Mars Sliding Behind The Sun

Mars Exploration Rover Mission Status Report

For the fourth time since Opportunity landed on Mars on Jan. 25, 2004, Universal Time (Jan. 24, Pacific Time), the planets' orbits will put Mars almost directly behind the sun from Earth's perspective.

During the days surrounding such an alignment, called a solar conjunction, the sun can disrupt radio transmissions between Earth and Mars. To avoid the chance of a command being corrupted by the sun and harming a spacecraft, NASA temporarily refrains from sending commands from Earth to Mars spacecraft in orbit and on the surface. This year, the commanding moratorium will be Jan. 27 to Feb. 11 for Opportunity, with similar periods for the Mars Reconnaissance Orbiter and Mars Odyssey orbiter.

Downlinks from Mars spacecraft will continue during the conjunction period, though at a much reduced rate. Mars-to-Earth communication does not present risk to spacecraft safety, even if transmissions are corrupted by the sun.

NASA's Mars Reconnaissance Orbiter will scale back its observations of Mars during the conjunction period due to reduced capability to download data to Earth and a limit on how much can be stored onboard.

Opportunity will continue sending data daily to the Odyssey orbiter for relay to Earth. "Overall, we expect to receive a smaller volume of daily data from Opportunity and none at all during the deepest four days of conjunction," said Alfonso Herrera, a rover mission manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

The rover team has developed a set of commands to be sent to Opportunity in advance so that the rover can continue science activities during the command moratorium.

"The goal is to characterize the materials in an area that shows up with a mineralogical signal, as seen from orbit, that's different from anywhere else Opportunity has been," said JPL's Bruce Banerdt, project scientist for Opportunity and its rover twin, Spirit. The area is at the southeastern edge of a crater called "Santa Maria," which Opportunity approached from the west last month.

Drives last week brought Opportunity to the position where it will spend the conjunction period. From that position, the rover's robotic arm can reach an outcrop target called "Luis de Torres." The rover's Moessbauer spectrometer will be placed onto the target for several days during the conjunction to assess the types of minerals present. The instrument uses a small amount of radioactive cobalt-57 to elicit information from the target. With a half-life of less than a year, the cobalt has substantially depleted during Opportunity's seven years on Mars, so readings lasting several days are necessary now to be equivalent to much shorter readings when the mission was newer.

Opportunity will also make atmospheric measurements during the conjunction period. After conjunction, it will spend several more days investigating Santa Maria crater before resuming a long-term trek toward Endurance crater, which is about 22 kilometers (14 miles) in diameter and, at its closest edge, about 6 kilometers (4 miles) from Santa Maria.

Opportunity's drives to the southeastern edge of Santa Maria brought the total distance driven by the rover during its seventh year on Mars to 7.4 kilometers (4.6 miles), which is more than in any previous year. The rover's total odometry for its seventh anniversary is 26.7 kilometers (16.6 miles).

Opportunity and Spirit, which landed three weeks apart, successfully completed their three-month prime missions in April 2004, then began years of bonus extended missions. Both have made important discoveries about wet environments on ancient Mars that may have been favorable for supporting microbial life. Spirit's most recent communication was on March 22, 2010. On the possibility that Spirit may yet awaken from a low-power hibernation status, NASA engineers continue to listen for a signal from that rover.

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How Sun Steals Martian Atmosphere II

Although the solar wind might be the primary method, like an accomplished burglar, the sun’s emissions can steal the martian atmosphere in many ways. However, most follow a basic M.O., the solar wind and the sun’s ultraviolet radiation turns the uncharged atoms and molecules in Mars' upper atmosphere into electrically charged particles (ions). Once electrically charged, electric fields generated by the solar wind carry them away. The electric field is produced by the motion of the charged, electrically conducting solar wind across the interplanetary, solar-produced magnetic field, the same dynamic generators use to produce electrical power.

An exception to this dominant M.O. are atoms and molecules that have enough speed from solar heating to simply run away, they remain electrically neutral, but become hot enough to escape Mars' gravity. Also, solar extreme ultraviolet radiation can be absorbed by molecules, breaking them into their constituent atoms and giving each atom enough energy that it might be able to escape from the planet.

There are other suspects. Mars has more than 20 ancient craters larger than 600 miles across, scars from giant impacts by asteroids the size of small moons. This bombardment could have blasted large amounts of the martian atmosphere into space. However, huge martian volcanoes that erupted after the impacts, like Olympus Mons, could have replenished the martian atmosphere by venting massive amounts of gas from the planet's interior.

It's possible that the hijacked martian air was an organized crime, with both impacts and the solar wind contributing. Without the protection of its magnetic shield, any replacement martian atmosphere that may have issued from volcanic eruptions eventually would also have been stripped away by the solar wind.

Earlier Mars spacecraft missions have caught glimpses of the heist. For example, flows of ions from Mars' upper atmosphere have been seen by both NASA's Mars Global Surveyor and the European Space Agency's Mars Express spacecraft.

"Previous observations gave us 'proof of the crime' but only provided tantalizing hints at how the sun pulls it off — the various ways Mars can lose its atmosphere to solar activity," said Joseph Grebowsky of NASA's Goddard Space Flight Center in Greenbelt, Md. "MAVEN will examine all known ways the sun is currently swiping the Martian atmosphere, and may discover new ones as well. It will also watch how the loss changes as solar activity changes over a year. Linking different loss rates to changes in solar activity will let us go back in time to estimate how quickly solar activity eroded the Martian atmosphere as the sun evolved." Grebowsky is the Project Scientist for MAVEN.

As the martian atmosphere thinned, the planet got drier as well, because water vapor in the atmosphere was also lost to space, and because any remaining water froze out as the temperatures dropped when the atmosphere disappeared. MAVEN can discover how much water has been lost to space by measuring hydrogen isotope ratios.

Isotopes are heavier versions of an element. For example, deuterium is a heavy version of hydrogen. Normally, two atoms of hydrogen join to an oxygen atom to make a water molecule, but sometimes the heavy and rare, deuterium takes a hydrogen atom's place.

On Mars, hydrogen escapes faster because it is lighter than deuterium. Since the lighter version escapes more often, over time, the martian atmosphere has less and less hydrogen compared to the amount of deuterium remaining. The martian atmosphere therefore becomes richer and richer in deuterium.

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How Sun Steals Martian Atmosphere I

The Red Planet bleeds. Not blood, but its atmosphere, slowly trickling away to space. The culprit is our sun, which is using its own breath, the solar wind, and its radiation to rob Mars of its air. The crime may have condemned the planet's surface, once apparently promising for life, to a cold and sterile existence.

Features on Mars resembling dry riverbeds, and the discovery of minerals that form in the presence of water, indicate that Mars once had a thicker atmosphere and was warm enough for liquid water to flow on the surface. However, somehow that thick atmosphere got lost in space. It appears Mars has been cold and dry for billions of years, with an atmosphere so thin, any liquid water on the surface quickly boils away while the sun's ultraviolet radiation scours the ground.

Such harsh conditions are the end of the road for known forms of life. Although it's possible that martian life went underground, where liquid water may still exist and radiation can't reach.

The lead suspect for the theft is the sun, and its favorite M.O. may be the solar wind. All planets in our solar system are constantly blasted by the solar wind, a thin stream of electrically charged gas that continuously blows from the sun's surface into space. On Earth, our planet's global magnetic field shields our atmosphere by diverting most of the solar wind around it. The solar wind’s electrically charged particles, ions and electrons, have difficulty crossing magnetic fields.

"Mars can't protect itself from the solar wind because it no longer has a shield, the planet's global magnetic field is dead," said Bruce Jakosky of the University of Colorado, Boulder. Jakosky is the Principal Investigator for NASA's MAVEN mission, which will investigate what is responsible for the loss of the martian atmosphere.

Mars lost its global magnetic field in its youth billions of years ago. Once its planet-wide magnetic field disappeared, Mars' atmosphere was exposed to the solar wind and most of it could have been gradually stripped away. "Fossil" magnetic fields remaining in ancient surfaces and other local areas on Mars don't provide enough coverage to shield much of the atmosphere from the solar wind.

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Virtual Exploration of Mars

Besides providing a rich, immersive 3D view of Mars that will aid public understanding of Mars science, the new mode, Google Mars 3D, also gives researchers a platform for sharing data similar to what Google Earth provides for Earth scientists.

The mode enables users to fly virtually through enormous canyons and scale huge mountains on Mars that are much larger than any found on Earth. Users also can explore the Red Planet through the eyes of the Mars rovers and other Mars missions, providing a unique perspective of the entire planet.

Users can see some of the latest satellite imagery from NASA's Mars Reconnaissance Orbiter and other probes orbiting the Red Planet. Viewers can learn about new discoveries and explore indexes of available Mars imagery. The new Mars mode also allows users to add their own 3D content to the Mars map to share with the world.

Today's announcement is the latest benefit from a Space Act Agreement NASA's Ames Research Center in Moffett Field, Calif., signed with Google in November 2006. Under its terms, NASA and Google agreed to collaborate to make NASA's data sets available to the world.

NASA Ames, along with its partners at Google, Carnegie Mellon University, SETI, and other institutions, helped produce the data to make this possible.

Google's innovative search technologies connect millions of people around the world with information every day. Google is headquartered close to Ames in Silicon Valley with offices throughout the Americas, Europe and Asia.

For more information about NASA and agency programs, visit:

http://www.nasa.gov

For more information about Google, visit:

http://www.google.com

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Sensor on Mars Rover to Measure Radiation Environment

About eight months before the NASA rover Curiosity touches down on Mars in August 2012, the mission's science measurements will begin much closer to Earth.
The Mars Science Laboratory mission's Radiation Assessment Detector, or RAD, will monitor naturally occurring radiation that can be unhealthful if absorbed by living organisms. It will do so on the surface of Mars, where there has never before been such an instrument, as well as during the trip between Mars and Earth.

RAD's measurements on Mars will help fulfill the mission's key goals of assessing whether Curiosity's landing region on Mars has had conditions favorable for life and for preserving evidence about life. This instrument also will do an additional job. Unlike any of the nine others in this robotic mission's science payload, RAD has a special task and funding from the part of NASA that is planning human exploration beyond Earth orbit. It will aid design of human missions by reducing uncertainty about how much shielding from radiation future astronauts will need. The measurements between Earth and Mars, as well as the measurements on Mars, will serve that purpose.

"No one has fully characterized the radiation environment on the surface of another planet. If we want to send humans there, we need to do that," said RAD Principal Investigator Don Hassler of the Boulder, Colo., branch of the Southwest Research Institute.
Whether the first destination for human exploration beyond the moon is an asteroid or Mars, the travelers will need protection from the radiation environment in interplanetary space. Hassler said, "The measurements we get during the cruise from Earth to Mars will help map the distribution of radiation throughout the solar system and be useful in mission design for wherever we send astronauts."

RAD will monitor high-energy atomic and subatomic particles coming from the sun, from distant supernovas and from other sources. These particles constitute the radiation that could be harmful to any microbes near the surface of Mars or to astronauts on a Mars mission. Galactic cosmic rays, coming from supernova explosions and other events extremely far from our own solar system, are a variable shower of charged particles. In addition, the sun itself spews electrons, protons and heavier ions in "solar particle events" fed by solar flares and ejections of matter from the sun's corona. Astronauts might need to move into havens with extra shielding on an interplanetary spacecraft or on Mars during solar particle events.

Earth's magnetic field and atmosphere provide effective shielding for our home planet against the possible deadly effects of galactic cosmic rays and solar particle events. Mars, though, lacks a global magnetic field and has only about one percent as much atmosphere as Earth. Just to find high-enough radiation levels on Earth for checking and calibrating RAD, the instrument team needed to put it inside major particle-accelerator research facilities in the United States, Europe, Japan and South Africa.

An instrument on NASA's Mars Odyssey orbiter, which reached Mars in 2001, assessed radiation levels above the Martian atmosphere. Current estimates of the radiation environment at the planet's surface rely on modeling of how the thin atmosphere affects the energetic particles, but uncertainty in the modeling remains large. "A single energetic particle hitting the top of the atmosphere can break up into many particles -- a cascade of lower-energy particles that might be more damaging to life than a single high-energy particle," Hassler noted.

The 1.7-kilogram (3.8-pound) RAD instrument has an upward-pointing, wide-angle telescope with detectors for charged particles with masses up to that of iron. It can also detect secondary neutrons coming from both the Mars atmosphere above and Mars surface material below. Hassler's international RAD team includes experts in instrument design, astronaut safety, atmospheric science, geology and other fields.
Southwest Research Institute, in Boulder and in San Antonio, Texas, and Christian Albrechts University, in Kiel, Germany, built RAD with funding from the NASA Exploration Systems Mission Directorate and Germany's national aerospace research center: Deutschen Zentrum für Luft- und Raumfahrt. The team assembling and testing the Mars Science Laboratory spacecraft at NASA's Jet Propulsion Laboratory in Pasadena, Calif., installed RAD onto Curiosity last month for the late-2011 launch.

RAD measurements during the trip from Earth to Mars will enable correlations with instruments on other spacecraft that monitor solar particle events and galactic cosmic rays in Earth's neighborhood, then will yield data about the radiation environment farther from Earth.Once on Mars, the rover's prime mission will last a full Martian year -- nearly two Earth years. A one-time set of measurements by RAD would not suffice for determining the radiation environment on the surface, because radiation levels vary on time frames both longer than a year and shorter than an hour. Operational planning for Curiosity anticipates that RAD will record measurements for 15 minutes of every hour throughout the prime mission.

Radiation levels probably make the surface of modern Mars inhospitable for microbial life. The measurements from RAD will feed calculations of how deeply a possible future robot on a life-detection mission might need to dig or drill to reach a microbial safe zone. For assessing whether the surface radiation environment could have been hospitable for microbes in Mars' distant past, researchers will combine RAD's measurements with estimates of how the activity of the sun and the atmosphere of Mars have changed in the past few billion years.

"The primary science goal of Curiosity is to determine whether its landing site is, or ever was, a habitable environment, a place friendly to life," said JPL's Ashwin Vasavada, deputy project scientist for the Mars Science Laboratory. "That involves looking both for conditions that would support life as well as for those that would be hazardous to life or its chemical predecessors. Natural, high-energy radiation is just such a hazard, and RAD will give us the first look at the present level of this radiation and help us to better estimate radiation levels throughout Mars' history."

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MAVEN Mission to Investigate How Sun Steals Martian Atmosphere

The Red Planet bleeds. Not blood, but its atmosphere, slowly trickling away to space. The culprit is our sun, which is using its own breath, the solar wind, and its radiation to rob Mars of its air. The crime may have condemned the planet's surface, once apparently promising for life, to a cold and sterile existence.

Features on Mars resembling dry riverbeds, and the discovery of minerals that form in the presence of water, indicate that Mars once had a thicker atmosphere and was warm enough for liquid water to flow on the surface. However, somehow that thick atmosphere got lost in space. It appears Mars has been cold and dry for billions of years, with an atmosphere so thin, any liquid water on the surface quickly boils away while the sun's ultraviolet radiation scours the ground.

Such harsh conditions are the end of the road for known forms of life. Although it's possible that martian life went underground, where liquid water may still exist and radiation can't reach.

The lead suspect for the theft is the sun, and its favorite M.O. may be the solar wind. All planets in our solar system are constantly blasted by the solar wind, a thin stream of electrically charged gas that continuously blows from the sun's surface into space. On Earth, our planet's global magnetic field shields our atmosphere by diverting most of the solar wind around it. The solar wind’s electrically charged particles, ions and electrons, have difficulty crossing magnetic fields.

"Mars can't protect itself from the solar wind because it no longer has a shield, the planet's global magnetic field is dead," said Bruce Jakosky of the University of Colorado, Boulder. Jakosky is the Principal Investigator for NASA's MAVEN mission, which will investigate what is responsible for the loss of the martian atmosphere. NASA selected the MAVEN (Mars Atmosphere and Volatile Evolution Mission) on September 15, 2008.

Mars lost its global magnetic field in its youth billions of years ago. Once its planet-wide magnetic field disappeared, Mars' atmosphere was exposed to the solar wind and most of it could have been gradually stripped away. "Fossil" magnetic fields remaining in ancient surfaces and other local areas on Mars don't provide enough coverage to shield much of the atmosphere from the solar wind.

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