New Tool Allows Astronomers to Directly Observe Exoplanets

CHARIS detection of the three planets orbiting HR8799. Image: Kasdin, et al./Princeton
CHARIS detection of the three planets orbiting HR8799. Image: Kasdin, et al./Princeton
In the two decades since the discovery of the first exoplanet in 1995, another 3500 exoplanets have been found ranging in size from double Earth’s moon to almost twice the size of Jupiter. While this “exoplanet bonanza” is undoubtedly exciting, astronomers know remarkably little about the exoplanets being discovered.

By Daniel Oberhaus | MOTHERBOARD

However our exoplanet ignorance may soon be over thanks to CHARIS, a new instrument for Hawaii’s Subaru telescope which recently allowed astronomers to directly observe large exoplanets 50-light years away. By isolating light reflecting off of these exoplanets, CHARIS will provide insight into the planets’ size, age, and atmosphere—details that were difficult if not impossible to obtain with previous methods of exoplanet observation.

Prior to the early 2000s, astronomers seeking exoplanets almost exclusively relied on Doppler spectroscopy for their discoveries. This method indirectly detects exoplanets by measuring shifts in a star’s light spectrum, which slightly changes as the star responds to the gravitational pull of an orbiting planet. To date, this method accounts for roughly 30 percent of all exoplanet discoveries, but gives astronomers almost no information about the planet itself beyond its minimum mass.

Over the last decade, the exoplanet detection method à la mode has become transit photometry. This method involves measuring changes in a star’s brightness—when an exoplanet passes in front of its host star, the brightness of that star drops for the observer on Earth. This method reveals the size of the planet, which can be combined with measurements of the planet’s mass via Doppler spectroscopy to determine the density of the planet and thus some aspects of its physical structure.

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