the InSight lander to Mars to peer into its interior for the first time. The European Space Agency is launching two ExoMars missions—one in 2016 and the other, in collaboration with the Russian Federal Space Agency, in 2018. And in 2020 NASA's Mars Exploration Program continues with the launch of another rover, which will collect samples and bring them back to Earth.

Because the slopes featuring these briny water flows are steep, they're not good landing places for rovers. Nimble-footed astronauts, on the other hand, might one day be able to make the climb for a closer look.

"We are on a journey to Mars, and science is leading the way. Each time we learn something new about Mars, Mars becomes more and more interesting," Grunsfeld said. "I think it's going to provide us with a great sense of our place in the universe and our solar system in particular."

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8 Useful Facts About Uranus
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Uranus as seen by the human eye (left) and with colored filters (right).

The first planet to be discovered by telescope, Uranus is the nearest of the two "ice giants" in the solar system. Because we've not visited in over 30 years, much of the planet and its inner workings remain unknown. What scientists do know, however, suggests a mind-blowing world of diamond rain and mysterious moons. Here is what you need to know about Uranus.


Uranus is the seventh planet from the Sun, the fourth largest by size, and ranks seventh by density. (Saturn wins as least-dense.) It has 27 known moons, each named for characters from the works of William Shakespeare and Alexander Pope. It is about 1784 million miles from the Sun (we're 93 million miles away from the Sun, or 1 astronomical unit), and is four times wider than Earth. Planning a trip? Bring a jacket, as the effective temperature of its upper atmosphere is -357°F. One Uranian year last 84 Earth years, which seems pretty long, until you consider one Uranian day, which lasts 42 Earth years. Why?


Most planets, as they orbit the Sun, rotate upright, spinning like tops—some faster, some slower, but top-spinning all the same. Not Uranus! As it circles the Sun, its motion is more like a ball rolling along its orbit. This means that for each hemisphere of the planet to go from day to night, you need to complete half an orbit: 42 Earth years. (Note that this is not the length of a complete rotation, which takes about 17.25 hours.) While nobody knows for sure what caused this 98-degree tilt, the prevailing hypothesis involves a major planetary collision early in its history. And unlike Earth (but like Venus!), it rotates east to west.


You might have noticed that every non-Earth planet in the solar system is named for a Roman deity. (Earth didn't make the cut because when it was named, nobody knew it was a planet. It was just … everything.) There is an exception to the Roman-god rule: Uranus. Moving outward from Earth, Mars is (sometimes) the son of Jupiter, and Jupiter is the son of Saturn. So who is Saturn's father? Good question! In Greek mythology, it is Ouranos, who has no precise equivalent in Roman mythology (Caelus is close), though his name was on occasion Latinized by poets as—you guessed it!—Uranus. So to keep things nice and tidy, Uranus it was when finally naming this newly discovered world. Little did astronomers realize how greatly they would disrupt science classrooms evermore.

Incidentally, it is not pronounced "your anus," but rather, "urine us" … which is hardly an improvement.


Uranus and Neptune comprise the solar system's ice giants. (Other classes of planets include the terrestrial planets, the gas giants, and the dwarf planets.) Ice giants are not giant chunks of ice in space. Rather, the name refers to their formation in the interstellar medium. Hydrogen and helium, which only exist as gases in interstellar space, formed planets like Jupiter and Saturn. Silicates and irons, meanwhile, formed places like Earth. In the interstellar medium, molecules like water, methane, and ammonia comprise an in-between state, able to exist as gases or ices depending on the local conditions. When those molecules were found by Voyager to have an extensive presence in Uranus and Neptune, scientists called them "ice giants."


Planets form hot. A small planet can cool off and radiate away heat over the age of the solar system. A large planet cannot. It hasn't cooled enough entirely on the inside after formation, and thus radiates heat. Jupiter, Saturn, and Neptune all give off significantly more heat than they receive from the Sun. Puzzlingly, Uranus is different.

"Uranus is the only giant planet that is not giving off significantly more heat than it is receiving from the Sun, and we don't know why that is," says Mark Hofstadter, a planetary scientist at NASA's Jet Propulsion Laboratory. He tells Mental Floss that Uranus and Neptune are thought to be similar in terms of where and how they formed.

So why is Uranus the only planet not giving off heat? "The big question is whether that heat is trapped on the inside, and so the interior is much hotter than we expect, right now," Hofstadter says. "Or did something happen in its history that let all the internal heat get released much more quickly than expected?"

The planet's extreme tilt might be related. If it were caused by an impact event, it is possible that the collision overturned the innards of the planet and helped it cool more rapidly. "The bottom line," says Hofstadter, "is that we don't know."


Although it's really cold in the Uranian upper atmosphere, it gets really hot, really fast as you reach deeper. Couple that with the tremendous pressure in the Uranian interior, and you get the conditions for literal diamond rain. And not just little rain diamondlets, either, but diamonds that are millions of carats each—bigger than your average grizzly bear. Note also that this heat means the ice giants contain relatively little ice. Surrounding a rocky core is what is thought to be a massive ocean—though one unlike you might find on Earth. Down there, the heat and pressure keep the ocean in an "in between" state that is highly reactive and ionic.


Unlike Saturn's preening hoops, the 13 rings of Uranus are dark and foreboding, likely comprised of ice and radiation-processed organic material. The rings are made more of chunks than of dust, and are probably very young indeed: something on the order of 600 million years old. (For comparison, the oldest known dinosaurs roamed the Earth 240 million years ago.)


The only spacecraft to ever visit Uranus was NASA's Voyager 2 in 1986, which discovered 10 new moons and two new rings during its single pass from 50,000 miles up. Because of the sheer weirdness and wonder of the planet, scientists have been itching to return ever since. Some questions can only be answered with a new spacecraft mission. Key among them: What is the composition of the planet? What are the interactions of the solar wind with the magnetic field? (That's important for understanding various processes such as the heating of the upper atmosphere and the planet's energy deposition.) What are the geological details of its satellites, and the structure of the rings?

The Voyager spacecraft gave scientists a peek at the two ice giants, and now it's time to study them up close and in depth. Hofstadter compares the need for an ice-giants mission to what happened after the Voyagers visited Jupiter and Saturn. NASA launched Galileo to Jupiter in 1989 and Cassini to Saturn in 1997. (Cassini was recently sent on a suicide mission into Saturn.) Those missions arrived at their respective systems and proved transformative to the field of planetary science.

"Just as we had to get a closer look at Europa and Enceladus to realize that there are potentially habitable oceans there, the Uranus and Neptune systems can have similar things," says Hofstadter. "We'd like to go there and see them up close. We need to go into the system." 

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ESO / M. Kornmesser
Astronomers Discover Another Earth-Like Planet Near Our Solar System
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ESO / M. Kornmesser

Astronomers with the European Southern Observatory (ESO) have discovered an exoplanet orbiting a star just 11 light-years from our own Sun. It's roughly the size of Earth and is predicted to have a temperate climate, making it the second-nearest Earth-like planet known to exist.

As reported in the journal Astronomy & Astrophysics [PDF], the planet, dubbed Ross 128 b, circles the inactive red dwarf star Ross 128. Its orbit is 20 times closer to its star than Earth's is to the Sun, but the exoplanet receives only 1.38 times more radiation than we do. Ross 128 is much cooler than our Sun, and calmer than typical red dwarfs. Researchers estimate the planet's equilibrium temperature to be between -76°F and 68°F, making it temperate like our home planet.

The discovery was made by an international team of astronomers working with the ESO's High Accuracy Radial Velocity Planet Searcher (HARPS) at the La Silla Observatory in Chile. Popular Mechanics reports that instead of waiting for the exoplanet's shadow to pass across its star (what's known as the transit method), the scientists monitored the star's radial velocity. The gravitational pull of orbiting planets can cause their stars to wobble slightly, and by measuring these disturbances, researchers can estimate everything from a planet's mass to its location.

At just 11 light-years away, Ross 128 b is close, though not close enough to make it our nearest Earth-like neighbor. That title belongs to Proxima b, a planet similar in size, mass, and temperature to Earth that orbits the star Proxima Centauri. But Ross 128 is creeping closer to Earth, and in just 79,000 years, it could occupy the No. 1 slot. In the meantime, scientists will study Ross 128 b along with other close exoplanets to determine if they can support life.


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