Not all pale blue dots in space are Earth-like. Some, it turns out, are very different and much less hospitable than our home planet. Take the exoplanet HD 189733b, for instance, an alien world that was discovered in 2005 and resides about 63 light years from Earth in the constellation Vulpecula. In the category of planets known as hot Jupiters, it is much hotter and larger than Earth. Unlike our rocky planet it is a gas giant slightly larger than Jupiter that whizzes round its star in a mere 2.2 Earth days. Because it orbits so closely it is tidally locked, with the same side always facing its star, just as the same side of the moon always faces Earth.
HD 189733b would also be most inhospitable to life. In 2007 NASA’s Spitzer Space Telescope helped scientist Heather Knutson and colleagues map its weather by producing one of the first ever temperature maps of an exoplanet. Temperatures there were found to range from about 1,200 degrees Fahrenheit on the dark side to about 1,700 degrees Fahrenheit on the side facing the star, with the 500 degree difference causing strong winds to blow from the light side to the dark side at speeds of up to 5,400 miles per hour, or about seven times the speed of sound.
In addition, instead of water, it most likely rains glass, propelled sideways by the howling winds. According to NASA, for any hapless space traveler in the vicinity it would be “death by a thousand cuts.”
Another strange feature of the planet is that its temperature increases with altitude, and ultraviolet and X-ray radiation from its star are evaporating its atmosphere over time.
Given that it is so different from Earth, why then would it appear so similar from space? In 2013 its blue color was established using observations from the Hubble Space Telescope, marking the first time scientists had observed the color of a distant exoplanet. However, its blue color has a very different source from that of Earth. According to NASA officials, “The cobalt blue color comes not from the reflection of a tropical ocean, as on Earth, but rather a hazy, blow-torched atmosphere containing high clouds laced with silicate particles.” The blue color is caused by light scattering off the silicate particles in its atmosphere, and the glass rain derives from the silicate particles.
HD 189733b is not the only blue planet out there without an ocean. In our own solar system alone both Neptune and Uranus fit the bill. The outer atmospheres of these ice giants contain methane, which reflects blue wavelengths of light back into space. With such variation known to us already, how many other ways might there be to form an alien blue world?
Join the Springfield Stars Club on Tuesday, February 28th at 7:00pm at the Springfield Science Museum for a talk by Alan Rifkin on “Astronomical Uses of a 3D Printer.” Rifkin is president of the Springfield Stars Club and owner of FAR Laboratories, currently the only telescope dealership in Massachusetts. Refreshments will be served, and the public is welcome. The meeting is free of charge for members, with a suggested donation of $2 per nonmember.
Copyright © Amanda Jermyn