MAVEN, the next Mars Mission

The Mars Atmosphere and Volatile Evolution Mission (MAVEN) is scheduled for launch between November 18 and December 7, 2013. [br]If it is launched November 18, it will arrive at Mars on September 16, 2014 for its year-long mission to investigate what is responsible for the loss of the Martian atmosphere. MAVEN was selected by NASA on September 15, 2008 as the next mission after MSL Curiosity. Bruce Jakosky is the Principal Investigator, Watch his LASP public lecture about this mission on 2 December 2009 here
MAVEN spacecraft orbiting MarsAn artist’s conception of the MAVEN spacecraft orbiting Mars. NASA/Goddard Space Flight Center

The Red Planet bleeds. Not blood, but its atmosphere, slowly trickling away to space. This bleeding is caused by our sun. The solar wind slowly robs Mars of its atmosphere. At least that is the leading theory at the moment. The idea is that as Mars is not protected by a magneto sphere, like our Earth, the solar wind and solar radiation can strike the atmosphere of Mars without any hindrance. According to this theory Earth’s atmosphere does not bleed off like the atmosphere of Mars because Earth does have a magneto sphere. However, in the last few years we have found that the solar wind is taking molecules from our Earth atmosphere after all. So we will have to see whether this explanation of Mars having such a thin atmosphere today is correct. Be that as it may, MAVEN is set to test the theory with its measurements from late 2013 on.

We all have seen images of Mars resembling dry riverbeds and other waterlike features on the rim of craters. The leading theory here (and that is a recent theory) is that Mars had a period, long ago (how long ago is under fierce debate) that was warm and wet. Mars then also had a thicker atmosphere, or the water could not have been liquid on the Martian sufrace. The warm and wet Mars idea is born out time and again by the discovery of minerals that form in the presence of water. Those findings tell us that indeed Mars must have once had a thicker atmosphere and must have been warm enough for liquid water to flow on the surface. However, somehow that thick atmosphere got lost in space. We believe now that Mars has been cold and dry for billions of years (or thousands of million of years to bring this number down to more human scale). The present Martian atmosphere is so thin, that any liquid water on the surface quickly boils away while the sun’s ultraviolet radiation scours the ground.

Because of these harsh conditions we don’t expect to find life, or at least the forms of life that we know, to be present at the surface. It is ofcourse entirely possible that martian life went underground, where liquid water may still exist and radiation can’t reach. Only 2.5 centimeters (1 inch) of soil is enough to protect life from the radiation hitting the surface of Mars. And we know from our research on Earth that life is very hardy and very capable of finding itself safer places to habitate.

Hubble image of Mars showing cloudsAll 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. Earth’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.[br]Plans exists (like the LightSail 1 solar sail project of the Planetary Society) to use that solar wind to our advantage in moving goods from Earth to other bodies in our solar system. So not all is bad about the Solar wind.

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.

The first indication of the weakness of the magnetic field of Mars was obtained during the Mariner 4 spacecraft flyby in 1965. At a closest approach of 3.9 Mars radii, no indication of the Earth-like dipole magnetic field was detected. Most subsequent magnetic field measurements in the vicinity of Mars were carried out on a series of five MARS spacecraft launched by the Soviet Union between 1971 and 1974 (see Soviet MARS missions). Several of these successfully operated in orbit for periods long enough to both confirm the Mariner 4 results and to measure the disturbance of the interplanetary magnetic field caused by Mars. However, none of these spacecraft approached Mars closer than ~ 1300 km or ~ 1.3 Mars radii from the center of the planet, and none probed the solar wind wake inside of the optical shadow, where the magnetotail of an intrinsic magnetosphere resembling a weak version of Earth’s would be found.

br] The Viking landers did not carry magnetic field experiments, although they made ionospheric measurements of relevance to the magnetic field question. [br]In 1989  the Soviet Phobos-2 spacecraft in 1989 took magnetic field measurements of the wake of Mars (e.g. Nature. 341. 19 October 1989). The orbit of Phobos 2 went into the deep wake of Mars, for the first time providing magnetic field data in the optical shadow at distances as close as ~ 2.7 Mars radii and as distant as ~ 20 Mars radii. These measurements showed beyond a doubt that the magnetic fields in the wake of Mars are determined by the interplanetary field orientation, and are thus not Earth- like.

In 1997, while aerobreaking, the Mars Global Surveyor dipped deeper into the Martian atmosphere than had been planned. As a result we have measurements of part of the Martian surface, showing remnants of a magnetic field still present, but scattered. Scientists believe that their presence is a possible sign that Mars had plate tectonics, and it is unclear what shut down those plate movements and when. Some think as early as 4 billion years ago. The bands themselves are quite strong; nearly as strong as Earth’s magnetic field, and can extend hundreds of kilometers into the atmosphere. They interact with the solar wind to create auroras much like those seen as the Northern Lights here. By 2008 scientists had observed already over 13,000 of these aurora events.

Today, the only other ‘direct’ information that Martian magnetism is from a special class of meteorites known as the SNC meteorites which are thought to come from Mars.[br]SNC meteorites are named after three locations where this rare type of meteorite was first found: “S”hergotty (India), “N”akhla (Egypt), and “C”hassigny (France).[br]The 14 SNC meteorites are all igneous rocks, either basalts or basaltic cumulates. They are thought to have come from Mars based on direct comparison with Martian materials and on consistency with theories about Mars. Most telling is that the SNC meteorites contain traces of gas which is very similar in elemental and isotopic compositions to the modern Martian atmosphere as measured by Viking landers on Mars and as measured by spectroscopy from Earth.

Magnetic field analyses of these possible samples of the Martian crust indicate that magnetic fields of ~ 1000 nT may have been present on the surface of Mars at the time that these meteorites were ejected by a giant impact some 180 million years ago. For comparison, the present field on Earth near the equator is about 3 X 104 nT.

Now how does the Sun steal molecules from the Martian atmosphere? The basic way is that 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, in the same way that generators use to produce electrical power.

At the same time the heat of the sun warms the atoms and molecules of the Martian atmosphere to a point that they have enough speed from this solar heating to simply run away. These atoms and molecules remain electrically neutral, but become hot enough to escape Mars’ gravity. The third effect of our Sun on the atmosphere is that the 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.

Ofcourse the many crater impacts on Mars give another answer to the question of why Mars has such a thin atmosphere today. Mars shows more than 20 ancient craters larger than 900 kilometers (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.[br]It’s possible that both the impacts and the solar wind together removed much of the atmosphere. 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.[br]Earlier Mars spacecraft missions like the Mars Global Surveyor of NASA and the European Space Agency’s Mars Express have observed flows of ions from Mars’ upper atmosphere.

MAVEN will examine all known ways the sun is currently swiping the Martian atmosphere, and may discover new ones. 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 make it possible to estimate how quickly solar activity eroded the Martian atmosphere as the sun evolved.

As the martian atmosphere thinned, the planet got drier as well, because water vapor in the atmosphere was also lost to space. Without atmosphere the warmth of the Sun is not kept. 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.[br]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.[br]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.

Because of this effect MAVEN will measure the amount of hydrogen compared to the amount of deuterium in Mars’ upper atmosphere. This will give the planet’s present-day hydrogen to deuterium (H/D) ratio. They will compare it to the ratio Mars had when it was young — the original H/D ratio. The original ratio is estimated from observations of the H/D ratio in comets and asteroids, which are believed to be pristine, “fossil” remnants of our solar system’s formation.

Comparing the present and original H/D ratios will allow the team to calculate how much hydrogen, and therefore water, has been lost over Mars’ lifetime. For example, if the team discovers the martian atmosphere is ten times richer in deuterium today, the planet’s original quantity of water must have been at least ten times greater than that seen today.

MAVEN will also help determine how much martian atmosphere has been lost over time by measuring the isotope ratios of other elements in the air, such as nitrogen, oxygen, and carbon.

MAVEN is part of NASA’s Mars Scout program, funded by NASA Headquarters in Washington, DC.[br]The University of Colorado will coordinate the science team and science operations. [br]NASA Goddard will manage the project and provide mission systems engineering, mission design, and safety and mission assurance.[br] NASA’s Jet Propulsion Laboratory, Pasadena, California, will navigate the spacecraft, provide the Deep Space Network, and an Electra telecommunications relay package. [br]Instruments on the spacecraft will be provided by the University of California, Berkeley, the University of Colorado, Boulder, and NASA Goddard, with the Centre d’Etude Spatiale des Rayonnements, Toulouse, France, providing the sensor for one instrument.[br] Lockheed Martin Corporation, Bethesda, Maryland., will develop the spacecraft, conduct assembly, test and launch operations, and provide mission operations at their Littleton, Colorado facility.

Artist impression of the Solar wind affecting Venus, Earth and Mars, where only Earth has a magnetic field to bend the winds around the planet.

Daily Briefing

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National Geographic

In National Geographic’s e-short book ‘Mars Landing 2012,’ written by Washington Post science correspondent Marc Kaufman and published just as the suspense builds, with Curiosity hurtling toward Mars, space science readers

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