Exciting new technology that will aide astronomers in locating and observing exoplanets has just been installed on the European Southern Observatory’s (ESO) Very Large Telescope (VLT). The Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument passed required European acceptance tests back in December 2013 before arriving at the Paranal Observatory in Chile. This revolutionary new instrument is expected to out perform any existing instruments as well as produce stunning views of circumstellar discs surrounding nearby stars. SPHERE will employ many advanced techniques in conjunction with one another.
The goal of SPHERE is to achieve the highest contrast for direct exoplanet imaging and is expected to far exceed its predecessor, NACO, which captured the first ever direct image of an exoplanet. SPHERE is an incredibly complex instrument, requiring advanced adaptive optics, coronagraph components as well as special detectors.
There are multiple techniques astronomers use to detect exoplanets – including measuring the radial velocity variations of the host star, looking for dips in the star’s brightness due to an exoplanet passing in front of it and even through direct imaging. Direct imaging is the most difficult method due to the close proximity of the planet to its star and host stars tend to outshine their orbiting planets. Even with the best conditions, star light completely engulfs the weak planet glow. That’s where SPHERE comes in, with a designed intended to achieve the highest contrast possible in the area surrounding a star.
First, SPHERE uses adaptive optics designed to correct for any effects due to the Earth’s atmosphere, and sharpening the image. Next, a coronagraph helps to further increase the contrast by blocking out the star’s light. Finally, a differential imaging technique is applied, highlighting color and polarization difference between the planet’s light and the star light. This technique is important because these subtle differences can often reveal an invisible exoplanet.
SPHERE is also capable of feats no other grand-based telescope can accomplish. Thanks to differential imaging, SPHERE will be able to peer through the foggy haze on places such as Titan, currently capable only with near-inrafred technologies. The light scattered by Titan’s haze is highly polarized, just like the blue light from our sky. SPHERE’s highly-sensitive polarimeters can record how strongly light is polarized and will employ this technique in its search for exoplanets.
During it’s first light testing, SPHERE observed several preliminary targets, testing out the instruments different modes. Astronomers were delighted to see one of the best images ever captured of the star HR 4796A and its surrounding dust ring. The image showed the dusty ring in great detail as well as proved how well SPHERE can suppress the star’s bright light.
This is just the beginning of SPHERE’s capabilities and the instrument will be available to astronomers for use later this year after further scientific verifications and testing.
So what does this all mean for us? Well exoplanets are all the rage these days. By making advancements in technologies, we are able to see further and further into the Universe as well as see surrounding stars and planets in greater detail. So far this year, we have discovered the first Earth-sized planet in a star’s habitable zone as well as discovered a new class of exoplanet – the mega-Earth. With the help of SPHERE we will likely see more of these types of discoveries and learn even more about the exoplanets we have already discovered. It’s very exciting to think of the planets we may have missed because we did not possess the technology capable of detecting them.