sexta-feira, 16 de junho de 2017
NASA WEB · Martian Crater Provides Reminder of Apollo Moonwalk NASA's Mars Exploration Rover Opportunity passed near a young crater this spring during the 45th anniversary of Apollo 16's trip to Earth's moon, prompting a connection between two missions
|Martian Crater Provides Reminder of Apollo MoonwalkNASA's Mars Exploration Rover Opportunity passed near a young crater this spring during the 45th anniversary of Apollo 16's trip to Earth's moon, prompting a connection between two missions.|
Opportunity's science team informally named the Martian feature "Orion Crater." The name honors the Apollo 16 lunar module, Orion, which carried astronauts John Young and Charles Duke to and from the surface of the moon in April 1972 while crewmate Ken Mattingly piloted the Apollo 16 command module, Casper, in orbit around the moon. Orion is also the name of NASA's new spacecraft that will carry humans into deep space and sustain them during travel beyond Earth orbit.
Opportunity's Panoramic Camera (Pancam) took component images for this view of Orion Crater on April 26, 2017. The crater is about 90 feet (27 meters) wide and estimated to be no older than 10 million years.
"It turns out that Orion Crater is almost exactly the same size as Plum Crater on the moon, which John Young and Charles Duke explored on their first of three moonwalks taken while investigating the lunar surface using their lunar rover," said Opportunity science-team member Jim Rice, of the Planetary Science Institute, Tucson, Arizona.
Rice sent Duke the Pancam mosaic of Mars' Orion Crater, and Duke responded, "This is fantastic. What a great job! I wish I could be standing on the rim of Orion like I was standing on the rim of Plum Crater 45 years ago."
NASA WEB · The moon hanging in the night sky sent Robert Hurt's mind into deep space -- to a region some 40 light years away, in fact, where seven Earth-sized planets crowded close to a dim, red sun.
|The Art of ExoplanetsThe moon hanging in the night sky sent Robert Hurt's mind into deep space -- to a region some 40 light years away, in fact, where seven Earth-sized planets crowded close to a dim, red sun.|
Hurt, a visualization scientist at Caltech's IPAC center, was walking outside his home in Mar Vista, California, shortly after he learned of the discovery of these rocky worlds around a star called TRAPPIST-1 and got the assignment to visualize them. The planets had been revealed by NASA's Spitzer Space Telescope and ground-based observatories.
"I just stopped dead in my tracks, and I just stared at it," Hurt said in an interview. "I was imagining that could be, not our moon, but the next planet over - what it would be like to be in a system where you could look up and see continental features on the next planet."
› DOWNLOAD VIDEO Art of AstrophysicsSo began a kind of inspirational avalanche. Hurt and his colleague, multimedia producer Tim Pyle, developed a series of arresting, photorealistic images of what the new system's tightly packed planets might look like -- so tightly packed that they would loom large in each other's skies. Their visions of the TRAPPIST-1 system would appear in leading news outlets around the world.
Artists like Hurt and Pyle, who render vibrant visualizations based on data from Spitzer and other missions, are hybrids of sorts, blending expertise in both science and art. From squiggles on charts and columns of numbers, they conjure red, blue and green worlds, with half-frozen oceans or bubbling lava. Or they transport us to the surface of a world with a red-orange sun fixed in place, and a sky full of planetary companions.
"For the public, the value of this is not just giving them a picture of something somebody made up," said Douglas Hudgins, a program scientist for the Exoplanet Exploration Program at NASA Headquarters in Washington. "These are real, educated guesses of how something might look to human beings. An image is worth a thousand words."
Hurt says he and Pyle are building on the work of artistic pioneers.
"There's actually a long history and tradition for space art and science-based illustration," he said. "If you trace its roots back to the artist Chesley Bonestell (famous in the 1950s and '60s), he really was the artist who got this idea: Let's go and imagine what the planets in our solar system might actually look like if you were, say, on Jupiter's moon, Io. How big would Jupiter appear in the sky, and what angle would we be viewing it from?"
To begin work on their visualizations, Hurt divided up the seven TRAPPIST-1 planets with Pyle, who shares an office with him at Caltech's IPAC center in Pasadena, California.
Hurt holds a Ph.D. in astrophysics, and has worked at the center since he was a post-doctoral researcher in 1996 - when astronomical art was just his hobby.
"They created a job for me," he said.
Pyle, whose background is in Hollywood special effects, joined Hurt in 2004.
Hurt turns to Pyle for artistic inspiration, while Pyle relies on Hurt to check his science.
"Robert and I have our desks right next to each other, so we're constantly giving each other feedback," Pyle said. "We're each upping each other's game, I think."
The TRAPPIST-1 worlds offered both of them a unique challenge. The two already had a reputation for illustrating many exoplanets - planets around stars beyond our own -- but never seven Earth-sized worlds in a single system. The planets cluster so close to their star that a "year" on each of them -- the time they take to complete a single orbit -- can be numbered in Earth days.
And like the overwhelming majority of the thousands of exoplanets found so far, they were detected using indirect means. No telescope exists today that is powerful enough to photograph them.
Real science informed their artistic vision. Using data from the telescopes that reveal each planet's diameter as well as its "weight," or mass, and known stellar physics to determine the amount of light each planet would receive, the artists went to work.
Both consulted closely with the planets' discovery team as they planned for a NASA announcement to coincide with a report in the journal Nature.
"When we're doing these artist's concepts, we're never saying, 'This is what these planets actually look like,'" Pyle said. "We're doing plausible illustrations of what they could look like, based on what we know so far. Having this wide range of seven planets actually let us illustrate almost the whole breadth of what would be plausible. This was going to be this incredible interstellar laboratory for what could happen on an Earth-sized planet."
For TRAPPIST-1b, Pyle took Jupiter's volcanic moon, Io, as an inspiration, based on suggestions from the science team. For the outermost world, TRAPPIST-1h, he chose two other Jovian moons, the ice-encased Ganymede and Europa.
After talking to the scientists, Hurt portrayed TRAPPIST-1c as dry and rocky. But because all seven planets are probably tidally locked, forever presenting one face to their star and the other to the cosmos, he placed an ice cap on the dark side.
TRAPPIST-1d was one of three that fall inside the "habitable zone" of the star, or the right distance away from it to allow possible liquid water on the surface.
"The researchers told us they would like to see it portrayed as something they called an 'eyeball world,'" Hurt said. "You have a dry, hot side that's facing the star and an ice cap on the back side. But somewhere in between, you have (a zone) where the ice could melt and be sustained as liquid water."
At this point, Hurt said, art intervened. The scientists rejected his first version of the planet, which showed liquid water intruding far into the "dayside" of TRAPPIST-1d. They argued that the water would most likely be found well within the planet's dark half.
"Then I kind of pushed back, and said, 'If it's on the dark side, no one can look at it and understand we're saying there's water there,'" Hurt said. They struck a compromise: more water toward the dayside than the science team might expect, but a better visual representation of the science.
The same push and pull between science and art extends to other forms of astronomical visualization, whether it's a Valentine's Day cartoon of a star pulsing like a heart in time with its planet, or materials for the blockbuster announcement of the first detection of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory in February 2016. They've also illustrated asteroids, neutron stars, pulsars and brown dwarfs.
Visualizations based on data can also inform science, leading to genuine scientific insights. The scientists' conclusions about TRAPPIST-1 at first seemed to suggest the planets would be bathed in red light, potentially obscuring features like blue-hued bodies of water.
"It makes it hard to really differentiate what is going on," Hurt said.
Hurt decided to investigate. A colleague provided him with a spectrum of a red dwarf star similar to TRAPPIST-1. He overlaid that with the "responsivity curves" of the human eye, and found that most of the scientists' "red" came from infrared light, invisible to human eyes. Subtract that, and what is left is a more reddish-orange hue that we might see standing on the surface of a TRAPPIST-1 world -- "kind of the same color you would expect to get from a low-wattage light bulb," Hurt said. "And the scientists looked at that and said, 'Oh, ok, great, it's orange.' When the math tells you the answer, there really isn't a lot to argue about."
For Hurt, the real goal of scientific illustration is to excite the public, engage them in the science, and provide a snapshot of scientific knowledge.
"If you look at the whole history of space art, reaching back many, many decades, you will find you have a visual record," he said. "The art is a historical record of our changing understanding of the universe. It becomes a part of the story, and a part of the research, I think."
quarta-feira, 7 de junho de 2017
|Flares May Threaten Planet Habitability Near Red DwarfsCool dwarf stars are hot targets for exoplanet hunting right now. The discoveries of planets in the habitable zones of the TRAPPIST-1 and LHS 1140 systems, for example, suggest that Earth-sized worlds might circle billions of red dwarf stars, the most common type of star in our galaxy. But, like our own sun, many of these stars erupt with intense flares. Are red dwarfs really as friendly to life as they appear, or do these flares make the surfaces of any orbiting planets inhospitable?|
To address this question, a team of scientists has combed 10 years of ultraviolet observations by NASA's Galaxy Evolution Explorer (GALEX) spacecraft looking for rapid increases in the brightness of stars due to flares. Flares emit radiation across a wide swath of wavelengths, with a significant fraction of their total energy released in the ultraviolet bands where GALEX observed. At the same time, the red dwarfs from which the flares arise are relatively dim in ultraviolet. This contrast, combined with the GALEX detectors' sensitivity to fast changes, allowed the team to measure events with less total energy than many previously detected flares. This is important because, although individually less energetic and therefore less hostile to life, smaller flares might be much more frequent and add up over time to create an inhospitable environment.
"What if planets are constantly bathed by these smaller, but still significant, flares?" asked Scott Fleming of the Space Telescope Science Institute (STScI) in Baltimore. "There could be a cumulative effect."
To detect and accurately measure these flares, the team had to analyze data over very short time intervals. From images with exposure times of nearly half an hour, the team was able to reveal stellar variations lasting just seconds.
First author Chase Million of Million Concepts in State College, Pennsylvania, led a project called gPhoton that reprocessed more than 100 terabytes of GALEX data held at the Mikulski Archive for Space Telescopes (MAST), located at the Space Telescope Science Institute. The team then used custom software developed by Million and Clara Brasseur, also at the institute, to search several hundred red dwarf stars, and they detected dozens of flares.
"We have found dwarf star flares in the whole range that we expected GALEX to be sensitive to, from itty bitty baby flares that last a few seconds, to monster flares that make a star hundreds of times brighter for a few minutes," said Million.
The flares GALEX detected are similar in strength to flares produced by our own sun. However, because a planet would have to orbit much closer to a cool, red dwarf star to maintain a temperature friendly to life as we know it, such planets would be subjected to more of a flare's energy than Earth.
Large flares can strip away a planet's atmosphere. Strong ultraviolet light from flares that penetrates to a planet's surface could damage organisms or prevent life from arising.
Currently, team members Rachel Osten and Brasseur are examining stars observed by both the GALEX and Kepler missions to look for similar flares. The team expects to eventually find hundreds of thousands of flares hidden in the GALEX data.
"These results show the value of a survey mission like GALEX, which was instigated to study the evolution of galaxies across cosmic time and is now having an impact on the study of nearby habitable planets," said Don Neill, research scientist at Caltech in Pasadena, who was part of the GALEX collaboration. "We did not anticipate that GALEX would be used for exoplanets when the mission was designed."
New and powerful instruments like NASA's James Webb Space Telescope, scheduled for launch in 2018, ultimately will be needed to study atmospheres of planets orbiting nearby red dwarf stars and search for signs of life. But as researchers pose new questions about the cosmos, archives of data from past projects and missions, like those held at MAST, continue to produce exciting new scientific results.
These results were presented in a news conference at a meeting of the American Astronomical Society in Austin, Texas.
The GALEX mission, which ended in 2013 after more than a decade of scanning the skies in ultraviolet light, was led by scientists at Caltech. NASA's Jet Propulsion Laboratory, also in Pasadena, managed the mission and built the science instrument. JPL is managed by Caltech for NASA.
STScI conducts Hubble Space Telescope science operations and is the mission and science operations center for the James Webb Space Telescope. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington.