How Quickly Can a Planet Orbit Its Star?

Astronomers have identified an exoplanet that orbits its star (located in the constellation Hercules) in just 16 hours - the shortest orbit ever discovered.
Astronomers have identified an exoplanet that orbits its star (located in the constellation Hercules) in just 16 hours - the shortest orbit ever discovered.

In our solar system, the planet Mercury has the fastest orbit around the Sun, with an orbital speed of 107,082 miles per hour (47.87 km/sec), so that it completes its trek every 88 days, compared to Earth's 365 days. In fact, Mercury is so fleet-footed that it’s named after the messenger god of Roman mythology. But there are many other planetary systems in the vastness of space, with planets of all shapes and sizes spiraling around their stars.

Recently, astronomers identified TOI-2109b, a gaseous mass 855 light-years away that orbits its star in the constellation Hercules in only 16 hours, making that planet’s orbital period the shortest of any known gas giant.

Because the planet’s orbit is so tight, it’s also very, very hot – its dayside temperature is estimated to be close to 6,000 degrees Fahrenheit (3,300 degrees Celsius).

That's one "hot Jupiter":

  • Astronomers think TOI-2109b is in “orbital decay,” and that it will soon spiral into its star. The discovery, made by NASA’s Transiting Exoplanet Survey Satellite (TESS), helps explain how planets behave as they are swallowed up by their stars.

  • Using optical and infrared wavelengths, the team determined that TOI-2109b is 35 percent larger than Jupiter, and extremely close to its star – about 1.5 million miles (2.4 million km) away. By comparison, Mercury is an average of 36 million miles (58 million km) from our Sun.

  • TOI-2109b belongs to a category containing around 400 exoplanets that scientists refer to as "hot Jupiters." These planets are around the size of Jupiter but orbit their stars much more quickly. "From the beginning of exoplanetary science, hot Jupiters have been seen as oddballs," says scientist Avi Shporer, an exoplanet specialist at the Massachusetts Institute of Technology.

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    • Astronomers have identified an exoplanet that orbits its star (located in the constellation Hercules) in just 16 hours - the shortest orbit ever discovered.
      By: Internet Archive Book Images
      Astronomers have identified an exoplanet that orbits its star (located in the constellation Hercules) in just 16 hours - the shortest orbit ever discovered.