Venus is the second planet from the Sun and the closest in size to Earth, with 95 percent of its diameter and 82 percent of its mass. The resemblance ends there. A carbon dioxide atmosphere roughly 90 times as massive as Earth's traps heat in a runaway greenhouse, holding the surface near 465 °C, hotter than Mercury despite Venus orbiting nearly twice as far from the Sun. Surface pressure reaches 92 bar, and an unbroken deck of concentrated sulfuric acid clouds hides the ground from view.
Venus is the brightest natural object in Earth's sky after the Sun and the Moon, and it was the first planet visited by a spacecraft, yet it has spent most of the past three decades ignored. A disputed 2020 claim of phosphine gas in its clouds, along with evidence that the planet may once have had oceans, has pulled attention back. Four missions are now in development, though since contact with Japan's Akatsuki orbiter was lost in 2024 no spacecraft has been operating there.
Runaway greenhouse and surface conditions
Conditions at the surface are remarkably uniform: because the massive atmosphere transports heat efficiently, temperatures barely differ between equator and poles or day and night. Near the ground, carbon dioxide is compressed into a supercritical fluid, and the gentle winds push against a lander like a slow ocean current. The planet rotates backward once every 243 Earth days, longer than its 225-day year, yet the upper atmosphere super-rotates, with cloud-top winds near 360 km/h circling the planet every four days.
The greenhouse was probably self-inflicted. As the young Sun brightened, any surface water evaporated; water vapor amplified the warming, ultraviolet light split the molecules, and the hydrogen escaped to space. The evidence survives in the atmosphere's deuterium-to-hydrogen ratio, roughly 100 times Earth's, the signature of a planet that lost a large water inventory. Without water to lubricate plate tectonics or sustain a carbon cycle, carbon dioxide simply accumulated.
Did Venus once have oceans?
Whether Venus was ever habitable is genuinely unsettled. Climate modeling by scientists at NASA's Goddard Institute for Space Studies in 2016 found that with its slow rotation and a shallow ocean, early Venus could have kept moderate surface temperatures for as long as two billion years, with thick daytime clouds shading the surface.[1] Emissivity data from orbit hint that the highland tesserae may be granite-like rock, which on Earth forms in the presence of water. A 2021 modeling study countered that water may never have condensed on Venus at all, with rain evaporating before reaching the hot early surface, and Earth escaping the same fate only because the faint young Sun gave it time to cool.[2] The lack of leftover oxygen in today's atmosphere also argues against a late, rapid ocean loss. Deciding between these histories requires isotopic and geologic ground truth, which is exactly what the next generation of missions is designed to collect.
The phosphine debate
In September 2020 a team led by Jane Greaves reported phosphine gas at about 20 parts per billion in Venus's cloud deck, based on observations with the James Clerk Maxwell Telescope (JCMT) and the ALMA array. The claim drew attention because on Earth phosphine is produced mainly by anaerobic microbes and industry, and no known Venusian chemistry makes it in such quantities.[3] Independent groups quickly challenged the result: reanalyses of the ALMA data shrank or erased the signal, and skeptics argued that an overlapping sulfur dioxide line or calibration artifacts could mimic phosphine. The discovery team reprocessed its data and maintained a weaker detection, and a long-running JCMT monitoring program has continued to report absorption consistent with phosphine that varies over time.[4]
As of 2026 there is no consensus that phosphine is present, and reviews of the controversy conclude the question must stay open until multiple independent techniques, ideally including measurements made inside the atmosphere, converge.[3][4] The dispute has nonetheless reshaped the field, reviving serious study of whether Venus's temperate cloud layers, around 50 km up, could host any form of aerial life.
Venera landings and early exploration
Venus was the proving ground of early planetary flight. NASA's Mariner 2 performed the first successful planetary flyby in December 1962 and confirmed the scorching surface. The Soviet Union then mounted the Venera program, the only campaign ever to operate landers there. Venera 7 achieved the first survivable landing on another planet on December 15, 1970, transmitting for about 23 minutes; Venera 9 returned the first photographs from another planet's surface in October 1975; and Venera 13, on March 1, 1982, sent color panoramas and analyzed a drilled soil sample, enduring 127 minutes in an environment it was designed to survive for half an hour. The twin Vega missions of 1985 added balloons that drifted for nearly two days in the temperate cloud layer. No lander has ever lasted longer than about two hours on the surface.
Magellan and the mapped surface
NASA's Magellan orbiter radar-mapped 98 percent of Venus between 1990 and 1994, revealing tens of thousands of volcanoes, long lava channels, crumpled tessera highlands, and fewer than 1,000 impact craters, implying the surface is only a few hundred million years old. In 2023, researchers comparing Magellan images taken eight months apart in 1991 found a volcanic vent near Maat Mons that had changed shape and grown, the first direct evidence of an eruption in progress on Venus. The European Space Agency's Venus Express orbiter (2006-2014) and JAXA's Akatsuki (2015-2024) studied the atmosphere and its super-rotation before falling silent, leaving the planet unattended.
Upcoming missions
| Mission | Lead | Type | Target launch |
|---|---|---|---|
| Venus Life Finder | Rocket Lab / MIT | Atmospheric probe | No earlier than mid-2026 |
| DAVINCI | NASA | Descent probe and flybys | About 2031 |
| VERITAS | NASA | Radar mapping orbiter | About 2031 |
| EnVision | ESA | Radar and spectroscopy orbiter | November 2031 |
NASA's two Venus missions survived a near-death experience: the administration's fiscal 2026 budget request proposed cancelling both, but the appropriations act passed in January 2026 restored them, providing 99 million dollars to keep the DAVINCI descent-probe mission moving toward a launch around 2031 while VERITAS ramps up more slowly toward the same window.[5][6] DAVINCI will measure noble gases and the deuterium ratio all the way down and photograph the tesserae up close; VERITAS will map topography and surface composition globally. ESA's EnVision, adopted in January 2024, is set to launch on an Ariane 6 in November 2031, then spend 15 months cruising and nearly a year aerobraking into a low orbit, pairing radar imaging and a subsurface sounder with atmosphere-watching spectrometers.[7]
The first of the new wave may be private. Rocket Lab, working with an MIT science team, plans to send a 17 kg probe on an Electron-launched Photon cruise stage, targeting launch no earlier than summer 2026. The probe carries a single instrument, an autofluorescing nephelometer, and will get about five minutes inside the 45-65 km cloud layer to search droplets for organic molecules, a first attempt at a privately funded mission to another planet.[8]
References
- NASA Climate Modeling Suggests Venus May Have Been Habitable - NASA Goddard Institute for Space Studies.
- A new Climate Model Suggests That Venus Never had Oceans - Universe Today.
- Life on Venus? - PMC / National Institutes of Health.
- Source of phosphine on Venus, an unsolved problem - Frontiers in Astronomy and Space Sciences.
- NASA's Budget Woes Are Over, For Now - Sky & Telescope.
- NASA's ambitious 'decade of Venus' exploration may bank on 1 probe - Space.com.
- Envision factsheet - European Space Agency.
- Venus Life Finder - Wikipedia.
