Exoplanets: Weird Worlds
Exoplanets: Weird Worlds

Exoplanets: Weird Worlds

OAS Society Talk ~ August 2019 ~ Prof. Chris Lintott FRAS

Being on the society committee can have its golden moments and for me there was one at this meeting.  We have a growing inclusive membership, supplemented at this meeting by some visitors from another society, and from the start the meeting just buzzed. Watching everyone mixing, getting involved or just relishing being an amateur astronomer and getting together across a range of ages and skills is what the society seeks to achieve.  Be clear I’m not taking all the credit here.  We have a good, engaged Committee with us all ably led by our Chair Roy Peters.  It’s just good seeing all the ‘behind the scenes’ efforts come together.  Not forgetting that homemade biscuits and cakes at the tea break added an extra touch!

Having a celebrity speaker at a meeting does give it an extra frisson of excitement, of course, and Prof. Chris Lintott¹ had been greatly expected.  He is Professor of Astrophysics/Citizen Science Lead at the University of Oxford, a Fellow of the Royal Astronomical Society, author and broadcaster; most famously as the primary presenter for the BBC television series ‘Sky at Night’.

Chris is charming and having arrived early took the time to mix with members as they required, signing autographs and smiling for photos as needed.  His easy going general manner is much reflected in his presentation style but backed by a prodigious knowledge of the astronomy subject, which led to a wonderful lecture. Like many good communicators he made it look easy but, of course, it is not.  He was very warmly applauded by the audience both before and after his presentation and rightly so.

Exoplanets² (planets that orbit a star outside of the Solar System), so it seems, are actually not too hard to find.  Much to the chagrin of the Kepler Space Telescope team who had their bids for funding refused a number times ~ and the launch delayed from 2006 to 2009 ~ only to find that once launched, the exoplanets began to appear in great numbers; numbering 4,043 at the time of writing.  Currently, something like 10 new exoplanets a week are being added to the list.  However, being so numerous, generally none are specifically named but rather numbered.  In short, we are now sure that exoplanets are far more numerous than stars, exponentially adding to the total number of galaxy celestial bodies.

Reminding us of how the Solar System formed, Chris ranged across a number of exoplanet discoveries and how, what began as a search for Earth like bodies, became a stream of discoveries of worlds that were weird in relation to Earth; thus the title of the talk.

Very few exoplanets have been noted as near Earth mass ~ around 1.1/1.2 times mass; see Teegarden’s Star³ ~ , with most discovered exoplanets being far from similar with many being much larger than Earth; quite often gas giant like.  This, however, probably being because larger exoplanets are easier to find, given the galactic distances to the host stars, and the discovery methods.  By far the highest number of exoplanet discoveries has been via the ‘Transit Method’ with the ‘Radial Velocity’ method the next highest.  Planets with an orbit greater than 4 years may also not be seen as the survey period may expire before they can be noted; so many new exoplanets are also close to their host star.

Chris highlighted one or two star system examples and then included the potential of the exoplanet being within the ‘habitable zone’ of the host star and the potentials for life that may exist as a result.  Perhaps something on an exoplanet out there is looking at exoplanet Earth?

Segueing across the topic, Chris discussed the impact of exoplanet discoveries upon the current theory of Solar System planetary evolution.  So where our Solar System has smaller rocky planets nearest the star, with planets being gas giants, then ice giants as they get farther away, this does not seem to be generally applicable across the galaxy with some gas giants existing much closer to the star than thought possible, and large and smaller planets at mixed distances from their stars.

One highlighted star system, K2-138 has a number of exoplanets with orbital resonance as the exoplanet distance gets further away from the star.  So that where planet ‘a’ orbits 3 times, planet ‘b’ orbits 2 times; but when planet ‘b’ orbits 3 times, planet ‘c’ orbits 2 times ~ the resonance continuing outwards. Interestingly, the identified outer planet is much further out than some of the inner planets but when the resonance is calculated, it indicates that two other planets should be in the space between! 

Of course, remembering that most stars are double stars, exoplanets have been found orbiting double stars, even a double star within a quadruple star system.  Circumstances can be very complicated!  Indeed, Chris, perhaps with some ‘tongue in cheek’ intent, threw the arrival of ‘Oumuamua into the mix and whether these interstellar visitors could impact upon the planetary formation dynamic.  ‘Oumuamua had been the first such visitor to be confirmed but, given the difficulty in spotting and identifying these fast moving interstellar objects, the potential for many more to be around (perhaps up to 20 within the orbit of the planets at any one time) added to the mix of possible factors.

Launched in 2018, ‘TESS’, the Transiting Exoplanet Survey Satellite, will expand on Kepler’s work and a target of 20,000 exoplanets could be attained. Looking ahead, ‘PLATO’, the PLAnetary Transits and Oscillations of stars space telescope will further enhance exoplanet understanding.  The next ten years will be very interesting!

One snippet of information worth remembering is that it may become possible to also see moons around an exoplanet at some time, even a moon around a moon; the official name of which is ‘Moonmoons’.  Bear that fact in mind for the Christmas quiz (although my research has shown that these may also be called exomoons or submoons)!

Of course, Chris is also known for his ‘Galaxy Zoo’⁴ initiative involving amateur astronomers in identifying galaxy types and he wants to get similar amateur astronomer help with exoplanet hunting TESS⁵.  So perhaps you will be interested in assisting the search for unusual worlds?

To conclude, Chris also has a new book out soon titled ‘Crowd and the Cosmos: Adventures in the Zooniverse’, a personal account of his web-based Zooniverse project.  Perhaps one for a birthday or the Christmas stocking?

Hugh Alford FRAS

¹: ~ https://www2.physics.ox.ac.uk/contacts/people/lintott

²: ~ https://exoplanetarchive.ipac.caltech.edu/docs/counts_detail.html

³: ~ https://en.wikipedia.org/wiki/Teegarden%27s_Star

⁴: ~ https://www.zooniverse.org/projects/zookeeper/galaxy-zoo/

⁵: ~ https://www.zooniverse.org/projects/ianc2/exoplanet-explorers