![]() "Is there a temperature inversion, where the temperature decreases then gets hotter, like what happens on Earth?" ![]() Instruments, called spectrometers, split it into a spectrum from infrared to visible light, like a rainbow.Īstronomers can then see which colours are missing from the rainbow and start to model what the atmosphere is like, Dr McKemmish says.Īnd not just what molecules are floating around. Telescopes on and orbiting Earth capture that light. ( Supplied: Christine Daniloff/MIT, Julien de Wit) In 2021, astronomers found a way to estimate an exoplanet's mass from the momentary eclipse as it circles its star. Loading How do astronomers calculate exoplanet size and mass?Īn exoplanet's girth and heft are calculated from its star's wink and wobble too.Ī larger exoplanet produces a more substantial star wink, purely because it blocks more light, and an exoplanet's mass is given away by the amount it makes its star wobble.įactor in how quickly an exoplanet travels around its star, measured by the time between winks, and astronomers can start to get some idea of what it's like out there.įor instance, a sizeable wobble and strong, fast winks points to something like a hot Jupiter - a gas giant that loops around its star quickly and closely. Only around 50 exoplanets have been directly imaged. The winking method's clocked up more than 3,700 exoplanets the wobble method's found around 900.Īdd to these another 120 exoplanets that were spotted using a technique called gravitational lensing, where light from a star far, far off in the distance bends around an exoplanet. "Some of them will have planets that are lined up just right that they pass between us and their star every time they go around, and you'll see that star periodically winking." "When you're looking at enough stars, you're playing a numbers game. "The beauty of that is that you can use a wide-field camera and simultaneously measure the brightness of a large number of stars at a time," Professor Horner said. If an exoplanet's journey around its star is in Earth's line of sight, we'll see that starlight momentarily, but periodically, dip in brightness. A few exoplanet 'firsts'ġ992: The first exoplanets were discovered - two rocky planets orbiting a dead neutron starġ995: First exoplanet orbiting a Sun-like star is found: 51 Pegasi b, a gas giant around half the size of JupiterĢ001: An exoplanet is spotted in a "habitable zone", where life as we know it may potentially existĢ011: Astronomers map an exoplanet's clouds for the first timeĢ014: An Earth-sized exoplanet within its star's habitable zone is discoveredĢ016: Our nearest stellar neighbour, Proxima Centauri, is found to have a probably rocky, Earth-ish-sized planet.īut spotting these stellar wobbles is labour-intensive, sometimes requiring years of staring at a single star to see if its light appears to get redder and bluer over time.Įnter: the transit - or "wink" - method, the second primary way to detect exoplanets. This way of detecting exoplanets is known as the radial-velocity method, or, as University of Southern Queensland astronomer Jonti Horner calls it, the "wobble method".Īnd it was the dominant way of finding exoplanets for a decade or so after the first confirmed detections in the 1990s. It's generally too hard for telescopes to see a star's subtle side-to-side shimmy.īut as a star moves away from and towards Earth, its light stretches and becomes redder, then compresses and becomes slightly bluer - a change that telescopes can pick up. ![]() They're pulled into their own small circular or elliptical path by the gravitational tug of their planets. The first relies on the fact that stars with planets don't sit motionless in the centre of their solar system. So with this in mind, how do astronomers know what an exoplanet is made of - and if it might be a contender for harbouring life? How to spot an exoplanetįor a start, astronomers need to detect these far-away solar systems. They're too small or far away to see with a telescope, or the brilliance of their sun overwhelms what little light they give off. Yet with very few exceptions, exoplanets can't be seen directly. In recent years, astronomers have not only discovered these extra-solar planets, or exoplanets - and more - they can also paint often incredibly vivid planetary descriptions. ![]() They sound like distant destinations ripped from the pages of science fiction: a deep blue gas giant where it rains molten glass, or a little iron "cannonball" world which cuts a lap around its star every eight hours. ![]()
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