Planets Orbiting Distant Stars

An ‘exoplanet’ is a planet beyond our solar system which orbits a star in the Milky Way galaxy. For a long time, it was thought other stars must have planets of their own, but there was no way to detect them. It wasn’t until 1992 the first exoplanet was confirmed. Gradually more were discovered. Then in 2009, the Kepler Space Telescope was launched, which discovered thousands and confirmed exoplanets are common throughout the Milky Way!


Wobbling Stars Betray Their Planets

Despite claims throughout history, it wasn’t until early 1992 that two scientists using the Arecibo Radio Observatory discovered the first confirmed exoplanets around a pulsar (a star which remains after a supernova).

The first exoplanet to be discovered around a ‘main-sequence’ type star similar to our Sun was in 1995!  This was a large gas giant (half the size of Jupiter) that tugged so hard on its parent star, during its rapid four-day orbit, that the star’s wobbling was observed by an Earth-based telescope. These regular patterns in a stars radial velocity became the favoured method of early exoplanet hunters and represented the equivalent of the ‘exoplanet low hanging fruit’!

The race by other ground-based facilities joined the search; gradually the tally of confirmed exoplanets rose into the low hundreds until a new space telescope and planet-hunting method burst onto the scene.

Starring Contest: Waiting For Stars To Blink!

The NASA Kepler Space Telescope primary goal was to find Earth-like exoplanets that orbit main-sequence stars in the habitable zone. It wouldn’t take long before Kepler found one and would take science from only a handful of exoplanets to more than 3,700 (with over 4,500 candidate exoplanets awaiting confirmation) in a few short years.

Kepler hunts exoplanets by starring at a fixed small patch of sky, waiting to catch tiny dips in the light coming from individual stars, caused by their planets transits. With only a few small sections of our Milky Way galaxy surveyed, it has been estimated at least one planet orbits each star in the Milky Way. This means there are likely a trillion planets in our galaxy alone, many of them in Earth’s size range.

Known Exoplanet Facts And Records!

  • As of late 2018 (latest figures here), there are 3,800 exoplanets in over 2,800 star systems
  • 621 star systems having more than one planet
  • Kepler 16b is the first exoplanet detected orbiting two stars, 200 light-years from Earth - Just like the planet Tatooine from the movie Star Wars!
  • It has been estimated that there are possibly 10 billion potentially habitable Earth-sized planets orbiting Sun-like stars in the Milky Way galaxy
  • The smallest known exoplanet is called Draugr (twice the mass of the Moon)
  • The largest exoplanet is about 30 times the mass of Jupiter, although it might be too large to be a planet and in fact be a brown dwarf
  • Some exoplanets orbit so close to their star that they take only a few hours to go around it. Others are so far away that they take thousands of years to complete an orbit
  • The nearest exoplanet to us is Proxima Centauri b, 4.2 light-years from Earth and orbits the star closest to the Sun
  • The most distant known planets are discovered are approximately 27,700 light-years from the Sun

Future Exoplanet Hunting

Up to now, the majority of exoplanets detected have been observed via indirect methods; exoplanet transits or measuring a stars wobble. The future will involve direct imaging of the exoplanets (and possibly discovering extragalactic planets!), but this will require new technology and advanced spacecraft such as the new James Webb Space Telescope.

As the space-based technology increases we’re likely to eventually be able to capture actual images of distant exoplanets and not just the large ‘gas giants’, but successively smaller and smaller exoplanets. Maybe even an Earth-like exoplanet with a surface of liquid water and possibly extraterrestrial life!

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