In less than 30 years, humanity has discovered more than 4,000 exoplanets, and to celebrate the milestone, NASA created a map that puts that number into a more visual perspective.
The video assigns a sound and color to the method used to detect each planet, whether radial velocity, transit method, imaging, or microlensing. Watching these previously unknown celestial bodies blink into our observed existence makes for a deeply moving video about space exploration and discovery.
The first exoplanets—a world not in our own solar system but orbiting another star—was spotted in 1992 going round the pulsar PSR 1257+12.
In the 27 years since the first exoplanets were spotted,the rest of the discoveries came at a trickle, before a flood of new finds thanks to dedicated telescopes.
All are tracked in the known catalogue of exoplanets and often receive complex names to keep track of their identity.
But how have we discovered so many exoplanets so quickly? Well, we can thank the now-retired Kepler Telescope for a lot of the rapid growth. The number of planets found increased substantially once Kepler began helping in the search for exoplanets. Kepler would measure any dips in brightness in front of a star which may indicate the passing of a planet. It then analysed this signature to find out details of its atmosphere and size.
TESS took up the mantle of chief planet hunter following the demise of Kepler when it eventually died earlier this year as its fuel tank finally emptied.
NASA has just weeks ago discovered exoplanet L 98-59 tweeting: 'The tiniest exoplanet! 'Our NASA Transiting Exoplanet Survey Satellite mission discovered a world that's smaller than Earth and larger than Mars, orbiting a bright, cool, nearby star about 35 light-years away.'
New tech like the Kepler Telescope uses radial velocity which measures the movements and the color signature of a star.
Spectrographs are used to track the changes in color of the star and to see if it moves in a cyclical pattern (i.e.: days, weeks, or years) towards or away from Earth which indicate that a body is circling the star causing the star's patterned movement. The body is considered a planet if it has a dense, low mass.
Another method of discovering exoplanets is transit photometry. This measures the dimness of a star across regular intervals by observing how dim the star is as a planet in orbit passing between it and Earth. If the star dims in fixed or regular periods, then the chances that an exoplanet is in orbit are high.
Now that Kepler is retired, NASA's Hubble successor, the James Webb Telescope, will take over some of Kepler's responsibilities. The James Webb Telescope is set to reach orbit in 2021 where it will be able to find exoplanets and have the ability to discern whether the foreign planets would be able to sustain life.
Additionally, NASA's Transiting Exoplanet Survey Satellite (TESS) is also working to fill in Kepler's shoes by looking for new exoplanets. TESS has reportedly found more than 700 new exoplanets during just its first year in orbit.
Expect that 4,000 milestone to be eclipsed very soon.
WHAT IS THE KEPLER TELESCOPE?
The Kepler mission has spotted thousands of exoplanets since 2014, with 30 planets less than twice the size of Earth now known to orbit within the habitable zones of their stars. Launched from Cape Canaveral on March 7th 2009, the Kepler telescope has helped in the search for planets outside of the solar system. It captured its last ever image on September 25, 2018 and ran out of fuel five days later. When it was launched it weighed 2,320 lbs (1,052 kg) and is 15.4 feet long by 8.9 feet wide (4.7 m × 2.7 m). The satellite typically looks for 'Earth-like' planets, meaning they are rocky and orbit within the that orbit within the habitable or 'Goldilocks' zone of a star. In total, Kepler has found around 5,000 unconfirmed 'candidate' exoplanets, with a further 2,500 'confirmed' exoplanets that scientists have since shown to be real. While the mission has found thousands of exoplanets, five in particular have stuck out.
1) 'Earth 2.0'
In 2014 the telescope made one of its biggest discoveries when it spotted exoplanet Kepler-452b, dubbed 'Earth 2.0'. The object shares many characteristics with our planet despite sitting 1,400 light years away. It has a similar size orbit to Earth, receives roughly the same amount of sun light and has same length of year. Experts still aren't sure whether the planet hosts life, but say if plants were transferred there, they would likely survive.
2) The first planet found to orbit two stars
Kepler found a planet that orbits two stars, known as a binary star system, in 2011. The system, known as Kepler-16b, is roughly 200 light years from Earth. Experts compared the system to the famous 'double-sunset' pictured on Luke Skywalker's home planet Tatooine in 'Star Wars: A New Hope'.
3) Finding the first habitable planet outside of the solar system
Scientists found Kepler-22b in 2011, the first habitable planet found by astronomers outside of the solar system. The habitable super-Earth appears to be a large, rocky planet with a surface temperature of about 72°F (22°C), similar to a spring day on Earth.
4) Discovering a 'super-Earth'
The telescope found its first 'super-Earth' in April 2017, a huge planet called LHS 1140b. It orbits a red dwarf star around 40 million light years away, and scientists think it holds giant oceans of magma.
5) Finding the 'Trappist-1' star system
The Trappist-1 star system, which hosts a record seven Earth-like planets, was one of the biggest discoveries of 2017. Each of the planets, which orbit a dwarf star just 39 million light years, likely holds water at its surface. Three of the planets have such good conditions that scientists say life may have already evolved on them.
How does Kepler discover planets?
The telescope has an incredibly sensitive instrument known as a photometer that detects the slightest changes in light emitted from stars. It tracks 100,000 stars simultaneously, looking for telltale drops in light intensity that indicate an orbiting planet passing between the satellite and its distant target. When a planet passes in front of a star as viewed from Earth, the event is called a 'transit'. Tiny dips in the brightness of a star during a transit can help scientists determine the orbit and size of the planet, as well as the size of the star. Based on these calculations, scientists can determine whether the planet sits in the star's 'habitable zone', and therefore whether it might host the conditions for alien life to grow.