The Wildest Alien Planets of 2012

From massive bodies that fell just short of becoming stars to the tiniest solar systems known, 2012 has brought an array of intriguing exoplanets to light. And double-star systems that once seemed unlikely to host planets have produced a wealth of them this year. 

Here's a look at some of the most exciting alien planets discovered in 2012:

Potentially habitable worlds

In the fall of 2012, astronomers announced two new planets, discovered separately, that may have the potential to support life outside of our solar system. Both planets were found in the habitable zone of their stars, the region where a planet could hold liquid water on its surface. Water is thought to be a key ingredient in the formation of life.

HD4030g, a "super-Earth" announced in November, is approximately seven times as massive as the planet we live on. The planet, which could be either rocky or a Neptune-like gas giant, sits in the middle of its habitable zone, making it possible for water to exist. 

HD 40307g is the most distant of the six planets in its system, taking approximately 200 days to orbit its star. Its distance means that it isn't tidally locked, with one face perpetually turned toward its star, making it more likely to have Earth-like conditions. Because the planet is only 42 light-years away from Earth, it could potentially be imaged by telescopes in the future. Its parent star is smaller and dimmer than the sun.

Gliese 163c also lies within its star's habitable zone, although it skirts the edge. Like HD 40307g, it is approximately seven times the mass of Earth, and could be a large rocky planet or a smaller gas giant. The planet orbits a red dwarf that is slightly dimmer than our sun, flying around it once every 26 days. Depending on its composition, Gliese 163c could host an ocean and a dense atmosphere, or it could be too hot for life to exist.

Both planets were found using the High Accuracy Radial Velocity Planet Searcher, or HARPS, the European Southern Observatory's telescope located at the La Silla Observatory in Chile.

Two suns, four stars

A number of double-sun systems were discovered in 2012, but perhaps the most astonishing was found by amateur astronomers. The gas giant PH1 orbits a pair of stars that are part of a four-star system, the first discovery of its kind.

A close binary set of stars with masses about 1.5 and 0.41 times that of the sun, the twin stars at the core of the system dance around each other every 20 days. Two more stars circle the pair at about a thousand times the Earth's distance to the sun.

Circling the central pair once every 138 days, PH1 is a gas giant, with a temperature ranging from 484 degrees Fahrenheit (251 degrees Celsius) to 644 F (340 C). Just bigger than Neptune, the planet could potentially host rocky moons, but such moons would also be too hot for liquid water.

PH1 was discovered by two amateur astronomers participating in the citizen scientist program Planet Hunters. A dip in the light from the system signified the potential presence of a planet, which was then confirmed by a team of professional astronomers.

In addition to being the first planet discovered by Planet Hunters, PH1 is also the first planet found orbiting a double star in a quadruple system and the first planet found in a quadruple system.

Near-habitable Tatooine system

Scientists discovered two separate binary systems this year with planets that lay near their habitable zone. Often referred to as "Tatooine planets," due to the famous double-star-system home of Luke Skywalker in the film "Star Wars," planets orbiting a binary star system have two suns overhead. Kepler-34b and Kepler-35b are particularly notable because they lay near their stars' habitable zone.

Kepler-34b is a gas giant with almost 70 times the mass of Earth. It travels around two sunlike stars once every 289 days, staying about as far away as Earth stays from the sun. It lies 4,900 light-years from Earth.

Kepler-35b weighs in at about an eighth of Jupiter's mass. It takes 131 days to travel around its parent pair, which are both slightly smaller than the sun. The system is only 5,400 light-years from Earth.

Both systems were found using NASA's Kepler space telescope.

Tatooine twins

In another double-star system twist, two planets were found orbiting a binary pair, the first time multiple planets have been seen around twin stars. The Kepler-47 stars are 5,000 light-years from Earth. One is sunlike, while the other is smaller and fainter. They orbit each other once every 7.5 days.

Kepler-47c is a gas giant that takes 303 days to circle its suns, and rests in the habitable zone of its stars. Although it is considered unsuitable for life, its existence means that other planets could survive in the habitable zones of twin-star systems. It could also host rocky moons that have the potential for life.

Kepler-47b takes less than 50 days to orbit the pair of stars. Only three times the radius of Earth, it is the smallest known planet orbiting in a binary system. Scientists think the rocky planet may be a sweltering world with a thick atmosphere.

Closest known exoplanet

Earth's closest star system, Alpha Centauri, hosts a molten terrestrial planet, scientists found. A rocky planet orbits Alpha Centauri B, one of the three stars in the system with 90 percent the mass of the sun, once every 3.2 days. The planet passes within only a few million miles of its star, hovering at a tenth of the distance between Mercury and the sun.

Although the overheated planet likely has a scorched surface too hot for life, scientists think the system has the potential to contain other planets. Only 4.2 light-years from Earth, such planets would be easier to image with telescopes in the not-too-distant future than more faraway candidates. Astronomers used HARPS to identify the nearby planet.

Tiniest solar system

Most of the newly discovered planets have been "super"-size: super-Earths, super-Jupiters, and so on. Larger planets are generally easier to find. But three new planets only a fraction the size of Earth, including one Mars-size body, make up the smallest alien system found to date.

Smaller and dimmer than the sun, red dwarfs are the most common type of star in the Milky Way galaxy. Scientists once thought they were too small to have a sustainable habitable zone, but a separate study earlier this year showed that more could maintain planets with the potential to host life. Such small planets would have been a challenge to find around a larger, sunlike star.

Kepler found the planets orbiting their star KOI-961 between 0.6 to 1.5 percent of Earth's distance to the sun, tearing around the red dwarf in less than two days. The rocky bodies have temperatures ranging from 350 F (177 C) to 836 F (447 C), resulting in broiling hot surfaces unlikely to support life. The three planets have diameters 0.78, 0.73, and 0.57 times that of Earth, with the smallest being Mars-size.

A planet that's almost a star

Kappa Andromedae b, or Kappa And b, is a massive planet that came in just shy of the ability to be a star. The gas giant, which is 13 times as massive as Jupiter, fell just short of having enough mass to be classified as a brown dwarf, failed stars too low in mass to sustain fusion in their core.

Astronomers were able to take a rare direct photo of the planet using Japan's Subaru telescope at Mauna Kea in Hawaii.The wannabe star orbits Kappa Andromedae, a star 2.5 times as massive as the sun that lies 170 light-years away. Circling the young star at almost twice Neptune's wide-reaching orbit, Kappa And b averages 2,600 F (1,400 C) and would appear bright red if seen up close.

Source of Article : space.com

Gigantic Black Holes Just Got Even Bigger

A number of the largest black holes in the universe may be even bigger than previously thought, researchers say.

"Ultramassive black holes — that is, black holes with masses exceeding 10 billion solar masses — are probably not rare; several and even dozens of these colossal black holes may exist," study lead author Julie Hlavacek-Larrondo, an astrophysicist at Stanford University told.

At the heart of virtually every large galaxy is a supermassive black hole weighing millions to billions of times the mass of the sun. Astronomers can detect the existence and approximate size of these black holes based on how they disturb the space and matter around them.

Now, using data from NASA's Chandra X-ray Observatory, researchers analyzing the brightest galaxies in a sample of 18 galaxy clusters find that at least 10 of the black holes in these galaxies are actually a whopping 10 billion to 40 billion times the mass of the sun. [Strangest Black Holes in the Universe]

Ultra-big

"Some of our black hole mass predictions are just lower limits, so they could be higher," Hlavacek-Larrondo said. "Just how big do I think they can get? I would bet that a least one 100-billion-solar-mass black hole exists among our objects, which really is ultra-big."

The scientists estimated the masses of the black holes in this sample by analyzing the amount of X-rays and radio waves they generate when they gobble surrounding gas, dust and stars. In addition to the X-ray data from Chandra, the investigators also used radio data from the Very Large Array in New Mexico and the Australia Telescope Compact Array, as well as infrared data from the 2-Micron All-Sky Survey.

Once they had this data, the scientists deduced the size of the black holes by using known relationships between the amount of radiation they put out and black hole masses. This relationship, called the fundamental plane of black hole activity, applies to data on black holes with masses ranging from 10 solar masses to 1 billion solar masses.

Oddly, these black holes are about 10 times larger than one would expect from the size of their host galaxies.

"These results may mean we don't really understand how the very biggest black holes coexist with their host galaxies," said study author Andrew Fabian of England's Cambridge University. "It looks like the behavior of these huge black holes has to differ from that of their less massive cousins in an important way."

Galaxy clusters

The answer to this mystery may have to do with where these black holes were discovered. All of these potentially ultramassive black holes lie in galaxies at the centers of massive galaxy clusters containing huge amounts of hot gas. Black holes probably generate the outbursts of energy that keep this hot gas from cooling and forming huge numbers of stars, researchers say.

To power these outbursts, the black holes must gorge on large amounts of the hot gas. Since the largest black holes can swallow the most gas and power the largest outbursts, astronomers had already predicted ultramassive black holes probably existed in these galaxy clusters in order to explain the number of stars contained within them. The extreme environments these ultramassive black holes and their galaxies experience may explain why the standard relationship between galaxies and black holes does not apply here.

To confirm these results, the researchers need to make detailed mass estimates of black holes by modeling the motions of stars and gas in the vicinity of these monsters. For instance, when it comes to the black hole in the center of the galaxy M87 — the central galaxy in the Virgo Cluster, the nearest galaxy cluster to Earth — stellar motions suggest M87's black hole is 6.6 billion solar masses, significantly higher than an estimate of 800 million solar masses calculated from infrared data.

"Our next step is to measure the mass of these monster black holes in a similar way to M87, and confirm their existence. I wouldn't be surprised if we end up finding the biggest black holes in the universe," said Hlavacek-Larrondo. "If our results are confirmed, they will have important ramifications for understanding the formation and evolution of black holes across cosmic time." 

How black holes grow

Current models of black hole evolution "can explain ultramassive black holes, but you really have to push the models to do so," Hlavacek-Larrondo said. "If we are correct, and these objects are much more common and massive than previously thought, then we might need to rethink how they can grow to such masses."

"What strengthens our result is that we already know that supermassive black holes exist very early on after the Big Bang, and you can build some ultramassive black holes from these," Hlavacek-Larrondo said. "These supermassive black holes appear to exist when the universe was still very young, only 5 percent of its actual age. So the question becomes, how can you build supermassive black holes so quickly after the Big Bang? Some models can explain this, but it all remains theoretical. The good news is that the upcoming James Webb Space Telescope will be able to provide some answers, since it will have the power to observe the formation of the first supermassive black holes."

That telescope, being constructed as a successor to the Hubble Space Telescope, is due to launch in 2018.

Hlavacek-Larrondo, Fabian and their colleagues Alastair Edge and Mike Hogan detailed their findings at the Einstein Fellows Symposium on Oct. 23 at Cambridge, Mass.

Source of Article : space.com

Backlit Saturn Shines in Stunning New Photo

NASA's Cassini spacecraft has captured a gorgeous backlit image of Saturn and its rings, providing a holiday treat for scientists and the public alike.

Cassini took the photo — actually a mosaic of 60 images — on Oct. 17, while looking back toward the sun from a spot within Saturn's shadow. Such a view can reveal details about the planet's atmosphere and rings that aren't otherwise visible, researchers said.

The image also highlights the beauty of the ringed planet, which everyone can appreciate.

"This glorious image is our special gift to you, the people of the world, in this holiday season that brings the year 2012 to a close," Cassini imaging team lead Carolyn Porco, of the Space Science Institute in Boulder, Colo., said in a statement. 

"I fervently hope it serves as a reminder that we humans, though troubled and warlike, are also the dreamers, thinkers, and explorers inhabiting one achingly beautiful planet, yearning for the sublime, and capable of the magnificent," she added.

Two of Saturn's many moons are visible in the newly released photo as tiny white dots below and to the left of the planet's rings. Geyser-spewing Enceladus, which likely harbors an ocean of liquid water beneath its icy shell, is closer to the rings; Tethys sits farther below and to the left.

Cassini last took a similar backlit Saturn shot in September 2006, researchers said. Earth could be seen as a pale dot in that mosaic, which was called "In Saturn's Shadow." (Like the sun, our planet is obscured by Saturn in the new photo.)

The 60 images composing the new mosaic were taken in violet, visible and near infrared wavelengths, researchers said. The overall image was processed in false color.

The $3.2 billion Cassini mission is a collaboration involving NASA, the European Space Agency and the Italian Space Agency. Cassini launched in 1997, arrived at Saturn in 2004 and delivered the Huygens lander to the surface of Saturn's huge moon Titan in January 2005.

Cassini should continue studying Saturn and its moons for years to come; its mission has been extended though at least 2017.






Source of Article : space.com

Chinese Spacecraft Flies by Asteroid Toutatis

A Chinese repurposed lunar orbiter, Chang'e-2, has flown by asteroid Toutatis, Chinese space officials announced.

Chang'e-2 was launched on Oct. 1, 2010, the second moon probe launched by China as part of a three-phase lunar exploration effort.

The spacecraft's main mission was to scout for potential landing sites for China's first moon lander, the Chang'e-3 spacecraft, which is being readied for launch next year.

In a celestial hop-scotch scheme, the probe wrapped up its primary objective of orbiting the moon in June 2011. It then departed lunar orbit for the Earth–Sun L2 Lagrangian point, where Earth's gravity and the sun's pull just about cancel out. Arriving at that location in August 2011, the spacecraft was used to evaluate China's deep-space tracking and control network.

In mid-April of this year, Chang'e-2 departed its L2 position and headed for a rendezvous with asteroid 4179 Toutatis.

Pictures taken

According to China's Xinhua state news service, Chang'e-2 successfully conducted a maneuver in which it flew by the asteroid Toutatis. The flyby took place on Dec. 13 and was announced by the State Administration of Science, Technology and Industry for National Defense (SASTIND).

Chang'e-2 reportedly came as close as 2 miles (3.2 kilometers) from Toutatis and took pictures of the asteroid.

"The success of the extended missions also embodies that China now possesses spacecraft capable of interplanetary flight," said Wu Weiren, chief designer of China's lunar probe program, according to the Xinhua story.

Great accomplishment

"I have heard they have accomplished this … it would be a great accomplishment and demonstration of Chinese space navigational and operational capability," said Mark Sykes, director of the Planetary Science Institute in Tucson, Ariz.

"I will be very interested in seeing how any direct imagery of Toutatis compares with the radar imaging models — this would be a significant contribution to our science," Sykes told SPACE.com.

Toutatis was also observed by planetary radar specialists at NASA's Jet Propulsion Laboratory in Pasadena, Calif., snagging a sequence of images of the space rock as it whisked by Earth Dec. 12.

The observing campaign of Toutatis was carried out at the Goldstone facility in California.

4179 Toutatis was discovered by C. Pollas in Caussols, France in January of 1989.  Toutatis has been making close approaches to Earth at four-year intervals since its discovery, and as a result, it was studied extensively with radar in 1992, 1996, 2000, 2004, and 2008, and also at a variety of optical and infrared wavelengths in 1992 to 1993. 

Radar scans

Toutatis is an irregular and very elongated object. It's also a very slow rotator characterized by 5.4-day rotation about the long axis.

A number of radar images were taken using the Goldstone radio dish. Toutatis approached within 0.0463 Earth-sun distances to our planet (18 lunar distances) on Dec. 12.

The next opportunity for radar imaging of Toutatis will occur in late 2016 and early 2017. The next time Toutatis will approach at least this close to Earth is in November of 2069.

Source of Article : space.com

Ancient Galaxy May Be Most Distant Ever Seen

Astronomers have spotted seven galaxies that existed just a few hundred million years after the universe's birth, including one that may be the oldest found to date.

The potential record-holding galaxy, known as UDFj-39546284, likely existed when the universe was just 380 million years old, researchers said, and may be the farthest galaxy ever seen. The other six distant galaxies all formed within 600 million years of the Big Bang, which created our universe 13.7 billion years ago.

UDFj-39546284 was detected previously, and researchers had thought it formed just 500 million years or so after the Big Bang. The new observations, made using NASA's Hubble Space Telescope, push its probable formation time back even further.

The seven galaxies constitute the first reliable census of the epoch from 400 million to 600 million years after the universe's birth, researchers said. This census detects a steady increase in galaxies over this period, suggesting that the formation of the first stars and galaxies — the so-called "cosmic dawn" — happened gradually rather than suddenly.

"The cosmic dawn was probably not a single, dramatic event," study lead author Richard Ellis, of Caltech in Pasadena, told reporters today (Dec. 12).

Ellis and his team pointed Hubble at a small patch of sky known as the Hubble Ultra Deep Field, which the telescope observed for many hours to build up enough light to spot extremely faint, distant objects. The researchers used Hubble's Wide Field Camera 3 to study the deep field in near-infrared wavelengths during August and September 2012.

The astronomers used special filters to measure the galaxies' redshifts — how much their light has been stretched by the expansion of space. From the redshifts, the researchers were able to calculate the distance to each galaxy, revealing their ages.

The results "reprensent our cosmic roots," said Harvard astronomer Abraham Loeb, who was not involved in the study. The new Hubble data "comes from the biggest archeological dig that we have of the universe."

The team pushed Hubble to its limits, and the telescope probably won't be able to see back in time any further, Ellis said. But NASA's James Webb Space Telescope, which is slated to launch in 2018, will dig even deeper into the universe's past.

"Hubble has, in a sense, set the stage for Webb," team member Anton Koekemoer, of the Space Telescope Science Institute in Baltimore, said in a statement. "Our work indicates there is a rich field of even earlier galaxies that Webb will be able to study."

The new study has been accepted for publication in The Astrophysical Journal Letters.

Source of Article : space.com

Men Were Last on Moon 40 Years Ago Today

The last men to walk on the moon blasted off its surface for a final time 40 years ago today.

After three days exploring the Taurus-Littrow lunar valley, Apollo 17 astronauts Eugene Cernan and Harrison Schmitt lit the engine on the upper (ascent) stage of their lunar module "Challenger" and launched off the surface at 5:55 p.m. EST (2255 GMT) on Dec. 14, 1972.

The last word spoken by a man on the moon (to date) — "Ignition" — was voiced by Schmitt, the first geologist and professional scientist to fly on a NASA mission. Cernan, as Apollo 17 commander, delivered the order to leave — "Let's get off" — just moments before.

(In the four decades since he left the moon, Cernan came to believe his remark was something slightly longer and a whole lot more colorful, "Let's get this mother out of here," although the transcripts and audio recordings disagree.)

Footage of that last lunar liftoff was broadcast live back to Earth via a color television camera mounted on the lunar roving vehicle, or lunar rover, which the astronauts parked on the moon a short distance from their landing site. The video, which was timed and directed by Mission Control from a quarter of a million miles away on Earth, captured the small spacecraft as it soared away into the blackness of space.

And so ended humankind's first "small steps" on another celestial body.

The Apollo 17 mission crowned six lunar landings for the United States and brought back the final 244 pounds (111 kilograms) of lunar material (including 741 individual moon rock and soil samples and a deep drill core with material from 10 feet, or 3 meters, below the lunar surface) out of the total 842 pounds (382 kilograms) collected by the astronauts who walked on the moon.

Notably, among the Apollo 17 lunar samples was a small but unique cache of orange soil, which was confirmed later as microscopic glass beads and fragments formed during volcanic activity on the moon.

Return to Earth

"As the Challenger leaves the surface of the moon, we are conscious not of what we leave behind, but of what lies before us," read the statement from the White House, as was radioed by Mission Control in Houston to the Apollo 17 astronauts. "This may be the last time in this century that men will walk on the moon, but space exploration will continue, the benefits of space exploration will continue, and there will be new dreams to pursue, based upon what we have learned."

"Few events have ever marked so clearly the passage of history from one epoch to another," the statement, which was signed by President Richard Nixon, concluded. "If we understand this about the last flight of Apollo, then truly we shall have touched a 'many splendored thing.'"

The presidential message was radioed soon after the two moonwalkers met up with Ronald Evans, Apollo 17's third member, who had been circling the moon on the command module "America" as Cernan and Schmitt explored below.

The trip back to Earth included a spacewalk by Evans to retrieve exposed film from an exterior equipment bay on the America module. Before leaving lunar orbit, the crew jettisoned Challenger's ascent stage, sending it crashing back into the moon. The resulting impact was recorded by seismometers that were deployed by Cernan and Schmitt while on the surface.

Twelve days and 14 hours after launching for the moon, Cernan, Schmitt and Evans splashed down in the South Pacific Ocean at 2:25 p.m. EST (1925 GMT) on Dec. 19, 1972. The USS Ticonderoga aircraft carrier recovered the command module and the astronauts from the sea.

Return to the moon

For 40 years, Apollo 17 has retained the distinction as the last human voyage to the moon. Schmitt is still the 12th out of only 12 men to step foot on the moon and Cernan, as the last to climb up the ladder into Challenger, is still the final man to leave his footprints on the lunar surface.

Before he took his final step off the moon, Cernan said, "America's challenge of today has forged man's destiny of tomorrow. And, as we leave the moon at Taurus-Littrow, we leave as we came and, God willing, as we shall return, with peace and hope for all mankind."

Momentum is now building to return humans to the moon, both through government and commercial efforts.

Schmitt says that if he had the opportunity today to revisit Taurus-Littrow, he would return to the site where he found the orange soil and then venture to an area where he and Cernan didn't explore.

"I would want to go back to Shorty Crater and spend more time really trying to define the geological context of the orange soil that we found and sampled," the moonwalker told collectSPACE.com in an recent interview.

"The other thing though, would be to go to the area that was northeast of the landing site, an area we called the 'Sculptured Hills' and really try to traverse across those hills and gather as many different kinds of rock samples as we could possibly do," Schmitt said, explaining that the insight gained over the past 40 years now suggests the Hills may be "a very large, relatively coherent piece of deep crust" that was thrown from an impact basin.

Ultimately though, Schmitt said he would look beyond his old landing site for the next steps on the surface.

"Given the chance to go back to Taurus Littrow, I would probably argue that there are more important places to go right now, as we do have samples and observations from [there]," Schmitt said. "The thing I'd like to see us sample is the older [impact] basins. We know they are older but we do not know how much older they are."

Source of Article : space.com

NASA Eyes Mission to Jupiter Moon Europa

SAN FRANCISCO — Though NASA is devoting many of its exploration resources to Mars these days, the agency still has its eye on an icy moon of Jupiter that may be capable of supporting life as we know it.

Last week, NASA officials announced that they plan to launch a $1.5 billion rover to Mars in 2020, adding to a string of Red Planet missions already on the docket. The Curiosity rover just landed this past August, for example, and an orbiter called Maven and a lander named InSight are slated to blast off in 2013 and 2016, respectively.

But NASA is also thinking about ways to investigate the possible habitability of Europa, Jupiter's fourth-largest moon. One concept that may be gaining traction is a so-called "clipper" probe that would make multiple flybys of the moon, studying its icy shell and suspected subsurface ocean as it zooms past.

"We briefed [NASA] headquarters on Monday, and they responded very positively," mission proponent David Senske, of NASA's Jet Propulsion Laboratory in Pasadena, Calif., said here Dec. 7 at the annual fall meeting of the American Geophysical Union.

The $2 billion unmanned Europa Clipper, which could be ready to launch by 2021 or so, would also do vital reconnaissance work for a potential lander mission in the future.

Intriguing Europa

Astrobiologists regard Europa, which is about 1,900 miles (3,100 kilometers) wide, as one of the best bets in our solar system to host life beyond Earth.

The moon is believed to harbor a large ocean of liquid water beneath its icy shell. Further, this ocean is likely in direct contact with Europa's rocky mantle, raising the possibility of all sorts of interesting chemical reactions, Senske said.

The irradiation of Europa's surface and tidal heating of its interior also mean the moon likely has ample energy sources — another key requirement for life as we know it.

NASA has long been interested in exploring the icy moon and its ocean. Several years back, the agency drew up an ambitious mission concept called the Jupiter Europa Orbiter (JEO), which would have made detailed studies of Europa and the incredibly volcanic Jupiter moon Io.

The science returns from such a mission would have been impressive, according to the 2011 Planetary Science Decadal Survey, which outlined the scientific community's goals in the field over the coming decade.

The decadal survey ranked JEO as the second-highest priority among large-scale missions, just behind Mars sample-return. But the report said its $4.7 billion price tag was just too high.

"The recommendation was, immediately go and do a de-scope," said Senske, who was also involved in JEO. "They loved the science; the science was great. But focus it."

Paring it down

So researchers got to work developing a leaner, cheaper Europa mission that would fit under a firm $2 billion cost cap. They came up with two main options: the clipper and a Europa orbiter (a lander was ruled out as premature).

Because of the intense radiation environment around Europa, the orbiter would have to be heavily shielded, adding weight and cost. Even with this armor, the concept initially called for a nominal design life at Europa of just 30 days, with later versions boosting that up to 109 days, Senske said.

While the orbiter would gather a great deal of interesting and valuable information, it falls short of what the flyby concept could deliver on a dollar-to-dollar basis, Senske said. For example, a $2 billion orbiter would not be able to carry an instrument that could investigate the composition and chemistry of Europa's surface and atmosphere (and, by extension, its ocean).

"In terms of an apples-to-apples comparison, Clipper really does rise to the top," Senske said.

The Europa Clipper

The Clipper would carry a number of scientific instruments, including ice-penetrating radar, a topographical imager, a magnetometer, an infrared spectrometer, a neutral mass spectrometer and a high-gain antenna.

To squeeze all of this gear aboard and still stay under the $2 billion cap, Clipper may need to be powered by solar arrays rather than advanced stirling radioisotope generators as originally envisioned, Senske said. Solar panels are considerably cheaper than ASRGs, which convert the heat from plutonium-238's radioactive decay into eletricity.

NASA's Jupiter-bound Juno probe also sports solar arrays, so there is precedent for sending a solar-powered spacecraft so far from the sun. But a Europa mission would present some additional challenges to address, including eclipses and radiation doses about two times higher than Juno will receive.

"We have some things that we need to test," Senske said.

The Clipper would enter into orbit around Jupiter, then study Europa during dozens of flybys over the course of 2.3 years. On its closest passes, it would come within just 15 miles (25 km) of the moon's frozen surface.

These close encounters should help the probe crack some of Europa's most intriguing mysteries, such as the thickness of its ice shell and the saltiness and approximate depth of its ocean (as well as confirming that the ocean exists), Senske said.

This information, along with the spacecraft's detailed imagery of the moon's surface, could help guide a potential lender mission that would search for signs of Europan life sometime down the road.

The Clipper could probably be ready to launch between 2020 and 2022, Senske said. Its journey to Europa would take about six years.

The Europa Clipper is not on NASA's books yet, but agency higher-ups and advisory committees both inside and outside the agency have given it high marks thus far, Senske said.

He and the rest of the team will continue developing the mission concept and see what happens.

"In April, we want to do what we're calling a preliminary concept review, start working out the bugs, and then working with headquarters to define when we would have what's known as a mission concept review that would start getting us on the road as a full-up mission," Senske said.

Some scientists who want close-up studies of potentially habitable moons such as Europa and the Saturn satellite Enceladus were disappointed that NASA selected another Mars rover mission for 2020. But Senske said the agency's mounting successes at the Red Planet — and the public interest missions such as Curiosity have generated — could eventually make more far-flung exploration efforts possible.

"It could potentially be the tide that raises all ships," Senske said.

Source of Article : space.com