Extra-solar planets come in all sizes - from dinky rocky worlds that measure up to Mercury to massive gas giants that would dwarf Jupiter. Exoplanet hunters have developed a sophisticated array of telescopes and techniques to detect this multitude of exoplanetary girths, but we are now on the verge of potentially detecting exoplanets of different shapes.
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Exoplanets orbit many types of star, but perhaps one of the more exciting targets are red dwarfs, the most abundant category of star in our galaxy.
In our epic hunt for habitable exoplanets - i.e. worlds that orbit their star in the habitable zone, the distance at which its not too hot and not too cold for liquid water to persist on a planet's rocky surface - astronomers have found that red dwarfs hold huge potential. As they are cooler and smaller than our sun, red dwarfs' habitable zones are more compact. This means any habitable world in tow will orbit their red dwarf host closer and faster. This orbital attribute is a bonus as there will be more opportunities for telescopes to detect transit events, as the exoplanet passes in front of its star, slightly blocking some sunlight from view.
Because of their lightweight mass, red dwarfs are also ancient stars. As they are so old, there are more possibilities for stable planetary systems that could remain habitable for aeons. The longer the period of habitability, the longer hypothetical lifeforms may have evolved, possibly emerging as what we would consider to be intelligent life.
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Of course, red dwarfs come with their setbacks that ensure life-giving habitable worlds aren't without their challenges. Red dwarfs are known to be tempestuous little stars, kicking off powerful stellar flares that would likely irradiate any nearby world. Also, their habitable zones would be so compact that any world within that orbit will be tidally locked with the star.
Tidal locking means that one side of the exoplanet, whether it's a small rocky world or a gas giant, will be continuously facing the star - one hemisphere would be in constant "daylight" and the farside in constant "night." This tough tidal environment could also have a rather bizarre impact on that planet's shape; it could be squished like an egg.
In new research published in the journal Monthly Notices of the Royal Astronomical Society, researchers from George Mason University, Va., focus on how exoplanet-hunting efforts could detect significant tidal distortions in gas giant worlds orbiting close to red dwarf stars and how that relates to smaller habitable planets.
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Understanding the shapes of exoplanets orbiting close to their host stars has a practical purpose - tidal distortion of an exoplanet can lead to underestimations of that planet's radius, therefore leading to overestimations of its density. When studying exoplanets tens to hundreds of light-years away, these measurement uncertainties can seriously impact our understanding of exoplanetary characteristics. Gaining an insight to the exoplanet's distorted shape could also glean new insights to its structure.
"Imagine taking a planet like the Earth or Mars, placing it near a cool red star and stretching it out," said astrophysicist Prabal Saxena, lead researcher of this study. "Analyzing the new shape alone will tell us a lot about the otherwise impossible to see internal structure of the planet and how it changes over time."
By modeling several exoplanetary configurations around red dwarf stars, Prabal's team in the cases where planetary bodies were tidally locked, their elongated shapes should be detectable, using current technology, as those worlds pass in front of their star. As pointed out by the researchers, detecting these tidal distortions should become easier when next-generation observatories like the James Webb Space Telescope (JWST) and the European Extremely Large Telescope (E-ELT) come online in the next few years.
It will be interesting to find one of these misshapen exoplanets, but even more interesting to spot a habitable world with this tidal distortion. Then scientists can really get to work understanding how its shape may impact its life-giving potential.
Source: Royal Astronomical Society