- What happened to electrons fired at mercury vapour once their speed crossed a certain threshold?
Mars Exploration
Missions and discoveries about the Red Planet.
- How did Luna 3 photograph, develop, and transmit images of the lunar far side back to Earth in 1959?
- What did Arecibo reveal about the true rotation period of Mercury?
- What did a century of telescopic observation lead scientists to believe about Mars before Mariner 4's flyby?
- What did Mariner 4's 22 photographs actually show about the Martian surface and atmosphere?
- What was the purpose of the Apollo Lunar Surface Experiments Package first deployed on Apollo 12?
- What geological features did Mariner 6 and 7 image without immediately understanding them?
- How did Mariner 6 and 7's findings build on what Mariner 4 discovered in 1965?
- What happened when Mariner 9 arrived at Mars in November 1971, and how did the mission team respond?
- What did Mariner 9's images reveal about Olympus Mons and Valles Marineris once the dust storm cleared?
- How did Mariner 9's photographs of sinuous channels change scientific thinking about water on Mars?
- What did Viking 2 photograph at Utopia Planitia that Viking 1 could not, given its more northern landing site?
- Why was Viking 2's seismometer unable to produce useful data about marsquakes?
- How long did it take before scientists got a genuine Martian seismic record after Viking 2's seismometer failed?
- What kinds of data did the Viking landers send back about Mars despite not finding definitive evidence of life?
- Why was landing softly on Mars so difficult given the planet's thin atmosphere?
- What did the labelled release experiment detect that made some scientists argue it was evidence of life on Mars?
- What is the leading explanation for the labelled release experiment's positive signal if not living organisms?
- Why did NASA choose 20 July 1976 as the date for Viking 1's landing?
- What search strategy did Robert Ballard use to locate the Titanic instead of a systematic grid search?
- What complication delayed Mars Global Surveyor's aerobraking manoeuvre into its mapping orbit?
- What evidence did the spacecraft's camera find for liquid water once carving gullies into Martian crater walls?
- What did the remnant magnetism in Mars's southern crust suggest about the planet's past?
- How did Mars Pathfinder's airbag landing system work, and why was it a departure from prior methods?
- What instrument did the Sojourner rover use to analyse the composition of Martian rocks?
- How did Pathfinder's landing technology influence the later Spirit and Opportunity rover missions?
- How much did the entire Mars Pathfinder mission cost, and was it delivered on budget?
- What did the 1976 Viking 1 image of Cydonia actually show, and at what resolution?
- How did the sharper Mars Global Surveyor images in 1998 resolve the 'face on Mars' controversy?
- How did Mars Odyssey use aerobraking to settle into its mapping orbit around Mars?
- What did Mars Odyssey's gamma-ray spectrometer find near the Martian poles?
- Why is Mars Odyssey notable among spacecraft that have orbited other planets?
- How did Mars Odyssey's gamma-ray spectrometer detect water ice beneath the Martian surface?
- How much water ice did the south polar region of Mars appear to hold?
- Why did near-surface ice make plans for future human presence on Mars more feasible?
- What evidence did Opportunity find at Meridiani Planum that pointed to a watery past on Mars?
- How did the rovers land on Mars, and why is that method notable?
- What are evaporites, and why do they indicate ancient saltwater on Mars?
- How long did Opportunity actually operate compared to its planned 90-day mission?
- Why did NASA choose the Martian arctic as the Phoenix Lander's landing site?
- How did the Phoenix Lander confirm the presence of water ice on Mars?
- Does the discovery of water ice on Mars mean the planet could support life?
- How did the disappearance of white material over four Martian days prove it was water ice rather than dry ice?
- Why was the Martian arctic chosen as Phoenix's landing site in the first place?
- What did Phoenix's discovery of perchlorates in Martian soil complicate about thinking on habitability?
- How did MESSENGER use flybys of Earth, Venus, and Mercury to slow down enough to enter orbit?
- How can water ice survive on Mercury despite daytime surface temperatures of 430 degrees Celsius?
- Why are Mercury's polar craters permanently shadowed even though the planet orbits so close to the Sun?
- Why was Curiosity too heavy for the airbag landing system used by earlier Mars rovers?
- How did the sky crane system lower Curiosity onto the Martian surface using cables?
- Why did NASA engineers call the landing sequence 'seven minutes of terror'?
- What evidence did Curiosity find that Gale Crater was once a habitable environment?
- What are recurring slope lineae and when do they appear on Mars?
- What chemical signature suggested the streaks were caused by briny water rather than dry sediment?
- Why has the liquid-water interpretation of these streaks become more contested since 2015?
- How did the MARSIS radar detect a bright, flat reflection beneath the Martian south polar ice cap?
- Why shouldn't liquid water exist at the cold Martian poles, and what could keep it from freezing?
- What remains uncertain about whether the detected feature is truly a habitable lake?
- Why was InSight sent to the flattest, least interesting place on Mars?
- How sensitive is InSight's seismometer, and what can it detect about marsquakes?
- What did scientists hope to learn about Mars's crust, mantle, and core by listening to marsquakes?
- What eventually ended InSight's mission in 2022?
- Why had no spacecraft ever landed on the Moon's far side before Chang'e 4 in 2019?
- How did the Queqiao relay satellite solve the communication problem for a lander on the Moon's far side?
- Where did Chang'e 4 land, and why is the South Pole–Aitken Basin scientifically significant?
- How long did the Opportunity rover operate compared to its originally planned ninety-day mission?
- What caused the 2018 dust storm to end communication with Opportunity, and why couldn't the panels recover?
- What song did NASA play during its final attempt to contact Opportunity, and why was it chosen?
- Why does an efficient launch window to Mars only open once every 26 months?
- What made the UAE's Hope orbiter mission historically significant?
- What did China's Tianwen-1 mission accomplish with a single launch?
- What historic first did NASA's Ingenuity helicopter achieve after arriving on Perseverance?
- Why was Jezero Crater chosen as Perseverance's landing site?
- Why must the Mars entry, descent, and landing sequence be fully automated?
- How did Ingenuity manage to generate lift in an atmosphere a hundred times thinner than Earth's?
- How did Chandrayaan-3's landing differ from earlier Moon landings by the Soviet Union, the United States, and China?
- What happened to Russia's Luna-25 mission just before Chandrayaan-3's landing?
- What did the Pragyan rover find in the lunar regolith during its two weeks of operation?
- What role is Starship intended to play in NASA's Artemis program and future Mars missions?
- Who were the four astronauts on Artemis II, and what made the crew notable?
- How close did the Orion capsule get to the lunar surface, and how did that compare to Apollo-era distances?
- What crewed spaceflight distance record did Artemis II set, and how did it surpass Apollo 13?
- Why was Artemis II a flyby rather than a landing, and what comes next in the Artemis program?