ON THIS DAY AUGUST 4 2023

This Day in History: August 4

Featured Event

2007




The U.S. space probe Phoenix was launched, and a year later it landed on Mars. Among its most-important discoveries was the existence of water ice beneath the planet's surface.





Phoenix, U.S. space probe launched by the National Aeronautics and Space Administration (NASA) on Aug. 4, 2007; it landed on May 25, 2008, in the north polar region of Mars. Phoenix’s main objective was to collect and analyze soil samples in order to provide answers to the questions of whether the Martian arctic can support life, what the history of water is at the landing site, and how Martian climate is affected by polar dynamics.



Phoenix space probe
Phoenix more closely resembled the Viking landers of the 1970s than the twin rovers Spirit and Opportunity, which landed on Mars in 2004 and roamed their respective landing sites for years. Like the Viking landers, Phoenix was slowed in its descent to the Martian surface by thrusters rather than air bags, which were used by the twin rovers. Phoenix stayed at a single location in the Martian arctic and drilled for rock samples with a 2.35-metre (7.7-foot) robotic arm, the arm placing the samples for analysis in a small self-contained chemistry laboratory. Other instruments included a small weather station and a camera.


One of Phoenix’s most important discoveries was the existence of water ice beneath the surface of Mars. Phoenix’s robotic arm dug a trench that uncovered a white material that sublimed directly into the atmosphere and therefore was water ice. Minerals, such as calcium carbonate, that form in the presence of water were found. The soil at the landing site was found to be alkaline with a pH between 8 and 9. (Earlier missions to Mars had detected acidic soil.) Compounds containing the perchlorate ion (ClO₄⁻) were also discovered. Phoenix ceased transmitting to Earth on Nov. 2, 2008, as its solar panels received less and less light in the gathering Martian winter.



Images acquired by Phoenix's Surface Stereo Imager on June 15 and 19, 2008, showing sublimation of ice on the surface of Mars. (Left) On June 15 subsurface ice has been exposed by a scoop on the end of the lander's robotic arm; (right) by June 19 some of the ice has disappeared, having sublimated directly into the Martian atmosphere.

Featured Biography

Barack Obama
president of United States




Barack Obama, in full Barack Hussein Obama II, (born August 4, 1961, Honolulu, Hawaii, U.S.), 44th president of the United States (2009–17) and the first African American to hold the office. Before winning the presidency, Obama represented Illinois in the U.S. Senate (2005–08). He was the third African American to be elected to that body since the end of Reconstruction (1877). In 2009 he was awarded the Nobel Peace Prize “for his extraordinary efforts to strengthen international diplomacy and cooperation between peoples.”




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