As we dream of becoming a multi-planet species, studying real planets orbiting distant stars offers a glimpse at a really interesting future for humans. This compelling sci-fi future is wrapped up in the latest, most detailed map yet made of the air temperatures and water on a distant exoplanet—but don't expect to move there anytime soon.
The planet in question is called WASP-43b. Located 260 light-years away, it was first discovered in 2011 by the transit method. Astronomers detected the planet by observing dips in the light of its parent star every time it passed between that star and the Earth.
Unfortunately, WASP-43b won't be our next home, even if we could somehow get that far across the universe to check it out. Using the Hubble Space Telescope, scientists have confirmed that the planet is extreme, to say the least.
The planet is roughly the size of Jupiter but has twice as much mass, and it's so close to its parent star that it makes one full orbit every 19 hours. It's also gravitationally locked such that one face is always facing the star in a perpetual day and the face experiences a perpetual night. It's the same way the Moon always shows the same face to the Earth.
Because only half the planet is heated by its star's light, it creates a hellish environment. Winds blow at the speed of sound from the 3,000 degree Fahrenheit day side of the planet—which is hot enough to melt steel—into the pitch black night side that is a relatively cool 1,000 degrees Fahrenheit.
There's not really a surface to speak of on this planet. It's a hot ball of hydrogen, devoid of surface features like oceans or landmasses, the things that would help us track rotation. The only notable feature is the shift between the scorching days and cool nights.
This video shows WASP-43b's weather over the course of a solar rotation. The side getting cooked by its star gets really cooked. For more, see this page.
Regardless of missing features, scientists have a few ways to figure out what an exoplanet is like. In the case of WASP-43b, they combined data from two methods to determine the planet's atmosphere. Spectroscopy revealed the abundance of water and the temperature structure of the atmosphere while observations of the planet's rotation revealed water abundances and temperatures at different longitudes.
All told, this data became a map detailing the temperatures at different layers of the exoplanet's atmosphere and the distribution of water vapor.
The findings have ramifications for the understanding of atmospheric dynamics and the formation of giant planets like Jupiter. "The observations are a proof of concept that atmospheres of transiting exoplanet can be characterized through various techniques," said Ray Villard of the Space Telescope Science Institute in Baltimore.
So it's not a new Earth—we're going to need massive new telescopes to determine the atmospheres of Earth-like exoplanets—but it's still significant. "These measurements have opened the door for a new kind of comparative planetology," said team leader Jacob Bean of the University of Chicago. These observations can serve as a benchmark for modeling other exoplanet atmospheres and dynamic structures.
WASP-43b is also an interesting case study. We don't have the same kind of extreme worlds in our solar system, so this is an interesting example of planet formation and planetary physics in action—especially where water in concerned.
There's water in our solar system that's locked away beneath the surface or crystallized in icy clouds like on Jupiter. Seeing what form water vapor has taken on an extreme exoplanet helps put our own giant planets into perspective.
Plus, elemental composition is central to understanding how planets form. Finding that WASP-43b has roughly the same amount of water as a gas giant with roughly the composition of the Sun tells us about the fundamentals of that planet's formation.
Of course, WASP-43b isn't anywhere near Earth-like and the discovery of water in its atmosphere has no bearing on the number or structures of possible Earth-like exoplanets. Still, it's good to know more about the planets that are out there, so when the James Webb Space Telescope finally launches we'll be better equipped to look in the right places for a possible new home.