Mars

What it is

Mars is the fourth planet from the Sun and seventh largest in the solar system, with a diameter of 6,779 km, roughly half Earth's, and a Martian day of 24 hours and 37 minutes. Its atmosphere, 95% carbon dioxide by volume, provides less than 1% of Earth's surface pressure, exposing the surface to intense ultraviolet radiation and precluding liquid water under current conditions. Average surface temperature is approximately -60 degrees Celsius. Mars has two small moons, Phobos and Deimos, both likely captured asteroids. It hosts the solar system's tallest volcano, Olympus Mons at 21.9 km, and its longest canyon system, Valles Marineris, stretching roughly 4,000 km. Ancient riverbeds, deltas, and mineral deposits confirm that liquid water existed on the surface billions of years ago. As of July 2026, Mars hosts more active spacecraft than any planet besides Earth.

History

Systematic telescopic observation of Mars dates to the 17th century; Giovanni Cassini measured its rotation period in 1666. NASA's Mariner 4 flyby in 1965 returned the first close images and confirmed a tenuous, largely carbon dioxide atmosphere with no global magnetic field. Soviet and US missions attempted surface landings throughout the 1970s. NASA's Viking 1 and 2 landers (1976) were the first to operate successfully on the surface and ran life-detection experiments whose results remain contested. NASA's twin rovers Spirit and Opportunity (both 2004) found mineralogical evidence of past liquid water; Opportunity operated for 14.5 years before going silent in June 2018. Curiosity, landing in Gale Crater on August 6, 2012, confirmed ancient habitability. China's Tianwen-1 mission placed the Zhurong rover on the Utopia Planitia plain in May 2021, making China only the third entity, after the US and Soviet Union, to land successfully on Mars.

Current state

Four NASA assets are active at Mars as of July 2026: the Perseverance rover (Jezero Crater, landed February 18, 2021), Curiosity, Mars Reconnaissance Orbiter (arrived March 2006), and Mars Odyssey (arrived October 2001). NASA's MAVEN orbiter went unrecoverable in late 2025 after more than 11 years of atmospheric science. Perseverance has sealed more than 20 rock core samples in titanium tubes cached at a surface depot in Jezero Crater, intended for return to Earth. In January 2026, the US Congress declined to fund NASA's Mars Sample Return mission, effectively cancelling the program. That decision handed China a lead: China's Tianwen-3 is in the spacecraft construction phase, targeting a 2028 launch and a 2031 sample return, with CNSA's chief scientist confirming 20 kg of payload reserved for international science instruments. ESA's Trace Gas Orbiter and the UAE's Hope orbiter remain operational in Martian orbit.

Relationships

Mars sits at the intersection of the US-China space rivalry in planetary science, with sample return as the central contest. ESA's Rosalind Franklin rover, targeting a 2028 launch aboard a SpaceX Falcon Heavy from NASA's Kennedy Space Center, is a joint ESA-NASA project; NASA's agency approved full hardware participation in April 2026, with the first braking engines delivered to France in June 2026. Japan's Martian Moons eXploration mission targets a late 2026 launch to study Phobos and Deimos and return a Phobos sample to Earth in the early 2030s. China's Tianwen-2, targeting near-Earth asteroid Kamooalewa rather than Mars, separately demonstrates CNSA's broader sample-return engineering capability. SpaceX has publicly stated a long-term goal of crewed Mars missions using the Starship launch system, though no funded crewed program exists as of mid-2026.

What to watch

The next Earth-Mars launch window opens in late 2028, when Tianwen-3, ESA's Rosalind Franklin, and Japan's MMX all target departure. NASA's twin ESCAPADE spacecraft will use an Earth gravity assist in November 2026 before arriving at Mars in September 2027 to study how solar wind strips the Martian atmosphere, the same process that turned Mars from a warm, wet world into its present state. The fate of Perseverance's cached surface samples, and whether the US Congress funds any retrieval mechanism, is the defining programmatic question for NASA's Mars science program through the 2030s. A Chinese sample return before a US one would mark the most significant shift in planetary science leadership since the Apollo era.