Discovering a habitable world outside the Solar System has been a goal of many astronomers and enthusiasts. Thanks to powerful Earth based telescopes and space telescopes like Hubble and Spitzer, we started detecting exoplanets in the early 1990s. The first method used was Radial Velocity, and most recently the Transit Photometry method. Until recently it was nearly impossible to directly image a planet to due to the brightness of the parent star.
The earliest confirmed exoplanets were found around pulsars (very unlikely places to find planets due to the radiation pulsars give off.) The first being PSR B1257+12 discovered in 1992, which is orbited by three planets. 51 Pegasi B was the first exoplanet found orbiting a Main Sequence star like our own Sun in 1995. The planet was the first of the hot Jupiters, large gas giants orbiting very close to their stars.
Radial Velocity (also known as Doppler spectroscopy) was the method used to detect these early exoplanets. This process involves observing the stars spectra as its planet or planets move around a common center of mass. This Doppler shift shows as blue when the star is moving towards Earth, and red when it moves away. The vast majority of exoplanets have been discovered using this method.
Transit Photometry is a second common way of detecting exoplanets. This method measures the dip in a stars brightness as a planet passes in front of it. This also allows astronomers to detect the makeup of the planet’s atmosphere by measuring what light is being blocked from the star’s spectra. Discovered in 1999 exoplanet HD 209458 b (also a hot Jupiter) was the first planet to be detected by the Transit method in 2001, using Hubble telescope’s Space Telescope Imaging Spectrograph instrument. The only drawback to this method is a planet has to pass in front of a star as it faces earth, so planets with long orbital periods would take a long time to detect. The Kepler telescope was launched in 2009, specifically for searching for Earth sized exoplanets, and has confirmed many of the exoplanets discovered using the Transit method.
Direct imaging is the most difficult method at the moment. Due to the brightness of a star it’s very difficult to detect the light (especially visible light) a planet gives off. The first exoplanet to be detected in this manner is controversial, some astronomers believed the found one orbiting brown dwarf 2M1207 (brown dwarfs are failed stars) , other astronomers don’t think what was found is another planet. First confirmed planet found using direct imaging is Fomalhaut b (nicknamed Eye of Sauron). Fomalhaut is a very young star (440 million years) most likely still in early formation as suggested by the dust that surrounds it.
While telescopes like Spitzer can directly image planets, they do so using infrared light. Telescope’s like James Webb (Hubble’s much bigger and more powerful cousin) and WFIRST (Another infrared telescope which will have a field view 100 times wider than the infrared instrument Hubble uses.) will give us more detailed views of exoplanets. Unfortunately the Webb won’t be put into orbit until 2018 and WFIRST sometime in the mid-2020s. Until then we have CHARIS.
CHARIS (Coronagraphic High Angular Resolution Imaging Spectrograph) is an spectrograph instrument used on the Subaru Telescope at Mauna Kea, Hawaii. Designed and built by a team of Princeton researches led by N. Jeremy Kasdin, CHARIS will allow direct imaging of light reflected from planets. It will also be able to detect the mass, temperature and age of the exoplanets, by analyzing the planet’s spectra. When the team used it on star HR8799, it took an image of three planet orbiting the star. In February of next year, CHARIS will be opened up for science to everyone.
Since the discovery of the first exoplanet, over 2000 planets have been confirmed. With CHARIS and soon the Jason Webb and WFIRST, that number will increase. With advancing instruments and telescopes like these we will get more detailed images of planets orbiting other stars. Hot Jupiters orbiting their stars, at break neck speeds. Super earth’s and maybe even worlds teeming with life.