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Comparison of the night sky with the night sky of a hypothetical planet within the Milky Way 10 billion years ago, at an age of about 3.6 billion years and 5 billion years before the Sun formed. [261] Globular clusters are among the oldest objects in the Milky Way, which thus set a lower limit on the age of the Milky Way.
The Sun is part of one of the Milky Way's outer spiral arms, known as the Orion–Cygnus Arm or Local Spur. [270] [271] It is a member of the thin disk population of stars orbiting close to the galactic plane. [272] Its speed around the center of the Milky Way is about 220 km/s, so that it completes one revolution every 240 million years. [269]
From the total of 4,949 stars known to have exoplanets (as of July 24, 2024), there are a total of 1007 known multiplanetary systems, [1] or stars with at least two confirmed planets, beyond the Solar System. This list includes systems with at least three confirmed planets or two confirmed planets where additional candidates have been proposed.
There are eight planets within the Solar System; planets outside of the solar system are also known as exoplanets. Artist's concept of the potentially habitable exoplanet Kepler-186f. As of 19 December 2024, there are 5,811 confirmed exoplanets in 4,340 planetary systems, with 973 systems having more than one planet. [1]
This star, known as HD 110067, may have even more planets. The six found so far are roughly two to three times the size of Earth, but with densities closer to the gas giants in our own solar system.
90% of planets with known distances are within about 2000 light years of Earth, as of July 2014. The Milky Way is 100,000 light-years across, but 90% of planets with known distances are within about 2000 light years of Earth, as of July 2014. One method that can detect planets much further away is microlensing.
There could be 300 million planets in the Milky Way Galaxy that support life, according to NASA estimates. The planets are all rocky, similar in size to Earth and orbit in the “Goldilocks zone ...
As many as 15% of them could have Earth-sized planets in the habitable zones. [6] On November 4, 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarf stars within the Milky Way galaxy.