Temperatures rise 700 degrees in 6 hours
An extraordinarily skew orbit causes extreme temperature fluctuations and violent winds on the HD 80606b gas giant.
The HD 80606b exoplanet orbits its star in an extremely skew path. When the planet is farthest away from its star, the distance is 29 times longer than when it is closest. The comet-like orbit means that the planet gets so close to the star that temperatures rise from 530 °C to 1,230 °C in only six hours every 111. days, according to scientists from the US University of California, Santa Cruz, who base their conclusion on infrared data from the Spitzer space telescope. The sudden heating makes the atmosphere expand tremendously, causing pressure waves, which trigger wind gusts of up to 18,000 km/h. Moreover, the expansion probably means that the upper atmosphere explodes.
Based on the data, astronomers can calculate the conditions on the surface of the planet. If an atmosphere with a high pressure contains iron atoms, and if temperatures are higher than the melting point of iron, scientists have strong indications that iron drops could rain down over the planet. Astronomers can also predict the wind conditions of the alien planets. Some of the hot Jupiters – gas planets orbiting close to their stars – are locked in a bound rotation, so the same side always faces the star. The result is major temperature differences between the planet’s dark and bright sides. Scientists can convert the differences into approximate wind speeds. Astronomers use spectroscopy to measure wind speeds in an exoplanet’s atmosphere. In an atmosphere characterized by powerful wind systems, one half of the atmosphere will travel towards the observer, whereas the other will travel in the opposite direction. Based on the shifting wave- lengths measured via spectroscopy in both situations, scientists can calculate how quickly the winds have moved the atmosphere.
Shield blocks out the light
So far, space telescopes such as Kepler and Spitzer have produced the most weather forecast data, but as the light from the exoplanets is only 1/100,000,000 of the star’s, it is a tough job even for the sharpest of telescopes.
To make things easier, astronomers could try to block out part of the star’s light and study the exoplanet’s atmosphere directly. For this purpose, astronomers use a coronagraph. The device was invented in 1931 by French astronomer Bernard Ferdinand Lyot, who aimed to take a close look at the Sun’s corona. The coronagraph causes an artificial solar eclipse by blocking out the direct light from the Sun, so it is possible to see the corona.
Today, astronomers use coronagraphs to search for exoplanets orbiting other planets, and NASA’s new prestigious James Webb telescope, which will be launched in 2019, is equipped with a coronagraph.
Scientists from NASA’s Jet Propulsion Laboratory and the Goddard Space Flight Centre have recently improved coronagraph efficiency. With the new PISCES instrument – an integral field spectrograph – scientists have improved the ability to differ between light and darkness in a larger portion of the wavelengths that coronagraph telescopes observe, so now they
can see 18 % of the spectrum as compared to the previous 10. Scientists expect the result to improve the ability of the WFIRST (Wide-Field Infrared Survey Telescope), which NASA will launch in the mid-2020s, to characterize exoplanet atmospheres – and so weather.
More telescopes to study weather
The WFIRST is not alone, as astronomers can look forward to a considerable upgrade of their arsenal of telescopes both on Earth and in space in the years to come.
In the spring of 2019, NASA will launch the James Webb space telescope, the successor of the Hubble telescope, which was launched in 1990. With its 6.5 m mirror – as compared to Hubble’s 2.4 m – James Webb is much more powerful than its predecessor, and it can be used to find out if the atmospheres of the seven planets in the recently discovered TRAPPIST system include water. In 2023, NASA will launch another space telescope, FINESSE, which specializes in exoplanets. The telescope is still on the drawing board, but according to plan, it will study the atmospheres of about 500 exoplanets by means of transmission spectroscopy, providing scientists with new knowledge about weather conditions and climate.
Huge, Earth-based telescopes are also under construction, and according to plan, the ELT (Extremely Large Telescope) will be finished in the Atacama Desert of Chile in 2024. The ELT, which will be the world’s largest optical telescope, will have a primary mirror with a diameter of 39.9 m and will primarily search for small, Earth-like planets orbiting other stars. With its huge mirror, the telescope is 100 times sharper than its predecessors and will be able to take direct pictures of the largest planets and their atmospheres.
Soon, astronomers will also have access to the AURA space telescope with a 12 m mirror. The project is supported by almost 50 universities, and according to plan, the telescope will be launched in the 2030s. It will not only be 100 times more light-sensitive than the Hubble telescope, it will also have a 25 times higher dissolution. With such a powerful telescope, it will not only be possible to describe atmospheres and weather better than previously, it will also be possible to differ between exoplanets, which are very much like Earth, and those that just look like it, but are too hot to support biological life. So, astronomers might – in the swarm of remote, alien planets – be able for the first time to spot a world that does not only have the right climate and perfect weather conditions, but will also be home to alien life.