Structure of the Martian atmosphere from ε-Gem occultation observations

We have collected information about Martian atmospheric scale heights derived from observations of the occultation of ? Gem by Mars on April 8, 1976. The observations give data in the altitude range ～50 to 80 km. A rough, unweighted average of results so far available yields a temperature of ～165°K. Excursions of ～±40°K about this mean may be present as a function of both altitude and areographic coordinates.     

Humans and robots: hand in grip

As we move boldly forward into the 21st century, there has rarely been a more exciting time in which to contemplate the future of space exploration. The President of the United States has made a new and ambitious commitment to exploration of the solar system and beyond. Robotic partners will play a vital role in ensuring that the Vision is truly "sustainable and affordable". Relevant science and technology will be discussed with particular emphasis on expertise from NASA Ames Research Center of which the author is Director. The likely evolution of the balance between human explorers and robotic explorers will be addressed.     

Following the water,the new program for Mars exploration

In the wake of the loss of Mars Climate Orbiter and Mars Polar Lander in late 1999, NASA embarked on a major review of the failures and subsequently restructured all aspects of what was then called the Mars Surveyor Program--now renamed the Mars Exploration Program. This paper presents the process and results of this reexamination and defines a new approach which we have called "Program System Engineering". Emphasis is given to the scientific, technological, and programmatic strategies that were used to shape the new Program. A scientific approach known as "follow the water" is described, as is an exploration strategy we have called "seek--in situ--sample". An overview of the mission queue from continuing Mars Global Surveyor through a possible Mars Sample Return Mission launch in 2011 is provided. In addition, key proposed international collaborations, especially those between NASA, CNES and ASI are outlined, as is an approach for a robust telecommunications infrastructure.     

Structure of Jupiter and Saturn

Understanding of the planetary interiors depends upon our knowledge of the equations of state and of the transport properties of matter at high pressures and temperatures. The present status of this knowledge in relation to hydrogen and helium is discussed in detail including electrical and thermal conductivity, viscosity, diffusivity, etc. On this basis the various possible models of the internal structure of Jupiter and of Saturn are presented and their agreement with observational constraints such as the multipole gravitational coefficients analyzed. Relevance of planetary magnetic fields, basic atmospheric information and the Great Red Spot of Jupiter to the models of the interiors are discussed.     

The significance of atmospheric measurements for interior models of the major planets

We present a discussion of proposed models for interior processes in Jupiter and Saturn, and discuss how these models can be tested by atmospheric measurements by space vehicles. The importance of measurements at Uranus and Neptune is also discussed.This conclusion follows directly from consideration of the mass, radius, and oblateness of Jupiter and Saturn (DeMarcus 1958; Peebles, 1964; Hubbard, 1970): the point is also discussed in the papers by Cameron and Lewis, this issue, pp. 383–400 and 401–411.This is one of the publications by the Science Advisory Group.     

The Juno Mission

The selection of the Discovery Program InSight landing site took over four years from initial identification of possible areas that met engineering constraints, to downselection via targeted data from orbiters (especially Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) and High-Resolution Imaging Science Experiment (HiRISE) images), to selection and certification via sophisticated entry, descent and landing (EDL) simulations. Constraints on elevation (\({\leq}{-}2.5\ \mbox{km}\) for sufficient atmosphere to slow the lander), latitude (initially 15°S–5°N and later 3°N–5°N for solar power and thermal management of the spacecraft), ellipse size (130 km by 27 km from ballistic entry and descent), and a load bearing surface without thick deposits of dust, severely limited acceptable areas to western Elysium Planitia. Within this area, 16 prospective ellipses were identified, which lie ～600 km north of the Mars Science Laboratory (MSL) rover. Mapping of terrains in rapidly acquired CTX images identified especially benign smooth terrain and led to the downselection to four northern ellipses. Acquisition of nearly continuous HiRISE, additional Thermal Emission Imaging System (THEMIS), and High Resolution Stereo Camera (HRSC) images, along with radar data confirmed that ellipse E9 met all landing site constraints: with slopes <15° at 84 m and 2 m length scales for radar tracking and touchdown stability, low rock abundance (<10 %) to avoid impact and spacecraft tip over, instrument deployment constraints, which included identical slope and rock abundance constraints, a radar reflective and load bearing surface, and a fragmented regolith ～5 m thick for full penetration of the heat flow probe. Unlike other Mars landers, science objectives did not directly influence landing site selection.