Exoplanets

Astronomers Try to Directly Observe Epsilon Eridani b. No Luck. Maybe Webb Can Find it?

Back in the year 2000, Epsilon Eridani b was discovered. It is a Jupiter-like exoplanet 10.5 light years away but it has taken decades of observations to learn more about the planet. One thing that remains a mystery is it’s orbit which, until recently has been unknown. There has never been a direct image of the planet either, so now, it’s the turn of JWST to see what it can do. 

The concept of exoplanets has been around for a few decades now but the first confirmed discovery occurred in 1992. Astronomers at the Arecibo Observatory discovered a number of Earth-mass planets orbiting around the pulsar PSR B1257+12. Since then, over 5,000 planets have been discovered around other star systems. Astronomers use a number of Studying them once they have been confirmed requires more direct study.

The Arecibo Radio Telescope Credit: UCF

One such exoplanet is known as Epsilon Eridani b which also goes by the name AEgir. Exoplanets are named after their host star (in this case Epsilon Eridani) and the letter ‘b’ designates that it was the first exoplanet discovered around that star. The next to be discovered would be ‘c’ and so on although in the case of Epsilon Eridani it is the only planet. It is thought to orbit around the star at a distance of 3.5 astronomical units (where 1 AU is the average distance between the Sun and Earth) and takes about 7.6 years to complete one orbit.  

One area of exoplanet study that has been lacking over recent years is the study of the surface and atmospheric conditions, in particular a study into their potential habitability. Cold exoplanets seem to have received the least study due to their faint appearance in the mid-infrared wavelength. Due to the properties of these cold planets, direct imaging techniques are required and must employ high contrast processes.  To date, no instrument has been capable of delivering. 

The crux of the challenge is that the cold exoplanets have no intrinsic energy source and only re-use the radiation from the host star. Their luminosity is based upon their size and distance from host star but usually the radiation is at the same wavelength as the emission from the star. To address this challenge, a paper has been published in ‘Astronomy & Astrophysics’ journal by a team led by C. Tschudi from the Institute for Particle Physics and Astrophysics in Switzerland.

The paper provides an insight into high contrast observations of Epsilon Eridani taken in 20198 and 2020 using the VLT (Very Large Telescope). Using the SPHERE instrument (Spectro-Polarimetric High-contrast Exoplanet Research) as part of the ongoing RefPlanets programme, the team were able to use polarising technology to search for signals from the planet. 

In mid-August 2010 ESO Photo Ambassador Yuri Beletsky snapped this amazing photo at ESO’s Paranal Observatory. A group of astronomers were observing the centre of the Milky Way using the laser guide star facility at Yepun, one of the four Unit Telescopes of the Very Large Telescope (VLT). Yepun’s laser beam crosses the majestic southern sky and creates an artificial star at an altitude of 90 km high in the Earth’s mesosphere. The Laser Guide Star (LGS) is part of the VLT’s adaptive optics system and is used as a reference to correct the blurring effect of the atmosphere on images. The colour of the laser is precisely tuned to energise a layer of sodium atoms found in one of the upper layers of the atmosphere — one can recognise the familiar colour of sodium street lamps in the colour of the laser. This layer of sodium atoms is thought to be a leftover from meteorites entering the Earth’s atmosphere. When excited by the light from the laser, the atoms start glowing, forming a small bright spot that can be used as an artificial reference star for the adaptive optics. Using this technique, astronomers can obtain sharper observations. For example, when looking towards the centre of our Milky Way, researchers can better monitor the galactic core, where a central supermassive black hole, surrounded by closely orbiting stars, is swallowing gas and dust. The photo, which was chosen as Astronomy Picture of the Day for 6 September 2010 and Wikimedia Picture of the Year 2010, was taken with a wide-angle lens and covers about 180 degrees of the sky.   This image is available as a mounted image in the ESOshop.   #L

Unfortunately the team were unable to successfully detect Epsilon Eridani b despite a total exposure time of 38.5 hours spread over 12 nights. This was however, useful at understanding the limitations of the instrumentation. What next then? Well it looks like we have to wait for a next generation of infrared sensitive instruments to peer deeper into the system. The James Webb telescope is a fine example of such a device and, once it turns its sights onto Epsilon Eridani maybe the mysteries will finally be resolved.

Source : SPHERE RefPlanets: Search for ? Eridani b and warm dust

Mark Thompson

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