Kepler space telescope
To date, a huge majority of exoplanets we know of have been discovered by the Kepler space telescope team. Launched on 7 March 2009, Kepler sits in an Earth-trailing orbit around the Sun. Before its launch it was considered possible that planets in the universe were rare. Now, however, its thought that almost every star plays host to at least one planet.
The telescope uses photometry to simultaneously observe thousands of stars. It watches for dips in the brightness of these stars as a planet passes in front, known as a transit, and measuring three of these transits confirms the planet’s existence as well as its size owing to the amount the star dims. The orbital period can also be calculated from multiple planets, and ultimately its distance from its host star can be determined. Scientists have been poring over Kepler’s data looking in earnest for the holy grail of planet hunting, a world similar in size to our own residing in the habitable zone of its star.
Of the hundreds of planets Kepler has found, though, it was the very first that elicited the most excitement. “The most exciting planet discovery was probably the very first one, when we actually looked at a light curve that came down very early on in the mission almost in real time and you could see the transit by eye,” said Kepler project scientist Dr Steve Howell. “It was a planet that had been discovered before Kepler had launched so we knew it was there. It was a really big planet, and, boy, if we couldn’t have found that we were in real trouble.”
Aside from the early excitement that confirmed Kepler was in full working order, there have been a number of recent discoveries that have been just as interesting. “In the last few months we’ve found the planets Kepler-69 and Kepler-62 around stars kind of like the Sun,” said Dr Howell. “They are planets that aren’t much bigger than the Earth and these planets are in their star’s habitable zone. They’re probably rocky, or at least very water-rich planets. They are very exciting, they are really getting us towards the true Earth-analogue kind of planet.”
At the time of writing a fault with one of Kepler’s reaction wheels has left the telescope unable to do the precise positional movements needed to perform photometry and find new planets. However, the team are confident that even if the telescope can’t continue hunting for planets, there is still plenty of data to be analysed and, even then, it leaves a lasting legacy that has led to the development of other planet-hunting telescopes.
“Kepler’s been critically important,” said Dr Howell. “I think that if Kepler had not been launched, other planet-hunting telescopes would have never even been thought about, and certainly wouldn’t have been selected [for development]. The chances of these missions going ahead have increased because planets are such a hot topic these days.”