The interface between the Earth's surface and outer space. The Kármán line at an altitude of 100 km (62 mi) is shown. The layers of the atmosphere are drawn to scale, whereas objects within them, such as the International Space Station, are not.

Outer space, or just space, is the expanse that exists beyond the Earth and between celestial bodies. Outer space is not completely empty—it is a hard vacuum containing a low density of particles, predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, neutrinos, dust, and cosmic rays. The baseline temperature, as set by the background radiation from the Big Bang, is 2.7 kelvins (−270.45 °C; −454.81 °F). The plasma between galaxies accounts for about half of the baryonic (ordinary) matter in the universe; it has a number density of less than one hydrogen atom per cubic metre and a temperature of millions of kelvins; local concentrations of this plasma have condensed into stars and galaxies. Studies indicate that 90% of the mass in most galaxies is in an unknown form, called dark matter, which interacts with other matter through gravitational but not electromagnetic forces. Observations suggest that the majority of the mass-energy in the observable universe is a poorly understood vacuum energy of space, which astronomers label dark energy. Intergalactic space takes up most of the volume of the universe, but even galaxies and star systems consist almost entirely of empty space.

Outer space does not begin at a definite altitude above the Earth's surface. However, the Kármán line, an altitude of 100 km (62 mi) above sea level, is conventionally used as the start of outer space in space treaties and for aerospace records keeping. The framework for international space law was established by the Outer Space Treaty, which entered into force on 10 October 1967. This treaty precludes any claims of national sovereignty and permits all states to freely explore outer space. Despite the drafting of UN resolutions for the peaceful uses of outer space, anti-satellite weapons have been tested in Earth orbit.

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In the news

18 March 2019 – Kamchatka superbolide
NASA reports that it has detected a huge meteor explosion in Earth's atmosphere on December 18, 2018, above Russia's Kamchatka Peninsula. The explosion went largely unnoticed due to its location. The explosion, which was ten times more powerful than the atomic bomb dropped on Hiroshima, was the second largest of its kind in 30 years. (BBC)
3 March 2019 – 2019 in spaceflight
SpaceX's unmanned spacecraft Dragon 2 successfully docks with the International Space Station (ISS) for the first time. (BBC) (NASA Spaceflight)
2 March 2019 – 2019 in spaceflight
SpaceX launches the first Crew Dragon spacecraft to the International Space Station as part of the Crew Dragon Demo-1 mission, with the first stage of its Falcon 9 launch vehicle making a successful landing on the drone ship Of Course I Still Love You. (The New York Times)
13 February 2019 – Exploration of Mars
The mission of NASA's Opportunity rover on Mars comes to an end. The rover stopped communicating in June 2018 after a Martian dust storm, and attempts to reestablish communications have not been successful. (NASA)
12 February 2019 –
Retired NASA astronaut Mark Kelly announces that he will run for the 2020 United States Senate special election in Arizona. (CNN)
11 February 2019 –
Mars One, a private Dutch organization that had claimed it would send humans on a one-way trip to Mars starting in 2024, releases a statement saying it has been declared bankrupt. (CBC)


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