EXOPLANETS – PART 1
When was the first exoplanet discovered?
An exoplanet is defined as any planet beyond our solar system. The majority orbit other stars, but there are a few free-floating exoplanets (called rogue planets), which orbit the galactic centre and are untethered to any star.
In 2019 Michael Mayor & Didier Queloz were awarded half the Nobel Prize in physics for their discovery of the exoplanet 51 Pegasi b in 1995. (The other half of the split award went to James Peebles “for theoretical discoveries in physical cosmology.”)
Queloz & Mayor
Before going further, it might be best to explain how exoplanets are named. Exoplanets are given their star’s name followed by a lowercase letter, starting with b for the first planet, c for the second and so on. Hence, from its name, 51 Pegasi b, the planet they discovered, orbits the star 51 Pegasi. For a more complete example, if 3 planets were found orbiting Canopus they would be named Canopus b, Canopus c, and Canopus d. The letters are assigned in the order of discovery, not their closeness to the star.
But a question remains, was the identification of 51 Pegasi b in 1995 actually the first discovered
exoplanet?
The answer is a pretty resounding no.
Technically, the honour for the first discovery of an exoplanet belongs to a team led by astronomer David Latham. In 1989, they identified an object orbiting a star 126 light-years away in the constellation Coma Berenices, near the zodiac sign of Leo.
Its correct name is HD 114762 b, but as this is quite a mouthful, it is often simply referred to as “Latham’s planet”. It is at least 11 times more massive than Jupiter and orbits its star as close as Mercury does our sun. Many astronomers thought it was actually a brown dwarf (a sort of failed star that didn’t get massive enough to fully ignite), rather than a planet. However, its status as an exoplanet was confirmed in 2012
In 1992, astronomers Aleksander Wolszczan and Dale Frail were the first in history to announce and confirm the existence of planets outside our solar system. The pair of planets, nicknamed Poltergeist and Phobetor, orbit around a rapidly spinning star, known as a pulsar, 2,300 light-years away from us.
Pulsars are the remnants of supernovae and emit radio waves in an extremely regular way as they spin. It was via alterations to their radio emissions that these 2 planets were discovered. A further 2 planets were discovered via the same technique prior to 1995.
Our count is now 5 exoplanets prior to 1995.
Artist impression of 51 Pegasi b
The main reason that Mayor & Queloz got the gong is that they had pioneered a new, reliable method of finding exoplanets. Their method is called Radial Velocity measurement (RV for short) which is a way of measuring a star’s wobble as the planet orbits it.
In next week’s article I’ll be looking at the 6 different methods that have been used to find exoplanets.
