The Mars Scout Program was a NASA initiative to send a series of small, low-cost robotic missions to Mars, competitively selected from innovative proposals by the scientific community. The program had an array of missions destined to reach Mars, and study it at relatively low costs. Each Scout project was to cost less than US$485 million. The Phoenix lander and MAVEN orbiter were selected and developed before the program was retired in 2010.
First Scout mission 
Ice clouds in the Martian arctic
The first robotic spacecraft in this program was Phoenix, a lander originally intended for the canceled Mars Surveyor mission but adapted to the new mission. Phoenix was launched on August 4, 2007, and landed in the icy northern polar region of the planet on May 25, 2008. Phoenix was designed to search for environments suitable for microbial life on Mars, and to research the history of water there. The 90 day primary mission was successful and the overall mission was concluded on November 10, 2008, after engineers were unable to contact the craft. The lander last made a brief communication with Earth on November 2, 2008.
Second Scout mission 
On September 15, 2008, NASA announced that it had selected MAVEN to be the second mission. This mission was budgeted (as of 2007) for no more than US$475 million. The mission is programmed for launch late on 2013.
While this mission was originally supposed to be a "double" in which two orbiter units were sent, NASA is currently only planning to fund one mission. Multiple lines of evidence suggest that Mars lost most of its atmosphere billions of years ago. The MAVEN orbiter would study the current rate of atmospheric loss with an emphasis on the role of the solar wind, whose rapidly moving ions and magnetic field may be responsible for Mars' current condition.
Previous candidates 
Previous missions considered for the Mars Scout Program are listed below:
||The mission would have directly determined the basic processes in Martian atmospheric evolution by measuring the structure and dynamics of the upper atmosphere. In addition, potentially biogenic atmospheric constituents such as methane would have been measured. The principal investigator is Dr. Alan Stern, Southwest Research Institute, Boulder, Colorado. Southwest Research Institute, San Antonio, would have provided project management.
||This mission would launch up to four saucer-shaped landers, two feet (0.61m) in diameter, from a "mother ship" orbiting Mars. Each would parachute onto the surface, analyzing the soil and atmosphere. Two of the four landers would be targeted at the polar regions.
||This mission plans to send an unmanned airplane into the Martian atmosphere to observe the planet.
||This mission would consist of a probe designed to melt through a polar ice cap using heated jets. It would travel up to 100 yards (91m) below the surface, analyzing the melted water to determine the climatic history of Mars.
||This mission would create three or four winged gliders with approximately six-foot (1.83m) wingspans and would explore the Valles Marineris canyon system. The gliders would carry infrared spectrometers and cameras.
||With infrared telescopes on Earth and a spectrometer on the Mars Express Orbiter, methane was discovered in the Martian atmosphere. The presence of methane on Mars is very intriguing, since as an unstable gas it indicates that there must be an active source of the gas on the planet. The latest research suggests that the methane destruction lifetime is as long ~4 Earth years and as short as ~0.6 Earth years. In either case, the destruction lifetime for methane is much shorter than the timescale (~350 years) estimated for photochemical (UV radiation) destruction. The Mars Organics Observer would use an orbiter to characterize the Martian methane: where it is being emitted, how much is being emitted and how often it is being emitted.
||Named for nymphs of springs, lakes, and rivers from Greek mythology, this mission would send two landers to a region which likely holds groundwater. The landers would search for the groundwater using low-frequency electromagnetics and other instruments.
||A sample return mission that would briefly pass into the Martian atmosphere to scoop up about 1000 dust grains and a few liters of air without slowing from escape velocity.
||Similar to NASA's Deep Impact, this mission would impact two copper spheres into Mars' surface to create craters in a region known to have water ice, and maybe liquid water, a few meters under the surface. An accompanying orbiter would analyze the craters from orbit. Although this mission was not selected, ice was later observed in fresh natural impacts.
||This mission calls for a lander/rover pair designed to analyze the ages of rocks. It would be targeted for the Cerberus Highlands region, and would look for specific minerals to help scientists compare the cratering of Mars with that of the Moon.
||Orbiter with spectrometers would look for volcanic emissions and life
||Melt probe for ice caps
||24 mini weather stations. Also proposed in the Discovery Program.
||Mars Environmental Orbiter—study atmosphere and hydrology
||Mars Atmospheric Constellation Observatory—a network of microsatellites study the atmosphere
||Mars Scout Radar—Synthetic Aperture Radar (SAR) to study sub-surface
||Six Deep Space 2-like hard impact landers with subsurface penetrators
Ice in craters 
Ice in a fresh Martian impact crater
See also 
External links