Although Jupiter is large as planets go, it would need to be about 75 times its current mass to ignite nuclear fusion in its core and become a star.

Key takeaways

  • Jupiter is the largest planet in our solar system but would need to be 75 times more massive to ignite nuclear fusion and become a star.
  • Galileo’s 1610 telescope observations revealed Jupiter’s four largest moons, changing our understanding of celestial bodies.
  • Jupiter is primarily made of hydrogen and helium with no solid surface, featuring layers of gas and liquid hydrogen.
  • NASA missions, including Voyager and Juno, have provided extensive data on Jupiter’s atmosphere, moons, and magnetic fields.
  • While some call Jupiter a “failed star,” it lacks the mass necessary to become even a brown dwarf, which requires at least 13 times its current mass.

Jupiter, a magnificent planet, dazzles everyone with a clear sky. Jupiter was called after the Roman state’s patron deity in accordance with Greek mythology, which linked it to the supreme god Zeus. However, when Galileo pointed his telescope aloft in 1610, Jupiter took on new significance. Galileo found the planet’s four major moons and made the first definite discovery of celestial motions centered on a body other than Earth.

JUPITER UP CLOSE. NASA’s Cassini spacecraft snapped this image of giant Jupiter when it flew past the planet in December 2000. This detailed global image shows features as small as 60 miles (97 kilometers) across. NASA/JPL

Long before spacecraft offered extensive exploration, astronomers recognized Jupiter as the largest planet in the solar system. The planet’s massive size – 88,846 miles (142,984 kilometers) near the equator — contains 2.5 times the mass of all other planets put together. Jupiter is now the solar system’s most prominent body after the Sun. The planet has so much volume that 1,321 Earths could fit inside it.

Jupiter is an excellent example of a gas giant planet. It has no solid surface and is made up of a small rocky core wrapped in a shell of metallic hydrogen, which is surrounding by liquid hydrogen, which is then blanketed by hydrogen gas. The atmosphere contains around 90% hydrogen and 10% helium.

Jupiter’s supremacy in the solar system has resulted in numerous spacecraft missions, beginning with Pioneer 10’s 1973 flyby. A year later, Pioneer 11 flew over the enormous planet. The twin flybys of NASA’s Voyagers in 1979, however, marked the beginning of comprehensive, close-up study of the massive planet.
Voyagers 1 and 2 significantly expanded our knowledge of Jupiter. They studied Jupiter’s moons, captured comprehensive photographs of its complicated atmosphere, and identified a faint pair of rings.

NASA’s Galileo spacecraft, which entered Jupiter orbit in 1995, provided scientists with another windfall. Even as it reached Jupiter in 1994, Galileo witnessed one of the solar system’s most spectacular collisions: Comet Shoemaker-Levy 9. Galileo sent a probe that crashed into Jupiter’s atmosphere. The probe sampled the atmosphere directly and returned a wealth of information before succumbing to severe pressure deep beneath Jupiter’s clouds. Galileo experienced the same fate when the mission ended in 2003.

NASA’s Juno spacecraft entered orbit above Jupiter to begin a new series of scientific studies. Juno allowed astronomers to precisely map Jupiter’s gravitational and magnetic fields, learn a lot about the planet’s cluster of polar cyclones, and reveal that the gas giant rotates like a solid body only under its turbulent cloud tops.

Jupiter’s size and structural similarities to brown dwarfs and tiny stars have prompted some to call it a “failed star.” They suggest that if the planet had formed with more mass, Jupiter would have sparked nuclear fusion, resulting in a double-star system. Life may never have evolved on Earth because the temperature would have been too high and the atmospheric parameters were incorrect.

JOVIAN TURBULENCE. True-color (left) and false-color mosaics show how eastward and westward bands of air between the planet’s equator and polar regions control Jupiter’s atmosphere. NASA/JPL

However, while Jupiter is a big planet, it would need to be 75 times its current mass to initiate nuclear fusion in its core and form a star. Astronomers have discovered other stars orbited by planets significantly more massive than Jupiter.

How about substellar brown dwarfs? Our largest planet is still no match for these “almost stars.” Brown dwarfs are defined by astronomers as bodies having a mass at least 13 times that of Jupiter. At this stage, deuterium, a hydrogen isotope, can fuse early in a brown dwarf’s life.

So, while Jupiter is a planetary giant, its mass is far from sufficient to classify it as a failed star.

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