Plato May Be the Third Cosmic Vision

The concept known as Plato seems destined to be the next mission in ESA's Cosmic Vision program. Plato was chosen by an expert panel as the standout candidate in a competition run by the European Space Agency (ESA). The Paris-based organization's Science Policy Committee will now have the final say at its meeting in February. If given the go-ahead, Plato would probably not launch until 2024.

The name of the mission is an acronym that stands for PLAnetary Transits and Oscillations of stars. It is not really one telescope but rather a suite of 34 telescopes mounted on a single satellite. The intention is for Plato to sweep about half the sky, to investigate some of its brightest and nearest stars. It would monitor these stars for the tell-tale tiny dips in light that occur when planets move across their faces.

Critically, Plato would be tuned to seek out rocky worlds orbiting in the "habitable zone" - the region around a star where water can keep a liquid state. A fundamental part of its quest would be to perform an intricate study of the host stars themselves, using their pulsations to probe their structure and properties.

Such observations, termed asteroseismology, would provide key, complementary information for the proper characterization of the rocky worlds. Although other missions have pursued this kind of science before, Plato is described as a major leap forward in capability. The hope is that it could find really promising targets for follow-up by the big ground-based telescopes due to come online in the next decade. These facilities, which will have primary mirrors measuring tens of meters in diameter, should be able to examine the atmospheres of distant worlds for possible life signatures. The James Webb Space Telescope, the successor to Hubble, due for launch at the end of this decade, would likely still be working in 2024/2025 and could also pursue Plato's discoveries.

Plato has spent the past two years in an assessment process that has pitted it against four other concepts. These alternatives included another planet observatory (Echo), an asteroid mission (Marco Polo-R), an X-ray telescope (Loft), and a satellite that would perform a precise test of Einstein's equivalence principle (STE-Quest).

All were competing to be the third medium-class launch opportunity to be offered under ESA's so-called Cosmic Vision program, which defines the organization's space science priorities. "Medium class" means a cost to the agency of no more than about 600m euros (£490m; $820m), although following the practice of previous missions this does not include the budget for instruments. These are usually provided directly by ESA's national member agencies and mean the final price tag can approach one billion euros. All the competitors were invited to make a final presentation to representatives of the scientific community, industry, and national member agencies on January 21. This was followed by closed-session discussions by two working groups, which rated the quality of the missions. Their recommendations were then passed to ESA's top space science advisory committee (SSAC) to make an evaluation. It proposed that Plato be carried forward as the mission of choice, and this preference has now been sent on by ESA's executive to the SPC. The committee has the prerogative of "selection" at its February 19 gathering, and could still reject Plato - but this would be a major surprise.

The final green light is known as "adoption" in ESA-speak. This is unlikely to happen until 2015, after member states have made firm commitments on their participation and an industrial team to build the satellite has been identified. One big industrial contribution from the UK seems assured. This would be the camera detector at the base of the telescope suite. Supplied by e2v in Chelmsford, the array of more than 130 charge-coupled devices would be 0.9 square meters in area. This would make it the largest camera system ever flown in space, and twice the size of the array e2v produced for ESA's recently launched Gaia telescope.

The first two medium-class missions to be selected under ESA's Cosmic Vision program in 2011 were Solar Orbiter, a space telescope to study the Sun, to launch in 2017; and Euclid, a telescope to investigate "dark energy", to fly in 2020.

NASA plans a similar mission to Plato called Tess (Transiting Exoplanet Survey Satellite) in 2017, but the specifications mean that its rocky worlds will probably be in closer orbits around lower-mass stars than the discoveries made by the European project. In other words, the Plato planets are more likely to be in the habitable zones of more Sun-like stars.

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NEOWISE Reactivation Plus 25 Days

In its first 25 days of operations, the newly reactivated NEOWISE mission has detected 857 minor bodies in our solar system, including 22 near-Earth objects (NEOs) and four comets. Three of the NEOs are new discoveries; all three are hundreds of meters in diameter and dark as coal.


NEOWISE originally was called the Wide-field Infrared Survey Explorer (WISE), which had made the most comprehensive survey to date of asteroids and comets. The spacecraft was shut down in 2011 after its primary mission was completed. But in September 2013, it was reactivated, renamed and given a new mission, which is to assist NASA's efforts to identify the population of potentially hazardous near-Earth objects (NEOs). NEOWISE also can assist in characterizing previously detected asteroids that could be considered potential targets for future exploration missions.

More than 100 asteroids were captured in the above view from NASA's Wide-field Infrared Survey Explorer, or WISE, during its primary all-sky survey. Image credit: NASA/JPL-Caltech/UCLA

The NEOWISE mission has just passed its post-restart survey readiness review, and the project has verified that the ability to measure asteroid positions and brightness is as good as it was before the spacecraft entered hibernation in early 2011. At the present rate, NEOWISE is observing and characterizing approximately one NEO per day, giving astronomers a much better idea of the objects' sizes and compositions.

Out of the more than 10,500 NEOs that have been discovered to date, only about 10 percent have had any physical measurements made of them; the reactivated NEOWISE will more than double that number.

JPL 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, Colo., 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.

More information on NEOWISE is online at: http://www.jpl.nasa.gov/wise/ .

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Landers That "Think On Their Feet", So to Speak

Engineers at NASA's Jet Propulsion Laboratory in Pasadena, California, are testing a sophisticated flight-control algorithm that could allow for more precise, pinpoint landings of future Martian spacecraft.

Flight testing of the new Fuel Optimal Large Divert Guidance algorithm - G-FOLD for short - for planetary pinpoint landing is being conducted jointly by JPL engineers in cooperation with Masten Space Systems in Mojave, Calif., using Masten's XA-0.1B "Xombie" vertical-launch, vertical-landing experimental rocket.

NASA's Space Technology Mission Directorate is facilitating the tests via its Game-Changing Development and Flight Opportunities Programs; the latter managed at NASA's Dryden Flight Research Center at Edwards Air Force Base, Calif. The two space technology programs work together to test game-changing technologies by taking advantage of Flight Opportunities' commercially provided suborbital platforms and flights.

Current powered-descent guidance algorithms used for spacecraft landings are inherited from the Apollo era. These algorithms do not optimize fuel usage and significantly limit how far the landing craft can be diverted during descent. The new G-FOLD algorithm invented by JPL autonomously generates fuel-optimal landing trajectories in real time and provides a key new technology required for planetary pinpoint landing. Pinpoint landing capability will allow robotic missions to access currently inaccessible science targets. For crewed missions, it will allow increased precision with minimal fuel requirements to enable landing larger payloads in close proximity to predetermined targets.

Masten Space Systems launched the Xombie July 30, 2013 from the company's test pad at the Mojave Air and Space Port. JPL and Masten are planning to conduct a second flight test with a more complicated divert profile in August, pending data analysis.

To simulate a course correction during a Martian entry in the July test, Masten's Xombie was given a vertical descent profile to an incorrect landing point. About 90 feet into the profile, the G-FOLD flight control software was automatically triggered to calculate a new flight profile in real-time, and the rocket was successfully diverted to the "correct" landing point some 2,460 feet away.

On September 20, 2013, another flight was made at the Mojave Air and Space Sport in the California desert. This flight was the conclusion of the test campaign to assess the performance of the G-FOLD algorithm under mission conditions. More ambitious than the previous flights, this test had the Xombie vehicle initially travel diagonally away from the target landing site. This simulated a worst-case spacecraft landing maneuver and forced the G-FOLD algorithm to calculate, in real time, a flight path that crossed over itself to reach the safe landing site.

The accurately executed half-mile-long (0.8-kilometer), three-dimensional divert shows the potential of what G-FOLD could mean for future space missions. Compared to the software used to land NASA's Mars Curiosity rover in August 2012, G-FOLD can provide six times more divert range for a lander of that class. Such a capability would be needed for landing on Europa or for human missions to Mars. G-FOLD also may reduce the difficulty of future robotic missions to Mars, allowing rovers to land closer to features of interest instead of driving long distances to reach them. A future rover similar to Curiosity might be able to land right next to a target of scientific interest like Mount Sharp instead of driving for a year to get there.

Even though this is the culmination of the current round of testing, JPL still has far-reaching plans for G-FOLD and for further tests of other landing technologies. "G-FOLD presents a dramatic improvement in our ability to execute large divert maneuvers with limited fuel," said Martin Regehr, who leads JPL's Autonomous Descent and Ascent Powered-flight Testbed (ADAPT). To further enhance future mission capability, JPL plans to use ADAPT to demonstrate terrain-relative navigation using the Lander Vision System (LVS) together with G-FOLD in 2014.

Click Here to Watch the September 20 Flight.

This effort was performed by JPL, with participation from the University of Texas at Austin; Masten Space Systems, Inc., Mojave, California; and NASA's Flight Opportunity Program, which is managed by NASA's Dryden Flight Research Center, Edwards, California.

Masten Space Systems is one of seven suborbital reusable launch companies contracted by NASA's Flight Opportunities Program to fly experiments in sub-orbital space to verify new technologies work as expected in this harsh environment.

JPL, a division of the California Institute of Technology, Pasadena, manages the Curiosity project for NASA's Science Mission Directorate, Washington. For information about Curiosity's accomplishments over the past year, visit: http://mars.jpl.nasa.gov/msl .

For more on flight tests of Curiosity's landing radar, visit: http://www.nasa.gov/topics/solarsystem/features/F-18_flying_msl_radar.html .

For more on NASA's Space Technology Mission Directorate, visit: http://www.nasa.gov/directorates/spacetech/home/ .


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Herschel Detects Water on Ceres!

Scientists using the Herschel space observatory have made the first definitive detection of water vapor on Ceres, the largest and roundest object in the asteroid belt. Plumes of water vapor are thought to shoot up periodically from Ceres when portions of its icy surface warm slightly. Ceres is classified as a dwarf planet, a solar system body bigger than an asteroid and smaller than a planet. Herschel is a European Space Agency (ESA) mission with important NASA contributions.

Artist impression of dwarf planet Ceres, at lower left, surrounded by a cloud of water vapor. Image Credit: ESA/ATG medialab

“This is the first time water vapor has been unequivocally detected on Ceres or any other object in the asteroid belt and provides proof that Ceres has an icy surface and an atmosphere,” said Michael Küppers of ESA in Spain, lead author of a paper in the journal Nature.

The results come at the right time for NASA's Dawn mission, which is on its way to Ceres now after spending more than a year orbiting the large asteroid Vesta. Dawn is scheduled to arrive at Ceres in the spring of 2015, where it will take the closest look ever at its surface.

“We've got a spacecraft on the way to Ceres, so we don't have to wait long before getting more context on this intriguing result, right from the source itself,” said Carol Raymond, the deputy principal investigator for Dawn at NASA's Jet Propulsion Laboratory in Pasadena, Calif. “Dawn will map the geology and chemistry of the surface in high resolution, revealing the processes that drive the outgassing activity.”

For more than the last century, Ceres was known as the largest asteroid in our solar system. But in 2006, the International Astronomical Union, the governing organization responsible for naming planetary objects, reclassified Ceres as a dwarf planet because of its large size. It is roughly 590 miles (950 kilometers) in diameter. When it first was spotted in 1801, astronomers thought it was a planet orbiting between Mars and Jupiter. Later, other cosmic bodies with similar orbits were found, marking the discovery of our solar system's main belt of asteroids.

This graph shows variability in the intensity of the water absorption signal detected at Ceres by the Herschel space observatory on March 6, 2013. Full Image and Caption Scientists believe Ceres contains rock in its interior with a thick mantle of ice that, if melted, would amount to more fresh water than is present on all of Earth. The materials making up Ceres likely date from the first few million years of our solar system's existence and accumulated before the planets formed.

Until now, ice had been theorized to exist on Ceres but had not been detected conclusively. It took Herschel's far-infrared vision to see, finally, a clear spectral signature of the water vapor. But Herschel did not see water vapor every time it looked. While the telescope spied water vapor four different times, on one occasion there was no signature.

Here is what scientists think is happening: when Ceres swings through the part of its orbit that is closer to the sun, a portion of its icy surface becomes warm enough to cause water vapor to escape in plumes at a rate of about 6 kilograms (13 pounds) per second. When Ceres is in the colder part of its orbit, no water escapes.

The strength of the signal also varied over hours, weeks and months, because of the water vapor plumes rotating in and out of Herschel's views as the object spun on its axis. This enabled the scientists to localize the source of water to two darker spots on the surface of Ceres, previously seen by NASA's Hubble Space Telescope and ground-based telescopes. The dark spots might be more likely to outgas because dark material warms faster than light material. When the Dawn spacecraft arrives at Ceres, it will be able to investigate these features.

The results are somewhat unexpected because comets, the icier cousins of asteroids, are known typically to sprout jets and plumes, while objects in the asteroid belt are not.

“The lines are becoming more and more blurred between comets and asteroids,” said Seungwon Lee of JPL, who helped with the water vapor models along with Paul von Allmen, also of JPL. “We knew before about main belt asteroids that show comet-like activity, but this is the first detection of water vapor in an asteroid-like object.”

The research is part of the Measurements of 11 Asteroids and Comets Using Herschel (MACH-11) program, which used Herschel to look at small bodies that have been or will be visited by spacecraft, including the targets of NASA's previous Deep Impact mission and upcoming Origins Spectral Interpretation Resource Identification Security Regolith Explorer (OSIRIS-Rex). Laurence O' Rourke of the European Space Agency is the principal investigator of the MACH-11 program.

Herschel is a European Space Agency mission, with science instruments provided by consortia of European institutes and with important participation by NASA. While the observatory stopped making science observations in April 2013, after running out of liquid coolant, as expected, scientists continue to analyze its data. NASA's Herschel Project Office is based at JPL. JPL contributed mission-enabling technology for two of Herschel's three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena, supports the U.S. astronomical community.

Dawn's mission is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Ala. UCLA is responsible for overall Dawn mission science. Orbital Sciences Corp. in Dulles, Va., designed and built the spacecraft. The German Aerospace Center, the Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute are international partners on the mission team. Caltech manages JPL for NASA.

More information about Herschel is online at: http://www.esa.int/SPECIALS/herschel . More information about NASA's role in Herschel is available at: http://www.nasa.gov/herschel . For more information about NASA's Dawn mission, visit: http://www.nasa.gov/dawn .


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Before and After on "Murray Ridge"

Sometime between December 26, 2013 and January 8, 2014, a span of just 13 days, a bright rock came into view near NASA's Mars Exploration Rover Opportunity, on "Murray Ridge," a section of the rim of Endeavour Crater where Opportunity is working on north-facing slopes during the rover's sixth Martian winter. The images below show the evidence of the appearance.

Image Credit: NASA/JPL-Caltech

The Opportunity rover had completed a short drive just before taking the second image, and one of its wheels likely knocked the rock -- dubbed "Pinnacle Island" -- to this position. The rock is about the size of a doughnut.

The above images are from Opportunity's panoramic camera (Pancam). The one on the left is from 3,528th Martian day, or sol, of the rover's work on Mars (December 26, 2013). The one on the right, with the newly arrived rock, is from Sol 3540 (January 8, 2014). Much of the rock is bright-toned, nearly white. A portion is deep red in color. Pinnacle Island may have been flipped upside down when a wheel dislodged it, providing an unusual circumstance for examining the underside of a Martian rock.

Opportunity landed on Mars on January 24, 2004 PST (January 25, 2004 UTC) on what was to be a three-month mission, but instead the rover has lived beyond its prime mission and roved the planet for nearly 10 years. Mission highlights, including a gallery of selected images from both rovers is at http://mars.nasa.gov/mer10/.

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John Lowry Dobson (1915-2014)

John Lowry Dobson (September 14, 1915 – January 15, 2014) was an amateur astronomer and best known for the Dobsonian telescope, a portable, low-cost altazimuth/Newtonian reflector telescope. The Dobsonian design is considered revolutionary since it allowed amateur astronomers to build fairly large telescopes. Dobson was less known for his efforts to promote awareness of astronomy (and his unorthodox views of cosmology) through public lectures including his performances of "sidewalk astronomy." Dobson was also the co-founder of the amateur astronomical group, the San Francisco Sidewalk Astronomers.

Dobson was born in Beijing, China. His maternal grandfather founded Peking University, originally known then as Imperial University of Peking, in 1898. Dobson’s  mother was a musician and his father taught zoology at the University. In 1927, Dobson and his parents moved to San Francisco, California. His father accepted a teaching position at Lowell High School and taught there until the 1950s. Dobson spent 23 years in a Vedanta Society monastery, after which he became more active in promoting astronomy.

As a teen, John Dobson became a “belligerent” atheist. He said: “I could see that these two notions cannot arise in the same being: ‘do unto others as you would that they do unto’ and ‘if you're not a good boy, it's into hell for keeps.’… They must be spoofing us. So I became an atheist, a belligerent atheist. If anybody started a conversation about the subject, I was a belligerent atheist.”

Over time, Dobson became interested in the universe and its workings. He earned a masters degree in chemistry at the University of California, Berkeley in 1943, working in E. O. Lawrence's lab. In 1944, Dobson attended a lecture by a Vedantan swami. Dobson said the swami “revealed to him a world he had never seen.” That same year, Dobson joined the Vedanta Society monastery in San Francisco, becoming a monk of the Ramakrishna Order. One of John's responsibilities at the monastery was to reconcile astronomy with the teachings of Vedanta. That job led him to build telescopes on the side. He took to wheeling them around outside the monastery, fascinating the neighbors who would congregate around him.

Dobson’s interest in telescope building was in part to better understand the universe, and in part to inspire in others a curiosity about the cosmos. To this end, Dobson often offered assistance and corresponded about his work with those outside the monastery. Telescope building was not part of the curriculum at the monastery, however, and much of Dobson’s correspondence was written in code so as to attract less attention. For instance, a telescope was referred to as a "geranium", which is a type of flower. A "potted geranium" referred to a telescope in a tube and rocker, while a "geranium in bloom" referred to a telescope whose mirror was now aluminized.

Eventually, Dobson was given the option of ceasing his telescope building or leaving the order. He chose to stop building telescopes so that he could remain at the monastery. But one day, another monk wrongly accused him as missing and reported him to the head swami. Dobson was expelled in 1967. However, he maintained that the accusation was not the true reason for his expulsion. The true reason, Dobson contended, was a result of a misunderstanding. The head swami read a paper that was presumably written by Dobson that contradicted the reconciliation of science with Vedanta, and the swami thought Dobson had rejected the swami's teachings.

After leaving the order in 1967, Dobson, along with Bruce Sams and Jeffery Roloff,  founded the San Francisco Sidewalk Astronomers, an amateur astronomy organization dedicated to popularizing astronomy among people on the street. Sams had built a large telescope but, because he was only 12 at the time, Sams was not eligible for membership in the only local club, the San Francisco Amateur Astronomers. And so, the "San Francisco Sidewalk Astronomers" was born. It was also at this time that Dobson's simple form of telescope, which came to be known as the Dobsonian, became well known after he started teaching classes to the public on how to make your own telescope.

Dobson was later asked to speak at the Vedanta Society of Southern California in Hollywood, and continued to spend two months there each year teaching telescope and cosmology classes. Dobson spent two more months at his home in San Francisco, and spent most of the rest of each year traveling as an invited guest for astronomical societies, where he spoke about telescope building, sidewalk astronomy, and his views of cosmology and the scientific establishment. Dobson claimed the Big Bang model did not hold up to scrutiny, and instead advocated a non-standard cosmology; a “Recycling” Steady State model of the universe where matter in the universe is forever expanding outward, but matter also “recycles” over time via quantum tunneling. In an essay entitled, “Origins”, Dobson also argued that such a universe could allow for life to be ubiquitous and ever-present.

In 2004, the Crater Lake Institute presented John Dobson with its Annual Award for Excellence in Public Service for pioneering sidewalk astronomy in the national parks and forests, "where curious minds and dark skies collide." In 2005, the Smithsonian magazine listed John Dobson as among 35 individuals who have made a major difference during the lifetime of that periodical.

Dobson, with editor Norman Sperling, authored the 1991 book How and Why to Make a User-Friendly Sidewalk Telescope. This book helped popularize what came to be known as the Dobsonian mount, and treats the "why" as importantly as the "how". It covers Dobson's background and his philosophy on astronomy and the universe, and his belief in the importance of popular access to astronomy for proper appreciation of the universe. John Dobson is now in the process of publishing Beyond Space and Time (2004) and The Moon is New (2008).

Dobson's life and ideas were the subject of the 2005 documentary A Sidewalk Astronomer. He was also featured in the PBS series The Astronomers, and appeared twice on The Tonight Show Starring Johnny Carson. Dobson also appears as one of the speakers in Universe: The Cosmology Quest, a documentary about non-standard cosmological theories.

On January 15, 2014, John Dobson died peacefully at a hospital in Burbank, California. He was 98.

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Rosetta Answers Wakeup Call

On Monday, January 20, ESA's Rosetta spacecraft responded to communications from mission controllers after being in deliberate hibernation for 31 months.

Rosetta is chasing down Comet 67P/Churyumov-Gerasimenko, where it will become the first space mission to rendezvous with a comet, the first to attempt a landing on a comet’s surface, and the first to follow a comet as it swings around the Sun.

Since its launch in 2004, Rosetta has made three flybys of Earth and one of Mars to help it on course to its rendezvous with 67P/Churyumov-Gerasimenko, encountering asteroids Steins and Lutetia along the way.

Operating on solar energy alone, Rosetta was placed into a deep space slumber in June 2011 as it cruised out to a distance of nearly 800 million km from the warmth of the Sun, close to the orbit of Jupiter.

Now, as Rosetta’s orbit has brought it back to within ‘only’ 673 million km from the Sun, there is enough solar energy to power the spacecraft fully again.

Thus today, still about 9 million km from the comet, Rosetta’s pre-programmed internal ‘alarm clock’ woke up the spacecraft. After warming up its key navigation instruments, coming out of a stabilizing spin, and aiming its main radio antenna at Earth, Rosetta sent a signal to let mission operators know it had survived the most distant part of its journey.

The signal was received by NASA’s Goldstone ground station in California at 18:18 GMT, during the first window of opportunity the spacecraft had to communicate with Earth. It was immediately confirmed in ESA’s space operations center in Darmstadt and the successful wake-up announced via the @ESA_Rosetta twitter account, which tweeted: "Hello, world!"

“We have our comet-chaser back,” says Alvaro Giménez, ESA’s Director of Science and Robotic Exploration. “With Rosetta, we will take comet exploration to a new level. This incredible mission continues our history of ‘firsts’ at comets, building on the technological and scientific achievements of our first deep space mission Giotto, which returned the first close-up images of a comet nucleus as it flew past Halley in 1986.”

“This was one alarm clock not to hit snooze on, and after a tense day we are absolutely delighted to have our spacecraft awake and back online,” adds Fred Jansen, ESA’s Rosetta mission manager.
Comets are considered the primitive building blocks of the Solar System and likely helped to ‘seed’ Earth with water, perhaps even the ingredients for life. But many fundamental questions about these enigmatic objects remain, and through its comprehensive, in situ study of Comet 67P/Churyumov-Gerasimenko, Rosetta aims to unlock the secrets contained within.

“All other comet missions have been flybys, capturing fleeting moments in the life of these icy treasure chests,” says Matt Taylor, ESA’s Rosetta project scientist. “With Rosetta, we will track the evolution of a comet on a daily basis and for over a year, giving us a unique insight into a comet’s behavior and ultimately helping us to decipher their role in the formation of the Solar System.”
But first, essential health checks on the spacecraft must be completed. Then the eleven instruments on the orbiter and ten on the lander will be turned on and prepared for studying Comet 67P/Churyumov-Gerasimenko.

“We have a busy few months ahead preparing the spacecraft and its instruments for the operational challenges demanded by a lengthy, close-up study of a comet that, until we get there, we know very little about,” says Andrea Accomazzo, ESA’s Rosetta operations manager.

Rosetta’s first images of 67P/Churyumov-Gerasimenko are expected in May, when the spacecraft is still 2 million km from its target. Towards the end of May, the spacecraft will execute a major manoeuver to line up for its critical rendezvous with the comet in August.

After rendezvous, Rosetta will start with two months of extensive mapping of the comet’s surface, and will also make important measurements of the comet’s gravity, mass and shape, and assess its gaseous, dust-laden atmosphere, or coma. The orbiter will also probe the plasma environment and analyze how it interacts with the Sun’s outer atmosphere, the solar wind.

Using these data, scientists will choose a landing site for the mission’s 100 kg Philae probe. The landing is currently scheduled for 11 November and will be the first time that a landing on a comet has ever been attempted.

In fact, given the almost negligible gravity of the comet’s 4 km-wide nucleus, Philae will have to use ice screws and harpoons to stop it from rebounding back into space after touchdown.

Among its wide range of scientific measurements, Philae will send back a panorama of its surroundings, as well as very high-resolution pictures of the surface. It will also perform an on-the-spot analysis of the composition of the ices and organic material, including drilling down to 23 cm below the surface and feeding samples to Philae’s on-board laboratory for analysis.

The focus of the mission will then move to the ‘escort’ phase, during which Rosetta will stay alongside the comet as it moves closer to the Sun, monitoring the ever-changing conditions on the surface as the comet warms up and its ices sublimate.

The comet will reach its closest distance to the Sun on 13 August 2015 at about 185 million km, roughly between the orbits of Earth and Mars. Rosetta will follow the comet throughout the remainder of 2015, as it heads away from the Sun and activity begins to subside.

“We will face many challenges this year as we explore the unknown territory of comet 67P/Churyumov-Gerasimenko and I’m sure there will be plenty of surprises, but today we are just extremely happy to be back on speaking terms with our spacecraft,” adds Matt Taylor.

Rosetta is a mission of the European Space Agency, Paris, with contributions from its member states and NASA. Rosetta's Philae lander is provided by a consortium led by the German Aerospace Center, the Max Planck Institute for Solar System Research, the French National Space Agency and the Italian Space Agency. JPL manages the U.S. contribution of the Rosetta mission for NASA's Science Mission Directorate in Washington. The Microwave Instrument for the Rosetta Orbiter was built at JPL and JPL is home to its principal investigator, Samuel Gulkis. The Southwest Research Institute, San Antonio, developed the Rosetta orbiter's Ion and Electron Sensor (IES) and is home to its principal investigator, James Burch. The Southwest Research Institute, Boulder, Colo., developed the Alice instrument and is home to its principal investigator, Alan Stern.

More information about Rosetta is available online at: http://www.esa.int/rosetta and http://rosetta.jpl.nasa.gov .

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