December 9, 2013
Shortly after NASA’s Curiosity rover landed on Mars in August 2012, the scientists guiding the device decided to make a temporary detour before heading to the mission’s ultimate destination, Mount Sharp. Last spring, they guided the six-wheeled machine towards Yellowknife Bay, a slight depression with intriguingly lighter-toned sedimentary rocks, and drilled its first two holes in Martian rock in order to collect samples.
Afterward, as Curiosity drove away from Yellowknife Bay, onboard equipment ground the rock samples to a fine dust and chemically analyzed their content in extreme detail to learn as much as possible about the site. Today, the results of that analysis were finally published in a series of articles in Science, and it’s safe to say that the scientists probably don’t regret making that brief detour. Yellowknife Bay, they discovered, was likely once home to a calm freshwater lake that lasted for tens of thousands of years, and theoretically had all the right ingredients to sustain microbial life.
“This is a huge positive step for the exploration of Mars,” said Sanjeev Gupta, an Earth scientist at Imperial College London and a member of the Curiosity team, in a press statement on the discovery. “It is exciting to think that billions of years ago, ancient microbial life may have existed in the lake’s calm waters, converting a rich array of elements into energy.”
Previously, Curiosity found ancient evidence of flowing water and an unusual type of rock that likely formed near water, but this is the strongest evidence so far that Mars may have once sustained life. The chemical analysis of the two rocks (named “John Klein” and “Cumberland”) showed that they were mudstones, a type of fine-grained sedimentary rock that generally forms at the bottom of a calm body of water, as small sediment particles gradually settle on one another and are eventually cemented together.
Isotope analysis indicated that these rocks formed sometime between 4.5 and 3.6 billion years ago, either during Mars’ Noachian period (in which the planet was likely much warmer, had a thicker atmosphere and may have had abundant surface water) or early on in its Hesperian period (in which it shifted to the dry, colder planet we see currently).
Additionally, a number of key elements for the establishment of life on Earth—including carbon, hydrogen, oxygen, sulfur, nitrogen and phosphorous—were found in detectable quantities in the rocks, and chemical analysis indicated that the water was likely of a relatively neutral pH and low in salt content. All of these discoveries increase the chance that the ancient lake could have served as a habitat for living organisms.
The scientists hypothesize that the microorganisms most likely to live in this environment would have been chemolithoautotrophs, a type of microbe that derives energy by breaking down rocks and incorporates carbon dioxide from the air. On Earth, these types of organisms are most often found near hydrothermal vents on the ocean floor, where they thrive off chemicals emitted into the water.
Obviously, this isn’t direct proof of life, but rather circumstantial evidence that it may have once existed. Still, it’s yet another vindication of Curiosity’s mission, which is to determine the planet’s habitability. Over the coming months and years, the scientists guiding the rover plan to keep sampling sedimentary rocks on the planet’s surface, hoping to find further evidence of potentially-habitable ancient environments and perhaps even direct evidence of now-extinct living organisms.
For more, head over to NASA’s live webcast of the press conference announcing the findings, starting today at noon EST.
November 4, 2013
Over the past 18 years, astronomers have discovered 1038 planets orbiting distant stars. Disappointingly, though, the vast majority don’t seem like candidates to support life as we know it—they’re either so close to their home star that all water would likely evaporate, or so far away that all of it would freeze, or they’re made up of gas instead of rock and more closely resemble our solar system’s gas giants than Earth.
Or so we thought. Today, a group of scientists from UC Berkeley and the University of Hawaii published a calculation suggesting that we’ve overlooked evidence of a vast number of Earth-sized exoplanets in the habitable zone of their stars, simply because these planets are harder to detect with current methods. They believe that, on average, 22% of Sun-like stars (that is, stars with a size and temperature similar to the Sun) harbor a planet that’s roughly Earth-sized in their habitable zones.
“With about 100 billion stars in our Milky Way galaxy, that’s about 20 billion such planets,” said Andrew Howard, one of the study’s co-authors, in a press conference on the findings. “That’s a few Earth-sized planets for every human being on the planet Earth.”
The team, led by Erik Petigura, came to these conclusions by taking an unconventional approach to planet-finding. Instead of counting how many exoplanets we’ve found, they sought to determine how many planets we’re unable to see.
Exoplanets are detected as a result of rhythmic dimming in a star’s brightness, which indicates that there’s a planet orbiting it and passing between the star and our vantage point. Because of this method, large planets that orbit closely to their stars have been the easiest to find—they block more light, more often—and thus disproportionately dominate the list of known exoplanets.
To estimate the number of exoplanets this technique misses, the Berkeley team wrote a software program that analyzed data from the Kepler mission, an exoplanet-hunting NASA telescope launched into orbit in 2009. Initially, to confirm the program’s accuracy, they fed it the same data from 42,557 Sun-like stars that had already been scrutinized by other astronomers, and it indeed detected 603 candidate planets, all of which had already been found.
When it parsed the data further to find Earth-like planets—using the length of time between dimmings to indicate how far out the planet orbits the star, and the degree of dimming to indicate us how much of the star is blocked by the planet, and thus the exoplanet’s size—it found 10 potential exoplanets that are between one and two times the size of Earth and orbit in what is likely the star’s habitable zone. This, too, aligned with previous findings, showing the program could accurately detect planets.
But what the researchers really wanted to do was determine the overall prevalence of Earth-like exoplanets. To calculate this number, they first had to determine just how many weren’t detected in the survey. “One way of thinking of it is that we’re doing a census of habitable exoplanets, but not everyone’s answering the door,” Petigura explained.
There are a few reasons that a planet might not be detected. If its orbit doesn’t take it into a location that would block the path of light between its star and our telescopes, we’d have no way of seeing it. Alternately, it could successfully block starlight, but the event could be lost amid natural variation in the brightness of the star as we perceive it on Earth.
Both of these possibilities, it turns out, make it disproportionately hard to find Earth-like exoplanets. “Planets are easier to detect if they’re bigger, and closer to their host stars,” Howard said. “Thus it’s no accident that hot Jupiters were the first planets to be discovered.” Simply by virtue of physics, smaller, Earth-sized planets that may orbit a bit farther out are less likely to pass directly in front of their stars, from our perspective.
To finding out how many Earth-like planets we likely miss as a result, the scientists altered the Kepler data by artificially introducing 40,000 more exoplanets similar to Earth—roughly one per star—then feeding the resulting data back into the planet detection software. This time, it only found about one percent of the Earth-like planets introduced, because the vast majority didn’t cause a detectable dimming of their star.
This means that, with current detection methods, 99 out of 100 Earth-like aren’t coming to the door when to answer our interstellar census. Accounting for this level of imperfection, the researchers calculated that far more Sun-like stars are home to a potentially habitable, Earth-sized exoplanet than we previously thought.
It’s important to note that this is a theoretical calculation: The scientists didn’t actually discover these sorts of planets orbiting 22% of the stars. But if the underlying assumptions are accurate, it does give hope to the possibility that we’ll find more potentially habitable planets in the future. In fact, the researchers calculated that if the prevalence of these sorts of planets is uniform across the galaxy, odds are that one can be found tantalizingly nearby—about 12 light years away from Earth.
It’s still unknown whether these planets might have the other ingredients that we believe are likely necessary for life: a protective atmosphere, the presence of water and a rocky surface. But the researchers say another recent finding makes them hopeful that some of them have potential. Earlier this week, scientists found a rocky, Earth-sized exoplanet roughly 700 light-years away. Although that planet is certainly too hot to harbor life, it has density similar to that of Earth—suggesting that at least some of the Earth-sized planets we’ve failed to detect so far have a geologic composition similar to our own planet’s.
October 31, 2013
For the past 10 years, the European Space Agency’s Mars Express probe has flown around and around the red planet, orbiting it more than 12,500 times in total.
All the while, it’s been collecting detailed topographic data on Mars’ surface with a suite of remote sensing instruments, including high-resolution cameras, radar-sensing devices and spectrometers that can detect the minerals present on the planet by analyzing the spectrum of infrared light they emit.
This video, released earlier this week by the ESA, gives you a look at some of the probe’s most dramatic views to date. The ESA built this simulated flyover from computer graphics based off real-world data, so this clip is (currently) the closest you can possibly get to flying over Mars’ surface yourself.
October 10, 2013
The star GD61 is a white dwarf. As such, it’s insanely dense—similar in diameter to Earth, but with a mass roughly that of the Sun, so that a teaspoon of it is estimated to weigh about 5.5 tons. All things considered, it’s not a particularly promising stellar locale to find evidence of life.
But a new analysis of the debris surrounding the star suggests that, long ago, GD61 may have provided a much more hospitable environment. As part of a study published today in Science, scientists found that the crushed rock and dust near the star were once part of a small planet or asteroid made up of 26 precent water by volume. The discovery is the first time we’ve found water in a rocky, Earth-like planetary body (as opposed to a gas giant) in another star system.
“Those two ingredients—a rocky surface and water—are key in the hunt for habitable planets,” Boris Gänsicke of the University of Warwick in the UK, one of the study’s authors, said in a press statement. “So it’s very exciting to find them together for the first time outside our solar system.”
Why was water found in such a seemingly unhospitable place? Because once upon a time, GD61 wasn’t so different from our Sun, scientists speculate. But roughly 200 million years ago, when it exhausted its supply of fuel and could no longer sustain fusion reactions, its outer layers were blown out as part of a nebula, and its inner core collapsed inward, forming a white dwarf. (Incidentally, this fate will befall an estimated 97 percent of the stars in the Milky Way, including the Sun.)
When that happened, the tiny planet or asteroid in question—along with all the other bodies orbiting GD61—were violently knocked out of orbit, sucked inward, and ripped apart by the force of the star’s gravity. The clouds of dust, broken rock and water that the scientists recently discovered near the star are the remnants of these planets.
Even in its heyday, the watery body was probably still very small—perhaps comparable in size to our solar system’s dwarf planet Ceres, which orbits in the asteroid belt and is about .015 percent the mass of Earth. Additionally, like Ceres, the ancient planet or asteroid was extremely water-rich (26 percent water, far more than Earth’s .023 percent), and this water was similarly constituted as ice locked within a rocky crust.
To find all this out, the group of scientists (which also includes Jay Farihi of the University of Cambridge and Detlev Koester of the University of Kiel) used observations from two sources: a spectrograph on board the Hubble Space Telescope, through which they obtained data on ultraviolet light emitted by GD61, and a telescope at the W.M. Keck Observatory on Mauna Kea on Hawaii.
By looking at the light emitted from the star, which glows in certain patterns depending on the chemical signatures of gases present, they were able to determine the proportions of a number of elements (including oxygen, magnesium, aluminum, silicon, calcium and iron) contained within the cloud of dust that surrounds it. Using computer simulations of this stellar atmosphere, they were able to rule out a number of alternate possibilities that could have accounted for the abundance of oxygen, leaving only the explanation that it was brought there in water form.
Based on the amount of water and rocky minerals detected in the star’s atmosphere—and assuming it all came from one body—scientists speculate that the small planet or asteroid ripped up by the white dwarf was at least 56 miles in diameter, but perhaps much larger.
Although the star certainly isn’t home to any life at the moment due to its relatively cold temperature, the finding makes it seem more likely that other exoplanets contain water, which is necessary for life as we know it. Many scientists have speculated that small planets and asteroids like Ceres delivered water to Earth in the first place, so finding evidence of a watery body like this in another star system raises the possibility that the same process may have brought water to an Earth-sized planet elsewhere too.
“The finding of water in a large asteroid means the building blocks of habitable planets existed—and maybe still exist—in the GD 61 system, and likely also around a substantial number of similar parent stars,” Farihi said. “These water-rich building blocks, and the terrestrial planets they build, may in fact be common.”
September 26, 2013
Some 46 Martian days after landing on Mars in August 2012, after traveling nearly 1,000 feet from its landing site, Curiosity came upon a pyramid-shaped rock, roughly 20 inches tall. Researchers had been looking for a rock to use for calibrating a number of the rover’s high-tech instruments, and as principal investigator Roger Wiens said at a press conference at the time, “It was the first good-size rock that we found along the way.”
For the first time, scientists used the rover’s Hand Lens Imager (which takes ultra-high resolution photos of a rock’s surface) and the Alpha Particle X-ray Spectrometer (which bombards a rock with alpha particles and X-rays, kicking off electrons in patterns that allow scientists to identify the elements locked within it). They also used the ChemCam, a device that fires a laser at a rock and measures the abundances of elements vaporized.
Curiosity, for its part, commemorated the event with a pithy tweet:
I did a science! 1st contact science on rock target Jake. Here’s an action shot pic.twitter.com/pzcgH6Bk
— Curiosity Rover (@MarsCuriosity) September 22, 2012
A year later, the Curiosity team’s analysis of the data collected by these instruments, published today in Science, shows that they made a pretty lucky choice in finding a rock to start with. The rock, dubbed “Jake_M” (after engineer Jake Matijevic, who died a few days after Curiosity touched down), is unlike any rock previously found on Mars—and its composition intriguingly suggests that it formed after molten rock cooled quickly in the presence of underground water.
The new discovery was published as part of a special series of papers in Science that describe the initial geologic data collected by Curiosity’s full suite of scientific instrumentation. One of the other significant findings is a chemical analysis of a scoop of Martian soil—heated to 835 degrees Celsius inside the Sample Analysis at Mars instrument mechanism—showing that it contains between 1.5 and 3 percent water by weight, a level higher than scientists expected.
But what’s most exciting about the series of findings is the surprising chemical analysis of Jake_M. The researchers determined that it is likely igneous (formed by the solidification of magma) and, unlike any other igneous rocks previously found on Mars, has a mineral composition most similar to a class of basaltic rocks on Earth called mugearites.
“On Earth, we have a pretty good idea how mugearites and rocks like them are formed,” Martin Fisk, an Oregon State University geologist and co-author of the paper, said in a press statement. “It starts with magma deep within the Earth that crystallizes in the presence of one to two percent water. The crystals settle out of the magma, and what doesn’t crystallize is the mugearite magma, which can eventually make its way to the surface as a volcanic eruption.” This happens most frequently in underground areas where molten rock comes into contact with water—places like mid-ocean rifts and volcanic islands.
The fact that Jake_M closely resembles mugearites indicates that it likely took the same path, forming after other minerals crystallized in the presence of underground water and the remaining minerals were sent to the surface. This would suggest that, at least at some time in the past, Mars contained reserves of underground water.
The analysis is part of a growing body of evidence that Mars was once home to liquid water. Last September, images taken by Curiosity showed geologic features that suggested the one-time presence of flowing water at the surface. Here on Earth, analyses of several meteorites that originated on Mars have also indicated that, at some point long ago, the planet held reserves of liquid water deep underground.
This has scientists and members of the public excited, of course, because (at least as far as we know) water is a necessity for the evolution of life. If Mars was once a water-rich planet, as Curiosity’s findings increasingly suggest, it’s possible that life may have once evolved there long ago—and there may even be organic compounds or other remnants of life waiting to be found by the rover in the future.