The hunt for exoplanets – worlds beyond our own solar system – has progressed in leaps and bounds since the first detection in 1995. To date over 3700 planets of all shapes and sizes in a huge variety of planetary systems have been discovered, and the number keeps on growing. Instruments and techniques have become advanced enough to detect the tiniest of signals, not only of planets orbiting distant suns, but maybe even moons orbiting those planets. Yes, exomoons! Earlier this month researchers announced evidence based on Kepler and Hubble telescope observations that could indicate a moon around a gas giant planet 8000 light years away, although further observations are needed to confirm this detection. How amazing would that be?!
The star of the exoplanet hunt has been the Kepler Space Telescope, launched in 2009, with over 2600 planet discoveries to date. So the recent news that its useful life is ending - it is running out of fuel, and appears to be losing the ability to point precisely – may seem to signal the end of an era.
In fact, on the contrary, the business of hunting for alien worlds has taken a great step forward this year, with the launch in June 2018 of NASA’s Transiting Exoplanet Survey Satellite (TESS). Like Kepler, it will use the transit system to find planets, looking for regularly repeating dips in the brightness of a star indicating an object passing in front of it at regular intervals. But unlike Kepler, which targeted distant Sun-like stars, TESS will concentrate on much brighter and closer stars, which gives a clear advantage for follow-up analysis of results by other telescopes, both space- and earth-based. TESS has already released its first data-set of 73 ‘objects of interest’ for astronomers to observe in more detail, and no doubt there are many exciting discoveries to come.
Wobbly Stars
Another method of identifying exoplanets is by measuring the apparent ‘wobble’ of a star caused by a planet’s gravitational pull as it orbits. One of the most successful exoplanet-finder to use this method is earth-based: the HARPS instrument (High Accuracy Radial Velocity Planet Scanner) on the 3.6 m telescope at ESO’s La Silla observatory in Chile. It has been particularly successful in detecting planets smaller than Neptune, and its many achievements include the detection of an earth-sized planet in the habitable zone around our nearest neighbour, Proxima Centauri, about 4 light years distant. However, it is unlikely to host life as its closeness to its host star leave it extremely exposed to radiation and flare activity.
The ‘Red Dots’ project is continuing the hunt for planetary neighbours, using HARPS to also target two other nearby stars less than 10 light years away. Unlike TESS’s target stars, these are dim red dwarfs – being much smaller and cooler, the conditions for planetary formation there are very different. This type of star is believed to be by far the most common in our galaxy, but due to their dimness they are difficult to observe, so observing the systems around our nearest neighbours is perhaps the only way to improve our understanding of likely planetary systems around red dwarfs.
Baby planet
Another ground-breaking exoplanet detection was recently made using another ESO ground-based instrument. In July this year researchers using the SPHERE high-contrast imager at the Very Large Telescope (VLT), published the first clear image of a young planet forming in the primordial dust disc around a star. As you can see in this image, the baby planet carves a clear path through the dust from which it has formed. What an exciting insight into how planets are born!
https://www.nasa.gov/press-release/astronomers-find-first-evidence-of-possible-moon-outside-our-solar-system
https://www.nasa.gov/feature/goddard/2018/nasa-s-tess-shares-first-science-image-in-hunt-to-find-new-worlds
https://reddots.space/goals/
https://www.eso.org/public/news/eso1821/ First Confirmed Image of Newborn Planet Caught with ESO’s VLT
1. NASA Goddard https://www.youtube.com/watch?time_continue=22&v=Q8QFyOaTdZk
2. ESO/M. Kornmesser https://www.eso.org/public/images/eso1629e/
3. ESO/A. Müller et al. https://www.eso.org/public/images/eso1821a/